CN115217164A

CN115217164A - Small strain detection method for miniature pile

Info

Publication number: CN115217164A
Application number: CN202110428434.1A
Authority: CN
Inventors: 鄢旭冉; 方晴; 曾凡兴; 张传义; 胡国勇; 薛少强; 刘天慈; 吕辉; 王早桂
Original assignee: University of Electronic Science and Technology of China; Suizhou Power Supply Co of State Grid Hubei Electric Power Co Ltd; PowerChina Hubei Electric Engineering Co Ltd
Current assignee: University of Electronic Science and Technology of China; Suizhou Power Supply Co of State Grid Hubei Electric Power Co Ltd; PowerChina Hubei Electric Engineering Co Ltd
Priority date: 2021-04-21
Filing date: 2021-04-21
Publication date: 2022-10-21

Abstract

The invention belongs to the technical field of electric power construction, and particularly relates to a method for detecting small strain of a miniature pile, which adopts a reflection wave method specified in JGJ93-95 to test and is characterized in that: arranging the excitation position at 1/2 of the wall thickness of the top of the pile pipe, installing the measuring sensor at the top of the grouting layer to enable the sensor testing point to be located at the 1/2 of the wall thickness, and enabling the excitation position and the sensor testing point to be on the same straight line and pass through the central axis of the pipe pile. The method mainly solves the technical problem that no corresponding detection method is suitable in the prior art, and mainly has the following beneficial technical effects: the method makes up the defects of the testing method in the prior art, and the testing method is more accurate and reliable, and is simple to test and easy to execute.

Description

Small strain detection method for miniature pile

Technical Field

The invention belongs to the technical field of electric power construction, and particularly relates to a method for detecting small strain of a miniature pile.

Background

The low strain test method has the advantages of light and simple instrument and equipment, high detection speed, low cost and the like, and becomes a common method for detecting the integrity of the pile body at present. For a pile with a complete pile body, the waveform is regular, the wave train is clear, and the wave speed is normal; the method has mature detection means because of pile bottom reflection and no inter-pile reflection, and is listed in the foundation pile low strain dynamic detection regulation (JGJ 93-95).

However, for the embedded type post-grouting pipe pile, the difference from the conventional press-in pipe pile is that: the outer wall of the embedded pipe pile is provided with a layer of cement paste with the thickness of about 50mm, the pile body is composed of the cement paste and high-strength concrete, and the method specified in JGJ93-95 cannot be completely suitable for detection.

The quality detection of the pile foundation, which is the most important basic form, has been concerned by the engineering industry. In the domestic pile foundation dynamic detection, a low-strain reflection wave detection method and a sound wave transmission method are common and representative.

The traditional low-strain detection method only places one sensor at the pile top, and when the pile length is detected, on one hand, the pile bottom is too deep, so that the sensor cannot receive the reflected wave at the pile bottom, and on the other hand, the concrete wave speed adopted in calculation is usually set according to experience, so that large errors exist, and the calculation result is greatly different from the actual situation.

The sound wave transmission method is characterized in that a transmitting end and a receiving end are placed in the pre-buried sound measuring pipe, and the integrity of the pile body is detected by actually measuring the sound time, the wave speed and the like of sound waves transmitted in concrete. This method has the following disadvantages: firstly, when the outer side of the sound measuring tube has defects and even the main ribs are exposed, the method cannot detect the defects. Secondly, when the acoustic pipe is locally wrapped with mud, isolated with concrete, etc., the failure of the local measuring point can be caused.

Disclosure of Invention

In order to solve the problems, the invention aims to disclose a method for detecting small strain of a micro pile, which is realized by adopting the following technical scheme.

A method for detecting small strain of a miniature pile is used for testing by adopting a reflection wave method specified in JGJ93-95 and is characterized in that: arranging the excitation position at 1/2 of the wall thickness of the top of the pile pipe, installing the measuring sensor at the top of the grouting layer to enable the sensor testing point to be located at the 1/2 of the wall thickness, and enabling the excitation position and the sensor testing point to be on the same straight line and pass through the central axis of the pipe pile.

The excitation position and the sensor test point are in the same straight line, namely the excitation position and the sensor test point form 180 degrees with the central connecting line of the tubular pile.

The method for detecting the small strain of the miniature pile is characterized in that the wall thickness of the top of the pile tube is 20-80mm.

The method for detecting the small strain of the miniature pile is characterized in that the pile pipe is a concrete pile, and the interior of the pile pipe is provided with the steel bars and the steel bar hoop body.

The method for detecting the small strain of the miniature pile is characterized in that the wall thickness of the top of a grouting layer is 50 +/-10 mm.

The method for detecting the small strain of the miniature pile is characterized in that the grouting layer is made of concrete.

Small strain in this application may also be referred to as micro-strain or low strain.

The application mainly has the following beneficial technical effects: the method makes up the defects of the testing method in the prior art, and the testing method is more accurate, more reliable, simple in testing and easy to execute.

Drawings

Fig. 1 is a layout diagram of excitation points and sensor mounting points according to the present application.

Fig. 2 is a cross-sectional view of a test pile layout plan for testing a test pile having 3 piles in a practical embodiment of the present invention.

Fig. 3 is a waveform detected by pile # 1.

Fig. 4 is a waveform detected by pile # 2.

Fig. 5 is a waveform detected by pile # 3.

In fig. 1: the test method comprises the following steps of 1-pipe pile, 2-grouting layer, A-excitation position and B-sensor test point.

Detailed Description

Referring to fig. 1 to 5, the low strain test method is based on the stress wave one-dimensional rod fluctuation theory, and referring to JGJ93-95 and the prior art, in fact, the grout body and the high-strength concrete pile are continuous elastic one-dimensional rod members, and when the pile top is deformed after being instantaneously excited, the axial strain between the grout body and the high-strength concrete pile is the same, and the deformation is coordinated, so that the one-dimensional fluctuation theory can still be used for solving the composite wave velocity V of the stress wave _sc ：

In the formula: a. The _s 、ρ _s And E _s -the cross-sectional area, mass density and elastic modulus of the slurry body, respectively;

A _c 、ρ _c and E _c One is the cross-sectional area, mass density and elastic modulus of the high strength concrete.

Therefore, the integrity of the grouting body, the integrity of the tubular pile and the bonding degree of the grouting body and the outer wall of the tubular pile can be checked through the waveform and the wave velocity; the performance is the detected waveform, if the waveform is consistent with that in JGJ93-95 judgment, the waveform meets the use requirement and reaches the qualified standard through practical trial and inspection.

A method for detecting small strain of a miniature pile is used for testing by adopting a reflection wave method specified in JGJ93-95 and is characterized in that: arranging the excitation position A at 1/2 of the wall thickness of the top of the pile pipe 1, installing the measuring sensor at the top of the grouting layer 2 to enable the sensor testing point B to be located at the 1/2 of the wall thickness, and enabling the excitation position A and the sensor testing point B to be on the same straight line and to pass through the central axis of the pile.

By adopting the method, the applicant tries and applies the method in test piles of No. G36 tower No. 1, no. 2 and No. 3 of line engineering matched with a traction station of No. 15 kV in the Tanzhou city of the Ten-Han railway, and the stratum section of a test pile plane layout diagram is shown in a figure 2.

The small strain detection results of the No. 1#, no. 2# and No. 3 embedded post-grouting pipe piles are shown in the following table, and the attached waveform diagrams are shown in FIGS. 3-5.

Small strain detection result

From the above results, it can be seen that:

(1) The 1#, 2#, 3# piles have regular wave forms, clear wave trains, normal wave velocity, pile bottom reflection and no inter-pile reflection, and can be considered according to foundation pile low strain dynamic detection rules (JGJ 93-95): the integrity of the grouting body, the integrity of the pipe pile and the bonding degree of the grout and the pipe pile are good;

(2) The strength grade of the pile body of the pipe pile is C80, and the wave velocity of concrete is V _c =4425m/s. The wave velocity detected at this time is the composite wave velocity v of the tubular pile and grouting body _sc Wave velocity V lower than that of concrete _c Therefore, the testing method in the application is effective, makes up for the defects of the prior art, and is accurate and reliable in testing.

On the basis of a traditional low-strain detection method, one sensor is placed on the pile top, the other sensor is placed inside a pile body through a pre-buried pipe, and the placement depth of the sensor is determined according to the placement length of a sensor lead. The detection results of the pile top sensor and the sensors in the holes are combined, and the purpose of more accurately detecting the concrete elastic longitudinal wave velocity, the pile length or the integrity of the pile body of the foundation pile to be detected is achieved.

The sensor that uses in this application is the use among the prior art, and the sensor of test stake pole, pile foundation can both use among the prior art.

The foregoing has described the general principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are intended to illustrate the principles of the invention, but rather, should be construed in breadth and scope in accordance with the appended claims. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. A method for detecting small strain of a micro pile is tested by adopting a reflection wave method specified in JGJ93-95, and is characterized in that: arranging the excitation position at 1/2 of the wall thickness of the top of the pile pipe, installing the measuring sensor at the top of the grouting layer to enable the sensor testing point to be located at the 1/2 of the wall thickness, and enabling the excitation position and the sensor testing point to be on the same straight line and pass through the central axis of the pipe pile.

2. The method of claim 1, wherein the top wall thickness of the pile tube is 20-80mm.

3. The method for detecting the small strain of the micro-pile according to claim 1, wherein the pile tube is a concrete pile, and the interior of the pile tube is provided with a steel bar and a steel bar hoop body.

4. The method for detecting the small strain of the micro-pile as claimed in claim 1, wherein the wall thickness of the top of the grouting layer is 50mm plus or minus 10mm.

5. The method for detecting the small strain of the micro-pile as claimed in claim 1, wherein the material of the grouting layer is concrete.