Atividade - Mecânica dos Solos 2

loading approach the shear strength the strains resulting from this undrained loading followed by consolidation will exceed the strains caused by the same stresses applied slowly PROBLEMS 281 Refer to Fig 284 Assuming that u o that the soil is saturated and that A 3 write expressions for the pore pressures and effective stresses at steps 2 and 3 282 Refer to Figs 287 and 2810 Find the shear strength and water content at failure for specimens con a Triaxial compression unloading undrained 283 Refer to Figs 288 and 2811 Find the shear strength and water content at failure for specimens consolidated to 120 psi and then rebounded to 16 psi Answer the same four cases as in Problem 282 284 Refer to Figs 287 and 2813 A specimen of clay is first normally consolidated to an effective stress of 16 psi Then without permitting further drainage the chamber pressure is increased to 66 psi Then still without permitting further drainage the specimen is loaded in triaxial compression Find the shear strength and the values of o 63 and pore pressure at failure Hint Draw total and effective stress paths 454 PART V SOIL WITH WATERTRANSIENT FLOW 2910 SUMMARY OF MAIN POINTS This chapter has emphasized that it is not a simple matter to obtain accurate measurements of undrained strength In particular great care must be taken in sampling and in preparation of test specimens To obtain very accurate strengths all aspects of the in situ stress conditions should be reproduced in the tests Stress history has a great effect upon undrained strength Strength during repetitive undrained shear can be much less than during a single loading PROBLEMS 291 Refer to Fig 2918 What is the value of pore pressure at point J for the unconfined compression test specimen 292 Refer to Fig 2918 Derive the following equation for os o9ps o0K0 Au1 KO where Au u sh ov sh is an A parameter for undrained unloading from K0 stresses to isotropic stresses 293 The concept of a unique relationship between effective stress and undrained strength for a soil is only valid under certain conditions List the factors discussed in Chapter 29 that can influence this relationship 294 Refer to the lower part of Fig 294 For the four tests shown on this figure a In which tests did cavitation occur b What was the value of pore pressure at which cavitation occurred c Plot the four Mohr circles in terms of effective stresses and show the pore pressure at failure for each test Answer a Cavitation occurred in the tests with o3 53 psi and 20 psi ie those tests with p 0 b c Draw effective stress envelopes through the origin c 0 and at 0 32 All circles must be tangent to this envelope o3 6 3 u 53 200 147 20 347 147 cavitation 45 57 12 98 57 41 no cavitation 3 281 Etapa 1 u un Bo B 1 u co 1co 0 ov o u o co h o u o Etapa 3 ov o Aoa u un Bo A Aoa h os u co o 1 1 3 ôv o Ao u o Ao 1 Ao 3 ôv oc 2 Ao ôh os u o 1 Ao 3 Digitalizado com CamScanner 284 u 66 16 50 psi σ3 66 psi q σ1 σ3 2 p σ1 σ3 2 σ3 16 psi q 0375 p σ1 σ1 u σ1 σ1 50 σ1 66 2 0375 σ1 50 16 2 σ1 852 psi 0625 σ1 5325 σ1 352 psi σ3 16 psi τ σ tan φ τf qf σ1 σ3 2 382 16 2 τf 96 psi