In the construction of cast-in-place piles, the quality of the holes directly affects the quality of the piles after the concrete is poured. Analyze the relevant content and technical methods of hole-forming quality inspection to provide reference for practical work. Keywords: pile foundation engineering; hole-forming quality type extrusion oxazine 407.9
Document identification code: A
Article number: 16723198(2009)19030701お
In the construction of cast-in-place piles, the quality of the hole formation directly affects the quality of the pile after concrete pouring: if the diameter of the pile hole is too small, the side friction resistance of the pile and the bearing capacity of the pile tip will be reduced, and the overall pile will be damaged. The bearing capacity is reduced; the expansion of the upper part of the pile hole will cause the upper side resistance of the pile to increase, while the lower side resistance cannot be fully exerted. At the same time, the amount of concrete pouring for a single pile increases and the cost increases; the deflection of the pile hole changes the pile to a certain extent. The vertical load-bearing characteristics weaken the effective performance of the bearing capacity of the foundation piles, and are prone to problems such as difficulty in hoisting the steel cage, collapsed holes, and insufficient thickness of the steel protective layer. Excessive sediment at the bottom of the pile reduces the length of the pile. For the end The pile bearing directly affects the end bearing capacity of the pile tip. Therefore, it is particularly important to check the hole quality of cast-in-place piles before concrete pouring to control the pile quality. The content of hole quality inspection mainly includes pile hole position, hole depth, hole diameter, verticality, sediment thickness, mud index, etc. 1 Pile position deviation check Pile position deviation, that is, the difference between the actual pile position and the designed position. Since the load position of the superstructure acting on the foundation cannot be changed, after the pile is deflected, the stress state of the pile has changed. Even if remedial measures such as patching piles, increasing the bottom beam or cap of the foundation are taken, it is often difficult to achieve the desired results. The original design requirements of the pile. The consequences of pile deviation lead to reduced pile reliability, increased project cost, and extended construction period. During construction, due to the influence of various factors, such as measurement and setting out errors, deviations when burying the protection, incorrect alignment of the drilling rig, deviations caused by hole inclination during drilling, deviations when lowering the steel cage, etc., the pile position will deviate from the design. Location. Therefore, to ensure the correctness of the pile position, first of all, the deviation in each link should be controlled to the minimum during construction. 2. Pile aperture and verticality detection: Aperture and verticality detection are two important contents in the hole quality inspection. Most of the instruments currently used for aperture detection can measure the verticality of piles at the same time. The methods for detecting pile aperture and verticality are roughly divided into: simple method detection, umbrella aperture meter detection, and acoustic wave method detection. First, simple method detection: after many years of construction and detection of cast-in-place piles, engineering and technical personnel have researched and summarized some simple aperture and verticality detection methods and means, which are suitable for use in the absence of special aperture and verticality instruments. Hole forming quality inspection. The inspection equipment is a simple instrument, such as a steel cage type, a six-sided wood hinge type, a caliper type and other types of hole detectors. Among them, the steel cage type is a widely used hole inspection instrument in simple method detection. Its equipment is simple to make and the detection method is convenient and feasible. Second, umbrella aperture detection. The umbrella aperture meter is a testing system consisting of three parts: an aperture meter, a hole inclinometer, and a sediment thickness meter. Since the probe head part of the hole in the system is shaped like an umbrella, it is also the main part of the system. This system is often colloquially referred to as an umbrella aperture meter. In the umbrella aperture meter, the instrument part in the hole that measures aperture, hole inclination and sediment is independent, and the ground instrument is for exclusive use. The instrument consists of aperture probe, automatic recorder, electric winch, etc. 3. The methods for detecting the thickness of the sediment at the bottom of the hole and the thickness of the shell are roughly the hammer method, the resistivity method, the capacitance method, the sonic method, etc. First, the hammer measurement method. The hammer method has been widely used in sediment detection because of its simple equipment, easy operation and low cost. Since the hammer method measurement requires the human hand to judge the location of the sediment, it is prone to errors. On the other hand, the depth value of the sediment position is measured by a measuring rope, and the length, tightness and reading of the measuring rope will also cause errors. In short, the accuracy of detection using the hammer method is low and the error is large. Second, resistivity method. The principle of measuring sediment thickness by resistivity method is based on the difference in conductivity of different media. For example, water, mud and sediment particles have different conductive properties. The sediment thickness can be judged by measuring the change in resistance value of the medium.
There are two ways to measure sediment thickness by resistivity method: the first method is to use the change in voltage value caused by the different resistivity of the medium to measure and judge the sediment thickness by measuring the change in voltage value; the other is to directly measure the resistance of the medium rate, and determine the sediment thickness based on the resistivity change curve of the measured medium. Third, the capacitance method. The capacitance method determines the sediment thickness by using the difference in dielectric constant of media such as water, mud and sediment, which results in a change in the capacitance of the probe. The sediment thickness is determined based on the change in the capacitance value of the probe. Fourth, the acoustic wave method. The principle of the acoustic wave method to measure sediment thickness is a measuring instrument made by using the reflection of sound waves when they encounter different interfaces during propagation. The probe emits sound waves to the bottom of the pile. When the sound waves encounter the surface of the sediment, part of the sound waves are reflected back and received by the probe. The other part of the sound waves passes through the sediment and continues to propagate to the bottom of the hole. When it encounters the undisturbed soil of the bearing layer at the bottom of the hole, The sound waves are reflected back again. References [1]@ Zhu Xiyuan, Huang Wentong. A brief discussion on pile foundation detection methods and development [J]. Shanxi Architecture, 2007, (20): 129. [2] @ Zhou Xingping. Research status and prospects of foundation pile detection technology [ J]. Geotechnical Foundation, 2005, (3): 8687.