11:03 AM sakai.uri.edu 1. A contractor plans to dig an excavation as show in Fig
ID: 1712928 • Letter: 1
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11:03 AM sakai.uri.edu 1. A contractor plans to dig an excavation as show in Fig. P7-31. If the river is at level A, what is the factor of safety against failure of the clay at the bottom of the excavation (i.e. "blow out")? The factor of safety in this problem can be defined as the ratio of the resisting force to the driving force. Neglect any vertical shear in the clay. To what elevation can the water rise before a "blow out" will develop? (Holtz, Kovacs, and Sheahan 2010) 30 Level A (Elev. = +18) 2 Excavation 10 River Clay, -2000 kg/m3 0 Very pervious sand -10 Fig. P7-31 2. An unconfined aquifer with a saturated thickness of 15 m (ho). Observation wells are located distances of 30, 60, and 120 m from the pumping well. Water is pumped from the well at a rate of 0.2 m/s. After pumping 24 hr, the following drawdown information was collected: at r,-30 m, z,-0.58 m, at r. = 60 m, 22 = 0.41 m, at r,-120 m, 23 = 0.24 m. Evaluate the hydraulic conductivity in cm's (Holtz, Kovacs, and Sheahan 2010).Explanation / Answer
Here it can be seen that excavation is made in clay but we know that blow out can only occur in cohesionless soil but clay is a cohesive soil hence blow out will not occur in this case .
Therefore, Factor of Safety = 1
and water level can be raise fully upto 30m.
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