There are three types of test piles at the pile foundation construction site, including design test piles, pre-construction test piles and post-construction test piles. Design test pile for pile foundation construction: according to geological report and local experience, select pile type and characteristic value of vertical bearing capacity of single pile.

The significance of pile foundation construction test pile is as follows:

The first is to further determine the construction feasibility of the selected pile type to avoid the pile type not suitable for on-site construction or the pile bearing capacity is far lower than the calculated value provided in the geological report after the pile driver is fully mobilized. At this point, changing the pile type will delay the construction period and increase the cost. Secondly, the characteristic value of vertical bearing capacity of single pile is determined according to the vertical static load test of single pile. Since the values provided in the geological report are usually conservative, according to the static load report, the pile bearing capacity can be improved and the number of piles can be reduced.

When the static pressure pile foundation construction method is adopted, the construction pile pressure is related to the characteristic value of the single pile bearing capacity, but not the absolute value. Depending on experience and local standards, 1.5 to 2.5 of the characteristic values may be used. As long as the static load test meets the requirements, the pressure of the construction pile can be used in the whole construction process. Pre-construction pile test: decide whether to carry out pre-construction pile test according to the actual situation of the project. Test piles before construction can be retained as engineering piles. Among them, there are three cases that must be tested before construction according to the specifications:

1. Pile foundation with design grade A and B;

2. Complex geological conditions and low reliability of pile foundation construction quality;

3. New pile types or new processes adopted in the area.

Pile test after construction: According to the geological report and local experience, the vertical bearing capacity is of significant value after large-scale construction, a certain number of piles are randomly selected for static loading test and dynamic test to verify the quality of the pile, that is, the single pile bearing capacity that meets the design requirements. Otherwise, reinforcement measures should be taken. Generally, test piles should be designed first for inexperienced or important projects. After the pile foundation construction is completed, all works shall be subject to construction pile inspection, and quality evaluation and acceptance shall be carried out according to the pile test report.

The purpose of pile foundation construction test is as follows:

Pile testing is to provide first-hand construction parameter data for a wide range of pile sinking operations, including effective pile length, rock penetration depth, sediment, grouting degree, pile welding and bearing capacity.

1. When selecting the pile type, pile length and pile end bearing layer of engineering piles for pile test, the following requirements shall be met:

① The engineering geological conditions of the test pile location shall be representative.

② In the process of piling, the piles shall be tested one by one according to the soil layer entering the pile end; when the bearing layer is thick, multiple tests shall be carried out in the same soil layer.

2, according to the test pile driving results of the bearing capacity and penetration of the relationship, combined with the field geotechnical engineering survey report, comprehensively determine the pile end bearing layer.