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Transcript of Are you prepared?
Are you prepared?
How principals can avoid subsurface
surprises
Studies have shown that a substantial proportion of failure costs in the construction industry are linked to the subsurface:
“The knowledge platform SBR has calculated that geo-engineering failure costs account for 25% of all construction costs. The Dutch Association for Foundation Contractors (NVAF) found that failure costs make up 20% of the turnover of pile driving contractors. TNO Building and Construction Research has said that efficiency shortfalls in the construction process associated with geo-engineering failures cost more than nine million euros.”
Source (in Dutch): ‘Breng geo-risico’s zo vroeg mogelijk in beeld’, Fugro Info, July 2013
For these reasons, the Geo-Impuls programme was launched in 2009 to develop tools that will help to prevent geo-engineering failure. This booklet is one of those tools. On www.geoimpuls.org (in Dutch) you can find more products that can help you to manage subsurface risks.
IntroductionLet’s say you’re about to go on holiday. A week on a
tropical island. It doesn’t matter how simple your plans
are – lounging around on the beach, an occasional bite
to eat – you mustn’t forget the essentials. You check
your passport, you decide what to pack. Obviously.
Construction projects are no different. Nobody just
issues instructions for a design or for construction
without taking pause for thought, to take a good
look at the project and the locality. And you check for
potential risks. That is where this booklet comes in.
This publication tells you about the possible subsurface
risks that may affect your construction project. This
isn’t your field? No worries: what matters is to get
thinking about the subsurface early and throughout
the process (during the planning phase as well). That
can produce major benefits. Even though each project
is unique, there are still some subsurface risks that
recur regularly. Keeping an eye on them can prevent
delays, cost overruns and damage to your reputation.
There will also be openings for smart solutions that
will give your project added value.
Of course, this booklet won’t eliminate subsurface
risks or identify every conceivable risk, but it will give
you a clearer picture. It could be the key to success for
your construction project.
This booklet primarily targets principals of construction projects, project developers, contractors and architects.
However detailed our surveys and investigations, we cannot map out every cubic centimetre below a construction site. So there are always subsurface risks, often related to geo-engineering (which can be roughly summed up as ‘subsurface technologies’), such as the construction of foundations, site preparation works, or digging a construction pit.
As you leaf through this booklet, you will see pages with tick boxes.
These pages list project factors that may affect subsurface risks. Does
one of these factors apply to your project, or are you are unsure? Then
turn the page to find information that will help you take the right
decisions about your project. If none of the factors apply, you can
move on to the next focus point.
Is everything important?
As you are reading, you may get the impression that all focus points
are relevant to your project. That may be right, because this booklet
addresses issues that crop up frequently. In reality, there are many
more focus points to consider. This booklet shows the most important
themes for an initial assessment.
Guide for the reader
Contents
1 INTRODUCTION
3 FOCUS POINTS
3 Local conditions
5 Challenging structures
7 Time and space constraints
9 Water defences
11 Groundwater
13 Subsurface composition
15 Unexpected obstacles
17 PAST SUCCESSES
18 Conservatorium Hotel
20 Villapark Eikelenburgh
22 University Medical Center Groningen
24 Boxtel-Oost overflow replacement
FOC
US P
OIN
Tpage 3
>>>>
Local conditionsThis focus point refers to the immediate physical locality of your construction project: the rule of thumb is an area of at least twenty-five metres around the site. It can extend to more than two hundred metres when drainage work and vibrations are involved.
Have you ticked one or more boxes, or do you have any doubts about an answer?
Read the information overleaf!
Are there any buildings that are particularly vulnerable to vibrations or settlement? These may be old or brick-walled buildings, buildings
with shallow foundations or premises where people work with sensitive electronic equipment.
Is there a railway nearby?
Are there any vulnerable cables or lines in the subsurface, such as high-pressure gas pipes, sewers or high-voltage cables?
Are there access routes that are crucial for the surrounding area?
If you haven’t ticked any boxes and you
are sure about the answers, then you can
go straight to the next focus area.
>>>>
PossibilitiesYou can obtain information
about the locality from,
for example, the Land
Registry or municipal
authority. Many municipal
authorities keep records
about building foundations.
The Netherlands’ Cadastre,
Land Registry and
Mapping Agency (Kadaster)
offers information about
subsurface cables and
pipes. A geo-engineering
consultant specialising in
excavation pits and risk
management for the local
area can provide you with
detailed advice.
Construction work, and particularly
subsurface construction, can easily
cause soil deformation or vibrations
in the vicinity. Sheet piles, for
example, are vibro-driven or pile-
driven: these vibrations can cause
permanent deformation in the
subsurface or have a direct impact
on nearby cables, pipes or buildings
through the foundations. Digging a
construction pit can also cause soil
deformation. For all these reasons,
the success of your project depends
upon a close inspection beforehand
of all the local structures. That
way you will for instance know in
good time whether extra support
is needed for the sheet piling or
whether you should use vibration-
free techniques (such as pressing-in
sheet piles or casting piles on-site).
Local conditions
FOC
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Tpage 5
Of course, every structure needs to be robust but there are times when new foundations need extra attention. This focus point addresses these situations.
Challenging structures
>>>>Is the structure or the activity in a building particularly
vulnerable to vibrations? Will the building be used to house, for instance, sensitive electronic equipment?
Are there special requirements relating to the deformation (bending, settlement, etc.) of the structure? This is often
the case when an extension is added to an existing building, for example.
Will the load on the subsurface be distributed unevenly? Is one side of the building higher than the other?
Is it a complex structure such as an extremely high building or a structure that is built completely or partially underground?
Have you ticked one or more boxes, or do you have any doubts about an answer?
Read the information overleaf!
If you haven’t ticked any boxes and you
are sure about the answers, then you can
go straight to the next focus area.
PossibilitiesIn the Netherlands
the DINOloket (www.
dinoloket.nl) is a free on-
line database containing
subsurface data. Geological
Surveys in other countries
offer comparable services.
You can call in a geo-
engineering consultancy
for a soil survey. Specialist
foundation consultancies
can also provide you with
specific information and/or
detailed recommendations
about the right foundations
for your project.
Challenging structures
>>>>The foundations hold up the
structure and they are a major
factor in safeguarding stability.
So if requirements relating to
deformations and vibrations
in the structure are strict, it
certainly makes sense to make
the foundations stronger. This in
turn requires a clear picture of
what is below the ground since
the effectiveness of foundations
greatly depends on the particular
subsurface. For example, if a
number of foundation piles don’t
reach the right layer, your building
may tilt or crack. You certainly
don’t want that to happen.
FOC
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OIN
Tpage 7
Is there a lack of space to work in, for example because the construction takes place in a city
centre, in an existing building or below a bridge?
Are there major time pressures affecting your project?
Is access to your project difficult?
>>>>Time and space are really two separate themes but they amount to the same thing in terms of subsurface risks: the project conditions complicate the work.
Have you ticked one or more boxes, or do you have any doubts about an answer?
Read the information overleaf!
If you haven’t ticked any boxes and you
are sure about the answers, then you can
go straight to the next focus area.
Time and space constraints
Time and space constraints
PossibilitiesIt helps if you don’t let
yourself be rushed during
the preparation stages:
if something goes wrong
during the operational
stage, any time you
gained will be lost again
(many times over), your
reputation could be at risk
and cost overruns may
occur. Try and find out
exactly where the time
pressures come from, and
talk to the responsible
party. You could also
look for a contractor who
specialises in working in
unusual conditions.>>>>When a project has to be completed
quickly, sound soil surveys are often
neglected, even though there are
actually more risks in busy locations.
Special techniques, such as pile
driving below an existing structure,
can prevent problems in good time.
Special measures and alternative
methods – such as more manpower,
lighter equipment or modular
construction systems – are often
needed to complete the project when
the schedule is tight or space is at a
premium. In general, this will mean
more costs, additional preparations
and extra supervision, all things that
you need to take into account.
FOC
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OIN
Tpage 9
Is there a water defence structure within a distance of about twenty-five metres from the construction site?
Water defencesFor many people, ‘water defences’ mean dikes and dunes. But not all water defences are so easily recognisable. Many towns and villages have water defences that no one notices because they comprise a road or the ground supporting a row of houses.
>>>>Have you ticked the box, or do you have any doubts about the answer? Read the
information overleaf!
If you haven’t ticked the box and you are
sure about the answer, then you can go
straight to the next focus area.
Water defences
PossibilitiesThe local water management
authority will have maps
showing all water defences,
and areas where you are
not allowed to build or dig.
For information about the
specific risks on your project,
you are best advised to get
in touch with a hydraulic
engineering consultant or a
geo-engineering consultant
specialising in hydraulic
engineering. It is also useful to
arrange for a meeting between
your consultant and the water
management authority.
>>>>
Construction can have a
negative impact on water
defences. For example, if soil
settles when a construction
pit is excavated, the resulting
deformation can stop a dike
working effectively. The same
applies to the installation
of foundation elements or
using heavy cranes. Rules
and permits relating to water
defences are strict, and the
procedures often take a long
time. So you should engage at
an early stage in discussions
about permits for (temporary)
adjustments in the water
defences, or avoid working
close to the defences.
FOC
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Tpage 11
Will you be building below the water table, for example to construct a cellar or tunnel?
GroundwaterThe groundwater level is a major factor in each construction project. In the Netherlands, levels vary from less than a metre to some tens of metres below ground level.
Do you need a dry construction pit?
>>>>Have you ticked one or more boxes, or do you have any doubts about an answer?
Read the information overleaf!
If you haven’t ticked any boxes and you
are sure about the answers, then you can
go straight to the next focus area.
Groundwater
PossibilitiesYou can obtain information
about groundwater
levels from the local
water management
authority and/or make
a rough estimate on
the basis of the water
levels in open water.
Be aware though that
groundwater levels can
be a lot higher or lower
in surrounding waters.
A drainage specialist
with a geo-engineering
or geohydrological
background can provide
you with specific
information and/or
detailed advice. You
should also arrange for
a discussion with the
licensing authority’s
geohydrologist.>>>>
If you want to work in a dry
construction pit below the water
table, there are – broadly speaking
– two options: drainage (lowering
the groundwater level) or excavating
in a pit with water retaining walls.
The first option is subject to strict
regulations and requires a permit
because drainage affects the water
regime throughout a wide area.
Lowering the water table can result in
land subsidence, the diffusion of soil
pollution and, if drainage continues
over a period of months, in the rotting
of the foundation piles. Groundwater
can also be a significant factor
when watertight walls are used. The
bottom of the construction pit may,
for example, burst open as a result
of the pressure of the water. So you
should not underestimate the impact
of groundwater on your project.
FOC
US P
OIN
Tpage 13
>>>>Are you planning to build in or on soft soils such as
peat, soft clay or loosely-packed sand?
Subsurface compositionDigging in soft soil is of course easier than in hard soil. But building in or on soft soil is a different story. The structure and composition of the subsurface are factors that play a crucial role in your construction project.
Could there be gravel layers in the subsurface?
Are you planning to build on an extremely hard subsurface?
Is the subsurface composition extremely varied; could it change drastically over very short distances?
Have you ticked one or more boxes, or do you have any doubts about an answer?
Read the information overleaf!
If you haven’t ticked any boxes and you
are sure about the answers, then you can
go straight to the next focus area.
Subsurface composition
PossibilitiesFor your project, it can
make sense to commission
additional geo-engineering
soil and laboratory testing.
You should ask a range of
agencies for quotations for
risk-based soil surveys and
base your appraisal of their
proposals primarily on the
arguments put forward. You
may also wish to consider
agencies and experts from
Belgium and Germany who
have, for example, more
experience with limestone.
>>>>
A soft soil settles relatively quickly as
a result of subsurface construction or
surface loads. This can result in local
damage or render the new structure
unstable. On the other hand, hard,
stony ground is not ideal either: gravel,
for example, represents an obstacle
to pile driving and the installation of
sheet piling. Furthermore, a varied
soil profile can make for unwelcome
surprises. To select and apply the right
techniques it is therefore important
to establish a clear picture of the
local subsurface structure. A wide
margin of uncertainty about the
subsurface means that there will also
be considerable uncertainty about
the robustness and feasibility of the
project as designed.
FOC
US P
OIN
Tpage 15
>>>>Have any archaeological remains been
excavated in this locality?
Unexpected obstacles
Is there a meaningful probability of soil contamination?
Is it likely that unexploded ordnance will be located below the surface?
There are few locations in the Netherlands where the subsurface is entirely undisturbed. So you should already be thinking about the obstacles that you could encounter.
Has there been subsurface building activity before in this location? Could there be any
old grout anchors, for instance?
Have you ticked one or more boxes, or do you have any doubts about an answer?
Read the information overleaf!
If you haven’t ticked any boxes and you
are sure about the answers, then you can
go straight to the next focus area.
Unexpected obstacles
PossibilitiesStudying records
and local enquiries
about how the site
has been used earlier
make it possible to
assess the risk of
unexpected obstacles.
An agency specialising
in archaeology or
environmental science,
for instance, can
supply you with more
detailed information
or specific advice
about your project.
>>>>
Unexpected obstacles can
easily cause delays. Work
may have to be suspended
to look at archaeological
finds and action is often
required when soil pollution
is discovered. Not only this,
obstacles can also make it
impossible to dig founda-
tions to the right depth, with
the effect that different
engineering solutions are
required. Thorough explora-
tory studies, both in archives
and in the field, can prevent
many delays and unexpected
costs.
To show you how checking subsurface risks can
produce genuine benefits, we have collected a number
of stories about real-life situations. These demonstrate
how an early and ongoing focus on the subsurface
contributes to project successes. The stories also
show that it is not difficult to take subsurface risks
into account and that doing so is a logical part of any
project preparations.
Past successes
Conservatorium Hotel
A strong emphasis on geo-engineering was one of the success factors in the renovation of the Conservatorium Hotel in Amsterdam. Between 2008 and 2011, the listed building dating back to 1897 was transformed into a luxury property. The busy location, with tourist attractions and other historical buildings, in combination with the client’s stringent standards, resulted in a complex geo-engineering challenge.
This project covered the following areas:
Local conditions, page 3Challenging structures, page 5 Time and space constraints, page 7Groundwater, page 11
PAST SU
CC
ESSpage 19
One requirement was a cellar with a pool in the courtyard of
the building. Space was very much at a premium: the walls of
the construction pit were less than one and a half metres from
the outer wall. Extensive soil surveys and a range of design
calculations were used to obtain a detailed picture of how
the excavation of the construction pit could affect the existing
building. A monitoring plan was then established with limits
and alarm levels, and there were extensive discussions with all
stakeholders about the measures that would be triggered by
exceedances of the limit values.
The thorough preparations proved their worth on several
occasions during the construction phase: as a construction
pit was being pumped dry, it was noted that a section of the
second strut frame had subsided. The supervisor was able
to intervene quickly, and work out and implement measures
immediately using the monitoring data available. The strut
frame was repaired within two weeks and the construction pit
was completed without any significant delay. Other incidents
were managed without any meaningful additional costs or
delays as well. The resulting savings more than compensated
for any of the investments made in advance.
Villapark Eikelenburgh
On Friday, 9 November 2012, the first pile for Villapark Eikelenburgh was driven in Rijswijk. Approximately three hundred homes will be built during the construction phases for this new residential area. Site preparation work began in 2012. The costs were reduced considerably by taking the local subsurface structure into account.
This project covered the following areas:
Groundwater, page 11 Subsurface composition, page 13
PAST SU
CC
ESSpage 21
The site preparation work for Villapark Eikelenburgh used the
conventional method of pre-loading with sand and soil to prevent
subsidence in the subsurface in the future. This process can be
accelerated using vertical drains that remove the groundwater.
The residual settlement requirement (to what extent will the
subsurface still settle after the construction phase?) determines
whether drainage is required, the depth of the drains and how
thick the sand and soil layer needs to be.
Usually, the same residual settlement requirement is used for the
entire area under development but the contractor here split up
the area into four sections, tailoring the requirements in line with
future use. He also decided to conduct additional soil surveys.
It emerged that the local subsurface was less susceptible to
settlement than expected: the subsurface consisted of small layers
of clay and sand, a composition that could not have been identified
earlier when the geo-engineering advisory report was drafted.
The new information and adapted residual settlement
requirements resulted in a number of changes to the pre-loading
plan. Drainage was installed in only half of the area and, in the
other half, the drains were installed at a depth of six, rather than
eighteen, metres. In addition, it emerged that the pre-loading
material did not have to be two metres high everywhere: fifty
centimetres was adequate in one third of the area. Given the
size of the area under development as a whole, these changes
represented considerable cost savings.
UMC Groningen
In 2001, a new facilities building was built at the University Medical Center Groningen (UMCG). A three-storey parking lot and a new logistical transfer facility were built below this building. A smart approach was adopted to benfit from the local subsurface conditions.
This project covered the following areas:
Groundwater, page 11 Subsurface composition, page 13
PAST SU
CC
ESSpage 23
The UMCG is located on the edge of what was a glacier
during the ice age and so the subsurface contains
very dense clay. This glacial clay is ‘overconsolidated’:
the pressure of the glacier caused the soil to be pre-
loaded and very compact. This can represent a major
geo-engineering challenge. It may, for example, often
be difficult to insert foundation piles to the required
depth. Glacial clay is also so strong that, when it
swells (after the removal of the top load), it can push
up structural elements in unexpected ways.
However, the client was able to use the difficult
conditions to everybody’s advantage. A detailed
survey looking at the subsurface structure was
conducted with a geo-engineering consultant in the
early stages so that the conditions could be taken
into account during the design of the car park. As
a result, the water-tight layer of glacial clay has now
been used as the floor of the car park, cutting costs
considerably. The size and shape of the car park were
also adapted specially on the basis of the soil survey
to make optimal use of the natural conditions.
Boxtel-Oost overflow replacement
To prevent flooding and other problems with excess water, the Boxtel municipal authority replaced four overflow facilities in 2012. That involved digging down to a depth of about three metres close to housing that was known to be highly vulnerable to construction activity. As a result, the municipality was particularly critical during the preparatory stages and in the selection of a contractor.
This project covered the following areas:
Local conditions, page 3 Subsurface composition, page 13
PAST SU
CC
ESSpage 25
The authority commissioned an extensive soil survey
and the local subsurface proved to be extremely
unpredictable, so it was difficult to say what the
impact on the locality would be. The geo-engineering
consultant was asked to draft a proposal for the work
that took the vulnerable surroundings into account. The
proposal included a recommendation not to use steel
sheet piles because of the risk of vibration damage but
to conduct excavations using trench shoring. It also
noted that compensatory measures could be required
locally to prevent damage.
The consultant’s suggestions were included as an
information document with the specifications. The
municipality, the specifications writer and the geo-
engineering consultant then made a joint assessment
of the tenders on the basis of completeness and quality.
The contractor who was selected followed the proposed
approach in most respects. A compensatory measure
that was adopted involved installing a return drainage
system between the excavated area and the houses.
This measure, the thorough preparations and the
meticulous approach to execution meant that the work
was completed without any noteworthy problems.
This booklet was published by the working group Subsurface to the forefront, as part of Geo-Impuls.
The national Geo-Impuls programme brings together more than thirty organisations from the civil and
hydraulic engineering sector with the aim of reducing geo-engineering failures. For more information, see
www.geoimpuls.org (in Dutch).
By focusing on subsurface risks in good time and continuously, it will be possible to manage geo-
engineering risks better. This booklet therefore helps projects to be geØké, in other words to keep geo-
engineering risks well under control.
Working groupAnnemarij Kooistra (chair), IBA - Auke Balder, CRUX
Engineering - Jurjen van Deen, Deltares - Jan Pieter Eelants, CROW - Jan Jaap Heerema, Rijkswaterstaat - Mario
Niese, Royal HaskoningDHV - Bart van Paassen, BAM Infraconsult - Maarten Profittlich, Fugro - Stijn Schoen, Royal
HaskoningDHV - Gerhard Wibbens, BAM Infraconsult
PrintFirst edition: December 2013
Second, improved edition: June 2014
TextMembers of the working group, see above
TranslationPete Thomas Vertalingen/Translations
Editing and layoutMarije Nieuwenhuizen
Digital versionThis publication is available free
of charge in digital form from www.geoimpuls.org
Cover photoVincent Basler
Images accompanying projects• Pages 18/19, all images: CRUX Engineering• Pages 20/21, all images: AM• Pages 22/23, from top to bottom:
UMCG/KuiperCompagnons, KuiperCompagnons, KuiperCompagnons, Fugro/Ingenieursbureau Wassenaar, KuiperCompagnons
• Pages 24/25, all images: Fugro
CopyrightThe text in this booklet may be quoted freely on condition that the source is clearly stated. To use imagery, you should contact the relevant source (see above).
ARE YOU PREPARED? How principals can avoid
subsurface surprises