Design of a spillway dam on shell piles and method of static calculation of its foundation

Abstract

UDC 627.82 : 624.154.041 This article gives a general idea of the design and method of static calculation of the foundation of a mediumhead spillway dam on shell piles constructed on a nourock base.* The design of a dam on shell piles which guarantees its static stability is depicted in the following form (Fig. i). The upstream face, rigidly joined with the spillway slab, consists of shell sheet piling which is placed along the entire length of the upstream face of the dam. All locks of the sheet piles are cemented with the exception of those in the axial plane of the piers, where they are not filled with mortar but with a bituminous material for independent movement of the wall sections. The sheet piling is embedded into the ground and is nowhere directly connected with the pier foundations; it transmits the load on them only through the spillway slab, projections of which freely pass into the grooves of the piers. This design permits assuming the sheet piling undergoes plane bending, which protects the lock joints. The bottom on the lower pool side immediately beyond the dam is reinforced with rock fill. The calculated surface of the base (CSB) is taken with consideration of local scour and possible zones of shear and heaving of the soil. The spillway slab over the length of the upstream face also has two joints on the axes of the piers. It is made with a nose to divert the stream from the structure. The upstream edge of the spillway dam is made monolithic with the sheet piling and its end projections rest on the foundation parts of the piers. Asphaltic filler blocks are placed in the joints on its upper-pool side. The foundations of the piers are tall pile grillages composed of separately standing vertical and batter shell piles which permit a fuller utilization of the bearing capacity of the foundation. The piles are connected by a single pile superstructure passing into the pier, in the base of which are grooves for the projections of the spillway slab. This permits us to regard the pier and foundation as a single disk, which is taken to be rigid in the calculation. The static calculation of the foundation of the spillway dam on shell piers can be reduced, with certain assumptions to a plane problem with forces collected within one span. The calculation scheme represents a tall pile grillage connected by a rigid spillway slab with the sheet piling perpendicular to the working axis of the grillage. The design loads on the spillway dam are established in comformity with the existing technical specifications. The upstream face is under the action of a load distributed over the length of the sheet piles and is composed of the hydrostatic and hydrodynamic pressures and pressure of the sediment or soil (in the case of unilateral erosion). All other loads directly absorbed by the spillway slab and upper structure of the dam are reduced according to the rules of mechanics of an ideally rigid body to a point lying at the level of the foot of the slab of the pile grillage on the axis of symmetry of the vertical shell piles (Fig. 2). The calculation is performed for displacement of the grillage and bending of the sheet piling in the direction of action of the horizontal load. The spillway slab of the calculation scheme is incorporated into the rigid disk of the grillage, since when the horizontal forces from the upstream face are absorbed it will bend in a horizontal direction as a beam-wall and its deformations will obviously be negligible. The vertical forces at the point of embedment will be quite small as a consequence of the general rotation of the dam under load toward the lower pool, and therefore can be considered *A. IL Berezinskii's article "Shell-Pile Spillway Dam" (Gidrotekhnicheskoe Stroitel'stvo, No. S, 1961) gave one of the original versions of such a design which is substantially developed in this article.