The traditional static load test method has been considered as the most direct and reliable method to determine the bearing capacity of single pile, but it has some disadvantages, such as inconvenient operation, laborious test, high cost, and being time-consuming. In this paper, a new type of pile testing method, self-anchored pile testing method, was proposed, and the in situ test was carried out for the first time. This method allows the upper and lower piles to provide force to each other and does not occupy other construction spaces. It had the advantages of simple operation and being economical and practical. Based on the Q-w curve, axial force distribution curve, and hyperbolic function model of load transfer, this paper studied the evolution law of friction of self-anchored test pile and the load transfer process of self-anchored test pile. The results show that the load transfer process of self-anchored pile-soil interface can be divided into three stages: elastic, elastic-plastic, and limit state. The friction of the upper and lower piles starts from the bottom of each pile and then gradually increases. The soil around the upper and lower piles gradually undergoes nonlinear deformation and shear failure, and the pile soil reaches the yield state. By analyzing the hyperbolic function model of load transfer, it shows that the hyperbolic function model can be better applied to the self-anchored test pile, which has reference value for the selection of the function model of self-anchored test pile in the future.

To study the formation mechanism of the lower shaft resistance of uplift piles compared to compression piles, the additional stress caused by uplift and compressive piles in the soil is obtained through indoor model tests with embedded micro earth pressure cells. The study shows that the uplift pile has an unloading effect in pile side soil, and the compressive pile has a loading effect in pile side soil. Closer to the loading point, the unloading effect of the uplift pile and the loading effect of the compressive pile becomes more obvious. The unloading effect decreases the shaft resistance of the uplift pile, and the loading effect increases the shaft resistance of the compressive pile. The tests also reveal that the distribution range of additional stress caused by a single pile is within 6 d from the axis of the pile. After considering the effects of loading and unloading of a single pile, the calculated uplift pile bearing capacity is close to the values of formulas such as Meyerhof and Deshmukh and the measured value.

The bearing capacity of the post-grouting super-long bored pile, calculated by the standard enhancement coefficient, is 66% larger than that of the measured. The FEM analysis shows that when the grouting radius at the pile end is 1.5 d and the permeating height of the cement slurry is 4.05 m from the pile end, the end resistance enhancement coefficient is 1.17, and the pile side average friction resistance enhancement coefficient is 1.31 within 12 m above the pile end. The calculated bearing capacity is close to the measured bearing capacity of the post-grouting pile by those enhancement coefficients. The calculation shows that: a) in the case of no grouting, the pile end reaction force is about 5.78% of the pile top load; b) in the case of grouting, when the grouting diffusion radius at the pile end is 1.5 d and the permeating height from the pile end is 4.05 m, the post-grouting pile end reaction force is about 6.78% of the pile top load; and c) after grouting, the load transmitted to the pile end cannot be significantly increased; d) using the reinforcement coefficient suggested by the Standard, the calculated bearing capacity is larger than the measured.

This paper compares and analyzes the difference in the skin friction between pile-end soilless compressive pile and conventional compressive pile at various stages during loading by the in situ test method. The influence of pile-end soil on the load transfer law of compressive piles in clay-dominated stratified foundations is further investigated. The results show that the overall load–displacement curves of the pile-end soilless compressive pile and the conventional compressive pile both present a slow decline followed by a steep drop. The length of the linear section on the load–displacement curve of the pile-end soilless compressive pile is less than that of the linear stage of the conventional compressive pile. Under the vertical load, the distribution laws and distribution forms of the skin friction ratio of the pile sections of the two piles are more consistent. The pile-end soil of the conventional compressive pile restricts the skin friction of the pile’s middle-lower and lower pile segments when compared to the pile-end soilless compressive pile. This restriction manifests itself as a reduction in pile skin friction, and the weakening effect decreases from bottom to top.

Undercrossing shield construction of a subway, the tunnel vault is about 3.0m away from the foundation pile tip of the existing building. In order to analyze the influence of shield undercrossing construction on the existing building and the influence of the existing building load on the tunnel structure, the calculation and analysis are carried out for the existing foundation forms, foundation reinforcement into raft, addition of equal length piles and increase of unequal length piles. Using the method of foundation reinforcement into raft foundation and long pile tip exceeding 0.5m below the tunnel floor can transmit the load of the upper building structure to the soil layer below the tunnel floor and reduce the load of the tunnel roof, thereby achieving the underpinning effect. According to the allowable deformation value of existing building, allowable internal force of segment and allowable deformation value of segment, using this underpinning method can meet the requirements of the various of allowable values of existing building, tunnels, etc.