Single pile bearing capacity physical model testing device and method based on static load test

Abstract

The invention belongs to the technical field of geotechnical engineering, and particularly relates to a single-pile bearing capacity physical model testing device and method based on a static load test. The test cylinder is arranged at the top end of the counterweight seat and is used for containing a test sample; the supporting and guiding assembly is arranged at the top end of the counterweight seat, and the supporting and guiding assembly is circumferentially arranged on the outer side of the test cylinder; the pressure applying mechanism is movably arranged at the top end of the supporting and guiding assembly, the pressure applying mechanism is matched with the test cylinder and vertically corresponds to the test cylinder, the pressure applying mechanism is used for applying pressure to the test sample in the test cylinder, and the supporting and guiding assembly is used for guiding vertical movement of the pressure applying mechanism. According to the model device, an indoor single-pile static load test can be carried out, test results are sorted out, the influence of the pile body size and the volcanic soil compaction degree on the single-pile bearing capacity, the end resistance load sharing ratio and the pile side friction resistance in a volcanic soil foundation is analyzed, and compared with a field test, the time cost and the economic cost of the model test are easy to control.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and in particular relates to a physical model testing device and method for single pile bearing capacity based on static load test. Background Art

[0002] The pile foundation model test can design accurate and appropriate boundary conditions and material properties of each part of the test, and can conduct a more focused study on the mechanical properties between the pile and the soil. In addition, compared with field tests, the time and economic costs of model tests are easier to control.

[0003] A self-designed model device was used to carry out indoor single pile static load test. The test results were collated and analyzed to obtain the load-settlement curve of the pile top, the pile side friction resistance and the pile end resistance changes. The influence of pile size and volcanic soil compaction on the bearing capacity of single pile in volcanic soil foundation, end resistance load sharing ratio and pile side friction resistance were analyzed.

[0004] The existing static load test for testing the bearing capacity of pile foundations is costly, and the traditional test equipment regards the pile side friction resistance as a constant value and cannot be adjusted to simulate different overburden pressures.

[0005] Therefore, it is necessary to design a physical model testing device and method for single pile bearing capacity based on static load test to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to provide a physical model testing device and method for the bearing capacity of a single pile based on a static load test, and to use a self-designed model device to conduct an indoor single pile static load test to analyze the influence of pile size and volcanic soil compaction on the bearing capacity of a single pile in a volcanic soil foundation, the end resistance load sharing ratio and the pile side friction resistance.

[0007] To achieve the above object, the present invention provides the following solution: a physical model testing device for the bearing capacity of a single pile based on a static load test, comprising:

[0008] Counterweight seat;

[0009] A test cylinder is arranged on the top of the counterweight seat, and is used to hold the test sample;

[0010] A support guide assembly is arranged at the top end of the counterweight seat, and the support guide assembly is circumferentially arranged outside the test cylinder;

[0011] A pressure applying mechanism is movably arranged at the top end of the support and guide assembly. The pressure applying mechanism is adapted to the test cylinder and corresponds to each other up and down. The pressure applying mechanism is used to apply pressure to the test sample in the test cylinder. The support and guide assembly is used to guide the up and down movement of the pressure applying mechanism.

[0012] A single pile bearing capacity physical model testing device based on a static load test according to the present invention, the pressure applying mechanism includes a cross reaction beam, the cross reaction beam is movably arranged at the top of the support guide assembly, the center of the cross reaction beam is fixedly connected with a lifting drive part, the lifting drive part is threadedly connected to the top of the support guide assembly, the lifting drive part is used to drive the cross reaction beam to move up and down on the support guide assembly, the bottom end of the cross reaction beam is fixedly connected with a first pressure applying part and a second pressure applying part, the second pressure applying part is located at the center of the first pressure applying part, and the first pressure applying part and the second pressure applying part are used to apply pressure to the test sample in the test cylinder.

[0013] According to a physical model testing device for the bearing capacity of a single pile based on a static load test of the present invention, the lifting drive unit includes a motor assembly, the motor assembly is fixedly arranged at the center position of the cross reaction beam, the output end of the motor assembly is coaxially fixedly connected with a center gear, the center gear is meshed with a plurality of co-located gear sleeve shafts, the co-located gear sleeve shafts are threadedly connected to the top end of the support guide assembly, and the plurality of co-located gear sleeve shafts correspond one-to-one to the ends of the cross reaction beam and are rotatably connected.

[0014] According to a physical model testing device for single pile bearing capacity based on static load test of the present invention, the first pressure applying part includes an external pressure plate, the external pressure plate is fixedly connected to the bottom end of the cross reaction beam through a plurality of pre-stressing components, a clearance hole is opened in the center of the external pressure plate, and the second pressure applying part is movably arranged in the clearance hole.

[0015] According to a physical model testing device for the bearing capacity of a single pile based on a static load test of the present invention, the second pressure applying part includes an inner pressure plate, the inner pressure plate is movably arranged in the give way hole, the inner pressure plate is fixedly connected to the bottom end of the cross reaction beam through a booster assembly, pressure sensors are arranged between the top end of the booster assembly and the bottom end of the cross reaction beam, and between the bottom end of the booster assembly and the top end of the inner pressure plate, and a displacement meter is arranged on the outer side wall of the booster assembly.

[0016] A physical model testing device for the bearing capacity of a single pile based on a static load test according to the present invention, the test cylinder comprises a fixed bottom cylinder and at least one layered sleeve, the fixed bottom cylinder is arranged at the top of the counterweight seat, the layered sleeve is detachably arranged at the top of the fixed bottom cylinder, and a locking portion is provided at the connecting end of the fixed bottom cylinder and the layered sleeve and at the connecting ends of two adjacent layered sleeves.

[0017] A single pile bearing capacity physical model testing device based on a static load test according to the present invention, the locking part includes two closing lock hoops, the two closing lock hoops are respectively arranged at the ends where the fixed bottom cylinder and the layered sleeve are connected, the outer side wall of the closing lock hoop is provided with a plurality of locking grooves, the plurality of locking grooves are arranged at equal intervals along the circumferential direction of the outer side wall of the closing lock hoop, and locking rod assemblies are arranged in the locking grooves corresponding to the two closing lock hoops.

[0018] A physical model testing device for the bearing capacity of a single pile based on a static load test is disclosed herein, wherein the support and guide assembly comprises a plurality of threaded screws, the threaded screws are vertically arranged and the bottom ends are fixedly connected to the top end of the counterweight seat, a plurality of the threaded screws are circumferentially and evenly spaced apart on the outside of the test cylinder, the inner side wall of the co-located gear sleeve is threadedly connected to the top end of the outer side wall of the threaded screw, and the end of the cross reaction beam is movably connected to the top end of the threaded screw.

[0019] According to a physical model testing device for single pile bearing capacity based on static load test of the present invention, a bearing sleeve is fixedly arranged inside the end of the cross reaction beam, and the inner side wall of the bearing sleeve is slidably connected to the top end of the outer side wall of the cross reaction beam.

[0020] A testing method of a single pile bearing capacity physical model testing device based on a static load test comprises the following steps:

[0021] Make test piles;

[0022] Prepare PVC pipes according to the set pile diameter and pile length, cut the PVC pipes into two halves and wipe them clean, use stainless steel clamps to fix the cut PVC pipes at the upper and lower ends, put steel cages into the PVC pipes and pour concrete, vibrate until no bubbles are generated, remove the molds after 48 hours, and carry out natural curing for 28 days. After the curing is completed, take out the test piles;

[0023] Fill the test cylinder with soil;

[0024] Clean the test cylinder, lay a supporting soil layer at the bottom of the test cylinder, then place the test pile on top of the supporting soil layer, place multiple strain gauge pressure sensors on the surface of the test pile, and then fill the surrounding soil layer outside the test pile;

[0025] The first pressure applying part is placed above the surrounding soil layer, and the second pressure applying part is placed on the top of the test pile. The first pressure applying part is used to apply a preload, and then a static load test is performed through the second pressure applying part.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] The present invention adopts a self-designed model device to carry out indoor single pile static load test, organizes the test results and analyzes the load-settlement curve of the pile top, the pile side friction resistance and the pile end resistance change, analyzes the influence of the pile body size and the compaction degree of volcanic soil on the single pile bearing capacity, the end resistance load sharing ratio and the pile side friction resistance in the volcanic soil foundation, and compared with the field test, the time cost and economic cost of the model test are easy to control. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work:

[0029] Figure 1 It is the front view of the present invention;

[0030] Figure 2 It is a side view of the present invention;

[0031] Figure 3 It is a cross-sectional view of the present invention;

[0032] Figure 4 It is a schematic diagram of the decomposition of the present invention;

[0033] Figure 5 It is a schematic diagram of the counterweight seat and the test cylinder of the present invention;

[0034] Figure 6 This is an example of the second embodiment of the present invention. Figure 1 ;

[0035] Figure 7 This is an example of the second embodiment of the present invention. Figure 2 ;

[0036] Figure 8 This is an example of the second embodiment of the present invention. Figure 3 ;

[0037] Fig. 9 It is a schematic diagram of the load-settlement curve of the present invention;

[0038] Fig.10 It is a schematic diagram for comparing total loads of different pile diameters of the present invention;

[0039] Fig.11 It is a schematic diagram comparing the load sharing ratios of the end resistance of different pile diameters according to the present invention;

[0040] Fig.12 It is a schematic diagram of the comparison structure of pile side friction resistance of different pile diameters of the present invention;

[0041] Fig.13 It is a schematic diagram of total load comparison of different pile lengths of the present invention;

[0042] Fig.14 It is a schematic diagram comparing the load sharing ratio of the end resistance of different pile lengths of the present invention;

[0043] Fig.15 It is a schematic diagram of the comparison structure of pile side friction resistance of different pile lengths of the present invention;

[0044] Fig.16 It is a schematic diagram of total load comparison of different pile lengths of the present invention;

[0045] Fig.17 It is a schematic diagram comparing the load sharing ratio of the end resistance of different pile lengths of the present invention;

[0046] Fig.18 It is a schematic diagram of the comparative structure of pile side friction resistance of different pile lengths according to the present invention.

[0047] Among them, 1. counterweight seat; 2. threaded screw; 3. test cylinder; 4. cross reaction beam; 5. outer pressure plate; 6. inner pressure plate; 7. central gear; 8. test pile; 9. strain gauge pressure sensor; 101. bottom support; 102. preload chamber; 103. limit gasket; 104. probe rod; 105. support and pressure assembly; 106. displacement sensor assembly; 1011. azimuth line groove; 1012. probe groove; 1013. sealing ring shaft; 1041, transfer support shaft; 1042, pressure spring; 301, fixed bottom cylinder; 302, layered sleeve; 303, closing lock hoop; 3031, lock groove; 3032, lock rod assembly; 401, bearing sleeve; 501, pre-load assembly; 601, boost assembly; 602, pressure sensor; 603, displacement meter; 701, motor assembly; 702, co-located gear sleeve shaft; 801, surrounding soil layer; 802, supporting soil layer. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] Embodiment 1:

[0051] Reference Figures 1 to 5As shown, this embodiment provides a physical model testing device for single pile bearing capacity based on static load test, comprising:

[0052] Counterweight seat 1;

[0053] A test tube 3 is arranged on the top of the counterweight seat 1, and is used to hold the test sample;

[0054] A support guide assembly is arranged at the top of the counterweight seat 1, and the support guide assembly is circumferentially arranged outside the test cylinder 3;

[0055] The pressure applying mechanism is movably arranged at the top of the support and guide assembly. The pressure applying mechanism is adapted to the test cylinder 3 and corresponds to each other up and down. The pressure applying mechanism is used to apply pressure to the test sample in the test cylinder 3. The support and guide assembly is used to guide the up and down movement of the pressure applying mechanism.

[0056] Furthermore, the pressure applying mechanism includes a cross reaction beam 4, which is movably arranged at the top of the support and guide assembly. A lifting drive unit is fixedly connected to the center of the cross reaction beam 4. The lifting drive unit is threadedly connected to the top of the support and guide assembly. The lifting drive unit is used to drive the cross reaction beam 4 to move up and down on the support and guide assembly. A first pressure applying unit and a second pressure applying unit are fixedly connected to the bottom end of the cross reaction beam 4. The second pressure applying unit is located at the center of the first pressure applying unit. The first pressure applying unit and the second pressure applying unit are used to apply pressure to the test sample in the test cylinder 3.

[0057] Furthermore, the lifting drive unit includes a motor assembly 701, which is fixedly arranged at the center position of the cross reaction beam 4. The output end of the motor assembly 701 is coaxially fixedly connected with a center gear 7. The center gear 7 is meshed with a plurality of coaxial gear sleeve shafts 702. The coaxial gear sleeve shafts 702 are threadedly connected to the top of the support guide assembly. The plurality of coaxial gear sleeve shafts 702 correspond one by one to the end portions of the cross reaction beam 4 and are rotatably connected.

[0058] When the center gear 7 rotates clockwise, the co-located gear sleeve shaft 702 will rotate counterclockwise. At this time, the co-located gear sleeve shaft 702 moves downward along the threaded screw 2, thereby pushing the cross reaction beam 4 to move downward. The co-located gear sleeve shaft 702 is used to realize the synchronous lifting operation of the four axial directions of the cross reaction beam 4. At the same time, the co-located gear sleeve shaft 702 can also lock the cross reaction beam 4 to prevent the cross reaction beam 4 from moving in the opposite direction during the process of applying pressure.

[0059] Furthermore, the first pressure applying part includes an outer pressure plate 5, which is fixedly connected to the bottom end of the cross reaction beam 4 through a plurality of pre-pressure components 501, and a clearance hole is opened in the center of the outer pressure plate 5, and the second pressure applying part is movably arranged in the clearance hole.

[0060] A constant force is applied through the preloading component 501, and different vertical forces are applied on the upper part of the soil layer by using the preloading component 501 to simulate the overburden pressure of the soil layer at different depths, so as to calculate and study the variation law of the pile-soil side friction resistance.

[0061] Furthermore, the second pressure applying part includes an inner pressure plate 6, which is movably arranged in the make way hole. The inner pressure plate 6 is fixedly connected to the bottom end of the cross reaction beam 4 through a booster assembly 601. Pressure sensors 602 are arranged between the top end of the booster assembly 601 and the bottom end of the cross reaction beam 4, and between the bottom end of the booster assembly 601 and the top end of the inner pressure plate 6. A displacement meter 603 is arranged on the outer wall of the booster assembly 601.

[0062] Furthermore, the test cylinder 3 includes a fixed base cylinder 301 and at least one layered sleeve 302. The fixed base cylinder 301 is arranged at the top of the counterweight seat 1, and the layered sleeve 302 is detachably arranged at the top of the fixed base cylinder 301. The connecting end between the fixed base cylinder 301 and the layered sleeve 302 and the connecting ends of two adjacent layered sleeves 302 are both provided with locking parts.

[0063] Furthermore, the locking portion includes two closing locking hoops 303, which are respectively arranged at the ends where the fixed base cylinder 301 is connected to the layered sleeve 302. The outer wall of the closing locking hoop 303 is provided with a plurality of locking grooves 3031, and the plurality of locking grooves 3031 are arranged at equal intervals along the circumferential direction of the outer wall of the closing locking hoop 303. Locking rod assemblies 3032 are arranged in the corresponding locking grooves 3031 of the two closing locking hoops 303.

[0064] The test tube 3 adopts a split structure design. When in use, the number of layered sleeves 302 to be used can be selected according to the length of the test pile 8. It is only necessary to fit the closing lock hoop 303 at the bottom of the layered sleeve 302 with the closing lock hoop 303 at the top of the fixed bottom tube 301, and then insert the locking rod assembly 3032 into the locking groove 3031 to lock it.

[0065] Furthermore, the supporting and guiding assembly includes a plurality of threaded screws 2, which are vertically arranged and whose bottom ends are fixedly connected to the top of the counterweight seat 1, and a plurality of threaded screws 2 are circumferentially evenly spaced on the outside of the test tube 3, the inner wall of the co-located gear sleeve shaft 702 is threadedly connected to the top of the outer wall of the threaded screw 2, and the end of the cross reaction beam 4 is movably connected to the top of the threaded screw 2.

[0066] Furthermore, a bearing sleeve 401 is fixedly disposed inside the end of the cross reaction beam 4 , and the inner wall of the bearing sleeve 401 is slidably connected to the top end of the outer wall of the cross reaction beam 4 .

[0067] A testing method of a single pile bearing capacity physical model testing device based on a static load test comprises the following steps:

[0068] Making test piles 8;

[0069] Prepare a PVC pipe according to the pile diameter and pile length of the set pile, cut the PVC pipe into two halves and wipe them clean, use stainless steel clamps to fix the cut PVC pipe into two halves at the upper and lower ends, put a steel cage into the PVC pipe and pour concrete, vibrate until no bubbles are generated, remove the mold after 48 hours, and carry out natural curing for 28 days. After the curing is completed, take out the test pile 8;

[0070] Fill the test tube 3 with soil;

[0071] Clean the test tube 3, lay a supporting soil layer 802 at the bottom of the test tube 3, then place the test pile 8 on the top of the supporting soil layer 802, place multiple strain gauge pressure sensors 9 on the surface of the test pile 8, and then fill the surrounding soil layer 801 outside the test pile 8;

[0072] Clean the test cylinder 3, and when filling the supporting soil layer 802 below the test pile 8, use layered filling, use a hammer to manually compact and level after filling every 20 cm, make marks inside the test cylinder 3, accurately place the test pile 8, place a pressure sensor 602 at the bottom of the test pile 8 to record the pile bottom load, and place multiple strain gauge pressure sensors 9 on the surface of the test pile 8 to detect the horizontal force on the pile body, then fill the surrounding soil layer 801 outside the pile body, and the surrounding soil layer 801 is also filled in layers and compacted and leveled;

[0073] The first pressure applying part is placed above the surrounding soil layer 801, and the second pressure applying part is placed on the top of the test pile 8. The first pressure applying part is used to apply a preload, and then a static load test is performed through the second pressure applying part.

[0074] The outer pressure plate 5 is used in conjunction with the pre-pressure assembly 501 to apply pre-pressure. After the pressure gauge reading is stable, a static load test is performed through the inner pressure plate 6 in conjunction with the booster assembly 601.

[0075] Embodiment 2:

[0076] In order to solve the problem that in the existing single pile static load test, the pile body may break during the actual settlement process due to the influence of the pile body casting structure and materials, and the test personnel cannot intuitively understand the structural changes of the pile body, which will lead to deviations in the test data; this embodiment provides the following technical solutions.

[0077] Reference Figures 6 to 8As shown, the difference between this embodiment and the first embodiment is that a pre-compression chamber 102 is provided inside the counterweight seat 1, and a bottom bracket 101 is provided above the pre-compression chamber 102, wherein a support and pressure assembly 105 is provided at the bottom of the bottom bracket 101, and a sealing ring shaft 1013 is provided on the outer side of the bottom of the bottom bracket 101, and eight azimuth line grooves 1011 are provided on the outer surface of the bottom bracket 101, and exploration grooves 1012 are provided on both sides of the azimuth line grooves 1011, wherein a probe rod 104 is provided inside the exploration groove 1012. The probe rod 104 is telescopically connected to the bottom bracket 101 through the probe groove 1012. The bottom of the probe rod 104 is provided with a transfer support shaft 1041, and the bottom of the transfer support shaft 1041 is provided with a pressure spring 1042. The bottom of the pre-compression chamber 102 is provided with a displacement sensor component 106, and the displacement sensor component 106 corresponds to the probe rod 104. Among them, the outer side of the displacement sensor component 106 is provided with a limited position gasket 103. When filling the soil, the probe rod 104 and the bottom bracket 101 maintain the same horizontal height. After the filling is completed, After the soil and pile burying operations, the soil layer is compacted by using a pressure plate, and the probe rod 104 drops under the influence of the pressure of the soil layer. At this time, the distance information of each probe rod 104 point is recorded by the displacement sensor component 106. In the process of compacting the soil layer, the bottom support 101 and the support and pressure component 105 at the bottom thereof will shrink and settle until the sealing ring shaft 1013 outside the bottom support 101 contacts the limit gasket 103. At this time, the bottom support 101 can no longer descend, and the probe rod 104 will be inserted into the interior of the soil layer. When the pile body settles, the soil layer will be squeezed and move and deform. Under normal conditions, the soil layer at the bottom of the pile body is evenly stressed, and the settlement depth error of the surrounding soil layers is small. When the pile body breaks, the stress point of the bottom soil layer will change. At this time, the probe rod 104 in the area on the side with heavier stress will remain in its original state or drop, while the probe rod 104 in the area on the side with lighter stress will rise. In this way, it can be timely fed back in which direction of the pile body is broken, so that the staff can make a judgment.

[0078] Test example:

[0079] Since the use of bored piles in the model box has the disadvantages of high time cost, low success rate, inaccurate measurement, etc., the present invention selects prefabricated reinforced concrete piles and scrapes the pile side to simulate the contact state between the bored pile and the soil. The core pile material is C30 concrete; volcanic soil is prepared according to the optimal moisture content and weighed for standby use. According to different pile lengths, pile diameters and volcanic soil compaction, a total of six groups of experiments are designed, as shown in the following table:

[0080]

[0081] See also Fig. 9,It can be seen from the load-settlement curve in the figure that the curves under different test conditions show a high degree of similarity. From the overall trend, with the increase of pile top settlement, the total load on the pile top, the pile end load and the pile side friction resistance all increase accordingly. In the early stage of loading, the total load on the pile top maintains a linear growth trend similar to the pile side friction resistance;

[0082] Subsequently, the pile side friction resistance was fully exerted and remained stable under a small displacement, and the curve showed an obvious inflection point, and the total load on the pile top showed a slow growth trend similar to the pile end resistance. This shows that after the pile side friction resistance was fully exerted, the total load on the pile top was gradually borne by the pile end resistance;

[0083] The analysis shows that after the vertical load begins to be applied to the pile top, the pile body is compressed downward and displaced, the pile side moves relative to the adjacent soil, the soil particles are affected by the pile body and displace with each other and produce bite effects, while friction is generated with the pile body interface, and the pile body begins to be subject to upward friction resistance from the soil.

[0084] As the load continues to increase, the lateral friction resistance at the bottom of the pile body gradually begins to bear the vertical pressure; when it increases to a certain value, the pile end begins to displace downward, which means that the reaction force at the pile end begins to play a role at this time; when the displacement reaches a certain value, the pile side friction resistance has been fully exerted, while the pile end resistance continues to increase; during the loading process, the pile side friction resistance fluctuates to varying degrees with the increase of displacement. The reason is that in the process of relative displacement between the pile side soil and the pile body and the generation of friction resistance, the volcanic soil produces different degrees of particle crushing, and the rearrangement of particles leads to fluctuations in the pile side friction resistance-settlement curve.

[0085] See also Fig.10 It can be seen that when other conditions remain unchanged, the development trends of the total load-settlement curves of pile tops with different pile diameters are similar; in the early stage of loading, the curves all show a linear growth trend; when loading continues, the curves all show obvious inflection points, showing a steep drop type;

[0086] As can be seen from Figure (a), when the compaction degree of volcanic soil is 85% and the pile length is 300mm, the relationship curves between the total load and settlement of the pile top of P1 (pile diameter 50mm) and P4 (pile diameter 100mm) have similar trends, but after the load approaches the ultimate bearing capacity, the difference between the curves tends to expand. The total settlement of the piles is 1.45mm and 3.02mm, respectively, and the settlement has increased by 1.57mm; according to the Qs curve turning point method for determining the vertical ultimate bearing capacity of a single pile, the ultimate bearing capacity of the single piles of P1 and P4 is 2290N and 2410N, respectively; with the increase of the pile diameter, the ultimate bearing capacity increases by 120N, an increase of 5.24%;

[0087] As can be seen from Figure (b), when the compaction degree of volcanic soil is 97% and the pile length is 300mm, the load-settlement curves of P2 (pile diameter 50mm) and P5 (pile diameter 100mm) are relatively consistent under the initial low load, but as the load continues to increase, the effect of the increase in pile diameter on the load-settlement curve gradually becomes apparent; the ultimate bearing capacity of P2 and P5 is 2430N and 2670N respectively, and the ultimate bearing capacity increases by 240N, an increase of 9.88%; the final settlements are 2.01mm and 2.16mm respectively, with small changes;

[0088] As can be seen from Figure (c), when the compaction degree of volcanic soil is 97% and the pile length is 450mm, the ultimate bearing capacity of the single pile of P3 (pile diameter 50mm) and P6 (pile diameter 100mm) is 2630N and 2840N respectively, which increases by 210N, an increase of 7.98%. The final settlement is 1.35mm and 2.51mm, and the settlement increases by 1.16mm; From the above analysis, it can be seen that the increase in pile diameter increases the settlement and ultimate bearing capacity of the pile body when it is unstable to varying degrees; when the compaction degree of volcanic soil is 97%, the increase in the ultimate bearing capacity of the single pile caused by the increase in pile diameter is more obvious;

[0089] See also Fig.11 It can be seen that the end resistance load sharing ratio is the ratio of the pile end resistance to the total load on the pile top. Assuming the total load on the pile top is Q, the pile end resistance is Qb, and the end resistance load sharing ratio is Qb / Q. The curve of the change of the end resistance load sharing ratio with the total load on the pile top under different pile diameters is as follows: Fig.10 As shown;

[0090] The overall trend of the total load on the pile top - end resistance load sharing ratio curves under different pile diameters is similar. In the early stage of loading, the end resistance load sharing ratio increases slowly, and then there is an obvious inflection point, and the slope begins to increase. Analysis shows that this is because the side friction resistance of the pile is fully exerted in the early stage of loading, and the end resistance load sharing is relatively small, while the continued increase in the total load on the pile top is mainly borne by the pile end resistance;

[0091] As can be seen from Figure (a), when the compaction degree of volcanic soil is 85% and the pile length is 300mm, the end resistance load sharing ratio of the two pile diameters first increases linearly with the increase of the total load on the pile top in the early stage of loading, and then the curve drops sharply, P1 increases slowly, and P4 decreases slightly, but overall remains stable. With continued loading, the end resistance load sharing ratio maintains a high growth rate. When the pile body becomes unstable, the end resistance load sharing ratio of P1 is 35.37%, and the end resistance load sharing ratio of P4 is 33.61%, and the end resistance load sharing ratio does not change much;

[0092] It can be seen from Figure (b) that when the compaction degree of volcanic soil is 97% and the pile length is 300 mm, the curve change trend is similar to that of Figure (a). When the pile body is unstable, the end resistance load sharing ratio of P2 is 28.40%, and the end resistance load sharing ratio of P5 is 32.03%, which increases by 3.63%.

[0093] As can be seen from Figure (c), when the compaction degree of volcanic soil is 97% and the pile length is 450mm, the early loading trend is similar to (a) and (b); the difference is that with the increase of load, the growth rate of the end resistance load sharing ratio of P6 is greater than that of P3. When the pile body is unstable, the end resistance load sharing ratio of P3 is 22.05%, and the end resistance load sharing ratio of P6 is 28.5%, with a difference of 6.45%, which is relatively large. From the above analysis, it can be seen that when the pile length is 300mm, changing the pile diameter and thus changing the aspect ratio l / d has little effect on the change of the end resistance load sharing ratio when the pile body is unstable; when the pile length increases from 300mm to 450mm, the pile diameter increases, the aspect ratio decreases, and the end resistance load sharing ratio when the pile body is unstable increases significantly. It can be seen that when the pile length is large, the expansion of the pile diameter will cause an increase in the end resistance load sharing ratio.

[0094] Depend on Fig.12 It can be seen that when the pile body is unstable, the pile side friction resistance of P1 and P4 is 1480N and 1600N respectively. With the increase of pile diameter, the pile side friction resistance increases by 120N, and the growth rate is 8.11%.

[0095] It can be seen from Figure (b) that when the pile body is unstable, the pile side friction resistance of P2 and P5 is 1740N and 1800N respectively, and the increase ratio is 3.45%;

[0096] Figure (c) shows that the pile side friction resistance of P3 and P6 is 2050N and 2139N respectively when the pile body is unstable, which increases by 4.34%. From the above analysis, it can be seen that the pile diameter is positively correlated with the pile side friction resistance, and the increase of pile diameter will cause the increase of pile side friction resistance.

[0097] from Fig.13 It can be seen that when other conditions remain unchanged, the development trends of the total load-settlement curves of the pile tops with different pile lengths are similar. In the early stage of loading, the curves show a linear growth trend. When the loading continues, the curves show obvious inflection points, showing a steep drop.

[0098] As can be seen from Figure (a), when the pile diameter is 50mm and the volcanic soil compaction degree is 97%, the final settlements of P2 and P3 are 2.01mm and 1.35mm respectively, which is a decrease of 0.66mm. The ultimate bearing capacity of the single pile is 2430N and 2630N, which is an increase of 8.23%.

[0099] It can be seen from the curve in Figure (b) that the settlement of P5 and P6 when the pile body was unstable was 2.16mm and 2.51mm respectively, an increase of 0.35mm. The ultimate bearing capacity of the single pile was 2670N and 2840N, and the ultimate bearing capacity increased by 170N, an increase of 6.37%. It can be seen that increasing the pile length has no regular effect on the change of settlement, but has a relatively obvious effect on improving the ultimate bearing capacity of the single pile.

[0100] Depend on Fig.14 It can be seen that the end resistance load sharing ratio under different pile lengths shows an increasing trend with the increase of the total load on the pile top; when the pile body is unstable, the end resistance load sharing ratios of P2 and P3 are 28.4% and 22.5% respectively. With the increase of pile length, the aspect ratio of the pile increases from 6 to 9, and the end resistance load sharing ratio decreases by 20.77%.

[0101] The end resistance load sharing ratios of P5 and P6 are 32.03% and 28.5% respectively. With the increase of pile length, the end resistance load sharing ratio decreases by 11.02%. From the above analysis, it can be seen that compared with the change of pile diameter, the change of length-diameter ratio caused by the change of pile length has a more significant effect on the end resistance load sharing ratio. As the length-diameter ratio increases, the end resistance load sharing ratio decreases.

[0102] Depend on Fig.15 It can be seen that the increase of pile length has a significant promoting effect on the increase of pile side friction when the pile body is unstable. When the pile body is unstable, the pile side friction of P2 and P3 is 1740N and 2050N respectively, with an increase of 17.82%.

[0103] The pile side friction resistance of P5 and P6 are 1800N and 2139N respectively, which increases by 339N, and the growth rate is 18.83%. The analysis shows that the increase of pile length means the increase of pile side area, and the increase of contact interface between pile body and soil, which increases the pile side friction resistance. From the above analysis, it can be seen that the increase of pile length will cause a significant increase in pile side friction resistance. Compared with pile diameter, the change of pile length has a more obvious effect on pile side friction resistance.

[0104] Depend on Fig.16 It can be seen that by comparing Figure (a) and Figure (b), the increase in pile diameter makes the difference in the curves more obvious. Figure (a) shows that in the early stage of loading, the curve trajectories of P1 and P2 are highly similar. As the load approaches the ultimate bearing capacity, the difference between the two curves gradually increases. When the pile body is unstable, the settlement of P1 and P2 is 1.45mm and 2.01mm respectively;

[0105] The ultimate bearing capacity is 2290N and 2430N, respectively, an increase of 6.11%. The settlement of P4 and P5 is 3.02mm and 2.16mm respectively; the ultimate bearing capacity is 2410N and 2670N, respectively, and the bearing capacity increase reaches 10.79%. It can be seen that the increase in compaction degree has no obvious effect on the settlement of the pile body, but has a relatively obvious effect on the increase of bearing capacity.

[0106] Depend on Fig.17 It can be seen that, by comparing (a) and (b), the curves all show a plateau during the loading process, which is the same as the above-mentioned law of different pile diameters and pile lengths;

[0107] As shown in Figure (a), the end resistance load sharing ratios of P1 and P2 are 35.37% and 28.40% respectively. With the increase of compaction degree, the end resistance load sharing ratio decreases by 19.71%.

[0108] As shown in Figure (b), the end resistance load sharing ratios of P4 and P5 are 33.61% and 32.03% respectively. With the increase of compaction degree, the end resistance load sharing ratio decreases by 4.7%. From the above analysis, it can be concluded that increasing the compaction degree increases the pile side friction resistance and reduces the end resistance load sharing ratio.

[0109] Depend on Fig.18 It can be seen from Figure (a) that when the pile body is unstable, the pile side friction resistance of P1 and P2 is 1480N and 1740N respectively, which increases by 260N, and the increase is 17.57%;

[0110] Figure (b) shows that the side friction resistance of P5 increased by 200N compared with P4, with an increase rate of 12.5%. Analysis shows that the increase in compaction reduces the pores between the soil and increases the contact area between the soil and the pile body. During the test, the friction resistance required for the mutual engagement, dislocation and rearrangement of soil particles increases.

[0111] At the same time, studies have shown that the particle angle and surface roughness of volcanic soil are much higher than those of general angular gravel soil, so the more compact volcanic soil will produce greater side friction resistance when in contact with the pile body. Therefore, in actual engineering, the side friction resistance of the pile can be fully utilized to bear the pile top load by increasing the compaction degree of volcanic soil.

[0112] In summary, enlarging the pile diameter can significantly increase the ultimate bearing capacity of a single pile, and will cause an increase in the settlement of the pile top and the load sharing ratio of the end resistance. When the compaction degree of volcanic soil is 97%, the increase in the ultimate bearing capacity of a single pile caused by the increase in the pile diameter is more obvious.

[0113] Increasing the pile length has a better effect on improving the ultimate bearing capacity of a single pile. Compared with the pile diameter, the change of pile length has a more significant effect on the end resistance load sharing ratio. As the pile length increases, the end resistance load sharing ratio decreases.

[0114] The increase of compaction degree can significantly improve the ultimate bearing capacity of a single pile. The volcanic soil with greater compaction degree will produce greater side friction resistance in the process of interaction with the pile, and the load sharing ratio of the end resistance will also decrease.

[0115] The increase of pile diameter, pile length and volcanic soil compaction can increase the pile side friction resistance. Among them, the change of pile length has the greatest impact on the pile side friction resistance, and the pile diameter has the least impact on it.

[0116] In the description of the present invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0117] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the protection scope of the present invention.

Claims

1. A physical model testing device for single pile bearing capacity based on static load test, characterized in that: include Counterweight seat (1); A test cylinder (3) is arranged on the top of the counterweight seat (1), and the test cylinder (3) is used to hold the test sample; A support guide assembly is arranged at the top end of the counterweight seat (1), and the support guide assembly is circumferentially arranged outside the test cylinder (3); A pressure applying mechanism is movably arranged at the top end of the support and guide assembly. The pressure applying mechanism is adapted to the test cylinder (3) and corresponds to each other up and down. The pressure applying mechanism is used to apply pressure to the test sample in the test cylinder (3). The support and guide assembly is used to guide the up and down movement of the pressure applying mechanism.

2. A physical model testing device for single pile bearing capacity based on static load test according to claim 1, characterized in that: The pressure applying mechanism comprises a cross reaction beam (4), the cross reaction beam (4) is movably arranged at the top end of the support guide assembly, a lifting drive unit is fixedly connected to the center of the cross reaction beam (4), the lifting drive unit is threadedly connected to the top end of the support guide assembly, the lifting drive unit is used to drive the cross reaction beam (4) to move up and down on the support guide assembly, the bottom end of the cross reaction beam (4) is fixedly connected to a first pressure applying unit and a second pressure applying unit, the second pressure applying unit is located at the center of the first pressure applying unit, and the first pressure applying unit and the second pressure applying unit are used to apply pressure to the test sample in the test cylinder (3).

3. A physical model testing device for single pile bearing capacity based on static load test according to claim 2, characterized in that: The lifting drive unit comprises a motor assembly (701), the motor assembly (701) is fixedly arranged at the center position of the cross reaction beam (4), the output end of the motor assembly (701) is coaxially fixedly connected with a central gear (7), the central gear (7) is meshed with a plurality of co-located gear sleeve shafts (702), the co-located gear sleeve shafts (702) are threadedly connected to the top end of the support guide assembly, and the plurality of co-located gear sleeve shafts (702) correspond to the ends of the cross reaction beam (4) one by one and are rotatably connected.

4. A physical model testing device for single pile bearing capacity based on static load test according to claim 2, characterized in that: The first pressure applying part comprises an external pressure plate (5), the external pressure plate (5) being fixedly connected to the bottom end of the cross reaction beam (4) via a plurality of pre-pressure components (501), a clearance hole being provided at the center of the external pressure plate (5), and the second pressure applying part being movably arranged in the clearance hole.

5. A physical model testing device for single pile bearing capacity based on static load test according to claim 4, characterized in that: The second pressure applying part comprises an inner pressure plate (6), the inner pressure plate (6) being movably arranged in the clearance hole, the inner pressure plate (6) being fixedly connected to the bottom end of the cross reaction beam (4) via a booster assembly (601), pressure sensors (602) being arranged between the top end of the booster assembly (601) and the bottom end of the cross reaction beam (4), and between the bottom end of the booster assembly (601) and the top end of the inner pressure plate (6), and a displacement meter (603) being arranged on the outer wall of the booster assembly (601).

6. A physical model testing device for single pile bearing capacity based on static load test according to claim 1, characterized in that: The test cylinder (3) comprises a fixed base cylinder (301) and at least one layered sleeve (302); the fixed base cylinder (301) is arranged at the top of the counterweight seat (1); the layered sleeve (302) is detachably arranged at the top of the fixed base cylinder (301); the connection end between the fixed base cylinder (301) and the layered sleeve (302) and the connection ends of two adjacent layered sleeves (302) are both provided with locking parts.

7. A physical model testing device for single pile bearing capacity based on static load test according to claim 6, characterized in that: The locking portion comprises two closing locking hoops (303), the two closing locking hoops (303) are respectively arranged at the ends where the fixed bottom cylinder (301) is connected to the layered sleeve (302), the outer wall of the closing locking hoop (303) is provided with a plurality of locking grooves (3031), the plurality of locking grooves (3031) are arranged at equal intervals along the circumferential direction of the outer wall of the closing locking hoop (303), and locking rod assemblies (3032) are arranged in the locking grooves (3031) corresponding to the two closing locking hoops (303).

8. The physical model testing device for single pile bearing capacity based on static load test according to claim 3, characterized in that: The support and guide assembly comprises a plurality of threaded screws (2), wherein the threaded screws (2) are vertically arranged and the bottom ends are fixedly connected to the top end of the counterweight seat (1), and the plurality of threaded screws (2) are circumferentially arranged at equal intervals on the outside of the test cylinder (3), the inner wall of the co-located gear sleeve (702) is threadedly connected to the top end of the outer wall of the threaded screw (2), and the end of the cross reaction beam (4) is movably connected to the top end of the threaded screw (2).

9. A physical model testing device for single pile bearing capacity based on static load test according to claim 8, characterized in that: A bearing sleeve (401) is fixedly arranged inside the end of the cross reaction beam (4), and the inner side wall of the bearing sleeve (401) is slidably connected to the top end of the outer side wall of the cross reaction beam (4).

10. A testing method for a physical model testing device for single pile bearing capacity based on static load test according to any one of claims 1 to 9, characterized in that: The following steps are involved: Making a test pile (8); Prepare a PVC pipe according to the set pile diameter and pile length, cut the PVC pipe into two halves and wipe them clean, use stainless steel clamps to fix the cut PVC pipe at the upper and lower ends, put a steel cage into the PVC pipe and pour concrete, vibrate until no bubbles are generated, remove the mold after 48 hours, and carry out natural curing for 28 days. After the curing is completed, take out the test pile (8); The test cylinder (3) is filled with soil; Clean the test tube (3), lay a supporting soil layer (802) at the bottom of the test tube (3), then place a test pile (8) on the top of the supporting soil layer (802), place a plurality of strain gauge pressure sensors (9) on the surface of the test pile (8), and then fill the surrounding soil layer (801) outside the test pile (8); The first pressure applying part is placed above the surrounding soil layer (801), and the second pressure applying part is placed on the top of the test pile (8). The first pressure applying part is used to apply a preload, and then a static load test is performed through the second pressure applying part.

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