CN111894051A - Reverse self-balancing model test device and test method for pile foundation bearing capacity - Google Patents
Reverse self-balancing model test device and test method for pile foundation bearing capacity Download PDFInfo
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- CN111894051A CN111894051A CN202010756992.6A CN202010756992A CN111894051A CN 111894051 A CN111894051 A CN 111894051A CN 202010756992 A CN202010756992 A CN 202010756992A CN 111894051 A CN111894051 A CN 111894051A
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D33/00—Testing foundations or foundation structures
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
- G01N3/04—Chucks
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
- G01N3/12—Pressure testing
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D2600/00—Miscellaneous
- E02D2600/10—Miscellaneous comprising sensor means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0075—Strain-stress relations or elastic constants
Abstract
The invention discloses a reverse self-balancing model test device for pile foundation bearing capacity and a test method thereof, wherein the device comprises a model box, model piles, a counter-force anchoring system, a loading system, a jack protection box and a measuring system, wherein a simulation rock stratum is poured at the bottom in the model box, a soil filling layer is arranged above the simulation rock stratum, the model piles comprise upper-section piles and lower-section piles, the upper-section piles and the lower-section piles are connected together through anchor cables and pile top counter-force end plates, the upper-section piles and the lower-section piles are all prefabricated hollow tubular piles, and the top and the bottom of the lower-section piles and the top and the bottom of the upper-section piles are all provided with end sealing; when the method is used for pouring, the lower section pile is buried in a simulated rock stratum, loads of the upper section pile and the lower section pile which move oppositely and oppositely are applied by using the two jacks, and the strain and the displacement of the model pile and the model box are measured by using the measuring system. The method can be used for researching the applicability and the bearing characteristic of the reverse self-balancing pile test method and can provide guidance for the design of a relevant model test in the future.
Description
Technical Field
The invention belongs to the field of pile foundation engineering, relates to a pile foundation bearing capacity testing technology, and particularly relates to a reverse self-balancing model testing device and a testing method for pile foundation bearing capacity.
Background
At present, in engineering, the method for determining the bearing capacity of a single pile mainly comprises a static load test method, a dynamic pile measurement method and a self-balancing pile test method. The dynamic pile measuring method is essentially based on the stress wave propagation principle, has high dynamic components and poor reliability of actual field test results, so that the method can only be used for auxiliary detection of static load test detection of the building pile foundation and is not suitable for bearing capacity detection of large-diameter cast-in-place piles. The static load test method can select a pile loading method and an anchor pile method according to field conditions, wherein the pile loading method is characterized in that a pile loading material is uniformly and stably placed on a ballast platform at one time, a jack between a pile top and a cross beam pushes the pile loading material in a pressurizing mode so as to transfer force to the pile top, and the anchor pile test method mainly uses a reaction frame formed by a main beam and a secondary beam to transfer the jacking force of the jack to an anchor pile so as to achieve the purpose of vertical compression test on the test pile. Although the static load test method is the most reliable method for the pile bearing capacity, the problems of long construction period, high test cost and the like exist, and the static load test method is particularly limited by factors such as construction sites, test pile tonnage and the like, so that the static load test method is difficult to meet the test of the bearing capacity of special sites and large-tonnage foundation piles. The self-balancing test utilizes the dead weight and the frictional resistance of the pile as the counter force of the pile end resistance, so that a very high test load can be obtained, the method has the advantages of time and labor saving, convenient test, strong adaptability and the like, but the stress state of the self-balancing test is different from that of the traditional static load test pile, one of the key problems still needs to be researched, namely, the determination of the conversion coefficient from the negative frictional resistance to the positive frictional resistance of the self-balancing test pile is realized, so that the method is still limited in the detection of the pile bearing capacity. In order to improve and perfect the defects of the self-balancing test, patent numbers CN105839678A and CN105735378A respectively disclose an improved pile foundation vertical bearing capacity test reverse self-balancing method and a test device, and a pile foundation vertical bearing capacity test reverse self-balancing method and a test device. In the method, a vertical loading device is added on a pile top on the basis of a self-balancing test, a load box of a pile body and a jack of the pile top are loaded respectively during pile testing, so that an upper-section pile and a lower-section pile generate opposite displacement and same-direction displacement respectively to obtain two load-displacement curves, and thus the vertical bearing capacity of the pile can be judged, the problem that positive and negative frictional resistance conversion is required in the self-balancing test is solved, and the vertical uplift resistance of the pile can be obtained simultaneously; for the latter, different from the traditional self-balancing test, the method has the advantages that the loading device is arranged on the pile top, the anchor cable anchored with the lower section of pile is tensioned through the pile top jack, the upper section of pile and the lower section of pile move in the same direction, a Q-s curve is obtained, and the vertical bearing capacity of the pile is further measured. Currently, as a brand-new pile foundation bearing capacity testing method, a reverse self-balancing test needs to be compared and corrected with a traditional static load test before being widely applied to engineering practice so as to judge the accuracy of the pile bearing capacity test in the pile foundation engineering by the reverse self-balancing test and the feasibility of a testing device. However, in the pile foundation engineering, a large amount of manpower, material resources and time are needed for carrying out the in-situ experiment of the pile, and the indoor model experiment is to establish a model with a similar rule to the actual pile according to the stress state of the pile in the actual engineering, so that experimental data and research demonstration can be provided for the theoretical research of the pile, the experimental cost is low, and the repeated experiment can be carried out for many times. However, no device and research related to the pile foundation bearing capacity reverse self-balancing model test is available at present. Therefore, it is necessary to design a method and a device for testing a reverse self-balancing model of pile bearing capacity to solve the above problems.
Disclosure of Invention
The invention aims to provide a reverse self-balancing model test device for bearing capacity of a pile foundation, which is used for solving the problem of a reverse self-balancing model test related to the bearing capacity of the pile foundation.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
the utility model provides a reverse self-balancing model test device of pile foundation bearing capacity which characterized in that: the device comprises a model box, model piles, a counter-force anchoring system, a loading system, a jack protection box and a measuring system, wherein a simulation rock stratum is poured at the bottom in the model box, a soil filling layer is filled above the simulation rock stratum, the model piles comprise upper-section piles and lower-section piles, the upper-section piles and the lower-section piles are prefabricated hollow tubular piles, and sealing plates are arranged at the tops of the lower-section piles and the tops and bottoms of the upper-section piles;
the loading system comprises a pile body jack and a pile jack, the pile body jack is arranged between the upper section pile bottom end sealing plate and the lower section pile top end sealing plate, and the pile jack is arranged on the upper section pile top end sealing plate;
the counter-force anchoring system comprises a pile top counter-force end plate and an anchor rope, wherein the pile top counter-force end plate is arranged above a pile top jack, the top of the anchor rope is anchored and connected with the pile top counter-force end plate, and the lower end of the anchor rope sequentially penetrates through an upper section of pile and three end sealing plates downwards and then is anchored in a lower section of pile;
the measuring system comprises a load measuring device and a displacement measuring device, wherein the load measuring device comprises an upper pressure sensor and a lower pressure sensor, the upper pressure sensor is arranged between the pile jack and the pile top counterforce end plate and is used for measuring the load applied by the pile jack, and the lower pressure sensor is arranged between the pile body jack and the end sealing plate at the top of the pile body jack and is used for measuring the load applied by the pile body jack; the two displacement measuring devices are respectively used for measuring the vertical displacement of the upper section pile and the lower section pile;
the jack protection box is arranged between the upper section pile and the lower section pile and used for wrapping and protecting the pile body jack and the lower pressure sensor.
Further, the lower end of the anchor cable is fixed on the pile body of the lower section of pile through a steel shaft bolt.
Further, the displacement measuring device comprises a displacement measuring instrument and a displacement rod, the top of the displacement rod is connected with the displacement measuring instrument, the displacement measuring instrument is fixed on a structural member or a supporting member, the lower end of the displacement rod is connected with the model pile, the displacement rod of one displacement measuring device freely penetrates through the pile top counter-force end plate and the end sealing plate at the top of the upper section pile and then is fixed on the end sealing plate at the bottom of the upper section pile, and the displacement rod of the other displacement measuring device freely penetrates through the pile top counter-force end plate, the end sealing plate at the top of the upper section pile and the end sealing plate at the bottom of the upper section pile and then is fixed on the end sealing plate.
Furthermore, the measuring system further comprises a plurality of strain gauges and a strain acquisition instrument, wherein the strain gauges are divided into model pile strain gauges and model box strain gauges, the model pile strain gauges are symmetrically attached to two sides of the upper-section pile and the lower-section pile, and the model box strain gauges are symmetrically attached to inner walls of two sides of the model box.
Furthermore, the measuring system also comprises a distributed optical fiber and an optical fiber acquisition instrument, wherein the distributed optical fiber is sequentially and continuously arranged on the model box, the upper section of pile and the lower section of pile.
Further, the distributed optical fibers are arranged in parallel to each other in the mold box to form U-shaped connections on two sides of the mold box.
Further, the upper section pile and the lower section pile are provided with spiral grooves for distributed optical fiber arrangement.
Furthermore, the jack protection box is a square or round box body, round holes matched with the upper section of piles and the lower section of piles are respectively formed in the top and the bottom of the box body, and a reserved hole for leading out a jack oil pipe and a measuring system signal line is formed in the side wall of the box body.
Furthermore, third round holes for steel shaft bolts to penetrate are formed in two sides of the lower section of pile, second round holes for pile body jack oil pipes and measuring system signal lines to be led out are formed in the side wall of the model box, first round holes which are coaxially penetrated corresponding to the third round holes are further formed in the side wall of the lower portion of the model box, and fourth round holes for temporarily fixing the upper section of pile are formed in the upper portion of the upper section of pile.
A test method of the pile foundation bearing capacity reverse self-balancing model test device is characterized by comprising the following steps:
step 3, temporarily fixing the lower section pile by enabling one steel bar to cross the first round hole at the lower part of the model box and the third round hole of the lower section pile, enabling the other steel bar to penetrate the fourth round hole at the upper part of the upper section pile, and supporting the lower section pile by a temporary support;
step 4, according to the object to be simulated, according to a certain similarity ratio, selecting a simulation material to be poured into a model box to reach the designed elevation of a simulation rock stratum, then maintaining, after the maintenance is finished, drawing out the steel bars in the third round hole and the first round hole, penetrating the steel shaft bolt through the third round hole of the lower-section pile, then arranging the anchor cable, and fixedly connecting the lower end of the anchor cable with the steel shaft bolt;
and 6, filling soil around the model pile in the model box to a set elevation, loading a pile body jack, fixing the position of a third end plate, sequentially installing a pile jack, an upper pressure sensor and a pile top counter-force end plate at the top of the upper-section pile, fixing the upper end of an anchor cable and the pile top counter-force end plate, installing the rest parts of the measuring system, and loading the pile jack, thereby completing the reverse self-balancing model test of the bearing capacity of the pile foundation.
The invention has the beneficial effects that:
the invention has the following remarkable advantages: (1) the pile foundation bearing capacity reverse self-balancing pile testing method is a new technology, and the device can provide a basis for design of a later-mentioned relevant model test and can provide direct guidance for a self-balancing model test. (2) By adopting the strain gauge and the distributed optical fiber for comprehensive utilization, more test data can be measured, and mutual verification can be carried out. (3) The device comprises a model box, a jack, a pressure sensor, a model pile and the like which can be repeatedly used.
Drawings
Fig. 1 is an elevation view of a pile foundation bearing capacity reverse self-balancing model test device.
FIG. 2 is a schematic view of a mold box, wherein FIG. 2(a) is a top view of the mold box and FIG. 2(b) is a schematic cross-sectional view of the mold box.
Fig. 3 is an elevation view of a model pile.
Fig. 4 is a first end cap plate configuration diagram.
Fig. 5 is a schematic structural diagram of the jack protection box of the invention.
Fig. 6 is a view showing the arrangement of the distributed optical fiber of the present invention in a dummy post (front view direction).
FIG. 7 is a view showing the arrangement of the distribution optical fiber of the present invention in a mold box (direction of cross-sectional view).
Fig. 8 is a view showing the arrangement of the strain gage of the present invention in a model pile and a model box.
Fig. 9 is a flowchart of a manufacturing and testing process of the pile foundation bearing capacity reverse self-balancing model testing apparatus of the present invention, where fig. 9(a) is a schematic diagram in step 4, fig. 9(b) is a schematic diagram in step 5, fig. 9(c) is a schematic diagram in step 6, fig. 9(d) is a schematic diagram of the back movement of the upper pile and the lower pile in step 7, and fig. 9(e) is a schematic diagram of the opposite movement of the upper pile and the lower pile in step 7.
Fig. 10 is a schematic view of a model pile load-displacement curve under the loading of a pile body jack in the embodiment of the invention.
Fig. 11 is a schematic view of a model pile load-displacement curve under the loading of a pile jack in the embodiment of the invention.
1-model box, 101-first round hole, 102-second round hole, 103-top opening outer edge, 104-bolt hole, 105-bolt, 106-nut, 2-model pile, 201-upper pile, 202-lower pile, 203-model pile reserved section, 204-spiral groove, 205-third round hole, 206-fourth round hole, 31-first end sealing plate, 32-second end sealing plate, 33-third end sealing plate, 34-pile top counter-force end plate, 41-first displacement rod, 42-second displacement rod, 5-anchor cable, 6-steel shaft bolt, 7-anchor cable sleeve, 81-pile top jack, 82-pile body jack, 91-upper pressure sensor, 92-lower pressure sensor, 10-filling soil, 11-simulated rock stratum, 12-iron plate, 13-strain gauge, 131-strain gauge wire, 14-distributed optical fiber, 15-displacement measuring instrument, 16-oil pipe, 17-pressure sensor wire, 18-jack protection box, 181-fifth round hole, 182-square hole, 19-displacement rod hole, 20-anchor cable hole, 21-temporary support, 22-first steel bar, 23-second steel bar and 24-camera.
Detailed Description
The embodiments of the present invention will be described in further detail with reference to the drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
In the description of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "connected" and "connected" are to be interpreted broadly, e.g., as being fixed or detachable or integrally connected; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The invention will be further described in detail with reference to the drawings and specific embodiments for better understanding, but they are not intended to limit the invention thereto.
As shown in fig. 1-9, the invention discloses a reverse self-balancing model test device for pile foundation bearing capacity, which mainly comprises a model box 1, a model pile 2, a loading system, a counter-force anchoring system, a jack protection box 18 and a measuring system.
As shown in fig. 1 and 2, the mold box 1 has a circular barrel structure without a cover and a bottom, and is used for containing model test materials, the two semicircular barrels are detachably spliced through bolts 105 and nuts 106, so that the model materials in the barrels can be conveniently unloaded and bedrocks can be removed after the test is completed, meanwhile, the stress of the mold box 1 with a cylindrical barrel structure is more uniform, and the mold box 1 can be recycled.
Preferably, a plurality of bolt holes 104 with equal distance are reserved on the outer edge 103 of the top opening of the model box 1, and the model box 1 is vertically butted with another model box 1 through bolts and nuts, so that the model box 1 can be suitable for model pile 2 tests with various lengths.
Preferably, the model box 1 is made of high-strength PVC transparent material, so that the mode of observing the pile-soil effect in all directions in the test process is facilitated.
The upper section pile 201, the lower section pile 202 and the end sealing plate of the model pile 2. As shown in fig. 1, the model pile 2 is formed by cutting a hollow pile into a pile body, and is divided into an upper pile section 201 and a lower pile section 202. A model pile reserved section 203 is defined between the upper pile section 201 and the lower pile section 202, and the jack protection box 18 is arranged at the model pile reserved section 203. Two communicated fourth round holes 206 are symmetrically reserved at a distance from the top opening of the upper section pile 201, and two communicated third round holes 205 are symmetrically reserved at proper positions at a distance from the top opening of the lower section pile 202, so that the upper section pile 201 can be supported conveniently in the later period by the aid of the steel bars supported on the temporary support 21 penetrating through the fourth round holes 206; the lower pile 202 is supported by passing steel bars through the first circular hole 101 of the model box 1 and the third circular hole 205 of the lower pile 202, and the third circular hole 205 is also a through hole for mounting the steel shaft bolt 6.
As shown in fig. 3, the surfaces of the upper pile section 201 and the lower pile section 202 are made into spiral grooves with a pitch h by machining, the size of the grooves is slightly larger than the size of the cross section of the optical fiber, so that the distributed optical fiber 14 can be conveniently wound and fixed in the grooves in the later period, the optical fiber is prevented from being broken during the test, and the arrangement length of the optical fiber on the surface of the model pile 2 can be lengthened by adopting a spiral form, so that more test data can be obtained.
As shown in fig. 1 and 4, the end-sealing plate of the model pile 2 is divided into a first end-sealing plate 31, a second end-sealing plate 32 and a third end-sealing plate 33, which are made of steel plates, the three end-sealing plates are basically the same in shape and size and are circular plates, and the three end-sealing plates are provided with anchor cable holes 20 for the anchor cables 5 to pass through and displacement rod holes 19 for the displacement rods to pass through. The diameter of end plate is the same with the external diameter of model pile 2 basically, and first end plate 31 passes through welded fastening at lower section stake 202 fore-set, and second end plate 32 passes through welded fastening at upper segment end opening, and third end plate 33 passes through welded fastening at upper segment stake 201 fore-set, will guarantee that the round hole of all end plates is vertical to be overlapped when fixed. Two sides of a proper position of the end sealing plate are symmetrically reserved with 2 anchor cable holes 20 and 2 displacement rod holes 19, and as shown in fig. 4, the top view of the first end sealing plate 31 is shown; the size of the hole is slightly larger than the cross-sectional dimensions of the anchor cable 5 and the displacement rod, so that the anchor cable 5 and the displacement rod can conveniently vertically penetrate through the hole, the lower end of the first displacement rod 41 is vertically welded on the displacement rod hole 19 of the first end sealing plate 31, the lower end of the second displacement rod 42 is vertically welded on the displacement rod hole 19 of the second end sealing plate 32, the first displacement rod 41 penetrates through the model box reserved section 203 between the upper pile and the lower pile, the displacement rod hole 19 of the second end sealing plate 32, the upper pile 201 and the pile top counter-force end plate 34 from bottom to top, the top of the first displacement rod 41 is connected with a displacement measuring instrument, and the displacement measuring instrument is installed on a structural member or a supporting member; the second displacement rod 42 penetrates through the upper-section pile 201 and the pile top reaction end plate 34 from bottom to top, and the top of the second displacement rod 42 is connected with another displacement measuring instrument which is arranged on a structural member or a supporting member. The first displacement rod 41 and the second displacement rod 42 are mostly thin round smooth steel bars with certain bending resistance.
As shown in fig. 1, the reaction force anchoring system is composed of a pile top reaction force end plate 34, an anchor cable 5 and a steel shaft bolt 6, wherein the lower end of the anchor cable 5 is connected with the steel shaft bolt 6 penetrating through a third circular hole 205 on a lower section pile 202 and anchored in the lower section pile 202, the anchor cable 5 penetrates through an anchor cable hole 20 of a first end sealing plate 31, a model box reserved section 203 between an upper section pile 202 and a lower section pile 202, an anchor cable hole 20 of a second end sealing plate 32, an upper section pile 201 and an anchor cable hole 20 of a third end sealing plate 33 from bottom to top, and finally the upper end of the anchor cable 5 is connected and anchored on the pile top reaction force end plate 34 through an anchor cable sleeve 7 to form the reaction.
As shown in fig. 1, the pile top reaction end plate 34 is substantially the same shape as the end cap plate, is slightly larger than the end cap plate, and is a circular plate or a square plate, and the anchor cable holes 20 and the displacement rod holes 19 of the pile top reaction end plate 34 are reserved at the same positions as the end cap plate so that the displacement rods and the anchor cables 5 can penetrate through the end cap plate.
The tensile strength of the anchor cable 5 is not less than 2 times of the maximum value of the bearing capacity of the upper pile 201 and the bearing capacity of the lower pile 202, and the anchor cable has sufficient safety factor. The anchor cables 5 are symmetrically arranged around the axis of the model pile 2.
The loading system mainly comprises: a jack, a jack protection box 18 and a fixed anchor cable 5.
The jacks are conventional hydraulic jacks and are divided into a pile jack 81 and a pile body jack 82 according to different action positions. Is connected with an oil pump outside the model box 1 through an oil pipe 16. The central axis of the jack and the model pile 2 are positioned on the same central axis, and the maximum value of the bearing capacity of the upper section pile 201 and the bearing capacity of the lower section pile 202 is not less than 2 times of the loading rated tonnage. Preferably, the jack is a small-size jack, and the requirement meets the space requirement of a model test. Preferably, the jack has the function of automatic return of return oil.
The pile jack 81 is a cylindrical jack, the plane size of the pile body jack 82 does not influence the passing of the anchor cable 5 and the displacement rod, and the pile jack 81 acts on the middle position of the third end sealing plate 33 at the top of the upper section pile 201. The pile jack 81 is connected with an oil pump outside the model box 1 through an oil pipe 16, and the upper pile 201 and the lower pile 202 move towards each other through pressurization and extension of the pile jack 81.
The pile body jack 82 is a cylindrical jack, the plane size of the pile body jack 82 does not influence the passing of the anchor cable 5 and the displacement rod, the pile body jack 82 acts on the reserved section 203 of the model box between the upper pile 202 and the lower pile 202, the reserved section is fixed to the central position of the first end sealing plate 31 at the top of the lower pile 202 through welding, and the upper pile 201 and the lower pile 202 move back to back through the pressurization and extension of the pile body jack 82.
The jack protection box 18 is coaxially arranged between the upper section pile 201 and the lower section pile 202, and is mainly used for protecting the pile body jack 82 and preventing model materials from influencing the jack, the passing optical fibers and the anchor cable 5. As shown in fig. 5, the jack protection box 18 has no bottom and a cover, is circular or square, has a plane size slightly larger than that of the model pile 2, has a hole reserved in a side wall, and is convenient for connecting the jack with the oil pipe 16 and leading out a strain gauge wire and a pressure sensor wire 17, and a fifth round hole 181 with the same outer diameter as that of the upper-section pile 201 is arranged at the top of the jack protection box 18.
Preferably, install small-size camera 24 on jack protection box 18 inner wall, camera 24 passes through wireless connection with the computer, and the convenience is observed pressure sensor and the contact condition of upper segment stake 201 and the stroke of pile body jack 82 etc. in the test process.
The measuring system mainly comprises a pressure sensor, a displacement measuring instrument, a strain gauge 13, an optical fiber, a pressure sensor acquisition instrument, a strain acquisition instrument and an optical fiber acquisition instrument.
The pressure sensor is a small pressure sensor, is divided into an upper pressure sensor 91 and a lower pressure sensor 92 according to different action positions, and is connected with an external acquisition instrument through a pressure sensor lead 17. The central axis of the pressure sensor is positioned on the same straight line with the central axis of the model pile 2 and the jack, and the measuring range of the pressure sensor is not less than 2 times of the maximum value of the bearing capacity of the upper pile 201 and the bearing capacity of the lower pile 202. Preferably, the pressure sensor has a certain offset load resistance and sufficient accuracy.
The upper pressure sensor 91 is fixed in the center of the pile jack 81, is in close contact with the pile jack reaction end plate 34, and measures the loading force of the pile jack 81 during loading.
The down pressure sensor 92 is fixed at the center of the top of the pile body jack 82, is in close contact with the second end sealing plate 32, and measures the loading force of the pile body jack 82 during loading.
Wherein the displacement measuring instrument is a dial indicator or a dial indicator; the displacement measuring instrument acts on the top end of the displacement rod and is in close contact with the displacement rod.
As shown in fig. 8, the strain gauge 13 is divided into a model pile strain gauge, a lower pile strain gauge and an upper pile strain gauge according to different positions. Is connected with the strain gauge through a lead. The strain gauges 13 are symmetrically adhered to the inner wall of the model box 1 and the two sides of the model pile 2 at a certain interval, so that the change condition of strain generated in the test process of the model box 1 and the model pile 2 is measured, whether the design of the plane size of the model box 1 is reasonable or not is judged, and the pile body axial force of the model pile 2 is obtained through calculation.
Preferably, the model box strain gauge and the upper section pile strain gauge are directly led out from the top opening of the model box 1 after being connected with the lead, the lower section pile strain gauge is connected with the lead and then sequentially led out from the hole of the protection box and the first round hole 101 of the model box 1, all the lead wires are connected with the strain acquisition instrument, and 1/4 bridges or half bridges are mostly adopted as the connection mode.
The optical fiber is a distributed optical fiber 14, as shown in fig. 6, a strain value can be measured every 5cm, the starting port of the distributed optical fiber 14 is connected with an optical fiber acquisition instrument, and the distributed optical fiber 14 is sequentially and continuously arranged on the model box 1, the upper section pile 201 and the lower section pile 202, so that the strain of the model pile 2 and the strain of the model box 1 can be simultaneously obtained.
The distributed optical fibers 14 are continuously arranged on the inner wall of the mold box 1 in a U-shaped manner at a certain interval as shown in fig. 7, the interval is to ensure that the optical fibers can be normally welded after the section is broken, and the U-shaped arrangement mode can measure more test data on the mold box 1; the optical fiber is arranged on the model pile 2 from top to bottom along the model pile 2 spiral groove 204.
Preferably, the optical fiber is reserved with a proper length between the outlet of the model box 1 and the inlet of the upper-section pile 201, and the reserved section 203 of the model pile is reserved with more optical fibers 10CM, so that the optical fiber is prevented from being broken when the upper-section pile 202 and the lower-section pile 202 are displaced in a reverse direction. The fiber is sealed with epoxy at the exit of the lower section stub 202.
A test method of a pile foundation bearing capacity reverse self-balancing model test device comprises the following steps:
step 3, as shown in fig. 3, temporarily fixing the lower pile 202 by making a first steel bar traverse a third round hole 205 at the lower part of the model box 1 and a first round hole 101 of the lower pile 202, making a second steel bar 23 pass through a fourth round hole 206 at the upper part of the upper pile 201, and supporting the second steel bar 23 by a temporary support 21, thereby temporarily fixing the position of the upper pile 201;
step 4, as shown in fig. 9(a), selecting similar simulation materials according to an object to be simulated, pouring the similar simulation materials in the model box 1 to the elevation of the simulated rock stratum 11 (generally lower than the height of the first round hole 101), then maintaining, after the maintenance is finished, drawing out the third round hole 205 and the first steel bar 22 in the first round hole 101, using the similar simulation materials as the steel shaft bolt 6 to penetrate through the third round hole 205 of the lower-section pile 202, then arranging the anchor cable 5, and fixedly connecting the lower end of the anchor cable 5 with the steel shaft bolt 6;
and 6, as shown in fig. 9(c), filling soil 10 around the model pile 2 in the model box 1 to a set elevation, installing the rest parts of the measuring system, and completing the preparation of the reverse self-balancing model test device for the bearing capacity of the pile foundation.
Step 7, as shown in fig. 9(d), the third end sealing plate 33 penetrates through the displacement rod and the anchor cable 5 to be fixed at the top opening of the upper pile 201, the displacement measuring instrument is tightly contacted with the first displacement rod 41, the lower end of the first displacement rod 41 is welded and fixed on the first end plate 31, the pile body jack 82 is loaded in a grading manner, the upper pile 201 and the lower pile 202 displace in opposite directions, the Q-s curve of the upper pile 202 and the lower pile 202 can be drawn through the load Q obtained by the lower pressure sensor 92 and the displacement s measured by the displacement measuring instrument, and the negative bearing capacity of the upper pile 201 is obtained
And positive bearing capacity of lower pile 202
Then the pile body jack 82 returns oil;
as shown in fig. 9(e), the pile jack 81 and the upper pressure sensor 91 are arranged, the pile top reaction end plate 34 is passed through the displacement rod and the anchor cable 5, laid on the top surface of the upper pressure sensor 91, the lower end of the second displacement rod 42 is welded and fixed on the second end plate 32, and the outlet end of the anchor cable 5 and the upper pressure sensor 91 are connectedThe thick round thread reinforcing steel bar is fixed, so that the fixed thick round thread reinforcing steel bar is in close contact with the top surface of the pile top counter-force end plate 34. Loading the pile jack 81 to make the upper pile 201 and the lower pile 202 generate opposite displacement, and measuring the positive bearing capacity of the upper pile 201 through the Q-s curve of the upper pile 202 and the lower pile 202
And the lower pile 202 bears the load
Finally, the vertical compression-resistant total ultimate bearing capacity of the model pile 2 is the sum of the positive bearing capacity of the upper pile 201 and the positive bearing capacity of the lower pile 202 plus the dead weight of the pile body, namely
As shown in fig. 10. The total vertical uplift bearing capacity of the model pile 2 is the sum of the negative bearing capacity of the upper pile 201 and the negative bearing capacity of the lower pile 202, namely the dead weight of the pile body is reduced
As shown in fig. 11.
The above embodiments are merely illustrative of the present invention and are not to be construed as limiting the invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that various combinations, modifications or equivalents may be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention, and the technical solution of the present invention is covered by the claims of the present invention.
Claims (10)
1. The utility model provides a reverse self-balancing model test device of pile foundation bearing capacity which characterized in that: the device comprises a model box, model piles, a counter-force anchoring system, a loading system, a jack protection box and a measuring system, wherein a simulation rock stratum is poured at the bottom in the model box, a soil filling layer is filled above the simulation rock stratum, the model piles comprise upper-section piles and lower-section piles, the upper-section piles and the lower-section piles are prefabricated hollow tubular piles, and sealing plates are arranged at the tops of the lower-section piles and the tops and bottoms of the upper-section piles;
the loading system comprises a pile body jack and a pile jack, the pile body jack is arranged between the upper section pile bottom end sealing plate and the lower section pile top end sealing plate, and the pile jack is arranged on the upper section pile top end sealing plate;
the counter-force anchoring system comprises a pile top counter-force end plate and an anchor rope, wherein the pile top counter-force end plate is arranged above a pile top jack, the top of the anchor rope is anchored and connected with the pile top counter-force end plate, and the lower end of the anchor rope sequentially penetrates through an upper section of pile and three end sealing plates downwards and then is anchored in a lower section of pile;
the measuring system comprises a load measuring device and a displacement measuring device, wherein the load measuring device comprises an upper pressure sensor and a lower pressure sensor, the upper pressure sensor is arranged between the pile jack and the pile top counterforce end plate and is used for measuring the load applied by the pile jack, and the lower pressure sensor is arranged between the pile body jack and the end sealing plate at the top of the pile body jack and is used for measuring the load applied by the pile body jack; the two displacement measuring devices are respectively used for measuring the vertical displacement of the upper section pile and the lower section pile;
the jack protection box is arranged between the upper section pile and the lower section pile and used for wrapping and protecting the pile body jack and the lower pressure sensor.
2. The pile foundation bearing capacity reverse self-balancing model test device of claim 1, wherein: and the lower end of the anchor cable is fixed on the pile body of the lower-section pile through a steel shaft bolt.
3. The pile foundation bearing capacity reverse self-balancing model test device of claim 2, characterized in that: the displacement measurement device comprises a displacement measurement instrument and a displacement rod, the top of the displacement rod is connected with the displacement measurement instrument, the displacement measurement instrument is fixed on a structural member or a supporting member, the lower end of the displacement rod is connected with the model pile, the displacement rod of one displacement measurement device freely penetrates through the pile top counter-force end plate and the end sealing plate at the top of the upper pile and then is fixed on the end sealing plate at the bottom of the upper pile, and the displacement rod of the other displacement measurement device freely penetrates through the pile top counter-force end plate, the end sealing plate at the top of the upper pile and the end sealing plate at the bottom of the upper pile and then is fixed on the end sealing plate at the.
4. The pile foundation bearing capacity reverse self-balancing model test device of claim 3, wherein: the measuring system further comprises a plurality of strain gauges and a strain acquisition instrument, wherein the strain gauges are divided into model pile strain gauges and model box strain gauges, the model pile strain gauges are symmetrically attached to two sides of the upper section pile and the lower section pile, and the model box strain gauges are symmetrically attached to inner walls of two sides of the model box.
5. The pile foundation bearing capacity reverse self-balancing model test device of claim 4, wherein: the measuring system further comprises a distributed optical fiber and an optical fiber acquisition instrument, wherein the distributed optical fiber is sequentially and continuously arranged on the model box, the upper section of pile and the lower section of pile.
6. The pile foundation bearing capacity reverse self-balancing model test device of claim 5, wherein: the distributed optical fibers are arranged in parallel to each other in the model box back and forth, and U-shaped connections are formed on two sides of the model box.
7. The pile foundation bearing capacity reverse self-balancing model test device of claim 5, wherein: and the upper section pile and the lower section pile are provided with spiral grooves for distributed optical fiber arrangement.
8. The pile foundation bearing capacity reverse self-balancing model test device of claim 1, wherein: the jack protection box is a square or round box body, round holes matched with the upper section pile and the lower section pile are respectively formed in the top and the bottom of the box body, and a reserved hole for leading out a pile body jack oil pipe and a measuring system signal wire is formed in the side wall of the box body.
9. The pile foundation bearing capacity reverse self-balancing model test device of claim 2, characterized in that: third round holes for steel shaft bolts to penetrate are formed in two sides of the lower section pile, second round holes for jacking jack oil pipes and leading out of measuring system signal lines are formed in the side wall of the model box, first round holes which correspond to the third round holes and coaxially penetrate through the side wall of the lower portion of the model box, and fourth round holes for temporarily fixing the upper section pile are formed in the upper portion of the upper section pile.
10. A testing method of the pile foundation bearing capacity reverse self-balancing model testing device of any one of claims 1-9, characterized by comprising the following steps:
step 1, placing a model box on a flat iron plate before testing, and then arranging a measuring system on the model box and a model pile;
step 2, defining a reserved section of the model pile between the upper section of the pile and the lower section of the pile, sequentially placing the first end sealing plate and the second end sealing plate into the reserved section of the model pile, and placing the first end sealing plate and the second end sealing plate into the middle part of the model box along with the upper section of the pile and the lower section of the pile;
step 3, temporarily fixing the lower section pile by enabling one steel bar to cross the first round hole at the lower part of the model box and the third round hole of the lower section pile, enabling the other steel bar to penetrate the fourth round hole at the upper part of the upper section pile, and supporting the lower section pile by a temporary support;
step 4, according to the object to be simulated, according to a certain similarity ratio, selecting a simulation material to be poured into a model box to a simulation rock stratum design elevation, then maintaining, after the maintenance is finished, drawing out the steel bars in the third round hole and the first round hole, penetrating the steel shaft bolt serving as the steel shaft bolt through the third round hole of the lower-section pile, then arranging an anchor cable, and fixedly connecting the lower end of the anchor cable with the steel shaft bolt;
step 5, adjusting the positions of the first end sealing plate and the second end sealing plate, sequentially placing a pile body jack and a lower pressure sensor between the first end sealing plate and the second end sealing plate, removing a temporary support, adjusting the position and the height of an upper section pile to enable the upper section pile to be supported on the lower pressure sensor, placing a jack protection box on a model pile reserved section and enabling the jack protection box to be supported on a simulated rock stratum, leading out an oil pipe of the pile body jack and a signal line of a measuring system through a second round hole in a model box, and removing the temporary support;
and 6, filling soil around the model pile in the model box to a set elevation, loading a pile body jack, fixing the position of a third end plate, sequentially installing a pile jack, an upper pressure sensor and a pile top counter-force end plate at the top of the upper-section pile, fixing the upper end of an anchor cable and the pile top counter-force end plate, installing the rest parts of the measuring system, and loading the pile jack, thereby completing the reverse self-balancing model test of the bearing capacity of the pile foundation.
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