The foundation composite structures comprising retaining structures, foundation floors, and piles located in confined aquifers affect the long-term seepage environment of groundwater. Laboratory tests were conducted based on the typical shallow hydrological stratum including sandy phreatic and confined aquifers separated by a clayey aquitard in Shanghai, China. The tests were conducted to study the long-term influence of the foundation composite structures on the groundwater level. The influencing parameters include foundation width along the seepage path (L), distance between the foundation floor and underlying aquitard floor (D), length of pile (Pl), and insertion depth of the retaining structure (Dw) as the design factors, and the head difference of the upstream and downstream water tanks (ΔH) as a natural factor. With a decrease in L or D, or an increase in P or Dw, the groundwater level increases upstream and decreases downstream outside the foundation structure. The groundwater level difference between the upstream and downstream side of the retaining structures (Δh) is positively correlated with Pl, Dw, and ΔH, and negatively correlated with L and D. The velocity at the outlet (v) is positively correlated with L, D, and ΔH, and negatively correlated with Pl and Dw. Weight analysis of the influence of each parameter on Δh and v indicated that ΔH has the highest influence, whereas the degree of influence of Δh and v of L, D, Pl, and Dw were relatively similar. This means that the barrier effect on groundwater seepage is the result of the comprehensive action of the four design factors of the foundation composite structures.
Li et al. (Thu,) studied this question.