An approach for quantifying the calcium leaching effect on service performance of concrete cutoff wall of embankment dams

Abstract

Calcium leaching is one of the essential diseases of concrete impermeable structures; therefore, an effective numerical approach to quantifying the effect of calcium leaching on concrete impermeable structures is critical for evaluating the long-term service performance of the structure. To this end, a seepage and dissolution coupling model for simulating the degradation of hydraulic concrete properties is proposed in this paper by introducing performance parameter evolutionary models based on saturated–unsaturated seepage and calcium dissolution and migration theories. The model is developed in COMSOL with a staggered solution scheme, and a detailed numerical implementation method is presented. The effectiveness of the proposed method is examined by laboratory calcium leaching tests. On this basis, the model was applied to evaluate the effect of calcium leaching on the service performance of a concrete cutoff wall (CCW) of an embankment dam in Shaanxi Province, China. The results demonstrate that the proposed method can effectively reproduce the calcium leaching process of concrete, and the variation of leaching depth based on model simulations is highly consistent with the experimental results. Calcium leaching primarily occurs at the CCW’s upstream waterfront surface, bypass seepage area and the partition of adjacent soil layers where the permeability varies greatly. Under seepage dissolution, the amount of leached calcium, average porosity, diffusion coefficient and hydraulic conductivity of the CCW increased exponentially with service duration, and solid-phase calcium leaching was the underlying cause of structural performance degradation. The length of the seepage path in the CCW decreases as the service duration increases, and the hydraulic gradient within it gradually increases. Based on the allowable hydraulic gradient of CCW, the safe service life of the CCW considering the calcium leaching effect was determined to be approximately 52a.