Question

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[15) 3. Two lines of sheet pile walls are driven into a river bed to allow excavation of a trench. Water level in the trench is maintained at the bottiom of the excavation (level C-F) by pumping Elevations are as follows: Impervious layer (level E-G; datum): Oft Soil surface (level B-B') Water level & soil level in trench (C-F): 40t Water level in river (A-A'): 75 t Tip of sheet pile wall (D) 55 ft 17.5 ft The flow net for one half of the excavation is shown in the Figure below (drawn to scale; note AB sheet pile wall sheet pile wall water B' soll line of symmety impervious a) How many equipotential drops and flow channels does this (half) flow net possess? b) The coefficient of permeability k is 100 ft/hr. Estimate the total volume Q which is flowing into the trench per hour, per foot of trench from botlh sides of the excavation. Assume the soil conditions on the right of the excavation are symmetric with the left side. c) How high would water rise in a standpipe placed at point 1 (ie what is the pressure head hp)? d) For points 4 in the flow net, what is the vertical hydraulic gradient I using the geometry of the last head drop at this location? Does this increase or decrease the effective vertical stress at this point?

Answer 1

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