A model test device and test method for studying expanded pile sinking

Abstract

The present invention discloses a model test device and test method for studying the sinking of expanded piles. The test device includes a model box, a loading device, a force transmission frame, a tension and compression sensor, a positioning sleeve, a model pipe pile, a vertical guide device, and a PVC pipe. The test method includes: making a model pipe pile; filling the test soil and forming a hole in the soil; pouring the expansion material into the hole; positioning the model pipe pile; sinking the pile and monitoring the data; organizing the data and the test site. The present invention uses an assembled pile sinking model test device and designs the test method according to the construction process in engineering practice. It has great scientific research value and economic benefits for studying the sinking resistance of the expanded pile sinking process and exploring measures to reduce the resistance. Using this test device and method, the sinking resistance, pile end resistance and pile side friction resistance of the implanted expanded pile under various working conditions can be explored. The obtained data can be observed and analyzed to provide a theoretical basis for subsequent related research on the sinking process of the expanded pile.

Description

Technical Field

[0001] The invention relates to a model test for pile sinking using an expanded pile implantation method, in particular to a model test device and a test method for studying the pile sinking using an expanded pile implantation method. Background Art

[0002] Root-fixed piles and expanded-body piles are a composite type of pile developed in pile foundation engineering. They overcome long-standing technical bottlenecks of traditional cast-in-place piles, such as high energy consumption and high slurry emissions, backward precast pile technology, and difficulty penetrating hard soil layers. These piles significantly advance the state-of-the-art in pile foundation technology. Compared with traditional cast-in-place piles, root-fixed and expanded-body piles reduce their overall construction cost by approximately 20%-30%, resource consumption by 40%-60%, and carbon emissions by over 50%. Expanded-body piles are precast concrete piles with cement slurry, cement-soil mixtures, cement-sand mortar mixtures, fine aggregate concrete, and other materials surrounding the pile. These expanded-body piles are a type of root-fixed pile. Compared with traditional precast piles, expanded-body piles increase their horizontal bearing capacity by 30%-50% and their vertical bearing capacity by 70%-100%. While significantly improving bearing capacity and seismic performance, they also offer significant energy and emission reduction advantages.

[0003] Patent publication number CN113404098A discloses a pile-sinking model test device and test method according to the present invention. The test device includes an assembled model box, a test soil filled into the model box and provided with a color marking layer at a certain depth, a load applying device for applying pressure to the model pile and sinking the model pile into the test soil, and a monitoring system for monitoring the model pile and the test soil. The model box includes: a first half model chamber and a second half model chamber that are U-shaped and detachably connected at the U-shaped opening side; a transparent baffle that detachably blocks the U-shaped opening side of the first half model chamber; and a movable bracket including a crossbeam spanning the top of the first half model chamber, on which a horizontal movable device for connecting the load applying device is slidably installed along the length direction.

[0004] The patent application with publication number CN114215118AD discloses a pipe pile driving test device, including a model trough: used to hold sand samples; a support member: installed on the top of the model trough, the support member is equipped with a vertical displacement drive mechanism, and the vertical displacement drive mechanism can be fixedly connected to the model pile; a limiting mechanism: including at least three groups of limiting members installed on the support member, the limiting members can form a space for the model pile to pass through with the trough wall of the model trough, and can contact the outer side surface of the model pile, and work together with the trough wall of the model trough to limit the vertical movement of the model pile; the trough wall of the model trough is made of transparent material.

[0005] While a relatively comprehensive theoretical framework has been developed for the post-sinking research of expanded piles, research on the pile driving force of prefabricated tubular piles driven by static pile drivers during the pile driving process, particularly during the implantation method, is still in its infancy. In practical engineering, accurate estimation of the pile driving force, or the pile driving resistance, is crucial for evaluating the potential for pile sinking in different soils, selecting pile driving equipment, preventing engineering accidents, and improving economic efficiency. To address these deficiencies in theoretical research, a number of model tests are required for expanded piles. These tests involve loading and implanting model tubular piles, measuring the pile driving force, lateral resistance, and end resistance, and analyzing their variations. These tests are crucial for studying the sinking performance of expanded piles and controlling the sinking quality of prefabricated tubular piles. Therefore, it is essential to conduct relevant model tests using scientifically sound testing methods and equipment. Summary of the Invention

[0006] In order to address the deficiencies in the test apparatus and test method in the above-mentioned prior art in studying the distribution and variation patterns of the pile sinking resistance, pile end resistance and pile side friction resistance of prefabricated pipe piles when the expanded piles are sunk by the implantation method, the present invention provides a model test apparatus and test method for studying the sinking of expanded piles.

[0007] The object of the present invention is achieved like this:

[0008] A model test device for studying the sinking of an enlarged pile comprises a model box (1), a loading device (2), a force transmission frame (3), a tension and compression sensor (4), a positioning sleeve (5), a model pipe pile (6), a vertical guide device (7), and a PVC pipe (8). The model box (1) is used to fill the test soil. After filling to the bearing layer, the PVC pipe (8) is buried. After filling, the PVC pipe (8) is pulled out to form a hole, and the hole is filled with an enlarged material. When conducting the test, a model pipe pile (6) provided with a strain gauge (18) is sleeved on the vertical guide device (7), and the upper end of the model pipe pile is sleeved in the positioning sleeve (5). The model pipe pile (6) is sunk by the loading device (2). The pile sinking resistance, pile end resistance, and pile side friction resistance are monitored by the strain gauge (18) arranged on the model pipe pile (6) and the tension and compression sensor (4) on the loading device (2).

[0009] The vertical guide device (7) is formed by welding a ring (16) with a ball bearing (15) and a connecting steel rod (17). Symmetrical "T"-shaped steel rods (14) are welded to both ends of the upper ring (16). The vertical guide device (7) is installed in the reserved groove between the transparent acrylic plate (9) and the uppermost detachable steel plate (13).

[0010] The difference between the radius of the circular ring (16) and the radius of the ball bearing (15) is half the outer diameter of the model pipe pile, and the distance between the two circular rings (16) is 10 cm.

[0011] The model box (1) is connected to the base of the force transmission frame (3) via bolts to form an assembled whole.

[0012] The upper portion of the tension and compression sensor (4) is connected to the loading device (2) via bolts and a flange (12), and the lower portion is connected to the positioning sleeve (5) via bolts.

[0013] The detachable steel plate (13) is connected to the angle steels on both sides by bolts, and a circular handle is welded on the detachable steel plate (13) for easy disassembly.

[0014] The distance from the top of the model box (1) to the top plate of the force transmission frame (3) is greater than the sum of the length of the model pipe pile (6), the forward extension of the loading device (2), and the length of the tension and compression sensor.

[0015] The positioning sleeve (5) is provided with an opening to allow the wire to extend out.

[0016] The test method of the pile sinking model test device based on the above-mentioned expanded pile includes the following steps:

[0017] Step 1, making a model pipe pile (6): the model pipe pile (6) is divided into two halves along the axial direction, and grooves are carved on the outer wall (19) and the inner wall (20) of the two halves for pasting strain gauges (18) and arranging wires. Then, the grooves are filled with epoxy resin, and the half piles are glued together with glue to form a full pile. The wires are led out from the preset circular hole on the top of the pile.

[0018] Step 2, filling the test soil and drilling the soil: fill the box with soil through the detachable steel plate provided in the model box (1), bury the PVC pipe (8) when the soil is filled to the bearing layer, and continue to fill the soil to the predetermined elevation. After the soil is compacted, the pipe is pulled out to drill the hole. The outer diameter of the PVC pipe is the outer diameter of the expanded pile.

[0019] Step 3: Pour the expansion material into the hole: Pour in batches according to the designed pile length, pouring 20cm each time until the pouring is completed.

[0020] Step 4, positioning the model pipe pile: the model pipe pile (6) provided with the strain gauge (18) is fixed between the vertical guide device (7) and the positioning sleeve (5), and the vertical guide device (7) is installed at the corresponding groove of the model box (1).

[0021] Step 5, pile driving and data monitoring: Through the loading device, the model pipe pile (6) is pressed into the expansion material in stages by displacement control, with each stage pressed into 10 cm. During the pile driving process, the strain gauge (18) arranged on the model pipe pile (6) and the tension and compression sensor (4) on the loading device (2) are used to monitor the pile driving resistance, pile end resistance and pile side friction resistance.

[0022] Step 6: Organize data and test site: After each test, save and organize the data, and organize the test site to facilitate subsequent tests.

[0023] Positive and beneficial effects: This invention utilizes an assembled pile-sinking model test apparatus and designs a test method based on construction techniques used in engineering practice. This method has significant scientific research value and economic benefits for studying the sinking resistance of expanded piles and exploring measures to reduce this resistance. This test apparatus and its test method can be used to investigate the sinking resistance, pile end resistance, and pile side friction of implanted expanded piles under various working conditions. The data obtained can be analyzed and observed, providing a theoretical basis for subsequent research on the expanded pile sinking process. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the overall structure of the test device of the present invention;

[0025] Figure 2 It is a rear view of the model box of the present invention;

[0026] Figure 3 It is a schematic diagram of the vertical guide device of the present invention;

[0027] Figure 4 It is a schematic diagram of the positioning sleeve of the present invention;

[0028] Figure 5 This is a schematic diagram of a model pipe pile of the present invention;

[0029] Figure 6 Schematic diagram of the test method steps of the present invention;

[0030] The figure shows: model box 1, loading device 2, force transmission frame 3, tension and compression sensor 4, positioning sleeve 5, model pipe pile 6, vertical guide device 7, PVC pipe 8, transparent acrylic plate 9, model box side reinforcement rib 10, loading device connecting flange 11, tension and compression sensor connecting flange 12, detachable steel plate 13, "T"-shaped steel rod 14, ball bearing 15, ring 16, connecting steel rod 17, strain gauge 18, model pipe pile outer wall 19, model pipe pile inner wall 20. DETAILED DESCRIPTION

[0031] In order to make the purpose and technical solution of the present invention clearer and easier to understand, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] Example 1

[0033] like Figure 1The present invention provides a model test device for studying the sinking resistance of an enlarged pile, comprising a model box (1), a loading device (2), a force transmission frame (3), a tension and compression sensor (4), a positioning sleeve (5), a model pipe pile (6), a vertical guide device (7), and a PVC pipe (8). The model box (1) is used to fill the test soil, and after filling to the bearing layer, the PVC pipe (8) is buried. After filling, the PVC pipe (8) is pulled out to form a hole, and the hole is filled with an enlarged material. When conducting a test, a model pipe pile (6) provided with a strain gauge (18) is sleeved on the vertical guide device (7), and the upper end of the model pipe pile is sleeved in the positioning sleeve (5). The model pipe pile (6) is sunk by the loading device (2), and the pile sinking resistance, pile end resistance, and pile side friction resistance are monitored by the strain gauge (18) arranged on the model pipe pile (6) and the tension and compression sensor (4) on the loading device (2).

[0034] like Figure 1 and Figure 2 The size of the model box (1) should fully consider the influence of the boundary effect. The length and width of the box should not be less than 5 times the diameter of the expanded pile, and the height should not be less than the sum of the length of the expanded pile and 5 times the diameter of the pile. The length, width and height of the embodiment model box are 1000mm×1000mm×2000mm. The bottom plate is a steel plate with a thickness of 20mm. The surrounding frame is welded with 100mm×100mm×10mm angle steel. One side of the model box is four layers of 10mm thick detachable steel plates (13), the opposite side is a transparent acrylic plate (9), and both sides are 10mm integral fixed steel plates. Three reinforcing ribs (10) are distributed along the height of the box side. The detachable steel plate (13) and the transparent acrylic plate (9) are reserved with grooves for fixing the vertical guide device (7). The distance from the top of the model box (1) to the top plate of the force transmission frame (3) is greater than the sum of the length of the model pipe pile (6) and the forward extension of the loading device (2) to facilitate the positioning of the model pipe pile (6). The base of the force transmission frame (3) is connected to the model box (1) by bolts to form an assembled whole. The outer diameter of the PVC pipe (8) is equivalent to the pile diameter of the expanded pile studied in the model test. The pipe is pre-buried and then pulled out to simulate the rotary drilling of a hole in the soil. The embodiment model pipe pile has an outer diameter of 60mm, an inner diameter of 38mm, and a length of 1300mm. The outer diameter of the PVC pipe is the same as the outer diameter of the expanded pile, which is 80mm. The PVC pipe is 1200mm long.

[0035] like Figure 3 The vertical guide device (7) is made of a circular ring (16) with a ball bearing (15) and a connecting steel rod (17) welded together. Symmetrical "T"-shaped steel rods (14) are welded to both ends of the upper circular ring (16). The difference between the radius of the circular ring (16) and the radius of the ball bearing (15) is half the outer diameter of the model pipe pile (6). The distance between the two circular rings (16) is about 10 cm.

[0036] like Figure 4The sleeve is provided with an opening so that the wire can extend therefrom.

[0037] like Figure 5 The model pipe pile (6) is made of two pairs of half pipes combined into one. A groove with a width of 5 mm and a depth of about 4 mm is engraved on the outer wall (19) and the inner wall (20) of the model pipe pile. After polishing, the groove is wiped with alcohol. Then the strain gauge (18) is pasted and the wiring is arranged. It is filled with epoxy resin. Finally, the two halves of the pile are combined into one with glue. The wire is led out through the opening near the top of the pile to form a complete model pipe pile (6).

[0038] The test method operation steps are as follows:

[0039] Step 1: Divide the organic glass model pipe pile (6) into two halves along the axial direction, carve a groove with a width of 5 mm and a depth of 4 mm on the inner wall (20) and the outer wall (19) of the two halves, polish and wipe the groove with alcohol, mark the pasting position of the strain gauge (18), paste the strain gauge (18) according to the arrangement position, and then fill the groove with epoxy resin, and use adhesive to bond the half pile to form a full pile. The wire is led out from the opening near the top of the pile and connected to the static resistance strain gauge. In this embodiment, the CM-2B static resistance strain gauge is used for strain gauge detection. The strain gauge survival rate is 100% after detection.

[0040] Step 2, fill the model box (1) with test soil and silt in layers, install the first layer of removable steel plate (13) after filling a 200mm soil layer, compact the soil layer and continue filling, repeat the installation and filling steps until the height is 600mm, bury a PVC pipe of the same length as the pile, continue to repeat the installation and filling steps until the PVC pipe is completely buried, and pull out the pipe to form a hole after the soil is compacted;

[0041] Step 3: Pour the expansion material into the hole. The pouring height is calculated as 1100 mm based on the difference between the hole volume and the model pipe pile volume. Pour the material in batches of 200 mm each time until the pouring is completed. During the pouring process, pay attention to the state of the hole and the expansion material. In the embodiment, the expansion material is a cement mortar mixture.

[0042] Step 4, adjust the top plate of the force transmission frame (3) to a suitable height, fix it with bolts, fix the loading device flange (11) and install the loading device (2). This embodiment adopts oil cylinder loading, fix the tension and compression sensor connecting flange (12) and install the tension and compression sensor. This embodiment adopts an S-type tension and compression sensor with a range of 5t, connect the wire to the matching reading instrument, fix the sleeve and the tension and compression sensor with bolts, put the model pipe pile (6) equipped with strain gauges (18) on the vertical guide device (7), and then install the vertical guide device (7) at the corresponding groove of the model box (1), the top of the model pipe pile (6) extends into the sleeve, and the wire at the top of the model pipe pile (6) extends along the sleeve opening and is connected to the static resistance strain gauge;

[0043] Step 5, using displacement control to press the model pipe pile (6) into the expansion material in stages, with each stage pressed into 10 cm, and using the tension and compression sensor with a display instrument to read the pile sinking resistance during the pile pressing process, and using the static resistance strain gauge to collect the pile end resistance and pile side friction resistance.

[0044] Step 6: After the test is completed, organize the data to facilitate subsequent data analysis. Clean up the test site to facilitate the next test.

[0045] The above content is only for explaining the technical idea of ​​the present invention and cannot limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A model test device for studying the sinking of enlarged piles, characterized in that: The invention comprises a model box (1), a loading device (2), a force transmission frame (3), a tension and compression sensor (4), a positioning sleeve (5), a model pipe pile (6), a vertical guide device (7), and a PVC pipe (8). The model box (1) is used to fill the test soil, and after filling to the bearing layer, the PVC pipe (8) is buried. After filling, the PVC pipe (8) is pulled out to form a hole, and the hole is filled with expansion material. When the test is carried out, the model pipe pile (6) provided with a strain gauge (18) is sleeved on the vertical guide device (7), and the upper end of the model pipe pile is sleeved in the positioning sleeve (5). The model pipe pile (6) is sunk by the loading device (2), and the pile sinking resistance, pile end resistance and pile side friction resistance are monitored by the strain gauge (18) arranged on the model pipe pile (6) and the tension and compression sensor (4) on the loading device (2); The vertical guide device (7) is formed by welding a ring (16) with a ball bearing (15) and a connecting steel rod (17), and symmetrical "T"-shaped steel rods (14) are welded at both ends of the ring (16). The vertical guide device (7) is installed in the reserved groove between the transparent acrylic plate (9) and the uppermost detachable steel plate (13); The difference between the radius of the circular ring (16) and the radius of the ball bearing (15) is half the outer diameter of the model pipe pile, and the distance between the two circular rings (16) is 10 cm.

2. A model test device for studying expanded pile sinking according to claim 1, characterized in that: The model box (1) is connected to the base of the force transmission frame (3) via bolts to form an assembled whole.

3. A model test device for studying expanded pile sinking according to claim 1, characterized in that: The upper portion of the tension and compression sensor (4) is connected to the loading device (2) via bolts and a flange (12), and the lower portion is connected to the positioning sleeve (5) via bolts.

4. A model test device for studying expanded pile sinking according to claim 1, characterized in that: The detachable steel plate (13) is connected to the angle steels on both sides by bolts, and a circular handle is welded on the detachable steel plate (13) for easy disassembly.

5. The model test device for studying expanded pile sinking according to claim 1, characterized in that: The distance from the top of the model box (1) to the top plate of the force transmission frame (3) is greater than the sum of the length of the model pipe pile (6), the forward extension of the loading device (2), and the length of the tension and compression sensor.

6. The model test device for studying expanded pile sinking according to claim 1, characterized in that: The positioning sleeve (5) is provided with an opening to allow the wire to extend out.

7. A method for studying the sinking of enlarged piles using the test device according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1, making a model pipe pile (6): the model pipe pile (6) is divided into two halves along the axial direction, grooves are carved on the outer wall (19) and the inner wall (20) of the two halves for pasting strain gauges (18) and arranging wires, and then the grooves are filled with epoxy resin, and the half piles are glued together with glue to form a full pile, and the wires are led out from the preset circular hole at the top of the pile; Step 2, filling the test soil and forming a hole in the soil: fill the box with soil through the detachable steel plate (13) provided in the model box (1), bury the PVC pipe (8) when the soil is filled to the bearing layer, continue filling the soil to the predetermined elevation, and after the soil is compacted, pull out the pipe to form a hole. The outer diameter of the PVC pipe is the outer diameter of the expanded pile; Step 3: Pour the expansion material into the hole: pour in batches according to the designed pile length, pouring 20cm each time until the pouring is completed; Step 4, positioning the model pipe pile: the model pipe pile (6) provided with the strain gauge (18) is fixed between the vertical guide device (7) and the positioning sleeve (5), and the vertical guide device (7) is installed at the corresponding groove of the model box (1); Step 5, pile driving and data monitoring: the model pipe pile (6) is pressed into the expansion material in stages by means of displacement control through the loading device (2). During the pile driving process, the pile driving resistance, pile end resistance and pile side friction resistance are monitored by means of the strain gauges (18) arranged on the model pipe pile (6) and the tension and compression sensors (4) on the loading device (2); Step 6: Organize data and test site: After each test, save and organize the data, and organize the test site to facilitate subsequent tests.

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