Static drilling rooted pile soil contact surface bonding stress testing system and method

Abstract

According to the static drilling rooted pile soil contact surface bonding stress testing system and method, a fiber rib force measuring cage is used for installing an interface strain sensor, direct contact between the interface strain sensor and a cement soil-pile periphery soil interface is achieved, and an effective method for measuring the actual strain value of the cement soil-pile periphery soil interface is provided; the fiber bar force measuring cage is composed of fiber bars and tension bands, the elastic modulus of the fiber bars is close to that of a solidified cement soil body, so that the longitudinal rigidity of the static drill rooted pile body cannot be greatly weakened or enhanced due to the fiber bar force measuring cage, and compared with other testing devices, the fiber bar force measuring cage has the advantage that the longitudinal rigidity of the static drill rooted pile body is greatly improved under the same effect. The diameter of the device can be flexibly adjusted according to the diameter of a test pile hole at a test position, required materials are wide in acquisition path and low in purchase cost, the device can be directly bound and formed on site without independent customization, and the time required by the test is greatly shortened.

Description

Technical Field

[0001] The invention belongs to the technical field related to in-situ testing of geotechnical engineering, and in particular relates to a system and method for testing the bond stress of the soil contact surface of a statically drilled rooted pile. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Static drilled rooted piles are a new type of non-soil-squeezing composite pile foundation that has emerged in recent years. The construction process is as follows: first, drill a hole at the designed pile position, expand the bottom and grout when the drill bit reaches the pile end position, then grout around the pile to form a well-mixed cement soil in the pile hole, and finally implant the prefabricated pile into the pile hole. Therefore, there is no soil squeezing effect during the construction of static drilled rooted piles, and the soil in the borehole is recycled to form cement soil through grouting and mixing, and there is no mud discharge during the construction process. At present, the use of static drilled rooted piles in soft soil areas in eastern coastal areas of China has reached more than 6 million meters. The construction efficiency of static drilled rooted piles is more than 3 times higher than that of bored piles of the same diameter, and its cost is reduced by more than 10% compared with bored piles of the same bearing capacity, which has significant practical engineering application value.

[0004] The pile body of the static drilled rooted pile is composed of precast piles and cement soil. The pile top load is transmitted to the soil around the pile through the precast pile-cement soil-pile surrounding soil interface. When the side friction resistance of the precast pile-cement soil interface is greater than the side friction resistance of the cement soil-pile surrounding soil interface, the pile side friction resistance is provided by the cement soil-pile surrounding soil interface. When the side friction resistance of the precast pile-cement soil interface is less than the side friction resistance of the cement soil-pile surrounding soil interface, the pile side friction resistance is provided by the precast pile-cement soil interface. When designing static drilled rooted piles, it is necessary to ensure that the side friction resistance of the precast pile-cement soil interface is greater than the side friction resistance of the cement soil-pile surrounding soil interface.

[0005] At present, the research on the ultimate bearing capacity and construction technology of this type of pile is relatively mature, but the vertical load transfer law, the load-bearing ratio of pipe piles and cement soil, and the conditions that pipe piles and cement soil should meet for effective compounding need further research. At present, most domestic scholars have studied the overall bearing performance of static drilled root piles and the cement soil-pile soil interface through field tests, but there are few means to directly and accurately measure the bond stress between cement soil and pile soil, and it is relatively difficult. The research on the friction characteristics of the core pile-cement soil interface is usually carried out by model test method, and the relevant research content is relatively lacking at this stage.

[0006] In summary, the bearing capacity of static drilled rooted piles is affected by the friction characteristics of the core pile-cement soil interface and the cement soil-pile surrounding soil interface, and the friction characteristics and friction resistance distribution of the above two interfaces are equally important for analyzing the load transfer characteristics and bearing capacity of static drilled rooted piles. Studying the friction characteristics and load transfer mechanism of the core pile-cement soil interface and the cement soil-pile surrounding soil interface of static drilled rooted piles is of great significance for the bearing capacity analysis of static drilled rooted piles and the cost reduction and efficiency improvement of construction design. At the same time, in order to solve various problems encountered in the bond stress test of the pile-soil contact surface of static drilled rooted piles, some construction methods have also been proposed in this field.

[0007] In the existing scheme, Zhou Jiajin (2024) buried a vibrating-wire steel stress gauge as a stress test device on the steel cage during the prefabricated pile production process to obtain the distribution form and size of the pile axial stress during the static pressure or pull-out test of the static drilled rooted pile. The strain value of the steel bar inside the pile body replaced the strain value of the interface between the grouting body and the rock and soil body, and then estimated the side friction resistance of the test pile in each soil layer based on the numerical value, but did not provide an effective method for measuring the true strain value of the cement soil-pile surrounding soil interface, and the obtained side friction resistance of the cement soil-pile surrounding soil interface was inconsistent with the actual value; Chinese patent CN110331742A invented a model test device and test method for testing the friction characteristics of the pile-soil contact surface of static drilled rooted piles, which can be used to study the friction characteristics of the pile-soil contact surface of static drilled rooted piles under vertical downward pressure and upward pull-out loads, and provides an effective means for studying the side friction bearing performance of static drilled rooted piles. However, this test method is based on a model test with a pre-prepared grouting body, which is inconsistent with the actual service conditions of static drilled rooted piles.

[0008] In summary, it is a technical problem that needs to be solved at present to propose a test system that can measure static drilled rooted piles on site and to improve the accuracy and test efficiency of the bond stress test of the cement soil-pile soil interface of static drilled rooted piles. Summary of the invention

[0009] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a system and method for testing the bond stress of the pile-soil contact surface of a static drilled rooted pile. By setting a fiber reinforcement force measuring cage in the static drilled rooted pile and directly arranging an interface strain sensor at the cement soil-pile surrounding soil interface, the purpose of directly measuring the strain of the above-mentioned interface during the on-site vertical load test of the static drilled rooted pile is achieved, and the bond stress of the cement soil-pile surrounding soil interface is accurately obtained, and the accuracy and test efficiency of the bond stress test of the cement soil-pile surrounding soil interface of the static drilled rooted pile are improved.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] In a first aspect, the present invention provides a static drill rooted pile soil contact surface bonding stress testing system, comprising: a loading reaction force system, a data acquisition system, a fiber reinforcement force cage and an analysis system;

[0012] The loading reaction force system includes a load plate arranged above the static drill root pile body, which is used to provide the downward force required for the test;

[0013] The fiber reinforcement force measuring cage comprises a hoop and fiber reinforcement, wherein the hoop and the fiber reinforcement are bound together, and the fiber reinforcement force measuring cage is arranged outside the static drilled root pile body to realize direct contact between the interface strain sensor and the cement soil-pile surrounding soil interface;

[0014] The data acquisition system includes a load sensor and an interface strain sensor, wherein the load sensor is used to obtain the pressure provided by the loading reaction force system, and the interface strain sensor is arranged on the fiber reinforcement to obtain the strain of the cement soil-pile surrounding soil interface;

[0015] The analysis system is connected in communication with the data acquisition system, and according to the obtained strain of the cement soil-pile surrounding soil interface, the cement soil-rock soil interface bonding stress is analyzed and calculated, thereby exploring the vertical load transfer mechanism of the static drilled rooted pile.

[0016] In a second aspect, the present invention provides a method for testing the bond stress of the soil contact surface of a static drilled rooted pile, comprising:

[0017] The hoop is arranged outside the static drilled root pile body, and the hoop is bundled with fiber reinforcement;

[0018] installing an interface strain sensor on the fiber tendon;

[0019] Start the loading reaction force system and load the static drilled root pile according to the preset load level to make it sink;

[0020] Start the data acquisition system, obtain the pressure provided by the loading reaction system through the load sensor; obtain the strain of the cement soil-pile surrounding soil interface through the interface strain sensor;

[0021] When the load data of the loading reaction system reaches the test planned load level, the loading is stopped and the load is continued for a period of time, and the next level of load is loaded after it stabilizes.

[0022] One or more of the above technical solutions have the following beneficial effects:

[0023] In the present invention, a fiber reinforcement force cage is used for installing an interface strain sensor, so as to realize direct contact between the interface strain sensor and the cement soil-pile surrounding soil interface, and provide an effective method for measuring the actual strain value of the cement soil-pile surrounding soil interface.

[0024] In the present invention, the fiber reinforcement force cage is composed of fiber reinforcement and hoops. Since the elastic modulus of the fiber reinforcement is similar to the elastic modulus of the cement soil after consolidation, the existence of the fiber reinforcement force cage will not significantly weaken or enhance the longitudinal stiffness of the static drilled rooted pile body. Compared with other testing devices, the fiber reinforcement force cage can produce the same effect, and its diameter can be flexibly adjusted according to the diameter of the test pile hole at the test location. The required materials are widely available and have low procurement costs. They can be directly tied and formed on site without separate customization, which greatly shortens the time required for the test.

[0025] The system proposed in the present invention can directly and accurately measure the bond stress at the interface between the cement soil and the soil around the pile of static drilled rooted piles on site, thereby improving the accuracy and test efficiency of the test of the bond stress at the interface between the cement soil and the soil around the pile of static drilled rooted piles.

[0026] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0028] Figure 1 (a)-(b) are schematic diagrams of a static drill rooted pile soil contact surface bonding stress testing system in Example 1 of the present invention;

[0029] Figure 2 This is a structural diagram of a fiber reinforcement force cage of a static drilled root pile soil contact surface bonding stress testing system and method in the first embodiment of the present invention;

[0030] Figure 3 This is a pile structure diagram of a static drill root pile soil contact surface bonding stress testing system in the first embodiment of the present invention;

[0031] Figure 4 The present invention is a schematic diagram of an overall structure of a static drilled root pile soil contact surface bonding stress testing system in a first embodiment of the present invention.

[0032] Figure 5 A cross-sectional plan view of a static drilled root pile soil contact surface bonding stress testing system;

[0033] In the figure, 1-1, pile load, 1-2, secondary beam, 1-3, pier, 1-4, main beam, 1-5, jack, 1-6, hydraulic oil pump, 1-7 load plate, 2-1, load sensor, 2-2 load display, 2-3, displacement sensor, 2-4 sensor bracket, 2-5, interface strain sensor, 2-6, data acquisition instrument, 2-7 data processing terminal, 3-1 fiber reinforcement, 3-2 hoop, 4-1, PHC pile, 4-2, cement soil. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0035] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0036] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0037] Embodiment 1

[0038] This embodiment discloses a static drill root pile soil contact surface bonding stress test system, including: a loading reaction system, a data acquisition system, a fiber reinforcement force cage and an analysis system;

[0039] The loading reaction force system includes a load plate arranged above the static drill root pile body, which is used to provide the downward force required for the test;

[0040] The fiber reinforcement force measuring cage comprises a hoop and fiber reinforcement, wherein the hoop and the fiber reinforcement are bound together, and the fiber reinforcement force measuring cage is arranged outside the static drilled root pile body to realize direct contact between the interface strain sensor and the cement soil-pile surrounding soil interface;

[0041] The data acquisition system includes a load sensor and an interface strain sensor, wherein the load sensor is used to obtain the pressure provided by the loading reaction force system, and the interface strain sensor is arranged on the fiber reinforcement to obtain the strain of the cement soil-pile surrounding soil interface;

[0042] The analysis system is connected in communication with the data acquisition system, and according to the obtained strain of the cement soil-pile surrounding soil interface, the cement soil-rock soil interface bonding stress is directly analyzed and calculated on site, thereby exploring the vertical load transfer mechanism of static drill rooted piles.

[0043] Combine the following Figure 1-Figure 5A system for testing the bond stress of the soil contact surface of a statically drilled rooted pile proposed in this embodiment is described in detail.

[0044] In this embodiment, the loading reaction system includes a pile load 1-1, a secondary beam 1-2, a pier 1-3, a main beam 1-4, a jack 1-5, a hydraulic oil pump 1-6 and a load plate 1-7; the function of the loading reaction system 1 is mainly to provide the downward force required for the field test.

[0045] Specifically, the load 1-1 is a concrete counterweight block installed above the secondary beam 1-2 by a crane; the secondary beam 1-2 is installed above the pier 1-3 and the main beam 1-4, and the two piers 1-3 are symmetrically arranged at appropriate positions on both sides of the main beam 1-4; the main beam 1-4 is arranged above the load sensor 2-1 in a direction parallel to the long side of the pier 1-3, and the load sensor 2-1 is located at the centroid of the main beam 1-4.

[0046] The jack 1-5 is placed between the load sensor 2-1 and the load plate 1-7, and the central axes of the jack 1-5 and the load sensor 2-1 coincide, and the center of force of the jack 1-5 coincides with the centroid of the load plate 1-7; the model of the jack 1-5 can be determined according to the bearing capacity of the single pile; the jack 1-5 and the hydraulic oil pump 1-6 are connected by a hydraulic oil pipe; the jack 1-5 is an automatic hydraulic jack, which uses automatic pressurization to greatly shorten the test time, reduce the experimental steps, dynamically adjust the load parameters according to the test process, and improve the accuracy of the test results; the hydraulic oil pump 1-6 is placed on the natural ground around the test site that does not hinder construction operations and ensures the safety of data transmission.

[0047] The main function of the load plate 1-7 is to bear and disperse the load and protect other structures from damage; the load plate 1-7 is a square steel plate, which is placed above the pile head of the static drilled rooted pile, and its centroid coincides with the centroid of the pile head of the static drilled rooted pile body 4. The side length must be larger than the pile hole diameter and the diameter of the jack 1-5. The size of the load plate 1-7 itself is to be able to play its own load role in the on-site pull-out test without obvious bending damage as the minimum. In this embodiment, the size of the load plate 1-7 is 700mm×700mm×40mm.

[0048] In this embodiment, the data acquisition system includes a load sensor 2-1, a load display 2-2, a displacement sensor 2-3, a sensor bracket 2-4, an interface strain sensor 2-5, a data acquisition instrument 2-6, and a data processing terminal 2-7; the data acquisition system mainly collects cement soil-rock interface strain data, load data, and displacement data, and smoothly transmits the above data to the data processing terminal to directly obtain the cement soil-rock interface bond stress on site.

[0049] Specifically, the load sensor 2-1 is placed between the main beam 1-4 and the jack 1-5; the load sensor 2-1 and the load display 2-2 are connected by wire; the load display 2-2 displays the pressure provided by the jack 1-5 in real time.

[0050] There are four displacement sensors 2-3, which are installed above the load plate 1-7, and the four displacement sensors 2-3 are respectively installed at a certain distance from the four corners of the load plate 1-7; the four displacement sensors 2-3 are fixed in groups of two by four magnetic support arms on two sensor brackets 2-4 arranged on both sides of the load plate 1-7 along the direction of the main beam 1-4; the displacement sensor 2-3 displays the settlement of the static drill rooted pile body 4 in real time.

[0051] The interface strain sensor 2-5 is a FBG (fiber Bragg grating) sensor, which is used to collect the interface strain data between the grouting body and the rock and soil body; the interface strain sensor 2-5 is fixed to the fiber reinforcement 3-1 on both sides of the fiber reinforcement force cage 3 with strong glue and smeared with 704 silicone rubber and reinforcement glue for waterproofing and reinforcement treatment respectively, to ensure that the interface strain sensor 2-5 is not damaged during the static drilling root pile exploration and field test.

[0052] The interface strain sensor 2-3 is connected to the data acquisition instrument 2-6 through the same number of optical fibers as the interface strain sensor 2-3; the data acquisition instrument 2-6 is connected to the data processing terminal 2-7 through an optical fiber conductor.

[0053] As an implementable method, the fiber reinforcement force cage is formed by binding a number of circular steel hoops 3-2 with an inner diameter slightly smaller than the pile hole diameter and 6 fiber reinforcements 3-1 with an elastic modulus similar to that of C25 concrete mortar. The length of the fiber reinforcement force cage is equal to the depth of the pipe pile; the length of the fiber reinforcement 3-1 and the number and diameter of the hoops 3-2 are determined by field testing of the length and diameter data of the statically drilled rooted pile body; the fiber reinforcement 3-1 is tied to the outside of each hoop 3-2 by steel wire, and the position is arranged with reference to the vertices of the hexagon.

[0054] The fiber reinforcement force cage formed by binding has the minimum stiffness limit of not being easily twisted and deformed when lowered into the pile hole, and because the elastic modulus of the fiber reinforcement 3-1 is similar to that of C25 concrete mortar, the existence of the fiber reinforcement force cage will not significantly weaken or enhance the longitudinal stiffness of the static drilled rooted pile body; the fiber reinforcement force cage realizes direct contact between the interface strain sensor 2-5 and the cement soil-pile surrounding soil interface, and its diameter can be flexibly adjusted according to the pile hole diameter at the location of the on-site test, so as to achieve the purpose of directly measuring the strain of the cement soil-pile surrounding soil interface during the on-site vertical load test of the static drilled rooted pile, and accurately obtaining the bond stress of the cement soil-pile surrounding soil interface.

[0055] In this embodiment, the static drill rooted pile body is composed of a PHC pipe pile 4-1 and cement soil 4-2 consolidated inside and around the pile.

[0056] Embodiment 2

[0057] This embodiment provides a method for testing the bond stress of the soil contact surface of a static drilled rooted pile, comprising:

[0058] The hoop is arranged outside the static drilled root pile body, and the hoop is bundled with fiber reinforcement;

[0059] installing an interface strain sensor on the fiber tendon;

[0060] Start the loading reaction force system and load the static drilled root pile according to the preset load level to make it sink;

[0061] Start the data acquisition system, obtain the pressure provided by the loading reaction system through the load sensor; obtain the strain of the cement soil-pile surrounding soil interface through the interface strain sensor;

[0062] When the load data of the loading reaction system reaches the test planned load level, the loading is stopped and the load is continued for a period of time, and the next level of load is loaded after it stabilizes.

[0063] The present embodiment manufactures the test pile, including:

[0064] S10. Preliminary preparation work.

[0065] S101: Measurement and positioning: Specifically, the pile positions are measured and placed according to the measurement control network, and a cross control network and reference points are set up on the pile axis to ensure that the pile foundation is accurately positioned. When positioning, first, prepare the pile measurement and positioning map according to the design drawings, and ensure that the axis control points are not affected by soil squeezing when the piles are pressed. Secondly, according to the actual piling route map, the measurement and positioning control network is divided according to the construction area. Generally, 10-20 pile positions are placed in an area according to the daily construction progress, and a cross control network is driven into the ground at the center of the pile position. 30-40cm long steel bars are marked with red paint. After the pile driver is moved, a second check should be carried out to ensure that the pile position deviation is less than 10mm. Before construction, length marks in meters should be drawn on the matching engineering pile body according to the construction pile length, and the length of the pile should be marked from bottom to top in order to observe the depth of the pile into the soil.

[0066] S102: Drilling rig in place: Specifically, according to the pile position, the drilling rig is set, the drill tip is aligned with the pile center, the pile driver is kept horizontal and vertical, and the verticality deviation of the pile frame does not exceed 0.5%. The diameter D of the drill bit of the drilling rig satisfies: D=d+200, where d is the diameter of the prestressed pipe pile, in mm.

[0067] When the drilling rig arrives at the hole location, the roadbed is first leveled and filled, the drilling rig is positioned at the designated location, and the angles of the mast and drill rod are adjusted; when the drilling rig is aligned with the hole location, the cross method is used to center the hole location. After centering the hole location, the drilling rig shall not be moved, and the large and small arms shall not be raised or lowered at will.

[0068] S11, rotary drilling.

[0069] Specifically, a first drill bit of a corresponding type is selected according to the stratum, and a hole 0.3 to 0.5 meters deeper than the pre-buried depth of the casing and 0.2 to 0.4 meters larger in diameter than the casing is drilled at the pile position to the designed elevation of the casing, and corresponding hole cleaning work is performed;

[0070] S12. Bury casing.

[0071] Specifically, fill the bottom of the pit with 0.3 to 0.5 meters of clay and tamp it. Mark the center of the borehole at the bottom of the pit, put the casing into the pit, use a crosshair and a weight hammer to find the center of the casing, move the casing so that the center of the casing coincides with the center of the pit bottom, and the deviation between the central axis and the pile position shall not exceed 30mm, and the casing shall remain vertical, the buried inclination of the casing shall be controlled within 0.5%, and the casing shall be straightened with a level ruler. Finally, backfill and tamp the clay symmetrically and evenly around the casing.

[0072] As a feasible implementation method, the elevation of the casing top should be 1.5 to 2.0 m higher than the groundwater level and the highest construction water level. For drilling holes in waterless formations, since there is a grouting port at the top of the casing, the top of the casing should also be 0.2 to 0.3 m higher than the ground.

[0073] As a feasible implementation method, the bottom elevation of the casing should be lower than the lowest construction water level (generally lower than 0.1-0.3m). The casing buried in deep water should be sunk to a stable depth along the guide frame by means of deadweight, water jetting, vibration or hammering. The depth of burial in clay soil should reach 0.5-1m, and that in sandy soil should be 3-4m.

[0074] S13, Continue drilling. Continue drilling holes at the pile position until the designed elevation is reached.

[0075] Specifically, according to different strata, corresponding drill bits and processes are selected to carry out rotary drilling to the designed elevation of the static drill root pile and carry out corresponding hole cleaning work.

[0076] As an implementable method, the design diameter of the static drill root pile is 300mm, the diameter of the PHC pile 4-1 is 300mm, and a drilling rig is used to drill holes in the pile position. The diameter of the drill bit of the drilling rig can be slightly larger than 500mm; it can be understood that the diameter of the borehole is appropriately enlarged, and the pre-drilling or expansion of the hole slightly larger than the outer diameter of the pile provides space for the subsequent burial of the casing and the fiber reinforcement force cage, and can make the prestressed pile relatively easy to be buried in the soil, reduce the friction with the surrounding soil, reduce the resistance during the construction process, improve the efficiency of the prestressed pile sinking construction, and facilitate installation. Secondly, it can ensure the accurate installation position of the PHC pile, and avoid the displacement or improper installation of the prestressed pile due to the resistance of the soil.

[0077] After the hole is drilled, the integrity of the hole wall, hole diameter, hole depth and verticality are checked. Only after passing the inspection can the hole cleaning work be carried out. When cleaning the hole, the drill bit is placed at the bottom of the hole and rotated positively. The drill rod rotates while applying downward pressure and moves. After rotating for 20 to 30 circles, the rotation is stopped. The drill rod is lifted to lift the rotor out of the pile hole and unload the slag. If a lot of drill slag is found in the rotor, the next hole cleaning must be carried out until the drill slag at the bottom of the pile hole is thoroughly cleaned to ensure that the thickness of the sediment at the bottom of the bored pile hole meets the specifications and design requirements.

[0078] S14, lower into the fiber reinforcement force cage

[0079] Specifically, a plurality of interface strain sensors 2 - 5 are fixed on the fiber tendon 3 - 1 at corresponding designed intervals according to the field test plan.

[0080] The interface strain sensor 2-5 is fixed to the fiber tendons 3-1 on both sides of the fiber tendon force measurement cage with strong glue, and then the interface strain sensor 2-5 is connected to the corresponding optical fiber. The optical fiber is attached to one fiber tendon 3-1 on one side, and the two are fixed with a tie.

[0081] During the fiber optic deployment process, attention should also be paid to construction protection: when laying out the transmission optical fiber, the fusion joints between the optical fibers need to be protected by a jacket. Transmission optical fiber is afraid of bending and folding. When laying out the optical fiber on site, try to keep the optical fiber close to the fiber rib 3-1. You can use tape to fix the optical fiber on the fiber rib 3-1 at intervals. Do not make large bends when routing. At the junction of multiple optical fibers, the wires are easily entangled, which can easily lead to the loss of optical signals. Therefore, it is necessary to sort out the wiring in time to avoid entanglement and knotting.

[0082] After the wiring is completed, the survival rate of each set of interface strain sensors 2-5 and their corresponding optical fibers is tested, and the survival rate shall not be less than 95%. Then, the optical fibers are protected by casings and then wrapped and fixed with buffer materials. Then, 704 silicone rubber and rebar glue are applied to each interface strain sensor 2-5 for waterproofing and reinforcement treatment, respectively, to ensure that the interface strain sensor 2-5 is not damaged during the static drilling root pile exploration and field test.

[0083] Specifically, the fiber reinforcement force measuring cage 3 on which the interface strain sensor 2-5 is arranged in advance and tied with the hoop 3-2 is hoisted by a pile driver, and is hoisted by a one-point hoisting method, and then slowly sunk into the pile hole. During the whole process, the side wall of the force measuring steel cage is prevented from touching the inner wall of the pile hole as much as possible to prevent the interface strain sensor 2-5 arranged on the side wall of the fiber reinforcement force measuring cage 3 from failing.

[0084] S15, pouring outer core filling material.

[0085] Specifically, after the sediment at the bottom of the hole meets the requirements, the filling material is poured. Fine stone concrete with a strength of not less than C25 should be used for the filling material pouring, and a retarder should be added according to the time of pile planting.

[0086] The strength of fine stone concrete should be determined according to soil conditions and bearing capacity requirements, and is generally not less than C25; the fine stone concrete is mixed evenly and poured into the borehole from bottom to top by a mortar pump, and measures are taken to prevent slurry segregation; a flow meter is equipped during the transportation process to control the flow of slurry to prevent insufficient injection, and the flow rate is adjusted according to the lifting and lowering speed of the drilling rig; the corresponding admixture is added according to the actual situation, and the amount of admixture is determined through mix ratio tests and pile tests; the amount of fine stone concrete poured is determined according to the stratum, sediment and softening conditions at the pile end, which is 1.1 to 1.2 times the volume of the borehole minus the volume of the pile body and the volume between the slurry end surface and the hole top elevation surface, and is adjusted in time according to the on-site conditions; the cement mortar is poured into the completed hole according to the designed volume using the catheter method, and the workability of the mortar remains good.

[0087] S16. Pile driving construction.

[0088] Specifically, for pile driving construction: static pressure or hammer pile drivers can be selected. The verticality of the pile body should be controlled during the pile driving process. The pile driving construction can be completed when the pile is in place and meets the termination conditions required by different equipment performance.

[0089] When the pile is hoisted, the pile driver is used to hoist the PHC pile 4-1. Before the pile is hoisted, check whether the wire rope is damaged, otherwise it needs to be replaced; use paper pads or wooden pads to level the pile head, and when driving the pile, paperboard or square wood should be placed between the pile head and the pile hammer cap, but it should not be too thick, just meet the vibration reduction requirements, so as to avoid excessive elasticity and affect the pile planting.

[0090] The following requirements shall be met when sinking piles:

[0091] (1) When the PHC pile 4-1 is inserted, the verticality deviation shall not exceed 0.5%;

[0092] (2) The pile driver should be kept horizontal when driving piles; the holding pressure should not be greater than 1.1 times the allowable lateral pressure of the pile body;

[0093] (3) The piles should be sunk to the designed elevation continuously in one go, and the pause time should be shortened as much as possible. It should be avoided to connect the piles when approaching the bearing layer.

[0094] S17. Pull out the casing and maintain it.

[0095] Specifically, after the fine stone concrete is poured, the casing is pulled out and the concrete is cured. According to the concrete mix ratio and environmental conditions, appropriate curing measures are taken, such as covering with wet cloth, spraying water, etc., to ensure that the strength and durability of the concrete are in the best state. After the curing is completed, the cement soil 4-2 and the static drill root pile body 4 are formed.

[0096] The test process of the pile-soil contact surface bonding stress test of the static drilled rooted pile provided in this embodiment specifically includes:

[0097] S21. After the fine stone concrete is cured to form cement soil 4-2, the next step of the experimental operation can be carried out. First, remove the floating slurry at the overfilled position on the pile head, and make sure to chisel to the dense concrete layer. Then use grouting material to level the pile head so that the pile head is flush with the natural ground. Then put a pad on the pile head after leveling. The load plate 1-7 is configured so that the load is evenly applied to the top of the static drilled root pile body 4 through the load plate 1-7.

[0098] S22. Jack placement: Use a crane to place the jack 1-5 at the center of the load plate, so that the center of the combined force of the jack 1-5 coincides with the centroid of the pile head of the static drilled root pile. Use an oil pipe to connect the jack 1-5 and the hydraulic oil pump 1-6, and place the hydraulic oil pump 1-6 on the natural ground around the test site that does not hinder construction work and ensures data transmission security; then install the load sensor 2-1 at the center of the top of the jack 1-5, and make the central axes of the jack 1-5 and the load sensor 2-1 coincide.

[0099] S23. Pier placement: A group of piers 1-3 are respectively set up at appropriate positions symmetrically on the horizontal ground on both sides of the jacks 1-5 to support the upper counterweight.

[0100] S24, connect the multiple optical fiber lines reserved in advance at the pile top and protected by armor to the data acquisition instrument 2-6, and connect the data acquisition instrument 2-6 to the data processing terminal 2-7, debug and set relevant parameters, and then turn on the data acquisition instrument 2-6 to check whether it is connected with the interface strain sensor 2-5 and the optical fiber line smoothly to ensure that it can accurately and stably collect test data.

[0101] S25. Install displacement sensors: There are four displacement sensors 2-3, all of which are installed above the load plate 1-7, and the four displacement sensors 2-3 are installed at positions with a certain distance from the four corners of the load plate 1-7; the four displacement sensors 2-3 are grouped in pairs, and are fixed on two sensor brackets 2-4 arranged along the main beam 1-4 on both sides of the load plate 1-7 through four magnetic support arms;

[0102] S26. Hoisting the main beam and secondary beam: erect the main beam 1-4 above the load sensor 2-1 and the load sensor 2-1 is located at the centroid of the main beam 1-4, and sleepers are placed under both ends of the main beam 1-4.

[0103] S27. Placement of the pile load 1-1: Design and stack the required concrete block pile load according to the on-site test.

[0104] At this point, the static drilled root pile soil contact surface bonding stress test system has been installed, and the load sensor 2-1 and displacement sensor 2-3 have been calibrated to ensure the accuracy of the load applied at each level during the field test.

[0105] S28, operate the hydraulic oil pump 1-6 to control the jack 1-5 for loading, the reaction force of the jack 1-5 causes the static drill root pile body and the cement soil 4-2 to sink; monitor the load data added by the on-site test in real time through the load display instrument 2-2, when the test planned load level is reached, stop loading immediately and continue loading for a period of time, and load the next level of load only after the overall stability.

[0106] The on-site static load test adopts the slow-speed maintenance load method. This example test uses the YDC6500 jack, the JCQ-503A static load tester, and the CYB-10S oil pressure sensor. The loading reaction device uses an 8000kN static load test reaction frame, concrete blocks are used as counterweights, and the total counterweight is not less than 1.2 times the maximum test load. The displacement measurement uses an FP-50 displacement sensor. The test is carried out in strict accordance with the "Technical Specifications for Building Foundation Pile Inspection" (JGJ106-2014). The single pile static load test uses a 500mm load plate, and the load is evenly applied to the pipe pile through the load plate.

[0107] This test adopts the slow sustained load method, and conducts single pile vertical compressive static load test and single pile vertical pullout test according to the industry standard "Technical Specifications for Building Foundation Pile Testing" (JGJ106-2014) and the test standards and methods in related specifications, and determines the vertical ultimate bearing capacity of the single pile and the deformation of the pile top under various loads. The basic points in the vertical compressive static load test are as follows:

[0108] (1) The loading of the test is carried out in stages. The loading amount in each stage is the same, which is 1 / 10 of the maximum load or estimated bearing capacity. Special attention should be paid to the first load applied, which is twice the graded load.

[0109] (2) The unloading process should also be carried out in stages with equal amounts of unloading. The amount of unloading in each stage is twice the graded load during loading.

[0110] (3) During the loading and unloading process, the load acting on the pile should be uniform, continuous and impact-free, and the load variation range of each stage should be within ±10% of the graded load.

[0111] (4) The slow sustained load method test shall comply with the following provisions:

[0112] ① The pile top settlement should be measured at 5min, 15min, 30min, 45min and 60min after the load is applied. After one round of settlement measurement, the pile top settlement should be measured every 30min.

[0113] ② When the settlement within one hour is within 0.1mm and occurs twice in succession, it indicates that the settlement of the pile body has reached a relatively stable state (the calculation starts from the 30th minute after the load is applied, and the settlement observation value is calculated every 30 minutes for three consecutive times for 1.5 hours).

[0114] ③When the settlement rate of the pile top reaches a relatively stable standard, the next level of load is applied.

[0115] ④ During unloading, each level of load should be maintained for 1 hour. After measuring the settlement of the pile top at 15 minutes, 30 minutes and 60 minutes respectively, the next level of load can be unloaded. After unloading to zero, the residual settlement of the pile top should be measured and maintained for not less than 3 hours. The measuring time is at 15 minutes and 30 minutes respectively, and the residual settlement of the pile top should be measured every 30 minutes thereafter.

[0116] (5) When the static compressive load test reaches the state described below, the loading is terminated.

[0117] ① When loaded to a certain level of load, the measured pile settlement is greater than 5 times the settlement of the previous level of loading and the total settlement exceeds 40mm.

[0118] ② When loaded to a certain level of load, the measured settlement becomes twice the settlement at the previous level of loading, and the settlement does not reach the stable standard after 24 hours.

[0119] ③ The maximum load required by the design has been reached. When the engineering piles under test are used as anchor piles, the pull-out amount of the anchor piles has reached the allowable value.

[0120] ④ When the change of settlement is relatively slow compared with the change of load, the settlement reaches 60-80mm; if the bearing capacity of the pile end is not fully exerted, the cumulative settlement is loaded to more than 80mm.

[0121] S29, the data acquisition instrument 2-6 automatically records the relevant parameters required for calculating the cement soil-pile surrounding soil bond stress, and transmits the data to the data processing terminal 2-7 through the optical fiber conductor. The data processing terminal 2-7 automatically calculates the bond stress at each position of the static drilled root pile cement soil-pile surrounding soil interface. The calculation principle is mainly:

[0122] N i＝ πDEΔε / 4 (1)

[0123] Where: N i is the axial force (kN) at any section i of the measured structure, i.e. the cement soil-pile soil interface; E is the elastic modulus of the measured structure, i.e. the cement soil-pile soil interface; D is the diameter of the measured structure (mm); regarding the value of D: for the cement soil-pile soil interface, the diameter of the static drilled rooted pile is taken; Δε is the change in strain at the measured structure, i.e. the cement soil-pile soil interface, and the calculation of Δε is as follows:

[0124] Δε=Δλ / K (2)

[0125] Where: Δλ is the change in the central wavelength (nm); K is the strain sensitivity coefficient of the FBG strain sensor.

[0126] Substituting the axial force values ​​at various locations on the cement soil-pile soil interface into formula (3), the shear stress at various locations on the cement soil-pile soil interface is obtained:

[0127] τ i＝ (N i -N i-1 ) / πDΔL (3)

[0128] Where: N i is the axial force at a certain section i of the structure under test (kN); N i-1 is the axial force at the next section i-1 of the measured structure (kN); ΔL is the distance between section i and the next section i-1 (mm); τ i is the shear stress at the midpoint between the two sections, approximately considered to be the average shear stress (MPa).

[0129] The present invention innovates a system and method for testing the bond stress of the pile-soil contact surface of a static drilled rooted pile. By setting a fiber reinforcement force measuring cage in the static drilled rooted pile and directly arranging an interface strain sensor at the cement soil-pile surrounding soil interface, the purpose of directly measuring the strain of the above interface during the on-site vertical load test of the static drilled rooted pile is achieved, and the bond stress of the cement soil-pile surrounding soil interface is accurately obtained. The accuracy and test efficiency of the bond stress test of the cement soil-pile surrounding soil interface of the static drilled rooted pile are improved, and the vertical load transfer mechanism of the static drilled rooted pile is further revealed.

[0130] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A static drilled root pile soil contact surface bonding stress testing system, characterized in that: include: Loading reaction system, data acquisition system, fiber reinforcement force cage and analysis system; The loading reaction force system includes a load plate arranged above the static drill root pile body, which is used to provide the downward force required for the test; The fiber reinforcement force measuring cage comprises a hoop and fiber reinforcement, wherein the hoop and the fiber reinforcement are bound together, and the fiber reinforcement force measuring cage is arranged outside the static drilled root pile body to realize direct contact between the interface strain sensor and the cement soil-pile surrounding soil interface; The data acquisition system includes a load sensor and an interface strain sensor, wherein the load sensor is used to obtain the pressure provided by the loading reaction force system, and the interface strain sensor is arranged on the fiber reinforcement to obtain the strain of the cement soil-pile surrounding soil interface; The analysis system is connected in communication with the data acquisition system, and according to the obtained strain of the cement soil-pile surrounding soil interface, the cement soil-rock soil interface bonding stress is analyzed and calculated, thereby exploring the vertical load transfer mechanism of the static drilled rooted pile.

2. A static drilled root pile soil contact surface bonding stress testing system as claimed in claim 1, characterized in that: The loading reaction system also includes a main beam, a jack, a secondary beam and a pier; the main beam is arranged on the load sensor, and the load sensor is located at the centroid of the main beam; the jack is located between the load sensor and the load plate, the secondary beam is arranged above the pier and the main beam, and the piers are symmetrically arranged on both sides of the main beam.

3. A static drilled root pile soil contact surface bonding stress testing system as claimed in claim 2, characterized in that: The jack coincides with the central axis of the load sensor, and the resultant force center of the jack coincides with the centroid of the load plate.

4. A static drilled root pile soil contact surface bonding stress testing system as claimed in claim 2 or 3, characterized in that: A pile load is arranged above the secondary beam; the centroid of the load plate coincides with the centroid of the pile head of the static drill root pile.

5. A static drilled root pile soil contact surface bonding stress testing system as claimed in claim 1, characterized in that: The data acquisition system further comprises a displacement sensor, which is arranged above the load plate and is used to measure the settlement of the static drill rooted pile body.

6. A static drilled root pile soil contact surface bonding stress testing system as claimed in claim 5, characterized in that: The displacement sensors are arranged at the four corners of the load plate and fixed on the sensor brackets through magnetic support arms. The sensor brackets are arranged on both sides of the load plate along the direction of the main beam.

7. A static drilled root pile soil contact surface bonding stress testing system as claimed in claim 1, characterized in that: The interface strain sensor is fixed on two symmetrical sides of the fiber reinforcement force measuring cage.

8. A method for testing the bond stress of the soil contact surface of a statically drilled rooted pile, characterized in that: include: The hoop is arranged outside the static drilled root pile body, and the hoop is bundled with fiber reinforcement; installing an interface strain sensor on the fiber tendon; Start the loading reaction force system and load the static drilled root pile according to the preset load level to make it sink; Start the data acquisition system, obtain the pressure provided by the loading reaction system through the load sensor; obtain the strain of the cement soil-pile surrounding soil interface through the interface strain sensor; When the load data of the loading reaction system reaches the test planned load level, the loading is stopped and the load is continued for a period of time, and the next level of load is loaded after it stabilizes.

9. A method for testing the bond stress of the soil contact surface of a statically drilled rooted pile as claimed in claim 8, characterized in that: The axial force of a section at a certain position on the cement soil-soil around the pile interface is calculated based on the diameter of the static drilled rooted pile, the elastic modulus at the cement soil-soil around the pile interface, and the change in strain at the cement soil-soil around the pile interface; the shear stress at each position on the cement soil-soil around the pile interface is calculated based on the axial force values ​​at sections at different positions on the cement soil-soil around the pile interface, the distances between different sections, and the shear stress at the midpoints between different sections.

10. A method for testing the bond stress of the soil contact surface of a statically drilled rooted pile as claimed in claim 8, characterized in that: The static load test was carried out using the slow sustained load method.

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