CIVE 530 Midterm, Fall 2004

CIVE530 – Foundation Engineering MIDTERM – Fall 2004-2005 1/3 MIDTERM CIVE 530 – Foundation Engineering Fall 2004-2005 December 3, 2004 Programmable Calculators are NOT allowed Question Sheets MUST be returned with the Answer Booklet Name : I.D. # : Read the exam before you start! Start with problems you are most confident about! Manage your time carefully! Good Luck! PROBLEM – 1 ( 10 Points) A sample of dense sand tested in a trixial CD test (Consolidated-Drained), failed along a well defined failure plane at an angle of 67o with the horizontal. Find the effective confining pressure (σ3f’) if the principal stress difference at failure was equal to 120kPa. PROBLEM – 2 ( 10 Points) A drained trixial test is performed on a sand with the effective confining stress σ3f’=500kPa. At failure the maximum shear τmax=660 kPa. Find σ1f’, (σ1f’- σ3f’) and φ’ PROBLEM – 3 ( 10 Points) A vane shest test was conducted on a saturated clay. The height and diameter of the vanes were 4’ and 2” respectively. During the test, the ultimate torque applied was 23lb-ft. Determine the undrained shear strength of the clay in lb/ft2. CIVE530 – Foundation Engineering MIDTERM – Fall 2004-2005 2/3 PROBLEM – 4 (5 Points) A standard penetration test (SPT) was performed on a deposit of dry clean sand. At a depth of 3m, the number of blows to drive the sampler 18in. was 5 for the first 6”, 8 for the second 6” and 9 for the third 6”. Calculate the measured SPT, and estimate the in-situ relative density of the sand (properly reference your answer). PROBLEM - 3 (15 Points) A 120ft diameter cylindrical tank with an empty weight of 1,800,000 lbs (including the weight of the cylindrical mat foundation) is to be built. The bottom of the mat wil be at a depth of 3 ft below the ground surface. The tank is to be filled with a petroleum by- prodcut having a unit weight =50lb/ft3. The underlying soil is an undrained clay with cu = 800lb/ft2 and unit weight γ = 115 lb/ft3. Compute the maximum allowable height of fluid in the tank, that will maintain a Factor of Safety of 3.0 against bearing capacity failure. Assume that the weight of the tank is spread uniformly across the bottom of the tank. PROBLEM - 5 (20Points) A strip footing will be constructed on a silty sand deposit, which has the following shear strength characteristics: c=0 and φ = 28o γT = 17.5 kN/m3 Assume the strip footing will be 1.5m wide and embedded 1.0m below the ground surface. (a) Using a factor of safety against bearing failure FS=3, and assuming that the water table is well below the bottom of the footing, determine the safe bearing pressure. (b) Assume that the actual vertical load exerted by the strip footing is 200 kN/linear meter of wall length and that this load is offset from the centerline of the strip footing by 0.3m. Is the footing size acceptable? If not determine an acceptable footing width, based on bearing capacity considerations and FS=3. CIVE530 – Foundation Engineering MIDTERM – Fall 2004-2005 3/3 PROBLEM - 6 (10 Points) A 15 ft wide strip footing is placed at the surface of a dry sand deposit having a unit weight of 120 lb/ft3. If qult is given as 40kips/ft2, what is the internal friction angle of the sand deposit, φ ? PROBLEM – 7 (20 Points) For the conditions shown below, determine the ultimate bearing capacity of the foundation, qult. 2.5m x 5m footing SAND: c=0; φ=33o and γ=18.5 kN/m3 CLAY: c=40 kN/m2; φ=0o and γ=20 kN/m3 2.0m