English：

During the renovation of urban flood control seawalls, the construction of the anti-seepagesystem often encounters fragmented rock stratum due to seawater scouring. Accurate grouting andachieving integrated anti-seepage prevention in such strata are currently critical challenges in seawallengineering. To address this, based on the pore-filling theory for fragmented rock, a combined anti-seepage system comprising cement-mortar filling grouting and high-pressure jet grouting piles wasestablished, considering factors such as aperture and layout. Its effectiveness was subsequentlyverified.Furthermore, guided by the stress diffusion principle and taking into account the influences of flowingwater and grout diffusion, the construction parameters for the anti-seepage system were optimized, andkey construction techniques were summarized. The research results show that the combined systemenables the pile body to achieve a 28d compressive strength greater than 1.2MPa and a permeabilitycoefficient less than or equal to 10-5cm / s, meeting the design requirements. The pile bodywas relativelyfragmented before implementing the combined system but became more integrated afterward. The systemhas good reliability,which can solve the problems of low early strength of grouting body in fragmentedrock stratum and large diffusion range of slurry under dynamic water conditions to a certain extent.