Question

3. Shear Strength a. Plot the effective stress Mohr-Coulomb failure envelope for a soil with c'-500 b. A plane through a sample of this soil has an effective normal stress of c. Use a Mohr circle that touches the failure enve psf and 32 deg. acting on it. What is the shear strength of the soil on that plane? of 2000 psf to estimate the values of σ, and σ, at a state of shear failure 2000 psf lope at an effective normal stress 4. Drained Shear Strength A project site has a 10 ft thick layer of clay fill at the ground surface with total unit weight of 125 pcf. A layer of fine uniform poorly-graded sand is present from depths of 10 to 30 ft. The sand is not saturated. The corrected SPT blowcounts for the layer are: Corrected SPT blowcount, No Depth (ft) 15 18 13.5-15 18.5-20 23.5-25 28.5-30 17 Use multiple correlations (presented in class) to estimate the effective stress friction angle (or range of friction angles) for this layer. You may need to estimate a total unit weight for the sand to use correlations that require effective normal stress. 5. Undrained Shear Strength Clay layers are encountered at a project site. The consolidation properties are listed in the table below. Total unit Depth (ft) weight (pcf) USRNC OCR 10 4 Layer Overconsolidated5 clay (0 to 10 ft) Normally consolidated clay |ーー20 (10 to 30 ft) 122.4 122.4 102.4 102.4 0.25 0.25 0.28 12 0.28 102.4 0.28 ! 28 Calculate undrained shear strength of the clay at each of the five depths using provided data. Plot the undrained shear strength vs. depth. the

Answer 1

Given c^verticalline = 500 psf phi^verticalline = 32 degrees. To plot the effective stress Mohr-coulomb failure envelopr. (Ref. graph) . Given sigma^verticalline = 2000 psf. We know that, by Mohr-Coulomb theory, effective shear stress tou = C^verticalline + sigma^verticalline tan p^verticalline = 500 + (2000) times tan 32 degree = 1749.74 psf therefore shear stress tou = 1749.74 psf. To find sigma^verticalline_1 and sigma^verticalline_3 from Mohic circle. given sigma^verticalline = 2000 psf Using tou = c^verticalline + sigma tan phi, the point P is given as P(sigma, tou) = P(2000, 1749.71), The value of sigma_ verticalline and sigma_3 are taken from the graph. (The values in the table are calculated for reference) \r\n \r\n \r\n

If the Mohr's circle is drawn ,then the values of principal stresses can be directly taken from the graph based on where the circle touches the x-axis (ie., sigma axis).