Cloth bag pile construction method

Abstract

The cloth bag pile construction method comprises the following steps that S1, a circle of positioning ribs are welded to a reinforcement cage every several meters, and a circle of positioning ferrule is installed on the basis of the welded positioning ribs; s2, geotechnical cloth is adopted for first-layer wrapping from bottom to top, the bottom is fixed to a positioning ferrule in a winding and wrapping mode, and iron wires are used for binding every designated interval; s3, a PE plastic film is adopted for second-layer wrapping from bottom to top, and adhesive tape is used for fixing every specified interval; and S4, geotextile is adopted for second-layer wrapping from bottom to top, the bottom is fixed to the positioning ferrule in a winding wrapping mode, iron wires are used for binding every specified interval, the geotextile is longitudinally connected in a lap joint mode, longitudinal joints of the geotextile and longitudinal joints of the first-layer geotextile are staggered, and installation of the geomembrane bag is completed. According to the construction method, loss of slurry can be effectively reduced, the bearing capacity and stability of the cast-in-place pile are guaranteed, and the construction method can be well applied to construction of the cast-in-place pile containing the karst cave or the soil cave.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation construction, and in particular to a bag pile construction 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] Therefore, in the construction of bored piles in karst areas, due to the particularity of geological conditions such as karst caves and soil caves, the flow of groundwater is relatively complex. The commonly used pile foundation construction methods are prone to cause the loss of bored pile slurry during transportation, thus affecting the quality and safety of bored piles. On the one hand, the loss of bored pile slurry will lead to insufficient strength of bored piles, affecting the bearing capacity and stability of the piles, which may lead to problems such as pile foundation settlement and tilt. On the other hand, the loss of bored pile slurry will increase the cost of bored piles and also affect the construction progress and period. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, a bag pile construction 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 construction method, comprising the following steps:

[0007] S1: 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;

[0008] S2: Use geotextile to wrap the first layer from bottom to top, and fix the bottom on the positioning ring by wrapping. Use iron wire to tie at specified intervals, and the geotextile should be overlapped at least 50cm in the longitudinal direction.

[0009] S3: Use PE plastic film to wrap the second layer from bottom to top, overlap at least 50cm in the longitudinal direction, and fix each layer with tape at specified intervals;

[0010] S4: Use geotextile to wrap the second layer from bottom to top, and fix the bottom on the positioning ring by wrapping. Use wire to tie 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 the geomembrane bag.

[0011] Preferably, before bored pile construction, the location and size of karst caves and soil holes at the pile foundation are determined based on cross-hole CT imaging, cross-hole radar detection, and tube wave detection methods;

[0012] 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.

[0013] The tube wave detection method includes a single-hole detection device using a single transmitter and receiver with a fixed transmitter-receiver distance;

[0014] 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.

[0015] Preferably, construction surveying and laying out are carried out, and then casing is buried, and clay is backfilled around the casing and compacted in layers.

[0016] Preferably, mud is prepared and circulated, the mud in the mud pool is prepared with bentonite and soda ash, a prefabricated mud pool and sedimentation tank are placed near the pile hole and connected with a circulating hose, bentonite is used to make the mud, a mud pool and a sedimentation tank are set when drilling, the mud is circulated, precipitated and purified in the mud pool and sedimentation tank, and the mud circulation order is: new mud, mud pool, pile hole, sedimentation tank, mud pool, pile hole.

[0017] Preferably, the drilling construction adopts the method of excavation of piles by rotary drilling rigs. 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.

[0018] 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.

[0019] Preferably, during the 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 uses the pile guard to check whether the drill wire rope or the drill bit 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 measuring hammer. The measuring rope is calibrated with a steel ruler before each use, and an ultrasonic borehole probe is used to detect the pile diameter and inclination.

[0020] Preferably, after the hole is cleaned for the first time and the hole is drilled to the designed 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. The geomembrane bag is installed based on the location and size of the karst caves and soil holes at the test pile determined by the cross-hole CT scan, as well as the type of pile foundation.

[0021] Preferably, when the steel cage is hoisted and put into the hole, a shoulder pole type hanger is used for hoisting the steel cage. A shoulder pole type lifting point is set at 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 steel cage is installed, the center of the pile position is located by a wire pulling method. Positioning ribs are set on the pile foundation steel cage and evenly arranged around the pile foundation reinforcement ribs. Ultrasonic detection tubes are evenly distributed on each pile foundation. The ultrasonic detection tubes are connected by snap-on connection, and the lower end of the ultrasonic detection tube is capped with a steel plate.

[0022] Preferably, the conduit is installed, and a trial assembly and watertight test are carried out before the conduit is used. The conduit 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. The conduit is subjected to a watertight test before use and is placed in the center of the borehole. Before pouring concrete, a lifting test is carried out. The concrete pouring bracket is made of steel sections 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 carried out. 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 index discharged from the hole meets the requirements of the mud discharged or extracted from the hole. After the second hole cleaning is completed, underwater concrete is poured. The dry excavated hole is hoisted out as a whole after the steel cage is hoisted out, and the sediment at the bottom of the pile is cleaned again with a rotary drilling rig slag bucket. After the re-test is qualified, the steel cage is hoisted again for installation.

[0023] Preferably, for underwater concrete pouring, after the hole is cleaned and meets the requirements, the pile body concrete is poured. For the mud wall hole, the thickness of the mud sedimentation at the bottom of the hole is detected before pouring underwater concrete, and the water-cement ratio of the concrete is determined. The concrete is centrally mixed by a mixing station, transported to the site by a concrete transport vehicle, and poured with a catheter. Before pouring underwater concrete, the slump, expansion, air content, and temperature of the concrete are first detected. 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, the height of the concrete surface is measured, and the depth of the catheter buried in the concrete is calculated. After the first batch of concrete falls, the concrete is poured continuously, the ball is cut, the bolt is pulled, or the valve is opened. After the first batch of concrete is poured into the bottom of the hole, the height of the concrete surface in the hole is measured, and the buried depth in the catheter is calculated. If it meets the requirements, normal pouring is carried out;

[0024] 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;

[0025] 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.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The bag pile construction method proposed in the present invention has been demonstrated in practice for many times and can effectively reduce the loss of slurry, effectively reduce the leakage of cast-in-place piles and the formation of holes due to the flow of cast-in-place slurry from the pile hole connecting the karst cave or the soil hole to fill the karst cave, effectively reduce the collapse of pile foundation drilling holes, shorten the construction period, improve the construction efficiency of the pile foundation, reduce the project volume and cost, ensure the bearing capacity and stability of the cast-in-place piles, and at the same time ensure the construction safety and project quality, and can be well applied to the construction of cast-in-place piles containing karst caves or soil caves. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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:

[0029] Figure 1 It is the overall flow chart of the present invention;

[0030] Figure 2 This is a schematic diagram of the installation position of the geomembrane bag of the bag pile;

[0031] Figure 3 This is a schematic diagram of the geomembrane bag size of the bag pile;

[0032] Figure 4 This is a schematic diagram of fixing geomembrane bags on bag piles;

[0033] Figure 5 It is a schematic diagram of the cross-bore CT imaging method;

[0034] Figure 6 It is a schematic diagram of the tube wave detection method;

[0035] Figure 7 This is a schematic diagram of the cross-hole radar detection method;

[0036] Figure 8 This is a schematic diagram of bag pile concrete pouring elevation detection;

[0037] Fig. 9 This is a schematic diagram of the calculation of the cylindrical bag pile shape;

[0038] Fig.10 It is a schematic diagram of the deduction and calculation of the branch-shaped load-bearing plate pile shape. DETAILED DESCRIPTION

[0039] 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.

[0040] like Figure 1-Figure 10 As shown, this embodiment proposes a bag pile construction method, comprising the following steps:

[0041] S1: 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;

[0042] S2: Use geotextile to wrap the first layer from bottom to top, and fix the bottom on the positioning ring by wrapping, and tie with wire at a distance of 15cm. The geotextile should be overlapped at least 50cm in the longitudinal direction;

[0043] S3: Use PE plastic film to wrap the second layer from bottom to top, overlap at least 50cm in the longitudinal direction, and fix each layer with tape at 50cm intervals;

[0044] S4: Use geotextile to wrap the second layer from bottom to top, and fix the bottom on the positioning ring by wrapping it. Use wire to tie it with a spacing of 15cm. 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 the geomembrane bag.

[0045] Geotextile is made of high-strength polypropylene filament geotextile, which has high strength, light weight, wear resistance and water permeability. It is made of polypropylene fiber as raw material and through a special process. It has the characteristics of environmental protection, good weather resistance and strong corrosion resistance.

[0046] In addition, high-strength polyester stitched fabric can also be used, which has high strength, wear resistance and water permeability. It is made of polyester filaments through stitching technology and has the characteristics of durability, high tensile strength, strong corrosion resistance and good water permeability. Or polyethylene geomembrane can be used, which has high strength, wear resistance and water permeability. It is made of polyethylene as raw material through special technology and has the characteristics of softness, corrosion resistance and good water permeability.

[0047] PE plastic film: good toughness, not easy to wear, light, corrosion-resistant, cheap and low construction cost. The iron wire is No. 14 galvanized iron wire, which has good corrosion resistance, low tensile strength, good plasticity and easy to apply.

[0048] In S1, a circle of positioning reinforcement is welded every 1m from the bottom of the steel cage to 3m upward and a circle of positioning ring is installed.

[0049] The size and installation location of the geomembrane bag are determined according to the diameter and length of the pile foundation, as well as the location and size of the karst caves surveyed by the cross-hole radar. To ensure that the geomembrane bag effectively covers the karst caves, the geomembrane bag should cover the remaining rock layer after retaining the 3m bearing layer thickness at the bottom of the pile. To effectively prevent the loss of cast-in-place pile concrete and form a pile bearing plate at the location of the cast-in-place pile karst caves and soil holes, the radius of the designed geomembrane bag should be slightly larger than the pile diameter.

[0050] According to the designed geomembrane bag size, the geomembrane is cut and sewn according to the size and shape, passed through the cylindrical geomembrane bag, and the pull ring and reinforcement tie belt are sewn at the two sections of the geomembrane bag and 50cm in the middle. The size of the tie belt is consistent with the size of the geomembrane bag. During the production process, attention should be paid to the firmness and sealing of the suture position to ensure the quality and use effect of the geomembrane bag.

[0051] Install the prepared geomembrane bag on the steel cage of the cast-in-place pile and fix it with a tie or steel wire to ensure that the geomembrane bag is tightly combined with the steel cage and will not shift or deform during the pouring process. Determine the location of the geomembrane bag on the steel cage according to the location of the cave and soil hole, and fix the geomembrane bag at both ends of the steel cage. To ensure that the integrity of the pile body is not affected by the geomembrane bag (concrete protective layer), the geomembrane bag must be kept at a distance of more than 50mm from the steel cage. This can be achieved by fixing a steel support ring at least 50mm away from the steel cage between the geomembrane bag and the steel cage.

[0052] In order to ensure that the geomembrane bags effectively cover the locations of karst caves and soil holes, before the bored pile construction, the locations and sizes of karst caves and soil holes at the pile foundation are determined based on cross-hole CT imaging, cross-hole radar detection, and tube wave detection methods;

[0053] The cross-hole CT imaging method involves using two boreholes and adopting a one-shot-multiple-receiver fan-shaped receiving method. After several points of excitation (electric spark or explosive), a dense ray network is formed in the observation area.

[0054] The tube wave detection method includes a single-hole detection device using a single transmitter and receiver with a fixed transmitter-receiver distance;

[0055] 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. In order to reduce the influence of geometric position, the two boreholes are in the same two-dimensional plane, and the medium to be investigated is between the two boreholes, which can have high precision and accuracy. When conducting engineering surveys, more than three survey holes should be set within the diameter range of the bored pile position to accurately determine the location and size of the karst caves and soil caves, and ensure that the geomembrane bags effectively cover the karst caves and soil caves.

[0056] Conduct construction survey and layout. Before construction survey and layout, lay out the survey control network as required, supplement the bridge and culvert centerline piles and leveling points required in the construction, accurately layout the pile position coordinates after the site is leveled, and recheck the relative position of the center of each pile after the layout is completed. After the recheck is correct, measure and lay the guard piles in time. The guard piles use 4 steel bars with a diameter of 12mm, which are inserted into the ground for not less than 0.5m, and the height exposed above the ground should meet the requirements of the rechecked pile position.

[0057] After that, the casing is buried. When the surface soil is soft, the casing should be buried at least 0.5m in a harder and denser soil layer, and clay should be backfilled around the casing and compacted in layers. The casing can also be sunk by hammering, pressurizing, vibrating and other methods. The deviation between the center of the top surface of the casing and the center of the designed pile position shall not exceed 5cm, and the inclination shall not exceed 1%. The inner diameter of the casing is 20cm larger than the pile diameter, and the top surface of the casing is 50cm higher than the construction ground. The buried depth of the casing should ensure that the clay soil is not less than 1m, and the sand soil is not less than 2m. When the surface soil is soft, bury the casing in a harder and denser soil layer for at least 0.5m. Backfill clay around the casing and compact it in layers.

[0058] Mud preparation and circulation (this step is omitted for dry excavation). The mud in the mud pool is made of bentonite and soda ash. The mud properties are adjusted in time according to the formation conditions. Prefabricated mud pools and sedimentation tanks are placed near the pile holes 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.

[0059] 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.

[0060] During the drilling process of the rotary drilling rig, when the protective wall cannot keep the hole wall stable, steel casing is used for wall protection or low-grade concrete backfill treatment. 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 type of geology, record it in the record sheet (especially the location of karst caves and soil caves), and compare it with the geological profile provided by the design.

[0061] 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 with a scale accuracy of 2cm 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.

[0062] For the first hole cleaning, after drilling to the designed hole depth, the time for removing the slag from the rotary drilling drum is relatively extended, but without pressurization, to ensure that all the drilling slag is removed and to avoid over-drilling. If the mud is relatively dense, a high-pressure water pipe is inserted into the bottom of the hole to spray water until the mud performance indicators meet the requirements. The mud performance indicators and sediment thickness requirements for the first hole cleaning are: specific gravity not more than 1.1, sand content less than 2%, viscosity 17s~20s; the sediment thickness requires that the end bearing pile is not more than 5cm.

[0063] The geomembrane bag is installed in combination with the location and size of the karst caves and soil holes at the test piles determined by cross-hole CT scanning, as well as the type of pile foundation. In order to ensure the covering effect of the geomembrane bag, an overall installation plan is adopted, and the geomembrane bag should be installed in other rock layers below the bottom of the soil layer and above the bearing layer. The bearing layer should reserve a rock penetration depth of at least 3m to meet the requirements of pile foundation compression, pull-out resistance, bearing capacity and other indicators.

[0064] When lifting the steel cage and putting it into the hole, a shoulder pole type hanger is used to prevent height imbalance and deformation caused by tightening. A shoulder pole type lifting point is set at 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 lifted into the hole as a whole. Avoid touching the hole wall during the lifting process to prevent the hole wall from collapsing or puncturing the geomembrane bag. After the steel cage is installed, 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 ribs. Ultrasonic detection tubes are evenly distributed on each pile foundation. The ultrasonic detection tubes are connected by snap-on connection, and the lower end of the ultrasonic detection tube is sealed with a steel plate.

[0065] Installation of the conduit. Before using the conduit, it is tested for assembly and watertightness. The conduit 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. Before using, the conduit is tested for watertightness. The conduit is placed in the center of the borehole. Before pouring concrete, a lifting test is performed. The distance between the bottom end of the conduit and the bottom of the hole is controlled at 40cm, and it can be ensured that the water-blocking ball plug or other water-blocking objects can be smoothly discharged from the pipe after falling along the conduit to the bottom of the conduit. The concrete pouring bracket is made of steel and is used to support the suspended conduit. A funnel for pouring concrete is placed on the top. After the conduit is installed, the sediment at the bottom of the hole is measured.

[0066] When the sediment thickness does not meet the requirements, the hole is cleaned for the second time. After the installation of the catheter, 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 circulated and purified continuously until the mud indicators discharged from the hole meet the requirements. The mud discharged or extracted from the hole meets the requirements. The extracted mud has no 2-3mm particles when touched by hand, the mud specific gravity is not more than 1.1, the sand content is less than 2%, and the viscosity is 17s-20s; the thickness of the sediment at the bottom of the hole is not more than 5cm for column piles, and not more than 20cm for friction piles. After the second hole cleaning is completed, underwater concrete is poured, and the dry-excavated hole is hoisted out as a whole after the steel cage is hoisted, and the sediment at the bottom of the pile is cleaned again with a rotary drilling rig with a slag bucket. After the re-test is qualified, the steel cage is hoisted again for installation.

[0067] Underwater concrete pouring, after the hole cleaning is completed and meets the requirements, the pile body concrete is poured. For mud wall drilling, the mud sediment thickness at the bottom of the hole is checked before pouring underwater concrete. If it is greater than the designed hole cleaning requirements, the hole is cleaned again until it meets the requirements to ensure the quality of hole cleaning and drilling, determine the concrete water-cement ratio, and use a mixing station to mix the concrete centrally, transport it to the site by concrete transport trucks, and pour it using a conduit.

[0068] 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, the depth of the conduit buried in the concrete shall not be less than 1m and not more than 3m. A water-blocking device shall be set at the bottom of the funnel, and it can be smoothly discharged from the bottom of the conduit. 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.

[0069] During pouring, use a plumb hammer to accurately measure the elevation of the top surface of the concrete in the hole, and keep the buried depth of the conduit within the range of 2 to 6 meters. The minimum buried depth shall not be less than 1 meter at any time. When the pouring speed is faster, the conduit is stronger and has sufficient lifting capacity, the buried depth can be appropriately increased, but not more than 8 meters. When pouring concrete, the mud height in the hole must be maintained to prevent collapse. Underwater concrete is poured continuously without pause. During the pouring process, detect the position of the top surface of the concrete in the hole, adjust the buried depth of the conduit, observe the drop of concrete in the pipe and the rise and fall of the water level in the hole, and measure the height of the concrete surface in the hole;

[0070] 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, and ensure that the top surface of the concrete is poured to 0.5m to 1m above the design elevation of the pile top to ensure the quality of the pile body.

[0071] The bag pile construction method proposed in this application has been demonstrated in practice many times and can effectively reduce the loss of slurry, effectively reduce the leakage of bored piles and the formation of holes due to the flow of the injected slurry from the pile hole connecting the karst cave or the soil hole to fill the cave, effectively reduce the collapse of the pile foundation drilling hole, shorten the construction period, improve the construction efficiency of the pile foundation, reduce the project volume and cost, ensure the bearing capacity and stability of the bored pile, and at the same time ensure the construction safety and project quality, and can be better applied to the construction of bored piles containing caves or soil holes.

[0072] In view of the complexity of bag pile structure, the pouring of bag pile concrete should be tested in real time, the shape of bag pile should be estimated, and the strength of geomembrane bag should be checked. The concrete pouring elevation of bag pile is detected by measuring rope during the pouring process of bag pile concrete, which provides basic data support for the deduction of bag pile shape. The specific detection method is as follows:

[0073] S11: Preparation: Reserve a measuring port in the casing at the top of the pile. The size of the measuring port should not be less than 100mm, so that the measuring rope can be inserted when pouring concrete.

[0074] S12: According to the design requirements, concrete is poured into the pouring hole through the funnel and the catheter. During the concrete pouring process, 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.

[0075] S13: By adjusting the position of the measuring rope, the rope is stopped when the gyro of the measuring rope contacts the surface of the cast-in-place concrete, and the depth of the measuring rope is measured and recorded, and the elevation of the concrete surface of the cast-in-place pile can be converted.

[0076] 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 S13 for each measurement, and obtain the elevation and concrete pouring volume of the piles in batches and sections.

[0077] The calculation method of bag pile formation and bearing plate is to determine the concrete volume △V through a funnel, and use a measuring rope to detect the surface elevation of the bored pile concrete to obtain the increased height △h of the bored pile, which can be converted to the cross-sectional area A of the bored pile. The calculation equation can be expressed as follows: △V=A×△h.

[0078] 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 can be calculated by the cross-sectional area of ​​the bag pile. The calculation equation is: A = π × R 2 .

[0079] The shape of the bag pile can be calculated by measuring the concrete pouring volume and the elevation of the bag pile in sections and multiple times. The shape of the cast-in-place pile can be calculated based on the changing trend of the data.

[0080] 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. Therefore, the length L of the branch-shaped bearing plate of the bag pile can be approximately calculated using the following equation: A = π × r 2 / 2+L 2 .

[0081] It should be noted that when calculating the shape of cast-in-place piles, the accuracy and reliability of the measurement data should be guaranteed as much as possible. At the same time, the shape of the bag piles with different shapes of bearing plates produced by the bag piles should also be considered according to the size and shape of the cave.

[0082] Calculation of physical and mechanical parameters of drum-shaped body: Estimate the protruding thickness of drum-shaped body and actual maximum tensile stress according to the over-pouring volume of concrete. Over-pouring volume of concrete = actual pouring volume - designed volume.

[0083] 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:

[0084]

[0085] 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;

[0086] According to formula (2), the maximum tensile stress σ is calculated max , the formula is as follows:

[0087]

[0088]

[0089] Where: l is the length (arc 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;

[0090] 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:

[0091]

[0092] The dimensionless number P is taken from:

[0093]

[0094] 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.

[0095] The constant c is solved from:

[0096] ν=2cf′(c)f -1 (c)+l

[0097]

[0098] The g(c) value is taken from:

[0099]

[0100] The calculation of the tensile strength of the membrane bag on the outer side of the drum is similar to estimating the protruding thickness of the drum and the actual maximum tensile stress based on the over-filling volume of concrete.

[0101] The strength of the geomembrane bag is checked and calculated. In order to ensure that the material meets the design and construction requirements, the most unfavorable pile with the deepest cave depth is used for verification. The maximum pressure P at the bottom of the cave is obtained by the following formula:

[0102] P=ρ 混 gh 混 -ρ 水 gh 水 (7);

[0103] The formula for calculating the bursting strength of geomembrane bags is as follows:

[0104]

[0105] Where, d 顶 is the diameter of the top pressure rod, σ 顶 It is the bursting strength of geomembrane bag;

[0106] Geomembrane bag tensile strength verification, sample tensile strength T max , the formula is as follows:

[0107] T max =F max / B(9);

[0108] 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:

[0109] σ 设 =T max / d (10);

[0110] 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:

[0111] E=σ 设 / ε max (11);

[0112] 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.

[0113] 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 construction method, characterized in that: The following steps are involved: S1: 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; S2: Use geotextile to wrap the first layer from bottom to top, and fix the bottom on the positioning ring by wrapping. Use iron wire to tie at specified intervals, and overlap the geotextile longitudinally by at least 50cm; S3: Use PE plastic film to wrap the second layer from bottom to top, overlap at least 50cm in the longitudinal direction, and fix each layer with tape at specified intervals; S4: Use geotextile to wrap the second layer from bottom to top, and fix the bottom on the positioning ring by wrapping. Use wire to tie 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 the geomembrane bag.

2. A bag pile construction method according to claim 1, characterized in that: Before bored pile construction, the location and size of karst caves and soil holes at the pile foundation are determined based on cross-hole CT imaging, cross-hole radar detection, and tube wave detection methods; The cross-hole CT imaging method involves using two drill holes and adopting a fan-shaped receiving method of one shot and multiple receptions. After several points of excitation, a dense ray network is formed in the observation area. The tube wave detection method includes a single-hole detection device using a single transmitter and receiver with a fixed transmitter-receiver distance; 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.

3. A bag pile construction method according to claim 1, characterized in that: Carry out construction survey and layout, then bury the casing and backfill clay around the casing and compact it layer by layer.

4. A bag pile construction method according to claim 1, characterized in that: 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.

5. A bag pile construction method according to claim 1, characterized in that: 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. 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.

6. A bag pile construction method according to claim 1, characterized in that: 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.

7. A bag pile construction method according to claim 1, characterized in that: 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.

8. The bag pile construction method according to claim 1, characterized in that: 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.

9. A bag pile construction method according to claim 1, characterized in that: 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.

10. A bag pile construction method according to claim 1, characterized in that: 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; 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; 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.

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