Method for testing actual bearing load of existing engineering pile

Abstract

The invention provides a method for testing the actual bearing load of an existing engineering pile, and the method comprises the steps: cutting off a pile to be tested into an upper pile section and a lower pile section, enabling a foundation slab above the pile to be tested to settle, and obtaining the sinking height of a detection point on the foundation slab; a jacking device is installed on the upper end face of the lower pile section, the upper pile section is jacked, and when the foundation bottom plate is lifted back to the original position, the jacking force of the jacking device serves as the measured value P of the actual bearing load of the to-be-measured pile before cutting off; jacking continues, the load and settlement displacement of the lower pile section are recorded, a load-settlement displacement curve of the lower pile section is drawn, and the vertical ultimate bearing capacity N of the pile to be measured is obtained based on the load-settlement displacement curve of the lower pile section; and taking the arithmetic mean value of P and N as a final report value of the actual bearing load of the to-be-tested pile. According to the method, the average value of the measured value P and the vertical ultimate bearing capacity N serves as the final report value of the actual bearing load of the pile to be measured, and uncontrollable errors generated when indirect calculation is adopted are avoided.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering testing and reinforcement technology, and specifically relates to a testing method for the actual load borne by existing engineering piles. Background Technology

[0002] As my country's urban construction enters a stock-based era, a large number of existing buildings and bridges are entering a maintenance and reinforcement period. Tilting of buildings and structures caused by uneven foundation settlement is a common problem, and pile cutting for forced settlement correction is a widely used method. This method involves cutting off a portion of the engineering piles on the side with less settlement, transferring the load to the soil and adjacent piles, inducing controlled settlement, and achieving tilt recovery. However,

[0003] The core bottleneck of this technology lies in the fact that the actual load distribution of existing building pile foundations is unknown and uneven in height. This leads to:

[0004] Low efficiency of correction: Blindly cutting off piles may only cut off piles with less stress, resulting in insufficient load transfer, poor forced landing effect, and delay in construction period.

[0005] The safety risks are enormous: if a critical pile under heavy load is cut off, the instantaneous transfer of its load may cause overload damage to adjacent piles, leading to foundation instability or even structural collapse.

[0006] Currently, there is a lack of effective post-construction testing methods to measure the actual working load of pile foundations.

[0007] Traditional direct methods (such as steel gauges and strain gauges): need to be pre-embedded during construction and are not suitable for existing buildings.

[0008] Indirect inference methods (such as static load tests and high-strain methods) aim to determine the ultimate bearing capacity (capacity attribute) of a pile, rather than its current actual working load (state attribute). This information cannot be used to assess the safety and efficiency of pile cutting.

[0009] Numerical simulation: Its results are greatly affected by model assumptions, constitutive relations and parameter selection, and may deviate significantly from the actual working state of pile foundations under complex working conditions.

[0010] Therefore, there is an urgent need for a method that can perform post-hoc, in-situ, direct, and reliable load testing on monopiles of existing buildings. Summary of the Invention

[0011] To address the aforementioned issues, this application proposes a testing method for the actual load borne by existing engineering piles, comprising the following steps:

[0012] (1) Cut off the pile to be tested, so that the foundation plate above the pile to be tested will settle, and obtain the settlement height of the test point on the foundation plate. The settlement height of the test point is represented by X. The pile to be tested is cut into an upper pile segment and a lower pile segment, wherein the upper pile segment is located above the lower pile segment, and a lifting space is formed between the upper pile segment and the lower pile segment. The height of the lifting space is greater than X. The test point is located at the intersection of the upper surface of the foundation plate and the central axis of the pile to be tested.

[0013] (2) Install the jacking device on the upper end face of the lower pile segment and jack the upper pile segment. During the jacking process, the lower pile segment settles at the same time. The jacking force of the jacking device is taken as the load on the lower pile segment. Record the load and settlement displacement of the lower pile segment. The load is represented by Q and the settlement displacement is represented by S. When the foundation plate is raised back to its original position, the jacking force of the jacking device is taken as the measured value of the actual load borne by the pile before it is cut off. The measured value is represented by P.

[0014] (3) Continue to lift and record Q and S, draw the load-settlement displacement curve of the lower pile segment, and verify the vertical ultimate bearing capacity of the pile to be lateralized; based on the load-settlement displacement curve of the lower pile segment, obtain the vertical ultimate bearing capacity of the pile to be lateralized, and represent the vertical ultimate bearing capacity of the pile to be lateralized by N.

[0015] (4) The arithmetic mean of P and N is taken as the final reported value of the actual load borne by the pile under test.

[0016] Before testing the piles to be tested, the engineering piles on the side of the inclined building or structure with smaller settlement are first divided into several pile groups. Each pile group includes 4-12 engineering piles. One engineering pile is randomly selected from each pile group as the pile to be tested. The test data of the pile to be tested is used as the test data of all engineering piles in its pile group.

[0017] This application uses the average of the directly measured value P and the vertical ultimate bearing capacity N of the pile under test as the final reported value of the actual load borne by the pile under test, avoiding the uncontrollable errors caused by indirect calculation. Because of the verification mechanism of direct measurement and indirect verification, the test results are mutually verified, ensuring high accuracy and high reliability. After obtaining the test data of each pile group, high-load piles can be accurately screened for priority truncation, significantly improving the efficiency of correction; at the same time, high-risk piles can be identified and avoided to prevent overload damage and ensure construction safety.

[0018] Specifically, for ease of operation, in step (1), before cutting off the pile to be tested, the measuring instrument is first installed above the detection point, and the detection head of the measuring instrument is positioned directly above the detection point. Then, the initial position of the detection point is measured. After the pile to be tested is cut off and the foundation slab settles and stabilizes, the settlement position of the detection point is measured. The difference between this settlement position and the initial position is the settlement height of the detection point. The criterion for judging the stability of the foundation slab settlement is: the settlement rate is less than 0.01 mm / min during a continuous 30-minute observation period.

[0019] Furthermore, to minimize the impact on the foundation slab at the top of the pile to be tested, before cutting off the pile, the earthwork around the top of the pile to be tested is first excavated to form an underground cavity around the top of the pile. The cut-off position of the pile to be tested is located in this underground cavity, and the pile to be tested is located in the center of the underground cavity. The underground cavity has an outlet. When the outlet is located outside the building or structure where the pile to be tested is located, the distance between the outlet and the pile to be tested is 1-2m. When the outlet is located inside the building or structure where the pile to be tested is located, the distance between the outlet and the pile to be tested is 5-10m.

[0020] Furthermore, to minimize the impact of settlement of the foundation slab at the top of the pile to be tested, the length of the underground chamber is 2-2.5m and the width of the underground chamber is 2-2.5m.

[0021] Specifically, to avoid impact damage to the pile body and minimize disturbance to the surrounding soil and adjacent piles, step (1) involves using a static cutting method to cut the pile. The tools used in the static cutting method can be a diamond wire saw or a disc saw. Using a static cutting method avoids pile damage, stress concentration, and severe disturbance to the surrounding soil and adjacent piles caused by traditional methods such as hammering and blasting.

[0022] Furthermore, to ensure smooth jacking of the upper pile segment, the lower end face of the upper pile segment and the upper end face of the lower pile segment are leveled before jacking. This creates a first leveling plane on the lower end face of the upper pile segment and a second leveling plane on the upper end face of the lower pile segment. The jacking device is then installed on the second leveling plane. Leveling can be achieved using high-strength grouting or cross-sectional grinding. To improve the flatness and stability of the load-bearing surface, bearing plates are preferably installed on the lower side of the first leveling plane and the upper side of the second leveling plane. The jacking device is installed on the bearing plate on the upper side of the second leveling plane, and the upper pile end is jacked using the bearing plate on the lower side of the first leveling plane. The bearing plates are preferably double-sided flat steel plates. Through precise leveling of the truncated pile head and the installation of bearing plates, uniform, stable, and accurate load transfer during jacking is ensured, laying a solid foundation for accurate load measurement. Attached Figure Description

[0023] Figure 1 This is a schematic diagram showing the underground cavity excavation completed around the pile to be tested.

[0024] Figure 2 This is a schematic diagram showing the pile to be tested after it has been cut off and the foundation slab has settled and stabilized.

[0025] Figure 3 This is a schematic diagram showing the lifting device after installation.

[0026] Figure 4 for Figure 3 Enlarged view of part A in the middle.

[0027] Figure 5 This is a schematic diagram showing the completed lifting operation.

[0028] Figure 6 This is a load-settlement displacement curve. Detailed Implementation

[0029] The following detailed description, in conjunction with the accompanying drawings, provides a further explanation of the testing method for the actual load borne by existing engineering piles in this application. Before describing the testing method, a brief overview of the structure of the building where the pile to be tested is located is provided. Please refer to [link / reference needed]. Figure 1 The building includes a foundation slab 12, structural columns 15 formed on the foundation slab, and floor slabs 13 supported on the structural columns. There are foundation piles 11 located in the soil below the foundation slab, and a pile cap 14 for supporting the foundation slab is located on top of the foundation piles. The pile to be tested 119 is one or more of the foundation piles. The foundation pile is a type of engineering pile.

[0030] First, the piles on the side of the tilted building or structure with less settlement are divided into five pile groups, each consisting of eight foundation piles. One foundation pile is randomly selected from each group as the pile to be tested. The test data of this pile is used as the test data for all piles in its group. That is, five piles need to be tested. The testing method for each pile is the same; the following explanation uses one of these piles as an example.

[0031] The testing method includes the following steps:

[0032] (1) Please continue reading Figure 1Before cutting off the pile 119 to be tested, the measuring instrument is first installed above the detection point 31, with the measuring instrument's detection head positioned directly above the detection point 31. In this embodiment, the measuring instrument 21 is installed on the lower surface of the lowest floor slab, specifically a laser rangefinder. The detection point 31 is located at the intersection of the upper surface 121 of the foundation slab 12 and the central axis 110 of the pile 119 to be tested. For clarity, the detection point 31 in the attached figure is represented by a small circle. The position of the measuring point is detected using the measuring instrument to obtain the initial distance L0 of the measuring detection point 31 relative to the measuring instrument.

[0033] Then, the earthwork around the top of the pile to be tested is excavated to form an underground chamber 30 around the top of the pile. The pile to be tested is located in the center of the underground chamber, and the cut-off position of the pile to be tested is located in the underground chamber. The underground chamber has an outlet; in this embodiment, the outlet is located inside the building where the pile to be tested is located, and the distance between the outlet and the pile to be tested is 8m. The outlet is not shown in the attached drawings.

[0034] During the excavation of underground chambers and corresponding passages, a temporary support system was erected to ensure the safety of the structure during the cutting of the piles to be tested. The temporary support system is not shown in the attached diagram; existing, mature support systems can be used, and will not be described further.

[0035] Please see Figure 2 After the excavation of the underground chamber 30 is completed, the pile to be tested is cut using a static cutting method. Specifically, in this embodiment, a diamond wire saw is used for cutting. It is understood that in other embodiments, a disc saw can also be used for cutting. The pile to be tested is cut into an upper pile segment 111 and a lower pile segment 112, wherein the upper pile segment 111 is located above the lower pile segment 112, and a lifting space 113 is formed between the upper pile segment 111 and the lower pile segment 112. The height of the lifting space 113 is greater than the sinking height described below. Before cutting the pile to be tested, it is necessary to estimate the sinking height of the pile to be tested to ensure that there is sufficient lifting space to avoid the upper pile segment and the lower pile segment coming into contact when the foundation slab sinks, which would affect the sinking of the foundation slab.

[0036] After the pile to be tested is cut off, the foundation slab above the pile begins to sink. The settlement rate of the test point is continuously observed using a measuring instrument. When the settlement rate is less than 0.01 mm / min during a continuous 30-minute observation period, it indicates that the settlement of the foundation slab has reached a stable state. After the settlement of the foundation slab stabilizes, the secondary detection distance L1 of the test point relative to the measuring instrument is measured. The difference between the secondary detection distance L1 and the initial distance L0 is the sinking height of the test point 30. The sinking height of the test point is represented by X. In this embodiment, X = 1.5 mm.

[0037] (2) Lifting preparation: Please refer to Figure 4 The lower end face of the upper pile segment and the upper end face of the lower pile segment are leveled to form a first leveling plane on the lower end face of the upper pile segment and a second leveling plane on the upper end face of the lower pile segment. Both the first and second leveling planes are horizontal. Then, a first bearing plate 116 is installed on the lower side of the first leveling plane and a second bearing plate 117 is installed on the upper side of the second leveling plane. Both the first and second bearing plates are flat steel plates with two flat surfaces. In this embodiment, high-strength grouting material is used for leveling. It can be understood that in other embodiments, cross-sectional grinding can also be used for leveling.

[0038] After the leveling process is completed, a displacement detection device is installed in the underground cavity 30. The displacement detection device includes a bracket 41, a positioning steel plate 42, and a dial indicator 43. The bracket 41 includes a vertical rod 411 fixedly inserted into the underground soil and a horizontal rod 412 fixed on the vertical rod. The positioning steel plate is fixed on the top of the outer periphery of the lower pile segment 112, and the lower surface of the positioning steel plate is horizontal. The dial indicator 43 is fixedly installed on the horizontal rod 412 of the bracket 41, and the pointer of the dial indicator 43 presses against the lower surface of the positioning steel plate.

[0039] The lifting device is installed in the lifting space 113. Specifically, in this embodiment, the lifting device is a hydraulic jack 50. The cylinder 51 of the hydraulic jack is fixedly installed on the second pressure plate 117, and the piston rod 52 of the hydraulic jack extends vertically upward and presses against the first pressure plate 116.

[0040] Hydraulic jack 50 is activated to lift the upper pile section. The rise of the foundation slab is monitored using measuring instruments. When the foundation slab returns to its original position, the lifting force generated by the hydraulic jack is acquired. This lifting force is taken as the measured value of the actual load borne by the pile before cutting, and is denoted by P. P is the product of the hydraulic pressure of the hydraulic jack and the inner cross-sectional area of ​​the cylinder. In this embodiment, P = 2945 kN.

[0041] During the jacking process, the pressure of the hydraulic jack and the settlement displacement data of the lower pile segment 112 displayed by the dial gauge 43 are recorded simultaneously. The pressure of the hydraulic jack is taken as the load applied to the lower pile segment, and the load is represented by Q. The settlement displacement of the lower pile segment is represented by S.

[0042] (3) Continue jacking up, and continue to record the load Q and settlement displacement S of the lower pile segment. Plot the load-settlement displacement curve of the lower pile segment as follows: Figure 6 As shown, the vertical ultimate bearing capacity of the pile to be lateralized is verified, and the vertical ultimate bearing capacity of the pile to be lateralized is represented by N. According to Figure 6The vertical ultimate bearing capacity of the pile to be lateralized is N = 4000kN.

[0043] (4) The arithmetic mean of P and N is taken as the final reported value of the actual load borne by the pile under test.

[0044] (P+N) / 2=(2945+4000) / 2=3472.5kN, rounded to 3470kN, the final reported value of the actual load borne by the pile to be tested is 3470kN.

Claims

1. A method for testing the actual load borne by existing engineering piles, characterized in that, Includes the following steps: (1) Cut off the pile to be tested, so that the foundation plate above the pile to be tested will settle, and obtain the settlement height of the test point on the foundation plate. The settlement height of the test point is represented by X. The pile to be tested is cut into an upper pile segment and a lower pile segment, wherein the upper pile segment is located above the lower pile segment, and a lifting space is formed between the upper pile segment and the lower pile segment. The height of the lifting space is greater than X. The test point is located at the intersection of the upper surface of the foundation plate and the central axis of the pile to be tested. (2) Install the jacking device on the upper end face of the lower pile segment and jack the upper pile segment. During the jacking process, the lower pile segment settles at the same time. The jacking force of the jacking device is taken as the load on the lower pile segment. Record the load and settlement displacement of the lower pile segment. The load is represented by Q and the settlement displacement is represented by S. When the foundation plate is raised back to its original position, the jacking force of the jacking device is taken as the measured value of the actual load borne by the pile before it is cut off. The measured value is represented by P. (3) Continue to lift and record Q and S, draw the load-settlement displacement curve of the lower pile segment, and verify the vertical ultimate bearing capacity of the pile to be lateralized; based on the load-settlement displacement curve of the lower pile segment, obtain the vertical ultimate bearing capacity of the pile to be lateralized, and represent the vertical ultimate bearing capacity of the pile to be lateralized by N. (4) The arithmetic mean of P and N is taken as the final reported value of the actual load borne by the pile under test.

2. The test method according to claim 1, characterized in that, In step (1), before cutting off the pile to be tested, the measuring instrument is first installed above the test point, and the test head of the measuring instrument is located directly above the test point. Then the initial position of the test point is measured. After the pile to be tested is cut off and the foundation plate settles and stabilizes, the sinking position of the test point is measured. The difference between the sinking position and the initial position is the sinking height of the test point.

3. The test method according to claim 1, characterized in that, Before cutting off the pile to be tested, the soil around the top of the pile is excavated to form an underground cavity. The pile to be tested is cut off in this underground cavity, and the pile is located in the center of the underground cavity. The underground cavity has an outlet. When the outlet is located outside the building or structure where the pile is located, the distance between the outlet and the pile is 1-2m. When the outlet is located inside the building or structure where the pile is located, the distance between the outlet and the pile is 5-10m.

4. The test method according to claim 3, characterized in that, The underground chamber is 2-2.5m long and 2-2.5m wide.

5. The test method according to claim 1, characterized in that, In step (1), the pile to be tested is cut off using the static cutting method.

6. The test method according to claim 1, characterized in that, Before jacking up the upper pile segment, the lower end face of the upper pile segment and the upper end face of the lower pile segment are first leveled to form a first leveling plane and the upper end face of the lower pile segment is formed a second leveling plane; the jacking device is installed on the second leveling plane.

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