CN113279435A

CN113279435A - Foundation pile quality nondestructive testing method based on side-hole diffraction wave analysis

Info

Publication number: CN113279435A
Application number: CN202110039418.3A
Authority: CN
Inventors: 吴宝杰; 杨桦; 黄林伟; 董跃; 黄永丰; 臧瑞
Original assignee: Zhejiang Provincial Construction Engineering Quality Inspection Station Co ltd
Current assignee: Zhejiang Provincial Construction Engineering Quality Inspection Station Co ltd
Priority date: 2021-01-13
Filing date: 2021-01-13
Publication date: 2021-08-20

Abstract

The invention discloses a foundation pile quality nondestructive testing method based on side-hole diffraction wave analysis, and belongs to the field of foundation test detection. The invention uses the diffraction phenomenon in the seismic wave propagation process to analyze the defect position and the pile bottom position of the foundation pile. The seismic waves are transmitted to the break points such as the defects of the pile body, the pile bottom and the like, and the break points can be regarded as a new seismic source like the phenomenon that light in physical optics is diffracted through a small hole, so that the diffracted waves generated by the new seismic source are transmitted to the surrounding soil body. And forming a hole beside the foundation pile, and receiving the diffracted waves transmitted from the pile body defects, the pile bottom and other discontinuities along the depth direction of the test hole by using an engineering seismometer. And generating a time-depth wave train diagram by using the received diffracted wave signals. On the wave train diagram, the corresponding depth of the signal intersection point of the uplink diffracted wave and the downlink diffracted wave is the position depth of a pile body defect or a discontinuity point such as a pile bottom. The diffracted wave analysis method can not only detect the quality of the foundation pile in a general state, but also detect the quality of the foundation pile under the existing building, the quality of the long-pile long-foundation pile and other problems which are difficult to solve by the traditional detection method.

Description

Foundation pile quality nondestructive testing method based on side-hole diffraction wave analysis

Technical Field

The invention belongs to the field of foundation test and detection, and particularly relates to a foundation pile quality nondestructive detection method based on side-hole diffraction wave analysis.

Background

Foundation engineering is an important component of building engineering, and the quality of foundation engineering is directly related to the structural safety of the whole building and the safety of people's lives and properties. Pile foundations are one of the main foundation forms and are the preferred or mandatory foundation form for many buildings.

The existing nondestructive detection method for the quality of the foundation pile mainly comprises a low-strain method, an acoustic transmission method and a side-hole transmission method. The low-strain method belongs to a reflection wave method, has high detection efficiency and low cost, but the foundation pile is not connected with other members during detection, is not suitable for quality detection of the foundation pile under the existing building, and has limited detection depth by the low-strain method. The acoustic transmission method belongs to a transmission direct wave method, and can detect the quality of the foundation pile more comprehensively due to the fact that more acoustic pipes are embedded, but the acoustic pipes must be embedded in advance in the construction process of the foundation pile. The side-hole transmission wave method belongs to a transmission direct wave method and can be used for detecting the quality of a foundation pile under the existing building, but the premise is that the wave velocity of soil around the pile and the wave velocity of a pile body are different to a certain extent.

The side hole diffraction wave analysis method has strong adaptability and few limited conditions, and not only can detect the quality of the foundation pile in a general state, but also can detect the quality of the foundation pile under the existing building and the quality of the long-pile long foundation pile.

Disclosure of Invention

The invention aims to provide a foundation pile quality nondestructive testing method based on side-hole diffraction wave analysis, which is used for analyzing the position of a defect (12) and the position of a pile bottom (13) of a foundation pile (11) by utilizing the diffraction phenomenon in the seismic wave propagation process under the condition that the foundation pile and an upper-layer existing building are not damaged.

The invention is realized by the following technical scheme: the method is characterized in that holes are formed beside foundation piles, and diffracted waves (14) transmitted from discontinuities such as pile body defects (12) and pile bottoms (13) are received along the depth direction of a test hole by utilizing an engineering seismometer. And generating a time-depth wave train diagram by using the received diffracted wave signals. On a wave train diagram, the corresponding depth of a signal intersection point (15) of the uplink diffracted wave (14) and the downlink diffracted wave (14) is the position depth of a discontinuity point such as a pile body defect (12) or a pile bottom (13).

The diffracted wave (14) signal acquisition method specifically comprises the following steps: a hole parallel to a pile body is pre-drilled in a certain range beside a tested foundation pile (11), a PVC pipe (5) is arranged in the drilled hole, clear water (6) is filled in the pipe, a geophone string (7) is placed in the pipe, during testing, seismic waves are generated by exciting on a bearing platform (10) or a pile top or an upright post, the geophone string (7) receives diffracted waves transmitted from discontinuities such as defects (12) and a pile bottom (13) of the foundation pile (11) along the depth direction of the tested hole, and the diffracted waves are recorded and stored by an engineering seismograph (1).

Before detection, a hole parallel to a foundation pile (11) is drilled within the range of being less than or equal to 1.5m away from the edge of the foundation pile (11) to be detected, the hole depth is at least 1.5m deeper than the pile bottom predicted by the foundation pile (11) to be detected, a PVC pipe (5) is placed in the drilled hole, the lower end of the PVC pipe (5) is closed, the upper end of the PVC pipe is covered, no foreign matter exists in the pipe, then clear water (6) is filled into the PVC pipe (5), and a gap between the PVC pipe (5) and a surrounding soil body (4) is filled with cement mortar or is kept still for a period of time so that the surrounding soil body (4) is filled with the gap.

When the invention is used for detection, an instrument is connected firstly to ensure smooth signal transmission and ensure that the detector string (7) is not blocked when being pulled in the PVC pipe (5), then the detector string (7) is put at the bottom of the PVC pipe (5), the bearing platform (10) is hammered by the vibration exciter (9), signals are collected and analyzed, if the signals are not good, the signals are sampled again, otherwise, the detector string (7) is lifted, the hammering sampling is continued until the detector string (7) is lifted to the pipe orifice, and the test of the detected pile is finished.

The invention generates a time-depth wave train map from the received diffracted wave (14) signal. On a wave train diagram, the corresponding depth of a signal intersection point (15) of the uplink diffracted wave (14) and the downlink diffracted wave (14) is the position depth of a discontinuity point such as a pile body defect (11) or a pile bottom (12).

The method analyzes the position of the defect (12) and the position of the pile bottom (13) of the foundation pile (11) by utilizing the diffraction phenomenon in the seismic wave propagation process, has clear and reliable principle, does not need complicated data processing, does not need to know the propagation speed of the wave on the pile body, and is intuitive and simple. The invention can be realized by adopting a common engineering seismograph and a borehole geophone string, and is easy to implement and popularize. The invention can detect the quality of the foundation pile under the ordinary state, can also detect the quality of the foundation pile under the existing building and the quality of the long foundation pile, has strong adaptability and few limited conditions.

Drawings

FIG. 1 is a schematic diagram of a foundation pile quality nondestructive testing method based on side-hole diffraction wave analysis.

FIG. 2 is a chart of diffracted wave time-depth wave arrays for # 1 piles.

FIG. 3 is a chart of diffracted wave time-depth wave trains for # 2 piles.

The names of the parts in the figure are marked as follows: 1-engineering seismograph, 2-lead, 3-pulley, 4-soil around pile, 5-PVC pipe, 6-clear water, 7-detector, 8-trigger, 9-vibration hammer, 10-bearing platform, 11-foundation pile, 12-defect, 13-pile bottom, 14-diffraction wave, 15-intersection point.

Detailed Description

The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.

The serial numbers of the piles to be tested in the embodiment are respectively 1# pile and 2# pile, and the piles are long spiral drilling pressure-grouting piles. The designed pile diameter of the No. 1 pile is 600mm, the designed effective pile length is 33m, the pile body concrete strength is C30, and the bearing stratum is strongly weathered gravel sandstone. The designed pile diameter of the 2# pile is 700mm, the designed effective pile length is 33m, the pile body concrete strength is C30, and the bearing stratum is strongly weathered gravel sandstone. Pile tops are all provided with bearing platforms, and the thickness of each bearing platform is 1 m. The vibration excitation mode is vertical hammering on the bearing platform. The detection principle is shown in fig. 1, and the specific implementation method and steps are as follows:

a test hole parallel to the pile was drilled at a distance of 0.8m from the edge of the pile # 1, and the depth of the hole was 36.5 m. A test hole was drilled parallel to the pile at a distance of 0.8m from the edge of the # 2 pile, with a hole depth of 35 m.

PVC pipes with the inner diameter of 0.1m and the wall thickness of 0.005m are placed in the drill holes, the placing depth is equal to the respective hole depth, the pipe openings are flush with the top surface of the bearing platform, and the pipes are placed and then are placed for one week for testing.

Digging out the bearing platform to expose the top surface of the bearing platform, leveling and cleaning. And placing the geophone string at the bottom of the hole, connecting a lead with an engineering seismometer to ensure smooth signal, hammering the top surface of the bearing platform by using an exciting hammer, receiving diffracted waves transmitted from discontinuous points such as defects of the foundation pile, the pile bottom and the like along the depth direction of the test hole by the geophone string, and recording and storing the diffracted waves by the engineering seismometer.

The received diffracted wave signals are used to generate time-depth wave trains, see fig. 2 and 3. On the wave train diagram, the corresponding depth of the signal intersection point of the uplink diffracted wave and the downlink diffracted wave is the position depth of a pile body defect or a discontinuity point such as a pile bottom.

The detection result of the pile number 1 is shown in fig. 2, and the intersection points of diffracted waves at the depths of 22m and 33.5m are known from the figure. Therefore, according to the principle analysis of the diffraction wave, a pile body defect occurs at an effective pile body 21m, and the effective pile length of the pile is 32.5m (the thickness of the bearing platform is 1 m).

The detection result of the 2# pile is shown in fig. 3, and the intersection point of diffracted waves at the depth of 33.75m is known from the figure. Therefore, according to the analysis of the principle of diffraction wave, the pile body of the pile is complete in quality, and the effective pile length of the pile is 32.75m (the thickness of the bearing platform is 1 m).

Claims

1. A foundation pile quality nondestructive testing method based on side-hole diffraction wave analysis is characterized in that the position of a defect (12) and the position of a pile bottom (13) of a foundation pile (11) are analyzed by utilizing a diffraction phenomenon in the seismic wave propagation process, and the position depth of a break point such as a pile body defect (12) and the position depth of the pile bottom (13) are determined according to an intersection point (15) of an upper-going diffraction wave signal (14) and a lower-going diffraction wave signal (14) on a wave train diagram.

2. A diffraction phenomenon as claimed in claim 1, characterized in that the seismic waves propagate to discontinuities such as pile body defects and pile bottom, as light in physical optics is diffracted through a small hole, and these discontinuities are regarded as a new seismic source, whereby the diffraction waves generated by the new seismic source propagate to the surrounding soil.

3. Foundation pile defects (12) according to claim 1, characterized by the general name of undesirable phenomena such as foundation pile shaft breakage, cracking, necking, mud (debris), voids, honeycombs, loosening, etc.

4. The wave train diagram according to claim 1, characterized in that the detector string (7) receives a time-depth wave train diagram generated from the diffracted wave signal (14).

5. The diffracted wave signal (14) of claim 1, acquired as follows:

A. drilling a hole for placing the PVC pipe (5) within the range of being less than or equal to 1.5m away from the edge of the foundation pile (11) to be measured, wherein the hole is close to the foundation pile (11) to be measured as far as possible, so that the influence of surrounding soil is reduced, the central line of the hole is parallel to the central axis of the foundation pile (11) as far as possible, and the distance between the hole and the foundation pile (11) is ensured to be unchanged;

B. the drilling depth is at least 1.5m deeper than the predicted pile bottom of the foundation pile (11) to be measured, which is to ensure that the acquired signal meets the depth requirement, and if the drilling depth does not exceed the bottom of the foundation pile (11) by a certain depth, the pile bottom is difficult to distinguish;

C. putting a PVC pipe (5) into the drilled hole, wherein the lower end of the PVC pipe (5) is closed, the upper end of the PVC pipe is covered, no foreign matter exists in the pipe, and the joint of the PVC pipe (5) is in smooth transition;

D. the PVC pipe (5) is filled with clear water, and the gap between the PVC pipe (5) and the surrounding soil body (4) is filled with cement mortar or is kept still for a period of time to enable the surrounding soil body (4) to fill the gap so that the geophone string (7) can receive the diffracted wave signal.

6. The diffracted wave signal (14) of claim 1, collected as follows:

A. the instrument is connected, so that smooth signal transmission is ensured, and the detector string (7) is prevented from being pulled in the PVC pipe (5);

B. the detector string (7) is placed at the bottom of the PVC pipe (5), a vibration hammer (9) is used for hammering a bearing platform (10) or a pile top or an upright post to acquire signals, and a trigger function (8) is used for triggering the instrument at the moment of hammering so as to enable the instrument to start recording signals, so that the simultaneity is ensured, and backward movement of a jump starting point time caused by artificial delay is avoided;

C. analyzing the signal quality, re-sampling if the signal quality is not good, otherwise, storing the waveform of the measuring point, lifting the detector string (7), and continuing hammering and sampling until the detector string (7) is lifted to the pipe orifice;

D. after the single-hole test is completed, the equipment is moved to the next test hole, and the method is repeated for testing.

7. The intersection point (15) of the upward diffracted wave signal (14) and the downward diffracted wave signal (14) according to claim 1 is the position depth of a discontinuity such as a pile body defect (12) or a pile bottom (13).