The document discusses shear strength of soils. It describes how soils generally fail in shear when the shear stress along the failure surface reaches the shear strength. It introduces the Mohr-Coulomb failure criterion, which states that the shear strength of a soil consists of a cohesive and frictional component. It also describes laboratory tests used to determine the shear strength parameters, including direct shear tests and triaxial shear tests.
CE 72.52 - Lecture 7 - Strut and Tie ModelsFawad Najam
The document discusses the strut-and-tie approach for analyzing concrete structures. It begins with background concepts such as Bernoulli's hypothesis, St. Venant's principle, and the lower bound theorem of plasticity. It then discusses how axial stresses, shear stresses, and the interaction of stresses affect concrete sections. The document outlines the ACI approach to shear-torsion design and provides equations from ACI 318 for calculating the concrete shear capacity. It introduces the concept of modeling concrete as a truss system and compares this to flexural behavior in beams. The strut-and-tie method is presented as a unified approach for considering all load effects. Guidelines are provided for developing an appropriate strut-and-tie model and
The document discusses different types of columns based on bracing, length, and reinforcement. It describes braced and unbraced columns, long and short columns, and tied, spiral, and composite columns. Requirements for minimum reinforcement, lateral ties, and selection of column size are also summarized.
This document is a seminar report on well foundations by Alauddin Aziz-ul-Haq Khan for their civil engineering course. It discusses the history and use of well foundations in India, including for important buildings and bridges. It describes some of the largest well foundations constructed, such as those for the Howrah Bridge. The report also outlines three types of well/caisson foundations and discusses problems encountered during well construction and solutions adopted. The aim is to understand the behavior of well foundation components under different loading conditions.
1. The document discusses the design of one-way reinforced concrete slabs according to Indian code IS 456:2000.
2. It defines one-way slabs as edge supported slabs spanning in one direction with a ratio of long to short span greater than or equal to 2.
3. The main considerations for slab design discussed are effective span, deflection control, reinforcement requirements including minimum area, maximum bar diameter and cover, and load calculations.
This document is a handbook on reinforcement and detailing produced by the Bureau of Indian Standards. It provides information on steel for reinforcement, including specifications for mild steel, medium tensile steel, high strength deformed steel bars, and hard-drawn steel wire fabric. It outlines the physical and mechanical properties required for different steel types, as well as tolerances for dimensions. The handbook serves as a companion to other documents on reinforced concrete, providing guidance on steel properties and specifications to inform proper reinforcement detailing.
ACI 318 - 2002
Requisitos de Reglamento para Concreto Estructural+Comentarios
En Ingles
--------------------------
Te invito a que visites mis sitios en internet:
_*Canal en youtube de ingenieria civil_*
https://www.youtube.com/@IngenieriaEstructural7
_*Blog de ingenieria civil*_
https://thejamez-one.blogspot.com
CE 72.52 - Lecture 7 - Strut and Tie ModelsFawad Najam
The document discusses the strut-and-tie approach for analyzing concrete structures. It begins with background concepts such as Bernoulli's hypothesis, St. Venant's principle, and the lower bound theorem of plasticity. It then discusses how axial stresses, shear stresses, and the interaction of stresses affect concrete sections. The document outlines the ACI approach to shear-torsion design and provides equations from ACI 318 for calculating the concrete shear capacity. It introduces the concept of modeling concrete as a truss system and compares this to flexural behavior in beams. The strut-and-tie method is presented as a unified approach for considering all load effects. Guidelines are provided for developing an appropriate strut-and-tie model and
The document discusses different types of columns based on bracing, length, and reinforcement. It describes braced and unbraced columns, long and short columns, and tied, spiral, and composite columns. Requirements for minimum reinforcement, lateral ties, and selection of column size are also summarized.
This document is a seminar report on well foundations by Alauddin Aziz-ul-Haq Khan for their civil engineering course. It discusses the history and use of well foundations in India, including for important buildings and bridges. It describes some of the largest well foundations constructed, such as those for the Howrah Bridge. The report also outlines three types of well/caisson foundations and discusses problems encountered during well construction and solutions adopted. The aim is to understand the behavior of well foundation components under different loading conditions.
1. The document discusses the design of one-way reinforced concrete slabs according to Indian code IS 456:2000.
2. It defines one-way slabs as edge supported slabs spanning in one direction with a ratio of long to short span greater than or equal to 2.
3. The main considerations for slab design discussed are effective span, deflection control, reinforcement requirements including minimum area, maximum bar diameter and cover, and load calculations.
This document is a handbook on reinforcement and detailing produced by the Bureau of Indian Standards. It provides information on steel for reinforcement, including specifications for mild steel, medium tensile steel, high strength deformed steel bars, and hard-drawn steel wire fabric. It outlines the physical and mechanical properties required for different steel types, as well as tolerances for dimensions. The handbook serves as a companion to other documents on reinforced concrete, providing guidance on steel properties and specifications to inform proper reinforcement detailing.
ACI 318 - 2002
Requisitos de Reglamento para Concreto Estructural+Comentarios
En Ingles
--------------------------
Te invito a que visites mis sitios en internet:
_*Canal en youtube de ingenieria civil_*
https://www.youtube.com/@IngenieriaEstructural7
_*Blog de ingenieria civil*_
https://thejamez-one.blogspot.com
CE 72.52 - Lecture 8a - Retrofitting of RC MembersFawad Najam
The document outlines a presentation on retrofitting concrete structures. It discusses two approaches to retrofitting: global (system) strengthening which adds new elements to enhance stiffness, and local (element) strengthening which targets insufficient member capacities. Examples of global retrofitting mentioned include adding reinforced concrete shear walls and buckling restrained braces. Local retrofitting examples discussed are reinforcement concrete jacketing of columns and beams.
This document discusses quality assurance for concrete construction. It outlines three key components of a quality management system: 1) a quality assurance plan, 2) quality control process, and 3) quality audits. The quality assurance plan establishes organizational responsibilities, control measures, acceptance criteria, and documentation requirements. Quality control ensures conformance to specifications. Quality audits verify that quality assurance and control programs are properly implemented. Factors that affect concrete properties like strength, permeability, cracking and durability are also summarized.
Introduction & under ground water tank problemdhineshkumar002
The document discusses the design of an underground rectangular reinforced concrete water tank. It provides steps for calculating earth pressure, determining member thicknesses, and designing reinforcement for the long walls, short walls, and roof slab. The long walls are designed as vertical cantilevers and the short walls as continuous slabs. Reinforcement is checked for bending and cracking stresses. The example shows calculating load intensities, bending moments, required depths and areas of steel for the tank walls and slab according to code specifications.
Calulation of deflection and crack width according to is 456 2000Vikas Mehta
This document discusses the calculation of crack width in reinforced concrete flexural members. It provides information on:
1) Crack width is calculated to satisfy serviceability limits and is only relevant for Type 3 pre-stressed concrete members that crack under service loads.
2) Crack width depends on factors like amount of pre-stress, tensile stress in bars, concrete cover thickness, bar diameter and spacing, member depth and location of neutral axis, bond strength, and concrete tensile strength.
3) The method of calculation involves determining the shortest distance from the surface to a bar and using equations involving member depth, neutral axis depth, average strain at the surface level. Permissible crack widths are specified depending on exposure
This is the presentation about the Plum concrete which is used under water to make a reservoir. This presentation is related to the Civil Engineering. The visual effect of the presentation can be seen after downloading it.
Roller-compacted concrete (RCC) is a concrete that is mixed in a pugmill and placed with dump trucks and spread with bulldozers. It is compacted in lifts of 100-250mm thick using vibratory steel drum rollers. RCC does not require internal vibration and can be used for port, rail, highway, and industrial facilities. Some advantages are reduced cement, no formwork, and ability to maintain traffic flow during placement. Limitations include a rougher surface and difficulty compacting near edges.
Prestressed concrete combines high-strength concrete and high-strength steel in an active manner by tensioning steel tendons and holding them against the concrete, putting it into compression. This transforms concrete from a brittle to a more elastic material. It allows for optimal use of each material's properties and better behavior under loads. Prestressed concrete was pioneered in the 1930s and its use has expanded, finding applications in bridges and other structures. Common methods are pretensioning and post-tensioning, using various tendon types, with bonded or unbonded configurations. Tensioning is done using mechanical, hydraulic, electrical or chemical devices.
A plate girder is a beam composed of welded or riveted steel plates. It consists of two flanges and a web plate. The flanges resist bending moments while the web resists shear forces. Plate girders are commonly used for longer spans than ordinary beams, with spans ranging from 14-40 meters for railroads and 24-46 meters for highways. They have a high depth to thickness ratio for the web, making it slender. Stiffeners are added to the web to prevent buckling. Plate girders are an economical choice for longer spans where their design can be optimized for requirements.
This document provides details on the construction process for the substructure of a bridge, including pile foundations and a pile cap. It describes the steps to construct cast-in-place concrete piles, which include boring holes for the piles, lowering reinforced steel cages into the holes, fitting tremie pipes to pour concrete, and flushing out debris. It also outlines the process for constructing the pile cap, such as excavating around the piles, chipping off excess concrete, forming shutters, placing reinforcing steel, and pouring concrete. The overall bridge construction process is divided into substructure and superstructure work.
The document discusses the design and estimation of an Intze tank. It includes an abstract that describes the need for water storage and supply. It then covers various topics related to designing water tanks such as estimating water demand based on population and consumption rates, classifying different types of water tanks, design requirements for concrete water tanks, and the design of specific elements like domes and overhead tanks. The document aims to provide theory and guidelines for designing a reinforced concrete elevated circular water tank with a domed roof and conical base using the working stress method.
This document provides an overview of the design of compression members (columns) in reinforced concrete structures. It discusses various types of columns based on reinforcement, loading conditions, and slenderness ratio. It describes the classification of columns as short or slender. The document also covers effective length, braced vs unbraced columns, codal provisions for reinforcement, and functions of longitudinal and transverse reinforcement. Key points include types of column reinforcement, minimum reinforcement requirements, cover requirements, and assumptions for the limit state of collapse under compression.
This document summarizes a British Standard regarding the structural use of concrete in buildings and structures. It provides recommendations for design, detailing, materials, specification, construction practices, and quality control. The standard excludes bridges and concrete made with high alumina cement. It incorporates previous amendments and is intended for use by qualified structural engineers and contractors.
This document provides details of the design of a headed concrete anchor and end plate connection supporting a reinforced concrete beam. Key details include:
- Supported member is a hopper applying 5000kg vertical force
- Anchor bolt diameter is 20mm
- There are 4 anchors in a 2x2 configuration spaced 50mm apart
- Concrete strength is 40MPa
- Checks are performed to ensure the connection has sufficient capacity for the applied tension and shear loads considering factors like concrete breakout strength, steel strength, pryout strength, etc. with all checks indicating the design is safe.
A raft foundation is a large concrete slab that interfaces columns with the base soil. It can support storage tanks, equipment, or tower structures. There are different types including flat plate, plate with thickened columns, and waffle slab. The structural design uses conventional rigid or flexible methods. It involves determining soil pressures, load eccentricities, moment and shear diagrams for strips, punching shear sections, steel reinforcement, and checking stresses. A beam-slab raft foundation design follows the same process as an inverted beam-slab roof.
This document discusses the use of prefabricated structural steel girders with composite reinforced concrete deck slabs for the construction of urban flyovers. Some key advantages of this system include reduced girder weights which allows for transportation and erection with smaller equipment, and the ability to construct longer obligatory spans by splicing shorter girder units together on site. Several deck systems are presented, including plate girders with cross diaphragms and cast-in-place slabs. The document concludes that while less common in India due to cost and maintenance needs, prefabricated steel girder systems can offer construction benefits for narrow urban sites.
The document summarizes a study on retrofitting beam-column joints with carbon fiber reinforced polymer (CFRP) composites under cyclic loading. It discusses how beam-column joints are vulnerable during earthquakes and describes traditional and CFRP retrofitting techniques. It outlines the objectives, methodology, modeling and analysis of retrofitted and non-retrofitted beam-column joints in ANSYS. The results show that the CFRP retrofitted joint had 27.7% less deflection and carried more load than the non-retrofitted joint. The conclusion is that CFRP improves joint confinement and capacity.
This document provides an overview of shear strength of soils. It discusses different types of shear failures in soils and the Mohr-Coulomb failure criterion. It describes the components of shear strength - cohesion and friction angle. It also summarizes different types of triaxial tests conducted to measure the shear strength parameters, including consolidated drained, consolidated undrained, and unconsolidated undrained tests. Furthermore, it discusses stress paths and pore pressure parameters related to shear strength testing of soils.
This document discusses soil shear strength, focusing on fine-grained soils. It covers topics like clay mineralogy, bonding mechanisms, structural units of common clay minerals like kaolinite and montmorillonite, double layer water, intergranular pressure, water pressure, the relationship between mineralogy and shear strength, soil fabric, Atterberg limits, ideal soil laboratory testing, and undisturbed Shelby tube sampling. In summary:
1) It describes the mineralogical composition and structure of common clay minerals and how they influence shear strength.
2) It explains concepts like double layer water, intergranular pressure, and how water pressure relates to shear strength.
3) There is a relationship
CE 72.52 - Lecture 8a - Retrofitting of RC MembersFawad Najam
The document outlines a presentation on retrofitting concrete structures. It discusses two approaches to retrofitting: global (system) strengthening which adds new elements to enhance stiffness, and local (element) strengthening which targets insufficient member capacities. Examples of global retrofitting mentioned include adding reinforced concrete shear walls and buckling restrained braces. Local retrofitting examples discussed are reinforcement concrete jacketing of columns and beams.
This document discusses quality assurance for concrete construction. It outlines three key components of a quality management system: 1) a quality assurance plan, 2) quality control process, and 3) quality audits. The quality assurance plan establishes organizational responsibilities, control measures, acceptance criteria, and documentation requirements. Quality control ensures conformance to specifications. Quality audits verify that quality assurance and control programs are properly implemented. Factors that affect concrete properties like strength, permeability, cracking and durability are also summarized.
Introduction & under ground water tank problemdhineshkumar002
The document discusses the design of an underground rectangular reinforced concrete water tank. It provides steps for calculating earth pressure, determining member thicknesses, and designing reinforcement for the long walls, short walls, and roof slab. The long walls are designed as vertical cantilevers and the short walls as continuous slabs. Reinforcement is checked for bending and cracking stresses. The example shows calculating load intensities, bending moments, required depths and areas of steel for the tank walls and slab according to code specifications.
Calulation of deflection and crack width according to is 456 2000Vikas Mehta
This document discusses the calculation of crack width in reinforced concrete flexural members. It provides information on:
1) Crack width is calculated to satisfy serviceability limits and is only relevant for Type 3 pre-stressed concrete members that crack under service loads.
2) Crack width depends on factors like amount of pre-stress, tensile stress in bars, concrete cover thickness, bar diameter and spacing, member depth and location of neutral axis, bond strength, and concrete tensile strength.
3) The method of calculation involves determining the shortest distance from the surface to a bar and using equations involving member depth, neutral axis depth, average strain at the surface level. Permissible crack widths are specified depending on exposure
This is the presentation about the Plum concrete which is used under water to make a reservoir. This presentation is related to the Civil Engineering. The visual effect of the presentation can be seen after downloading it.
Roller-compacted concrete (RCC) is a concrete that is mixed in a pugmill and placed with dump trucks and spread with bulldozers. It is compacted in lifts of 100-250mm thick using vibratory steel drum rollers. RCC does not require internal vibration and can be used for port, rail, highway, and industrial facilities. Some advantages are reduced cement, no formwork, and ability to maintain traffic flow during placement. Limitations include a rougher surface and difficulty compacting near edges.
Prestressed concrete combines high-strength concrete and high-strength steel in an active manner by tensioning steel tendons and holding them against the concrete, putting it into compression. This transforms concrete from a brittle to a more elastic material. It allows for optimal use of each material's properties and better behavior under loads. Prestressed concrete was pioneered in the 1930s and its use has expanded, finding applications in bridges and other structures. Common methods are pretensioning and post-tensioning, using various tendon types, with bonded or unbonded configurations. Tensioning is done using mechanical, hydraulic, electrical or chemical devices.
A plate girder is a beam composed of welded or riveted steel plates. It consists of two flanges and a web plate. The flanges resist bending moments while the web resists shear forces. Plate girders are commonly used for longer spans than ordinary beams, with spans ranging from 14-40 meters for railroads and 24-46 meters for highways. They have a high depth to thickness ratio for the web, making it slender. Stiffeners are added to the web to prevent buckling. Plate girders are an economical choice for longer spans where their design can be optimized for requirements.
This document provides details on the construction process for the substructure of a bridge, including pile foundations and a pile cap. It describes the steps to construct cast-in-place concrete piles, which include boring holes for the piles, lowering reinforced steel cages into the holes, fitting tremie pipes to pour concrete, and flushing out debris. It also outlines the process for constructing the pile cap, such as excavating around the piles, chipping off excess concrete, forming shutters, placing reinforcing steel, and pouring concrete. The overall bridge construction process is divided into substructure and superstructure work.
The document discusses the design and estimation of an Intze tank. It includes an abstract that describes the need for water storage and supply. It then covers various topics related to designing water tanks such as estimating water demand based on population and consumption rates, classifying different types of water tanks, design requirements for concrete water tanks, and the design of specific elements like domes and overhead tanks. The document aims to provide theory and guidelines for designing a reinforced concrete elevated circular water tank with a domed roof and conical base using the working stress method.
This document provides an overview of the design of compression members (columns) in reinforced concrete structures. It discusses various types of columns based on reinforcement, loading conditions, and slenderness ratio. It describes the classification of columns as short or slender. The document also covers effective length, braced vs unbraced columns, codal provisions for reinforcement, and functions of longitudinal and transverse reinforcement. Key points include types of column reinforcement, minimum reinforcement requirements, cover requirements, and assumptions for the limit state of collapse under compression.
This document summarizes a British Standard regarding the structural use of concrete in buildings and structures. It provides recommendations for design, detailing, materials, specification, construction practices, and quality control. The standard excludes bridges and concrete made with high alumina cement. It incorporates previous amendments and is intended for use by qualified structural engineers and contractors.
This document provides details of the design of a headed concrete anchor and end plate connection supporting a reinforced concrete beam. Key details include:
- Supported member is a hopper applying 5000kg vertical force
- Anchor bolt diameter is 20mm
- There are 4 anchors in a 2x2 configuration spaced 50mm apart
- Concrete strength is 40MPa
- Checks are performed to ensure the connection has sufficient capacity for the applied tension and shear loads considering factors like concrete breakout strength, steel strength, pryout strength, etc. with all checks indicating the design is safe.
A raft foundation is a large concrete slab that interfaces columns with the base soil. It can support storage tanks, equipment, or tower structures. There are different types including flat plate, plate with thickened columns, and waffle slab. The structural design uses conventional rigid or flexible methods. It involves determining soil pressures, load eccentricities, moment and shear diagrams for strips, punching shear sections, steel reinforcement, and checking stresses. A beam-slab raft foundation design follows the same process as an inverted beam-slab roof.
This document discusses the use of prefabricated structural steel girders with composite reinforced concrete deck slabs for the construction of urban flyovers. Some key advantages of this system include reduced girder weights which allows for transportation and erection with smaller equipment, and the ability to construct longer obligatory spans by splicing shorter girder units together on site. Several deck systems are presented, including plate girders with cross diaphragms and cast-in-place slabs. The document concludes that while less common in India due to cost and maintenance needs, prefabricated steel girder systems can offer construction benefits for narrow urban sites.
The document summarizes a study on retrofitting beam-column joints with carbon fiber reinforced polymer (CFRP) composites under cyclic loading. It discusses how beam-column joints are vulnerable during earthquakes and describes traditional and CFRP retrofitting techniques. It outlines the objectives, methodology, modeling and analysis of retrofitted and non-retrofitted beam-column joints in ANSYS. The results show that the CFRP retrofitted joint had 27.7% less deflection and carried more load than the non-retrofitted joint. The conclusion is that CFRP improves joint confinement and capacity.
This document provides an overview of shear strength of soils. It discusses different types of shear failures in soils and the Mohr-Coulomb failure criterion. It describes the components of shear strength - cohesion and friction angle. It also summarizes different types of triaxial tests conducted to measure the shear strength parameters, including consolidated drained, consolidated undrained, and unconsolidated undrained tests. Furthermore, it discusses stress paths and pore pressure parameters related to shear strength testing of soils.
This document discusses soil shear strength, focusing on fine-grained soils. It covers topics like clay mineralogy, bonding mechanisms, structural units of common clay minerals like kaolinite and montmorillonite, double layer water, intergranular pressure, water pressure, the relationship between mineralogy and shear strength, soil fabric, Atterberg limits, ideal soil laboratory testing, and undisturbed Shelby tube sampling. In summary:
1) It describes the mineralogical composition and structure of common clay minerals and how they influence shear strength.
2) It explains concepts like double layer water, intergranular pressure, and how water pressure relates to shear strength.
3) There is a relationship
This document discusses key concepts in geotechnical engineering including soil water, permeability, and shear strength. It defines different types of soil water, explains effective and total stress conditions, and explores stress diagrams under various saturated and unsaturated soil conditions. Darcy's law and factors affecting permeability are introduced. Shear strength is defined based on Mohr-Coulomb theory and different shear strength tests are described. Example problems are provided to calculate effective stresses at different depths and for a soil profile with a heave condition.
The document discusses triaxial shear testing of soils. It begins by explaining that soils fail primarily in shear and defining shear strength. It then details the process of a triaxial shear test, including sample preparation and testing stages. The key types of triaxial tests - consolidated drained (CD), consolidated undrained (CU), and unconsolidated undrained (UU) - are explained. Specifically, the document focuses on CD testing, showing how volume change is monitored during shearing and how stress-strain behavior varies with soil density. It also demonstrates how shear strength parameters (c, φ) are determined from CD test results and how the parameters relate to effective stresses and long-term soil behavior analysis.
The document discusses shear strength of soils. It describes how soils fail in shear when the shear stress along the failure surface reaches the shear strength. It then covers the Mohr-Coulomb failure criterion and how it relates the shear strength of a soil to the normal stress and shear stress parameters c, φ. Laboratory tests like direct shear tests and triaxial tests are used to determine the shear strength parameters from soil specimens.
Class 8 Triaxial Test ( Geotechnical Engineering )Hossam Shafiq I
The document summarizes laboratory tests conducted on sand and clay soils, including triaxial compression tests and unconfined compression tests. It describes the test procedures, equipment used, and how to analyze the results to determine soil shear strength parameters. Specifically, it outlines how to conduct a consolidated drained triaxial test on sand under three confining pressures and an unconfined compression test on clay to measure the undrained shear strength. Graphs and calculations of stress, strain, and shear strength are presented.
Class 6 Shear Strength - Direct Shear Test ( Geotechnical Engineering )Hossam Shafiq I
This document describes the direct shear test procedure used in a geotechnical engineering laboratory class to determine the shear strength parameters of soils. It discusses how the direct shear test is conducted by applying a normal stress and increasing shear stress to a soil sample until failure. Key steps of the test procedure are outlined, and the document explains how shear strength parameters like cohesion (C') and the internal friction angle (f) can be calculated from the test results and plotted on a Mohr-Coulomb failure envelope graph.
- Soils fail primarily in shear when the shear stress along a failure plane reaches the soil's shear strength.
- The shear strength of soils is governed by the Mohr-Coulomb failure criterion, which consists of cohesive and frictional components that depend on effective stresses.
- Laboratory tests like direct shear and triaxial tests are used to measure the shear strength parameters (c, φ) of soils by simulating the in-situ stress conditions.
Shear Strength of soil and behaviour of soil under shear actionsatish dulla
it contains details of property and theory of soil under shear action.Even the experiments to test the soil strength has given with illstrations
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- Soils fail primarily in shear when the shear stress along a failure plane reaches the soil's shear strength.
- The shear strength of soils is governed by the Mohr-Coulomb failure criterion, which consists of cohesive and frictional components that can be determined through laboratory tests such as direct shear and triaxial shear tests.
- These laboratory tests aim to simulate the in-situ stress conditions on soil samples and measure the shear stress and normal stress at failure to establish the shear strength parameters (c, φ) from the failure envelope.
The document discusses shear strength of soils. It defines shear strength as the soil's resistance to shearing stresses and deformation from particle displacement. Shear strength depends on cohesion between particles and frictional resistance, as modeled by the Mohr-Coulomb failure criterion. Laboratory tests like direct shear and triaxial shear tests are used to determine the shear strength parameters (c, φ) that describe a soil's failure envelope.
shear strength
Angle of repose of sand
Coulomb's law of shear strength
Mohr circle of Stress
Determination of shear strength parameters of soils
Direct shear test
Triaxial Shear Test
Consolidated drained (CD) test
Unconfined Compression Test
Vane shear test
Static Cone Penetrometer Test
Standard Penetration Test (SPT)
Triaxial shear test and shear strength properties of soilsatish dulla
1. The triaxial shear test is used to determine the shear strength parameters (c, φ) of soils by simulating the stress conditions around a soil element in the field.
2. In a consolidated-drained (CD) test, the soil sample is first consolidated under cell pressure and then sheared under drained conditions, allowing pore pressures to dissipate. This simulates long-term drained field conditions.
3. The results of multiple CD tests under varying cell pressures can be used to construct the Mohr-Coulomb failure envelope and determine the effective stress shear strength parameters c' and φ'.
1. The triaxial shear test is used to determine the shear strength parameters (c, φ) of soils by simulating the stresses around a soil sample in a three-dimensional state.
2. In the test, a soil specimen is enclosed in a triaxial cell where independent control is exerted on the cell pressure and axial load.
3. Based on drainage conditions during loading, there are three types of triaxial tests: consolidated-drained (CD), consolidated-undrained (CU), and unconsolidated-undrained (UU) tests. The CD test simulates long-term drained field conditions.
This document discusses determining the shear strength of soils. It explains that shear strength is the maximum shear stress a soil can withstand before failing. There are two main types of shear strength - drained and undrained. Laboratory tests like direct shear tests and triaxial tests are used to determine the shear strength parameters (c, φ) by simulating the in-situ stress conditions. The Mohr-Coulomb failure criterion relates shear strength to effective normal stress and describes shear failure. Parameters c' and φ' define the failure envelope in effective stress space.
This document discusses determining the shear strength of soils. It explains that soils fail in shear and their shear strength can be determined using laboratory tests like direct shear tests or triaxial tests on soil samples. The Mohr-Coulomb failure criterion describes the shear strength of a soil using parameters like cohesion (c) and friction angle (φ). These parameters can be estimated from the results of shear tests and used to assess shear strength and stability of soils under different field conditions.
This document discusses shear strength and failure criteria in soils. It introduces the Mohr-Coulomb failure criterion, where shear strength consists of cohesive and frictional components. It describes Mohr circles and how they relate to failure envelopes. It also summarizes different types of triaxial tests (consolidated drained, consolidated undrained, and unconsolidated undrained) used to measure shear strength parameters.
1) Shear strength is the resistance of soil to failure along internal surfaces and is dependent on factors like composition, structure, and initial state.
2) Common laboratory tests to determine shear strength parameters (cohesion c and friction angle φ) include direct shear tests and triaxial compression tests.
3) The Mohr-Coulomb failure criterion describes the shear strength of a soil in terms of the normal and shear stresses required to cause failure along an internal plane.
1) Shear strength is the resistance of soil to shear stresses and failure along internal surfaces. It is influenced by factors like mineralogy, density, pore water, and stress history.
2) Common laboratory tests to evaluate shear strength are the direct shear test and triaxial shear test, which apply stresses to soil samples to induce shear failure.
3) The Mohr-Coulomb failure criterion describes the shear strength of a soil in terms of cohesion and internal friction angle parameters, which can be determined from a series of direct shear tests under different normal stresses.
1. The document discusses shear failure in soils and the factors that influence a soil's shear strength.
2. It introduces the Mohr-Coulomb failure criterion, where shear strength is equal to the sum of the soil's cohesion and the frictional resistance along the failure plane.
3. It describes different types of triaxial tests (consolidated drained, consolidated undrained, and unconsolidated undrained) that are used to measure the shear strength parameters of cohesion, friction angle, and pore pressure characteristics.
1. The document discusses shear failure in soils and the factors that influence a soil's shear strength.
2. It introduces the Mohr-Coulomb failure criterion, where shear strength is a function of cohesion, friction angle, and normal stress.
3. It describes different types of triaxial tests (consolidated drained, consolidated undrained, and unconsolidated undrained) that are used to measure shear strength parameters.
1. The document discusses shear failure in soils and the factors that influence a soil's shear strength.
2. It introduces the Mohr-Coulomb failure criterion, where shear strength is equal to the sum of the soil's cohesion and the frictional resistance along the failure plane.
3. It describes different types of triaxial tests (consolidated drained, consolidated undrained, and unconsolidated undrained) that are used to measure the shear strength parameters of cohesion, friction angle, and pore pressure characteristics.
1. The document discusses shear failure in soils and the factors that influence a soil's shear strength.
2. It introduces the Mohr-Coulomb failure criterion, where shear strength is equal to the sum of the soil's cohesion and the frictional resistance along the failure plane.
3. It describes different types of triaxial tests (consolidated drained, consolidated undrained, and unconsolidated undrained) that are used to measure the shear strength parameters of cohesion, friction angle, and pore pressure characteristics.
The document discusses soil strength and different methods for measuring it. The Mohr-Coulomb failure criterion describes soil strength in terms of effective stresses. Laboratory tests like shear box and triaxial tests are used to measure soil strength parameters. The triaxial test can measure both drained (effective) and undrained strengths under controlled stress conditions. Interpretation of test results requires using concepts like effective and total stress Mohr circles.
This document discusses different types of triaxial tests used to determine shear strength parameters of soils, including consolidated drained (CD), consolidated undrained (CU), and unconsolidated undrained (UU) tests. It provides details on conducting UU triaxial tests, including applying cell pressure and deviator stress, and measuring resulting pore water pressure changes. UU tests are useful for modeling short-term undrained loading conditions in the field, such as rapid embankment construction. Both drained and undrained conditions depend on soil type, loading rate, and other factors. While undrained strength is not a fundamental property, it can be used to analyze total stresses under undrained loading.
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2. Strength of different materials Steel Tensile strength Concrete Compressive strength Soil Shear strength Presence of pore water Complex behavior
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6. Shear failure mechanism The soil grains slide over each other along the failure surface. No crushing of individual grains. failure surface
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 ) f is the maximum shear stress the soil can take without failure, under normal stress of . c failure envelope Cohesion Friction angle f
9. Mohr-Coulomb Failure Criterion ( in terms of effective stresses ) f is the maximum shear stress the soil can take without failure, under normal effective stress of ’. u = pore water pressure ’ c’ ’ failure envelope Effective cohesion Effective friction angle f ’
10. Mohr-Coulomb Failure Criterion Shear strength consists of two components: cohesive and frictional . ’ f f ’ ' c’ c’ cohesive component ’ f tan ’ frictional component
11. c and are measures of shear strength. Higher the values, higher the shear strength.
12. Mohr Circle of stress Resolving forces in and directions, Soil element ’ 1 ’ 1 ’ 3 ’ 3 ’
14. Mohr Circle of stress ’ P D = Pole w.r.t. plane ’ ,
15. Mohr Circles & Failure Envelope ’ Soil elements at different locations Failure surface X X X ~ failure Y Y Y ~ stable
16. Mohr Circles & Failure Envelope c The soil element does not fail if the Mohr circle is contained within the envelope GL Y c c Initially, Mohr circle is a point c +
17. Mohr Circles & Failure Envelope Y c GL c c As loading progresses, Mohr circle becomes larger… .. and finally failure occurs when Mohr circle touches the envelope
18. ’ Orientation of Failure Plane ’ Failure envelope P D = Pole w.r.t. plane ’ , f – Therefore, – ’ = 45 + ’ /2
19. Mohr circles in terms of total & effective stresses = X v ’ h ’ X u u + v ’ h ’ effective stresses u v h X v h total stresses or ’
20. Failure envelopes in terms of total & effective stresses = If X is on failure X v ’ h ’ X u u + v ’ h ’ effective stresses u v h X v h total stresses or ’ c Failure envelope in terms of total stresses ’ c’ Failure envelope in terms of effective stresses
21. Mohr Coulomb failure criterion with Mohr circle of stress X ’ v = ’ 1 ’ h = ’ 3 X is on failure ’ 1 ’ 3 effective stresses ’ ’ c’ Failure envelope in terms of effective stresses c’ Cot ’ ’ ’ ’ ’ Therefore,
25. Laboratory tests Field conditions z vc vc hc hc Before construction A representative soil sample z vc + hc hc After and during construction vc +
26. Laboratory tests Simulating field conditions in the laboratory Step 2 Apply the corresponding field stress conditions Step 1 Set the specimen in the apparatus and apply the initial stress condition vc vc hc hc Representative soil sample taken from the site 0 0 0 0 vc + hc hc vc + Traxial test vc vc Direct shear test
28. Direct shear test Preparation of a sand specimen Direct shear test is most suitable for consolidated drained tests specially on granular soils (e.g.: sand) or stiff clays Components of the shear box Preparation of a sand specimen Porous plates
29. Direct shear test Preparation of a sand specimen Leveling the top surface of specimen Specimen preparation completed Pressure plate
30. Direct shear test Test procedure Porous plates Pressure plate Steel ball Step 1: Apply a vertical load to the specimen and wait for consolidation P Proving ring to measure shear force S
31. Direct shear test Step 2: Lower box is subjected to a horizontal displacement at a constant rate 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
32. Direct shear test Shear box Loading frame to apply vertical load Dial gauge to measure vertical displacement Dial gauge to measure horizontal displacement Proving ring to measure shear force
33. Direct shear test Analysis of test results Note: Cross-sectional area of the sample changes with the horizontal displacement
34. Direct shear tests on sands Stress-strain relationship Shear stress, Shear displacement Dense sand/ OC clay f Loose sand/ NC clay f Dense sand/OC Clay Loose sand/NC Clay Change in height of the sample Expansion Compression Shear displacement
35. Direct shear tests on sands How to determine strength parameters c and f1 Normal stress = 1 Shear stress, Shear displacement f2 Normal stress = 2 f3 Normal stress = 3 Shear stress at failure, f Normal stress, Mohr – Coulomb failure envelope
36. Direct shear tests on sands Sand is cohesionless hence c = 0 Direct shear tests are drained and pore water pressures are dissipated, hence u = 0 Therefore, ’ = and c’ = c = 0 Some important facts on strength parameters c and of sand
37. Direct shear tests on clays Failure envelopes for clay from drained direct shear tests 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) Shear stress at failure, f Normal force, ’ Normally consolidated clay (c’ = 0) Overconsolidated clay (c’ ≠ 0)
38. 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, c a = adhesion, = angle of internal friction
43. Triaxial Shear Test Specimen preparation (undisturbed sample) Edges of the sample are carefully trimmed Setting up the sample in the triaxial cell
44. Triaxial Shear Test Specimen preparation (undisturbed sample) Sample is covered with a rubber membrane and sealed Cell is completely filled with water
45. Triaxial Shear Test Specimen preparation (undisturbed sample) In some tests Proving ring to measure the deviator load Dial gauge to measure vertical displacement
46. Types of Triaxial Tests Is the drainage valve open? Is the drainage valve open? yes no C onsolidated sample U nconsolidated sample yes no D rained loading U ndrained loading Under all-around cell pressure c c c c c Step 1 deviatoric stress ( = q) Shearing (loading) Step 2 c c c + q
47. Types of Triaxial Tests Is the drainage valve open? yes no C onsolidated sample U nconsolidated sample Under all-around cell pressure c Step 1 Is the drainage valve open? yes no D rained loading U ndrained loading Shearing (loading) Step 2 CD test CU test UU test
48. Consolidated- drained test (CD Test) Step 1: At the end of consolidation Step 2: During axial stress increase Step 3: At failure VC hC Total, = Neutral, u Effective, ’ + 0 ’ VC = VC ’ hC = hC VC + hC 0 ’ V = VC + = ’ 1 ’ h = hC = ’ 3 Drainage Drainage VC + f hC 0 ’ Vf = VC + f = ’ 1f ’ hf = hC = ’ 3f Drainage
49. Deviator stress (q or d ) = 1 – 3 Consolidated- drained test (CD Test) 1 = VC + 3 = hC
50. Volume change of sample during consolidation Consolidated- drained test (CD Test) Volume change of the sample Expansion Compression Time
51. Stress-strain relationship during shearing Consolidated- drained test (CD Test) Deviator stress, d Axial strain Dense sand or OC clay d ) f Dense sand or OC clay Loose sand or NC clay Volume change of the sample Expansion Compression Axial strain Loose sand or NC Clay d ) f
52. CD tests How to determine strength parameters c and Deviator stress, d Axial strain Shear stress, or ’ Mohr – Coulomb failure envelope d ) fa Confining stress = 3a d ) fb Confining stress = 3b d ) fc Confining stress = 3c 3c 1c 3a 1a ( d ) fa 3b 1b ( d ) fb 1 = 3 + ( d ) f 3
53. CD tests Since u = 0 in CD tests, = ’ Therefore, c = c’ and = ’ c d and d are used to denote them Strength parameters c and obtained from CD tests
54. CD tests Failure envelopes For sand and NC Clay, c d = 0 Therefore, one CD test would be sufficient to determine d of sand or NC clay Shear stress, or ’ d Mohr – Coulomb failure envelope 3a 1a ( d ) fa
55. CD tests Failure envelopes For OC Clay, c d ≠ 0 or ’ 3 1 ( d ) f c c OC NC
56. Some practical applications of CD analysis for clays = in situ drained shear strength 1. Embankment constructed very slowly, in layers over a soft clay deposit Soft clay
57. Some practical applications of CD analysis for clays 2. Earth dam with steady state seepage = drained shear strength of clay core Core
58. Some practical applications of CD analysis for clays 3. Excavation or natural slope in clay = In situ drained shear strength Note: CD test simulates the long term condition in the field. Thus, c d and d should be used to evaluate the long term behavior of soils
59. Consolidated- Undrained test (CU Test) Step 1: At the end of consolidation Step 2: During axial stress increase Step 3: At failure VC hC Total, = Neutral, u Effective, ’ + 0 ’ VC = VC ’ hC = hC VC + hC ± u Drainage VC + f hC No drainage No drainage ± u f ’ V = VC + ± u = ’ 1 ’ h = hC ± u = ’ 3 ’ Vf = VC + f ± u f = ’ 1f ’ hf = hC ± u f = ’ 3f
60. Volume change of sample during consolidation Consolidated- Undrained test (CU Test) Volume change of the sample Expansion Compression Time
61. Stress-strain relationship during shearing Consolidated- Undrained test (CU Test) Deviator stress, d Axial strain Dense sand or OC clay d ) f Dense sand or OC clay Loose sand /NC Clay u + - Axial strain Loose sand or NC Clay d ) f
62. CU tests How to determine strength parameters c and Deviator stress, d Axial strain Shear stress, or ’ d ) fb Confining stress = 3b 3b 1b 3a 1a ( d ) fa cu Mohr – Coulomb failure envelope in terms of total stresses c cu 1 = 3 + ( d ) f 3 Total stresses at failure d ) fa Confining stress = 3a
63. CU tests How to determine strength parameters c and cu Mohr – Coulomb failure envelope in terms of total stresses c cu Effective stresses at failure u f ( d ) fa Shear stress, or ’ 3b 1b 3a 1a ( d ) fa ’ 3b ’ 1b ’ 3a ’ 1a Mohr – Coulomb failure envelope in terms of effective stresses ’ C ’ u fa u fb ’ 1 = 3 + ( d ) f - u f ’ = 3 - u f
64. CU tests Shear strength parameters in terms of total stresses are c cu and cu Shear strength parameters in terms of effective stresses are c’ and ’ c’ = c d and ’ = d Strength parameters c and obtained from CD tests
65. CU tests Failure envelopes For sand and NC Clay, c cu and c’ = 0 Therefore, one CU test would be sufficient to determine cu and ’ = d ) of sand or NC clay Shear stress, or ’ cu Mohr – Coulomb failure envelope in terms of total stresses 3a 1a ( d ) fa 3a 1a ’ Mohr – Coulomb failure envelope in terms of effective stresses
66. Some practical applications of CU analysis for clays = in situ undrained shear strength 1. Embankment constructed rapidly over a soft clay deposit Soft clay
67. Some practical applications of CU analysis for clays 2. Rapid drawdown behind an earth dam = Undrained shear strength of clay core Core
68. Some practical applications of CU analysis for clays 3. Rapid construction of an embankment on a natural slope Note: Total stress parameters from CU test ( c cu and cu ) can be used for stability problems where, Soil have become fully consolidated and are at equilibrium with the existing stress state; Then for some reason additional stresses are applied quickly with no drainage occurring = In situ undrained shear strength
70. Unconsolidated- Undrained test (UU Test) Data analysis Initial volume of the sample = A 0 × H 0 Volume of the sample during shearing = A × H Since the test is conducted under undrained condition, A × H = A 0 × H 0 A ×(H 0 – H) = A 0 × H 0 A ×(1 – H/H 0 ) = A 0 C = 3 C = 3 No drainage Initial specimen condition 3 + d 3 No drainage Specimen condition during shearing
71. Unconsolidated- Undrained test (UU Test) Step 1: Immediately after sampling = + Step 2: After application of hydrostatic cell pressure u c = B 3 Note: If soil is fully saturated, then B = 1 (hence, u c = 3 ) 0 0 C = 3 C = 3 u c ’ 3 = 3 - u c ’ 3 = 3 - u c No drainage Increase of pwp due to increase of cell pressure Increase of cell pressure Skempton’s pore water pressure parameter, B
72. Unconsolidated- Undrained test (UU Test) Step 3: During application of axial load u d = AB d = + 3 + d 3 No drainage ’ 1 = 3 + d - u c u d ’ 3 = 3 - u c u d u c ± u d Increase of pwp due to increase of deviator stress Increase of deviator stress Skempton’s pore water pressure parameter, A
73. Unconsolidated- Undrained test (UU Test) Combining steps 2 and 3, u = u c + u d Total pore water pressure increment at any stage, u u = B [ 3 + A d ] u c = B 3 u d = AB d Skempton’s pore water pressure equation u = B [ 3 + A( 1 – 3 ]
75. Step 1 :Increment of isotropic stress Derivation of Skempton’s pore water pressure equation Increase in effective stress in each direction = 3 - u c 2 3 1 No drainage 1 + 3 3 + 3 2 + 3 No drainage u c
76. Step 2 :Increment of major principal stress Derivation of Skempton’s pore water pressure equation Increase in effective stress in 1 direction = 1 - u d Increase in effective stress in 2 and 3 directions = - u d Average Increase in effective stress = ( 1 - u d - u d – u d )/3 2 3 1 No drainage 1 + 1 3 + 0 2 + 0 No drainage u c
78. Typical values for parameter A NC Clay (low sensitivity) (A = 0.5 – 1.0) NC Clay (High sensitivity) (A > 1.0) Collapse of soil structure may occur in high sensitivity clays due to very high pore water pressure generation 1 – 3 u Axial strain Axial strain u 1 – 3
79. Typical values for parameter A OC Clay (Lightly overconsolidated) (A = 0.0 – 0.5) OC Clay (Heavily overconsolidated) (A = -0.5 - 0.0) During the increase of major principal stress pore water pressure can become negative in heavily overconsolidated clays due to dilation of specimen 1 – 3 Axial strain u 1 – 3 Axial strain u
81. Unconsolidated- Undrained test (UU Test) Step 1: Immediately after sampling Step 2: After application of hydrostatic cell pressure Step 3: During application of axial load Step 3: At failure 0 0 Total, = Neutral, u Effective, ’ + -u r ’ V0 = u r ’ h0 = u r C C -u r u c = -u r c (S r = 100% ; B = 1) C + C No drainage No drainage -u r c ± u ’ VC = C + u r - C = u r ’ h = u r ’ V = C + + u r - c u ’ h = C + u r - c u ’ hf = C + u r - c u f = ’ 3f ’ Vf = C + f + u r - c u f = ’ 1f -u r c ± u f C C + f No drainage
82. Unconsolidated- Undrained test (UU Test) Mohr circle in terms of effective stresses do not depend on the cell pressure. Therefore, we get only one Mohr circle in terms of effective stress for different cell pressures Total, = Neutral, u Effective, ’ + Step 3: At failure ’ hf = C + u r - c u f = ’ 3f ’ Vf = C + f + u r - c u f = ’ 1f -u r c ± u f C C + f No drainage ’ ’ 3 ’ 1 f
83. Unconsolidated- Undrained test (UU Test) Mohr circles in terms of total stresses 3b 1b 3a 1a f ’ 3 ’ 1 Total, = Neutral, u Effective, ’ + Step 3: At failure ’ hf = C + u r - c u f = ’ 3f ’ Vf = C + f + u r - c u f = ’ 1f -u r c ± u f C C + f No drainage or ’ u a u b Failure envelope, u = 0 c u
84. Unconsolidated- Undrained test (UU Test) Effect of degree of saturation on failure envelope S < 100% S > 100% 3b b 3a a 3c c or ’
85. Some practical applications of UU analysis for clays = in situ undrained shear strength 1. Embankment constructed rapidly over a soft clay deposit Soft clay
86. Some practical applications of UU analysis for clays 2. Large earth dam constructed rapidly with no change in water content of soft clay Core = Undrained shear strength of clay core
87. Some practical applications of UU analysis for clays 3. Footing placed rapidly on clay deposit Note: UU test simulates the short term condition in the field. Thus, c u can be used to analyze the short term behavior of soils = In situ undrained shear strength
89. Unconfined Compression Test (UC Test) Note: Theoritically q u = c u , However in the actual case q u < c u due to premature failure of the sample 1 = VC + f 3 = 0 Shear stress, Normal stress, q u
91. Stress Invariants ( p and q ) p (or s) = ( 1 + 3 )/2 q (or t) = ( 1 - 3 )/2 p and q can be used to illustrate the variation of the stress state of a soil specimen during a laboratory triaxial test 3 1 ( 1 + 3 )/2 ( 1 - 3 )/2 c
92. GL Stress Invariants ( p and q ) p (or s) = ( 1 + 3 )/2 q (or t) = ( 1 - 3 )/2 c c c or q or p Failure envelope Stress path
94. p (or s) = ( 1 + 3 )/2 q (or t) = ( 1 - 3 )/2 Mohr Coulomb failure envelope in terms of stress invariants Therefore, sin = tan or q or p f = c + tan q = c cos + p sin = sin -1 (tan c cos
95. Stress path for CD triaxial test In CD tests pore water pressure is equal to zero. Therefore, total and effective stresses are equal p, p’ (or s, s’) = 3 q (or t) = 0 p, p’ (or s, s’) = 3 + d /2 q (or t) = d /2 3 p, p’ (or s, s’) = ( 1 + 3 )/2 = ( ’ 1 + ’ 3 )/2 q (or t) = ( 1 - 3 )/2 or q or p Failure envelope Step 1 3 3 Step 2 3 + d 3 d Stress path 45 0
96. Stress path for CU triaxial test In CU tests pore water pressure develops during shearing p, p’ (or s, s’) = 3 q (or t) = 0 p (or s) = 3 + d /2 q (or t) = d /2 3 = ’ 3 p (or s) = ( 1 + 3 )/2 p’ (or s’) = ( 1 + 3 )/2 - u q (or t) = ( 1 - 3 )/2 Step 1 3 3 d Total stress path 45 0 u d Step 2 3 + d 3 u d Effective stress path q ’ or p, p’
100. Direct simple shear test Direct shear test Direct simple shear test = 80 mm Soil specimen Porous stones Spiral wire in rubber membrane
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102. Torsional ring shear test Peak Residual Shear displacement f ’ ’ max ’ res
103. Torsional ring shear test Preparation of ring shaped undisturbed samples is very difficult. Therefore, remoulded samples are used in most cases N
108. Vane shear test This is one of the most versatile and widely used devices used for investigating undrained shear strength (C u ) and sensitivity of soft clays Rate of rotation : 6 0 – 12 0 per minute Test can be conducted at 0.5 m vertical intervals PLAN VIEW Bore hole (diameter = D B ) h > 3D B ) Vane D H Applied Torque, T Vane T Rupture surface Disturbed soil
109. Vane shear test Since the test is very fast, Unconsolidated Undrained (UU) can be expected T = M s + M e + M e = M s + 2M e M e – Assuming a uniform distribution of shear strength C u C u d/2 d/2 C u h
110. Vane shear test Since the test is very fast, Unconsolidated Undrained (UU) can be expected M s – Shaft shear resistance along the circumference T = M s + M e + M e = M s + 2M e C u C u
111. Vane shear test Since the test is very fast, Unconsolidated Undrained (UU) can be expected T = M s + M e + M e = M s + 2M e M e – Assuming a triangular distribution of shear strength Can you derive this ??? C u C u h d/2 d/2 C u
112. Vane shear test Since the test is very fast, Unconsolidated Undrained (UU) can be expected T = M s + M e + M e = M s + 2M e M e – Assuming a parabolic distribution of shear strength Can you derive this ??? C u C u h d/2 d/2 C u
113. Vane shear test Since the test is very fast, Unconsolidated Undrained (UU) can be expected After the initial test, vane can be rapidly rotated through several revolutions until the clay become remoulded C u C u h peak ultimate Shear displacement
114. Some important facts on vane shear test Insertion of vane into soft clays and silts disrupts the natural soil structure around the vane causing reduction of shear strength The above reduction is partially regained after some time C u as determined by vane shear test may be a function of the rate of angular rotation of the vane
115. Correction for the strength parameters obtained from vane shear test Bjerrum (1974) has shown that as the plasticity of soils increases, C u obtained by vane shear tests may give unsafe results for foundation design. Therefore, he proposed the following correction. C u(design) = C u(vane shear) Where, = correction factor = 1.7 – 0.54 log (PI) PI = Plasticity Index
119. Pocket Penetrometer Pushed directly into the soil. The unconfined compression strength (q u ) is measured by a calibrated spring.
120. Swedish Fall Cone (suitable for very soft to soft clays) The test must be calibrated Soil sample C u ∞ Mass of the cone ∞ 1/(penetration) 2
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122. Pressuremeter Pre – bored or self – bored hole Guard cell Measuring cell Guard cell Coaxial tube Water Air
123. Pressuremeter Pre – bored or self – bored hole Guard cell Measuring cell Guard cell Coaxial tube Water Air Pressure Volumetric expansion Time Pressure Volumetric expansion Pseudo- elastic phase Elastic phase
124.
125. Static Cone Penetrometer test Cone penetrometers with pore water pressure measurement capability are known as piezocones 40 mm 40 mm 40 mm 40 mm
126. Static Cone Penetrometer test Force required for the inner rod to push the tip (F c ) and the total force required to push both the tip and the sleeve (F c + F s ) will be measured Point resistance ( q c ) = F c / area of the tip Sleeve resistance ( q s ) = F s / area of the sleeve in contact with soil Friction Ratio ( f r ) = q s / q c ×100 (%) Various correlations have been developed to determine soil strength parameters (c, ect) from f r
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128. Standard Penetration Test, SPT SPT is the most widely used test procedure to determine the properties of in-situ soils Standard penetration resistance (SPT N) = N 2 + N 3 Number of blows for the first 150 mm penetration is disregarded due to the disturbance likely to exist at the bottom of the drill hole The test can be conducted at every 1m vertical intervals Various correlations have been developed to determine soil strength parameters (c, ect) from N 63.5 kg 0.76 m Drill rod 0.15 m 0.15 m 0.15 m Number of blows = N 1 Number of blows = N 2 Number of blows = N 3
130. Various correlations for shear strength For NC clays, the undrained shear strength (c u ) increases with the effective overburden pressure, ’ 0 For OC clays, the following relationship is approximately true For NC clays, the effective friction angle ( ’) is related to PI as follows Skempton (1957) Plasticity Index as a % Ladd (1977) Kenny (1959)
131. Shear strength of partially saturated soils In the previous sections, we were discussing the shear strength of saturated soils. However, in most of the cases, we will encounter unsaturated soils in tropical countries like Sri Lanka Pore water pressure can be negative in unsaturated soils Solid Water Saturated soils Pore water pressure, u Effective stress, ’ Solid Unsaturated soils Pore water pressure, u w Effective stress, ’ Water Air Pore air pressure, u a
132.
133. Shear strength of partially saturated soils Therefore, strength of unsaturated soils is much higher than the strength of saturated soils due to matric suction Same as saturated soils Apparent cohesion due to matric suction - u a ’ u a – u w = 0 (u a – u w ) 1 > 0 (u a – u w ) 2 > (u a – u w ) 1
134. How it become possible build a sand castle - u a Same as saturated soils Apparent cohesion due to matric suction ’ u a – u w = 0 Failure envelope for saturated sand (c’ = 0) (u a – u w ) > 0 Failure envelope for unsaturated sand Apparent cohesion