A silo containing Portland cement is to be built at an industrial site. The silo will...

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A silo containing Portland cement is to be built at an industrial site. The silo will be supported on a reinforced concrete pad foundation, 6.2 m x 6.2 m in plan and 400 mm thick, which is cast in situ in an excavation 0.6 m deep. The level in the silo will fluctuate throughout the design life; when it is full the total weight (including the pad foundation) will be (5650 +10X) kN (e.g. if X= 4, the total weight is 5690 kN). The idealised ground profile is as follows: Depth (m) 0-0.6 0.6-11.5 >11.5 Description Made ground Medium dense medium sand Siltstone Unit weight (kN/m³) 17.8 (18.2 + X/10) above GWL (18.7+X/10) below GWL The sand is overconsolidated with the previous maximum effective stress at foundation level o', estimated to be 30 kPa, and an angle of shear resistance d' = (30+X/10)°. Standard penetration testing was carried out in a borehole at the intended silo location prior to construction and the following values recorded: Depth below GL (m) 1.00 1.75 2.50 3.25 4.00 4.75 5.50 6.25 7.00 7.75 SPT 'N' 11 13 13 16 18 19 22 23 25 29 Ground water was first encountered in the borehole at 2.5 m below ground level (GL). (a) Applying all relevant correction factors and justifying any assumptions that you make, calculate the ultimate bearing capacity of the pad foundation, and thus the actual (global) load factor against collapse when the silo is full. Comment on your answers. [13] (b) There is some concern that non-uniform filling levels in the silo will cause eccentric vertical loading on the pad foundation. Repeat the calculations in part (a) assuming eccentricities of ex = ey = 250 mm for the line of action of the total weight. Comment on the impact this has on your answers from (a). [4] (c) Use the method of Burland and Burbidge (1985) to estimate the average settlement of the pad foundation (i) immediately after construction and filling of the silo, and (ii) after 10 years of continuous operation of the silo. Comment on your answers. [12] (d) Identify any other aspects of this foundation that should be checked, explaining what the potential issue is in each case. [4] A silo containing Portland cement is to be built at an industrial site. The silo will be supported on a reinforced concrete pad foundation, 6.2 m x 6.2 m in plan and 400 mm thick, which is cast in situ in an excavation 0.6 m deep. The level in the silo will fluctuate throughout the design life; when it is full the total weight (including the pad foundation) will be (5650 +10X) kN (e.g. if X= 4, the total weight is 5690 kN). The idealised ground profile is as follows: Depth (m) 0-0.6 0.6-11.5 >11.5 Description Made ground Medium dense medium sand Siltstone Unit weight (kN/m³) 17.8 (18.2 + X/10) above GWL (18.7+X/10) below GWL The sand is overconsolidated with the previous maximum effective stress at foundation level o', estimated to be 30 kPa, and an angle of shear resistance d' = (30+X/10)°. Standard penetration testing was carried out in a borehole at the intended silo location prior to construction and the following values recorded: Depth below GL (m) 1.00 1.75 2.50 3.25 4.00 4.75 5.50 6.25 7.00 7.75 SPT 'N' 11 13 13 16 18 19 22 23 25 29 Ground water was first encountered in the borehole at 2.5 m below ground level (GL). (a) Applying all relevant correction factors and justifying any assumptions that you make, calculate the ultimate bearing capacity of the pad foundation, and thus the actual (global) load factor against collapse when the silo is full. Comment on your answers. [13] (b) There is some concern that non-uniform filling levels in the silo will cause eccentric vertical loading on the pad foundation. Repeat the calculations in part (a) assuming eccentricities of ex = ey = 250 mm for the line of action of the total weight. Comment on the impact this has on your answers from (a). [4] (c) Use the method of Burland and Burbidge (1985) to estimate the average settlement of the pad foundation (i) immediately after construction and filling of the silo, and (ii) after 10 years of continuous operation of the silo. Comment on your answers. [12] (d) Identify any other aspects of this foundation that should be checked, explaining what the potential issue is in each case. [4]

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Answer a Ultimate Bearing Capacity and Global Load Factor Against Collapse The ultimate bearing capacity of the pad foundation can be calculated using ... View the full answer