There are many kinds of pile foundation detection methods, each of which can achieve different detection purposes. In order to improve the reliability of the detection results and reduce the existence of Engineering hidden dangers, it is necessary to detect the pile foundation, and deal with the abnormal pile foundation in the process of detection in time, so as to meet the construction requirements. What practical pile foundation detection methods do we have!
1、 Core drilling method
This detection method is a pile foundation detection method by drilling core samples from drilling rig. By detecting the pile length, pile body defects and the sediment thickness at the bottom of the pile, the rock and soil properties at the pile end can be determined, and whether the strength, continuity or compactness of the pile body concrete are good. It is very suitable when the concrete suffers from frost damage, fire, chemical erosion or other damage, or when it is necessary to test the strength of concrete in building structures or structures which have been used for many years. However, because the design load of large straight bored pile is generally large, it is difficult to use static pile test method. Therefore, geological drilling rig is commonly used to drill core samples along the length direction of the pile body, and the quality of the pile is determined by observing and testing the core sample.
2、 Static load test method
According to the use function of the pile, axial pressure, axial pull-up force are applied to the pile top step by step, or the water leveling force is applied at the same elevation of the pile cap bottom. The settlement, uplift displacement or horizontal displacement of the corresponding detection points of the pile with time are observed. According to the relationship between load and displacement, the corresponding vertical compressive bearing capacity, vertical uplift bearing capacity or water level of single pile are determined The method of plane bearing capacity test. Static load test is the most objective pile foundation detection method, but because it is destructive detection, and the detection cycle is long, the equipment is huge, the cost is high, in fact, it can only be a small proportion of sampling inspection, it is difficult to carry out a large proportion of pile quality and bearing capacity census. Therefore, the static load test can not be used as a comprehensive inspection method for pile foundation quality.
3、 Low strain dynamic testing method
The purpose of this method is to survey the integrity of pile body and determine the degree and location of pile defects. The reflected wave method is based on the wave theory of one-dimensional elastic rod. The vertical vibration is carried out on the top of the pile body, and the elastic wave propagates downward along the pile body. When there are obvious interface of wave impedance difference in the pile body, such as broken pile at the bottom of pile, serious separation position, diameter reduction and diameter expansion, the reflected information from different parts of the pile body can be identified by receiving amplification filtering and digital processing According to the velocity and phase change of wave propagation in the pile, the pile quality and defect location are determined. It is suitable for testing the integrity of concrete pile body, determining the degree and location of pile defects and the detection of pile length range, which should be determined by field test.
4、 High strain method
The application principle of this method is to hammer the pile top with a heavy hammer (the weight is greater than 1.0% - 1.5% of the estimated ultimate bearing capacity of a single pile), and the geophone can measure the curve of the force and velocity of the pile top with time. The measured force or velocity curve is used as the input boundary condition, and the velocity or force curve of the pile top is inversely calculated by solving the wave equation mathematically. However, this method can be used to test the vertical compressive bearing capacity and integrity of the pile body, monitor the pile stress and hammer energy transfer ratio during the driving of precast pile, and provide the basis for the selection of pile sinking process parameters and pile length. At the same time, when testing the vertical compressive bearing capacity of cast-in-place pile, it should have field measurement experience and reliable comparative verification data under similar conditions in this region.