SOIL MECHANICS AND FOUNDATION ENGINEERING-III (CE 434) PILE FOUNDATIONS Classification based on the function End bearing piles Friction piles Compaction piles Tension piles or uplift piles Anchor piles Fender piles or dolphins Batter piles Sheet piles Classification based on materials and composition Concrete piles Precast Cast in situ Driven piles: Cased or Uncased Bored piles: pressure piles and under reamed piles Timber Piles Steel Piles H-piles Pipe piles Sheet piles Composite piles Concrete and timber Concrete and steel BEARING CAPACITY OF DEEP FOUNDATION Theoretical Approach Pile Load Test Approach The Pile Driving Resistance Approach Theoretical Approach Unit End Bearing: 𝑞𝑏 = 𝜎𝑁𝑞 Unit Skin Friction: 𝑓𝑠 = 𝜎ℎ 𝑡𝑎𝑛𝛿 = 𝐾 𝜎𝑣 𝑡𝑎𝑛𝛿 Where K is the coefficient of earth pressure that converts vertical stress to lateral stress and d is interface friction angle. K=1 for hammered piles; = 0.7 or less for piles when hole is made first. d = 0.8 to 0.9 f’ for rough surface; 0.6 to 0.7 f’ for smooth surface LIMITING VALUES ULTIMATE LOAD FOR SINGLE TYPE OF SOIL 𝑄𝑢 = 𝑓𝑠 𝐴𝑠 + 𝑞𝑏 𝐴𝑏 FOR LAYERED SOIL 𝑄𝑢 = 𝑛𝑖=1 𝑓𝑠𝑖 𝐴𝑠𝑖 + 𝑞𝑏 𝐴𝑏 Soil Type 𝑞𝑏 (kN/m2) 𝑓𝑠 (kN/m2) Clean sand 10 000 100 Silty sand 5 000 85 Sandy silt 3 000 70 Problem A 600mm diameter pile is to be installed at a site that is characterized by two sand layers. The top layer is 12m thick, has a g=20kN/m3 and f=300. The bottom layer is 20m thick, has a g=22kN/m3 and f=350. The ground water table is at the ground surface. Compute the Unit End Bearing and the Unit Skin Friction at depths of 10, 15, 20 and 25m below the ground surface. Use Nq=20 for f=300 and Nq=50 for f=350. Take d=f and K=1.0. Also Calculate the Ultimate Load of the Pile if the length of the pile is 25m. Pile Load Test Approach Pile Load Test Approach When the soil is dense sand or stiff clay: Safe load = 𝑈𝑙𝑡𝑖𝑚𝑎𝑡𝑒 𝐿𝑜𝑎𝑑 𝐹𝑎𝑐𝑡𝑜𝑟 𝑜𝑓 𝑆𝑎𝑓𝑒𝑡𝑦 When the soil is not stiff and dense: The safe load is taken as LOWER of the following: Half the load at which pile settlement 10% of pile diameter two-third of the load at which pile settlement is 12mm. Problem Data from a pile load test on a 300mm diameter pile is given below. Determine the design load on the pile. Load (kN) 20 40 60 80 100 120 140 160 180 200 Settlement (mm) 3 5 10 13 17 22 27 34 44 62