【Excerpts】7 methods of pile foundation detection, comprehensive summary!

Pile foundation testing is divided into testing before and after construction: before construction, test pile testing provides the basis for design, mainly determines the ultimate bearing capacity of ① single pile：after construction, engineering pile testing provides the basis for acceptance, mainly for ① single pile bearing capacity and ② pile integrity testing.

7 methods of pile foundation detection

1、Vertical compression and static load test of single pile

The vertical static load test of the single pile means that the vertical load is uniformly transmitted to the building foundation pile, and through the measurement of the top settlement of the single pile under different loads, the Q-s curve and the auxiliary curve of the static load test are obtained, and then the characteristic value of the vertical compressive bearing capacity of the single pile is calculated according to the curve.

Objective To determine the vertical ultimate bearing capacity of single pile; determine whether the vertical compressive bearing capacity meets the design requirements; determine the resistance of pile side and pile end, through pile strain and displacement test, and verify the test results of single pile with high transformer.

2、Vertical tensile and static load test of single pile

The vertical tensile force is applied to the top of the pile step by step to observe the tensile displacement of the top of the pile with time to determine the corresponding test method of the vertical tensile bearing capacity of the single pile.

Objective To determine the ultimate bearing capacity of single pile; determine whether the vertical bearing capacity meets the design requirements and determine the lateral resistance through pile strain and displacement test.

3、Single pile water calm load test

The test method of testing and evaluating the horizontal bearing capacity of engineering pile is used to determine the horizontal resistance coefficient of the horizontal bearing capacity of single pile and the horizontal bearing capacity of foundation pile. The horizontal load test of single pile should adopt one-way multi-cycle loading and unloading test method, and slow maintenance load method should be adopted when the pile stress or strain is needed.

Objective To determine the horizontal critical and ultimate bearing capacity of single pile, determine the soil resistance parameters; determine whether the horizontal bearing capacity or horizontal displacement meet the design requirements; and determine the pile bending moment through pile strain and displacement test.

4、Drill core method

The drilling core method mainly uses the drilling machine (generally with 10mm inner diameter) to sample the core of the pile foundation. According to the core sample, the length of the pile foundation, the concrete strength, the thickness of the pile bottom and the bearing layer can be clearly judged.

Objective To measure the pile length, pile concrete strength and pile bottom sediment thickness, judge or identify the rock and soil properties of pile end bearing layer, and determine the integrity category of pile body.

5、Low should change method

The low strain detection method is to use a small hammer to knock the top of the pile, receive the stress wave signal from the pile through the sensor bonded to the pile top, and the stress wave theory is used to study the dynamic response of the pile soil system, and analyze the measured speed signal and frequency signal, so as to obtain the integrity of the pile.

Objective To detect the defects and positions of pile body and determine the integrity category of pile body.

6、High should change method

High strain detection method is a kind of test pile pile integrity and single pile vertical bearing capacity method, the method is to hammer weight weight 10% or single pile vertical bearing capacity of heavy hammer to fall into the pile top, so as to obtain the relevant dynamic coefficient, the prescribed procedures, analysis and calculation, get the pile body integrity parameters and single pile vertical bearing capacity, also known as Case method or Cap-pee method.

Objective To determine whether the vertical compressive bearing capacity of single pile meets the design requirements; detect the pile defects and position, determine the integrity category of pile body; analyze the soil resistance of pile side and pile end; and monitor the pile driving process.

7、Sound wave transmission method

The acoustic transmission method is embedded in front of the concrete, using the ultrasonic detector to measure the acoustic parameters along the longitudinal axis of the pile, and then use a variety of specific numerical criteria or image judgment, after processing, give the pile defects and its position, determine the integrity of pile.

Objective To detect the defects and positions of pouring pile body and determine the integrity category of pile body.

The implementation points of pile foundation testing

The starting time of pile foundation testing shall meet the conditions:

(1) Using the variable method and the acoustic wave transmission method for detection, the concrete strength of the tested pile shall not be less than 70% of the design strength and shall not be less than 15MPa;

(2) Using the core drilling method, the concrete age of the inspected pile should reach 28d, or the strength of the curing test block under the same condition should meet the design strength requirements;

(3) Rest time before general bearing capacity testing: sand stone foundation not less than 7d, powder land foundation not less than 10d, unsaturated cohesive soil not less than 15d, and saturated cohesive soil not less than 25d. Mud wall pouring pile, should extend the rest time.

Selection conditions for acceptance test:

(1) Piles with doubt about construction quality;

(2) piles with abnormal local foundation conditions;

(3) Select some piles during the bearing capacity acceptance;

(4) Pile that the designer considers important;

(5) piles with different construction technology;

(6) It should be selected evenly and randomly according to the regulations.

During the acceptance test, it is advisable to test the integrity of the pile body first and then the bearing capacity. The pile body integrity test shall be conducted after the excavation of the foundation pit.

The integrity of pile body is classified into class I pile, class pile, class pile and class pile. Class I pile body is complete; it will not affect the normal performance of the pile structure and affect the bearing capacity of the pile structure; there are serious defects.

The characteristic value of vertical compressive bearing capacity of single pile shall be taken as 50% of the vertical compressive bearing capacity of single pile. The characteristic value of vertical bearing capacity of single pile shall be 50% of the ultimate bearing capacity of single pile. Determination of the characteristic value of the horizontal bearing capacity of single pile: first, when the reinforcement rate is less than 0.65%, take 0.75 times of the horizontal critical load; second, if the reinforcement rate of reinforced concrete precast pile, steel pile and pile is not less than 0.65% at the horizontal displacement of the designed pile top (horizontal displacement value: 6mm for the building sensitive to horizontal displacement, and 10mm for insensitive buildings, meeting the crack resistance requirements of pile body).

When selecting the core drilling method, the number and location of each pile less than 1.2m can be 1~2 holes; piles with a diameter of 1.2~1.6m should be 2 holes; the pile with a diameter greater than 1.6m should be 3 holes; the drilling position should be arranged uniformly and symmetrically from the center of the pile (0.15~0.25).

——Source: Luban Union of Construction Engineering 

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