Model investigation of the powerhouse section of a concrete gravity dam

Abstract

This article presents the results of model investigations of the stress state of the powerhouse section of a dam from the effect of static operating loads and also of the strength and stability of the structure in the limit stage of its work. Maximum attention was devoted to determining the character of the distribution of stresses in the contact region of the upstream face of the dam and in zones of verticalcolumn and diagonal structural joints. The task of the investigations included also a determination of the effect of grouting of the vertical joint between the toe of the dam and powerhouse on the stress state of the structure and value of the safety factor.A section of a concrete gravity dam with a height of 87.2 m (Fig. i) with a slope of the downstream face of 1:0.7 (1), a par t of the foundation with a different modulus of deformation, and schematically a powerhouse (2) with a spiral casing, turbine shaft, and draft tube were modeled.The downstream face of the section was made in the form of two buttresses (3), between which is the penstock (4), and the joints (5) between the buttresses and penstock were made through (without modeling elastic packing).The joints between the foundation part of the section and buttresses (6) and also the joints in,he zone of thrust of the buttresses and penstock against the toe (7) were reproduced as grouted.A characteristic feature of the models was reproduction on them of toothed ungrouted (R b = 0) column joints (8) in the upper and lower zones of the buttresses, in the lower part these joints were vertical. The joint between the toe of the dam and powerhouse (9) was realized on the models in two variants. On model i this joint was through and on model 2 it was grouted, which provided in this case interaction of the dam and powerhouse.Models were made in a scale of 1:150 from plaster.In the zone of the upstream face of the dam the weakened rock of the zone (B) in the foundation was modeled with a modulus of deformation twofold less than the modulus of deformation of the main mass (see Fig. i).The loads from the dead weight of the dam and powerhouse, hydrostatic pressure on the upstream face of the sections, and the seepage pressure on the base of the structure were reproduced on the models.The dead weight was created by hydraulic jacks and was transmitted through flexible nylon threads to anchors placed in the models.The hydrostatic load was transmitted to the models through a system of rods, crossbeam, and distributing plates.Deformations on the models were measured by resistance strain gauges. The readings were recorded by an electronic static deformation meter with a scale division value equal to 2.57. i0 ~6 units of strain.The investigations were conducted in two stages. The calculated values of the loads on the model in the operating stage of work of the structure (first stage) were determined from the relationship of the elastic characteristics of thematerials of the prototype and model, in which case it was assumed: modulus of deformation of the concrete E c = 20,...