# Axial Bearing Mechanism of Post-Grouted Piles in Calcareous Sand
## 2 Outline of the Model System
### Test Setup, Test Method and Instrumentation  
For ungrouted piles, the axial compressive load test is conducted after the completion of pile driving, and the standing time is not less than 24 h. For annular point grouted and ideal-geometry grouted piles, post-side-grouting is conducted immediately after the completion of pile driving, and the axial compressive load test is conducted on the grouted pile after the completion of grouting and not fewer than 20 days of rest. Based on the actual situation of the indoor model test, the axial compressive static load test adopts the rapid maintenance load method, and the maintenance time of each load level is not less than 1 h. When the settlement rate of the pile head under this load level converges, the next load level can be applied. The loading method was in accordance with the Chinese Technical Code for Testing of Building Foundation Piles [22]. The ultimate axial compressive bearing capacity of the ungrouted pile and grouted pile is preliminarily determined by the preloading test. Based on the 1/10 grading load of this value, the first loading amount is taken as twice the grading load, while the unloading amount of each stage is twice as high as that of the loading stage. The termination loading conditions are as follows: (1) the settlement of a single pile under a certain level of loading is five times that under the previous load level. (2) The settlement of a single pile, under a certain level of loading, is twice that under the previous load level, and it does not reach relative stability in that the settlement of the pile head does not exceed 0.1 mm after 1 h. (3) The single pile sinks sharply under a certain level of load so that it cannot be read. (4) The loading equipment reaches the maximum limit. The axial compressive static load test of a single pile is shown in Figure 3.  
To study the response of axially loaded single piles in calcareous sand, various strain gauges are symmetrically installed along the longitudinal direction of the inner side of the steel pipe pile to measure the strain of different sections of the steel pipe pile. Two strain gauges are symmetrically arranged for each section of the steel pipe pile, and seven sections are arranged in the pile shaft from top to bottom, according to the actual penetration depth. The specific arrangement is shown in Figure 3. During the loading process, the strain gauge data can be acquired by the testing system. The measurement of the pile head displacement is an important part of the static load test, which can be obtained by a dial indicator with an accuracy of 0.01 mm. A steel block is placed on the head of the model pile, two dial indicators are symmetrically arranged at the left and right ends of the steel block, and the average value of the results is used to determine the pile head settlement. In addition,  
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to measure the earth pressure at the pile base, a strained earth pressure cell R1, with a diameter of 17 mm, is arranged 2.5 cm from the end of the pile, as shown in Figure 3.