研究目的:既有挡护工程排水失效是常见病害。为研究既有挡护结构土压力与孔隙水压力的相互关系，揭示排水失效对既有挡护结构造成损害的作用机理，本文通过大型室内模型试验，开展两种不同粒径土样 (砂性土样与勃性土样)在三种排水条件下的土压力及孔隙水压力的变化规律研究，对排水前后土压力与孔隙水压力值进行对比分析。
研究结论:(1)在水的作用下，如果不及时排除挡护结构后的土中水，土压力将急速增长，试验中最大增幅可达145 %，墙背排水系统失效将导致挡护结构受力显著增加，挡护结构潜在被推移或推倒的可能。(2)墙背排水系统正常工作情况下，挡护结构墙背土体孔隙水压力会快速消散，但墙背排水系统部分失效将使墙背土体孔隙水压力消散时间明显延长。(3)工程应用中必须高度重视挡护结构的防排水设计。(4)该研究结果，可用于指导挡护工程设计以及既有挡护结构排水失效的处理。
Research purposes: The drainage-failure of the existing retaining structures is a common disease. In order to uncover the relationship between earth pressure and pore water pressure，and to reveal the damage mechanism of existing retaining structures caused by drainage system′s failure，a series of model experiments were done in the laboratory to research on the variation of earth pressure and pore water pressure under three kinds of drainage condition with two different diameters soil samples(sand and clay)，the value of earth pressure and pore water pressure before and after the water draining was also analyzed to identify this kind of change.
Research conclusions:(1)The test result shows that the earth pressure moved up sharply when soil was submerged in water, if the water in soil is not drained in time，and the maximum value of earth pressure could increase up to 145 % compared with the original value in the test. The failure of the wall drainage system will increase the stress of retaining structure significantly, and may result in the moving out or overturning of the structures.(2)Under the normal circumstances，the pore water pressure will dissipates rapidly. However, if the drainage system fails to work，the water discharge time will cast longer. (3)Therefore，the existing retaining structures should pay attention to drainage- failure in engineering application.(4)The research results may be a guidance for designs and managements of retaining structures.
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