## 5 Conclusions  
Against the background of shaft damage caused by hydrophobic consolidation settlement of the bottom aquifer of thick alluviums, a joint HPLTC-HPPNP test was carried out based on the ETAS test system. The results revealed nonlinear permeability characteristics and obtained the following main conclusions:  
Figure 17: Permeability mechanism of clayey sand. Under the actin of high stress, the \(k_{v}\) of low- and high-confined water both decreased with an increasing \(\sigma_{r}\). The \(k_{v}\) under an \(\sigma_{r}\) of 1 MPa was obviously greater than that under a high \(\sigma_{r}\). When the \(\sigma_{r}\) of the sample was greater than 4 MPa, the \(k_{v}\) under low and high pressure was less than 1 \(\times\) 10\({}^{-8}\) cm/s, and the relationship between the \(k_{v}\) and \(\sigma_{r}\) satisfied a power function. 2. In the clayey sand permeability test, the seepage flow was affected by the head pressure difference and the dissipation of pore water in the sample. During low- \(\sigma_{r}\) infiltration, the seepage flow was mainly affected by the head pressure difference, and upper and lower seepage occurred almost simultaneously, while the seepage flow time-history curve showed a good linear relationship. When the \(\sigma_{r}\) was high, changes in the \(\Delta Q_{1}\) resulted from the head pressure difference, while early changes in the \(\Delta Q_{2}\) came from the dissipation of internal pore water near the lower end of the sample caused by a sudden drop of the \(p_{2}\). As the influence of the internal pore water dissipation spread to the upper end of the sample, the changes in the \(\Delta Q_{2}\) were gradually influenced by the head pressure difference. 3. The variation law of low- and high- \(\sigma_{r}\) permeability coefficients with an increasing \(i\) was completely different. When the \(\sigma_{r}\) was low, Darcy infiltration of sandy soil was dominant, and with an increasing \(i\), the \(\sigma_{rp_{2}}\) increased continuously, resulting in a gradual decrease in sample \(k_{v}\). When the \(\sigma_{r}\) was high, the seepage process was influenced by the non-Darcy seepage of clayey soil and the Darcy seepage of sandy soil, and the \(k_{v}\) increased first and decreased with an increasing \(i\). 4. Under different stress states, the \(T_{2}\) spectrum distribution law of clayey sand remained almost the same, which was basically of the bispectrum peak type. The capillary and adsorbed water content in the sample decreased with an increasing \(\sigma_{r}\), but then decreased in different ways. The adsorbed water decreased through a linear relationship, while the capillary water decreased in a power function form. When the \(\sigma_{r}\) increased to 2 MPa, almost all of the capillary water was discharged. The content of the capillary water in the permeability hole plays a key role in the permeability of clayey sand. 5. The permeability characteristics of the bottom confined aquifer in the thick loose layer directly affected the drainage process of the bottom aquifer and the hydraulic replenishment rate of the surrounding aquifer. The initial drainage amount of the bottom aquifer was mainly supplemented by the surrounding water, while the later stage was mainly drained by pore water. Research has shown that the permeability of deep confined aquifers is poor. In order to avoid additional vertical force acting on the shaft caused by the consolidation of bottom aquifer drainage, it is necessary to control the bottom aquifer drainage at the peripheral hydraulic supply stage, to prevent closure of the permeability pore throat. Methodology, S.P. ; Validation, Z.L. and Y.X. ; Writing--review & editing, G.C. All authors have read and agreed to the published version of the manuscript. The work presented in this paper was financially supported by the National Natural Science Foundation of China (No.