Scandic Hotel Project

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Final ProjectProject B42, S11

Scandic Hotel in Aarhus

6/9/2011

Marta Marton

Sophie Eyler

Supervisor: Kirsten Malte Iversen

2011


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Scandic Hotel in Aarhus2011

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Contents

1. Introduction ............................................................................................................................. 3

2. Geological description ............................................................................................................. 5

2.1. Book: Engineering geology in Denmark ............................................................................... 5

2.2. Per Smed maps .................................................................................................................... 6

2.3. Contour lines map ................................................................................................................ 8

2.4. Pre quaternary surface map ................................................................................................ 8

2.5. Book: Underground studies in Arhus area ........................................................................... 9

2.6. GEUS map........................................................................................................................... 10

2.7. Danish area information .................................................................................................... 11

2.8. Drawing .............................................................................................................................. 13

3. Geotechnical description ....................................................................................................... 14

3.1. Informationonexistingbuildings ......................................................................................... 15

3.2. Soil conditions .................................................................................................................... 15

3.2.1. Groundwater conditions ................................................................................................ 17

3.2.2. Plasticity ......................................................................................................................... 17

3.2.3. Soil profiles ..................................................................................................................... 19

3.2.4. Strength, deformation parameters and unit weights .................................................... 20

3.3. Conclusion .......................................................................................................................... 22

4. Risk assessment ..................................................................................................................... 23

5. Excavation of the soil ............................................................................................................. 27

5.1. Demolition ......................................................................................................................... 27

5.2. Excavation of the soil ......................................................................................................... 28

5.2.1. The excavation process .................................................................................................. 31

5.3. Temporary dewatering ...................................................................................................... 33

5.4. Safety ................................................................................................................................. 34

6. Retaining walls ....................................................................................................................... 37


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6.1. Sheet pile walls .................................................................................................................. 39

6.1.1. Timber sheet pile walls .................................................................................................. 39

6.1.2. Concrete sheet pile walls ............................................................................................... 40

6.1.3. Steel sheet pile walls ...................................................................................................... 41

6.1.4. Berlin wall ....................................................................................................................... 42

6.1.5. Diaphragm wall .............................................................................................................. 43

6.1.6. Secant pile walls ............................................................................................................. 44

6.2. Conclusion .......................................................................................................................... 46

7. The design of the retaining walls ........................................................................................... 47

7.1. Steel sheet pile walls .......................................................................................................... 50

7.2. Secant pile walls ................................................................................................................. 54

7.2.1. Calculation of the reinforcement ................................................................................... 55

7.3. Conclusion .......................................................................................................................... 57

8. Ground anchors ..................................................................................................................... 58

8.1. Anchors for the steel sheet pile walls ................................................................................ 63

8.2. Secant pile walls ................................................................................................................. 64

8.3. Installation of the ground anchors .................................................................................... 65

9. Calculation of the foundations .............................................................................................. 68

9.1. Calculation of the reinforcement of the footings .............................................................. 72

10. Calculation of the bottom concrete plate ......................................................................... 73

11. Conclusion .......................................................................................................................... 78

Bibliography .................................................................................................................................. 79


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1. Introduction

The aim of this project is to construct the parking basement of a hotel in Aarhus, placed in an

urban area, in the heart of the city.

The parking basement will be provided for the Scandic Arhus City, which will be finished in

2012. To make way for the new hotel the city demolished some of the old buildings.

First of all a geological description of the building sites ground has to be made in order to ha ve

a guess of what kind of soil can be expected in the area of the excavation. It will also give any

special precaution that has to be taken regarding the pollution or the ground water for

example. The second step is to do a geotechnical description. Basically this will precise the

geological description and show what the soil is composed of, its strength, plasticity

The risk assessment is written in order to list each and every danger that can appear while

erecting the building.


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Then the excavation of the soil will be studied. First the existing buildings have to be

demolished in order to make place for the new hotel. The demolition method will be explained

in that part. Finally the excavation part will include the excavation process with the machinery,

the phase plan of the excavation in two levels, the dewatering and the dangers that can appear

all along the duration of the excavation work.

The next topic will be about retaining walls. Indeed the different types of retaining walls will be

compared and the best solution(s) will be chosen to insure that the ground is retained and the

excavation pit is dry. The design of the chosen solution(s) will be studied. For example the

reinforcement of the secant pile wall will be calculated and the sheet piles will be chosen

regarding the possible and available dimensions, the calculation of the anchors, the anchors

capacity, the soil conditions The reinforcement of the secant pile wall will be studied and the

steel section in the piles will be determined. Finally the lengths of the anchors in sheet piles and

secant piles walls will be calculated and the installation of the anchors will be explained.

After that comes a reinforced concrete calculation. The footings of the foundations will be

defined by using the loads from the upper levels of the building. The bottom concrete plate of

the parking basement at the level - 2 will be designed as well according to the imposed load

from the parking lot and the swelling pressing the other way from the bottom of the concrete

plate.


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2. Geological description

-by Sophie-

Before starting the excavation work, a geological description has to be made in order to get a

first overview of what the ground is made of. Once the different layers, thicknesses and

strengths that can be expected are known, then a first choice of retaining walls can be made.

Different maps showing the Danish underground and two books about the geology in Denmark

and the underground in the area of Arhus were used to make this geological description. Step

by step the different information are found starting with the general ones and ending with the

specific ones.

2.1. Book: Engineering geology in Denmark

The chapter 9 of the "Engineering geology in Denmark" book is used to find the type of soil that

can be generally expected in the area of the building site. However this chapter only gives

global information and the investigation needs to be pushed further to have specific datas

about the building site.

The shape of the level curves in this area are used to determine the type of landscape without

taking in account the changes brought by the human being.


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For example the "valley" in the lower left corner is not taken into account in the determination

of the landscape because it has been built for the railway of the train.

The contour lines are irregular and the surface is undulating. This shows a moraine landscape.

This type of landscape, formed by melting of ice, is the most common in Denmark. It consists ofmaterial that has melted free of the glaciers and has been released from the ice. In this

situation, moraine clay can be expected in the upper bed.

The contour lines are also closely spaced and the curves are closed corresponding to high

situated hills in the landscape. This shows that there was an ice marginal hill in this area. It's

been formed in front of a gradually advancing glacier where ice acted like a bulldozer on the

soil. The beds are disturbed that's why it is difficult to predict the nature of the soil.

To conclude, the information given by this chapter gives a moraine landscape. Moraine clayis

expected in the upper bed. The beds are also expected disturbed meaning that several

materialscan be expected in the same layer.

2.2. Per Smed maps

This map (Per Smed map number 2) shows the general type of soil that is usually found in the

area of Arhus in the period which goes from 1978 to 1982. This map will confirm the type of soil

found with the chapter 9 and specify it for the location of the building site.

It gives a good overview of the quaternary geological features in the landscape and shows the

relationship between the large valley systems and other landscape forms. It has to be taken

into account that this map only shows an interpretation of the landscape-forming processes.

That's why this map can be used to determinate the type of soil that can generally be expected

but without being specific about what layers will be found.


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The map is taken for the area of Arhus and a zoom is made on the location of the building site.

A thin red grid is found at that place. According to the legend, "moraine landscapes from

Weichsel glaciation, mainly with clayey soil" is expected at the building site.


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It does confirm the type of landscape found previously in the chapter 9. The building site is a

part of a moraine landscapewith clayey soiland it comes from a glaciation period, meaning

that meltwater materialscan be found in the ground.

2.3. Contour lines map

This map shows the contour line of the area nowadays. Associated with theorthophoto map of

the city, it gives the level of the ground surface exactly at the point of the building site.

2.4. Pre quaternary surface map

The Pre quaternary surface topography of Denmark map is the result of the landscape-forming

geological processes throughout the Tertiary and up to the present day. The contour lines are

the present topographical contour lines. Basically this map shows the ground surface level that

can be studied for the geological description.


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According to the pre quaternary surface map the colour found in the area of the building site

light green. The legend says that the corresponding level is between -25 and 0 m below the

sea level.

2.5. Book: Underground studies in Arhus area

This book gives a lot of information concerning the background, the groundwater and the type

of soil that can be found in the area of Arhus. Several typical soil profiles in this area had been

compared to finally draw the soil profile that we can expect for the building site.

Unfortunately the whole book and maps are in Danish so this only page below had been

studied.


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The picture above shows the different soil profiles that had been compared and themselves

compared with the rest of the information that have been gathered. That means that only the

type of soil that agree with the other information have been taken into account to draw the

hypothetic soil profile of the building site. The result is shown in point:8. Drawing.

2.6. GEUS map

The geological surface map from GEUS shows the dominant soils in 1m depth just below the

top soil. The technical boreholes will help to find the ground water level at the building site.


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As no technical boreholes had been found at the same place of the

building site two boreholes have been studied to determine the

ground water level.

The first borehole (the one shown as an example above) gave aground water level at + 5.4 and the second one (where is the star

above the building site) gave it at + 11.2. A calculation has been made

in order to interpolate the ground water level at the building site

itself. This gave the ground water at the level approximately+ 9m

above the sea level.

2.7. Danish area information

This web site displaysa lot of information about the environmental and planning datas in

specified locations. It shows also background maps, terrain conditions and contour line maps.

Basically this web site will help to find out if there are special care that has to be taken

regarding to the building site.

Activation / deactivation ofthe different layers

Building site


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First, the area of the building site is found so the scale is good enough and the informationis

clearly seen. Then every layer is checked in order to see what environmental and planning

parameter have to be taken into account while building the hotel.

The building site takes place at the parcel 333a. Just across the street there is a monumentprotection line but not close enough to be relevant for the building site itself. There are no

particular preservation for the nature

because the hotel is situated in an urban

area. The area has limited water interests

meaning that there are no specific

problems with the groundwater. This

picture shows the areas where the soil is

contaminated around the building site.

The soil shouldn't be especiallycontaminated at the building site area

but thatinformation should still be kept in

mind.

Finally the web site offers the opportunity to have a look at historical maps showing the

neighborhood from 1842 to 2008. All those maps show the same building at the exact same

place of the building site. This means that there was no former construction at that place. There

is no "construction material" below the existing building.

To conclude, except regarding the soil contamination, there is no specific preservationthat hasto be taken care off at the building site.


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2.8. Drawing


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3. Geotechnical description

-by Marta-

In this projectit is very important to have the geotechnical description ofthe building site, which

summarizes and evaluates all results obtained during investigation in the siteand in the

laboratories.In order to calculate the retaining walls, anchors and also the bottom plate some

parameters will be needed. For thisit were given all theall boring logs, laboratory test results

from the different drillings. With theseboringsit is be possible to draw the cross sections of the

soil, and to determine the strength and deformation properties of the soil in the specific area.

The borings are divided in two phases. The first phase includes 7 borings which performed

before the demolition of the existing buildings. The second phase includes 3 borings which

worked only after demolishing the existing buildings.

The report covers the results of the second investigation phase above construction: 3

geotechnical boreholes.

Figure 1 Place of the drillings


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3.1. Informationonexistingbuildings

While the future hotel will be located in an urban area, in the heart of Aarhus, it is really

important to have an overview on the surrounding buildings. For the new building there were

performed some surveys of the existing conditions of the area where it will be placed: in

stergade, between Hans HartvigSeedorffs StreetandSndergade. It is expected that the new

hotel will be built with a large car park below the hotel. The purpose of these studies is to give

historical data to such an extent that the existing building conditions around the proposed

building can be assessed, including age of the buildings, basement, the possible type of the

foundation, and the depth of the foundation.

The building has its border on the north up to stergade, on the west up to Hans Hartvig

Seedorffs Street, and to the east it borders up to the buildings on Sndergade.

The new buildings area is surrounded by other buildings, and roads, located next to the area

which will be excavated, possibly causing danger to these roads and buildings as a result of the

excavation and/or dewatering.

Many of the buildings in the surrounding are old, and they dont have a good ground in

accordance to the applicable rules and standards.

Because of the basement and car park below the new hotel, the excavation has to be done

below or on a level with the existing building foundation level.

The expected water level is about 3-4 meters from the ground. So it will be probably necessary

to perform a temporary dewatering for the excavation. Dewatering should then be arranged so

that the water table is lowered at least 0.5 meters below the excavation level.There will

probably be a dug in clay or moraine clay, in which case the dewatering of the excavation

possibly will be done by simple drainage.

3.2. Soil conditions

The studies in the second phase include drilling no. 3 and no. 10 to 25 m below ground and

drilling no. 8 to 11 m below ground. In the 3 new wells from ground level between 1.3 and 1.8m has been taken fill and between 4.2 up to approximately 11 m glacial deposits - mainly in the

form of moraine clay. Glacial deposits are found underneathof very fat tertiary clay from 4 to 11

meters depth (from 1.9 to 6.1 in elevation), with glacial sediments; however, this is not present

in drilling no. 8.In both bore no. 3 and 10, the upper zone of the Tertiary clay moved from its


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deposition siteduring the last ice age and now covers the static tertiary clay either as loose

flakes orpossibly as folded structures.

The static Tertiary succession is: at the top Viborg clay (upper Septarie clay),then Kysing marl

(upper Svind marl) and at the bottom Moesgrd clay (lower Septarie clay).

1. Fill layer

From the terrain is generally taken a coating and underlying base course.

2. Glacial deposits

Glacial deposits consist predominantly of clay, as in boring 10 it can be observed

alternationofrelatively thin flakes with very fat Septarie clay or micaand in boring 8 it can be

observed alternationwith relatively thin layers of glacial sand and silt.

Clay is mostly pretty cool, sporadic fat. Moreover, locally it was found embedded layer of very

fat local moraine of Septarie clay.

The strength of the clay increases with depth. As in most of the previous wells were right soft

clay deposits (cv700 kN/m2.

3. The Tertiary clay deposits

The static Tertiary deposits, which are only taken in hole 3 and 10, consists of top Viborg clay

(Septarie clay), then 0.9 to 2.2 m Kysing marl (Svind marl) and at the bottomMoesgrd clay

(Septarie clay), which is not penetrated 25 m below the ground, but having Svind marl in

slightly greater depth.

The new wells give rise to only minor adjustments to the chart below from the report of the

first phase.

Updated overview of vane tests and classification properties of Tertiary clay

Soil type Wing strength

cv[kN/m2]

Watercontent

w [%]

Unitweight

[kN/m3]

Flake of Tertiary clay 170 - 450 27 - 34 18.519.6

Mica >700 18


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3.2.1. Groundwater conditions

The depth to groundwater level is measured immediately after completion of the drilling. In

boring 8 the height of the water table was 10.1 meter, which corresponds 3.0 meters below

ground level. The drilling no. 10 was dry. In the boring no. 3 the water surface elevation was

measured 8.8 meter which is equivalentto 1.5 meters below ground.

In the project it will be considered a normal water table for the uplift calculations, which is

located in elevation 8.5 m along stergade and on the southerly direction in elevation approx.

9.5 m.

3.2.2. Plasticity

1. Viborg clay

Updated overview of plasticity forViborg clay

Drilling Test Ip[%]

32766/1 23 51

32766/2 21 77

3 31 70

32766/4 25 50

32766/4 26 61

32766/5 33 61

32766/6 19 55

32766/6 20 61

32766/7 31 51

32766/7 35 67

10 22 53

Viborgclay 180 - 690 28 - 37 18.019.2

Kysingmarl 350 - >700 27 - 38 19.019.5

Moesgrdclay 210 - >700 31 - 38 18.5 - 20


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10 32 69

COWI/B1 22 70

COWI/B1 30 74

Plasticity index is in the middle: 62%, i.e. significantly lower than for the lower Septarie

clay,Moesgrd clay.

2. Kysing marl (upper Svind marl)

Plasticity forKysing clay

Drilling Test Ip[%]

1 33 28

2 31 88

6 33 43

Plasticity index is in the middle: 53 %

3. Moesgrd clay (lower Septarie clay)

Updated overview of plasticity in Moesgrd clay

Drilling Test Ip[%]

32766/1 49 79

32766/2 42 84

3 49 73

32766/4 49 71

COWI/B1 38 131

COWI/B1 46 110

Plasticity index is in the middle 91%, i.e. significantly higher than the upper Septarie clay,Viborg

clay.


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3.2.3. Soil profiles

One useful method compiling subsurface

data is to draw the vertical cross-sections

across the site. These sections are most

easily developed when they intersect the

borings.

In the geotechnical report it was given all

the boring logs which were performed on

the site. By using these logs, and also by

adding some interpretation, when the

conditions between these borings were

not given, the soil profiles could be made.

Because of the lack of information

between the borings, the soil profiles are

not the exact mirror of the reality, and

because of the interpretation these soil

profiles are unique.

Figure 2 Example of a boring log

The method which was used drawing these profiles:

1. Determining the depth of the different drillings.

2. Drawing each boring in his exact place.

3. Drawing the different layers of the soil on each boring.

4. Connecting the same layers from one boring to another (where it is obvious).

5. Drawing the layers between two consecutive boring (estimation).

For this project two soil cross-sections were made: one where the borings no. 3, 6 and 10 were

performed and the other one where the borings no. 1, 4, 7 and 8 were performed.(See

Appendix no.2)


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3.2.4. Strength, deformation parameters and unit weights

For the later calculations it was important to determine some important parameters:undrained

shear strength, friction angle, effective cohesion, saturated unit weight, dry unit weight.

Some of these parameters could be determinedusing the boring logs: wing strength or shear

strength measured by vane test (cv), water content (w), and also the unit weight ().

To determine the wing strength in the different layers of the soils it was calculated the

arithmetic mean (average) of the wing strengths for each layer in each boring. Where the

difference was very big between twoconsecutive values, (like from cv=100 it changed to cv=370

and then again to cv=70) the very different value was disregarded. In some layers the values

differed quite much, thanks to the increase of the strength by the depth, because of this, the

layers were divided in an upper and a lower level (like the Viborg- and the moraine clay). First

the averages of the soil types were determined for each drilling, then for each soil profile, and

in the end the wing strengths were determined for the soil in the construction area.

To have a better security, in most of the cases for the wing strength it was taken a value lower

than the average, but never higher.(See Appendix no.2)

The undrained shear strength (cu) (or triaxial certain values of pressure) is determined using the

vane tests where

, unless if it is cracked clay or gyttja.

Another parameter which is important to be determined is the unit weight. For the future

calculations two types of unit weight will be needed: the saturated unit weight ( m), which is a

parameter characteristic for the layers situated under the water level, and the dry unit weight

(d), which is used for the layers situated above the water level.

From the Danish Technical Handbook (TekniskStbi) the different parameters for the typical

Danish natural soil deposits could be read, like the saturated unit weight (m), friction angle

(pl), effective cohesion (c).


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Figure 3 Classification-, strength- and deformation parameters for typical Danish natural soil deposits (from

TekniskStabi)

The effective cohesion (c)is a mathematical factor to represent the use of breaking the

condition of the form=c+*tan (Coulombs failure condition). Normally, one can assess (


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In order to calculate the dry unit weight the value of the void ratio was needed. In the project

an estimation of the void ratio was made due to the lack of information.

After the calculations all the parameters which will be needed in the later calculations are

shown in the following table for all the layers which are present in the specific area.

Parameters for the different type of soils

Soil typecu

[kN/m2]c

[kN/m2]

pl

[]

m[kN/m3]

d[kN/m3]

Fill 0 0 0 16 13

Moraine clay (upper level) 120 15 30 20 17

Moraine clay (lower level) 360 16 32 22 -

Moraine sand 0 0 40 22 -

Meltwater clay 140 10 26 20 -

Meltwater sand 0 0 37 19 -

Meltwater silt 160 10 26 20 -

Viborg clay 280 0 28 19 -

Mica (Glimmer clay) >702 0 25 19 -

Flakes (Glacial clay) 210 0 25 19 -

Kysing marl 380 0 25 18 -

Moesgrdclay 480 0 26 18 -

3.3. Conclusion

To conclude, comparing the geotechnical description with the geological one, it can be stated

that the expected soil conditions and groundwater level was demonstrated by the results from

the drillings executed on the site.


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4. Risk assessment

-by Marta-

The piling works for the construction of the new hotel include performance-related factors,

which threaten to cause damage on the surrounding buildings. The risk assessment covers only

existing buildings and structures located outside the neighbouring boundaries.

The greatest risks are associated with dewatering and the excavation work. During the

excavation close to the existing buildings, it will be hard to avoid the emergence of cracks and

small gaps in them resulted by the deformations of dewatering. It is a must to be prepared of

this, and to repair the damages.

The project includes a building with double basement and plate foundation. The bottom platewill be anchored with vertical anchors to avoid the heave. The lowest excavation level in

elevation is +4.2.

The retaining walls will consist of sheet pile walls and secant pile walls because there is

necessary to get close to the existing buildings i.e. along the adjacent boundary to the south

and along a ca. 22 m stretch of the southern part of neighbouring boundaries to the east.

Dewatering has to be placed so deeply that all the permeable layers to be are cut off.

To minimize the noise and vibrations at the steel sheet piles the sheet pile profiles must beforced down by hydraulic pressure with Crush Arrows. If it is required the sheet piles should be

supplemented with hosing/drilling so that the sheet piles achieve the projected toe level. Pre-

drilling will be done on the inside of the building pit and the eventual drilling during future

excavation levels will be done after injecting with cement stabilized bentonite.

The establishment of the secant pile walls will begin with building a guiding wall cast of

concrete so that the centre distance between each pile correspond to the desired overlap. The

secant pile walls are constructed with 80 cm diameter bore piles, which are provided with 8 cm

overlap.

Dewatering close to the buildings must be monitored for example by inclinometer

measurements.

Dewatering is anchored with drilled, temporary ground anchors. The anchors are placed in

different anchoring level and are installed at varying angles. The ground anchors are injected


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again (normally 24 hour after the first injection). It wont be taken into account any sewer lines

or other wiring by placing the anchor levels.

Risk factors

The piling works for the planned structure contains the following potentially risky moments on

the neighbouring buildings:

1. Demolition of existing buildings

2. Reducing steel sheet pile walls

3. Drilling down and casting of secant pile walls

4. Establishment of ground anchors for dewatering (drilling, injecting and holding it)

5. Temporary ground water lowering

6. Excavation

7. Establishment of ground anchors for bottom plate

Demolition of existing buildings

The risks associated with the demolition work have not been assessed.

Reducing steel sheet piles

It is reported that the steel sheet piles are forced down by hydraulic pressure, with Crush

Arrows. If it will be managed to reduce the steel sheet piles only by hydraulic pressure it will be

possible to meet even the most stringent vibration limitscompared to neighbouring buildings.

It will be a necessary extent to do hosing and/or drilling. Both of them potentially involve

substantial risks for neighbouring buildings and structures. The drilling will be performed only

inside of the sheet piles. The drilling occurs during sheet pile tip and liner and the liner is also

not close, so the effect of possible erosion damage, distortion from clamping, etc. must be

considered carefully.A risk of hosing and drilling thus requires a detailed description of

methodology and application, with reference to past assignments.

Drilling down and casting of secant pile walls

It would probably be impossible to keep even the most stringent vibration limits in relation to

neighbouring buildings. The greatest risk of vibration may occur if they hit bigger stones or

structural parts during drill work.


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There must be developed for this work a description of the work explaining detailed

performance of the drilling works, more specifically, how to ensure to avoid the surrounding

soil erosion damage from the inflowing water to thoroughly bore baths during drilling and

casting.

Establishment of ground anchors for dewatering

There must be developed for this work a description of the work explaining installation

performance, particularly how to ensure to avoid the surrounding soil erosion damage. In

addition should be explained the risk phrases of the anchors free length which is not injected.

Finally, it is important the presentation of the documentation that the anchors do not hit

underground structures and equipment - including wiring systems.

Excavation

Excavation leads to deformations of dewatering and hence deformation (vertical as well as

horizontally) of land and buildings, etc. behind the walls.

There must therefore be performed calculations explaining deformations size.

Deformations should be compared with limit values which must be already established for each

neighbouring building. There must also be prepared a job description that outlines that in which

stages must be excavated, and in what tempos to be installed stabilizing anchors or other form

of bracing.

Finally, it is estimated that the most vulnerable buildings will be monitored with benchmarks so

that excavation work can be stopped if the assumed values against the expected thingsare

exceeded. Furthermore inclinometer measurements (slope measurements) will be performed

on selected walls so that the walls current buckling mode can be evaluated in relation to

expectations.

It is scarcely possible to avoid the nearest neighbouring buildings cosmetic damage. Even very

small deformations are in danger of causing damage that might not otherwise have been

obtained at a later date. The limit for how big movementsbuildings can withstand before any

significant damage to their static system is building-dependent. There must be approved and

controlled retail calculations of all dewatering and anchorages in all relevant fracture and

serviceability limit state.


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Temporary ground water lowering

It is expected that it will probably be executed without risk to neighbouring buildings. In the

event of a finding substantial leaks - e.g. due to locking skip tests or other variations - the

situation can be reassessed.

Establishment of ground anchors for bottom plate

It is possible to install ground anchors for flat foundations without risk of significant nuisance

for neighbouring buildings.


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5. Excavation of the soil

-by Marta-

Deep excavations are needed e. g. for foundations,underground traffic routes and other

infrastructurefacilities. The dimensions of theexcavation are determined by the drawings from

the architects.The design of the excavation depends on several factors: like thelocal situation,

the conditions of the ground and thegroundwater and other circumstances. In urban areasthe

excavations must be done due to the adjacentbuildings by underpinnings or by retaining walls.

Nowadays, the land prices are high, and only small areas are available, therefore the investors

plan more and more basements. To solve the traffic problems new lines areplanned

underneath the existing ones. So the depthof the excavations increases and reaches values, for

which no local experiences exist.

The bottom and the walls of the excavations mustguarantee - with a certain factor of safety -

the structuralclearance and a certain amount of water impermeabilityif necessary. The ground

movement,which is unavoidable especially in cases with softand loose soils, has to be restricted

to such an extent,that no greater damages occur in the neighbourhood.Here the first

movements occur by establishing thewalls and the sealing of the ground.

5.1. Demolition

To make way for the new hotel,the

first thing which has to be done is

the demolition of the existing

buildings. For this the non-

explosive method will be used,

which means hydraulic excavators

will be brought to the construction

site to do the undermining process.

The demolition project manager

has to determine where the

undermining will be done. He also

has to take into account the safety

and clean-up considerations in order

to determine how the building will be undermined and ultimately demolished.

Figure 4The building site after the demolition


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Loaders or bulldozers may also be used to demolish the building. They are typically equipped

with "rakes" (thick pieces of steel that could be an I-beam or tube), so they will be used to ram

the building walls.

After the demolishing the construction site has to be cleaned, thanks to this the excavation itcan be made.

5.2. Excavation of the soil

Before any excavation work is undertaken, a risk assessment must be carriedoutfirst to assess

the degree of hazard (See Chapter no.4).

To excavate the soil it is necessary to estimate the amount of soil which is going to be

removed.By analysing the drawings, two plans were done for this process. To find the better

solution, the following aspects were compared:

Volume of soil removed;

The excavators operating time;

Cost;

Aesthetics.

Volume of soil removed

It depends on the excavated area and the depth of the

excavation. The geotechnical description says that the lowest excavation level is +4.2 meters,

which means that the height of the excavation will be 8.8 meters.

The excavators operating time

The chosen excavator which is going to work on the site is: CAT 336D L Hydraulic excavator

(Caterpillar), with a 2.55 m3 maximum bucket capacity. The cycle time is estimated to 0.50

minute. To calculate the effective cycles per hour the following are taken into account:

Cycle time 0.50 minute

Cycles/60 minute hour 60 / 0.50 = 120

Operator Skill/Efficiency 0.9 (90%)

Machine Availability 0.95 (95%)

Gen Operational Efficiency 0.83 (50 min/hr)

Effective Cycles per Hour 125 x 0.9 x 0.95 x 0.83 = 85

Figure 5The chosen excavator: CAT 336D L


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Therefore in an hour the amount of soil which it can be removed: 2.55* 85 = 216 m3/hour.

The cost of the rent of the excavator is estimated to 4000 DKK/day.

1stsolution

In this solution the excavation will be done until the Hans Hartvig Seedorffs Street, which will

have anexcavated areaof 2958 m2. Therefore the volume of the excavated soil will be:

For this amount of soil the excavator has to work:

By 8 hours working per day the excavator has to be rented for 15 days, costing 60000 DKK.


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2ndsolution

With this solution the neo-classicist buildings faade on Hans Hartvig Seedorffs Street wont be

demolished, because it is very characteristic on that area. This will reduce the excavated area:

2724 m2, the volume of soil:

and the excavators operating time:

These 110 hours of work means 13.75 days, therefore the cost of the rent for this period of the

excavator will be estimated to 55000 DKK.

This solution needs more attention in the demolition because of the old faade, which will be

supported during these works.


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Conclusion

Comparing the results of the first two aspects, it

can be noticed that there is not so big

difference, but still the second solution is more

likely, because it has less removed soil, and the

excavator will work 14 days instead of 15. The

cost also will be lower, but this doesnt really

count in a big construction like this.

The decisive aspect why the 2nd

solution was

chosen was the aesthetics.

5.2.1. The excavation process

For the excavation it was made a phase plan which shows the activities done for each day. (See

Appendix no.4 and no.5)Because of the two levels under the ground, the excavation will be

done during two phases: the first oneincludes the excavation works until the second level and

the other one is for the second level. Excavating one level takes 7 day. The area which is going

to be excavated per each day is:

By making this drawing the aim was to dividethe area in equal pieces. Of course this couldnt be exact: the smallest excavated area for one

day being 375 m2

and in the other hand the largest one 409 m2

.A ramp was made for eachphase from the Hans HartvigSeedorffs Street because of the access of the excavator. (See

Appendix no.3)

Regarding to the calculation of the ground

anchors (See Chapter no. 8) the following

drawing shows the number of anchors which

are going to be placed for each excavated area

for one level.

The numbers 1,2,3 7 show the order of theexcavated areas.

It is assumed that the drilling machine can drill

the hole for 5-6 anchors per day. This means

installing the anchors for one area can take

more days up to 7 days. Also it can be noticed

Figure 6The neo-classicist facade

Figure 7 Excavated areas and number of anchors per level


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that in the area no.5 no anchors will be placed.

In some of the corners was not possible to place anchors therefore in those placed inner

bracing will be used. The anchors are put in the ground the day after the soil has been

excavated. The secant pile walls will be placed where the present soil type is clay. Thanks to this

reinjection will be done in 24 hours after the drilling and injection of the anchors. On some days

lots of activities are done in the same time. Installing anchors can be possible while excavating

another area. The anchors resistance is tested 7 days after their implementation. For this

reasons, at the end of the excavation work, the last days are taken to test the anchors put the

week before. Testing and reinjection doesnt take a lot of time, so this wasnt a factor which has

to be considered carefully while planning the excavation. This is also shown on the detail below

made for two consecutive days. (See Appendix no.5)

Figure 8 Detail of the phase plan

The table gives the information about the week, and the day when the specific activities will be

done. The number in brackets shows the activity number for each set of installed anchors. This

meansfor one set of anchorsthe number(32) will be the number for each type of activity done:

installing (5 anchors), reinjection (if there is a case) and testing. Thanks to this will be easier to

follow which works have to be done on the specific day.

As a result the whole excavation works including the installation of the anchors will take 64

working days, starting from Day 1 until Day 89 with 13 weeks duration.


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5.3. Temporary dewatering

For the excavation it is necessary to perform a temporary dewatering. Dewatering should then

be arranged so that the water table is lowered at least 0.5 meters below the excavation level.

In principle there are four different methods for controlling groundwater in connection with a

building or construction project below the groundwater table:

Water is allowed to seep into the excavation and is removed by bilge pumping (possibly

with drain)

A temporary or permanent dewatering is established, whereby the groundwater table is

drawn down to below the construction/excavation level

The groundwater movement is cut off with tight walls, for example sheet pile walls, slot

walls, freezing, injection

The water pressure is withheld with air pressure, for instance in tunnels and caissons.

Figure 9 Selection method

There will probably be a dug in clay or moraine clay, in which case the dewatering of the

excavation will be done by simple drainage. This is the simplest and cheapest form of

groundwater drawdown which is pumping from a system of drains and pumping wells at thebottom of the excavation.


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Figure 10 Simple drainage

By simple drainage, the water is allowed to seep into the building pit and is subsequentlypumpedaway through a well point pump. The method is commonly applied by smaller/modest

wateramounts and when there is no risk of soil fractures.

The pump sump can be shaped as a 315 mm corrugated plastic well with slits, which is placed in

anexcavation filled with pearl stones and connected to the drain flow.

For a pump, an electrically powered, well point pump, sized as required (available with

capacitiesof up till approximately 100 m3/h) is chosen.

The method can be applied to excavation to moderate depth under the groundwater level in

freegroundwater depots, where the water-bearing beds consist of sand and gravel.Furthermore, themethod can be applied to excavation below the groundwater level in for

example moraine clay,where water-bearing beds of sand and gravel are often found.

5.4. Safety

During excavation works can be present the following hazards:

operator falling off from excavation machine

running over a pedestrian when travelling backing

destroy underground electrical cables

contact with overground electrical cables

collision with other vehicles

operation the machine by unauthorized person

machine upset

soil collapse


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getting caught in the pinch points of the bucket arms or the pivot area of an articulated

machine

spilling a load on others

falling over an edge

a raised bucket falling.

In order to prevent accidents, all the persons present on the site have to respect the following

instructions:

To avoid falling off during climbing or descent from machine they have to wear safety

shoes and clean the stairs.

To avoid running over a pedestrian, they have to check before starting the machine if all

the back-up alarm is working, to use properly adjusted rear view mirrors, and when

lighting is poor, use both front and rear lights, take care for any distance. They should

never throw the engine into reverse without looking behind them. No one, other than the operator, should ride the equipment. The bouncing and jarring

can cause passengers to be thrown off. The usual result is, the passenger is run over

Before starting excavation they have to ask a chart of underground cables. It is

forbidden to use the excavation machine near/ above the underground cables. In this

case excavation has to be done manually.

To avoid contact with overground electrical cables they have to respect the minimal

distance to the electrical cables (3 m)

To avoid collision with other vehicles have to be organised the internal transport on the

site. To avoid operation of the machine by unauthorised person, the operator has to take out

the key before leaving the machine.

In order to prevent machine upset, the operator have to be familiar with the

instructions described in the machine manual, and have to respect all the limits

described on it.

During manual excavation the operators have to take care of soil collapse. To prevent

this all the walls on the dig have to be protected with supports, have to be inspected

daily and after raining. The excavated soil has to be stored at the minim 70 cm distance

from excavation site. Articulated loaders have a very nasty pinch point at the pivot. Operators should always

check both sides of the machine before moving it, to make sure no one is in this

dangerous area.

In order to prevent spilling a load on others, if someone ventures into the danger zone

around where someone else is working, sounding a warning blast and stopping would


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certainly be in order. All the peoples from the site have to be instructed to have

cautions if they are around, between, or under a raised bucket or its arms.

The cage is designed to protect the operator in the event of rollover. In order to provide

this protection, the operator must be inside the cage, using his seat belt.

Have the bucket lowered to the ground unless the work they plan to do requires that itbe raised. Install jacks or blocks under raised buckets or arms so they cannot fall on

them if something goes wrong.


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6. Retaining walls

-by Marta-

The building site is located in an urban area; therefore the excavation has to be approximately

the same size as the building, in order not to disturb the surrounding buildings. While the future

building will have in the basement a parking place, it has to be done a deep excavation. The

solution for supporting this deep excavation is to place retaining walls in the specific area.

In order to find the best solution for this project, which means to choose the type of the

retaining walls which will be used, it isuseful to have an overview on the different type of the

walls.

A retaining wall is a structure that retains (holds back) any material (usually earth) and preventsit from sliding or eroding away. It is designed so that to resist the material pressure of the

material that it is holding back.

The retaining walls are used where it is not possible to

excavate in open pit due to:space, stability, and ground

water.The scopes of these walls are:

To restrict the deflection;

To restrict the bending moment and thus

weight ; To restrict the height of wall (driving depth);

Preventive measures by inadequate driving

depth;

To ensure structures against uplift (by

anchorage).

Figure 11 Retaining wall cross section

Before choosing the type of the retaining walls some conditions should be taken into

consideration:

The substrata

The soil layers that occur on the site:


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Moraine clay

Meltwater sand

Flakes (glacial clay)

Viborg clay

Kysing marl

Moesgrdclay

Tolerances

Risk of damage

Some damages can occur during the foundation works. Therefore it has to be prepared for

damages due to incorrect evaluation of the substrata and/or incorrect calculations, due to the

ground water-table or seeping in water, and damages caused by the excavation process.

Conditions pertaining to neighbours

The building is located in the centre of Aarhus, so it is important to take into account some

considerations like noise, dust vibrations, permanent- and temporary ground water-table

lowering in connection with the neighbouring buildings.

Noise: The noise coming from the building site is disturbing, for example from the

vehicles which transport the materials, from the installation of the pile walls, especially

in an urban area, where the buildings are really close to each other. Therefore the work

should be done by trying to use methods which do not generate a lot of noise.

Dust: It is impossible to avoid the dust from a building site, but it can be minimized. The

best solution for this to spray the area at regular intervals using a watering system that

can correspond to evaporation

Vibration: Another annoying factor which can cause damage to the existing buildings. To

avoid the unexpected subsidence in the existing buildings all surrounding constructions

foundations should be examined before the work is started.

Temporary ground water-table lowering: It can be a serious problem too, it has to be

done with attention, but in the project it is expected that it will probably be executed

without risk to neighbouring buildings

For more detailed explanation about the risks in connection with the retaining walls (See

Chapter no. 4)


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In order to choose the best solution for the future building it should be listed the advantages

and disadvantages of the different type of walls.

There are several types of retaining walls, from these some of them cant be chosen because

they dont fulfil from the start some considerations: for example the gravity- and the cantileverare used for lower constructions.

There are 4 types of walls which will be discussed more detailed:

6.1. Sheet pile walls

-by Marta-

Sheet piling is used on a large scale for retaining walls in excavation pits. Sheet piling can be

supplemented with up to several anchor levels in order to stabilize and fix a sheet pile wall in

large deep excavations. Sheet pile walls are constructed by driving prefabricated sections into

the ground. Soil conditions may allow for the sections to be vibrated into ground instead of it

being hammer driven. The full wall is formed by connecting the joints of adjacent sheet pile

sections in sequential installation. Sheet pile walls provide structural resistance by utilizing the

full section. Steel sheet piles are most commonly used in deep excavations, although reinforced

concrete sheet piles have also being used successfully.

The materials which can be used for sheet piling is primarily wood, concrete and steel.

6.1.1. Timber sheet pile wallsThis type of piling should be restricted to short to moderate wallheights (less than 3 meters)

and used only for temporary structures. The most common types oftimber sheet piles are

wooden planks and Wakefield piles. Wakefield piles are constructed bynailing three planks


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together in an offset manner. Wooded pile walls may be consideredpermanent if the wall is

permanent submerged underwater or if treated with preservatives.

Advantages:

Low cost;

Readily available;

Good aesthetics;

Easy of handling.

Disadvantages:

Difficult to install into dense or gravelly

soils;

Limited to short duration retaining wallsat construction sites;

Limited height of structures;

Decay of structures may be hidden.

6.1.2. Concrete sheet pile walls

Concrete piles are typically made with steel reinforcing and prestressing tendons to obtain the

tensile strength required, to survive handling and driving, and to provide sufficient bending

resistance.Long piles can be difficult to handle and transport. Pile joints can be used to join twoor more short piles to form one long pile. Pile joints can be used with both precast and

prestressed concrete piles.

Advantages:

Rigid and incur larger earth pressure and

greater bending stresses than a flexible

wall;

Longer service life than other walls;

Good aesthetics;

Advantageous in marine environments;

Capable of supporting significant axial

loads.


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Disadvantages:

Heavily and bulky and require larger equipment to deliver, handle and drive;

Higher material cost;

Large displacement piles and consideration must be given to adjacent structures; May cause settlement in soft soils;

6.1.3. Steel sheet pile walls

Steel is the preferred sheet pile material and represents over 95% of all sheet pile

constructions. The steel sheet pile is used both as a temporary and as a permanent

construction.

Advantages:

Provides high resistance;

Relatively light weight and easy to handle;

Can be used repeatedly;

Long service life;


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Less expensive;

Eliminate or reduce water;

Easy to increase pile length by welding or bolting.

Disadvantages:

Corrosion of steel sheet pile;

Not aesthetically pleasing in high profile situation;

Not good in hard soils;

Driving may cause neighborhood disturbance (noise, vibration);

Less tight;

Problems with the interlocks: they can break.

6.1.4. Berlin wall-by Sophie-

A Berlin wall, also called a soldier pile wall, is a temporary (in case of timber panels) or a

permanent (in case of concrete panels) retaining wall mostly used in case of urban area

constructions. It's one of the oldest methods known for establishing retaining walls in

connection with deep excavations. The Berlin wall, called in Denmark Copenhagener wall, is the

front runner for sheet

pile wall. The method

of implementation ofthat type of walls is still

very used today,

simple and durable.

This method is used for

large excavation which

is made along an

existing construction.

The method of

implementation is very

simple. First HEB-steel

profiles are driven or

vibrated into the

ground. The distance


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between them is going from 0.5 to 2m. To link the steel profile several materials can be used:

wooden panels, HEB steel profiles, fiber concrete or finally but very rarely, sheet pile profiles.

The panels are pressed down in stage between the HEB-steel profiles as the excavation goes

down. Generally, this type of wall can only support small soil pressures.

Advantages:

This method is for large excavation;

Berlin wall is often used along an existing building;

It's very convenient to urban areas;

The implementation is simple.

Disadvantages:

The Berlin wall is only used for small depth; This method can't be used in case of a high water-table level.

It mostly used for temporary structures.

6.1.5. Diaphragm wall

-by Sophie-

Diaphragm wall, also called slurry wall in United States, is a continuous retaining wall formed

and cast in a trench. The terms

"diaphragm" and "slurry wall'

come from the final step of the

implementation. The slurry is

replaced by concrete which acts

like structural system for

temporary retaining wall or as a

part of a permanent structure.

Diaphragm walls are mainly used

for deep excavations basements /parking and tunnels. They can

also be used as the future

foundations of the construction

above.


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The method of implementation is suitable for urban areas because it doesn't generate a lot of

noise or vibration compared to sheep pile driving. First a guide-wall made from in-situ cast

concrete, concrete elements, guide rail constructions will be placed on the ground to make sure

that the future will be straight. Then panels will be driven and filled in with bentonite so the

drilling will stay opened and not collapsed. After that, the traditionally bounded reinforcementis placed in the drilling. Finally the concrete is poured in the drilling as the bentonite is forced

out of the trenches. This fluid will be after cleaned and reused.

Advantages:

This method allows retaining walls of great depth (up to 100m);

It can be used in case of high water-table level;

Excavations can be made in difficult conditions of the soil;

The implementation can be made very close to existing construction;

The retaining wall can be a part of the final foundation of the construction.

Disadvantages:

There is a risk of variation in the thickness of the wall;

The implementation takes quite a long time;

This method is very expensive;

The construction of this type of wall requires the use of heavy construction

equipment;

It also takes a lot of space on the construction site and above it;

The excavated soil has to be moved somewhere else.

6.1.6. Secant pile walls

-by Marta-

Secant pile walls are formed by constructing interlocked concrete piles reinforced with either

steel rebar or steel beams. Used extensively in dense population areas due to the minimal

disturbance they cause to adjacent structures, secant walls are a form of top down construction

used for environmental remediation and soil retention.


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Figure 12 Scheme of principles

Primary piles are installed first with secondary piles constructed in between primary piles once

the latter gain sufficient strength. Pile overlap is typically in the order of 8 centimetres.

Advantages:

Can be used close to existing buildings (no noise and vibration);

Increased construction alignment flexibility;

Increased wall stiffness compared to sheet piles;

Can be installed in difficult ground (cobbles/boulders);

Can be used as a permanent construction;

Good a load bearing construction;

Can be used in very deep excavation (more 8m);

Gentle installation method (drilling).

Disadvantages:

Increased cost compared to sheet pile walls;

Takes a long time to install;

Using a lot of materials (steel and concrete);

Verticality tolerances may be hard to achieve for deep piles;

Total waterproofing is very difficult to obtain in joints.


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6.2. Conclusion

-by Marta-

Comparing the mentioned retaining walls the timber- and concrete sheet pile walls could be

disregarded as an option quite easily. That is because the timber sheet pile walls were not an

option considering the height of the construction and the concrete pile walls are too heavy and

too expensive.

The implementation of the diaphragm walls takes quite a long timeand also it is very expensive,

so in this way this type of wall was also not a good option.

The main reason why the berlin wall was not chosen is that it is not completely waterproof.

The steel sheet pile walls have also some disadvantages, but comparing with the other type of

walls they are still the best solution which could be used for this construction.

The secant pile walls were chosen from the start because there was a need to get close to the

existing buildings in one part of the building; therefore it was really important to choose a type

of wall which it can be implemented without noise and vibration.

The table below shows summarizes the advantages and disadvantages for the chosen wall

types:

Steel sheet pile wall Secant pile wall

Resistance + +

Stiffness of wall - +

Duration of installation + -

Installation in hard soils - +

Gentleness in installation method - +

Lifetime + +

Weight + -

Cost + -


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7. The design of the retaining walls

-by Marta-

The design of pile retaining walls requires several successive operations: evaluation of the

forces and lateral pressures that act on the wall, determination of therequired depth of piling

penetration, computation of the maximum bending momentsin the piling, computation of the

stresses in the wall and selection of the appropriatepiling section and the design of the walling

and anchorage system.

Before these operationscould be initiated some preliminary information must be obtained.

These include the elevation of the topof the wall, the elevation of the ground surface in front of

the wall, the maximum water level. It

was essential that a subsurface

investigation has beenperformed with

exploratory borings and laboratory

tests of representative samples. Onthis

basis, a soil profile could be drawn and

the engineering properties of the

different soilstrata could be accurately

determined. These properties should

reflect the field conditionsunder which

the wall is expected to operate. Onlyafter these preliminary steps could the

final design have done.

Now, by having all these necessary

information the calculation of the

retaining walls it can be made.

The picture shows where the sheet-

and secant pile walls placed. The blue

line indicates the place of the steel

sheet pile walls, and the red onethe

place of the secant pile walls.

Figure 13The place of the different type of retaining walls


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The dimensioning of the walls was examined in ultimate limit state. This limit state ensures

sufficient safety against failure, and as a basis of the calculation it uses the plasticity theory /

failure theory (Coulombs failure condition):=c+*tan .

To satisfy the ultimate limit state, the structure must not collapse when subjected to the peakdesign load for which it was designed. A structure is deemed to satisfy the ultimate limit state

criteria if all factored bending, shear and tensile or compressive stresses are below the factored

resistance calculated for the section under consideration.

The soil parameters taken from the geotechnical description are characteristic values; therefore

it is important to define the partial coefficients for these parameters and to determine the

design value of them.

The Danish National Annex (EN 1997-1 DK NA:2008) set up the following values for the

different parameters:

Figure 14 Partial coefficients for soil parameters (m)

The Danish National Annex it also says that depending on the structure whether it is a

permanent or a temporary one partial coefficients shall be used with values taken as (M)

where is a number for which the following applies: 0 <


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The long term stateuses the parameters cand , which are referred to as the drained

(effective) strength parameters. The clay now its rough, so in the calculations the effective

friction angle was going to be used.

The sand both in short and long term state is treated as a rough soil layer.

To calculate the sheet and the secant pile walls it was used Brinch Hansens general theory

about lateral soil pressure, which forms the basis for the calculation of traditional sheet piling in

Denmark. The fundamental principle of Brinch Hansens theory is that the lateral soil pressure

on a given wall is dependent on the walls direction of movement and the location of the point

around which the wall rotates.

It is important to mention here that because of the lack of information about how to calculate

the water pressure caused by the difference in water-tables between the back and the front

sides of the wall, it was considered that the water level on both side of the wall is in the samelevel.

It was important to choose the most economical solution; therefore more methods were used

in the calculations.

Through dimensioning, the walls total height is determined, as well the pull force in the

anchorand the maximal moment in the wall.

Because of the depth of penetration, the anchor force and the maximal moment are different

for thecalculation methods; it means that there will be different price levels for the different

walls. It ispossible, through a comparison of the calculations, to choose the most economic wall

ifconsideration must not be taken to a specific depth of penetration, a given anchorage or a

specificprofile.

Brinch Hansen has shown that a retaining wall that is correctly dimensioned under thecondition

of a specific fracture mode will not be able to fail in any other way.

With the calculations it was determined the following:

Toe level

Lengthof wall

Maximum bendingmoment

Horizontalanchorload


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There were performed both hand and computer calculation in order to have more secure

results. For this it was used the Danish software SPOOKS, which also uses the basis for the

calculation of sheet piling described by Brinch Hansen.

7.1. Steel sheet pile walls-by Marta-

The steel shite pile walls will be placed in the whole contour line of the excavation, except the

line along the adjacent boundary to the south and along a ca. 22 m stretch of the southern part

of neighbouring boundaries to the east.

Figure 15The different type of layers and their parameters used for the calculations

In order to find the best and cheapest solution the calculation was done by using 4 methods.

According to BrinchHansens soil pressure theory, one can choose different fracture methods,

which have an influence on thesheet piles final hammering depth and dimensions.


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The retaining walls are penetrated in clay so both the short term state (STS) and long term state

(LTS) was checked.

The steel sheet pile walls were designed

with:

1. One anchor with

a. 0 yield hinge

b. 1 yield hinge

c. 2 yield hinges

2. Two anchors

After all the calculations (See Appendix no.6)the results are shown in the following tables:

The results by using 1 anchor with 0, 1 or 2 yield hinges:

UNDRAINEDCONDITION

Toe level

Length (m)

Mmax (kNm/m)

A (kN/m)

0 yield hinge

+3.28

9.72

-8.25

547.52

1 yield hinge

+3.21

9.79

-92.66

558.26

2 yield hinges

+3.05

9.95

2.77

543.49

DRAINEDCONDITION

Toe level

Length (m)

Mmax (kNm/m)

A (kN/m)

0 yield hinge

+2.49

10.51

16.52

176.81

1 yield hinge

+3.09

9.91

56.55

120.50

2 yield hinges

+1.15

11.85

59.00

126.26

Figure 16 Anchored wall with 0, 1 and 2 yield hinges


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The results by using 2 anchors:

All these solutions are correct, but they will have big impact on the price of the wall.The

following can change the results:

The installation method of the sheet Soil conditions

The possible dimensions of the available sheet

The anchor capacity

Is this the final excavation level or is it only a temporary excavation level

Steel prices in different qualities

Comparing the results from both short and long term it seems that the long term solution used

for all of the methods should be used to make the calculation of the sheet walls.

To find the best price, first the length of the wall was considered. If the wall is shorter the price

can be reduced importantly.By designing the sheet pile walls with one anchor the results show

that using one yield hinge gives the shortest wall: 10.11 meters.Introducing one more anchor

the height of the wall will be reduced to +9.3 meters.

After this, the horizontal anchor loads give the result that the wall with two anchors has smaller

or more or less the same anchor pull than the one with just only one anchor.

The last thing was to compare the maximum bending moments. The values indicates that the

difference between the bending moments is not that big, so the appropriatesteel qualitywhichis going to be used can be the same for all of the methods.

As a final conclusion the cheapest method is the one with two anchors, thanks to its shorter

height and lower anchor pulls.

Toe level

Length (m)

Mmax (kNm/m)

A1(kN/m)

A2(kN/m)

UNDRAINEDCONDITION

+3.5

9.5

78.40

46.72

93.72

DRAINEDCONDITION

+3.7

9.3

135.73

60.73

74.9


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Now with these results, the steel quality has to be chosen. Because the bending moment in the

wall is quite small, the steel quality S 240 GPfrom the German HOESCH company was selected:

The value 240is the characteristic value of the yield strength: fyk= 240 MPa. The safety factor of

steel is equal to: f,steel=1.1. Therefore the design strength can be calculated as:

So: MPa.Now the steel quality is chosen, the next step is to find the most appropriate sheet type. For

this the necessary moment of resistance will be calculated with the following formula:

The last thing in the selection of the steel sheet pile walls is the shape of the walls, the profile.

The steel sheet piles are typically made of rolled steel U or Z profiles that have folded

lengthwise edges that lock together with the neighbouring profile and steer the profile whilst it

isbeing hammered down into the ground. For this construction the Z-shaped steel sheet pile is

going to be installed: they feature the joints located outside in the right and left when fit with

each other.


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Figure 17Thechosen profile and its dimnesions

7.2. Secant pile walls

-by Sophie-

Secant pile walls will be placed on the line along the adjacent boundary to the south and along

a ca. 22 m stretch of the southern part of neighbouring boundaries to the east.

Figure 18The different type of layers and their parameters used for the calculations


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The secant pile walls are placed mostly on clay which has a result that the calculation of them in

undrained condition wasnt working. Therefore these retaining walls were designed only in long

term state (LTS).

Two methods were used by designing these walls:

1. One anchor without yield hinge

2. Two anchors

Because the present layers are stiff it is not necessary to use any yield hinges.

After all the calculations (See Appendix no.7) the results are shown in the following table:

Comparing the results, first of all,they show that the shortest wall is given by the wall with two

anchors by the second solution. The maximum bending moment is the smallest in the wall

without yield hinge but the difference is not too big so the Solution 2 using 2 anchors is againthe winning method. Then it is noticed that the anchor pull (the summarized one) is almost the

same in each solution. The first solution of the secant pile wall with 2 anchors can be

disregarded easily because the Solution 2 in each aspect is the better solution. In the end, the

decisive aspect was the height of the wall, therefore the cheapest solution is considered to be

the Solution 2.

7.2.1. Calculation of the reinforcement

For this construction site, one of two secant pile is reinforced. (See Figure 12) This means thatthe reinforcement in the anchor has to be considered for one entire pile and two half of them.

Basically for the calculations two wall elements will be taken into account when determining

the reinforcement in the secant pile wall.

DRAINED

CONDITION

Toe level

Length (m)

Mmax (kNm/m)

A1(kN/m)

A2(kN/m)

0 yield hinge

+1.37

10.63

190.55

547.52

-

2 anchors

Solution 1

+3.0

9.0

342.80

510.6

48.2

2 anchors

Solution 2

+3.7

8.3

224.50

258.04

298.54


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The secant pile wall takes the load coming from the earth pressure corresponding to the

calculation of the retaining wall. Each wall element acts like a vertical beam with its bottom end

fixed in the ground. The diaphragms formed by the two levels of parking are not considered in

the calculations because the wall has to stand the earth pressure before the implementation of

the rest of the building. Thats why the earth pressure has a triangular distribution and themoment which is considered is quite big.

First the concrete strength, diameter of the pile and strength of steel are picked and those will

be verified with the calculations. In this case:

Concrete: C25/30

Fcd= 25 MPa

Steel: B550

Fyd= 458 MPa

Diameter of secant pile: d = 80 cm

Then, an assumption is made to start the calculations with z (which is the hight between the

centre of gravity of the reinforced part and the centre of gravity of the compression part.)


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The formula written above gives the exact dimensions of the compressed area. The centre of

gravity of the compressed area has to be calculated to find the exact z. after the same

calculation are done again to shows that the theoretical result found before was approaching

and of course to find the exact section of steel that has to be put in the pile.

The steel cage is placed all around the wall element even if in

the end, it will be really relevant only in the tensed part.

Finally the diameter of 80 cm is sufficient. The steel section found is:

As= 30.1 cm2

The solution that has been decided is 10 steel bars with a diameter of 32 each placed all around

the wall element. (See sketch below)

7.3. Conclusion

On the site will be installed two different types of retaining walls: in one hand steel sheet pile

walls and in the other hand secant pile walls. More methods were done in order to find the

most economical solution, and thiswas given in both cases by using two anchors. The steel

sheet pile walls will have a length of 9.3 meters and the secant pile walls will be with one meter

shorter: 8.3 meters. To show how these retaining walls will be placed on the site a drawing was

made. (See Appendix no.9)


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8. Ground anchors

-by Marta-

A ground anchor is defined as a steel bar or multi-strand tendon grouted in a drilled hole

inclined at an angle below horizontal, whichis capable of transmitting an applied tensile load to

a load bearing stratum, for the specifiedduration of the structure in which it is required to

withstand the design load.

Considering the type of the anchor which will be installed to the walls, the inclined anchors will

bring the best solution. The other option was the horizontal ones, but because of the problems

which would have been appeared during the installation, this solution was disregarded.

The retaining walls were designed, so the values for the anchor pulls are known. The type of theground anchors was also chosen so the next step is to calculate them.

To calculate the anchors it means to find out their length. The length of the anchors is formed

by the external-, free-, and the fixed length.

External length

It is approximated to 1 meter.

Free length

This is that length of the tendon which transmits no

load to the surrounding strata.

Coulombs theory says that potential failure plane

behind the wall forms an angle with the

horizontal: (See the picture).

Figure 19 Calculation of anchor length


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In order to make the calculations the partial coefficients have to be considered. The Danish

National Annex says that these coefficients for the ground anchors (Piles and anchors) are not

relevant in Denmark:

Figure 20 Partial coefficients for soil parameters (m)

It is important to note: because the retaining walls will be installed as permanent construction,

together with them the ground anchors will be permanent too. Therefore the same rule will be

applied here too: the value for in (M) is set to 1.0.

Different layers of soil are faced when calculating the anchors for the steel sheet pile wallswhich means it has to be taken into account that the layers have different friction angles. To

stay on the safe side, the lowest friction angle (30) was used in order to determine the free

length of the anchors.

As a normal procedure, the inclined anchors will have a 20 inclination; this of course can

change up to 2 because the drilling machines cannot be that precise.

To calculate the fixed length it can be used the figure shown above. From the triangle thelength of the c is known, which is the distance from the foot point of the wall to the anchor

point.

First, by dividing the triangle in two ones, the common leg of them could be expressed as:


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The ccan be calculated by summarizing the two adjacent legs of the triangles:

Then,bis determ

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