Table of Contents

Acknowledgement

Executive Summary

1.Introduction

1. Objective

2. Methodology

3. Description of the instruments used in the field

2.Study of Mass Movement

1. Introduction to mass movement

2. Types of mass movement

I. Slope Failure

II. Landslide

III. Debris Flow

3. observation of landslide in the field

4. Mitigation measure of landslide

3.Rock Mass and Rock Mass Classification

1. Introduction

2. Rock Type

3. Weathering

4. Intact Rock Strength

5. Discontinuities in Rock Mass

6. Characteristics of discontinuities in rock mass

7. Rock Mass Rating

8. Rock Mass Classification System

9. Rock Mass Rating Observation Table

4.Stability analysis of Rock Slope

1. Introduction

2. Failure Mechanism in rock slope and types of rock failure

3. Slope stability analysis

5. Tunnel and underground excavation

1. Introduction

2. Site selection

3. Geological consideration of successful tunnel

I. Importance of Rock Types

II. Importance of geological structures

III. Importance of groundwater

IV. Overbreak

6.Preparation of Engineering geological map

1. Introduction

2. Methodology

3. Engineering geological map

7.Study of Intact rock Weathering classification

8.Conclusion

9.Refrences

Acknowledgement

At every step, an engineer has to encounter earth and earth, as a material or as construction site. So it

proves the importance of geology to civil engineering professionals. He or she must go through the inner

core of engineering geology for his/her perfection and for professionalism.

The trip was really fruitful to us and certainly we got a lot of knowledge about the earth.

We would like to thank our Class Teachers: Mr. Basant Raj Adhikari and Prakash Chandra Ghhimire for

their guidelines during the trip. Without their collaboration, the trip would have been impossibile. Thank

you all our classmates who helped us during fieldwork. Thank you very much Mr. Om dai for your help in

preparing this report.

At last, we would like to express our gratitude to our college, institute of engineering. We are proud of

being students of pulchowk campus.

Executive Summary

G-4 Date:2072-05-10/11

Sibesh Kumar Singh (070/BCE/164)

Shrijan Basnet (070/BCE/163)

Sonu Shah(070/BCE/167)

Subash Shrestha (070/BCE/168)

Sobin Lal Pradhan (070/BCE/166)

1.Introduction

1.1 Objective

Study of rock mass and rock mass classification by rock mass rating system along the

Benighat to Aarughat road section .

Study of underground excavation and support system of test-adit of Budhigandaki

Hydroelectric project

Study of rock slope stability along Benighat to Aarughjat road-section.

Preparation of Engineering Geological Map along Malekhu to Bhandara road-section

Study of weathering profile of rock.

Study of mass movement

1.2 Methodology

Group was formed by 6 members. But we have 5 members only. On the first day of trip, RMR

Rating &Tunnel observations were done. And on the second day of trip, mass movement &

Preparation of engineering geological map were done.

Brunton compass was used for measurement of hill slope, dip amount, dip direction,

Bearing and geological hammer was used for splitting of rock

Location 1: RMR rating:

Strength of rock,RQD,spacing of discontinuities etc are observed and were rated

By group discussion. Hill slope, dip amount, dip direction was measured.

Location 2: weathering profile

How weathering profile is on a rock mass was observed.

Location 3: Tunnel recognition

We were brought to Budhigandaki hydropower project. 16 members of each group

were kept inside the tunnel and its features were observed.

Location 4:Mass movement

Along the highway, an example of mass movement was observed and type of failure

it may be was estimated.

Location 5:Map preparation

10m lengthwise road section was observed. Its bearing, Hill slope, Soil type, Rock

type, mass movement was observed.

1.3 Description of the instruments used in the field

Geological Hammer:

A Geologist’s hammer is a hammer used for splitting and breaking rocks. In field geology, they

are used To obtain a fresh surface of a rock in order to determine its composition, nature, mineralogy,

history and field estimate of rock strength.

Brunton Compass:

Arguably the most frequent use for the Brunton in the field is the calculation of the strike and

dip of Geological features( faults, contacts, foliation, sedimentary strata etc.) If next to the feature, the

strike is measured by leveling( with the bull’s eye level ). The compass along the plane being measured.

Dip is taken by laying the side of the compass perpendicular to the strike measurement and rotating

horizontal level until the bubble is stable and the reading has been made. If properly used and if field

condition follow, additional features of the compass allow user to measure such geological attributes

from a distance.

2.Study of mass movement

Mass movement is the detachment and downslope transport of soil and rock material under the

influence of gravity. The sliding or flowing of material is due to their position and to gravitational force

but mass movement is accelerates by presence of mainly water.

2.2 Type of mass movement

Mass movement has been classified in to main three types ie. Slope failure, landslide and debris flow in

accordance to their mechanisms, types of material and rate of movement.

1. Landslide – movement of large sediment block which has clear slide surface. Large dimension slow

continuous movement mainly affected by ground water.

2. Debris flow – movement of deposition or eroded sediments along the stream. Rapid movement

including large volume of water through the stream

3. Slope failure – movement of weathered surface soil layer rock of steep slope (small dimention and

rapid movement )

2.3 observation of landslide in the field

Location no: 4 Rock failure was observed.

2.4 Mitigation measure of landslide

Preventive measures of landslide :

1. Retaining wall: retaining are relatively rigid walls used for supporting the soil mass laterally so that

the soil can be retained at different level on the two sides

2. Pile works: Sheet pile of 200-600mm are driven through the sliding surface to control landslide

movement directly this is used in very urgent and important locations.

3. Anchor walls: an anchor wall is applied to prevent the landslide through the tensile strength of

steel wire or steel bar which anchor the sliding soil mass to the bed rock.

Corrective measures for maintaining stability of landslide

1. Reduction of pore water pressure: it can be reduces by improvement of surface and sub surface

water drainage. This can be done by construction of surface and sub-surface water drainage

system and prevention of water infiltration by application of bio engineering technology. Ie.

Armoring

2. Slope reformation: the soil removal after trimming of slope is main function of correction. Sliding

force can be reduce through a partial or entire removal of sliding mass from crown side of the

landslide mass.

3. A loading embankment work: it is made at the toe of a landslide to balance the sliding force with

the additional loading force. This method is also widely used because of its reliable and immediate

effect and sometimes is combines with soils removal work at the head of landslide.

3 Rock Mass and Rock Mass Classification

3.1Introduction

Rock mass is mass of rock interrupted by discontinuities with each constituent discrete block

having intact rock properties. Rock masses are heterogeneous because of differing rock types, presents of

discontinuities and varying degree of weathering. The stability and deformability of the rock is dependent

on the strength and deformability of the rock mass.

3.2.Rock type:

I. Igneous rock: Those rocks that are formed by the process of magmatism are known as igneous rock.

Properties:

Random orientation of rock and self interlocked

No bedding planes

Hard of massive

II. Sedimentary rock: Those rocks formed from the process of sedimentation are called sedimentary rocks.

sedimentation process is accumulation ,compaction, cementation, consolation of sediment from by the

weathering of old rock either igneous , metamorphic and are then transported by geological agents(water,

wind, ice etc).

Properties :

Random orientation of rocks and sediments

Sediments cemented by fine materials

Have thick bedding palne

III. Metamorphic rock Those rocks formed from the alternation of pre existing rocks sedimentary-igneous

by the process of metamorphism are called metamorphic rock

Properties :

Preffered orientation of minerals i.e.directional arrangements

Foliation plane

Having rock cleavage

3.3 weathering : it is defined as mechanical disintegration and chemical decomposition under the

influence of atmospheric condition of pre-existing rocks into small fragments , which makes the rock

minerals lose and separable.

3.4 intact rock strength:Strength is a fundamental quantitative engineering property of a rock

specimen. The applied stress may be compressive, shear or tensile in application giving rises to

compressive, shear and tensile strengths. Among them, compressive strength is the most commonly used

in engineering application. Grain size, Texture, mineralogy, and degree of foliation influence the strength

of rock.

3.5 discontinuities in rock mass: any structural or geological feature that changes the homogeneity

of rock. It constituents a tremendous range from structure upto several kilometers in extent down to a few

centimeters.

Bedding plane, foliation ,joints , faults and fault zones are all form of discontinuities.

Rock mass=intact rock + discontinuities

3.6 characteristics of discontinuities in rock mass:

a.Orientation: orientation of discontinuities are conformed by measuring attitude of the plane. A set of

discontinuity or intersection of discontinuity sets may cause rock instability according to the relation with

the hill slope.

b.Spacing: it is a perpendicular distance between the discontinuity planes with its adjacently parallel

another discontinuity plane .

c.Continuity(persistence): continuity reveals the length of joint and is measured in an exposed rock

surface.

d. Aperture and infilling materials: aperture is widening distance between two discontinuities .it may be

tight or open, and space may be empty , partially filled , of completely filled. The infilling material may be

clay, silt and sand.

e.Surface characteristics (roughness): the surface of discontinuity may be smooth or very rough. The

friction angle of rock depends on the degree of roughness .higher the degree of roughness higher will be

the frictional angle.

f. ground water condition(seepage): dry … damp ….. wet….. dripping….flowing

Increasing in the intensity of water flow

3.7Rock mass Rating (RMR): in 1976, bieniawski published the details of a rock mass classification

called the geomechanics classification and widely known as rock mass rating(RMR) system.

In this system, different rating values have been assigned to different parameter according to their

weight . in the field , all the parameters are measured and assigned to the respective rating values. Finally,

the summation of rating values of all the individual parameters give the final rating value and the rock

mass is classified as follows:

Class no Rating value Rock quality

I 100-81 Very good rock

II 80-61 Good rock

III 60-41 Fair rock

I V 40-21 Poor rock

V <20 Very poor rock

3.8 Rock Mass Classification system

3.9 Rock Mass Rating observation table

Location no:1 Along the Benighat to Aarughat road section

RMR=12+13+10+15+4+1+5+0+5=65

So, the given rock mass fall into Good Rock(80-61)

Hill Slope: 65deg 30 min

4.Stability analysis of rock slope

4.1 Introduction

Kinematic analysis is a method used to potential for various modes of rock slope failures (plane, wedge,

toppling failure), that occurs due to unfavorably oriented discontinuities.

4.2 failure mechanics in rock slope and type of rock failure

1. Plane failure:

Condition for plane failure:

- The joint plane and the hill slope should dip in same direction.

- The dipping of the join should be less than that of hill slope.

- The strike different should be less than 20

- The dip of the joint should be more than internal friction angle.

2. Toppling failure:

Condition for toppling failure

- The joint plane and the hill slope should dip in opposite direction.

- The strike difference should be less than 20

- The dip of the joint should be more than internal friction angle.

3. Wedge failure:

Condition for wedge failure

- The wedge and hill slope should dip in same direction.

- The dipping of wedge should be less than the dip of hill slope

- The strike difference should be between 20

- The dip of wedge should be more than internal friction angle.

4.3Slope stability analysis

Data collected from field are first plotted into a polar stereonet. This can be carried out from hand

or computer. From each dip and strike plotted in the stereonet cluster will form and each cluster will

represent a discontinuity.

Location No: 4 all types of failure was found.

5. Tunnel and underground excavation

5.1 Introduction

Tunnels are underground passages or routes through hills or mountains used for different purposes. They are

made by excavation of rocks below the surface or through the hills or mountains. Careful geological examinations should

be made with reference to the rock types occurring at the site, the structures associated with them and the prevailing

ground water conditions.

5.2 Site selection

Hard rocks like granite, quartzite, gneiss, etc is favourable than weak rocks like slate, phyllite,etc.

Horizontal or slighty dipping rocks with the stike parallel to the axis of the tunnel.

Steepy dipping formulations with the strike perpendicular to the axis of the tunnel.

Large quantity of water flow is very unfavourable ; this problem arises when the tunnel is located below the

‘water table’.

5.3 Geological consideration of successful tunnel

The safety, success and economy of tunneling depend heavily on the various geological conditions prevailing at

the site.

5.3.1Importyance of Rock Types

The nature of rock types which are encountered along the tunnel alignment is vey important for the safety and

stability of tunnel. In brief, the competent rocks i.e. those which are strong, hard and massive will lead to safe but slow

tunneling and the incompetent rocks which are loose or soft or fractured, though willing for easy tunneling, will be

unstable and hence require lining.

5.3.2 Importance of geological structures

The bearing of structures in tunnels is very important for two reasons:

1)They modify The competency and suitability of rocks for tunneling.

2)They may create or prevent ground water problems, which are of critical importance in tunneling. Joints, faults, folds,

and tilted structures are the most commonstructural features associated with rocks.

5.3.3 Importance of groundwater

Under the adverse condition, large quantities of ground water may gush out and inundate the tunnel. Ground

water makes easier the movement of rock mass upon eachother and will therefore promote slips along divisional planes

such as joints and bedding planes. If the tunnel lies below the position of water table then the ground water problem is

expected.

5.3.4 Overbreak

Overbreak indicates the quantity of rock broken and removed inexcess of what is required by the perimeter of

the proposed tunnel. The geological factors which govern the over break are:

1) The nature of the rocks.

2) The orientation and spacing of joints or weak zones in massive and soft rocks of a homogenous nature cause less

overbreak than harder rocks with well-developed joints or weak zones.

The factor of overbreak is important because it adds to the cost of tunneling, particulary if lining is required.

Location no:3 Tunnel was in T shape. 1m height &2m width. Rock bolt and screeding was observed.

6. Preparation of Engineering Geological map

6.1Introduction: The graphical representation of purpose specific geological information or data

Obtained from field( after site investigation) which can be quantified(in numbers0, with reference to north at certain scale is known as Engineering Geological map. It includes lithology( distribution of rock types), soil types( alluvial, colluvial, residual), geomorphology(river, stream,slope, aspect, inclination, slope stabilities like mass movement i.e landslide, debris flow, slope failure etc., existing infrastructure (road, canal, dam, bridge).

6.3 Engineering Geological map

Chainage Bearing Rock Type Hill slope Remarks

0+000 N41W 68-50-00 No vegetation

0+010 N41W 55-20 vegetation

0+020 N41W 41-30 Landslide

0+030 N41W 41-20 vegetation

0+040 N41W 52-50 vegetation

0+050 N41W 67-10 vegetation

0+060 N41W 65-10 vegetation

0+070 N41W 49-40 vegetation

0+080 N41W 50-50 vegetation

0+090 N41W 48-30 vegetation

0+100 N41W 48-20 vegetation

Location no:5 10m road section geological map was prepared.

7. Study of intact rock weathering classification

The weathering condition of the rock has a significant influence on the engineering properties of rock. The degree

to which chemical weathering or alteration has occurred in a given rock type is amenable to classification that

reduces compressive strength. The degree of weathering may differ in rock depending upon various factors such as

size, orientation of discontinuities and groundwater movement.

Grade Degree of weathering

Description

VI Residual soil

Rock discolored and completely changed to soil in which original rock fabric is destroyed. There is a large change in material volume. Hazards depends on water-content and natural slope.

V Completely weathered

The rock discolored and changed to soil but the original rock fabric is mainly preserved. There may be occasional core stones. The properties of the soil depend in part on the nature of the parent rocks. Severely hazardous.

IV Highly weathered

The rock discolored. Discontinuities may be open, discolored surface and original rock fabric discontinuities may be altered. The alteration penetrates deeply but core stones are present. Highly hazardous.

III Moderately The rock discolored. Discontinuities may be open and show discolored surfaces

weathered with alteration starting to penetrate in wards. Intact rock is noticeably weaker as determined in the field, than the fresh rocks Moderately hazardous.

II Slightly weathered

The rock may be slightly discolored particularly adjacent to discontinuities, which may be open will have slightly discolored surfaces. The intact rock is noticeably weaker as determined in the field, than the fresh rocks. It is considerably less hazardous.

I Fresh The parent rock is not discolored and there is no loss of strength. Free from hazards.

Location no:2 Highly weathered rock surface was seen.

8. Conclusion: Hence in our two day trip, we learned a lot of geological phenomenon. We could

perform practical aspect that we had studied in theoretical class. We learned how to classify rock mass,

how tunnel is made, how to prepare geological map, see mass movement.

Although the trip was fruitful, not sufficient.

9.Refrences:

Data collected during the field visit

Sketches drawn and photo taken in the field

Engineering Geology:

By Prakash Chandra Ghimire

Mahesh Singh Dhar

https://www.wikipedia.org/

Old Field Report(063)