弯应力作用下混凝土结构水力劈裂试验研究

混凝土重力坝坝踵在运行期间易出现拉应力,是坝体的薄弱区域。为研究该区域的水力劈裂问题,采用四点弯曲弯矩+高水压的联合施载方式,模拟混凝土重力坝坝踵受拉状态下的水力劈裂破坏过程。基于不同弯矩与水压值组合,研究坝踵因施工应力出现初始裂缝情况下的水力劈裂问题。结果表明,裂缝发展过程中,混凝土试件的应变可分为线性段及指数段,当应变进入指数段时,试样临近破坏;较小的荷载增量即会打破稳态,促使裂缝失稳扩展;劈裂水压与拉应力存在叠加效应,若最值作用位置相同,裂缝尖端应力集中现象明显,易引起水力劈裂破坏,若作用位置不同,则受拉截面应变分布较均匀,较大限度地发挥了混凝土受拉截面的抗劈拉能力,减弱了水力劈裂作用。

Experimental study on the hydraulic fracture of concrete structure under bending stress

Tensile stress is prone to be developed within the dam heel during the operation period of the concrete gravity dam, thereby leading to a weak area. To address the problem of hydraulic fracture in the weak area, experiments are conducted to simulate the hydraulic fracturing process of dam heel under tensile stress, in which a combined loading mode including four-point bending moment and high hydraulic pressure is used. The hydraulic fracturing problem due to initial cracks during construction is explored using different loading combinations. The experimental results show that the variation of the concrete strain is composed of linear and exponential stages during cracking process, and a fracture failure is prone to be developed when the exponential stage is reached. In this case, a small load increment applied will break the steady state with crack failure being extended. It is found that superposed effect is developed due to the splitting water pressure and the tensile stress. When the maximum values of the two stresses are applied at the same place, significant stress concentration at crack tip is developed, which would contribute to hydraulic fracture failure. In contrast, if the two maximum stresses act at different places, the strain distribution on the tensile section of the concrete would be more uniform with its tensile strength being largely mobilized, thereby reducing the hydraulic fracturing effect.