1. The number of test piles to provide basis for design shall meet the design requirements, and shall not be less than 3 under the same conditions; When the total number of engineering piles is estimated to be less than 50, the number of detection should not be less than 2.

2. The number of samples that provide the basis for design is not included in the total number of acceptance sampling inspections.

3. For the pile foundation designed for Class A and Class B foundations, the vertical compressive static load test of single pile should be adopted for bearing capacity acceptance. The number of inspection shall not be less than 1% of the total number of piles in the sub-project of pile foundation under the same conditions, and shall not be less than 3. When the total number of piles is less than 50, the inspection number should not be less than 2.

4. For uplift piles and pile foundation projects with horizontal bearing capacity requirements, vertical uplift static load test and horizontal static load test of single pile should be carried out, and the sampling number should not be less than 65438 0% of the total number of piles and not less than 3 piles.

5. The foundation design level is Grade A pile foundation, and the number of low strain tests is 100%.

6. The design grade of foundation is Grade B and Grade C. When evaluating the integrity of concrete cast-in-place piles with low strain, the sampling number should not be less than 50% of the total number of piles under the same conditions, and should not be less than 20 piles, and the sampling number of each pile cap should not be less than 1 root; For projects with four or more caps under the column, the sampling number should not be less than 50% of the corresponding pile number. When evaluating the integrity of precast piles with low strain, the number of sampling inspection shall not be less than 30% of the total number of piles under the same conditions, and shall not be less than 20, and the number of sampling inspection piles for each pile cap shall not be less than1; For projects with four or more caps under the column, the sampling number should not be less than 30% of the corresponding pile number.

7. For concrete cast-in-place piles with a diameter of not less than 800mm, the core drilling method or acoustic wave transmission method should be added to evaluate the integrity of the pile body, and the sampling number should be not less than 10% of the total number of piles and not less than 10.

8. High-strain dynamic test can be used for pile foundation engineering which has been designed by static load test and has comparative data of high-strain test and static load test. The sampling number shall not be less than 5% of the total number of piles under the same conditions, and shall not be less than 10.

Extended data:

A deep foundation (see figure) consisting of piles and caps connecting the top of piles, or a single pile foundation connected by columns and piles, referred to as pile foundation for short. If the pile body is completely buried in the soil and the bottom of the pile cap is in contact with the soil, it is called low pile cap pile foundation; If the upper part of the pile body is exposed to the ground and the bottom of the cap is exposed to the ground, it is called high cap pile foundation. Building pile foundation is usually a low pile cap pile foundation. Pile foundation is widely used in high-rise buildings.

Pile foundation is an ancient foundation type. Piling technology has experienced thousands of years of development. Both pile foundation materials and pile types, piling machinery and construction methods have made great progress and formed a modern foundation engineering system. In some cases, the use of pile foundation can greatly reduce the workload and material consumption on the construction site.

In 1970s, several major earthquakes occurred in China. Take the Tangshan earthquake as an example, the buildings with pile foundations are generally slightly damaged. This shows that the pile foundation has small deformation and good stability under the action of earthquake force, which is an effective measure to solve the seismic problems of weak foundation and earthquake liquefaction foundation in earthquake area.

The number and arrangement of piles in pile foundation should be determined according to the superstructure and load. The pile foundation under the column can adopt a pile or a group of piles, which are arranged in a polygon; Pile foundations under walls are often arranged in rows. When the load of buildings is large and the floor area is small, they should be arranged in pieces into full piles. When the load acting on the pile foundation is mainly vertical load, the pile is vertical; If there is a large horizontal load, it is necessary to arrange inclined piles to resist the horizontal force.

Due to the variety of pile foundations, great differences in construction technology and complex stratum changes, the pile body may have defects such as shrinkage, enlargement, mud inclusion, segregation and broken pile during construction. Of course, mechanical excavation and collision after construction will also cause shallow pile defects. The existence of pile defects will change the normal working characteristics of foundation piles, thus causing potential danger to the foundation. In order to ensure the safety of foundation, it is inevitable to evaluate the integrity of pile body through acceptance. A large number of practices have proved that the low-strain dynamic testing technology of foundation piles is a very effective means to judge the integrity of pile bodies (convenient, fast, economical and with a large number of tests).

American PDI Company is the most important company in the world to study the theory of dynamic testing of foundation piles and manufacture dynamic testing instruments. It is an advocate and leader in this field. Among them, PIT (Pile Integrity Tester) is a widely used pile integrity testing technology in the world, which is based on stress wave reflection theory.

Static load test

With the more and more extensive application of pile foundation in architectural design, the static load test technology of pile foundation has been developed. After the founding of New China, the static load test technology of pile foundation has gradually developed. The traditional static load test is carried out by manual pressurization, manual operation and manual recording. Since 1980s, with the pace of reform and opening up, the scale of capital construction has increased year by year, especially the extensive application of cast-in-place piles in engineering, and the static load test technology of pile foundation in China has entered a brand-new development period. So far, the static load test of pile foundation has been established as a method and is an undisputed pile foundation detection technology in theory.

Low strain treatment

In 1980s, low-strain integrity testing based on wave equation entered a period of rapid development, and various low-strain integrity testing made many valuable achievements in basic theory, mechanism, instrument research and development, field testing and signal processing technology, verification and research of engineering piles and model piles, and accumulation of practical experience.

The low strain dynamic testing method is to tap the pile top with a small hammer and receive the stress wave signal from the pile through the sensor attached to the pile top. The dynamic response of pile-soil system is studied by stress wave theory, and the measured velocity signal and frequency signal are analyzed by inverse analysis, so as to obtain the integrity of pile. This method is simple and quick, but how to obtain a good waveform and how to analyze the integrity of the pile is the key to the detection work.

References:

Baidu encyclopedia-pile foundation detection