Need and scope: In many engineering problems such as design of foundation, retaining walls, slab bridges, pipes, sheet piling, the value of the angle of internal friction and cohesion of the soil involved are required for the design. Direct shear test is used to predict these parameters quickly. The laboratory report cover the laboratory procedures for determining these values for cohesion less soils.
Planning and organization: Apparatus: 1. Direct shear box apparatus 2. Loading frame motor attached. Dial gauge. Proving ring. Straight edge. Balance to weigh upto mg. Aluminum container. APPARATUS Knowledge of equipment: Strain controlled direct shear machine consists of shear box, soil container, loading unit, proving ring, dial gauge to measure shear deformation and volume changes. A two piece square shear box is one type of soil container used. Procedure: 1. Check the inner dimension of the soil container.
Put the parts of the soil container together. Calculate the volume of the container. Weigh the container. Place the soil in smooth layers approximately 10 mm thick. If a dense sample is desired tamp the soil. Weigh the soil container, the difference of these two is the weight of the soil.
Calculate the density of the soil. Make the surface of the soil plane. Put the upper grating on stone and loading block on top of soil.
Measure the thickness of soil specimen. Apply the desired normal load. Remove the shear pin. Attach the dial gauge which measures the change of volume. Record the initial reading of the dial gauge and calibration values. Start the motor. Take the reading of the shear force and record the reading. Take volume change readings till failure. Add 5 kg normal stress 0.
Record carefully all the readings. Direct shear box apparatus, and Loading frame motor attached 2. Dial gauge for vertical deformation measurement 3. Dial gauge for horizontal deformation measurement 4. Proving ring for Shear force measurement. Loads are kept in loading frame for application of normal stress 5. Components of shear box with porous stone, filter paper etc.
In the shear box test, the specimen is not failing along its weakest plane but along a predetermined or induced failure plane i. This is the main drawback of this test. Moreover, during loading, the state of stress cannot be evaluated. It can be evaluated only at failure condition i. Also failure is progressive.
Direct shear test is simple and faster to operate. As thinner specimens are used in shear box, they facilitate drainage of pore water from a saturated sample in less time. This test is also useful to study friction between two materials one material in lower half of box and another material in the upper half of box.
The angle of shearing resistance of sands depends on state of compaction, coarseness of grains, particle shape and roughness of grain surface and grading. It varies between 28o uniformly graded sands with round grains in very loose state to 46o well graded sand with angular grains in dense state. The volume change in sandy soil is a complex phenomenon depending on gradation, particle shape, state and type of packing, orientation of principal planes, principal stress ratio, stress history, magnitude of minor principal stress, type of apparatus, test procedure, method of preparing specimen etc.
In general loose sands expand and dense sands contract in volume on shearing. There is a void ratio at which either expansion contraction in volume takes place. This void ratio is called critical void ratio. Expansion or contraction can be inferred from the movement of vertical dial gauge during shearing. The friction between sand particles is due to sliding and rolling friction and interlocking action. Need and scope: This test method covers the determination of the unconfined compressive strength of cohesive soil in the intact, remolded, or reconstituted condition, using strain-controlled application of the axial load.
This test method also provides an approximate value of the strength of cohesive soils in terms of total stresses. Record load, deformation, and time values at sufficient intervals to define the shape of the stress-strain curve usually 10 to 15 points are sufficient.
Need and scope: This test method covers determination of the strength and stress-strain relationships of a cylindrical specimen of either undisturbed or remolded cohesive soil. Specimens are subjected to a confining fluid pressure in a triaxial chamber. No drainage of the specimen is permitted during the test.
The specimen is sheared in compression without drainage at a constant rate of axial deformation strain controlled. This is shown by small deflection, maybe 2 divisions, as observed from the dial gauge. In this lab test, the machine was switched off when the proving ring gauge started going backwards. Then the Perspex cylinder top was removed and the soil sample extracted. This test can be done in laboratory or in the field directly on the ground.
Vane shear test gives accurate results for soils of low shear strength less than 0. Osttin Joel Rosales. A short summary of this paper. Details of the accompanying textbook Soil Mechanics: concepts and applications 2nd edition are on the website of the publisher www. No part of this book may be reprinted or reproduced or utilized in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, except for the downloading and printing of a single copy from the website of the publisher, without permission in writing from the publishers.
Publisher's note This book has been produced from camera ready copy provided by the authors Contents Chapter Question 6. In these solutions, the Newmark chart method is used in all cases. Assuming that the behaviour of soil can be Q6. Comment on these curves and explain the relationship between them. Which would be the more suitable for use in design, and why?
The deviator stress then falls quite rapidly to as possibly bsteady value although the test has not been continued to a high enough strain to be sure of this of about 87 kPa. It is likely that the sudden fall in deviator stress between 3.
The pore water pressure rises with the deviator stress until an axial strain of about 0. The pore water pressure reaches a maximum of about 58 kPa at an axial strain of about 2. A pipeline AA' runs Q6. Estimate the increase in vertical stress at a number of points along the pipeline AA', due to the construction of the new building. Present your results as a graph of increase in vertical stress against distance along the pipeline AA', indicating the extent of the foundation on the graph.
What is the main potential shortcoming of your analysis? Figure Q6. Calculation of increases in vertical effective stress and resulting soil settlements Q6. Using the Newmark chart or otherwise, sketch the long-term settlement profile along a line perpendicular to the causeway.
Given time, how might your analysis be refined? Calculate the increase in vertical take these as the representative increases in vertical stress for each layer.
The average one- dimensional stiffness of each layer is that at the centre, i. To obtain a profile of settlement along a line perpendicular to the causeway, we will need to calculate the increases in vertical effective stress at each of these depths at points on the centreline of the causeway point O on plan , halfway between the middle and the edge of the causeway point E , the edge of the causeway point A , and at distances of 2.
Where symmetry is used and only a half or a quarter of the causeway is drawn, n is the number of elements counted multiplied by two or four respectively. Briefly outline the main difficulties encountered in converting stresses into strains and settlements. Use a suitable approximate method to estimate the ultimate settlement of the raft. The main difficulty in attempting to convert an elastic stress distribution into strains and settlements is the choice of an appropriate elastic modulus that takes proper account of the stress paths followed by all the soil elements.
The usual approach is to use the one- dimensional modulus on the assumption that deformations are predominantly vertical. A possible problem that then arises is that this approach can only be used to calculate long- term, drained settlements after any excess pore water pressures induced by loading have dissipated, although empirical adjustments are available to estimate the short term settlements due to shearing of the soil at constant volume.
The solution procedure is as follows. Divide the soil into three layers 2. Use the Newmark chart to calculate the increase in vertical effective stress at the middle of each layer assuming that the surcharge can be idealised as flexible 3. Use the value of E'0 at the centre of the layer to calculate the compression of the layer assuming deformation is primarily due to one dimensional compression. The increase in stress in each case is whole foundation.
The numbers of chart elements covered and the increases in vertical effective stress at each depth, and the layer and total settlements, are given in the Table below. Newmark chart for Q6. The soil at the site Q6. The estimated stiffness in one- dimensional compression E'o increases with depth as indicated below.
Depth below founding E'o, MPa level, m 0 to 4 5 4 to 10 10 10 to 20 25 below 20 very stiff Use the Newmark chart Figure 6. Hence estimate the expected eventual settlement of the centre of the foundation. Suggest two possible shortcomings of your analysis. Draw plan views of the foundation, to these scales, with the centre of the foundation above the centre of the chart see Figure Q6.
The number of elements covered by the whole foundation. The raft foundation is stiff, so the loading transmitted to the soil will not in fact be uniform 2. The division of the soil into only three layers is quite crude and could be refined 3. It has been assumed that deformation is essentially by one dimensional compression, i.
The use of the elastic soil model may be unrealistic two only required. Use of standard formulae in conjunction with one-dimensional consolidation theory Chapter 4 Q6. In what circumstances might this be justified? What is the ultimate settlement due to this load? In practice, this occurs after six months has elapsed, and the additional load is then removed. Giving two or three actual values, sketch a graph showing the settlement of the silo as a function of time.
Assume that the principle of superposition can be applied, and use the curve of R against T given in Figure 4. State briefly the main shortcomings of your analysis. The soil is defined as the un-cemented aggregate of mineral grains and decayed organic matter which is filled with liquid and gas or both between them is known as soil.
The loads from any structure like a building, bridge, or dam have to be ultimately transmitted to the soil through the foundation.
Foundation is required to transmit the load of the structure to soil with safety, efficiently, without excessive settlement of the soil mass.
Because excessive settlement can make structure fail for efficient working. So, various types of foundation like spread foundation, foundation action, well foundation e.
When it is required to make a safe structure having a slope or there is less space to construct a structure then the structure is required to retain deep under the soil.
A Pavement is a hard crust made by compaction of soil for the purpose of providing a smooth and strong surface and transmitting the load of traffic and vehicles.
The behavior of pavement may swell, shrink under the various condition of loading environmental effect which causes the failure of the transportation system. Hence, to this kind of problem, we must know of soil mechanics.
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