University 

Subject  Foundation engineering 
Section A
1. Attempt this entire question.
(a) Figure A1a shows a borehole log and undrained shear strength profile. It is proposed to excavate to 1m below ground level and construct a 2m square, 0.5m deep concrete foundation carrying a total load of 200kN and a variable load of 100kN. Engineered fill is placed above the foundation up to ground level. The groundwater level is 1.5m below ground level. Using global factors, determine whether the foundation is acceptable.
(b) 0.3 diameter CFA piles will be used to support the slurry tank shown in Figure A1b. The tank will be a piled raft supported by 20 piles at 1m centers. The ground level around the building will be raised by 2m using engineered fill after the building is built. Assume that the walls and floor of the tank are 0.2m thick and the density of the slurry is 1100kg/m3. Calculate the maximum load on the pile group
Figure A1b Crosssection showing the soil profile and location of tank supported by piles
(c) Piles are to be used as anchors for ships tied up to a quay wall (Figure A1c). Calculate the lateral resistance of a 0.5 diameter 5m long concrete pile. The piles are installed in engineered fill, which is formed of coarsegrained soil. The river level is 2m below ground level. Assume the unit weight of the engineered fill above the groundwater level is 16kN/m3 and, below the groundwater level 19kN/m3. The angle of friction of the fill is 35o.
(d) A 5m diameter 3m high steel water tank is built on a 0.5m thick platform of engineered fill. The fill sits on the top of a 1m thick layer of firm clay, which is underlain by weathered rock. The coefficient of volume compressibility of the clay is 0.3m2/MN and that of the weathered rock, 0.03m2/MN. Estimate the average settlement of the tank which, when empty, weighs 71kN [8 marks]
(e) The external dimensions of a water tank are 3m deep, 4m wide and 8m long. It is constructed of 0.2m thick concrete walls and a base slab. The top of the tank is 0.3m above ground level. The tank is placed in a 2m deep excavation in a stiff overconsolidated clay as shown in Figure A1e. The groundwater level is at 0.5m below ground level. In order to construct the tank, the groundwater level near the excavation was lowered to 2.5m below ground level; i.e. the tank was built in a dry excavation. Determine the possible load combinations acting on the tank and calculate the design loads using Design Approach 1 Combination 1.
Section B Attempt all questions
2. It is proposed to build a 3m high approach embankment to a bridge over a river. Figure B2 shows the dimensions of the embankment and ground profile. The embankment is built on a compacted gravel layer, which has a unit weight of 17kN/m3. The gravel layer was in place six months before the embankment was constructed and replaced the topsoil. The engineered fill used to form the embankment has a unit weight of 17.5kN/m3. Estimate The total settlement of the embankment. The time it takes that settlement to occur.
There is a concern that the embankment will fail during construction. Therefore, the embankment will be built in two stages to allow the alluvial clay to consolidate between the stages thus increasing the strength. At the end of the first stage, the embankment will be 1.5m high. It will be left for six months while the clay consolidates. Estimate the settlement of the first stage of the embankment at the end of six months.
3. A contractor proposes to use 2m square pad foundations for the columns of the portal frame shown in Figure B3. The formation level of the foundations is 1.5m below ground level. The 0.4m thick reinforced concrete floor slab, which is 15m wide and 30m long, carries an imposed load of 7.5kPa. The vertical load on the foundations due to the selfweight of the structure is 23.6kN per column; the imposed load, 36kN per column. Ignore any horizontal loads or moments acting on the pad foundations. Calculate the total settlement of the pad foundations.
4. A reinforced concrete caisson is to be sunk into a riverbed to form a permanent foundation for a bridge pier. The geological profile is given in Figure B4 and the soil properties in Table B4. Once the caisson is in place, a base slab is cast to create the foundation. Calculate the unit design bearing resistance using Design Approach 1 Combination 2.
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