Shear strength of dam abutment fractured rock weakens critical water pressure and statistical damage constitutive model

The weakening of abutment rock strength under water-rock coupling has an important impact on the long-term safe and stable operation of high-arch dams. Under the joint action of prolonged arch thrust and high water pressure, the strength parameters of the rock in the weak interlayer of the dam abutment are reduced, which readily causes long-term stability problems such as structural instability, seepage damage, and bank slope sliding of the high dam hub.

Given the water pressure weakening effect of the shear strength parameters of the fractured marble at the dam abutment, the triaxial compression test of the fractured rock under the action of different seepage water pressures was performed using the rock mechanics testing system, and then the influence of seepage water pressure on the compressive strength, cohesion, and friction coefficient of the fractured rock was analyzed in combination with the rock stress-strain curve. Finally, the weakening critical water pressure of the rock was obtained by analyzing the effective stress principle. Furthermore, the statistical damage constitutive model of rock considering seepage pressure was studied.

The results showed that the influence of seepage water pressure on the shear strength parameters of the fractured marble was mainly manifested by a weakening effect on cohesion. The weakening rate of cohesion increased substantially with increasing seepage water pressure, and the maximum weakening rate was nearly 100%. The weakened cohesion decreased linearly with increasing water pressure; when the weakening rate of cohesion was 0, the water pressure was the weakening critical water pressure. When the water pressure was lower than the critical water pressure, the water pressure weakening effect of rock strength was obvious, and the cohesion decreased linearly with increasing water pressure until vanishing; when the water pressure exceeded the critical water pressure, the rock strength decreased insubstantially with increasing water pressure, and the water pressure weakening effect of rock strength was not obvious. Based on the influence of seepage water pressure on shear strength parameters, a statistical damage constitutive model of rock considering the weakening effect of water pressure was constructed, and the adaptability and rationality of the theoretical model were verified using test data.

The critical water pressure, as the limiting value of the weakening of the rock strength and cohesion by the seepage pressure, can be used to define the influence of the seepage pressure on the rock strength. The statistical damage constitutive model considering the weakening effect of the seepage pressure can calculate the evolution law of the entire process of rock fracture under the water-rock coupling effect. The research results provide strong support for the theory and testing of water pressure weakening and have certain reference values and scientific significance for studying the weakening effect of fractured rock and analyzing the stability of high-arch dam abutments.