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 perfe ction 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 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 o ur college, institute of engineering. We are proud of being students of pulchowk campus.
Executive Summary G-4 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)
Date:2072-05-10/11
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
1.2
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
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 ob served.
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 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 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 imp rovement 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 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 planes Hard of massive
II. Sedimentary rock: Those 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 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 fr agments , 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 t ensile in application giving rises to compressive, shear and tensile strengths. Among them, compressive compressive strength is the most commonly 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: mass: a.Orientation: a.Orientation: orientation of discontinuities are conformed by measuring attit ude of the plane. A set of discontinuity or intersection of discontinuity sets may cause rock instabili ty according to the relation with the hill slope. b.Spacing: b.Spacing: it 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 c.Continuity(persistence): continuity surface. d. Aperture d. Aperture and infilling materials: aperture materials: aperture is widening distance between two discontinuities .it may be tight or open, and space may be empty , partially fille d , of completely filled. The infilling material ma y be clay, silt and sand. e.Surface e.Surface characteristics (roughness): the (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): condition(seepage): dr dr y … damp ….. wet….. dripping….flowing Increasing in the intensity of water flow
): in 1976, bieniawski published the details details of a rock mass classification 3.7Rock mass Rating (RMR ): called the geomechanics classification and widely widel y 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 I II III IV V
Rating value 100-81 80-61 60-41 40-21 <20
3.8 Rock Mass Classification system
3.9 Rock Mass Rating observation table
Rock quality Very good rock Good rock Fair rock Poor rock Very poor rock
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 hi lls 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 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), g eomorphology(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
0+010
N41W
55-20
No vegetation 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 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 vario us factors such as size, orientation of discontinuities and gr oundwater movement. Grade VI
Degree of weathering Residual soil
V
Completely weathered
IV
Highly weathered
III
Moderately
Description 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. 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. 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. The rock discolored. Discontinuities may be open and show discolored surfaces
weathered
II
Slightly weathered
I
Fresh
with alteration alteration starting starting to penetrate in wards. Intact rock rock is noticeably weaker as determined in the field, than the fresh rocks Moderately hazardous. 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. 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)
