Support of Wall Pier w/Tremie Seal

[dscott]

I am designing a wall pier for a river crossing. The pier will be on a footing that will be founded on a tremie seal supported by piles. I have sample calcs of a pile design for a bridge pier with a tremie seal from US Steel-Highway Structures Design Handbook from the early 1970s. To design the piles, USS shows moments being summed from design forces (stream flow, wind, etc) at the top of footing. It then states, "Transfer the (governing) forces and moments acting at the top of the footing ... down to the top of the piles. To these forces add the weight of the footing the weight of the tremie seal, and the saturated weight of the soil and water acting on the footing and the tremie seal." Would it be more correct to design the piles for moments based on a moment arm that extends all the way to the bottom of the seal, or is that too conservative?

 

[wiktor]

dscott:
When you transfer the forces "down to the top of piles" your moments will increase due to additional arm

 

[seawaller]

how is a tremie seal made?

 

[dscott]

For a river crossing, a steel sheet pile cofferdam is driven through the water into the river bed. Divers install interior bracing in the cofferdam. Excavation to the desired new bottom of river elevation is performed through the water within the cofferdam. The tremie seal is then poured through the river water using tubes that maintain a constant flow of concrete at all times. Once the seal has cured, water within the cofferdam is pumped out so that workers can place the footing "in the dry". The seal depth is a function of how much water will be outside the cofferdam - if the seal is to thin (not heavy enough), the water outside the cofferdam will cause the soil at the bottom of the cofferdam to boil up, in order to maintain equilibrium.