CN111424734A

CN111424734A - Adjustable loading device for horizontal static load test of pile foundation and test method thereof

Info

Publication number: CN111424734A
Application number: CN202010257868.5A
Authority: CN
Inventors: 陈灿明; 苏晓栋; 何建新; 徐静文; 吴烨; 沈艳忱
Original assignee: Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources
Current assignee: Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources
Priority date: 2020-04-03
Filing date: 2020-04-03
Publication date: 2020-07-17

Abstract

The invention relates to an adjustable loading device for a horizontal static load test of a pile foundation, which comprises a loading system, a counter-force system and a measuring system, wherein the loading system is connected with the counter-force system; the loading system consists of a through jack, a bearing screw rod, a force transmission nut, a cross beam and two cross beam brackets; the beam is of a steel truss structure, and radial circular through holes are arranged in the middle of the beam at equal intervals; the counterforce system consists of a standard channel, two triangular counterforce frames and a counterforce frame fixing screw rod; the side surfaces of the two triangular reaction frames are oppositely and parallelly arranged, the two triangular reaction frames are fixed on the standard channel through reaction frame fixing screws, and the cross beam is placed on the cross beam bracket and is tightly leaned against the stress surface of the reaction frame; one end of the bearing screw rod sequentially penetrates through the force transmission nut, the through jack and the longitudinal through hole of the cross beam and is connected with the force sensor and the test pile, and the far pile side of the jack is connected with the force transmission nut; the force sensor is connected with a computer through a dynamic strain gauge. The invention can meet the test requirements of various pile foundations under the existing test foundation pit and channel conditions.

Description

Adjustable loading device for horizontal static load test of pile foundation and test method thereof

Technical Field

The invention relates to the field of pile foundation engineering test research, in particular to a pile foundation horizontal static load test loading and holding device with adjustable loading height and a test method thereof, which are suitable for any test pile foundation position, greatly improve the test efficiency and the test precision and reduce the test cost.

Background

With the high-speed development of the offshore wind power industry, the research and application of the ultra-large diameter single-pile foundation are more and more extensive. The offshore wind power single-pile foundation pile is large in diameter, the diameter of the existing mainstream pile reaches 3-9 m, and the difficulty and cost of field test research are extremely high, so that the research method mainly adopts an indoor physical model test with a certain scale.

The horizontal limit bearing capacity of the pile foundation is the key point of a physical model test of an offshore wind power single pile foundation, and the horizontal force applying conventional method is mainly realized by applying horizontal thrust to the pile top through a reaction frame and a hydraulic jack or applying horizontal tension through a steel wire rope, a weight and the like. When the loading adopts a mode that the jack directly applies horizontal thrust to the pile top, due to the limitation of the loading stroke of the jack, along with the increase of the elastic deformation and the plastic deformation of the pile top, the reaction frame and the traction system, the loading of a design load can not be carried out or the load is difficult to hold after the design load is reached; when horizontal tension is applied to the pile top through weights and the like, the loading capacity in the later loading period is large, the required loading time is overlong, the labor intensity is high, and the requirements of a pile foundation model test with a large scale cannot be met.

Based on the research result of 'the research result of influence of pile foundation parameters and load parameters on horizontal bearing performance of a winged pile' on basic scientific research service cost special capital subsidy project (Y418001) of Central level public welfare scientific research institute of Nanjing, the project test adopts the domestic largest pile foundation test scale (1: 25), the pile diameter of the test pile reaches 273mm, the test load is large (close to 80 kN), the loading height is high, the pile body displacement is large, the existing conventional test instrument is not applicable, and the maximum stroke of a piston of the conventional jack is far smaller than the horizontal displacement of the pile top under the condition that the thrust meets the requirement. If the deformation of a test pile, the deformation of a soil body, the deformation of a traction loading system, the deformation of a counter-force system and the like are comprehensively considered according to a conventional thought, theoretically, the test can be carried out by connecting 5-6 jacks in series, but on one hand, the number of equipment purchased in the test is obviously increased, on the other hand, because the jacks are of a long and thin structure, the length-diameter ratio of the 5-6 jacks is smaller when the jacks are connected in series for use, instability is very likely to occur when the loading capacity is larger, a huge safety risk exists, and the test requirements cannot be met.

In order to reduce the influence of soil layer parameters among different groups on test results during pile foundation tests, when the minimum distance between a test pile and a foundation pit wall and between the test pile and the test pile meet the standard requirements, the test piles are arranged in the foundation pit as much as possible, a multi-row staggered arrangement mode is generally adopted during arrangement, and the reaction frame position and loading equipment are adjusted according to the pile foundation position and the loading height requirement during loading. Meanwhile, in order to simulate various working conditions, the test piles are often repeatedly arranged and used, and test research is repeatedly carried out.

The pile body is generally provided with a large number of sensors such as a strain gauge, a soil pressure gauge, a displacement meter, an inclinometer and the like during large pile foundation tests, along with the richness and development of test means, the technology of externally applying distributed optical fibers on the inner side and the outer side of the pile body of a test pile to measure the stress strain of the whole pile body tends to be mature, the sensors such as the optical fibers and the like have high requirements on test conditions due to the fact that the sensors are precise and require smooth laying areas of the optical fibers without excessive bending, a loading point cannot be welded, additional pressure and lateral friction cannot be generated on the optical fibers during loading of loading facilities, necessary protection measures need to be taken when the test pile is repeatedly installed during test working condition conversion, and the integrity of precision equipment is ensured.

The patent with the application number of CN 201910109015.4 discloses a loading device for a pile foundation bearing capacity characteristic test under the effect of indoor combined load, and the loading device applies horizontal tension to a pile foundation through a steel wire rope, pulleys, weights and a stand column. The disadvantage is that the test bed is limited by the size of the weight and is only suitable for model tests with relatively small horizontal loads. Patent with application number CN201510454382.X discloses a one-dimensional horizontal cyclic load loading device and experimental method thereof, and this loading system passes through hydraulic servo actuator, computer control system, reaction frame, hydraulic jack, locating support etc. and comes to apply horizontal thrust to the pile foundation, and the shortcoming is that equipment cost is big, and moves the instrument equipment degree of difficulty great to different loading height and direction. Patent application No. CN 201410047563.6 discloses a model pile foundation with a horizontal power loading device, which applies load to the model through a loading spring, a loading shaft and a reciprocating driving mechanism. The model is mainly suitable for bidirectional dynamic loading of the pile foundation.

In order to meet the requirements of horizontal static load tests of large and complex pile foundations, a loading device and a testing method which aim at conditions of foundation pits and channels of tests of a conventional structural test hall, have different loading heights, large loading amount and loading stroke, can stably carry out load supplement and carry out single cycle or multi-cycle are urgently needed to be developed.

Disclosure of Invention

The invention aims to provide a loading method and a loading device for a pile foundation horizontal static load test, which aim at the conditions of a foundation pit and a channel of a test hall with a conventional structure and are suitable for different test pile positions and different loading heights, aiming at the defects of the prior art.

In order to achieve the aim, the invention provides an adjustable loading device for a horizontal static load test of a pile foundation, which can be suitable for pile foundation levels of different test pile positions and different loading heights.

The technical scheme for realizing the purpose of the invention is as follows: an adjustable loading device for a horizontal static load test of a pile foundation comprises a loading system, a counter-force system and a measuring system;

the loading system consists of a movable loading platform, a through jack, a bearing screw rod, a force transmission nut, a cross beam and two cross beam brackets; the cross beam is of a steel truss (formed by welding steel plates), and radial circular through holes are formed in the middle of the cross beam at equal intervals;

the counter force system consists of a standard channel, two triangular counter force frames and a counter force frame fixing screw rod;

the measuring system comprises a force sensor, a dynamic strain gauge and a computer;

the two triangular reaction frames are oppositely and parallelly arranged on the side surface and are fixed on a standard channel through reaction frame fixing screws, the two beam brackets are respectively arranged on the inner sides of the two triangular reaction frames, and the beam is placed on the beam brackets and is tightly leaned against the stress surface of the reaction frame; one end of the bearing screw rod sequentially penetrates through the force transmission nut, the through jack and the longitudinal through hole of the cross beam and is connected with the force sensor and the test pile, and the far pile side of the jack is connected with the force transmission nut; the force sensor is connected with a computer through a dynamic strain gauge; the through-center jack oil pump is placed on the movable loading platform.

In the technical scheme, the cross beam is of a steel truss structure and is used for transmitting the load borne by the load holding frame to the reaction frame. The length of the cross beam is larger than the distance between the reaction frames, generally not smaller than 2.50m, the middle part is provided with round through long holes at equal intervals, and the diameter of the round through long holes is slightly larger than the hollow steel pipe of the load holding frame. The loading position (vertical to the channel) can be adjusted arbitrarily by selecting proper beam holes and relative positions of the beam and the two reaction frames. And a plurality of test piles are determined according to the test purpose and the size of the foundation pit. The minimum distance between the test pile and the foundation pit wall and between the test pile and the test pile should meet the standard requirements. When a plurality of rows of test piles are arranged, the front row of test piles and the rear row of test piles are not on the same loading line (the direction of tension application), and the relative dislocation of the outer walls of the front row of test piles and the rear row of test piles on the loading axis is larger than 10 cm.

As a further improvement of the invention, a load holding frame is also arranged between the center-penetrating jack and the cross beam, the load holding frame is of a steel hollow frame structure and consists of a front steel frame, a rear steel frame, a load holding nut and a stand column, holes are formed in the middle of the front steel plate and the rear steel plate, the rear steel frame is provided with a hollow steel guide pipe, the length of the steel guide pipe is the same as the width of the cross beam, and the load holding frame can be stabilized after the steel guide pipe extends into the loading cross beam; the hollow length of the steel frame is 50mm greater than the maximum stroke of the center-penetrating jack; the diameter of the front hole and the rear hole of the steel frame is generally slightly larger than that of the bearing screw rod. When the bearing screw rod is installed, the load holding nut needs to be arranged in the load holding frame.

As a further improvement of the invention, the technical scheme also comprises a traction system, wherein the traction system comprises a lifting ring, a hanging strip (which can be combined by the same specification or different specifications), a turnbuckle bracket, an arc shackle and a soft contact cushion layer. The lifting ring is connected with the force sensor on one side of the bearing screw rod, and then the lifting ring is connected with the turnbuckle, the turnbuckle and the test pile through the hanging strip. The traction system can adapt to different test pile loading distances after being combined by a reasonable hanging strip. Preferably, in the above technical solution, the material, diameter and pitch of the bearing screw are determined according to the maximum load capacity and the connection mode of the force sensor, and a market-shaped product is preferably selected. For the test with the pile diameter less than 273mm and the load less than 80kN, a screw rod of carbon steel grade 12.9, the diameter of 24mm and the screw pitch of 3mm (standard screw pitch) can be selected. The length of the bearing screw rod is comprehensively determined according to the maximum horizontal displacement, the sling combination, the length of a jack, the height of a steel beam and the like which may occur in the loading process, the maximum horizontal movable amount of the traction system in the test is larger than the telescopic amount of the traction system in the maximum loading process and the horizontal displacement of a pile foundation (including a soil body), and the recommended length is 1.5-2.0 m.

Preferably, in the above technical solution, the two beam brackets are steel truss structures and are all disposed inside the reaction frame. There are three steel layer boards on every beam bracket, be fixed in the supporting leg through the buckle on, the buckle high interval is 50mm on the supporting leg. Firstly, an upper layer steel supporting plate is installed according to a designed loading height, the height of a cross beam is slightly lower than the height required by the design, and finally the height of the cross beam is accurately adjusted through standard gaskets of 10mm, 5mm, 2mm and 1mm until the design requirement is met, so that the loading height can be adjusted randomly; the middle parts of the three steel supporting plates are connected through certain rigidity, so that the weight of the cross beam can be uniformly transmitted to the supporting legs.

Preferably, in the above technical solution, the sling is generally used, and the sling with a length of 1m, 2m, 3m, 4m and 6m and a bearing capacity (dynamic) of 20kN or 40kN is recommended to be used for bifilar use. And during specific use, reasonable combination and determination are carried out according to the maximum loading value and the loading distance.

Preferably, in the technical scheme, the turnbuckle bracket is a light structure with the height from the top surface adjustable to the loading elevation and the top width similar to the length of the turnbuckle, is placed below the turnbuckle, and can eliminate the influence of the self weight of the turnbuckle on the direction and the load magnitude of the traction system when no load and small load are loaded.

Preferably, in the above technical scheme, the soft contact cushion layer is a protection cushion layer formed by single or multiple groups of soft elastic materials of a middle elastic mold and low-friction-coefficient plastic sheets through superposition, and is placed between the sling and the test pile to eliminate friction and extrusion between the distributed optical fibers and the sensor connecting wires arranged on the surface of the test pile due to slippage when the sling is balanced in the loading process, so that not only the optical fibers and the sensor connecting wires are protected, but also the additional stress on the distributed optical fibers is reduced, and the accuracy of test data is ensured.

The reaction frame, the channel, the lifting ring, the bow shackle and the turnbuckle are the same as those in the prior art, wherein the parameters of the lifting ring, the turnbuckle and the bow shackle are selected to be consistent with those of the bearing screw rod, and the reaction frame and the channel can be selected to meet the requirement of allowable bearing capacity (dynamic).

The invention also aims to provide a pile foundation single-cycle and multi-cycle static load test method capable of adjusting the loading height for test piles at any position, which comprises the following steps:

(1) presetting a test pile sensor and embedding a test pile: firstly, mounting and sticking corresponding sensors on all test piles, wherein the sensors comprise strain gauges, soil pressure gauges, displacement meters, inclinometers, distributed optical fiber sensors and the like. And then, burying a plurality of test piles in the foundation pit according to the design position, wherein the distribution of the test piles fully considers the affected range of the soil body of the pile foundation under the action of horizontal load. After the test pile is positioned, soil is filled in the foundation pit in a layered mode, water is discharged to a designed height when a marine or overwater structure is simulated, and the test is carried out after standing and solidifying for a certain period of time. When the soil body is filled, the test pile is temporarily fixed at multiple points, and the sensor takes protection measures to ensure that the position of the test pile is accurate and the sensor is intact after the soil body is filled; the thickness of the layering and the soil layer compacting method are the same in the soil filling process, and the lower soil body is guaranteed not to be scratched after the layering filling is completed.

(2) And the test pile body sensor is connected with the measuring system.

(3) Installing a loading system: firstly, a channel is selected according to the position of a test pile and a fixed reaction frame is installed, a channel is arranged between the two reaction frames at an interval, and the two reaction frames are kept on the same plane. And then selecting a proper combination of the buckle height on the supporting leg of the beam bracket and the standard gasket according to the loading height of the test pile, assembling the beam bracket and the standard gasket and placing the inner side of the reaction frame. And hoisting the cross beam on the cross beam bracket and abutting against one side of the reaction frame, and adjusting the position of the cross beam to enable the connecting line of the middle hole of the cross beam and the test pile to be consistent with the loading direction. The load holding frame is inserted into the bearing screw rod and then is integrally inserted into the middle hole of the cross beam, so that the guide steel pipe of the load holding frame is firmly fixed. And then inserting the penetrating jack into the bearing screw rod and clamping the penetrating jack into the circular groove of the load holding frame, screwing a force transmission nut into one side of the penetrating jack of the bearing screw rod to fix and clamp the penetrating jack, and then connecting the jack with an oil pump and placing the jack on a movable loading platform. And finally, installing a force sensor on the other side of the bearing screw rod, connecting the force sensor with a computer through a dynamic strain gauge, and displaying a load numerical value in real time.

(4) The loading system, the traction system and the test pile are connected: firstly, the hanging ring is connected with the force sensor, then the hanging strip penetrates through the hanging ring to form a double-strand hanging strip, and then the double-strand hanging strip is connected with a circular ring of the turnbuckle through the shackle, and at the moment, the turnbuckle is required to be kept at the maximum extension position in the initial state. Then another hanging strip is taken to bypass the back of the test pile and a soft contact cushion layer of the distributed optical fiber sensor (the hanging strip is positioned at the expected loading height and is temporarily fixed), a double strand is formed and then is connected with a C-shaped hook of the turn buckle, the turn buckle is properly tightened as required, and the turn buckle is supported by a turn buckle bracket until the traction system is tensioned to a certain extent, but the hanging strips at the two sides of the turn buckle are slightly loosened, and the tension is zero.

(5) Loading, loading and unloading:

1) loading and carrying: according to different test methods, the single-cycle test adopts grading step-by-step loading, and the multi-cycle test adopts grading one-time loading.

The primary loading process comprises the following steps: firstly, a load holding nut is screwed to one side of the rear steel framework, a valve of a jack is closed, oil pressure is added, a piston of a penetrating jack pushes a force transmission nut to drive a bearing screw rod to move towards the far pile side, and load is transmitted to a traction device from a loading device and finally transmitted to a test pile. The load value displayed by the computer and the position of the load holding nut should be paid attention to at any time in the loading process. The loading process may be as follows (the loading should be stopped and the next operation should be performed when the following conditions are met):

① the computer displays that the load value reaches the design load value, stops loading, and screws the holding nut to the rear steel frame side, thus the holding nut can hold the load;

② the computer shows that the load value does not reach the experimental design load value, when the load holding nut is about to reach the front steel frame, the load holding nut should be screwed to the rear steel frame side in time until the load is loaded to the design load;

③ when the piston of the jack reaches the maximum stroke but the computer shows that the load value does not reach the design load value, stopping loading, screwing the holding nut to the side of the rear steel frame for holding, loosening the oil valve of the jack to make the piston of the jack fall back to the initial position, screwing the front force nut of the jack to the piston of the jack and continuing loading until the design load.

④ in the process of loading, because the soil body plastic deformation, the horizontal displacement of the test pile will increase gradually along with the time of loading, resulting in the gradual decrease of the actual horizontal load, therefore, the load value displayed by the computer should be observed at any time in the process of loading, and the loading compensation operation is carried out in time.

2) Unloading:

the unloading process is the reverse operation of the loading process. According to different test methods, the single-cycle test adopts graded step-by-step unloading, and the multi-cycle test adopts graded one-time unloading. When the load is loaded to the designed load, the piston of the penetrating jack reaches a certain stroke, the bearing screw rod has large displacement in the direction away from the test pile, and the load can be unloaded to the next level of load or zero only by executing multiple unloading operations. One complete unloading operation is as follows:

① the load-holding nut is screwed to the side of the front steel frame, then the through jack oil valve is loosened slowly, the piston of the through jack falls back to 5-10 mm close to the initial position, the jack oil valve is closed, this is an unloading process, but the load is not unloaded to the next level load or zero at this time, and the unloading operation needs to be continued.

② adjusting the position of the load nut to the position of the rear steel frame for load, then slowly loosening the jack oil valve, and separating the force transmission nut from the jack piston.

③ the force transmission nut is screwed to the position slightly less than the maximum stroke of the jack piston, the jack oil valve is closed to start loading, when the jack piston approaches the force transmission nut, the load is slowly loaded until the load holding nut can be screwed.

④, repeating the unloading operations ① - ③ until the display shows that the load value is the next level of load or zero, and then completing the unloading.

(6) And carrying out graded loading and carrying to a designed load according to a load preset in the test, and then carrying out graded unloading, or repeating the loading, carrying and unloading operations according to the loading cycle times, and recording test data.

(7) The test was completed.

The beneficial effects are that can satisfy the test requirement of multiple different pile foundations under current experimental foundation ditch and channel condition:

(1) the horizontal load test of the pile foundation at any position can be realized by selecting the appropriate channel, the positions of the through holes arranged at intervals in the stressed cross beam and the relative positions of the cross beam and the reaction frame for adjustment.

(2) The horizontal load test of the long-distance test pile foundation can be realized by adjusting the combination of the hanging strips and combining the combined configuration of the turnbuckle and the long-length bearing screw rod.

(3) The height of accessible adjustment beam bracket realizes the experimental requirement of different pile foundation loading heights.

(4) The problem that the horizontal displacement of a pile foundation is far larger than the maximum stroke of a jack and the loading cannot be carried out is solved through the combination of systems such as a large-length bearing screw rod, a turnbuckle screw and a load holding frame, and the problem of load stability in the loading and unloading conversion process of the jack when the stroke is expanded in the loading process.

(5) The soft contact cushion layer is arranged and drawn by the hanging strip, so that the soft connection between the drawing device and the test pile in the loading process is realized, the damage of operations such as welding steel buckles and the like on a loading point in a conventional method to a precise sensor and a sensor connecting line in a pile body loading area is prevented, and the reliability of test data is ensured.

Drawings

FIG. 1 is an overall side view of the present invention;

FIG. 2 is a detailed view of the loading screw and the loading frame of the present invention;

FIG. 3 is a top view of the draft gear of the present invention;

FIG. 4 is a schematic view of a connection structure of a carrying screw and a hanging strip of the traction system;

FIG. 5 is a schematic view of the connection structure of the bolts of the flower basket and the hanging strip of the traction system.

Wherein: the device comprises a bearing screw 1, a piercing jack 2, a force transmission nut 3, a load holding frame 4, a crossbeam 5, an adjustable crossbeam bracket 6, a reaction frame 7, a force sensor 8, a standard channel 9, a movable loading platform 10, a reaction frame fixing screw 11, a lifting ring 12, a lifting belt 13, a basket screw 14, a basket screw bracket 15, an arch shackle 16, a soft contact cushion layer 17, a test pile 18, an oil pump 21, a front steel frame 41, a rear steel frame 42, a hollow steel guide pipe 43, a load holding nut 44, a steel supporting plate 61, a supporting leg 62, a buckle 63, a gasket 64, a C-shaped hook 141 and a circular ring 142.

Detailed Description

The invention is described in further detail below with reference to the following figures and embodiments:

the loading and holding device for the pile foundation horizontal static load test suitable for different test pile positions and different loading heights as shown in fig. 1, fig. 2 and fig. 3 comprises a loading system, a traction system and a measuring system.

The loading system comprises a bearing screw rod 1, a through jack 2, an oil pump 21, a force transmission nut 3, a load holding frame 4, a cross beam 5, an adjustable cross beam bracket 6, a reaction frame 7, a force sensor 8, a standard channel 9, a movable loading platform 10 and a reaction frame fixing screw rod 11. The beam 5 is placed on the adjustable beam bracket 6 and is abutted against the side of the reaction frame 7, and the reaction frame 7 is tightly connected with the channel 9 through a reaction frame fixing screw rod 11. After the bearing screw rod 1 sequentially passes through the through jack 2 and the load holding frame 4 (containing a load holding nut 44), the notch of the load holding frame 4 and the bearing screw rod 1 are inserted into the orifice of the cross beam 5 and then connected with the force sensor 8, and the far pile side of the jack 2 is fixed through the force transmission nut 3. The force sensor 8 is connected with a computer through a dynamic strain gauge to observe a load value in real time. The oil pump 21 of the feed-through jack 2 is placed on the movable loading table 10.

The traction system comprises a lifting ring 12, a hanging strip 13 (which can be combined by the same specification or different specifications), a turnbuckle 14, a turnbuckle 15, an arc shackle 16 and a soft contact cushion 17. As shown in fig. 4, the screw side of the hanging ring 12 is connected with the force sensor 8, and then the hanging ring 12 and the turnbuckle 14, the turnbuckle 14 and the test pile 18 are connected through the hanging strip 13. The traction system can be adapted to different loading distances of the test pile 18 after being combined by a reasonable hanging strip.

And a plurality of test piles 18 are determined according to test requirements and the size of the foundation pit. The minimum distance between the test pile 18 and the foundation pit wall and between the test pile and the test pile should meet the specification requirements. The two rows of test piles are not on the same loading line (in the direction of tension application), and the relative dislocation of the outer walls of the two rows of test piles on the loading axis is larger than 10 cm.

The material, the diameter and the screw pitch of the bearing screw rod 1 are determined according to the maximum loading capacity and the connection mode of the force sensor 8, and a market shaping product is preferentially selected. For the test with the pile diameter less than 273mm and the load less than 80kN, a screw rod of carbon steel grade 12.9, the diameter of 24mm and the screw pitch of 3mm (standard screw pitch) can be selected. The length of the bearing screw rod is comprehensively determined according to the maximum horizontal displacement, the sling combination, the length of a jack, the height of a steel beam and the like which may occur in the loading process, the maximum horizontal movable amount of the traction system in the test is larger than the telescopic amount of the traction system in the maximum loading process and the horizontal displacement of a pile foundation (including a soil body), and the recommended length is 1.5-2.0 m.

As shown in fig. 2, the load holding frame 4 is a hollow steel frame structure, and is composed of a front steel frame 41 and a rear steel frame 42, the middle of the steel frames are provided with holes, the rear steel frame is provided with a hollow steel conduit 43, the length of the steel conduit 43 is the same as the width of the beam 5, and the load holding frame 4 can be stable after the steel conduit 43 extends into the loading beam 5; the length between the front steel frame 41 and the rear steel frame 42 is greater than the maximum stroke of the center-penetrating jack by 50 mm; the diameters of the front hole and the rear hole of the steel frame are generally larger than the diameter of the bearing screw rod. When the bearing screw rod 1 is installed, the load holding nut 44 is required to be arranged in the load holding frame.

As shown in fig. 1 and 3, the cross beam 5 is a steel truss structure for transmitting the load borne by the load bearing frame 4 to the reaction frame 7. The length of the beam 5 is larger than the distance between the two reaction frames 7, generally not smaller than 2.50m, the middle part is provided with round through long holes 51 at equal intervals, and the diameter of the round through long holes is slightly larger than the hollow steel pipe 43 of the load holding frame 4. The loading position (vertical to the channel) can be adjusted arbitrarily by selecting appropriate beam holes, adjusting the relative positions of the beam and the two reaction frames.

The beam brackets 6 are of steel truss structures, and are arranged on the inner sides of the reaction frames 7. Three steel supporting plates 61 are fixed on the supporting legs 62 through buckles on each beam bracket, and the height intervals of the buckles 63 on the supporting legs 62 are 50 mm. Firstly, an upper layer steel supporting plate 61 is installed according to a designed loading height, the height of a cross beam is slightly lower than the height required by the design, and finally the height of the cross beam is adjusted through standard gaskets 64 of 10mm, 5mm, 2mm and 1mm until the design requirement is met, so that the loading height can be adjusted randomly; the middle parts of the three steel supporting plates 61 are connected through certain rigidity, so that the weight of the cross beam 5 can be uniformly transmitted to the supporting legs.

The straps 13 are preferably commonly used straps allowing a load bearing capacity (dynamic) of 20kN or 40kN and lengths of 1m, 2m, 3m, 4m and 6m, for bifilar use. And during specific use, reasonable combination determination is carried out according to the highest loading value and the loading distance.

The turnbuckle bracket 15 is a light structure with adjustable top height to loading elevation and top width similar to the length of the turnbuckle 14, is placed below the turnbuckle 14, and can eliminate the influence of the self weight of the turnbuckle 14 on the direction and load magnitude of the traction system when no load and little load are loaded.

The soft contact cushion layer 17 is a protective cushion layer formed by single or multiple groups of soft elastic materials of a middle elastic mold and plastic sheets with low friction coefficients through superposition, is placed between the hanging strip 13 and the test pile 18, and is used for reducing friction and extrusion between distributed optical fibers and data lines arranged on the surface of the test pile 18 when the hanging strip 13 is in force balance in the loading process, not only protecting the optical fibers and sensor connecting lines under the action of large load, but also reducing additional stress on the distributed optical fibers and ensuring the accuracy of test data.

The reaction frame 7, the channel 9, the hanging ring 12, the bow shackle 16 and the turnbuckle 14 are the same as those in the prior art, wherein the parameters of the hanging ring 12, the turnbuckle 14 and the bow shackle 16 are selected to be consistent with those of the bearing screw rod 1, and the reaction frame 7 and the channel 9 are selected to meet the bearing capacity requirement.

Based on the above-mentioned pull-type pile foundation horizontal static load test loading and holding device with different loading heights, a schematic diagram is used to describe in detail the single-cycle and multi-cycle horizontal static load test method of pile foundations with different loading heights, for convenience of description, the schematic diagram showing the structure of the device is not enlarged locally according to a general scale, and should not be taken as a limitation of the present invention, and in addition, in the actual manufacturing, three-dimensional space dimensions of length, width and height should be included.

The horizontal static load test method of the single-cycle and multi-cycle pile foundations with different loading heights is based on a horizontal loading and carrying device and specifically comprises the following steps:

1) presetting a test pile sensor and burying a test pile 18: firstly, all the test piles 18 are provided with corresponding sensors, including strain gauges, soil pressure gauges, displacement gauge inclinometers, distributed optical fiber sensors and the like. And then, burying a plurality of test piles 18 in the foundation pit according to the design position, wherein the distribution of the test piles 18 fully considers the influence range of the soil body of the pile foundation under the action of horizontal load. And after the test pile is positioned, filling soil bodies and draining water (simulating a marine or overwater structure) in the foundation pit in a layered mode, standing and consolidating for a certain period of time, and then carrying out a test. When the soil body is filled, the test pile is temporarily fixed at multiple points, and the sensor takes protective measures to ensure that the position of the test pile is accurate and the sensor is intact after the soil body is filled; the thickness of the layered soil body and the soil layer compacting method are the same in the soil body filling process, and the lower soil body is not disturbed after the layered filling is finished.

(2) And the test pile body sensor is connected with the measuring instrument.

(3) Installing a loading system: firstly, a channel 9 is selected according to the position of a test pile, and a reaction frame 7 is installed and fixed, wherein one channel 9 is arranged between the two reaction frames 7, and the two reaction frames 7 are kept at the same position. The top pallet 61 height of the beam bracket 6 is then calculated from the test pile 18 loading height (top pallet height = test pile loading height-beam height/2), and the beam bracket 6, top pallet 61 and standard shim 64 are installed and placed according to the calculation. And (3) hoisting the cross beam 5 on the cross beam bracket 6 and abutting against one side of the reaction frame 7, and adjusting the position of the cross beam 5 to enable the connecting line of the middle hole 51 of the cross beam and the test pile to be consistent with the loading direction. The bearing screw 1 is inserted into the load holding frame 4 and then is integrally inserted into the beam middle hole 51, so that the guide steel pipe 43 of the load holding frame 4 is firmly fixed. And then, inserting the bearing screw rod 1 into the through jack 2 and clamping the bearing screw rod into the circular groove of the load holding frame 4, screwing the force transmission nut 3 into one side of the through jack 2 of the bearing screw rod 1 to fix and clamp the through jack 2, and then placing the oil pump 21 on the movable loading platform 10. And finally, connecting a force sensor 8 to the other side of the bearing screw rod 1, connecting the force sensor to a computer through a dynamic strain gauge, and displaying a load numerical value in real time.

(4) The loading system, the traction system and the test pile 18 are connected: firstly, the hanging ring 12 is connected with the force sensor 8, then the hanging strip 13 is taken to penetrate through the hanging ring 12 to form a double-strand hanging strip, and then the double-strand hanging strip is connected with the circular ring 142 of the turnbuckle 14 through the shackle 16, and at the moment, the turnbuckle 14 needs to be kept at the maximum extension position in the initial state. Then another sling 13 is taken to bypass the back of the test pile 18 and a soft contact cushion layer 17 protection device of the distributed optical fiber sensor (the sling is positioned at the expected loading height and is temporarily fixed), a double strand is formed and then is connected with a C-shaped hook 141 of the turnbuckle, the turnbuckle 14 is properly tightened according to the requirement, the turnbuckle 14 is held up by the turnbuckle bracket 15 until the traction system is tensioned to a certain extent, but the slings 13 at two sides of the turnbuckle 14 are slightly loosened, and the tension is zero. The connection of the two ends of the turnbuckle 14 to the strap 13 is shown in fig. 5.

(5) Loading, loading and unloading:

The primary loading process comprises the following steps: firstly, a load holding nut 44 is screwed to one side of the rear steel framework 42, a valve of the jack 2 is closed, oil pressure is added, a piston of the penetrating jack 2 pushes a force transmission nut 3 to drive the bearing screw rod 1 to move towards the far pile side, and load is transmitted from a loading device to a traction device and finally transmitted to the test pile 18. The load value displayed by the computer and the position of the load holding nut 44 should be paid attention to at any time during the loading process. The loading process may be as follows (the loading should be stopped and the next operation should be performed when the following conditions are met):

① the computer displays that the loading is stopped when the load value reaches the design load value, the load holding nut 44 is screwed to return to the rear steel frame 42 side, and the load holding is realized;

② computer shows that the load value does not reach the experimental design load value, when the load holding nut 44 is about to reach the front steel frame 41, the load holding nut 44 should be screwed to the rear steel frame side 42 in time until the load is loaded to the design load;

③ when the piston of the center-penetrating jack 2 reaches the maximum stroke but the computer shows that the load value does not reach the experimental design load value, stopping loading, screwing the load holding nut 44 to the side of the rear steel frame 42 for holding, loosening the oil valve of the center-penetrating jack 2 to make the piston of the jack 2 fall back to the initial position, screwing the front force transmission nut 3 of the jack to the piston of the jack 2 and continuing loading until the design load.

2) Unloading:

the unloading process is the reverse operation of the loading process. According to different test methods, the single-cycle test adopts graded step-by-step unloading, and the multi-cycle test adopts graded one-time unloading. When the load is loaded to the design load, the piston of the penetrating jack 2 reaches a certain stroke, the bearing screw rod 1 has large displacement in the direction away from the test pile 18, and the load can be unloaded to the next level of load or zero only by carrying out multiple unloading operations. One complete unloading operation is as follows:

firstly screwing the load-holding nut 44 to the side of the front steel frame 41, then slowly loosening the oil valve of the penetrating jack 2 to enable the piston of the penetrating jack 2 to fall back to be close to the initial position by 5-10 mm, and closing the oil valve of the penetrating jack 2, namely, an unloading process, but at the moment, the load is not unloaded to the next stage of load or zero, and the unloading operation needs to be continued.

② adjusting the position of the load nut 44 to the position of the rear steel frame 42 for load, then slowly releasing the oil valve of the jack 2, and separating the force transmission nut 3 from the piston of the jack 2.

③ the force transmission nut 3 is screwed outwards to a position slightly less than the maximum stroke of the jack 2 piston, the oil valve of the jack 2 is closed to start loading, when the jack 2 piston approaches the force transmission nut 3, the load is slowly loaded until the load holding nut 44 can be screwed.

(7) The test was completed.

Finally, it should be noted that the above-mentioned list is only a specific embodiment of the present invention. It is obvious that the present invention is not limited to the above embodiments, but many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.

Claims

1. An adjustable loading device for a horizontal static load test of a pile foundation comprises a loading system, a counter-force system and a measuring system; the method is characterized in that:

the loading system consists of a movable loading platform (10), a through jack (2), a bearing screw (1), force transmission nuts (3) and (3), a cross beam (5) and two cross beam (5) brackets (6); the cross beam (5) is of a steel truss structure, and radial circular through holes are formed in the middle of the cross beam (5) at equal intervals;

the counter force system consists of a standard channel (9), two triangular counter force frames (7) and a counter force frame fixing screw rod (11);

the two triangular reaction frames (7) are arranged in parallel in a way that the side surfaces are opposite, and are fixed on a standard channel (9) through reaction frame fixing screws (11), the brackets (6) of the two cross beams (5) are respectively arranged at the inner sides of the two triangular reaction frames (7), and the cross beams (5) are placed on the brackets (6) of the cross beams (5) and are tightly leaned against the stress surface of the reaction frames (7); one end of the bearing screw rod (1) sequentially penetrates through a force transmission nut (3), a through jack (2) and a longitudinal through hole of the cross beam (5) and is connected with a force sensor and a test pile (18), and the far pile side of the jack (2) is connected with the force transmission nut (3); the force sensor is connected with a computer through a dynamic strain gauge; the oil pump of the center-penetrating jack (2) is placed on the movable loading platform.

2. The adjustable loading device for the horizontal static load test of the pile foundation as claimed in claim 1, further comprising a traction system, wherein the traction system comprises a lifting ring (12), a lifting belt (13), a turnbuckle (14), an arc shackle (16) and a soft contact cushion layer (17); one side of a screw rod of the lifting ring (12) is connected with the force sensor (8), the other side of the screw rod is connected with the hanging strip (13), the hanging strip (13) is connected with the turnbuckle (14), and the turnbuckle (14) is connected with the test pile (18) through the hanging strip (13).

3. The adjustable loading device for the horizontal static load test of the pile foundation as claimed in claim 1, wherein a loading frame (4) is further arranged between the through jack (2) and the cross beam (5); the load holding frame (4) is of a steel frame structure and consists of a front steel frame (41), a rear steel frame (42), a stand column and a load holding nut (44), holes are formed in the middle of the front steel frame (42) and the rear steel frame (42), a groove with the same outer diameter as that of the center penetrating jack (2) is formed in an opening of the front surface of the front steel frame (41), and a rear hollow steel guide pipe (43) which is perpendicular to the rear plate surface and extends backwards is arranged in an opening of the rear steel frame (42); the bearing screw rod (1) is inserted into the through jack (2) and clamped into the groove of the front steel frame (41), penetrates through the front steel frame 41, the load-holding nut (44), the rear steel frame (42) and the rear hollow steel guide pipe (43), and the rear hollow steel guide pipe (43) penetrates through the longitudinal through hole of the cross beam (5).

4. The adjustable loading device for the horizontal static load test of the pile foundation as claimed in claim 1, wherein the brackets (6) of the cross beams (5) are of a steel truss structure, and three steel supporting plates (61) are arranged on each bracket (6) of the cross beams (5) and are fixed on the supporting legs (62) through fasteners (63).

5. The adjustable loading device for the horizontal static load test of the pile foundation as claimed in claim 3, wherein the traction system further comprises a turnbuckle bracket (15) placed below the turnbuckle (14).

6. The adjustable loading device for the horizontal static load test of the pile foundation as claimed in claim 4, wherein the height interval of the buckles (63) on the supporting legs (62) is 50 mm.

7. The adjustable loading device for the horizontal static load test of the pile foundation as claimed in claim 4, wherein the bracket (6) of the cross beam (5) further comprises a standard gasket (64) arranged between the upper layer steel supporting plate (61) and the cross beam (5).

8. A loading test method for horizontal static load of a pile foundation is characterized in that a loading device is installed by the following steps:

(1) presetting a sensor of a test pile (18) and burying the test pile (18): installing and pasting corresponding sensors on all the test piles (18), and burying a plurality of test piles (18) in the foundation pit according to the design position;

(2) the pile body sensor of the test pile (18) is connected with a measuring instrument;

(3) installing a loading system:

(3.1) selecting a channel according to the position of the test pile and installing and fixing reaction frames (7), wherein one channel is arranged between the two reaction frames (7), and the rear lines of the two reaction frames (7) are vertical to the loading direction;

(3.2) calculating the top supporting plate height of the bracket (6) of the cross beam (5) according to the loading height of the test pile (18), and installing and placing the bracket (6) of the cross beam (5) and a standard gasket (64) according to the calculation result;

(3.3) hoisting the cross beam (5) and placing the cross beam on a bracket (6) of the cross beam (5) and abutting against one side of a reaction frame (7), and adjusting the position of the cross beam (5) to enable a connecting line of a middle hole of the cross beam (5) and a test pile (18) to be consistent with a loading direction; the load holding frame (4) is inserted into the bearing screw (1) and then integrally inserted into the middle hole of the cross beam (5), so that the guide steel pipe of the load holding frame (4) is firmly fixed; then inserting the penetrating jack (2) into the bearing screw (1) and clamping the penetrating jack into a circular groove of the load holding frame (4), screwing a force transmission nut (3) into one side of the penetrating jack (2) of the bearing screw (1) to fix and clamp the penetrating jack (2), and then placing an oil pump on a movable loading platform (10);

(3.4) screwing a force sensor into the other side of the bearing screw rod (1), connecting the force sensor with a computer through a dynamic strain gauge, and displaying a load numerical value in real time;

(4) the loading system, the traction system and the test pile (18) are connected:

(4.1) screwing the hanging ring (12) into the force sensor, connecting the hanging strip (13) with a circular ring of a turn-buckle screw (14) after the hanging strip (13) penetrates through the hanging ring (12) to form a double-strand hanging strip (13), and keeping the turn-buckle screw (14) at the maximum extension position in the initial state;

(4.2) another hanging strip (13) is taken to bypass the back of the test pile (18) and the soft contact cushion layer protection device of the distributed optical fiber sensor to form double strands, then the double strands are connected with the C-shaped hook of the turn buckle (14), the turn buckle (14) is tightened, the turn buckle (14) is supported by the turn buckle bracket (6) until the traction system is tensioned to a certain extent, the hanging strips (13) on the two sides of the turn buckle (14) are slightly loosened, and the tension force is zero.

9. The loading test method for the horizontal static load of the pile foundation as claimed in claim 8, wherein the single-cycle test adopts the step-by-step loading, and the multi-cycle test adopts the step-by-step loading;

the one-time loading process comprises the following steps: screwing a load-holding nut (44) to one side of the rear steel framework (42), closing a valve of the jack (2) and adding oil pressure, pushing a force-transmitting nut (3) by a piston of the penetrating jack (2), driving a bearing screw rod (1) to move to the far pile side, transmitting the load from a loading device to a traction device and finally transmitting the load to a test pile (18); during the loading process, the loading process is stopped and the next operation is carried out when the following conditions are met:

① the computer displays that the load value reaches the design value of the test load, stops loading, and screws the load holding nut (44) to the side of the rear steel frame (42) to hold the load;

② the computer shows that the load value does not reach the experimental design load value, when the load holding nut (44) is about to reach the front steel frame (41), the load holding nut (44) should be screwed in time to the rear steel frame (42) side until the load is loaded to the design load;

③ when the piston of the center-penetrating jack (2) reaches the maximum stroke, but the computer shows that the load value does not reach the experimental design load value, stopping loading, screwing the load holding nut (44) to the side of the rear steel frame (42) for holding, loosening the oil valve of the center-penetrating jack (2) to make the piston of the jack (2) fall back to the initial position, screwing the front force transmission nut (3) of the jack (2) to the piston of the jack (2) and then continuing loading until the design load;

④ in the process of carrying, because the soil body plastic deformation, the horizontal displacement of the test pile (18) will increase gradually along with the increase of the carrying time, which leads to the gradual decrease of the actual horizontal load, therefore, the load value displayed by the computer should be observed at any time in the process of carrying, and the carrying-up operation is carried out in time.

10. The loading test method for horizontal static load of pile foundation as claimed in claim 8, wherein the unloading step comprises:

firstly screwing a load-holding nut (44) to the side of a front steel frame (41), then slowly loosening an oil valve of a penetrating jack (2), enabling a piston of the penetrating jack (2) to fall back to be close to an initial position by 5-10 mm, and closing the oil valve of the jack (2), wherein the unloading process is a primary unloading process, but the load is not unloaded to the next stage of load or zero at the moment, and the unloading operation needs to be continued;

adjusting the position of a load-holding nut (44) to a rear steel framework (42) for holding, then slowly loosening an oil valve of the jack (2), and separating a force-transmitting nut (3) from a piston of the jack (2);

step (3), the force transmission nut (3) is screwed outwards to a position slightly smaller than the maximum stroke of the piston of the jack (2), an oil valve of the jack (2) is closed to start loading, and when the piston of the jack (2) approaches the force transmission nut (3), the load is slowly loaded until the load holding nut (44) can be screwed;

and (4) repeating the unloading operation steps (1) - (3) until the load numerical value displayed by the display is the next-stage load or zero, and then unloading is finished.