【Excerpt】Why do we need to test piles before pile foundation construction?

There are three types of test piles: design test piles, pre-construction test piles and post-construction test piles.

Design of test pile: according to the geological report and local experience, the type of pile and the characteristic value of vertical bearing capacity of single pile are selected.

Purpose

        The first is to further determine the construction feasibility of the selected pile type, so as to avoid the discovery that the pile type is not suitable for the site construction or the bearing capacity of the pile is far less than the calculation value provided in the geological report after the full entry of the pile machine. In this case, changing the pile type will delay the construction period and increase the cost.

        The second is to determine the characteristic value of vertical bearing capacity of a single pile according to the vertical static load test of a single pile. Since the values provided by the geological report are often conservative, the bearing capacity of the pile can be increased and the number of piles reduced according to the static load report.

        When the static pile construction method is adopted, the construction pile pressure force is related to the characteristic value of single pile bearing capacity, but it is not absolute. It can be 1.5~2.5 of the characteristic value according to experience and local standards, as long as the static load test meets the requirements. The construction pile pressure force can be adopted as the test pile standard in comprehensive construction.

Pile test before construction: according to the actual situation of the project, it is decided whether to do pile test before construction. The pile test before construction can be retained as the engineering pile.

        Among them, there are three kinds of cases that must be tested before construction according to the code:

1、Pile foundation with grade A and Grade B design.

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

3、New pile type or new technology adopted in this area.

Pile testing after construction: According to the geological report and local experience, the pile type and the characteristic value of vertical bearing capacity of a single pile are selected. After comprehensive construction, a certain number of piles are randomly selected for dynamic test and static load test to verify that the quality of the pile body, namely the characteristic value of vertical bearing capacity of a single pile, meets the design requirements. If not, reinforcement measures should be taken.

        Generally, test piles should be designed first when the experience is insufficient or important projects are to be carried out. All projects should carry out construction test piles after pile foundation construction, and quality evaluation and acceptance should be carried out according to the test report.

Significance of pile testing

        First, the construction feasibility of the selected pile type should be further determined to avoid the discovery that the pile type is not suitable for the site construction or the bearing capacity of the pile is far less than the calculation value provided in the geological report after the full entry of the pile machine. In this case, changing the pile type will delay the construction period and increase the cost.

        The second is to obtain the characteristic value of single pile bearing capacity. Because the values provided by geological reports are often conservative, the bearing capacity of piles can be increased and the number of piles reduced according to the static load report.

Purpose of pile testing

        The purpose of pile testing is to provide first-hand construction parameters for large-scale pile driving operations, including effective pile length, rock penetration depth, sedimentation, injection degree, pile welding and bearing capacity.

1、When selecting the type, length and bearing stratum of the end of the engineering pile for test drilling, the following provisions shall be complied with:

1) The engineering geological conditions of the test pile position should be representative.

2) During the test pile, the test should be carried out one by one according to the soil layer in which the pile end enters; when the bearing stratum is thick, multiple tests should be carried out in the same soil layer.

2、The bearing capacity of the pile end bearing stratum shall be comprehensively determined according to the bearing capacity and penetration degree relationship of the test pile results and the site geotechnical engineering investigation report.

——Source: What Engineers Say

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