Cloth bag pile performance checking method

Abstract

The invention discloses a cloth bag pile performance checking method. The method comprises the following steps that S1, tensile strength, tearing strength, puncture resistance and permeability tests are conducted on a geomembrane wrapping a cloth bag pile; s2, the concrete pouring elevation is detected in the cloth bag pile concrete pouring pile forming process based on the measuring rope; s3, the volume, the change elevation and the sectional area data of the cast-in-place concrete of the cloth bag pile are obtained through segmented multiple times of measurement, and the shape of the cloth bag pile is calculated according to the change trend of the data; and S4, estimating the bulged thickness of the drum-shaped body and the actual maximum tensile stress according to the concrete over-filling volume, comparing the maximum tensile stress with the standard tensile strength, and checking the strength of the geomembrane bag. According to the cloth bag pile performance checking method, before cloth bag pile construction is carried out, the related performance of the cloth bag pile is checked, the complexity of the cloth bag pile structure can be well dealt with, and the cloth bag pile performance checking method is better suitable for pile foundation construction of karst areas with the complex geographical environment.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation construction, and in particular to a bag pile performance verification method. Background Art

[0002] One of the most notable geological features of karst landforms is that groundwater in karst areas dissolves along rock cracks or sinkholes, forming interpenetrating or merging pipes and caves, and forming a large number of difficult-to-treat karst caves and soil caves, which pose a great quality and safety hazard to pile foundation construction. Construction in karst areas may encounter stone bud foundations and karst cave foundations, which can easily lead to problems such as insufficient bearing capacity of the foundation, uneven settlement of the foundation, deformation and instability. In addition, complex geological conditions bring many difficulties to construction. Some pile foundations collapse as soon as they are drilled, and can only be repeatedly backfilled and re-drilled, which leads to extended construction period and increased engineering volume and cost.

[0003] Bag pile is a construction technology used for soil reinforcement. It is often used for soft soil foundation treatment and can be well applied to the construction in karst landforms. The traditional construction technology of bag pile is to first use a geological drill or other hole-making machinery to drill a cylindrical hole at the designed position, then put the bag with the grouting pipe into the cylindrical hole, and then use the grouting pump to press the slurry from top to bottom step by step. The grouting speed cannot be too fast. Finally, the bag is opened to form a columnar or gourd-shaped pile body in the reinforced soil. However, after the bag pile construction is completed, there is currently no effective method to check the performance of the bag pile, which makes it impossible to better judge the performance of the pile foundation. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, a bag pile performance verification method is provided.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] The present invention proposes a bag pile performance verification method, comprising the following steps:

[0007] S1: Conduct tensile strength, tear strength, puncture resistance and permeability tests on geomembranes wrapped with bag piles;

[0008] S2: Using the measuring rope, the concrete pouring elevation is detected during the pouring of bag pile concrete;

[0009] S3: The volume of concrete poured into the bag pile, the change in elevation and the cross-sectional area data are obtained by segmented multiple measurements. The shape of the bag pile is estimated based on the change trend of the data.

[0010] S4: According to the over-filling volume of concrete, estimate the protruding thickness of the drum and the actual maximum tensile stress, compare the maximum tensile stress with the standard tensile strength, and perform strength verification of the geomembrane bag.

[0011] Preferably, the tensile strength test includes:

[0012] Place the geotextile sample on the tensile testing machine, and press the clamping device evenly on both ends of the sample;

[0013] Set the force application speed and start the tensile test;

[0014] Record the applied force and corresponding elongation at each time point until the sample breaks;

[0015] Based on the experimental data, the tensile strength of the geotextile is calculated.

[0016] Tear strength tests include:

[0017] Place the geotextile sample on the tear tester, and press the clamping device evenly on both ends of the sample;

[0018] Set the force application speed and start the tearing test;

[0019] Record the applied force and the corresponding tear length at each time point until the sample breaks.

[0020] Preferably, the puncture resistance test includes:

[0021] Randomly take samples from the geotextile and mark the location of the cone puncture on the sample;

[0022] Prepare the cone piercer, place the sample on a flat workbench, insert the cone piercer vertically into the center of the sample, and then apply downward pressure;

[0023] During the puncture process, the puncture force and penetration depth of the cone tip were recorded at each time point.

[0024] Preferably, the permeability test includes:

[0025] The permeability coefficient of the flexible material for concrete slurry penetration is calculated using Darcy's law, which expresses the relationship between the permeation flow rate and the permeation pressure, and the formula is: Q = KA△h / L;

[0026] In the formula, Q is the seepage flow rate, K is the permeability coefficient of the flexible material, A is the cross-sectional area of ​​the flexible material, △h is the head difference on both sides of the flexible material, and L is the length of the flexible material. According to Darcy's law, the permeability coefficient of concrete slurry penetrating the flexible material is calculated.

[0027] Preferably, the test steps include:

[0028] Prepare the sample: prepare the concrete slurry as required, fix the flexible material sample in the test equipment, measure the thickness of the flexible material and record it, measure the size of the sample and calculate the cross-sectional area of ​​the sample, measure the mass of the sample, place the sample on the balance, measure the mass of the sample and record it;

[0029] Pressurization: Pressurize the concrete paste in the test equipment to make it penetrate the flexible material;

[0030] Measure the permeability. During the pressurization process, record the permeability at different time points and calculate the permeability coefficient for each time period.

[0031] Test the strength of the remaining slurry. Take the remaining concrete slurry out of the test equipment, make it into a standard concrete sample, and test its strength value after the curing time reaches the standard;

[0032] The average permeability coefficient and the strength index of the concrete slurry after permeability are calculated based on the test data.

[0033] Preferably, in S2, the concrete pouring elevation detection method includes:

[0034] S11: A measuring port is reserved in the casing at the top of the cast-in-place pile;

[0035] S12: According to the design requirements, concrete is poured into the pouring hole through the funnel and the conduit. During the pouring of concrete, a measuring rope with a scale is connected to the conical gyroscope, and the measuring rope is placed into the reserved measuring port by the natural drooping of the gyroscope's gravity;

[0036] S13: by adjusting the position of the measuring rope, the rope is stopped when the measuring rope gyro contacts the cast concrete surface, the depth of the measuring rope is measured and recorded, and the elevation of the cast-in-place pile concrete surface is obtained by conversion;

[0037] S14: Determine the volume of concrete poured each time through a funnel, measure the surface elevation of the pile concrete each time concrete is poured, repeat steps S12 and S3 for each measurement, and obtain the elevation and concrete pouring volume of the piles in batches and sections.

[0038] Preferably, the bag pile forming and bearing plate calculation method is to determine the concrete volume △V through a funnel, use a measuring rope to detect the surface elevation of the cast-in-place pile concrete to obtain the increased height △h of the cast-in-place pile, and convert it to obtain the cross-sectional area A of the cast-in-place pile. The calculation equation is expressed as follows: △V=A×△h;

[0039] Assuming that the bearing plate formed by the bag pile and the karst position is cylindrical, the radius R of the pile body and the bearing plate is calculated by the cross-sectional area of ​​the bag pile. The calculation equation is: A = π × R 2 ;

[0040] The shape of the bag pile is estimated by measuring the concrete pouring volume and the bag pile elevation in sections and multiple times. The shape of the cast-in-place pile is estimated based on the changing trend of the data.

[0041] Assuming that the location of the bag pile cave is the pile side cave, a branch-shaped bearing plate is formed at the cave location during the bag pile construction process. Therefore, the length L of the branch-shaped bearing plate of the bag pile is approximately calculated using the following equation: A = π × r 2 / 2+L 2 ;

[0042] When calculating the shape of cast-in-place piles, the shape of bag piles with different shapes of bearing plates produced by bag piles according to the size and shape of the cave is considered.

[0043] Preferably, the physical and mechanical parameters of the drum-shaped body are calculated by estimating the protruding thickness of the drum-shaped body and the actual maximum tensile stress according to the over-injection volume of concrete, where the over-injection volume of concrete = actual injection volume - designed volume;

[0044] According to the design size of the geomembrane bag, the drum height h can be obtained. Under the condition of known pile diameter r, the drum volume V can be calculated by formula (1): 鼓状体 , the length of the drum relative to the center of the pile R, the volume of the bulging part V 超 , drum-shaped body protrusion thickness W max , the formula is as follows:

[0045]

[0046] In order to verify whether the tensile strength of the membrane bag outside the drum meets the design requirements, the actual maximum tensile stress σ can be estimated based on the drum height h and pile diameter r. max , compared with the standard provided film bag material design tensile strength σ 设 contrast;

[0047] According to formula (2), the maximum tensile stress σ is calculated max , the formula is as follows:

[0048]

[0049] In the formula: l is the length of the membrane bag after deformation, ε is the maximum tensile strain of the membrane bag, E is the elastic modulus of the membrane bag, and h is the original length of the drum-shaped body out of the membrane bag, which is equal to the height of the drum-shaped body.

[0050] Preferably, the drum-shaped body protrusion thickness is estimated according to the infusion pressure and the membrane material parameters. According to Qian Wei's long circular membrane deformation calculation formula, the drum-shaped body protrusion thickness W can be estimated according to the infusion pressure p and the membrane material parameters. max , the formula is as follows:

[0051]

[0052] The dimensionless number P is taken from:

[0053]

[0054] Where p is the pressure on the membrane bag, a is 1 / 2 of the height of the drum, E is the elastic modulus of the membrane bag, d is the thickness of the membrane bag, and v is the Poisson's ratio of the membrane bag.

[0055] The constant c is solved from:

[0056] v=2cf′(c)f′ -1 (c)+1

[0057]

[0058] The g(c) value is taken from:

[0059]

[0060] The calculation of the tensile strength of the membrane bag on the outside of the drum is similar. The protruding thickness of the drum and the actual maximum tensile stress are estimated based on the over-filled concrete volume.

[0061] Preferably, the strength check and calculation of the geomembrane bag is performed using the most unfavorable pile with the deepest cave depth, and the maximum pressure P at the bottom of the cave is obtained by the following formula:

[0062] P=ρ 混 gh 混 -ρ 水 gh 水 (7);

[0063] The formula for calculating the bursting strength of geomembrane bags is as follows:

[0064]

[0065] Where, d 顶 is the diameter of the top pressure rod, σ 顶 It is the bursting strength of geomembrane bag;

[0066] Geomembrane bag tensile strength verification, sample tensile strength T max , the formula is as follows:

[0067] T max =F max / B (9);

[0068] Where, B is the nominal width of the specimen, in m, and F max To record the maximum load, unit KN, from which the longitudinal and transverse design tensile stress σ of the film bag can be obtained 设 , the formula is as follows:

[0069] σ 设=T max / d (10);

[0070] The elongation at break of the film bag is the designed tensile stress σ 设 Corresponding strain value ε max Therefore, the elastic modulus of the geomembrane bag can be obtained by formula (11), as follows:

[0071] E=σ 设 / ε max (11);

[0072] Based on the drum-shaped body, using equations (1) and (2), the protruding thickness of the drum-shaped body and the actual maximum tensile stress are estimated according to the overfilled concrete volume, and the actual maximum tensile stress σ is estimated. max , compared with the standard provided film bag material design tensile strength σ 设 By comparison, we can determine whether the tensile strength of the material meets the design requirements.

[0073] Compared with the prior art, the present invention has the following beneficial effects:

[0074] The bag pile performance verification method proposed in the present invention can obtain how to better wrap the steel cage by conducting tensile strength, tear strength, puncture resistance and permeability tests on the geomembrane wrapped with the bag pile. Before the bag pile construction is carried out, by verifying the relevant performance of the bag pile, the complexity of the bag pile structure can be better coped with, and it is better suitable for pile foundation construction in karst areas with complex geographical environments, thereby improving the reliability of pile foundation construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0076] Figure 1 It is the overall flow chart of the present invention;

[0077] Figure 2 This is a schematic diagram of the installation position of the geomembrane bag of the bag pile;

[0078] Figure 3 This is a schematic diagram of the geomembrane bag size of the bag pile;

[0079] Figure 4 This is a schematic diagram of fixing geomembrane bags on bag piles;

[0080] Figure 5 This is a schematic diagram of bag pile concrete pouring elevation detection;

[0081] Figure 6 This is a schematic diagram of the calculation of the cylindrical bag pile shape;

[0082] Figure 7This is a schematic diagram of the deduction and calculation of the branch-shaped bearing plate pile shape;

[0083] Figure 8 This is a schematic diagram of the pile shape deduction results of the bag pile;

[0084] Fig. 9 It is a schematic diagram of the drum-shaped body;

[0085] Fig.10 It is a schematic diagram of circular membrane deformation. DETAILED DESCRIPTION

[0086] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0087] like Figure 1-Figure 10 As shown, this embodiment proposes a bag pile performance verification method, comprising the following steps:

[0088] S1: Conduct tensile strength, tear strength, puncture resistance and permeability tests on geomembranes wrapped with bag piles;

[0089] S2: Using the measuring rope, the concrete pouring elevation is detected during the pouring of bag pile concrete;

[0090] S3: The volume of concrete poured into the bag pile, the change in elevation and the cross-sectional area data are obtained by segmented multiple measurements. The shape of the bag pile is estimated based on the change trend of the data.

[0091] S4: According to the over-filling volume of concrete, estimate the protruding thickness of the drum and the actual maximum tensile stress, compare the maximum tensile stress with the standard tensile strength, and perform strength verification of the geomembrane bag.

[0092] Tensile strength tests include:

[0093] Place the geotextile sample on the tensile testing machine, and press the clamping device evenly on both ends of the sample;

[0094] Set the force application speed and start the tensile test;

[0095] Record the applied force and corresponding elongation at each time point until the sample breaks;

[0096] Based on the experimental data, the tensile strength of the geotextile is calculated.

[0097] Tear strength tests include:

[0098] Place the geotextile sample on the tear tester, and press the clamping device evenly on both ends of the sample;

[0099] Set the force application speed and start the tearing test;

[0100] Record the applied force and the corresponding tear length at each time point until the sample breaks.

[0101] Puncture resistance tests include:

[0102] Randomly take out a sample from the geotextile, usually in the shape of a square with a length and width of 150 mm, and mark the location of the cone puncture on the sample;

[0103] Prepare a conical piercer, or a metal rod with a conical head. The top angle of the conical head should be 90 degrees, and the bottom diameter of the conical head is generally 5mm. Place the sample on a flat workbench, insert the conical piercer vertically into the center of the sample, and then apply pressure downward at a certain speed;

[0104] During the puncture process, the puncture force and penetration depth of the cone head were recorded at each time point, and the puncture speed was 2 mm / min.

[0105] Because the workability of concrete slurry and the permeability of bag pile flexible materials have a great correlation with the formation and strength of the pile foundation drum, in order to ensure smooth pile formation, it is necessary to ensure that the membrane bag has good permeability characteristics of water permeability but not slurry permeability. The permeability of different bag pile flexible materials, different concrete slurry mix ratios, injection pressure, water level and other factors were studied, and the pile formation was tested and evaluated. The permeability test includes:

[0106] The permeability coefficient of the flexible material for concrete slurry penetration is calculated using Darcy's law, which expresses the relationship between the permeation flow rate and the permeation pressure, and the formula is: Q = KA△h / L;

[0107] Where Q is the permeate flow rate, in m 3 / s, K is the permeability coefficient of the flexible material, the unit is m / s, A is the cross-sectional area of ​​the flexible material, the unit is m 2 , △h is the water head difference on both sides of the flexible material, in m, L is the length of the flexible material, in m. According to Darcy's law, the permeability coefficient of concrete slurry penetrating the flexible material is calculated.

[0108] The test steps include:

[0109] Prepare the sample: prepare the concrete slurry as required, and fix the flexible material sample in the test equipment, such as the permeameter, etc., measure the thickness of the flexible material, use a vernier caliper or other tool to measure the thickness of the flexible material, and record it, measure the size of the sample, use a tape measure or other tool to measure the length and width of the sample, and calculate the cross-sectional area of ​​the sample, measure the mass of the sample, place the sample on a balance, measure the mass of the sample, and record it;

[0110] Pressurization: Pressurize the concrete paste in the test equipment to make it penetrate the flexible material;

[0111] Measure the permeability. During the pressurization process, record the permeability at different time points and calculate the permeability coefficient for each time period.

[0112] Test the strength of the remaining slurry. Take the remaining concrete slurry out of the test equipment, make it into a standard concrete sample, and test its strength value after the curing time reaches the standard;

[0113] The average permeability coefficient and the strength index of the concrete slurry after permeability are calculated based on the test data.

[0114] When conducting the test of concrete slurry penetration of flexible materials, the test method should be strictly followed to ensure the accuracy and reliability of the test results. At the same time, it is also necessary to formulate a reasonable concrete slurry mix ratio according to the test requirements, and strictly control environmental conditions such as temperature and humidity during the test. The permeability of different bag pile flexible materials, different concrete slurry mix ratios, injection pressure, water level and other factors are studied, and the pile formation is tested and evaluated.

[0115] In S2, Figure 5 As shown, Figure 5 This is a schematic diagram of bag pile concrete pouring elevation detection. The concrete pouring elevation detection methods include:

[0116] S11: A measuring port with a size of not less than 100 mm shall be reserved in the casing at the top of the pile to facilitate the insertion of a measuring rope during concrete pouring;

[0117] S12: According to the design requirements, concrete is poured into the pouring hole through the funnel and the conduit. During the pouring of concrete, a measuring rope with a scale is connected to the conical gyroscope, and the measuring rope is placed into the reserved measuring port by the natural drooping of the gyroscope's gravity;

[0118] S13: by adjusting the position of the measuring rope, the rope is stopped when the measuring rope gyro contacts the cast concrete surface, the depth of the measuring rope is measured and recorded, and the elevation of the cast-in-place pile concrete surface is obtained by conversion;

[0119] S14: Determine the volume of concrete poured each time through a funnel, measure the surface elevation of the pile concrete each time concrete is poured, repeat steps S12 and S3 for each measurement, and obtain the elevation and concrete pouring volume of the piles in batches and sections.

[0120] like Figure 6 As shown, Figure 6 It is a schematic diagram of the calculation of the shape of cylindrical bag piles, the calculation method of bag pile formation and bearing plate, the concrete volume △V is determined by a funnel, the increased height △h of the pile is obtained by measuring the surface elevation of the pile concrete using a measuring rope, and the cross-sectional area A of the pile is obtained by conversion. The calculation equation is expressed as follows: △V=A×△h;

[0121] Assuming that the bearing plate formed by the bag pile and the karst position is cylindrical, the radius R of the pile body and the bearing plate is calculated by the cross-sectional area of ​​the bag pile. The calculation equation is: A = π × R 2 ;

[0122] The shape of the bag pile is estimated by measuring the concrete pouring volume and the bag pile elevation in sections and multiple times. The shape of the cast-in-place pile is estimated based on the changing trend of the data.

[0123] Assuming that the location of the bag pile cave is the pile side cave (pile radius is r), a branch-shaped bearing plate is formed at the cave location during the bag pile construction process, such as Figure 7 As shown, Figure 7 This is a schematic diagram of the deduction and calculation of the branch-shaped bearing plate pile shape. Therefore, the length L of the branch-shaped bearing plate of the bag pile is approximately calculated using the following equation: A = π × r 2 / 2+L 2 ;

[0124] When calculating the shape of cast-in-place piles, the accuracy and reliability of the measured data should be guaranteed as much as possible, and the shape of bag piles with different shapes of bearing plates should be considered according to the size and shape of the cave.

[0125] Calculation of the physical and mechanical parameters of the drum-shaped body: the protruding thickness of the drum-shaped body and the actual maximum tensile stress are estimated based on the over-filled concrete volume. The over-filled concrete volume = actual poured volume - designed volume.

[0126] According to the design size of geomembrane bag, drum-shaped body (such as Fig. 9 As shown, Fig. 9 is a schematic diagram of a drum-shaped body) with a height h. Under the condition that the pile diameter r is known, the volume V of the drum-shaped body can be calculated by formula (1): 鼓状体 , the length of the drum relative to the center of the pile R, the volume of the bulging part V 超 , drum-shaped body protrusion thickness W max , the formula is as follows:

[0127]

[0128] In order to verify whether the tensile strength of the membrane bag outside the drum meets the design requirements, the actual maximum tensile stress σ can be estimated based on the drum height h and pile diameter r. max , compared with the standard provided film bag material design tensile strength σ 设 contrast;

[0129] According to formula (2), the maximum tensile stress σ is calculated max , the formula is as follows:

[0130]

[0131]

[0132] Where: l is the length of the membrane bag after deformation (arc length), ε is the maximum tensile strain of the membrane bag, E is the elastic modulus of the membrane bag, and h is the original length of the drum-shaped body out of the membrane bag, which is equal to the height of the drum-shaped body.

[0133] The protruding thickness of the drum-shaped body can be estimated based on the injection pressure and membrane material parameters. According to Qian Wei's long circular membrane deformation calculation formula, the protruding thickness of the drum-shaped body W can be estimated based on the injection pressure p (approximately uniform load) and membrane material parameters. max , the formula is as follows:

[0134]

[0135] The dimensionless number P is taken from:

[0136]

[0137] Where p is the pressure on the membrane bag, a is 1 / 2 of the height of the drum, E is the elastic modulus of the membrane bag, d is the thickness of the membrane bag, and v is the Poisson's ratio of the membrane bag.

[0138] The constant c is solved from:

[0139] ν=2cf′(c)f -1 (c)+1

[0140]

[0141] The g(c) value is taken from:

[0142]

[0143] The calculation of the tensile strength of the membrane bag on the outside of the drum is similar. The protruding thickness of the drum and the actual maximum tensile stress are estimated based on the over-filled concrete volume.

[0144] The strength of geomembrane bags is checked and calculated using the most unfavorable pile with the deepest cave depth. The SP1 pull-out pile has a 4m high unfilled cave, which is larger and deeper than the caves of other pile numbers. Therefore, the SP1 pull-out pile is checked and calculated for strength. The diameter of the SP1 pile is 1m, the depth of the cave relative to the ground is 21-25m, the stable water level elevation at the pile is 108.3m, and the water level elevation relative to the bottom of the cave is 11.2m. Based on the above design data, the maximum pressure on the bottom of the cave under the combined action of concrete and groundwater can be obtained.

[0145] Concrete density ρ 混 is 2400kg / m3, concrete height h 混 is 25m, water level height h 水 is 11.2m, water density ρ 水 Take 1000kg / m3, the pile radius R is 0.5m, and the gravity acceleration g is 9.8N / kg. The maximum pressure P at the bottom of the cave is obtained by the following formula:

[0146] P=ρ 混 gh 混 -ρ 水 gh 水 (7);

[0147] Substituting the data, we get P = 0.48 MPa.

[0148] The tensile strength of the film bag (longitudinal and transverse) q is 5.8kN / m, and the CBR bursting strength F 顶 is 1.1kN, the film bag thickness d is 0.0006m, and the film bag breaking elongation ε max 38%

[0149] The formula for calculating the bursting strength of geomembrane bags is as follows:

[0150]

[0151] Where, d 顶 is the diameter of the top pressure rod, σ 顶 It is the bursting strength of geomembrane bag;

[0152] σ 顶 =0.56MPa, P = 0.48MPa <σ 顶 =0.56MPa, the bursting strength of the selected material meets the design requirements.

[0153] Geomembrane bag tensile strength verification, sample tensile strength T max , the formula is as follows:

[0154] T max =F max / B (9);

[0155] Where, B is the nominal width of the specimen, in m, and F max To record the maximum load, unit KN, from which the longitudinal and transverse design tensile stress σ of the film bag can be obtained 设 , the formula is as follows:

[0156] σ 设 =T max / d (10);

[0157] It can be obtained that σ 设 =9.67MPa.

[0158] The elongation at break of the film bag is the designed tensile stress σ 设 Corresponding strain value ε max Therefore, the elastic modulus of the geomembrane bag can be obtained by formula (11), as follows:

[0159] E=σ 设 / ε max (11);

[0160] It can be obtained that E=25.45MPa.

[0161] According to the drum-shaped body, using equations (1) and (2), the tensile strength of the selected material meets the design requirements, and the protruding thickness of the drum-shaped body and the actual maximum tensile stress are estimated according to the overfilled concrete volume, and the actual maximum tensile stress σ is estimated. max , compared with the standard provided film bag material design tensile strength σ 设 By comparison, it is determined that the tensile strength of the material meets the design requirements. Among them, h = 4m, r = 0.5m, and ε = 0.367. Substituting E = 25.45MPa and ε = 0.367, we can get σ max =9.34MPa,σ max =9.34MPa<σ 设 =9.67MPa, the tensile strength of the selected material meets the design requirements.

[0162] The construction of bag piles includes, before the bored pile construction, the determination of the location and size of karst caves and soil holes at the pile foundation based on cross-hole CT imaging, cross-hole radar detection and tube wave detection methods;

[0163] The cross-hole CT imaging method involves using two drill holes and adopting a one-shot-multiple-receiver fan-shaped receiving method. After several point excitations, a dense ray network is formed in the observation area.

[0164] The tube wave detection method includes a single-hole detection device using a single transmitter and receiver with a fixed transmitter-receiver distance;

[0165] The cross-hole radar detection method includes placing a transmitting antenna and a receiving antenna in two boreholes for detection. In the cross-hole mode, the transmitting antenna and the receiving antenna are arranged in different boreholes. The two boreholes are in the same two-dimensional plane, and the medium to be investigated is between the two boreholes.

[0166] A circle of positioning bars is welded every several meters on the steel cage, and a circle of positioning rings is installed based on the welded positioning bars; the first layer of geotextile is wrapped from bottom to top, and the bottom is fixed on the positioning ring by wrapping, and iron wire is used to tie at a specified interval, and the geotextile is overlapped at least 50cm in the longitudinal direction;

[0167] Use PE plastic film to wrap the second layer from bottom to top, overlap at least 50cm longitudinally, and fix each layer with tape at specified intervals; use geotextile to wrap the second layer from bottom to top, fix the bottom on the positioning ring by wrapping, and use wire to tie each layer at specified intervals. The geotextile should overlap at least 50cm longitudinally and be staggered 180° with the longitudinal seam of the first layer of geotextile to complete the installation of geomembrane bag.

[0168] Carry out construction survey and layout, then bury the casing and backfill clay around the casing and compact it layer by layer.

[0169] Mud preparation and circulation. The mud in the mud pool is made of bentonite and soda ash. Prefabricated mud pools and sedimentation tanks are placed near the pile hole and connected with circulating hoses. Bentonite is used to make the mud. Mud pools and sedimentation tanks are set up when drilling. The mud is circulated, precipitated and purified in the mud pools and sedimentation tanks. The mud circulation order is: new mud, mud pool, pile hole, sedimentation tank, mud pool, pile hole.

[0170] Drilling construction uses rotary drilling rigs to excavate piles. The drill bits of rotary drilling rigs are selected according to the soil conditions and drilling methods. Rotary drill bits are used for clay, silt, fill, and sandy soil with medium density or above, and rock-embedded drill bits are used for crushed stone soil, medium-hard rock and weathered rock.

[0171] During the drilling process of the rotary drilling rig, when the protective wall cannot keep the hole wall stable, steel casing is used to protect the wall or low-grade concrete is used for backfilling. Different drilling speeds and drilling pressures are used for different soil layers. Slag samples are collected at the changes in the strata to determine the geological type, record it in the record sheet, and compare it with the geological profile provided by the design.

[0172] Hole inspection: when the drilling depth reaches the design requirement, the hole depth, hole diameter, hole position center and hole shape are checked. The inspection method uses a borehole inspection device and a pile guard to check whether the drill wire rope or the drill center is consistent with the pile position. The hammer method is used for inspection. The rope uses a non-shrinkage measuring rope to suspend a conical hammer. The measuring rope is calibrated with a steel ruler before each use. An ultrasonic borehole detector is used to detect the pile diameter and inclination.

[0173] During the first hole cleaning, after drilling to the designed hole depth, if the relative density of the mud is large, a high-pressure water pipe is inserted into the bottom of the hole to spray water until the mud performance indicators meet the requirements. Combined with the location and size of the karst caves and soil holes at the test piles determined by the cross-hole CT scan, as well as the type of pile foundation, the geomembrane bag is installed.

[0174] The steel cage is hoisted and put into the hole. A shoulder pole type hanger is used for hoisting. A shoulder pole type lifting point is set on the top of the steel cage, and another lifting point is set at one-third of the distance from the bottom of the steel cage. The steel cage is hoisted into the hole as a whole. After the installation of the steel cage is completed, the center of the pile position is located by the wire pulling method. Positioning ribs are set on the pile foundation steel cage and evenly arranged around the pile foundation reinforcement. Ultrasonic detection tubes are evenly distributed on each pile foundation. The ultrasonic detection tubes are connected with snap-on connections, and the lower end of the ultrasonic detection tubes is sealed with steel plates.

[0175] The conduit is installed and tested for watertightness before use. It is numbered and marked in order from bottom to top. The length of the conduit is determined by the hole depth and the height of the working platform. The conduit adopts a spiral threaded joint. It is tested for watertightness before use and placed in the center of the borehole. Before pouring concrete, a lifting test is performed. The concrete pouring bracket is made of steel and is used to support and suspend the conduit. A funnel for pouring concrete is placed on the upper part. After the conduit is installed, the sediment at the bottom of the hole is measured. When the sediment thickness does not meet the requirements, a second hole cleaning is performed. After the mud wall hole is installed, the mud is pressed into the bottom of the hole with a mud pump to replace the mud containing suspended drilling cuttings in the hole. The mud is continuously circulated and purified until the mud indicators discharged from the hole meet the requirements. After the second hole cleaning is completed, underwater concrete is poured. The dry excavated hole is hoisted out as a whole in the steel cage, and the sediment at the bottom of the pile is re-cleaned with a rotary drilling rig slag bucket. After the re-test is qualified, the steel cage is hoisted again for installation.

[0176] Underwater concrete pouring, after the hole is cleaned and meets the requirements, pour the pile body concrete. For mud wall holes, before pouring underwater concrete, detect the thickness of mud sediment at the bottom of the hole and determine the water-cement ratio of the concrete. The concrete is centrally mixed at a mixing station, transported to the site by a concrete transport truck, and poured with a conduit. Before pouring underwater concrete, first test the slump, expansion, air content, and temperature of the concrete. After the storage capacity of the concrete meets the requirements of the first batch of concrete entering the hole, a water-isolating device is set at the bottom of the funnel. During the concrete pouring process, measure the height of the concrete surface and calculate the depth of the conduit buried in the concrete. After the first batch of concrete falls, the concrete is poured continuously. Cut the ball, pull the bolt or open the valve. After the first batch of concrete is poured into the bottom of the hole, measure the height of the concrete surface in the hole and calculate the buried depth of the conduit. If it meets the requirements, normal pouring is carried out;

[0177] During pouring, a hammer is used to accurately measure the elevation of the top surface of the concrete in the hole. The underwater concrete is poured continuously. During the pouring process, the position of the top surface of the concrete in the hole is detected, the buried depth of the guide tube is adjusted, the drop of the concrete in the tube and the rise and fall of the water level in the hole are observed, and the height of the concrete surface in the hole is measured;

[0178] When lifting the conduit, keep the axis vertical and the position centered, and lift it gradually. If the conduit thread is hung on the steel frame, rotate the conduit to disengage it from the steel frame, and then move it to the center of the drill hole. When the concrete pouring surface is close to the design elevation, use a sampling box to directly take samples to determine the top surface position of the concrete.

[0179] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A bag pile performance verification method, characterized in that: The following steps are involved: S1: Conduct tensile strength, tear strength, puncture resistance and permeability tests on geomembranes wrapped with bag piles; S2: Using the measuring rope, the concrete pouring elevation is detected during the pouring of bag pile concrete; S3: The volume of concrete poured into the bag pile, the change in elevation and the cross-sectional area data are obtained by segmented multiple measurements. The shape of the bag pile is estimated based on the change trend of the data. S4: According to the over-filling volume of concrete, estimate the protruding thickness of the drum and the actual maximum tensile stress, compare the maximum tensile stress with the standard tensile strength, and perform strength verification of the geomembrane bag.

2. A bag pile performance verification method according to claim 1, characterized in that: Tensile strength tests include: Place the geotextile sample on the tensile testing machine, and press the clamping device evenly on both ends of the sample; Set the force application speed and start the tensile test; Record the applied force and corresponding elongation at each time point until the sample breaks; Based on the experimental data, the tensile strength of the geotextile is calculated; Tear strength tests include: Place the geotextile sample on the tear tester, and press the clamping device evenly on both ends of the sample; Set the force application speed and start the tearing test; The applied force and the corresponding tear length were recorded at each time point until the sample broke.

3. A bag pile performance verification method according to claim 1, characterized in that: Puncture resistance tests include: Randomly take samples from the geotextile and mark the locations where the cones are punctured on the samples; Prepare the cone piercer, place the sample on a flat workbench, insert the cone piercer vertically into the center of the sample, and then apply downward pressure; During the puncture process, the puncture force and penetration depth of the cone tip were recorded at each time point.

4. A bag pile performance verification method according to claim 1, characterized in that: Permeability testing includes: The permeability coefficient of the flexible material for concrete slurry penetration is calculated using Darcy's law, which expresses the relationship between the permeation flow rate and the permeation pressure, and the formula is: Q = KA△h / L; In the formula, Q is the seepage flow rate, K is the permeability coefficient of the flexible material, A is the cross-sectional area of ​​the flexible material, △h is the head difference on both sides of the flexible material, and L is the length of the flexible material. According to Darcy's law, the permeability coefficient of concrete slurry penetrating the flexible material is calculated.

5. A bag pile performance verification method according to claim 4, characterized in that: The test steps include: Prepare the sample: prepare the concrete slurry as required, fix the flexible material sample in the test equipment, measure the thickness of the flexible material and record it, measure the size of the sample and calculate the cross-sectional area of ​​the sample, measure the mass of the sample, place the sample on the balance, measure the mass of the sample and record it; Pressurization: Pressurize the concrete slurry in the test equipment to make it penetrate the flexible material; Measure the permeability. During the pressurization process, record the permeability at different time points and calculate the permeability coefficient for each time period. Test the strength of the remaining slurry. Take the remaining concrete slurry out of the test equipment, make it into a standard concrete sample, and test its strength value after the curing time reaches the standard; The average permeability coefficient and the strength index of the concrete slurry after permeability are calculated based on the test data.

6. A bag pile performance verification method according to claim 1, characterized in that: In S2, the concrete pouring elevation detection method includes: S11: A measuring port is reserved in the casing at the top of the cast-in-place pile; S12: According to the design requirements, concrete is poured into the pouring hole through the funnel and the conduit. During the pouring of concrete, a measuring rope with a scale is connected to the conical gyroscope, and the measuring rope is placed into the reserved measuring port by the natural drooping of the gyroscope's gravity; S13: by adjusting the position of the measuring rope, the rope is stopped when the measuring rope gyro contacts the cast concrete surface, the depth of the measuring rope is measured and recorded, and the elevation of the cast-in-place pile concrete surface is obtained by conversion; S14: Determine the volume of concrete poured each time through a funnel, measure the surface elevation of the pile concrete each time concrete is poured, repeat steps S12 and S3 for each measurement, and obtain the elevation and concrete pouring volume of the piles in batches and sections.

7. A bag pile performance verification method according to claim 1, characterized in that: The calculation method of bag pile and bearing plate is to determine the concrete volume △V through a funnel, use a measuring rope to detect the surface elevation of the cast-in-place pile concrete to obtain the increased height △h of the cast-in-place pile, and convert it to the cross-sectional area A of the cast-in-place pile. The calculation equation is as follows: △V=A×△h; Assuming that the bearing plate formed by the bag pile and the karst position is cylindrical, the radius R of the pile body and the bearing plate is calculated by the cross-sectional area of ​​the bag pile. The calculation equation is: A = π × R 2 ; The shape of the bag pile is estimated by measuring the concrete pouring volume and the bag pile elevation in sections and multiple times. The shape of the cast-in-place pile is estimated based on the changing trend of the data. Assuming that the location of the bag pile cave is the pile side cave, a branch-shaped bearing plate is formed at the cave location during the bag pile construction process. Therefore, the length L of the branch-shaped bearing plate of the bag pile is approximately calculated using the following equation: A = π × r 2 / 2+L 2 ; When calculating the shape of cast-in-place piles, the shape of bag piles with different shapes of bearing plates produced by bag piles according to the size and shape of the cave is considered.

8. A bag pile performance verification method according to claim 1, characterized in that: Calculation of the physical and mechanical parameters of the drum-shaped body: the protruding thickness of the drum-shaped body and the actual maximum tensile stress are estimated based on the over-filled concrete volume. The over-filled concrete volume = actual poured volume - designed volume. According to the design size of the geomembrane bag, the drum height h can be obtained. Under the condition of known pile diameter r, the drum volume V can be calculated by formula (1): 鼓状体 , the length of the drum relative to the center of the pile R, the volume of the bulging part V 超 , drum-shaped body protrusion thickness W max , the formula is as follows: In order to verify whether the tensile strength of the membrane bag outside the drum meets the design requirements, the actual maximum tensile stress σ can be estimated based on the drum height h and pile diameter r. max , compared with the standard provided film bag material design tensile strength σ 设 contrast; According to formula (2), the maximum tensile stress σ is calculated max , the formula is as follows: In the formula: l is the length of the membrane bag after deformation, ε is the maximum tensile strain of the membrane bag, E is the elastic modulus of the membrane bag, and h is the original length of the drum-shaped body out of the membrane bag, which is equal to the height of the drum-shaped body.

9. A bag pile performance verification method according to claim 1, characterized in that: The drum-shaped protrusion thickness can be estimated based on the infusion pressure and membrane material parameters. According to Qian Wei's long circular membrane deformation calculation formula, the drum-shaped protrusion thickness W can be estimated based on the infusion pressure p and membrane material parameters. max , the formula is as follows: The dimensionless number P is taken from: In the formula, p is the pressure on the membrane bag, a is 1 / 2 of the height of the drum, E is the elastic modulus of the membrane bag, d is the thickness of the membrane bag, and v is the Poisson's ratio of the membrane bag; The constant c is solved from: The g(c) value is taken from: The calculation of the tensile strength of the membrane bag on the outside of the drum is similar. The protruding thickness of the drum and the actual maximum tensile stress are estimated based on the over-filled concrete volume.

10. A bag pile performance verification method according to claim 8, characterized in that: The strength of the geomembrane bag is checked and calculated using the most unfavorable pile with the deepest cave depth. The maximum pressure P at the bottom of the cave is obtained by the following formula: P=ρ 混 gh 混 -ρ 水 gh 水 (7); The formula for calculating the bursting strength of geomembrane bags is as follows: Where, d 顶 is the diameter of the top pressure rod, σ 顶 It is the bursting strength of geomembrane bag; Geomembrane bag tensile strength verification, sample tensile strength T max , the formula is as follows: T max =F max / B (9); Where, B is the nominal width of the specimen, in m, and F max To record the maximum load, unit KN, from which the longitudinal and transverse design tensile stress σ of the film bag can be obtained 设 , the formula is as follows: s 设 =T max / d (10); The elongation at break of the film bag is the designed tensile stress σ 设 Corresponding strain value ε max Therefore, the elastic modulus of the geomembrane bag can be obtained by formula (11), as follows: E=σ 设 / e max (11); Based on the drum-shaped body, using equations (1) and (2), the protruding thickness of the drum-shaped body and the actual maximum tensile stress are estimated according to the overfilled concrete volume, and the actual maximum tensile stress σ is estimated. max , compared with the standard provided film bag material design tensile strength σ 设 By comparison, we can determine whether the tensile strength of the material meets the design requirements.

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