A monitoring auxiliary device applicable to vibroflotation gravel piles

Abstract

The present invention discloses a monitoring auxiliary device applicable to vibroflotation gravel piles, which is composed of a steel strand in series with multiple levels of blocking members; two steel strands are arranged in parallel and pass through the blocking members at each level arranged at intervals, and the lengths of the steel strands between the blocking members at each level are the same, forming parallel arrangement of each blocking member; each level of blocking member includes at least a backing plate and a double-hole anchor under the backing plate; wherein, the two steel strand perforations of the double-hole anchor are both positive conical holes, and a conical clamping piece with a structure matching the conical hole is sleeved on the steel strand perforation part and pre-tightened and fixed with the conical hole. The auxiliary device of the present invention shortens the time required for the test and saves costs. By pre-burying multiple levels of blocking members during the construction of vibroflotation gravel piles, the problem that the sensor cannot be buried in the pile body of the vibroflotation gravel pile due to the lack of bonding force of the pile body is overcome, and the monitoring of the stress magnitude and pore water pressure magnitude at a specified position of the pile body is realized by setting an annular pressure sensor and a pore water pressure gauge, achieving real-time monitoring of the vibroflotation gravel pile.

Description

Technical Field

[0001] The present invention relates to the field of detection of bearing capacity of building pile foundations, and particularly to a monitoring auxiliary device suitable for vibroflotation gravel piles. Background Art

[0002] In the engineering practice of strengthening soft soil foundations by the vibroflotation gravel pile composite foundation method in the past nearly half century, the bearing capacity of soft soil, sandy soil and other soft foundations has been enhanced by using the vibroflotation gravel pile method. For vibroflotation gravel piles, the most important thing is the detection of their bearing capacity. At present, the static load test method is generally used for the bearing capacity of single piles and composite foundations.

[0003] The pile foundation static load test is a test method that is closest to the load-bearing state of the pile foundation after the building is completed. It simulates the compression deformation and displacement changes of the pile body under long-term load, and even the corresponding changes in the soil layer around the pile. It is currently the most intuitive and effective method for testing the bearing capacity of single piles recognized at home and abroad. However, the pressed weights not only have a large volume, low operation efficiency, high requirements for transportation and mechanical equipment construction, but also have high risks and are prone to safety accidents.

[0004] The static load test of the anchor pile method mainly uses the reaction force provided by the reaction frame and the anchor pile / cable to conduct the test. It is mainly composed of components such as a reaction frame, an anchor pile / cable, and a jack. When the jack applies pressure to the test pile, the jack will generate an upward concentrated force on the reaction frame, and the reaction frame will distribute this concentrated force evenly on each anchor pile / cable in the form of an upward pulling force. Therefore, the static load test of the anchor pile method does not need to use stacking blocks, avoiding the heavy loading and unloading process during the heavy object stacking process. The reaction frame can be assembled at any time, and the assembly cost is low. Especially for extra-large tonnage test piles, it can save the space, time, etc. required for the test.

[0005] Vibroflotation gravel piles are different from cast-in-place piles. The gravel pile body has no cohesion, and its bearing capacity depends on the lateral confinement resistance of the surrounding soil to maintain its shape and bear the load. The bearing capacity of granular material piles depends mainly on the lateral confinement ability of the soil around the pile in addition to being related to the pile body material. Therefore, it is impossible to provide a reaction force like a cast-in-place pile and apply pressure to the test pile through the anchor pile method to conduct a static load test. On the other hand, due to the large vibroflotation force generated by the vibroflot during the construction of the gravel pile, it is very difficult to embed sensors in the pile body, and it is even more difficult to embed wires. Therefore, the detection of gravel piles is often through the pile top, lacking the detection of the quality of the pile body.

[0006] In view of the above engineering problems, a detection device suitable for vibroflotation gravel piles is needed to solve the limitation that the gravel piles in the project cannot provide a reaction force for static load tests, and at the same time monitor the stress magnitude and pore water pressure of the pile body. Summary of the Invention

[0007] The present invention discloses a monitoring auxiliary device applicable to vibroflotation gravel piles in view of the deficiencies of the prior art. The object of the present invention is to provide a monitoring auxiliary device applicable to vibroflotation gravel piles, so as to solve the problem that the vibroflotation gravel piles can only be detected for the single-pile bearing capacity by the surcharge method, shorten the time required for the test, save costs, and reduce the space required for the static load test; at the same time, the present invention solves the problem that the sensor cannot be buried in the pile body of the vibroflotation gravel pile, and realizes the stress magnitude and pore water pressure magnitude at the specified position of the pile body to judge the influence of the buoyancy of the groundwater on the gravel pile.

[0008] The present invention is realized through the following technical solutions:

[0009] A monitoring auxiliary device applicable to vibroflotation gravel piles, the auxiliary device is used to assist the anchor pile method to monitor the vibroflotation gravel piles, and is characterized in that: the auxiliary device is composed of a steel strand in series with multiple levels of blocking members;

[0010] Two steel strands are arranged in parallel and pass through the blocking members at each level arranged at intervals. The lengths of the steel strands between the blocking members at each level are the same, and the blocking members are arranged in parallel when the steel strands are in a straightened state;

[0011] Each level of blocking member at least includes a backing plate and a double-hole anchor under the backing plate. Two steel strand perforations are provided in the middle of the backing plate and the double-hole anchor; wherein, the two steel strand perforations of the double-hole anchor are both positive conical holes, and a conical clip with a structure matching the conical hole is sleeved on the steel strand perforation part and pre-tightened and fixed with the conical hole.

[0012] Furthermore, the steel strand is a multi-wire wound steel strand, and the core of the steel strand is provided with the leads of each sensor.

[0013] Furthermore, at least a ring pressure sensor is arranged at the bottom end of the multiple levels of blocking members. The ring pressure sensor passes through the steel strand in the middle and is fixed between the backing plate and the double-hole anchor. The ring pressure sensor is connected to an information acquisition instrument through a lead.

[0014] Furthermore, a pore water pressure gauge is arranged at the highest level of the multiple levels of blocking members. The pore water pressure gauge is arranged between the two steel strands on the upper surface of the backing plate, and baffles for protection are arranged on the other two sides. The pore water pressure gauge is connected to an information acquisition instrument through a lead.

[0015] The backing plate diameter of the present invention is smaller than the distance between the flange of the vibroflot and the pile wall and larger than the diameter of the stone material used for the vibroflotation gravel pile.

[0016] The length of the steel strand between the backing plates of each level of blocking members is less than or equal to 2 meters.

[0017] The conical clip of the present invention is a two-piece combined structure. The inner hole diameter formed after combination is smaller than the diameter of the steel strand, and serrations are arranged on the inner hole wall.

[0018] The buried depth of the bottom barrier in the multi-level barrier of the present invention is determined by the following method:

[0019] According to the maximum pressure required for the static load test, the maximum pull-out force that each anchor pile should provide is calculated, and the design value of the pull-out force of an auxiliary device f is obtained; the soil layer weight γ is determined by obtaining the on-site geological survey report, and the soil self-weight stress distribution diagram is determined. According to the pile friction coefficient φ and the soil side pressure coefficient k, the negative friction resistance is determined by the following formula (1);

[0020] α=k*tanφ*σ (1)

[0021] Where: α is the standard value of negative friction resistance on the pile side, k is the soil side pressure coefficient, φ is the effective internal friction angle of the soil, σ is the vertical effective stress of the soil;

[0022] The designed burial depth x of the auxiliary device is obtained by the following formula (2);

[0023]

[0024] Where: h1—soil thickness, r—pad radius, f max —The auxiliary device is designed to have maximum pull-out resistance.

[0025] The present invention can determine parameters such as the friction coefficient and the weight of the soil layer according to the geological survey report of the construction site, and determine the length of the steel strand and the number of blocking pieces according to the corresponding calculation formula. The two steel strands and the pad are combined into a whole by a double-hole anchor, and buried in the pile body according to the construction process of the vibro-impacted gravel pile to provide the reaction force required for the static load test of the anchor pile method. By arranging a blocking piece at the end of the steel strand to generate a certain end resistance, the maximum reaction force that the steel strand can provide is increased to meet the requirements of the static load test of the anchor pile method. The middle steel wire of the steel strand is replaced by a conductor, and the conductor is wrapped by six steel wires on the outside to prevent the conductor from being worn in the gravel pile. The conductor can pass through the gap between the two steel wires and be connected to the information collection instrument.

[0026] According to needs, at least one annular pressure sensor is arranged between the double-hole anchor of the bottom first-level blocking member and the base plate, which can be used to collect the stress size on the horizontal plane after the pile body is formed to determine the quality of the vibro-stone pile.

[0027] As needed, two baffles are welded above the pad of the upper first-level blocking member in a direction parallel to the steel strands, and a pore water pressure gauge is installed in the closed area formed by the baffles and the two steel strands. The pore water pressure gauge can be used to detect the changes in the pore water pressure of the pile body to determine the influence of groundwater on the pile body.

[0028] The embedding depth of the steel strand of the present invention is determined by the number of setting plates. The size of the setting plate is determined according to the gap width between the on-site vibroflot and the pile wall, and the distance between the setting plates is a fixed value. After determining the diameter of the setting plate, the magnitude of the frictional resistance provided between two setting plates is determined according to the corresponding calculation formula. The number of blocking members is determined according to the magnitude of the uplift force that each auxiliary device should provide, and then the embedding depth of the anti-auxiliary device is determined.

[0029] During combined installation, the steel strand is sequentially passed through the setting plate and the double-hole anchor. The setting plate and the double-hole anchor are slid to the designated position of the steel strand. Subsequently, the wedge-shaped clamp is installed in the hole of the double-hole anchor, and it is tightly embedded in the gap between the steel strand and the hole by using an external force. Finally, the setting plate and the double-hole anchor are simply fixed together with wire ties to prevent the two from separating during the movement of the auxiliary device.

[0030] During pre-embedding placement, according to the construction technology of the vibro-compaction gravel pile, during the process of backfilling gravel and vibrating and compacting it, the assembled auxiliary device is placed into the pile along the gap between the vibroflot and the pile wall. During the placement process, the setting plate and the anchor do not slide downwards because they are fixed with wire ties. After the auxiliary device is completely placed into the pile, continue to backfill gravel and vibrate and compact it. During the process of vibrating and compacting, the gravel and the auxiliary device are squeezed tightly to improve the uplift resistance of each level of blocking members of the auxiliary device.

[0031] During the static load test, the blocking members of the auxiliary device will be subjected to an upward uplift force, and the steel strand will have a tendency to move upwards. However, due to the blocking effect of the gravel, the setting plate and the double-hole anchor will stay in place due to the blocking of the gravel. There is a tendency of relative movement between the steel strand and the double-hole anchor. Under this tendency, the wedge-shaped clamp will be more tightly embedded between the steel strand and the tapered hole of the double-hole anchor, so that the steel strand and the double-hole anchor will be combined more firmly. The setting plate is located above the double-hole anchor, and the setting plate will not move downwards under the action of the double-hole anchor, thus providing a certain end resistance.

[0032] The setting plate of the device of the present invention is processed from a steel plate, and its diameter size is determined according to the distance between the vibroflot and the pile wall. The larger the diameter, the greater the maximum end resistance it can provide. After determining the diameter of the setting plate and the spacing between the setting plates, the magnitude of the end resistance borne by a single setting plate is determined, and the required thickness of the setting plate is calculated by using software according to the end resistance. The hole of the setting plate and the double-hole anchor are on the same vertical line to facilitate the passing of the steel strand.

[0033] In the production process of the steel strand of the device of the present invention, the middle steel wire is removed, and the wire used for passing through the data acquisition instrument is passed through later. The six outer steel wires wrap the wire inside to prevent damage to the wire during the construction of the vibro-compaction gravel pile. The wire passes out through the gap between the steel wires and is connected to each sensor.

[0034] The device of the present invention sets an annular pressure sensor between the double-hole anchor and the pad, which can be used to collect the stress on the horizontal plane after the pile body is formed to judge the quality of the vibro-stone pile. Most annular pressure sensors can achieve a close combination of the three under the pressure of themselves and the pad to reflect the pressure on a single pad during the pulling process of the auxiliary device. The annular pressure sensor transmits data to the surface through the wire in the steel strand.

[0035] According to the location to be detected, the present invention also installs a pore water pressure gauge above the pad. In order to prevent the gravel from damaging the pore water pressure gauge during the embedding process, two baffles are welded above the pad, and two steel strands are inside the baffles. The four form a closed area in which the pore water pressure gauge can be installed. After the pore water pressure gauge is installed, the pore water pressure gauge and the two steel strands are firmly tied together with a tie wire to prevent them from being separated from the auxiliary device during the embedding process.

[0036] The invention is beneficial. The auxiliary device of the invention solves the problem that the single pile bearing capacity test of vibro-compacted stone piles can only be carried out by the stacking method, shortens the time required for the test, saves costs, reduces the space required for the static load test, and the like; the auxiliary device adopts a multi-stage blocking member to be pre-buried and set during the construction process of the vibro-compacted stone pile, overcomes the problem that the vibro-compacted stone pile body has no adhesion and the sensor cannot be buried in the vibro-compacted stone pile body, and realizes the monitoring of the stress size and the pore water pressure size at the specified position of the pile body by setting an annular pressure sensor and a pore water pressure gauge, so as to judge the influence of the buoyancy of groundwater on the stone pile, and realize the real-time monitoring of the vibro-compacted stone pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a three-dimensional schematic diagram of the device of the present invention;

[0038] Figure 2 for Figure 1 3D exploded view of area A in the middle;

[0039] Figure 3 for Figure 1 3D exploded view of area B in the middle;

[0040] Figure 4 A three-dimensional diagram of the clip used in the present invention;

[0041] Figure 5 This is a structural diagram of the steel strand used in the present invention;

[0042] Figure 6 This is a simplified diagram for calculating negative friction.

[0043] In the figure: 1—baffle, 2—clamp, 3—steel strand, 4—base plate, 5—annular pressure sensor, 6—double-hole anchor, 7—pore water pressure gauge, 8—tie wire, 9—serration, 10—conductor wire, 11—steel wire. Detailed implementation manners

[0044] The present invention will be further described below in conjunction with the detailed implementation manners. The detailed implementation manners are further explanations of the principle of the present invention and do not limit the present invention in any way. The technologies identical or similar to the present invention are all within the protection scope of the present invention.

[0045] In conjunction with the accompanying drawings.

[0046] According to the maximum pressure required to be applied in the static load test, calculate the maximum pulling force that each anchor pile should provide, and obtain a design value f for the uplift resistance of an auxiliary device. The maximum pressure required to be applied in the static load test is obtained according to the specific engineering design requirements.

[0047] In this example, the distance between the bearing plates is determined to be 2m. According to the gap size between the vibroflot and the hole wall, determine the radius r of the bearing plate. Determine the unit weight γ of the soil layer according to the on-site geological exploration report, and determine the distribution diagram of the self-weight stress of the soil. According to the pile friction coefficient φ and the lateral earth pressure coefficient k of the soil, the magnitude of the negative skin friction can be determined according to formula (1).

[0048] α = k * tanφ * σ (1)

[0049] In the formula: α—the standard value of the negative skin friction on the pile side; k—the lateral earth pressure coefficient; φ—the effective internal friction angle of the soil; σ—the vertical effective stress of the soil.

[0050] As Figure 6 shown, Figure 6 is a simplified diagram of the negative skin friction calculation result, which shows the change of the negative skin friction under different soil layer thicknesses. In the figure, h2 represents the thickness of the first soil layer, h1 - h2 represents the thickness of the second soil layer, and a and b respectively represent the magnitudes of the negative skin friction at the bottom of each soil layer calculated by formula (1).

[0051] After obtaining the negative skin friction distribution as Figure 6 shown, according to the maximum pulling force of the auxiliary device design, the design burial depth x of the auxiliary device is obtained from formula (2).

[0052]

[0053] In the formula: α—the standard value of the negative skin friction on the pile side; h1—the soil layer thickness; r—the radius of the bearing plate; fmax—the maximum uplift resistance design of the auxiliary device.

[0054] After obtaining the buried depth of the auxiliary device, determine the number of backing plates according to the spacing between the backing plates, and slide the backing plates and double-hole anchors on the ground to the designated positions of the steel strands. The position sequence is that the backing plate is on the top, followed by the double-hole anchor, and finally the wedge grips that match the double-hole anchor. After the backing plates and double-hole anchors are placed, embed the wedge grips into the gap between the inner wall of the double-hole anchor and the steel strands, so that the double-hole anchor and the steel strands can be tightly combined. Finally, simply tie the backing plates and double-hole anchors together with binding wire to prevent the backing plates from moving when the auxiliary device is moved, and tie the two steel strands at regular intervals along the entire length with binding wire to prevent the auxiliary device from separating during the burying process.

[0055] According to the vibroflotation gravel pile construction technology, when the gravel is backfilled to a distance from the ground equal to the designed buried depth of the auxiliary device, stop the vibroflotation of the pile body, lift out the vibroflot, and slowly lower the auxiliary device of the present invention along the pile wall. After it is placed, put the vibroflot back in and continue the vibroflotation operation, and finally vibrate and squeeze the gravel and the auxiliary device tightly.

[0056] Since the wedge grips are below the double-hole anchor, and the wedge grips have a structure with one end larger and the other end smaller, and its inner wall has serrations to increase the friction force, and the double-hole anchor duct also has a structure with one end larger and the other end smaller. Under the self-weight of the double-hole anchor and the backing plate, the double-hole anchor and the steel strands will be more tightly combined.

[0057] A certain length of the steel strands of the auxiliary device will be exposed above the ground for later fixation with the reaction beam. During the pulling process of the auxiliary device, the uplift resistance is mainly composed of two parts; one part is the negative skin friction between the steel strands and the surrounding gravel, but since the steel strands are made of metal and the surface is relatively smooth, and the contact area between the gravel and the steel strands is small, the uplift resistance generated by this part is not sufficient to meet the reaction force requirements for the static load test; the other part of the uplift resistance is the end resistance generated by the blocking member composed of the backing plate, double-hole anchor, and wedge grips. The steel strands tend to move upward under the upward pulling force, and the backing plate and double-hole anchor have no tendency to move upward because they are surrounded by the pile body. The steel strands and the double-hole anchor tend to move relative to each other. Since the inner wall of the wedge grips is provided with serrations, this movement tendency will drive the wedge grips to move towards the end with a smaller size of the double-hole anchor duct, so that the wedge grips are more tightly embedded in the duct. By this method, the bonding degree between the double-hole anchor and the steel strands is increased to provide a large enough end resistance to generate uplift resistance.

[0058] As shown in the figure, the steel strand is composed of seven steel wires. Remove the middle steel wire from the steel strand to leave a channel for passing the wire. The wire can be protected from being worn by the gravel during the burying process under the wrapping of the six steel wires. The wire passes through the gap between the two steel wires at the sensor position and is connected to the sensor, and the other end is connected to the equipment on the ground.

[0059] A ring-shaped pressure sensor is arranged between the backing plate and the double-hole anchor, and the steel strand can pass through the ring-shaped pressure sensor. The ring-shaped pressure sensor can be closely attached together under the extrusion of the backing plate and the double-hole anchor. The ring-shaped pressure sensor can be used to detect the pressure magnitude at a specified position after the vibro-compaction gravel pile is formed, so as to calculate the corresponding stress magnitude and judge whether the vibro-compaction quality is qualified.

[0060] Two baffles are welded above the backing plate. The inner sides of the baffles are steel strands. A pore water piezometer is arranged in the area formed by the steel strands and the baffles. The outer baffles and steel strands can prevent the gravel from damaging the pore water piezometer during the embedding process of the present invention. Since the vibro-compaction gravel pile needs to be provided with an anti-filter layer according to different formation conditions, the design of the pore water piezometer can be used to detect the influence of pore water pressure on the pile body.

[0061] The ring-shaped pressure sensor and the pore water piezometer are connected to the wires led out from the inside of the steel strand, and the collected data is transmitted to the ground.

Claims

1. A monitoring auxiliary device applicable to vibroflotation gravel piles, the auxiliary device is used to assist the anchor pile method in monitoring vibroflotation gravel piles, and is characterized in that: The auxiliary device is composed of multiple levels of blocking members connected in series by steel strands; Two steel strands are arranged in parallel and pass through the blocking members at each level arranged at intervals. The lengths of the steel strands between the blocking members at each level are the same, so that the blocking members are arranged in parallel when the steel strands are in a straightened state; Each level of blocking member includes at least a backing plate and a double-hole anchor under the backing plate. Two steel strand perforations are provided in the middle of the backing plate and the double-hole anchor. Among them, the two steel strand perforations of the double-hole anchor are both positive conical holes, and a conical clamping piece with a structure matching the conical hole is sleeved on the steel strand perforation part and pre-fixed with the conical hole.

2. The monitoring auxiliary device applicable to vibroflotation gravel piles according to claim 1, characterized in that: The steel strand is a multi-wire wound steel strand, and the steel strand core is provided with each sensor wire.

3. The monitoring auxiliary device applicable to vibroflotation gravel piles according to claim 1, characterized in that: At least a ring-shaped pressure sensor is arranged at the bottom end level of the multiple levels of blocking members. The ring-shaped pressure sensor passes through the steel strand in the middle and is fixed between the backing plate and the double-hole anchor. The ring-shaped pressure sensor is connected to the information acquisition instrument through a wire.

4. The monitoring auxiliary device applicable to vibroflotation gravel piles according to claim 1, wherein: A pore water pressure gauge is arranged at the topmost level of the multiple levels of blocking members. The pore water pressure gauge is arranged between the two steel strands on the upper surface of the backing plate, and baffles for protection are arranged on the other two sides. The pore water pressure gauge is connected to the information acquisition instrument through a wire.

5. The monitoring auxiliary device applicable to vibroflotation gravel piles according to any one of claims 1 to 4, characterized in that: The diameter of the backing plate is smaller than the distance between the flange of the vibroflot and the pile wall and larger than the diameter of the stone used for the vibroflushed gravel pile.

6. The monitoring auxiliary device applicable to vibroflotation gravel piles according to claim 5, characterized in that: The length of the steel strand between the backing plates of the blocking members at each level is less than or equal to 2 meters.

7. The monitoring auxiliary device applicable to vibroflotation gravel piles according to claim 5, characterized in that: The conical clamping piece is a two-piece combined structure. The inner diameter formed after combination is smaller than the diameter of the steel strand, and serrations are arranged on the inner hole wall.

8. The monitoring auxiliary device applicable to vibroflotation gravel piles according to claim 5, characterized in that The burial depth of the bottommost level of blocking member in the multiple levels of blocking members is determined by the following method: According to the maximum pressure required to be applied in the static load test, calculate the maximum pulling force that each anchor pile should provide, and obtain the design value f of the uplift resistance of an anti-anchor member; Obtain the on-site geological exploration report to determine the soil unit weight γ, and determine the distribution diagram of the self-weight stress of the soil. According to the pile friction coefficient φ and the soil lateral pressure coefficient k, determine the magnitude of the negative skin friction by the following formula (1); α = k * tanφ * σ (1) In the formula: α—the standard value of the negative skin friction on the pile side, k—the soil lateral pressure coefficient, φ—the effective internal friction angle of the soil, σ—the vertical effective stress of the soil; Obtain the design burial depth x of the anti-anchor member by the following formula (2); Where: h1 is the thickness of the soil layer, r is the radius of the bearing plate, and f max — the maximum designed uplift force of the anti-anchoring component.

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