1. Static load test method
(1) test purpose and method
The purpose of static load test is to simulate the actual load, obtain a series of relationship curves through static loading and pressurization, determine the ultimate bearing capacity of a single pile, comprehensively evaluate and determine its allowable bearing capacity as the design basis, or conduct sampling inspection and evaluation on the bearing capacity of engineering piles. There are many kinds of load tests. Usually, single pile vertical compressive static load test, single pile vertical uplift static load test and single pile horizontal static load test are adopted.
(2) Test requirements
On the premise that the strength of precast pile meets the design requirements, it should not be less than 7 days for sandy soil; For silt and cohesive soil, it should not be less than15d; For silt or muddy soil, it should not be less than 25 days. Only when the combination of pile and soil tends to be stable can the test be carried out. On the premise that the concrete strength of pile body reaches the design grade, for sandy soil, the cast-in-place pile should be no less than10d; For general cohesive soil not less than 20 days or muddy soil not less than 30 days, the test can be carried out. Under the same conditions, the number of test piles should not be less than 1% of the total number of piles, and should not be less than 3. When the total number of engineering piles is less than 50, it should not be less than 2.
2. Dynamic measurement method
Dynamic testing method, also known as dynamic nondestructive testing method, is a new technology to test the bearing capacity and quality of pile foundation as a supplement to static load test.
(1) test method
Dynamic test method is relative to static load test method; It is to simplify the pile-soil system properly, establish a mathematical and mechanical model, collect the vibration parameters of the pile-soil system under a given dynamic load with the help of modern electronic technology and measuring equipment, and calculate it in combination with the actual pile-soil conditions. The obtained results are compared with the corresponding static load test results, and on the basis of accumulating a certain number of static and dynamic test results, some correlation between them is found out, which is used as the standard to determine the bearing capacity of pile foundation.
(2) Compared with the static load test
The general static load test can directly reflect the bearing capacity of piles and the pouring quality of concrete, and the data is reliable. However, the test device is complicated and bulky, and the disassembly and assembly operation is time-consuming, with high cost and limited test times, which is easy to damage the pile foundation. Dynamic test, the instrument is light and flexible, and the detection is fast; The test time of single pile is only about 1/50 of the static load test; Large quantity, no damage to pile foundation, relatively accurate, and can be used for general survey; Low cost, the cost of single pile test is about 1/30 of that of static load test, which can save a lot of manpower and material resources such as anchor pile, stacking, equipment transportation, hoisting and welding. At present, the number of dynamic test pile projects in China has accounted for about 70% of the total number of projects, and the number of test piles accounts for about 90% of the total number of test piles, which effectively fills the shortage of static test piles.
(3) Bearing capacity inspection
There are many kinds of dynamic testing methods for bearing capacity of single pile, and the representative ones in China are: dynamic parameter method, hammer penetration method, hydropower effect method, * * * * vibration method, mechanical impedance method, wave equation method and so on. Among them, the commonly used methods are dynamic parameter method and hammer penetration method.
(4) Pile quality inspection
Stress wave reflection method, also known as low (small) strain method, is widely used in dynamic nondestructive testing of pile foundation at home and abroad. Its principle is that according to the elastic wave reflection theory (wave theory) of one-dimensional bar, the integrity of pile body is detected by hammering vibration force method, that is, the quality of pile body is judged by the propagation characteristics of waves under different impedance and constraints.