A device for quickly testing the negative friction resistance of pile foundation in mountainous high fill site

Abstract

This utility model relates to the technical field of pile foundation skin friction testing, and discloses a device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas. The device includes backfill soil, beneath which lies a strongly weathered rock layer, and below that, a moderately weathered rock layer. A data acquisition system is installed on the left side of the top surface of the backfill soil, and a loading oil pump is installed on the right side. Utilizing the end resistance from the rock foundation load test to provide the reaction force, combined with data from pile stress sensors, the distribution characteristics of negative skin friction on the pile side in high-fill areas can be rapidly and quantitatively analyzed, providing a measured basis for pile foundation bearing capacity assessment and engineering design. This method uses the upward displacement of the pile under the action of a load cell to replace the settlement of the foundation soil, thereby efficiently testing the negative skin friction, significantly reducing testing costs and saving testing time.

Description

Technical Field

[0001] This utility model relates to the field of pile foundation skin friction testing technology, specifically a device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas. Background Technology

[0002] With rapid economic and social development, urban construction land in my country is becoming increasingly scarce, especially in mountainous cities in the west. High fill sites are often created in mountainous areas through engineering methods such as excavation and filling, with pile foundations used as the bearing layer. However, the self-weight consolidation deformation of the fill soil tens of meters deep in these high fill sites is not yet stable. The compression deformation of the fill layer generates significant negative skin friction in the pile foundations, severely affecting their bearing capacity. Furthermore, the fill material in these high fill sites mainly consists of sandstone, mudstone, and other boulders obtained from blasting in the mountains, resulting in poor gradation and significant site heterogeneity. Currently, research on the physical and mechanical properties of the compacted foundation soil in high fill sites in mountainous areas is scarce, and in-depth research on the negative skin friction of the piles is also lacking. There is a lack of relevant research and theoretical support, and the standards do not explicitly address this issue, leading to significant discrepancies between existing theoretical calculations and measured values.

[0003] In the past, accurate negative skin friction was often obtained through on-site testing. However, the generation process of negative skin friction in actual engineering is quite lengthy, which also prolongs the observation period for pile axial force and negative skin friction. Therefore, how to quickly and accurately test the negative skin friction of piles in high embankment sites is an urgent problem to be solved. Utility Model Content

[0004] (a) Technical problems to be solved

[0005] To address the shortcomings of existing technologies, this invention provides a device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas. It has the advantages of rapidly and accurately testing the negative skin friction of piles in high-fill areas, thus solving the aforementioned problems.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, this utility model provides the following technical solution: a device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas, comprising backfill soil, below which is a strongly weathered rock layer, and below which is a moderately weathered rock layer. A data acquisition system is installed on the left side of the top surface of the backfill soil, and a loading oil pump is installed on the right side of the top surface of the backfill soil. A reference beam is installed in the middle of the top surface of the backfill soil. A load cell is installed inside the strongly weathered rock layer above the moderately weathered rock layer. A displacement line is connected to the top of the load cell. One end of the loading oil pump is connected to an oil pipe. Longitudinal reinforcement bars for the pile are installed deep inside the backfill soil. Reinforcing bars are connected to multiple sections on the surface of the longitudinal reinforcement bars. A fixing component is installed on the top of the backfill soil. A displacement line is installed inside the fixing component. The fixing component includes a limiting half-plate. A wire hole is opened inside the limiting half-plate. Splicing plates are installed on both sides of the limiting half-plate. A through groove is opened inside the splicing plate. A clamping rod is inserted into the through groove.

[0008] Preferably, the top two sides of the locking rod are provided with movable grooves, a locking block is slidably disposed inside the movable groove, an auxiliary groove is provided inside the locking block, an insert rod is slidably disposed inside the auxiliary groove, and a spring is fixedly disposed on one side of the locking block.

[0009] Preferably, the longitudinal reinforcement bars of the pile and the oil pipe are connected by binding straps.

[0010] Preferably, the limiting half plate includes two sets, and the two sets of limiting half plates are spliced ​​together on both sides by two splicing plates, and the two splicing plates are connected by a through rod.

[0011] Preferably, the side of the locking block is an inclined surface, the opening of the auxiliary groove is provided with a locking block, the horizontal cross-section of the insertion rod is T-shaped, and the head of the insertion rod is engaged with the locking block.

[0012] (III) Beneficial Effects

[0013] Compared with the prior art, this utility model provides a device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas, which has the following beneficial effects:

[0014] 1. This device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas applies an upward load to the pile bottom using a load cell, actively causing the pile to displace upwards and creating relative movement between the pile and soil. This generates negative skin friction, quickly simulating the effect of soil settlement on the pile in actual engineering. By arranging steel stress gauges at different depths within the pile, the axial force of the pile is measured, and the negative skin friction is calculated, forming a testing process of self-balancing loading—relative displacement between pile and soil—axial force monitoring—negative skin friction calculation. Utilizing the end resistance from the rock foundation load test to provide reaction force, combined with data from pile stress sensors, the distribution characteristics of negative skin friction in high-fill sites can be rapidly and quantitatively analyzed, providing experimental basis for pile foundation bearing capacity assessment and engineering design. This method uses the upward displacement of the pile under load to replace soil settlement, thus efficiently testing negative skin friction, significantly reducing testing costs and saving testing time.

[0015] 2. This device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas effectively ensures the stability of the fixing components by setting up fixing parts, reducing the risk of wire tangling, invalid markings, and confusion of the lines, which could affect the accuracy of the test. Furthermore, wire tangling during operation would also affect the efficiency of the test. Therefore, the fixing part design effectively solves these problems. The disassembly process of the fixing parts is simple and convenient. Specifically, by pressing the two locking blocks, the blocks move inside the movable groove and compress the spring until the outer bottom of the locking blocks no longer contacts one side of the splicing plate. At this point, pulling the locking rod to move it away from the through groove separates the two splicing plates, thus separating the displacement line and the fixing parts. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of this utility model;

[0017] Figure 2 This is a top view of the fastener structure of this utility model;

[0018] Figure 3 This is an enlarged schematic diagram of the splicing panel structure of this utility model;

[0019] Figure 4 This utility model Figure 3 Enlarged schematic diagram of the structure at point A in the middle;

[0020] Figure 5 This is a process demonstration diagram of the present utility model.

[0021] In the diagram: 1. Backfill soil; 2. Strongly weathered rock layer; 3. Moderately weathered rock layer; 4. Base beam; 5. Loading oil pump; 6. Data acquisition system; 7. Displacement line; 8. Longitudinal reinforcement of pile; 9. Reinforcement gauge; 10. Oil pipe; 11. Load cell; 12. Fixture; 121. Limiting half plate; 122. Wire hole; 123. Splicing plate; 124. Through groove; 125. Clamping rod; 126. Movable groove; 127. Insert rod; 128. Clamping block; 129. Auxiliary groove; 1210. Spring. Detailed Implementation

[0022] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0023] Please see Figure 1-3 and Figure 5 A device for rapidly testing the negative skin friction of pile foundations in high-fill mountainous areas includes backfill soil 1, a strongly weathered rock layer 2 below the backfill soil 1, a moderately weathered rock layer 3 below the strongly weathered rock layer 2, a data acquisition system 6 on the left side of the top surface of the backfill soil 1, a loading oil pump 5 on the right side of the top surface of the backfill soil 1, a reference beam 4 in the middle of the top surface of the backfill soil 1, a load box 11 inside the strongly weathered rock layer 2 above the moderately weathered rock layer 3, a displacement line 7 connected to the top of the load box 11, an oil pipe 10 connected to one end of the loading oil pump 5, longitudinal reinforcement bars 8 deep inside the backfill soil 1, steel bars 9 connected to multiple sections of the surface of the longitudinal reinforcement bars 8, and a fixing element 12 on the top of the backfill soil 1, with the displacement line 7 inside the fixing element 12.

[0024] The data acquisition system 6 utilizes a pile dynamic testing instrument (also known as a dynamic testing instrument or low-strain gauge), a precision instrument used to detect the integrity of building pile foundations. Developed and manufactured by companies such as Shanghai Ruixin Instruments and Shanghai Meiyu Instruments, this equipment complies with multiple industry standards, including the "Technical Specification for Testing Building Pile Foundations JGJ106-2003," and is primarily used in construction, bridge, and highway engineering projects. It assesses the location of pile defects and structural performance using the reflected wave method.

[0025] The pile dynamic testing instrument adopts dual-channel synchronous acquisition technology, equipped with a 24-bit A / D converter and wavelet analysis algorithm, with a dynamic range of 184dB, and supports the connection of acceleration / velocity sensors. The built-in lithium battery provides 5-8 hours of continuous operation, and the entire unit weighs 1.8-2.3kg. It features a USB interface and mobile storage function, and can generate test reports on-site. The device integrates adaptive floating-point amplification, a wireless transmission module, and a strong light suppression screen, making it suitable for environments ranging from -20℃ to 50℃. During use, it must comply with shockproof and moisture-proof specifications and is equipped with sensors, which are also embedded in the load cell 11.

[0026] according to Figure 4 As shown, the fastener 12 includes a limiting half plate 121, the limiting half plate 121 has a wire hole 122 inside, and splicing plates 123 are provided on both sides of the limiting half plate 121. The splicing plate 123 has a through groove 124 inside, and a locking rod 125 is inserted into the through groove 124.

[0027] Among them, the longitudinal steel bars 8 and the oil pipe 10 of the pile are connected by binding straps. The limiting half plate 121 includes two sets. The two sides of the limiting half plate 121 are spliced ​​by two splicing plates 123 respectively. The two splicing plates 123 are connected by a clamping rod 125.

[0028] according to Figure 4 As shown, movable grooves 126 are provided on both sides of the top of the locking rod 125. A locking block 128 is slidably arranged inside the movable groove 126. An auxiliary groove 129 is provided inside the locking block 128. An insert rod 127 is slidably arranged inside the auxiliary groove 129. A spring 1210 is fixedly arranged on one side of the locking block 128.

[0029] The side of the locking block 128 is inclined, the opening of the auxiliary groove 129 is provided with a locking block, the horizontal section of the insertion rod 127 is T-shaped, and the head of the insertion rod 127 is engaged with the locking block.

[0030] During use, the fixing component 12 effectively ensures the stability of the line of the fixing component 12 during the placement of the displacement line 7, reduces the tangling of the wire ends of the fixing component 12, and prevents invalid markings and confusion of the line, which may affect the accuracy of the test. If the line is tangled during operation, it will affect the efficiency of the test. Therefore, the design of the fixing component 12 can effectively solve such problems. Moreover, the disassembly steps of the fixing component 12 are relatively simple and convenient to use. Specifically, by pressing the two locking blocks 128, the locking blocks 128 move inside the movable groove 126 and compress the spring 1210 until the outer bottom of the locking blocks 128 no longer contacts one side of the splicing plate 123. At this time, pull the locking rod 125 to move it and disengage the locking rod 125 from the through groove 124 to separate the two splicing plates 123, that is, to separate the displacement line 7 and the fixing component 12.

[0031] Working principle:

[0032] Step 1: Place the combined load cell 11 with the guide tube facing upwards on a flat surface, protecting the displacement line 7 during placement; pour concrete into the guide tube, then fully compact it with a vibrator, ensuring the concrete strength is not lower than the pile body concrete strength; do not move the load cell 11 within 10 hours after pouring; after the concrete in one guide tube has solidified, use a crane to flip it over and pour the other guide tube. The poured load cell 11 is then lifted from the side by a crane, and the lifted load cell 11 is welded to the longitudinal reinforcement 8 of the pile and the oil pipe 10 is tied.

[0033] Step Two: Reinforcement gauges 9 are installed at intervals of 2-3 meters from the surface of the backfill layer to the point where the pile tip enters the rock. The actual installation points for each pile are adjusted appropriately based on the borehole profile of the test pile and the site conditions. Two reinforcement gauges 9 are symmetrically arranged on the longitudinal reinforcement 8 of the pile at each point. On-site, after binding the reinforcement cage, the reinforcement to be tested is cut off at the installation point. The reinforcement gauges 9 are then tightened to the sleeve, and the readings are tested to ensure the reinforcement gauges 9 are effective and securely connected to the sleeve.

[0034] Step 3: Before lowering the reinforcing cage, the oil pipe 10 and the reinforcing bar 9 wires need to be tied and protected. Every 0.5m-1m, use cable ties to tie the wires or oil pipe 10 to the longitudinal reinforcing bars 8 of the pile, and mark and protect all wire ends after leading them out to the top of the pile. Place warning marks near the pile position on the ground, ensure that all main reinforcing bars are welded together, and ensure that the reinforcing cage and load box 11 will not detach when lifted.

[0035] Step 4: In conjunction with the rock foundation load test loading process, perform graded loading. Load the load in stages until the target load is reached. After the loading stabilizes, immediately use a frequency meter to measure the readings of the rebar gauge 9 and record the data.

[0036] Step 5: Obtain the axial force changes at various sections of the pile body based on the readings of the rebar gauge 9, and calculate the pile side friction resistance.

[0037] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A device for rapidly testing the negative skin friction of pile foundations in high embankment sites in mountainous areas, comprising backfill soil (1), below which is a strongly weathered rock layer (2), below which is a moderately weathered rock layer (3), a data acquisition system (6) is provided on the left side of the top surface of the backfill soil (1), a loading oil pump (5) is provided on the right side of the top surface of the backfill soil (1), a reference beam (4) is provided in the middle of the top surface of the backfill soil (1), and the internal position of the strongly weathered rock layer (2) is... A load cell (11) is provided above the moderately weathered rock layer (3). A displacement line (7) is connected to the top of the load cell (11). One end of the loading oil pump (5) is connected to an oil pipe (10). A longitudinal steel bar (8) is provided deep inside the backfill soil (1). A steel bar gauge (9) is connected to multiple sections of the surface of the longitudinal steel bar (8). A fixing element (12) is provided on the top of the backfill soil (1). A displacement line (7) is provided inside the fixing element (12). The feature is that: The fastener (12) includes a limiting half plate (121), the limiting half plate (121) has a wire hole (122) inside, splicing plates (123) are provided on both sides of the limiting half plate (121), the splicing plate (123) has a through groove (124) inside, and a locking rod (125) is inserted into the through groove (124).

2. The device for quickly testing the negative skin friction of pile foundation in mountainous high fill site according to claim 1, characterized in that: The top two sides of the lever (125) are provided with movable grooves (126), and a locking block (128) is slidably arranged inside the movable groove (126). An auxiliary groove (129) is provided inside the locking block (128), and a plug rod (127) is slidably arranged inside the auxiliary groove (129). A spring (1210) is fixedly arranged on one side of the locking block (128).

3. The device for quickly testing the negative skin friction of a pile foundation in a high fill site in a mountainous area according to claim 1, characterized in that: The longitudinal reinforcement (8) of the pile and the oil pipe (10) are connected by tie-down straps.

4. The device for quickly testing the negative friction resistance of a pile foundation in a high fill site in a mountainous area according to claim 1, characterized in that: The limiting half plate (121) includes two sets. The two sets of limiting half plates (121) are spliced ​​together on both sides by two splicing plates (123). The two splicing plates (123) are connected by a locking rod (125).

5. The device for quickly testing the negative skin friction of pile foundation in mountainous high fill site according to claim 2, characterized in that: The side of the card block (128) is an inclined surface, the opening of the auxiliary groove (129) is provided with a card block, the horizontal cross section of the insertion rod (127) is T-shaped, and the head of the insertion rod (127) is engaged with the card block.

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