The high-strain PDA test pile method is a kind of shock pulse with high energy applied to the top of the pile. The shock pulse will cause a certain permanent displacement between the pile and the soil during the process of propagating down the pile body, so as to sequentially excite the pile from top to bottom. A method for dynamically detecting the bearing capacity of foundation piles based on pile side and pile end rock-soil resistance.
The so-called "high" strain test pile is relative to the "low" strain test pile. The high-strain dynamic test pile uses a heavy hammer of tens or even hundreds of kilonewtons to strike the pile top, so that the dynamic displacement of the pile is close to the settlement level of the conventional static load test pile, so that the resistance of the rock and soil at the pile side and pile end is large and even full, that is, all or most of the soil around the pile produces plastic deformation, which is intuitively manifested as the penetration of the pile.
In high-strain dynamic load testing, the pile top is usually impacted with a heavy hammer, and the velocity and force time history curves near the pile top or at the top of the pile are tested. Through wave theory analysis, the vertical compressive bearing capacity of the single pile and the integrity of the pile body are analyzed.
The main purpose of high strain PDA testing is to determine whether the vertical bearing capacity of a single pile meets the design requirements.
The low-strain pile integrity test is a detection method that uses low-energy transient excitation at the top of the pile to measure the velocity time-history curve of the top of the pile, and judges the integrity of the pile body through time-domain analysis or frequency-domain analysis of wave theory. Low strain is suitable for detecting the integrity of concrete piles and determining the degree and location of pile defects. It can only be judged qualitatively, not quantitatively.
The main purpose of low-strain PIT testing is to detect pile defects and their positions, and to determine the type of pile integrity. Low strain PIT testing does not provide bearing capacity results.
The difference between "high strain" and "low strain"
1. The test method and the equipment used are different
High-strain tests are relatively costly and require a lot of on-site equipment. In addition to testing equipment, the site needs guide frames, hammers, hooks, plates, overweight machinery, etc., and some tools for installing sensors are also required. , such as electric drills, expansion screws, wrenches, etc.
Low-strain is relatively low-cost and easy to operate. In addition to testing equipment, it needs a couplant, which can be tested with tools such as hand hammers or force rods.
2. Test time
High strain can only be done when the concrete age of the inspected pile reaches 28 days or when the strength of the tested pile under the same conditions of curing reaches the design strength. Low strain requires that the concrete strength of the tested pile is not lower than 70% of the design strength and not lower than 15MPa.
3. The test data obtained by the two methods are different
Low strain (also called small strain) can only test the integrity of the pile body. The high strain (also called large strain) can test the integrity and bearing capacity of the pile body, which can be used to analyze the pile side and pile end resistance, and can also be used for pile driving monitoring.
4. The energy of high and low strain is different
High-strain hammering has higher energy and lower frequency, which can reflect the situation at a deeper level in the pile. However, the low-strain hammer impact energy is relatively small, and for piles with long pile lengths, the pile bottom is not easy to test.
