Application range of high strain dynamic load method

1.?Testing of single pile bearing capacity

Determining whether the bearing capacity of a single pile meets the design requirements is one of the main functions of the high-strain dynamic pile test method. The bearing capacity of a single pile depends on the bearing capacity of the pile structure and the resistance of the soil to the pile. Resistance control. Because the dynamic load?cannot quantitatively evaluate the bearing capacity of the pile structure, it is not suitable to use the high strain dynamic load?method to determine the single pile for piles with serious defects (the bearing capacity of the pile is likely to be controlled by the pile structure bearing capacity) and?the bearing capacity of a single pile.

The bearing capacity of a single pile determined by the high-strain dynamic load method refers to the resistance of the rock and soil to the pile caused by the dynamic test pile. Only when sufficient relative displacement between the pile and the soil is generated, can the bearing capacity of the pile be objectively evaluated. Compared with the static load test, the relative displacement between the pile and the soil using the strain method is still a significant distance. Therefore, the single pile bearing capacity determined by it is generally lower than the single pile ultimate load of the static load test (which is safer in engineering), especially when the matching capacity of the hammer and the pile is obviously insufficient, this contradiction is even more prominent.

Strictly speaking, the high-strain dynamic load method is a semi-empirical method and a semi-direct method. Therefore, the high-strain method uses the semi-quantitative and semi-qualitative term "judgment" instead of "determined" in testing the vertical compressive bearing capacity of a single pile. This strictly quantitative wording. For the same reason, the "direct method" should be used for the bearing capacity test that provides the basis for the design, that is, the single pile vertical static load?test.

2.?Pile body integrity inspection

Evaluation of pile integrity is another important function of high-strain dynamic pile testing.

Compared with low strain method which is quick and cheap to detect pile integrity, high strain method has disadvantages such as heavy equipment, low efficiency and high cost. However, due to the advantages of excitation energy and large effective depth of detection, when determining the defects of the pile body horizontal integration type gaps, precast pile joints, etc., it is possible to find out whether these "defects" affect the vertical compressive bearing capacity of the pile,

so as to determine the defects reasonably.?It can be used as a supplementary verification method for low strain detection of such defective piles.

From the actual detection case below, the pile length is 30m, and the bottom signal of the high strain detection is more obvious. At the same time, the high strain can reflect the increase of the shallow impedance.

From another case, we can clearly see that high-strain testing is easier to detect the bottom of the pile, while low-strain testing is easier to find small defects in the shallow part.

3.?Pile driving monitoring

Looking back at history, the CASE method was developed from the monitoring during the trial driving of precast piles, and monitoring the piling process is its unique function. It can monitor the pile body stress (tension and compression stress) when the precast pile is driven, the energy transfer rate of the impact system, and the change of the pile body integrity, and provide a basis for selecting pile driving equipment, pile type, and determining reasonable pile driving process parameters , To realize the informationized construction of the piling process, these functions cannot be achieved by the static load test.