An old building was constructed on a 20 m deep normally consolidated clay layer overlying an...

 

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An old building was constructed on a 20 m deep normally consolidated clay layer overlying an impermeable bedrock. The old building applies a uniform load of 100 kPa over a 10 m by 10 m area, as shown in Fig. 2. The old building has existed for a long time and experienced a total consolidation settlement of 700 mm. The old building is to be demolished to make way for a new building. The new building was constructed a long time after the demolition of the old building, and as such, you can assume that all excess pore water pressure due to the removal of the old building has dissipated. The new building will be located at the exact same location and will also apply a uniform load of 100 kPa over a 10 m by 10 m area. The contractor is concerned about the consolidation settlement of the building within its defect liability period of 2 years. Monitoring indicated that 50 mm consolidation settlement occurred within the first 6 months. Using 1D consolidation analysis, calculate the consolidation settlement of the new building after 2 years. There are limited site investigations available for the clay material, and as such, only the unit weight (= 20 kN/m³) and an initial void ratio (eo = 0.51) of the clay layer are known. The recompression index of the clay can be taken as Cr=0.5Cc. The water table is located at the ground surface. You may assume flexible footing conditions and that the buildings experience no ini- tial settlement. For 1D consolidation analysis, only consider a one-point estimate at the middle of the clay layer directly beneath the centre of the buildings. For conser- vatism, consider a small strain assumption were the thickness of the clay layer is taken as Ho = 20 m and the initial void ratio remains unchanged following construction of the new building. (10 marks) V 100 kPa 20 m 10 m by 10 m extent of old and new building Clay Impermeable Bedrock Figure 2: An old and new building applying a load of 100 kPa over a 10 m by 10 m area. An old building was constructed on a 20 m deep normally consolidated clay layer overlying an impermeable bedrock. The old building applies a uniform load of 100 kPa over a 10 m by 10 m area, as shown in Fig. 2. The old building has existed for a long time and experienced a total consolidation settlement of 700 mm. The old building is to be demolished to make way for a new building. The new building was constructed a long time after the demolition of the old building, and as such, you can assume that all excess pore water pressure due to the removal of the old building has dissipated. The new building will be located at the exact same location and will also apply a uniform load of 100 kPa over a 10 m by 10 m area. The contractor is concerned about the consolidation settlement of the building within its defect liability period of 2 years. Monitoring indicated that 50 mm consolidation settlement occurred within the first 6 months. Using 1D consolidation analysis, calculate the consolidation settlement of the new building after 2 years. There are limited site investigations available for the clay material, and as such, only the unit weight (= 20 kN/m³) and an initial void ratio (eo = 0.51) of the clay layer are known. The recompression index of the clay can be taken as Cr=0.5Cc. The water table is located at the ground surface. You may assume flexible footing conditions and that the buildings experience no ini- tial settlement. For 1D consolidation analysis, only consider a one-point estimate at the middle of the clay layer directly beneath the centre of the buildings. For conser- vatism, consider a small strain assumption were the thickness of the clay layer is taken as Ho = 20 m and the initial void ratio remains unchanged following construction of the new building. (10 marks) V 100 kPa 20 m 10 m by 10 m extent of old and new building Clay Impermeable Bedrock Figure 2: An old and new building applying a load of 100 kPa over a 10 m by 10 m area.

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