CN104912124A - Pile-soil interface shear simulation test device for open concrete pipe pile - Google Patents

Abstract

The invention belongs to the technical field of test equipment for construction, and relates to an open concrete pipe pile pile-soil interface shear simulation test device. The screw rod is vertically installed on the operating platform, and the upper and lower ends of the spring are respectively fixed on the detachable spring fixing plate. With the detachable spring lower fixed plate, the test soil sample is placed inside the upper shear box, the top is flush with the detachable spring lower fixed plate, and the left side of the upper shear box is rigidly connected with the operating platform; the lower shear box is built-in There are concrete samples, and there is a sliding track on the operating platform. The operating platform is connected to the lower shear box through rollers, and the CNC motor is rigidly connected to the lower shear box; the vertical displacement sensor is installed on the detachable spring lower fixing plate, and the horizontal The displacement sensor is installed between the upper shear box and the lower shear box. The load sensor is placed on the first steel rod on the left side of the upper shear box. widely.

Description

An open concrete pipe pile pile-soil interface shear simulation test device

Technical field:

The invention belongs to the technical field of test equipment for construction, and relates to an open concrete pipe pile pile-soil interface shear simulation test device.

Background technique:

At present, open concrete pipe piles have become one of the most important pile types in my country, and are widely used in the construction of industrial and civil buildings, port projects, and water conservancy projects. During the process of penetrating the foundation soil of open concrete pipe piles, Part of the soil is extruded into the pile hole to form a soil plug. The bearing capacity provided by the soil plug is an important part of the vertical compressive bearing capacity of the open concrete pipe pile, and the bearing capacity at the end of the soil plug is completely provided by the frictional resistance between the inner wall of the pile and the soil plug. Now the traditional field and model tests encounter the following problems in the process of studying the load transfer mechanism of open concrete pipe piles: First, the bearing capacity of soil on open concrete pipe piles is gradually in the order of outer resistance-pipe wall end resistance-inner resistance The resistance on the inside and outside of the pile wall is not synchronized, and the traditional load transfer model of pile foundation is no longer applicable. Second, because the inner wall of the concrete pipe pile is rough and easy to wear, and the pile hole is completely different from the surrounding pile. The existing load transfer theory function can no longer accurately describe the load transfer characteristics inside the pile wall; during the pile sinking process of open concrete pipe piles, due to the soil plug effect, the soil will be strongly compressed and expanded. The normal stress of the pile-soil contact surface changes greatly, but the normal stiffness of the soil remains basically unchanged. This type of soil cannot be tested for shear strength with the traditional direct shear instrument, and the traditional direct shear instrument cannot be used during the shearing process. The shear area decreases continuously, and the size effect is more obvious, which affects the test results. Therefore, a shear simulation test device for the pile-soil interface of open concrete pipe piles is sought to provide a new equipment for the study of load transfer between piles and soil.

Invention content:

The purpose of the present invention is to overcome the shortcoming that exists in the prior art, design and provide a kind of open concrete pipe pile pile soil interface shear simulation test device, by simulating the open concrete pipe pile pile soil internal and external interface shearing process, and then research Mechanism of load transfer at pile-soil interface.

In order to achieve the above object, the main structure of the present invention includes a screw, a detachable spring upper fixed plate, a spring, a detachable spring lower fixed plate, an upper shear box, a lower shear box, an operating platform, a roller, a numerical control motor, a lateral displacement sensor, vertical displacement sensor, load sensor, the first steel rod and the second steel rod, wherein the screw rod, the detachable spring upper fixed plate, the spring and the detachable spring lower fixed plate are combined to form a constant stiffness spring dynamic loading system, and the upper shear The combination of the box and the lower shear box constitutes a visual pile-soil interface shear simulation system, the operating platform, rollers and numerical control motors constitute a two-way transmission system for the rollers, and the lateral displacement sensor, vertical displacement sensor and load sensor constitute the test data measurement system; Four screws with a length of 800mm and a diameter of 20mm are vertically installed on the operation platform, and the screws are rigidly connected with the operation platform; the detachable spring upper fixing plate is made of 840mm*540mm rectangular steel plate with a thickness of 20mm, and the detachable spring upper fixing plate The four corners of the spring are slidingly connected with four screw rods to realize the up and down adjustment of the upper and lower fixing plates of the detachable springs; the 12 springs are symmetrically distributed between the upper and lower fixing plates of the detachable springs, each spring The upper and lower ends of the spring are respectively fixed on the detachable spring upper fixing plate and the detachable spring lower fixing plate. The distance between two adjacent springs is 135mm; the detachable spring lower fixing plate is made of a rectangular steel plate with a thickness of 700mm*400mm. 10mm; the upper shear box is a cubic structure that is closed up and down, and its length, width, and height are 700mm, 400mm, and 300mm respectively. Made of steel plate, the back of the upper shear box is rigidly connected with the left side and the right side respectively, the front of the upper shear box is made of plexiglass plate, the front of the upper shear box is respectively connected with the left side and the right side The steel plate is rigidly connected; the test soil sample is placed inside the upper shear box, and the top is flush with the fixed plate under the detachable spring. The left side of the upper shear box passes the first steel rod with a length of 200mm and a diameter of 20mm and the operating platform The vertical part of the U-shaped groove structure is rigidly connected; the two sides of the lower shear box of the U-shaped groove structure respectively leave a 5cm smooth section in close contact with the upper shear box, which is convenient for the lower shear box to reciprocate left and right under the action of the two-way transmission system of the roller. At the same time, ensure that the sand and soil do not flow out during the shearing process; the lower shear box is built with a concrete sample, and the rough surface of the concrete sample is cement with the same water-cement ratio and roughness as the side wall of the open concrete pipe pile; the upper shear box The side wall of the side wall and the smooth section of the lower shear box are coated with lubricating oil to reduce friction; the operating platform is made of L-shaped steel plate, and there is a sliding track on the operating platform, and the operating platform is connected with the lower shearing box through rollers. The length of the roller is 400mm and the diameter is 20mm; the CNC motor is rigidly connected to the lower shear box through the second steel rod with a length of 150mm and a diameter of 20mm; the vertical displacement sensor is installed on the detachable spring lower fixing plate for Measure the vertical displacement of the fixed plate under the detachable spring, and the lateral displacement sensor is installed between the upper shear box and the lower shear box to measure the upper shear The relative displacement between the cut box and the lower shear box; the load sensor is placed on the first steel rod on the left side of the upper shear box to measure the shear force between the upper shear box and the lower shear box.

The concrete process that the present invention realizes the shear simulation test of the pile-soil interface of the open concrete pipe pile is:

(1), preparation of test soil samples: take the soil samples at the construction site and carry out air-drying, crush the air-dried soil samples and pass through a 2mm sieve and place them in a dry and water-tight container. The prepared moisture content is calculated to be 16 ℅, 18℅, 20℅ of the amount of water required for the sample, stir evenly and seal it for 24 hours to obtain the test soil sample;

(2), test soil sample remodeling: lay the prepared test soil sample in three layers in the upper shear box, and the height of each layer of test soil sample after compaction is 1/3 of the height of the upper shear box, After the compaction of the first layer of test soil sample is completed, the surface of the test soil sample is planed, and the compaction of the other two layers of test soil samples is continued, the upper surface of the test soil sample is arranged, and the excess soil is scraped off to obtain a remodeled test soil sample;

(3) Installation and debugging of the test device: place the concrete sample in the lower shear box, adjust the position of the upper shear box so that the upper shear box is in close contact with the lower shear box, and then lay the test specimen in the upper shear box. Use sand, and arrange the upper surface of the test sand to be horizontal, and place a constant stiffness spring dynamic loading system to make the detachable spring lower fixed plate fit flatly with the top of the test sand, by adjusting the position of the detachable spring upper fixed plate on the screw , set the initial compression of the spring, place the lateral displacement sensor and the vertical displacement sensor, and calibrate the initial displacement; place the load sensor on the first steel rod on the left side of the upper shear box, and perform zeroing processing. And debug the installed test device;

(4) Pile-soil interface shear test: start the numerical control motor to conduct the pile-soil interface shear test at a cyclic shear rate of 0.8mm/min, the upper shear box is fixed, and the lower shear box is placed between the operating platform and the upper The shear box slides between the shear boxes, and the shear displacement is 5 cm. Shear failure occurs at the interface between the concrete sample and the remodeled sample soil sample, resulting in relative displacement. The lateral displacement sensor, vertical displacement sensor and load sensor respectively measure and record the upper shear The relative displacement of the cutting box and the lower shearing box, the vertical displacement of the fixed plate under the detachable spring, and the shear force between the upper and lower shearing boxes are measured by the CCD camera installed on the front of the upper shearing box. The displacement, rotation and crushing of soil particles at the interface and the wear of the pile wall were observed, and the pile-soil interface shear test was completed.

Compared with the prior art, the present invention has the following advantages: First, during the pile sinking process of the open concrete pipe pile, due to the soil plugging effect, the soil body will be strongly compressed and expanded, and the normal stress of the pile-soil contact surface changes greatly. large, but the normal stiffness of the soil is basically unchanged, and the constant stiffness spring dynamic loading system is more suitable for the shear strength test of this kind of soil, which is close to the actual engineering; the second is that the front of the upper shear box is made of transparent tempered glass , CCD camera equipment can be used to observe the displacement, rotation and crushing of soil particles at the pile-soil interface, as well as the wear of the pile wall, and analyze the shear characteristics of the pile-soil interface from a mesoscopic point of view; The contact surface is always kept constant, which avoids the influence of the size effect on the test results; the fourth is to use the two-way transmission system of the roller to realize the two-way cyclic shearing, which can study the residual shear strength of the softened soil; its structure is simple, the operation is convenient, and the principle Scientific, accurate test results, low cost and wide application.

Description of drawings:

Fig. 1 is the schematic diagram of the main structure of the present invention.

Fig. 2 is a schematic block diagram of the shear simulation test process of the present invention.

Detailed ways:

The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings.

Example:

The main structure of the open concrete pipe pile pile-soil interface shear simulation test device described in this embodiment includes a screw rod 1, a detachable spring upper fixing plate 2, a spring 3, a detachable spring lower fixing plate 4, an upper shear box 5, Lower shear box 6, operating platform 9, roller 8, numerical control motor 7, lateral displacement sensor 12, vertical displacement sensor 11, load sensor 10, first steel rod 13 and second steel rod 14, wherein screw rod 1, can Removing the spring upper fixing plate 2, spring 3 and detachable spring lower fixing plate 4 constitutes a constant stiffness spring dynamic loading system, the upper shear box 5 and the lower shear box 6 constitute a visual pile-soil interface shear simulation system, the operating platform 9, The roller 8 and the numerical control motor 7 form a two-way transmission system of the roller, and the lateral displacement sensor 12, the vertical displacement sensor 11 and the load sensor 10 form the test data measurement system; four screws 1 with a length of 800 mm and a diameter of 20 mm are vertically installed in the operating On the platform 9, the screw 1 is rigidly connected with the operating platform 9; the detachable spring upper fixed plate 2 is made of 840mm*540mm rectangular steel plate with a thickness of 20mm, and the four corners of the detachable spring upper fixed plate 2 are respectively connected with the four screws 1 Sliding connection to realize the up and down adjustment of the detachable spring upper fixing plate 2; 12 springs 3 are symmetrically distributed between the detachable spring upper fixing plate 2 and the detachable spring lower fixing plate 4, and the upper and lower ends of each spring 3 They are respectively fixed on the upper fixed plate 2 of the detachable spring and the lower fixed plate 4 of the detachable spring. The distance between two adjacent springs 3 is 135mm; The upper shear box 5 is a cube that is closed up and down, and its length, width, and height are 700mm, 400mm, and 300mm respectively. The back of the upper shear box 5 is rigidly connected with the left side and the right side respectively, the front of the upper shear box 5 is made of plexiglass plate, and the front of the upper shear box 5 is respectively connected with the left side , the right side of the steel plate is rigidly connected; the test soil sample is placed inside the upper shear box 5, the top is flush with the detachable spring lower fixing plate 4, and the left side of the upper shear box 5 passes through a 200 mm in length and 20 mm in diameter. The first steel rod 13 is rigidly connected with the vertical part of the operating platform 9; the two sides of the lower shear box 6 of the U-shaped groove structure are respectively reserved with a smooth section of 5 cm in close contact with the upper shear box 5, which is convenient for the lower shear box 6 Under the action of the two-way transmission system of the rollers, it reciprocates left and right while ensuring that the sand does not flow out during the shearing process; the lower shear box 6 has a built-in concrete sample, and the rough surface of the concrete sample is the same as the side wall of the open concrete pipe pile. Cement with water-cement ratio and roughness; the side wall of the upper shear box 5 and the smooth section of the lower shear box 6 are coated with lubricating oil to reduce friction; the operating platform 6 is made of L-shaped steel plate, and the operating platform 9 is There is a sliding track, the operating platform 9 is connected with the lower shear box 6 through the roller 8, the length of the roller 9 is 400mm, and the diameter is 20mm; Two steel rods 14 are rigidly connected with the lower shear box 6; the vertical displacement sensor 11 is installed on the detachable spring lower fixed plate 4 to measure the vertical displacement of the detachable spring lower fixed plate 4, and the lateral displacement sensor 12 is installed on the upper Between the shear box and the lower shear box, it is used to measure the relative displacement of the upper shear box and the lower shear box; the load cell 10 is arranged on the first steel rod 13 on the left side of the upper shear box 5, for measuring The shear force between the upper and lower shear boxes.

In this embodiment, 4 groups of constant stiffness shear tests are successively carried out according to the test content, and each group includes 30 shear cycles. The flow process is shown in Figure 2, and the specific process is as follows:

(1) Preparation of test soil samples: take the soil samples at the construction site and carry out air-drying, crush the air-dried soil samples and pass through a 2mm sieve and place them in a dry and watertight container. The prepared moisture content is calculated to be 16 ℅, 18℅, 20℅ of the amount of water required for the sample, stir evenly and seal it for 24 hours to obtain the test soil sample;

(2) Remodeling of test soil samples: lay the prepared test soil samples in three layers in the upper shear box, and the height of each layer of test soil samples after compaction is 1/3 of the height of the upper shear box 5 After completing the compaction of the first layer of test soil samples, planing the surface, continue to complete the compaction of the other two layers of test soil samples, arrange the upper surface of the test soil samples, scrape off excess soil, and obtain the remodeling test soil samples;

(3), installation and commissioning of the test device: place the concrete sample in the lower shear box 6, adjust the position of the upper shear box 5 so that the upper shear box 5 is in close contact with the lower shear box 6, and then shear the The test sand is laid in the box 5, and the upper surface of the test sand is adjusted to the level, and the constant stiffness spring dynamic loading system is placed, so that the fixed plate 4 under the detachable spring fits flatly with the top of the test sand, and is fixed by adjusting the detachable spring. Set the initial compression of the spring 3 at the position of the plate 2 on the screw 1, place the lateral displacement sensor 12 and the vertical displacement sensor 11, and calibrate the initial displacement; place the load sensor 10 on the left side of the upper shear box 5 On the first steel rod 13 on the side, carry out the zeroing process, and debug the installed test device;

(4), pile-soil interface shear test: start numerical control motor 7, carry out pile-soil interface shear test with the cyclic shear speed of 0.8mm/min, upper shear box 5 is fixed, and lower shear box 6 is in The operating platform 9 slides between the upper shear box 5, and the shear displacement is 5 cm. Shear failure occurs at the interface between the concrete sample and the remodeling test soil sample, resulting in relative displacement. The lateral displacement sensor, vertical displacement sensor and load sensor are respectively Measure and record the relative displacement between the upper shear box and the lower shear box, the vertical displacement of the fixed plate 4 under the detachable spring and the shear force between the upper shear box 5 and the lower shear box 6, through the upper shear box 5. The CCD camera installed on the front side observes the displacement, rotation and crushing of the soil particles at the pile-soil interface and the wear of the pile wall;

(5), change the concrete sample of different surface roughness, repeat step (4), after measuring data, the first group of spring and test soil sample are taken away and change another group of spring and test soil sample, return step ( 2) Repeat until all tests are completed.

Claims (3)

1. a uncovered concrete tubular pile stake Soil Interface shearing simulation experimental rig, it is characterized in that agent structure comprises screw rod, detachable spring upper mounted plate, spring, detachable spring bottom plate, upper shear box, down cut box, operating platform, roller bearing, numerical-control motor, lateral displacement sensor, vertical displacement sensor, load sensor, first steel pole and the second steel pole, wherein screw rod, detachable spring upper mounted plate, spring and the combination of detachable spring bottom plate form permanent rigid spring dynamic loading system, upper shear box and the combination of down cut box form visual stake Soil Interface shearing simulation system, operating platform, roller bearing and numerical-control motor form roller bearing bi-directional transmission system, lateral displacement sensor, vertical displacement sensor and load sensor form experimental data measurement system, the screw rod of four long 800mm, diameter 20mm is vertically installed on the operational platform, and screw rod and operating platform are rigidly connected, four angles place of detachable spring upper mounted plate is connected with four screw slide respectively, realizes the up-down adjustment of detachable spring upper mounted plate, 12 spring centers are symmetrically distributed between detachable spring upper mounted plate and detachable spring bottom plate, the two ends up and down of every root spring are separately fixed on detachable spring upper mounted plate and detachable spring bottom plate, and the spacing of adjacent two springs is 135mm, upper shear box is the cuboid of all round closure up/down perforation, the left surface of upper shear box, right flank and the back side all adopt thickness to be that the steel plate of 20mm is made, the back side of upper shear box is rigidly connected with left surface and right flank respectively, the front of upper shear box adopts poly (methyl methacrylate) plate to make, and the front of upper shear box is rigidly connected with left surface, right flank steel plate respectively, test soil sample is placed in the inside of upper shear box, and top is concordant with detachable spring bottom plate, the left surface of upper shear box by length be 200mm, diameter is that first steel pole of 20mm and the vertical part of operating platform are rigidly connected, the both sides of the down cut box of U-type groove structure reserve the smooth section of 5cm and upper shear box close contact respectively, are convenient to sand in the reciprocating guarantee simultaneously in down cut box left and right under the effect of roller bearing bi-directional transmission system shear history and do not outflow, down cut box is built-in with concrete sample, and the rough surface of concrete sample is the cement of the identical water/binder ratio of uncovered concrete tubular pile sidewall and roughness, the sidewall of upper shear box and the smooth section of down cut box are coated with lubrication oil, to reduce friction, operating platform adopts L-type steel plate to make, and operating platform is provided with sliding rail, and operating platform is connected with down cut box by roller bearing, numerical-control motor by length be 150mm, diameter is that second steel pole of 20mm and down cut box are rigidly connected, vertical displacement sensor is arranged on detachable spring bottom plate, is used for measuring the vertical displacement of detachable spring bottom plate, and lateral displacement sensor is arranged between shear box and down cut box, for measuring the relative displacement of upper shear box and down cut box, load sensor is placed on the first steel pole on the left of shear box, for measuring the shearing between upper shear box and down cut box.

2. uncovered concrete tubular pile stake Soil Interface shearing simulation experimental rig according to claim 1, it is characterized in that described detachable spring upper mounted plate adopts the rectangular steel plates of 840mm*540mm to make, its thickness is 20mm; Detachable spring bottom plate adopts the rectangular steel plates of 700mm*400mm to make, and its thickness is 10mm; The length of upper shear box is respectively 700mm, 400mm, 300mm; The length of roller bearing is 400mm, and diameter is 20mm.

3. uncovered concrete tubular pile stake Soil Interface shearing simulation experimental rig according to claim 2, is characterized in that the detailed process adopting described device to realize the test of uncovered concrete tubular pile stake Soil Interface shearing simulation is:

(1), the preparation of soil sample is tested: the soil sample of getting job site is carried out air-dry, soil sample after air-dry is pulverized and is placed in dry fluid-tight container after crossing 2mm sieve, the watering amount needed for sample of 16 ℅, 18 ℅, 20 ℅ is respectively by calculating preparation moisture content, seal preservation after stirring 24 hours, obtain testing soil sample;

(2), test soil sample to reinvent: divide three layers to be laid in upper shear box the test soil sample prepared, every layer of test soil sample hit real after height be on shear box height 1/3, complete after first floor tests native sample compacting and hair is dug on its surface, that has continued other two-layer test soil samples hits reality, the upper surface of repairing experiment soil sample, scrape off unnecessary soil, obtain remolding test soil sample;

(3), the installment and debugging of experimental rig: concrete sample is placed in down cut box, in adjustment, shear box position makes shear box and down cut box close contact, then in upper shear box, test sand is laid, and test sand upper surface is arranged to level, place permanent rigid spring dynamic loading system, detachable spring bottom plate and test sand upper flat are fitted, by adjusting the detachable position of spring upper mounted plate on screw rod, set the initial compression amount of spring, and place lateral displacement sensor and vertical displacement sensor, demarcate initial displacement amount, load sensor is placed on the first steel pole on the left of upper shear box, carries out return-to-zero, and mounted experimental rig is debugged,

(4), stake Soil Interface shear test: start numerical-control motor and carry out a Soil Interface shear test with the circulation shear speed of 0.8mm/min, upper shear box maintains static, down cut box is slided between operating platform and upper shear box, shear displacemant is 5cm, concrete sample with reinvent sample soil sample interface shear failure occur, produce relative displacement, lateral displacement sensor, vertical displacement sensor and load sensor measure respectively and record the relative displacement of shear box and down cut box, the vertical displacement of detachable spring bottom plate and the shearing between upper shear box and down cut box, the ccd video camera installed by upper shear box front is to the displacement of stake Soil Interface soil particle, rotate and observe with broken and pile lining wearing and tearing, complete a Soil Interface shear test.