2. Geotechnical Studies
These studies are considered as a fundamental requirement of
planning and design of any large civil engineering structures.
Purpose
1) To provide geotechnical inputs for construction of various civil engineering
structures.
2) Data generated during geotechnical investigations are incorporated during the
designing of structure so that it should last at least for designed time span or more.
3) To ensure that the proposed project is built at minimum cost without compromising with
quality & safety standards.
Depend on
Type, size of any civil structure/project, its design and purpose”
Investigations can not be same for surface structures and underground structures,
same way for dam, tunnel, cannel, barrage, bridges, river linking projects, railway
projects etc.
Stages of a project such as: Preliminary Stage, Main Stage and Concurrent Stage.
Broadly divided into two parts
Field Based Studies (Surface Investigations & Sub-Surface Investigations)
Laboratory Based Studies
3. Geotechnical investigation study includes
1. Surface geotechnical mapping on different scale
a) Topographical study,
b) Remote sensing/photo-geological study
c) Detailed geological mapping,
d) Traverse geological mapping
e) Foundation grade geological mapping
2. Sub-surface geotechnical interpretation
a) Drilling,
b) Drifting,
c) Water Percolation Test
d) Geophysical study i) Seismic ii) Electrical
3. Determination of various geotechnical properties of rock and soil
a) In field b) In Laboratory
4. In-situ Tests
5. Environmental Impact Assessment study
6. Miscellaneous Studies: Survey for construction material
4. 1.
Water Resources
Development Projects
(i) Hydro electric Projects:
(ii) Irrigation/ Domestic and Industrial water
supply project.
2.
Communication Projects
3.
Infrastructure Civil Projects
• Dams, Barrage, Weir
• Reservoirs
• Cannel
• Tunnel
• The communication projects include
Highways, Railway lines, airfield
runways , metro-trains, Ropeways,
Traffic tunnel and Bridges.
• The infra structure projects include
buildings, thermal power plants, nuclear
power plant, nuclear reactors,
ammunition dump sites, Bunkers, coastal
structures, underground oil storage tanks
etc.
Every project is unique and hence set of geological and geotechnical program has to be specific in
scales and detailing.
The major Civil Engineering Projects can broadly be divided under three categories:
Engineering Projects
5. SIZE OF THE PROJECT VERSUS INVESTIGATIONS
1. Many of the smaller projects will not require, at DPR stage, any information in addition to
that already obtained in the FR Stage.
2. The larger and more difficult projects will often require extensive additional surveys and
investigations.
3. However, project size is not the sole criterion with respect to the necessity for further
detailed studies. This may rest on a question of complexity of the site, of the foundation
conditions, and often of the hydrological factors.
4. Because of these complicating factors, the initial planning of a project is accomplished to a
considerable degree by the use of maps, statistical information, and published reports
before any field investigations are required.
6. Requirement of Geotechnical Investigations
To prepare detailed geological/geotechnical report, estimation of rock mass parameters for
safe, sturdy and economic design.
Stability and longevity of the civil engineering structures.
To minimize geological surprises.
To avoid or minimize cost over run.
To minimize the time period (hassle free construction schedule).
Investigations required for the project
The general geological setting in and around the project (Regional Geology).
The geological conditions related to the site (Site Specific).
The characteristics of soils and rocks (Geo-mechanical properties of the material).
Any other geologic condition that may influence design, construction, and long term
operation.
Seismicity of the area.
Availability of the construction material.
7. How to start geotechnical studies for any engineering project ?
(METHODS & PROCEDURES)
Consultation of available geological literature (reports / maps ) of the area.
Geological Mapping on different scale as per requirement (1:15,000,1:10,000, 1:5,000)
Subsurface exploration by Drilling and Drifting.
Geophysical Surveys.
Testing of foundation media/construction material in Field (in-situ) and Laboratory.
Synthesis and interpretation of data.
Preparation of report.
8. Stages of Geological Investigations
for
Civil Engineering Projects
1. General Reconnaissance or Pre-Feasibility Stage (PFR Stage).
2. Preliminary Investigation or Feasibility Stage (FR Stage).
3. Detailed Investigation (DPR stage)
The detailed geotechnical investigations form the main part of Detailed
Project Report (DPR Stage or Bankable DPR Stage).
4. Construction Stage (Pre construction stage & Post construction stage)
9. Investigations of different types are involved at various stages of a project for example:
(i) Preliminary Stage/Reconnaissance, (ii) Main Stage/DPR and (iii) Concurrent Stage/Construction
Preliminary Stage/Reconnaissanc:
At this stage a project is in planning stage.
It requires Office or Desk study which involves gleaning through already available literature in form of
topographic maps; aerial photographs satellite imageries, geological maps and reports etc.
The available topographic and geological maps may not be at suitable scales at this stage but will give a broad
idea about the area.
Site visit may then be undertaken for visual assessment of the area and to gather information available with
local populace.
A first hand idea about local topography and geology can be ascertained if experts are available with the
team.
A preliminary report can be made to chalk out detailed field work plan, once the feasibility of the project is
established.
10. Main Stage/DPR:-
Once the project gets green signal then multitude of site investigations are undertaken which involves
detailed fieldwork to have detailed information about the soil and rocks.
Fresh surveys are undertaken at small scales for ascertaining the topography and geology of the area.
For shallow subsurface information trial pits and trenches, exploratory adits or shaft may be made.
For knowing about deep underground conditions drilling, bore hole logging and geophysical surveys can
be carried out.
The samples of soil and rocks are collected for the laboratory tests and analysis. If some in-situ testing is
required it is also undertaken at this stage.
After corroborating the data from field and laboratory a final report is prepared.
Final report includes detailed topographic and geological maps at scales which can mirror the minute
details of the site.
Fence diagrams can be made to get three dimensional perspective of the site.
Detailed Field Study
Depending upon nature and size of the project detailed field study is undertaken which
involves surveys of different kinds made on the surface for alignment, topography, soil and rock types. Sub
surface exploration is also carried out to see extension of soil and rock underground and variation therein,
depth of soil-rock contact, presence of discontinuity surfaces in terms of kind, number and their potential of
causing problems.
11. Concurrent Stage (Construction Stage Investgations):-
Once it is decided that a particular site is good for the project the work related to
construction is started based on the information gathered at main stage of investigations.
Now excavations is done for creating opening or for laying foundation and if some new
situation arises which could not be detected in previous investigations should be taken into
consideration and changes can be recommended accordingly in the design.
Because it has been found that unforeseen and unwarranted problems can come up any
time especially in the hilly and/or rocky areas, hence it has been said that:
“Design as you go, be ready for the worst and hope for the best.”
Construction Stage Investigations
Actual rock mass conditions exposed at the foundation grade of the structure are studied to
adopt minor changes in design, if required, depending on the variations recorded in the
geological and structural features of the foundation grade.
In underground works, rock mass characteristics are ascertained, which influence the
choice of tunneling methods like drill/blast, TBM, multiple drifting, fore- poling and
shield method (in soft strata).
12. What are the important ground aspects need to be investigated in
any mega project?
The nature and type of investigations varies with nature and size of construction.
Following are the important aspects invariably investigated:
Thickness of overburden or depth of bed rock – Presence of soil or weathered rocks,
either to be removed for reaching the sound foundation rocks or to be located as thick
loose rock debris to be used as construction material.
Depth of bed rock - Depth and three dimensional extent i.e. basement relief of sound
rocks suitable for foundation.
Presence of weak zones – Detection of cavities, cavernous rocks, shear and fault
zones which may not only act as weak zones but may also act as zones of water
leakage as well as major rock structures.
Once project is finalized and started, even then some changes may have to be made
locally depending upon the situations and requirements during the construction phase.
13. 1. Surface Investigations
Traverse Geological Mapping / Geological Mapping (Surface):
Assessment of soil, overburden, geological formation, rock types and structure
Geotechnical studies
Visual assessment of depth to bedrock and Weathering status
Field testing of strength of rock mass
Estimation of RQD (Rock Quality Designation)
Quantification of GSI (Geological Strength Index) by joint condition and RQD
Alignment survey for tunnel etc
Selection of geologically suitable locations for underground structures (eg. Power House) and Surface
structures (dam , barrage, bridges, switchyard etc
Identification of adit portal site (inlet, Outlet), access tunnel locations
Collection of structural data for slope Stability Analysis (kinematic Analysis), Stereographic Projections
Rock Mass Classification (Q and RMR)
Hydrological studies (Performed during early stage survey)
Reservoir Competency Studies (for large storage dams/barrage)
Survey for construction material
2. In-situ Tests
In-situ Rock Mass tests are carried out to evaluate in-situ stresses before and after excavation,
deformation properties, rock load and plastic field by repeated loading and unloading tests.
(I) Field Based Geotechnical Studies
14. 2. Sub-surface Investigations Geological Mapping (Underground, 3-D geological mapping, face logging):
In-Direct Exploration: (1) Geophysical Survey
(2) Tomography techniques
(3) TSP (Tunnel Seismic Profiling)
Direct Exploration: (1) Drilling at surface , subsurface (probe drilling during tunelling)
(2) Drifting
(3) Pitting and Trenching.
Subsurface explorations are carried out:-
For fairly accurate assessment of depth to bedrock below thick overburden, limit of weathering status and in-
situ – rock mass properties (distressing of rock mass).
To prove/disprove interpreted features like shears/faults etc and to assess subsurface geological conditions for
underground cavities.
II) Laboratory Tests (Soil and Rock testing)
Grain size analysis, specific gravity, natural density, moisture content (maximum and optimum) porosity, void
ratio, compression index, Atterberg limits (liquid limit, plastic limit, shrinkage limit), free swell expansion
test, direct/triaxial shear texts (cohesion, angle of internal friction)
(I) Field Based Geotechnical Studies
15. Geological Mapping
(Objective to investigate the geological conditions of the project area and to help the civil
engineers in understanding the structure of the project)
Geological mapping should focus on the
• Detailed geological mapping is carried out for demarcating overburden rock contact and other
geological/structural features.
• Collection of geotechnically relevant rock mass parameters, to classifying the rock class
• Classification of rocks is done on the basis of joints and other parameters
• Joints/shears are classified into different sets/groups and orders based on their orientation, continuity and
frequency to understand geo-mechanical behavior of rock mass.
• Description of material characteristics (rock type, strength, structure, grain size, texture etc.)
• Description of rock mass characteristics (weathering, discontinuities, fracture state etc.)
• Making geological plan and Develop geological sections based on the surface mapping.
• Structural data is required for stability analysis of cut-slope and preparation of foundation treatment plan.
• Major shears delineated are helpful in interpreting inter-block tectonics at dam site.
• Stratum contour maps may also be required sometimes.
• Scale of mapping depends on purpose of mapping.
For example: on 1:100 to 1:200 in grid pattern (2mx2m) is carried out to assess foundation of
dam/spillway etc. 3-D logging is done on 1:100 to 1:200 scale.
17. Sub-Surface Mapping (3- D Logging)
Representation of Geological discontinuities / features observed in 3-dimension in any
under ground excavation in 2-dimension
Information from geological log
To assessment of nature and affect of discontinuity on the stability of Under Ground
Excavation. Wedges analysis on the basis of major joint sets data.
To classify the Rock mass for deciding the support system to be provided for a
particular section.
Information to be provided to the site engineers regarding the rock mass condition
likely to be encountered in next blasts for necessary arrangements.
Documentation of the geological features observed in excavation for post
construction references and maintenance.
Seepage condition- accordingly drainage holes may be provided, if required grouting
may be planned.
Over-break/undercut may be calculated, remedial measures may be adopted.
Condition of rock mass-accordingly support system may be provided.
Geological data may be projected for further excavation
18.
19. BASICS OF GEOLOGICAL LOGS
• Detailed two or three dimensional
representation of all geological
features exposed on the excavated
surface of an opening is termed as
‘Geological Log’
• Scale – 1:100 & 1:200 Drifts and
small dia tunnels are logged on
1:100 while for large dia openings
both scales may be used depending
upon the extent of details needed.
2-D Logging (Face Logging)
3-D logging
20. OPENING OF D-SHAPED TUNNEL CROWN
RSPL (RIGHT SPRING LEVEL)
RI (RIGHT INVERT)
LI (LEFT INVERT)
LSPL (LEFT SPRING LEVEL)
C RSPL RI
LI LSPL
1
2
3
4
2 π r
4
2 X 3.14 X 2.5
4
=
2.5m
3.5 m
= 3.925 m
3.925
3.925
3.5 3.5
RD’s in Meter
0
21. Types and Techniques of geological logging for Under ground openings
• Why we do mapping of underground openings?
• What we do during mapping of underground openings?
• Type of geological mapping: 1. Face logging 2. Wall logging. 3. 3-D logging of
Shaft/Caverns-MH-PH, IPS, Bus Ducts etc.,
• 3-D logging of the tunnel is done by two methods:
Invert Opening method :
In this method the tunnel section is opened from invert i.e. the crown portion is represented in
the centre of the log and invert in the sides. The crown region gets prominence in this
method and the geological features present in the crown region and the walls do not get
any break and are seen in continuity.
• Overt Opening method :
In this method the tunnel section is opened from crown i.e. the invert portion is represented
in the centre of the log and crown is divided into two parts and shown in the sides.
In this method the invert portion gets the prominence which is generally filled with muck
and no geological feature is visible and the crown where geological features are seen, get
divided into two.
27. ROCK MASS
• Geological Classification of
rocks.
• Igneous
• Sedimentary
• Metamorphic
• Rock Classification for
engineering requirements.
• Intact rock classification
(strength based-UCS)
• Rock mass classification
The rock mass is the assemblage of
blocks of intact rock, which are bounded
by various types of discontinuities, i. e.
joints, faults, shears, etc.
The rock mass has the characteristics of
both intact rock and discontinuities.
28.
29. CALCULATION OF RQD by Deere (1964)
• Rock Quality Designation index was
developed to provide a quantitative
estimate of rock mass quality from drill
core (NX size)
• RQD is the percentage of intact core
pieces in the total length of core.
RQD = {(37+65+18)x100}/ 200
= 60%
RQD = 115 – 3.3 Jv (Palmstrom, 1982)
Palmström (1982) suggested that, when no core is
available but discontinuity traces are visible in surface
exposures or exploration adits, the RQD may be estimated
from the number of discontinuities per unit volume. The
suggested relationship for clay-free rock masses is: RQD
= 115 - 3.3 Jv where Jv is the sum of the number of joints
per unit length for all joint (discontinuity) sets known as
the volumetric joint count
30.
31. Deer’s RQD Index (1967)
Σ length of core pieces > 10 cm
Total core run length
(RQD = ROCK QUALITY ESIGNATION)
RQD % Rock Quality
< 25 Very poor
25-50 poor
50-75 Fair
75-90 Good
90-100 Excellent
33. Rock Mass Classification
During the geotechnical investigation Rock mass Classification is essential for deciding
the rock support for open excavation and under ground support.
Rock mass is classified on the basis of Q-Value and RMR-Value.
“Q” Value is a function of
Rock Quality Designation, Number of Joint and their condition (Roughness of joint
plane and the alteration along the joint plane), ground water condition in the tunnel and
the rock cover over the crown of the tunnel.
RMR values are determined on the basis of
Strength of rock, Rock Quality Designation, Spacing of discontinuities, Orientation and
condition of discontinuities and Ground water condition.
On the basis of Q-Value and RMR Values
Rock mass class is determined and in turn the support system and rock reinforcement
are decided.
34. Based on the evaluation of large number of case histories, Barton, Lien
and Lunde (1974) of NGI proposed Tunnelling Quality Index (Q) to
classify the rock mass into 9 rock mass categories.
The Q-value varies on logarithmic scale from 0.001 to 1000 and it is defined by:
Block Size Shear strength Active Stress
Q = (RQD/ Jn) x (Jr/Ja) x (Jw /SRF)
Where:- RQD = Rock Quality Designation
Jn = Joint set number
Jr = Joint roughness number
Ja = Joint alteration number
Jw = Joint water reduction factor
SRF = Stress reduction factor
Barton’s Q-system
(NGI classification) 1974-1998
35. Q-SYSTEM (Barton et al., 1974)
• On the basis of Q-value, rock mass is classified
into 9 categories.
• “Q” Value Rock Mass Category
• 0.001 – 0.01 - Exceptionally Poor
• 0.01 – 0.1 - Extremely Poor
• 0.1 – 1.0 - Very Poor
• 1.0 – 4.0 - Poor
• 4.0 – 10 - Fair
• 10 – 40 - Good
• 40 – 100 - Very Good
• 100 – 400 - Extremely Good
• 400 – 1000 - Exceptionally Good
Rock masses are classified into six classes
for support designs.
• Class I Q= 40-100…….. Very good
• Class II Q= 10-40……… Good
• Class III Q= 4-10……… Fair
• Class IV Q= 1-4……… Poor
• Class V Q= 0.1-1.0…… Very Poor
• Class VI= 0.01-1.0…..Extremely poor
• Beyond class VI Q = < 0.01.. Adverse
Geological Occurrence (AGO)
•Support system includes rock bolting,
reinforced shotcreting using SFRS, steel
rib support
36. Geomechanics Classification (RMR)
(Bieniawski, 1973, 1976, 1989)
concept as an improved version of RSR
Parameters
A. UCS
B. RQD
C. Spacing of discontinuities
D. Condition of discontinuities
E. Ground water condition
F. Orientation of discontinuities &
tunnel direction (for adjustment)
RMR = A + B + C + D + E – F
(Max. RMR=100)
•Useful for modern tunnelling methods
•Widely practiced.
Ratings for 1 to 5 are added and corrected by 6
parameter to get RMR values.
Rock mass classified into 5 classes ranging from
very good to very poor
Each class has stand-up time, tunnel excavation
method & suitable support system.
Widely practiced classification.
39. Weathering Grade Description
Notation Nomenclature
W1 Fresh No visible sign of rock material weathering : Perhaps
slight discoloration on major discontinuity surfaces.
W2 Slightly
weathered
Discoloration indicates weathering of rock material and
discontinuity surfaces. All the rock material may be
discoloured by weathering and may be somewhat weaker
externally that in its fresh condition.
W3 Moderately
weathered
Less than half of the rock material decomposed and /or
disintegrated to a soil. Fresh or discoloured rock is present
either as a continuous framework or as core stones.
W4 Highly
weathered
More than half of the rock material is decomposed and / or
disintegrated to a soil. Fresh or discoloured rock is present
either as a discontinuous framework or as core stones.
W5 Completely
weathered
All rock material is decomposed and / or disintegrated to
soil. The original mass structure is still largely intact.
W6 Residual
soil
All rock material is converted soil. The mass structure
and material fabric are destroyed. There is a large change in
volume, but the soil has not been significantly transported.
40.
41. Geophysical Exploration
Geophysical exploration is carried out to know about subsurface geology of a larger area.
1) Seismic (Refraction) profiling,
2) Electrical Resistivity,
3) Sounding
4) Ultrasonic logging etc may be carried out
Seismic and resistivity surveys are used for
Determining depth to bed rock,
Disposition of fault or shear zone
and for assessing modulus of deformation of rock mass.
Modulus values can also be obtained by ultrasonic logging of drill cores.
Geophysical interpretation requires verification by drilling/drifting
42. Drilling (objective of core drilling)
•Drilling at project site is done to know:-
1) Quality of rock mass likely to be encountered
2) Sampling for laboratory (soil-rock-water)
3) Evaluation of ground water condition
4) Execution of geotechnical in-situ tests
5) Geophysical borehole tests
6) Depth of overburden
7) Depth of weathering & distressing of rock mass
8) Existence of shear zone
9) Rock cover over tunnel alignment/cavern
10)Localization of fault/shear or change in lithology
11)Hydrological installations (standpipe, piezometer),
12)Monitoring installations (extensometer, inclinometer etc.)
•Depth of drilling depends on type of project (Deepest holes for dam foundation are of 1H depth,
For underground structures 10-20m below invert level of tunnel/cavern)
43. •Drill core samples are used in Geotechnical (GT) lab to determine:-
• Compressive strength, Specific Gravity,
• Modulus of Elasticity,
• Poisson’s Ration, UCS (wet/dry),
• Tensile strength,
• Swelling Index and Hardness.
Accuracy in interpretation depends on:-
1) Drilling quality
2) Core recovery
3) Drilling equipment
• Water percolation tests are carried out in drill holes.
• Logging and assessment of borehole cores – rock mass classification and collection of samples for testing
mechanical properties in the laboratory
Core drilling quality depends on:-
1. Suitable equipment
2. Experienced screw
3. Adoption of equipment to changes of rock conditions, continuous monitoring of performance.
44. Drifting (objective of core drilling)
1) Drifts are planned at different levels to assess actual rock mass behavior.
2) 3-D Geological Mapping of drift is done on 1:100 or 1:200 scale.
3) Rock is rated in terms of ‘Q’ and ‘RMR’ etc.
4) In-situ tests are carried out in drifts to get information on strength and deformation
properties of rock mass required for design of engineering structures.
5) Drifts are essential to know weathering/striping limit.
6) Pilot drifts are made to assess actual tunneling condition.
7) Drift data is more reliable than drilling data.
45. Engineering Geological Modeling
• Engineering Geological Modeling of a project is carried out based on key parameters of
Rock Mass viz. lithology, inter-block Tectonics, permeability, faults, shears, fractures and
geomechanical properties of rock. This gives a total picture of the problem to the designer.
Numerical Modeling by Computer Simulation
• Rock mass parameters are used for understanding changed stress distribution pattern, after
excavation, by carrying out 2-D numerical modeling.
• This helps in finalizing support system, rock bolts and reinforced shotcreting or steel ribs
depending on circumstances.
• The subsurface geological and structural data is used for 3-D correlation at different depths
by using 3-DEC programme in computer. This study helps in predicting tunnel conditions
in the section ahead to minimize surprises.
• Instrumentation is necessary to understand the response of rock masses in post excavation
period even after provision of design support system.
• Critical areas as identified by instrumentation in UG openings are given additional support
preferably.
50. What is Rock Mechanics?
The study of rock behavior in the solid state under varying
environmental and internal conditions.
Main focus is how rocks respond to applied stresses, especially
those that naturally occur.
Different tests are carried out on rock and soil specimen with
the aim of finding out how the rock and soil will respond to a
particular phenomenon.
51. Rock Mechanics Tests
• Laboratory Tests
• Field Tests
The objective of both the tests are to
classify the rock for engineering
design purposes, hence these tests can
be further grouped under three major
heads i.e.
• Test for classification
• Tests for Design &
• Tests for Specific Purpose
Laboratory tests
Easy to conduct.
under controlled environment.
basis of all engineering classification
/design.
input parameters for numerical
modelling.
Field tests
Expensive
Time consuming due to site preparation
Difficult to conduct
Experience to analyze
True representative
52.
53. GEOTECHNICAL PROPERTIES
ROCK
ROCKS AGGREGATES
PHYSICAL
OR
INDEXING
PROPERTIES
MECHANICAL
OR
ENGINEERING
PROPERTIES
1. Density
2. Specific Gravity
3. Water absorption
4. Porosity
5. Void ratio
6. Hardness
1.Uniaxial Compressive Strength
2.Tensile Strength
3. Point Load Strenth Index
4. Young's modulus Poisson's ratio
5. Shear Parameters
6. P&S wave velocities
1. Crushing Strength
2. Aggregate Impact Value
3. Los Angles Abrasion
4. Daval’s attrition
5. Slake Durability Indexes
54. Laboratory test for soil
(i) Index property of soil
1) Bulk density
2) Natural water content
3) Void ratio
4) Dry density
5) Relative density (density index)
6) Specific gravity
7) Liquid and Plastic limits
8) Soil classification, grain size analysis
(ii) Engineering properties
1) Consolidation properties
2) Swelling tests
3) Unconfined Compressive Strength
4) Total & effective shear strength
parameters by tri-axial shear test
5) Bulk modulus and shear modulus
56. 1) Drilling
2) Pit excavation/Trenching
3) USC testing by use of Schmidt Hammer
4) Standard Penetration Test (SPT)
5) Load Bearing Capacity Test (Plate load Test)
6) Water Percolation Test
(WPT for Lugeon value; Measurement of the Permeability of rock mass)
7) Groutibilty tests
(to improve the strength and reduce the permeability of rock mass)
8) Earth (Soil) Resistivity Test
9) Seismic reflection test
(for deduction of sub-surface adverse geological discontinuity such as shear, fault)
10) Aggregate tests for construction material
In-situ Tests (Field Tests) in Rock Mechanics
57. 11) Tunnel Seismic Profiling (TSP )
( for deduction of water bearing zone ahead of tunnel face)
12) Tomography
(to know the shape and size of underground cavity)
13)Instrumentation.
(MPBX, load cell, TCP, etc., for measuring the deformation, convergence etc.)
14) Rock Bolt Pullout Tests.
15) Deformability of Rock Mass (Modulus of Deformation)
16) Measurements of In-situ Shear Strength
(To determine the shear strength parameter of Rock mass, Cohesion and Friction
Angle)
17) Measurements of In-situ Stresses
In-situ Tests (Field Tests) in Rock Mechanics
58. Schmidt
hardness
20 30 40 50 60
UCS(Mpa) 12 25 50 100 200
Schmidt Hammer test: surface strength estimation.
Hand held, spring loaded
hammer measures
rebound from rock
surface; rebound value
correlate with UCS and
decline significantly in
fractured rock.
Very rapid field test may
identify weaker or
weathered rock, or loose
fractured rocks, in
exposed rock surface.
59. Laboratory Tests for determining the following:-
• Physical properties of soil (bulk & particle density, porosity, consistence, etc.) and rock (Hardness, Fracture
etc.)
• Geo-mechanical properties of soil (shear strength, erodibility, permeability, compressibility etc.) and rock
(elastic modulus, Poisson,s ratio, etc.)
• Petrological Studies of Rock and Soil
1. Strength Parameter (Dry & Saturated)
• Uniaxial Compressive Strength (UCS)
• Tri-axial Compressive Strength
• Tensile Strength
2. Elastic properties
• Poisson’s ratio
• Young’s modulus
3. Shear parameters
• Cohesion and friction angle (angle of internal friction)
4. Physical Properties
• Density, porosity, Specific gravity, etc.
5. Slake Durability Test
Drill core samples are tested for determining Specific Gravity, Modulus of Elasticity, Poisson’s
Ration, UCS (wet/dry), Tensile strength, Swelling Index and Hardness
For the design of U/G openings, properties of rock and behaviour of the rock mass are required to
be studied.
Laboratory Tests
