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2012-2-14 · impact pressure; of the nater. and the con-crete, the external pressure of the back fill. The concrete will be placed b-, the Coum-mis--on and lorm- no prtn,f the contract. The inside diameter of the pen-itr. k- "ill n-,t be less; than I.I fl:t 6 inches, the platsc of wrought ir.n or zolt steel not leI-s rhann