Download presentation
Presentation is loading. Please wait.
1
Kuat Geser Tanah (Shear Strength) (Source : CIL-610 Foundation Engineering)
oleh: A. Adhe Noor PSH, ST., MT Staf Pengajar Program Studi Teknik Sipil Jurusan Teknik Fakultas Sains dan Teknik Universitas Jenderal Soedirman
2
Strength of different materials
Soil Shear strength Presence of pore water Complex behavior Steel Tensile strength Concrete Compressive strength
3
Shear failure of soils Soils generally fail in shear
Strip footing Embankment Failure surface Mobilized shear resistance At failure, shear stress along the failure surface (mobilized shear resistance) reaches the shear strength.
4
Shear failure of soils Soils generally fail in shear Retaining wall
5
Shear failure of soils Soils generally fail in shear
Failure surface Mobilized shear resistance Retaining wall At failure, shear stress along the failure surface (mobilized shear resistance) reaches the shear strength.
6
Shear failure mechanism
failure surface The soil grains slide over each other along the failure surface. No crushing of individual grains.
7
Shear failure mechanism
At failure, shear stress along the failure surface () reaches the shear strength (f).
8
Mohr-Coulomb Failure Criterion (in terms of total stresses)
c failure envelope Cohesion Friction angle f f is the maximum shear stress the soil can take without failure, under normal stress of .
9
Mohr-Coulomb Failure Criterion (in terms of effective stresses)
’ c’ ’ failure envelope Effective cohesion Effective friction angle f u = pore water pressure f is the maximum shear stress the soil can take without failure, under normal effective stress of ’.
10
Mohr-Coulomb Failure Criterion
Shear strength consists of two components: cohesive and frictional. ’f f ’ ' c’ ’f tan ’ frictional component c’ cohesive component
11
c and are measures of shear strength.
Higher the values, higher the shear strength.
12
Determination of shear strength parameters of soils (c, f or c’, f’)
Laboratory tests on specimens taken from representative undisturbed samples Field tests Vane shear test Torvane Pocket penetrometer Fall cone Pressuremeter Static cone penetrometer Standard penetration test Most common laboratory tests to determine the shear strength parameters are, Direct shear test Triaxial shear test Other laboratory tests include, Direct simple shear test, torsional ring shear test, plane strain triaxial test, laboratory vane shear test, laboratory fall cone test
13
Laboratory tests z svc + Ds shc After and during construction
Field conditions z svc shc Before construction A representative soil sample
14
Laboratory tests Simulating field conditions in the laboratory shc
svc + Ds shc Traxial test Laboratory tests Simulating field conditions in the laboratory Representative soil sample taken from the site Step 1 Set the specimen in the apparatus and apply the initial stress condition svc shc svc t Direct shear test Step 2 Apply the corresponding field stress conditions
15
Schematic diagram of the direct shear apparatus
Direct shear test Schematic diagram of the direct shear apparatus
16
Preparation of a sand specimen
Direct shear test Direct shear test is most suitable for consolidated drained tests specially on granular soils (e.g.: sand) or stiff clays Preparation of a sand specimen Components of the shear box Preparation of a sand specimen Porous plates
17
Preparation of a sand specimen
Direct shear test Preparation of a sand specimen Specimen preparation completed Pressure plate Leveling the top surface of specimen
18
Direct shear test Steel ball P Test procedure Pressure plate
Step 1: Apply a vertical load to the specimen and wait for consolidation P Pressure plate Porous plates Proving ring to measure shear force S
19
Direct shear test Steel ball P Test procedure Pressure plate
Step 1: Apply a vertical load to the specimen and wait for consolidation P Test procedure Pressure plate Steel ball Proving ring to measure shear force S Porous plates Step 2: Lower box is subjected to a horizontal displacement at a constant rate
20
Direct shear test Shear box Loading frame to apply vertical load
Dial gauge to measure vertical displacement Shear box Proving ring to measure shear force Dial gauge to measure horizontal displacement Loading frame to apply vertical load
21
Analysis of test results
Direct shear test Analysis of test results Note: Cross-sectional area of the sample changes with the horizontal displacement
22
Direct shear tests on sands
Stress-strain relationship Shear stress, t Shear displacement Dense sand/ OC clay tf Loose sand/ NC clay tf Change in height of the sample Expansion Compression Shear displacement Dense sand/OC Clay Loose sand/NC Clay
23
Direct shear tests on sands
How to determine strength parameters c and f Shear stress, t Shear displacement tf3 Normal stress = s3 tf2 Normal stress = s2 tf1 Normal stress = s1 Shear stress at failure, tf Normal stress, s f Mohr – Coulomb failure envelope
24
Direct shear tests on sands
Some important facts on strength parameters c and f of sand Direct shear tests are drained and pore water pressures are dissipated, hence u = 0 Sand is cohesionless hence c = 0 Therefore, f’ = f and c’ = c = 0
25
Direct shear tests on clays
In case of clay, horizontal displacement should be applied at a very slow rate to allow dissipation of pore water pressure (therefore, one test would take several days to finish) Failure envelopes for clay from drained direct shear tests Shear stress at failure, tf Normal force, s f’ Normally consolidated clay (c’ = 0) Overconsolidated clay (c’ ≠ 0)
26
Interface tests on direct shear apparatus
In many foundation design problems and retaining wall problems, it is required to determine the angle of internal friction between soil and the structural material (concrete, steel or wood) Where, ca = adhesion, d = angle of internal friction
27
THE END
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.