Construction method for pile foundation of super-thick permeable sand layer

Abstract

The invention discloses a construction method for a pile foundation of an ultra-thick permeable sand layer. The construction method comprises the following steps that 1, a site, a platform and a mud pit are prepared; cleaning a site, arranging a construction platform, and preparing a mud pit; 2, pile casing burying, wherein a steel pile casing with a proper height is buried according to geological conditions; 3, drilling machine in-place, specifically, the pile position is rechecked, and it is ensured that the drilling machine is stably in-place; appropriate clay is selected to prepare the slurry, the performance index of the slurry meets the requirement, and according to the construction method for the pile foundation of the super-thick water-permeable sand layer, accurate positioning and stable supporting of the pile foundation under the complex geological condition are achieved through dynamic anchoring and pressure monitoring. The device solves the problems of sand prevention failure and unreliable anchoring in the traditional process, is suitable for the adjacent water adjacent super-thick permeable sand layer, and has the advantages of high efficiency, environmental protection, safety and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of bridge construction, and specifically to a construction method for pile foundations in an ultra-thick permeable sand layer. Background Art

[0002] Bridge pile foundations are an important part of bridge engineering. Common foundation forms include flat plate type, pile type, and combined type, etc. The size and depth should be determined according to the load of the superstructure and geological conditions, and at the same time, the constructability should be considered. The layout of the pile foundations should be optimized based on the load distribution of the bridge and geological conditions to make full use of the bearing capacity of the stratum and reduce the settlement and displacement of the pile foundations.

[0003] Bridge pile foundation construction is one of the key links in the whole project. The hole-forming method should be selected according to geological conditions and construction conditions, such as mechanical hole-forming, manual hole-forming, punching, etc. The pouring technology should consider factors such as the mix ratio of concrete, pouring speed, and catheter embedment depth to ensure the quality of concrete and the integrity of the pile foundation. During the construction process, effective quality control measures should be taken, such as regular quality inspection, construction parameter control, etc., to ensure that the construction quality of the pile foundation meets the requirements.

[0004] During the construction process of bridge pile foundations, some special situations may be encountered, such as emergencies, underground obstacles, ultra-thick permeable sand layers, near-water construction, high-pressure bearing layers, etc. For these situations, corresponding treatment measures should be taken to ensure the smooth progress of construction and quality and safety. Summary of the Invention

[0005] The present invention is to solve the deficiencies existing in the above-mentioned prior art, and provides a construction method for pile foundations in an ultra-thick permeable sand layer to solve the problems mentioned in the background art.

[0006] To achieve the above object, the present invention provides the following technical solution:

[0007] A construction method for pile foundations in an ultra-thick permeable sand layer, comprising the following steps:

[0008] Step 1: Preparation of the site, platform, and mud pit; clean the site, set up the construction platform, and prepare the mud pit;

[0009] Step 2: Bury the casing: Bury a steel casing with an appropriate height according to geological conditions;

[0010] Step 3: Position the drill rig: Recheck the pile position to ensure the stable positioning of the drill rig;

[0011] Step 4: Prepare the mud: Select suitable clay to prepare the mud to make the mud performance indicators meet the requirements;

[0012] Step 5: Drill and form the hole: Drill at a suitable drilling speed and parameters, and take samples in time to judge the soil layer changes;

[0013] Step 6, final hole inspection: Use a hole forming detector to inspect the hole depth and hole diameter.

[0014] Step 7, installation of the support device: After combining the main body of the support device and the support strut system, hoist it to the designated position through the position limiting suspension rope system, and use the automatic spring - open anchoring device to anchor the main body of the support device to the hole wall.

[0015] Step 8, hole cleaning: Conduct hole cleaning twice to ensure that the sediment thickness at the bottom of the hole meets the design requirements.

[0016] Step 9, place the steel reinforcement cage and the conduit.

[0017] Step 10, pour concrete: Continuously pour concrete to the design elevation to ensure the quality of the formed pile.

[0018] Step 11, cut the pile head and conduct pile foundation inspection: After the foundation pit is excavated, cut off the pile head and conduct pile foundation quality inspection.

[0019] As a further technical solution of the present invention: Specifically, in Step 1: Use the total station coordinate lofting method to loft the center position of the pile, determine the center of the pile position, set up cross - shaped protective piles around with a radius greater than the pile body radius, make marks and fix them well. The measurement error is zero error. The pile position is marked with Steel bars with a length of 35 - 40 cm are driven 30 cm into the ground as the center point of the pile, filled with cement mortar or concrete for protection around, and marks are made around the pile position.

[0020] As a further technical solution of the present invention: Specifically, in Step 2: According to the geological conditions, during construction, a 3 - m - high steel casing is used. The diameter of the casing is 1.8 m, and the wall thickness is 6 mm. The bottom and around of the casing are filled and tamped with clay in layers. The buried depth of the casing is 2.7 m. The top of the casing is 0.3 m higher than the maximum wave height of the water surface, and a steel bar lifting lug is welded at the top. The vertical center line of the casing coincides with the pile center line, the allowable plane error is 50 mm, and the vertical inclination rate ≤ 1%. During the drilling process, check whether the casing is displaced or sunk and deal with it in a timely manner according to the inspection results.

[0021] As a further technical solution of the present invention: Specifically, in Step 3: Before the drill rig is in place, re - check the pile position. The ground where the drill rig is in place is compacted with a roller or backfilled to ensure that after the drill rig is in place, the center of the drill bit, the lofting point of the pile center are on the same vertical line, ensuring the correct pile position during hole formation and the stability of the drill rig during construction.

[0022] As a further technical solution of the present invention: Step 4 is specifically as follows: For the preparation of the mud, select clay with fast hydration, strong mud-making ability and high viscosity, and determine the various indicators of the clay through tests. During the drilling process, frequently measure the technical indicators of the mud. According to the requirements of the engineering drilling, adjust the relative density of the mud at any time to keep all indicators meeting the requirements, so as not to affect the progress due to the overly thick mud or cause hole collapse due to the overly thin mud.

[0023] As a further technical solution of the present invention: Step 5 specifically includes the following steps:

[0024] Step 5.1, Drilling speed control: Start drilling slowly at first. For the bottom of the casing, drill at a low gear and low speed to form a firm mud skin protection at the bottom. If the soil at the bottom of the casing is soft and slurry leakage occurs, the drill bit can be lifted, clay lumps can be poured into the hole, and then the drill bit can be put in and reversed to squeeze the clay into the hole wall to block the slurry leakage gap. After stabilizing the mud, continue drilling. After the drill bit passes through 2.0 m below the bottom of the casing, increase the speed and drill normally. The lifting and lowering speed of the drill bucket is controlled at 0.75 - 0.80 m / s;

[0025] Step 5.2, Geological sampling: When the soil layer changes during the drilling process, collect the slag samples at the soil layer change to identify the soil layer, record it in the record form, check it against the geological profile diagram, and at the same time conduct tests on the drilled hole, measure the mud specific gravity, viscosity, and sand ratio;

[0026] Step 5.3, Hole formation: Before the trial pile drilling, a trial hole formation should be carried out. During the formal construction of the trial pile, construct according to the actual on-site layout points. When the drilling rig encounters different geological conditions, adjust the drilling parameters in time. During drilling, strictly control the drilling speed to make the drilling speed adapt to the slurry supply and slag discharge capabilities. When the drilling speed is lower than the slurry supply and slag discharge speed, stop drilling first when adding drill pipes. Lift the drill tool off the bottom of the hole, wait for the mud to circulate for a few minutes, and then stop the pump to add drill pipes. The hole formation construction is completed continuously at one time. After the hole is formed to the designed hole depth, conduct preliminary hole cleaning first, and then check and accept. After passing the inspection, proceed to the next process.

[0027] As a further technical solution of the present invention: Step 6 is specifically as follows: When the drilling reaches the designed elevation and hole position, use a hole formation detector to check the hole depth, hole diameter, hole position, hole shape, verticality, and geological conditions at the bottom of the hole, then fill in the final hole record, and promptly notify the supervision engineer to come to the site for inspection and acceptance; only after passing the inspection can the next process be carried out. When the rotary drilling rig is approaching the final hole, use a bottom-sealing sand-grabbing drill bit to drill and take out the thick mud at the bottom of the hole. When reaching the final hole depth, stop for 20 - 30 min to allow the suspended matter in the mud to settle, and then use the drill bit to fish it out.

[0028] As a further technical solution of the present invention: Step 8 adopts a method of removing the sediment at the bottom of the hole twice, specifically including the following steps:

[0029] Step 8.1: After drilling reaches the designed hole depth, lift the drill bit 150 - 200 mm above the bottom of the hole, start the mud pump for normal circulation hole cleaning for not less than 20 minutes.

[0030] Step 8.2: Pile hole acceptance: After the finalization of the pile hole, first conduct self-inspection according to the design requirements, and then accept the final hole depth, sediment, and various indicators of the mud properties. After passing the acceptance, complete the on-site form filling and visa work.

[0031] Step 8.3: The steel reinforcement cage can be lowered only after the pile hole passes the acceptance. After the steel reinforcement cage and the perfusion conduit are properly placed, use the conduit for normal circulation for the second hole cleaning. It is required that after hole cleaning, the sediment at the bottom of the hole does not exceed 100 mm, and the time interval from hole cleaning to concrete perfusion does not exceed 30 minutes. If it exceeds 30 minutes, re-hole cleaning is required to meet the requirements before concrete perfusion can be carried out.

[0032] Step 8.4: After perfusion is completed, the speed of lifting the conduit needs to meet the following conditions: the concrete surface gradually closes, without mud mixing in, and without a muddy core.

[0033] Step 8.5: For each pile during pouring, two slump measurements need to be carried out. First, take samples to make test blocks, with no less than 3 test blocks made for each pile. Number them and indicate the sampling time, record it in the concrete perfusion record. The test blocks are demolded 24 hours after production, placed in a standard curing room for 28 days of curing, tested on time, and the test pressure results are filed for future reference.

[0034] Step 8.6: Before drilling, first use a level to determine the elevation of the casing, and use this as a reference point. Calculate the hole depth according to the designed bottom elevation of the hole, and determine the hole depth based on the length of the drill tool. The hole depth deviation is not shorter than the designed depth, and the over-drilling depth is not greater than 20 cm. When the drilling depth reaches the design requirements, check the hole depth, hole diameter, hole position, hole shape, and the thickness of the sediment at the bottom of the hole. The inspection method uses a cage-type hole checker. If necking occurs, reaming should be carried out.

[0035] As a further technical solution of the present invention: The specific steps of step 9 are as follows:

[0036] Step 9.1: Before the mechanical sleeve connection of the main steel bars of the steel reinforcement cage, use a straight thread threading machine for threading, and use a ring through gauge and a ring stop gauge for threading detection. After passing the detection, proceed to the next process. When installing the stiffeners, set one every 2 m; set one group of positioning bars every 2 m, with 4 bars in each group evenly arranged around the pile foundation stiffeners.

[0037] Step 9.2: Transport to the work site by flatbed truck, use a crane, set 2 lifting points, and use the method of lifting and sinking section by section for hoisting.

[0038] Step 9.3: For the placed steel reinforcement cage, use steel pipes or steel sections to temporarily support and fix this section through its stirrups; the upper section of the steel reinforcement cage is temporarily hoisted by a crane and is in a suspended state. After aligning the upper and lower sections to form a straight line, align the positions of the main steel bars and use a plumb bob to control the verticality from the front, back, left, and right. After the adjustment is completed, carry out mechanical sleeve connection;

[0039] Step 9.4: When connecting two sections of the steel reinforcement cage, the axes of the main steel bars of the upper and lower sections of the steel reinforcement cage must be aligned, and mechanical sleeve connection is adopted. After the upper and lower sections are butt-jointed, pull out the steel pipes or steel sections used for support and continue to sink the steel reinforcement cage;

[0040] Step 9.5: There are 4 lifting rings for the steel reinforcement cage to enter the hole. According to the elevation position of the control platform, calculate and determine the length and welding position. The lap length and weld of the lifting ring steel bars adopt standard welds; when placing the steel reinforcement cage, it needs to be aligned with the hole position, and the errors in its top elevation and plane position are both ≤ 10 mm;

[0041] Step 9.6: Place the conduit: The upper end of the acoustic logging tube is 30 cm higher than the top surface of the pile, and the lower end is suspended 10 cm. The length of each section of the acoustic logging tube corresponds to the section length of the steel reinforcement cage, and the sections are connected by sleeves with a sleeve length of 80 cm. The outer diameter of the inspection tube is 57 mm, the sleeve diameter is 60 mm. The acoustic logging tube is tied to the stirrup bars. Its bottom end is welded and sealed with a steel plate. Before pouring concrete, fill the tube with water and block it with a plug. When the pile diameter is less than 1.5 m, 3 inspection tubes are set; when the pile diameter ≥ 1.5 m, 4 inspection tubes are set.

[0042] As a further technical solution of the present invention: The specific content of the said Step 10 is:

[0043] Step 10.1: After the pouring starts, it needs to be carried out continuously, and the continuous pouring time of the concrete for the same pile is not greater than the initial setting time of the concrete;

[0044] Step 10.2: During the pouring process, it is necessary to prevent the concrete mixture from overflowing from the top of the funnel or falling into the bottom of the hole outside the funnel. During the pouring process, it is necessary to pay attention to observing the descent of the concrete in the tube and the rise and fall of the water level in the hole, and timely measure the height of the concrete surface in the hole;

[0045] Step 10.3: During the pouring process, when the concrete in the conduit is not full and contains air, the subsequent concrete should be poured slowly to prevent the formation of a high-pressure air bag in the conduit.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] Improve construction efficiency: The construction method provided by the present invention can effectively solve the problem of low construction efficiency of pile foundations under complex geological conditions such as adjacent to water and close to a super-thick permeable sand layer, and shorten the construction period.

[0048] Ensure the quality of pile formation: Through the support function of the support device body, effectively prevent problems such as hole collapse and slurry leakage, and ensure the quality of pile formation.

[0049] Reduce construction costs: Reduce rework and treatment costs, reduce the cost of making slurry, and have good economic benefits.

[0050] Environmentally friendly: Reduce the generation of solid waste, have little impact on the environment, and have good environmental benefits. Description of the Drawings

[0051] Figure 1 It is a construction schematic diagram of a super-deep large-diameter pile foundation adjacent to thick permeable sand layers near water.

[0052] Figure 2 It is a schematic diagram of the construction principle of a super-deep large-diameter pile foundation adjacent to thick permeable sand layers near water.

[0053] Figure 3 It is a process flow diagram of the construction of a super-deep large-diameter pile foundation adjacent to thick permeable sand layers near water.

[0054] Figure 4 It is a structural schematic diagram of the construction support device for a super-deep large-diameter pile foundation adjacent to thick permeable sand layers near water.

[0055] In the figure: 1 - Bored pile wellhead, 2 - Intermediate sliding rod, 3 - Position limit suspension rope, 4 - Limit device, 5 - Sliding collar, 6 - Automatically sprung anchor nail, 7 - Soil layer, 8 - Support strut, 9 - Mesh net, 10 - Connection device with strut, 11 - Support device body, 12 - Rigid iron ring, 51 - Main sliding collar, 52 - Sub-sliding collar. Detailed Implementation Modes

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0057] As Figures 1-3 shown, the present invention discloses a construction method for a pile foundation in a super-thick permeable sand layer, which includes the following steps:

[0058] Step 1. Preparation of Site, Platform and Mud Pit: After site cleaning, platform and mud pit construction, use the total station coordinate lofting method to loft the central position of the pile, determine the pile center position, set up cross-shaped reference piles around with a radius greater than the pile body radius centered on the center, make marks and fix them. The measurement error is zero error. Use a 10mm, 35 - 40cm long steel bar to drive 30cm into the ground (surrounded by cement mortar or concrete for protection) as the center point of the pile, and then make marks around the pile position, which is convenient for searching and can prevent the destruction of the reference piles when the machinery is displaced. After verification and approval by the resident supervision engineer, proceed to the next process.

[0059] Step 2. Burying the Casing: According to the geological conditions, use a 3m high steel casing during construction. The casing diameter is 1.8m and the wall thickness is 6mm. Fill and tamp the bottom and around of the casing with clay in layers. The casing is buried to a depth of 2.7m, and the top of the casing is 0.3m higher than the maximum wave height of the water surface, and weld steel bar lifting lugs at the top. The vertical line of the casing center coincides with the pile center line, the allowable plane error is 50mm, and the vertical inclination rate is not greater than 1%. During the drilling process, assign a special person to check whether the casing is displaced or subsided, and handle it in time if there are changes;

[0060] Step 3. Drilling Rig Positioning: Before the drilling rig is positioned, carefully recheck the pile position. Compact the ground where the drilling rig is positioned with a roller or replace the filling, etc., to ensure that after the drilling rig is positioned, the center of the drill bit and the lofting point of the pile center are on the same vertical line, ensuring the correct pile position during hole formation and the stability of the drilling rig during construction;

[0061] Step 4. Mud Preparation: Select clay with fast hydration, strong mud-making ability and high viscosity for mud preparation, and determine the various indicators of the clay through tests. Frequently measure the mud technical indicators during the drilling process, and adjust the mud relative density at any time according to the needs of engineering drilling to keep all indicators meeting the requirements, so as not to affect the progress due to too thick mud or cause hole collapse due to too thin mud, etc.;

[0062] The reference table for each index is Table 1;

[0063] Table 1: Mud Performance Index Table;

[0064]

[0065] Step 5. Drilling and Hole Formation:

[0066] Step 5.1. Drilling Speed At the beginning of drilling, start at a slow speed. For the bottom of the casing, use a low gear and slow speed for drilling to form a firm mud skin protection at the bottom. If the soil at the bottom of the casing is soft and there is slurry leakage, lift the drill bit, pour clay blocks into the hole, then put the drill bit in and reverse it to squeeze the clay into the hole wall to block the slurry leakage gap, stabilize the slurry and then continue drilling. After the drill bit passes through 2.0m below the bottom of the casing, increase the speed and drill normally. The lifting and lowering speed of the drill bucket is controlled at 0.75 - 0.80m / s.

[0067] Step 5.2: During the geological sampling and drilling process, always pay attention to the changes in the soil layer. Take slag samples at the place where the soil layer changes to identify the soil layer, and record them in the record sheet for verification with the geological profile. Regularly test the boreholes and measure the mud density, viscosity, and sand ratio in a timely manner. If the mud performance indicators do not meet the soil layer requirements, make timely adjustments. When handing over the shift, explain the drilling situation of the shift and the precautions to be taken when leaving get off work.

[0068] Step 5.3: Before drilling the test piles, a test hole should be drilled. During the formal construction of the test piles, the construction should be carried out according to the actual layout of the site. Operate the drilling rig to master the drilling parameters and pay attention to any abnormal conditions. For example, if the active drill rod shakes greatly, the penetration should be slowed down at this time, and normal drilling can be carried out after it passes through. The drilling speed should be strictly controlled during drilling. The drilling speed should be adapted to the slurry delivery and slag removal capacity. The drilling speed should be lower than the slurry delivery and slag removal speed to avoid drilling burial. When adding a drill rod, the drilling should be stopped first, the drill tool should be slightly lifted from the bottom of the hole, and the mud should be circulated for a few minutes before stopping the pump and adding a drill rod. The drilling construction should be completed continuously at one time, and drilling should not be stopped without reason. After the hole is drilled to the designed hole depth, the hole should be cleaned initially, and then the various requirements for the hole should be inspected and accepted together with the relevant parties of the project. The next process can be carried out only after passing the inspection.

[0069] Step 6, final hole inspection: When the borehole reaches the designed elevation, use a hole detector to check the hole depth, hole diameter, hole position and hole shape, verticality, and geological conditions at the bottom of the hole, then fill in the final hole record, and promptly notify the supervision engineer to come to the site for inspection and acceptance. Only after passing the inspection can it proceed to the next process. When the rotary drill approaches the final hole, a bottom sealing sand bailing drill bit should be used to drill, reduce the amount of footage per return (to about 30cm), and gradually remove the thick mud at the bottom of the hole. When the final hole depth is reached, stop for 20 to 30 minutes to allow the suspended matter in the mud to settle and scoop it out with a drill bit;

[0070] Step 7: Install the support device;

[0071] Step 7.1, Support strut system The support strut consists of a middle slide bar, a support strut, a support foot, three adjustable limit devices, a main sliding collar and two groups of eight support strut secondary sliding collars. The two groups of eight secondary sliding collars are connected to the upper and lower groups of support struts respectively. The secondary sliding collars are locked with the main sliding collars and can rotate freely with each other. The support struts can be opened under pressure and retracted under the action of gravity to keep parallel with the middle slide bar.

[0072] Step 7.2, Position Limiting Lifting Rope System The position limiting lifting rope is composed of steel strands with scales and covered with rubber. After the support rod and the device body are placed at the designated position, they are anchored on the ground outside the pile hole to limit the downward movement of the device body due to gravity. The lifting rope can be smoothly retracted after the device body is firmly anchored to the hole wall.

[0073] Step 7.3. Automatic pop-up anchoring device The automatic pop-up anchoring device mainly consists of a bracket, a spring, an anchor nail, a spring limit piece, and a trigger pop-up lock that are separately connected to the support strut foot. This device mainly triggers the spring limit piece after the support strut is subjected to downward pressure from above. Under the combined action of the downward pressure and the spring elastic force, the device body is anchored to the hole walls of the upper and lower strata of the sand layer through the anchor nail.

[0074] Step 7.4. Support device body The support device body consists of rigid iron rings spaced horizontally at 5 cm intervals and a dense mesh. The auxiliary facilities consist of an automatic pop-up device and a limit suspension rope loop, which together form the support device body.

[0075] Step 7.5. Device combination, hoisting and anchoring of the support body Connect the support strut to the device body through the automatic pop-up anchoring device, and connect the limit suspension rope to the suspension ring of the device body. After combining into a device system, lower it to the designated position with the help of a crane and the position limit suspension rope. Then, use a certain force to instantaneously press down the intermediate slide bar to realize the anchoring of the automatic pop-up anchoring device on the hole wall, achieving the support and anchoring effect for the ultra-thick permeable sand layer.

[0076] Step 8. Hole cleaning: Thoroughly removing the sediment at the bottom of the hole is one of the important measures to ensure the bearing capacity of the pile foundation. In this project, the method of removing the sediment at the bottom of the hole twice is adopted.

[0077] Step 8.1. When the drilling reaches the designed hole depth, lift the drill bit 150 - 200 mm above the bottom of the hole, start the mud pump for positive circulation hole cleaning, and the time shall not be less than 20 min.

[0078] Step 8.2. Pile hole acceptance: After the pile hole reaches the end hole, first conduct self-inspection according to the design requirements, and then invite the representatives of the Party A and the supervisor to accept various indicators such as the end hole depth, sediment, and mud performance. After passing the acceptance, complete the on-site filling and visa work.

[0079] Step 8.3. The steel reinforcement cage can be lowered only after the pile hole passes the acceptance. After the steel reinforcement cage and the perfusion conduit are lowered, use the conduit for positive circulation for the second hole cleaning. It is required that after the hole cleaning, the sediment at the bottom of the hole does not exceed 100 mm, and the time interval from the hole cleaning to the concrete perfusion shall not exceed 30 min. If it exceeds 30 min, the hole shall be re-cleaned to meet the requirements before the concrete perfusion can be carried out.

[0080] Step 8.4. After the perfusion is completed, lift the conduit slowly to make the concrete surface opening close slowly, preventing it from being pulled out too quickly, causing mud to mix in and forming a mixed mud core.

[0081] Step 8.5. For each pile being poured, the slump shall be measured twice. Special personnel shall take samples to make test blocks, and for each pile, at least one group (3 pieces) shall be made. Number them and indicate the sampling time, and record them in the concrete perfusion record. The test blocks shall be demolded 24 hours after being made, placed in a standard curing room for curing for 28 days, tested on time, and the test pressure results shall be filed for future reference.

[0082] Step 8.6, before drilling, use a level to determine the casing elevation, and use it as a base point. Calculate the hole depth according to the bottom elevation of the hole required by the design, and determine the hole depth by the length of the drill. The hole depth deviation should not be shorter than the design depth, and the overdrilling depth should not exceed 20cm. When the drilling depth reaches the design requirements, check the hole depth, hole diameter, hole position, hole shape and thickness of the bottom sediment of the hole. The inspection method uses a cage-type borehole detector. If the diameter shrinkage phenomenon occurs, the hole should be swept. Only after it meets the requirements of the specification can the next process be constructed. Inspection method: The crane hangs the upper end ring of the borehole detector and slowly lifts it to the top of the pile hole. Tie one end of the measuring rope to the lower end of the borehole detector. The center of the borehole detector is aligned with the center of the pile hole and slowly lowered to prevent the hole wall from collapsing. The measuring rope is lowered with the borehole detector and a special person is responsible for lowering the rope until the borehole detector is lowered to the bottom of the hole. Measure the pile hole depth and confirm that it meets the design requirements. After the supervision engineer signs and approves it, the bottom sediment cleaning and underwater concrete pouring preparation work can be carried out.

[0083] Step 9: Place the steel cage and conduit;

[0084] Step 9.1. Before the mechanical sleeve connection of the main reinforcement of the steel cage, a straight thread threading machine should be used for threading, and a ring-through gauge and a ring-stop gauge should be used for threading inspection. The next step can be carried out only after the inspection is qualified; when installing the reinforcement, one should be set every 2m; a group of positioning bars should be set every 2m, and each group of 4 bars should be evenly arranged around the pile foundation reinforcement.

[0085] Step 9.2: When transporting and hoisting the steel cage, protective measures must be taken to prevent deformation of the steel cage. A crane is used for hoisting, and two lifting points are set. During the hoisting process, it must be lifted and placed gently. A flatbed truck is used to transport it to the work site, and the steel cage is hoisted into the hole by a crane. When hoisting the steel cage into the hole, the center of the steel skeleton should be aligned with the pile hole and then placed into the hole. During the lowering process, the steel cage must be kept vertical.

[0086] Step 9.3: When sinking, the method of lifting and sinking section by section is adopted. The steel cage that has been placed is temporarily fixed by using steel pipes or steel sections through its reinforcing stirrups. The upper section of the steel cage is temporarily suspended by a crane. After the upper and lower sections are aligned to form a straight line, the main reinforcement position is found and the verticality is controlled from the front, back, left and right by using pendants. After the adjustment is completed, the mechanical casing connection is performed. The pile foundation steel bars are reasonably divided according to the pile length and on-site processing conditions to ensure the construction quality and progress.

[0087] Step 9.4: When connecting two sections of steel cage, the main reinforcement axis of the upper and lower sections must be aligned, and mechanical sleeves are used for connection. After the upper and lower sections are connected, pull out the supporting steel pipe or steel, and continue to sink the steel cage. To avoid the steel cage colliding with the hole wall, it should be slowly sunk, and the sling should be placed on the axis of the steel cage to prevent it from shaking.

[0088] Step 9.5, there must be 4 lifting rings for the steel cage to enter the hole. The length and welding position must be accurately calculated and determined according to the elevation position of the control platform to ensure the accuracy of the steel cage position elevation. The lap length and weld of the lifting ring steel bars shall adopt standard welds. The cross arm (steel pipe or other steel section) that fixes the steel cage must have sufficient strength and rigidity, the cross arm support point must be flat, and the clamping ring must be firm. Prevent the phenomenon of the overall tilting and floating of the steel cage caused by the elevation deviation of the steel lifting ring, the uneven cross arm support point and the loose clamping ring. The steel cage should be placed in line with the hole position, and the error of the top surface elevation and plane position shall not be greater than 10mm. After it is in place, it must be firmly positioned to avoid the cage falling or floating during the concrete pouring process.

[0089] Step 9.5, Place the guide tube: The upper end of the acoustic detection tube is 30cm higher than the top surface of the pile, and the lower end is suspended 10cm. The length of each section of the acoustic detection tube corresponds to the length of the steel cage section. The sections are connected with sleeves, and the sleeve length is 80cm. The outer diameter of the detection tube is 57mm, and the diameter of the sleeve is 60mm. The acoustic detection tube is tied to the reinforcing steel bar, and its bottom is welded with a steel plate to seal the bottom. It is required to be watertight. Before pouring concrete, fill the tube with water and plug it with a plug. If the pile diameter is less than 1.5m, set 3 detection tubes, and if the pile diameter is ≥1.5m, set 4 detection tubes.

[0090] Table 2: Quality standard for the production and installation of cast-in-place pile reinforcement skeleton:

[0091]

[0092]

[0093] Step 9.6, secondary hole cleaning. To ensure that the thickness of the sediment meets the design requirements, secondary hole cleaning is required. High-pressure air or high-pressure mud injection method is used. After the secondary hole cleaning, the mud specific gravity and sediment thickness are measured to determine whether concrete can be poured. If it does not meet the requirements, continue the secondary hole cleaning. For holes that are difficult to clean, use an air suction mud machine to clean the hole. After the secondary hole cleaning is completed, gently lower the catheter to the bottom, and then lift it up 30 to 40 cm, compare it with the theoretical length of the catheter, and after it matches, fix the catheter on the hole seat of the pouring platform. Before pouring concrete, check the sediment thickness and mud indicators at the bottom of the hole until they meet the design and specification requirements, then remove the head, connect the concrete initial pouring funnel, check the sediment thickness at the bottom of the hole, and start pouring concrete after it meets the specification requirements.

[0094] Step 10: pouring concrete: pouring concrete continuously to the designed elevation to ensure the quality of piles;

[0095] Step 10.1: After the pouring begins, it should be carried out continuously and compactly. Stopping work during the process is strictly prohibited. The continuous pouring time of concrete for the same pile should not exceed the initial setting time of the concrete. Try to shorten the time for removing the conduit and control the speed of material feeding. It should not be too fast or too violent to avoid air blockage.

[0096] Step 10.2: During the pouring process, prevent the concrete mixture from overflowing from the top of the funnel or falling into the bottom of the hole outside the funnel. This will cause the mud to thicken and solidify due to the inclusion of cement, making the depth measurement inaccurate. During the pouring process, observe the descent of the concrete in the pipe and the rise and fall of the water level in the hole, measure the height of the concrete surface in the hole in a timely manner, and correctly guide the lifting and removal of the conduit.

[0097] Step 10.3: During the pouring process, when the concrete in the conduit is not full and contains air, the subsequent concrete should be poured slowly. Do not pour an entire bucket into the hopper and conduit at once, so as to avoid forming a high-pressure air bag in the conduit, squeezing out the rubber gasket between the pipe joints, and causing the conduit to leak.

[0098] Step 11: Chiseling the pile head and pile foundation detection: After the foundation pit is excavated, accurately measure and mark the height of the pile penetrating into the pile cap beam. Use the circumcision method for construction and use a crane to lift the pile head away as a whole.

[0099] Conduct ultrasonic testing on the cast-in-place concrete piles to determine the quality of the cast-in-place concrete piles. If there are defects in the test results, core sampling testing should be carried out. The quality of the pile foundation must meet the requirements of Class I piles.

[0100] Figure 4 This is the structural diagram of the support device for this design, and its detailed structure is as follows:

[0101] 1. Composition of the support device body 11:

[0102] The rigid iron rings 12 are evenly arranged at a horizontal interval of 5 cm to form an annular framework, which is fixed to the outer periphery of the support device body 11 by welding or tying, serving as the support core.

[0103] The wire mesh 9 covers the space between adjacent rigid iron rings 12 and is fixed to the iron rings by tying or welding to form a continuous retaining wall barrier for preventing the collapse of the sand layer.

[0104] 2. Connection of the support strut system:

[0105] One end of the support strut 8 is connected to the rigid iron ring 12 of the support device body 11 through a hinge device 10 and can rotate around the connection point to realize the opening or closing of the strut. The other end is provided with an automatically sprung anchor pin 6, which is non-fixedly connected to the end of the strut through a spring and a trigger mechanism. When compressed, the anchor pin pops out and pierces into the soil layer 7 of the hole wall.

[0106] Sliding collar assembly: It includes a main sliding collar 51 and a secondary sliding collar 52. Both the main sliding collar 51 and the secondary sliding collar 52 are sleeved on the intermediate sliding rod 2 and can slide up and down along the rod.

[0107] The secondary sliding collar 52 is hinged to the middle of the support strut 8, and the support strut is lock-connected to the main collar 51 through the secondary collar to form a linkage structure to ensure the synchronous opening or closing of the strut.

[0108] 3. Trigger mechanism of the automatic spring - out anchoring device:

[0109] The automatic spring - out anchor pin 6 is connected to the end of the support strut 8 through a bracket, a spring and a trigger spring - out lock. When the middle sliding rod 2 is pressed downward by an external force, the main sliding collar 51 drives the auxiliary collar 52 to move downward, pushing the support strut 8 to open outward, triggering the spring limit piece, and the spring force pushes the anchor pin 6 out to anchor the support device body 11 to the soil layer 7 of the hole wall.

[0110] 4. Function of the position - limiting suspension rope system:

[0111] One end of the position - limiting suspension rope 3 is fixed to the top of the support device body 11 through a hanging ring, and the other end passes through the limiting device 4 and is anchored to the ground outside the pile hole.

[0112] Function: During hoisting, the lowering depth is controlled through the rope scale and the limiting device to ensure accurate positioning of the device; after anchoring, the suspension rope can be removed and recycled.

[0113] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above - mentioned exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any regard, the embodiments should be regarded as exemplary and non - restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0114] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only includes an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A construction method for pile foundations in a super-thick permeable sand layer, characterized in that It includes the following steps: Step 1: Prepare the site, platform and mud pit; clean the site, set up the construction platform and prepare the mud pit; Step 2: Bury the casing: Bury a steel casing with a suitable height according to the geological conditions; Step 3: Position the drilling rig: Recheck the pile position to ensure the stable positioning of the drilling rig; Step 4: Prepare the mud: Select suitable clay to prepare the mud and make the mud performance indicators meet the requirements; Step 5: Drill and form the hole: Drill at a suitable drilling speed and parameters, and take samples in time to judge the soil layer changes; Step 6: Final hole inspection: Use a hole forming detector to check the hole depth and hole diameter; Step 7: Install the support device: After combining the support device body and the support strut system, hoist it to the designated position through the position limit suspension rope system, and use the automatic spring-out anchoring device to anchor the support device body to the hole wall; Step 8: Clean the hole: Conduct two hole cleanings to ensure that the thickness of the sediment at the bottom of the hole meets the design requirements; Step 9: Place the steel reinforcement cage and the conduit; Step 10: Pour the concrete: Continuously pour the concrete to the design elevation to ensure the pile quality; Step 11: Chisel the pile head and conduct pile foundation inspection: Chisel the pile head after the foundation pit is excavated and conduct pile foundation quality inspection.

2. The pile foundation construction method for a super-thick permeable sand layer according to claim 1, characterized in that, The specific content of step 1 is as follows: Use the total station coordinate layout method to layout the center position of the pile, determine the pile position center, set up cross-shaped protective piles around with a radius greater than the pile body radius centered on the center, make marks and fix them well. The measurement error is zero error. The pile position is marked with Reinforcing bars with a length of 35 - 40 cm are driven 30 cm into the ground as the center point of the pile, and the surrounding is filled with cement mortar or concrete for protection, and marks are made around the pile position.

3. A construction method for a super-thick permeable sand layer pile foundation according to claim 1, characterized in that, Specifically, for Step 2: According to the geological conditions, during construction, a 3m high steel casing is used, the casing diameter is 1.8m, the wall thickness is 6mm, the bottom and around of the casing are filled with clay and tamped in layers, the buried depth of the casing is 2.7m, the top of the casing is 0.3m higher than the maximum wave height of the water surface, and steel bar lifting lugs are welded at the top. The vertical center line of the casing coincides with the pile center line, the plane allowable error is 50mm, the vertical inclination rate ≤ 1%. During the drilling process, check whether the casing is displaced or subsided and deal with it in time according to the inspection results.

4. A construction method for a super-thick permeable sand layer pile foundation according to claim 1, characterized in that, Specifically, for Step 3: Recheck the pile position before the drilling rig is positioned. The ground where the drilling rig is positioned is compacted by a roller or backfilled to ensure that after the drilling rig is positioned, the center of the drill bit and the center of the pile lofting point are on the same plumb line, ensuring the correct pile position during hole formation and the stability of the drilling rig during construction.

5. A construction method for a super-thick permeable sand layer pile foundation according to claim 1, characterized in that, Specifically, for Step 4: Select clay with fast hydration, strong slurry-making ability and high viscosity for preparing the mud, and determine the various indicators of the clay through tests; Frequently measure the mud technical indicators during the drilling process, and adjust the relative density of the mud at any time according to the needs of engineering drilling to keep all indicators meeting the requirements, so as not to affect the progress due to too thick mud or cause hole collapse due to too thin mud.

6. The construction method of a super-thick permeable sand layer pile foundation according to claim 1, characterized in that, Specifically, Step 5 includes the following steps: Step 5.1: Drill speed control: Start drilling slowly at first. For the bottom of the casing, drill at a low gear and low speed to form a firm mud skin at the bottom. If the soil at the bottom of the casing is soft and slurry leakage occurs, the drill bit can be lifted, clay lumps are poured into the hole, and then the drill bit is put in and reversed to make the clay mortar squeeze into the hole wall to block the slurry leakage gap. After stabilizing the mud, continue drilling; After the drill bit passes through 2.0m below the bottom of the casing, increase the speed and drill normally; The lifting and lowering speed of the drill bucket is controlled at 0.75 - 0.80m / s; Step 5.2: Geological sampling: When the soil layer changes during the drilling process, collect the slag samples at the soil layer change to identify the soil layer and record them in the record form, check them against the geological profile diagram, and at the same time conduct tests on the drilled hole to measure the mud specific gravity, viscosity and sand ratio; Step 5.3, Hole formation: Before drilling the test pile, a trial hole formation should be carried out. During the formal construction of the test pile, it should be constructed according to the actual on-site layout points. When operating the drill, adjust the drilling parameters in a timely manner when encountering different geological conditions. During drilling, strictly control the drilling speed to make the drilling speed adapt to the slurry supply and slag discharge capabilities. The drilling speed is lower than the slurry supply and slag discharge speed. When adding a drill pipe, first stop drilling, lift the drill tool off the bottom of the hole, wait for the slurry to circulate for a few minutes, and then stop the pump to add the drill pipe. The hole formation construction is completed continuously in one go. After the hole is formed to the designed hole depth, preliminary hole cleaning is first carried out, and then inspection and acceptance are carried out. After passing the inspection, the next process can be carried out.

7. A construction method for a super-thick permeable sand layer pile foundation according to claim 1, characterized in that The specific content of step 6 is as follows: When the drilling reaches the designed elevation and hole position, use a hole formation detector to check the hole depth, hole diameter, hole position, hole shape, verticality, and geological conditions at the bottom of the hole, then fill in the final hole record, and promptly notify the supervising engineer to come to the site for inspection and acceptance; only after passing the inspection can the next process be carried out. When the rotary drilling rig is approaching the final hole, use a bottom-sealing sand-bailing drill bit to drill and take out the thick slurry at the bottom of the hole; when the final hole depth is reached, stop for 20 - 30 minutes to allow the suspended matter in the slurry to precipitate, and use the drill bit to fish it out.

8. A construction method for a super-thick permeable sand layer pile foundation according to claim 1, characterized in that, Step 8 adopts the method of removing the sediment at the bottom of the hole twice, and specifically includes the following steps: Step 8.1: When the drilling reaches the designed hole depth, lift the drill bit 150 - 200 mm off the bottom of the hole, start the slurry pump for positive circulation hole cleaning for no less than 20 minutes; Step 8.2, Pile hole acceptance: After the pile hole reaches the final hole, first conduct self-inspection according to the design requirements, and then accept the final hole depth, sediment, and various indexes of the slurry performance. After passing the acceptance, do a good job in filling out the on-site visa form; Step 8.3: Only after the pile hole passes the acceptance can the steel reinforcement cage be lowered. After the steel reinforcement cage and the perfusion catheter are lowered, use the catheter for positive circulation for the second hole cleaning. It is required that after the hole cleaning, the sediment at the bottom of the hole does not exceed 100 mm, and the time interval from the hole cleaning to the concrete perfusion does not exceed 30 minutes. If it exceeds 30 minutes, it is necessary to re-clean the hole to meet the requirements before the concrete perfusion can be carried out; Step 8.4: After the perfusion is completed, the speed of lifting the catheter needs to meet the following conditions: the concrete surface gradually closes, there is no mud mixing in, and there is no mixed mud core; Step 8.5: For each pile poured, two slump measurements need to be carried out. First, take samples to make test blocks, and for each pile, no less than 3 blocks should be made. Number them and indicate the sampling time, record them in the concrete perfusion record. The test blocks are demolded 24 hours after being made, placed in a standard curing room for 28 days of curing, tested on time, and the test pressure results are filed for future reference; Step 8.6: Before drilling, use a level to determine the elevation of the casing, and use this as a reference point. Calculate the hole depth according to the designed bottom elevation of the hole, and determine the hole depth based on the length of the drill tool. The hole depth deviation is not shorter than the designed depth, and the over-drilling depth is not more than 20 cm; when the drilling depth reaches the design requirements, check the hole depth, hole diameter, hole position, hole shape, and sediment thickness at the bottom of the hole. The inspection method uses a cage-type hole detector; if the phenomenon of hole shrinkage occurs, hole reaming should be carried out.

9. A construction method for a super-thick permeable sand layer pile foundation according to claim 1, characterized in that The specific content of step 9 includes: Step 9.1: Before the mechanical sleeve connection of the main reinforcement bars of the steel cage, thread rolling is carried out using a straight thread rolling machine, and ring through gauges and ring stop gauges are used for thread rolling inspection. After passing the inspection, the next process is carried out; when installing the stiffeners, one set is provided every 2m; one group of positioning bars is provided every 2m, and each group of 4 bars is evenly arranged around the pile foundation stiffeners; Step 9.2: Transport it to the work site by flatbed truck, use a crane, set 2 lifting points, and use the method of segmental lifting and segmental sinking for hoisting; Step 9.3: For the placed steel cage, use steel pipes or steel profiles to support and temporarily fix this section through its stiffening stirrups; the upper section of the steel cage is temporarily lifted by a crane and is in a suspended state. After aligning the upper and lower sections to form a straight line, align the position of the main reinforcement bars and use a plumb bob to control the verticality from the front, back, left, and right. After adjustment, carry out mechanical sleeve connection; Step 9.4: When connecting two sections of the steel cage, the axes of the main reinforcement bars of the upper and lower sections must be aligned, and mechanical sleeve connection is adopted; after the upper and lower sections are butted, pull out the steel pipes or steel profiles used for support, and continue to sink the steel cage; Step 9.5: There are 4 hanging rings for the steel cage to enter the hole. According to the elevation position of the control platform, calculate and determine the length and welding position. The lap length and weld of the hanging ring steel bars adopt standard welds; when placing the steel cage, it needs to be aligned with the hole position, and the errors in its top elevation and plane position are both ≤ 10mm; Step 9.6: Place the conduit: The upper end of the acoustic pipe is 30cm higher than the pile top surface, and the lower end is suspended 10cm. The length of each section of the acoustic pipe corresponds to the section length of the steel cage, and the sections are connected by sleeves with a sleeve length of 80cm; the outer diameter of the inspection pipe is 57mm, the sleeve diameter is 60mm, the acoustic pipe is tied to the stiffening bars, and its bottom end is welded and sealed with a steel plate. Before pouring concrete, fill the pipe with water and block it with a plug. When the pile diameter is less than 1.5m, 3 inspection pipes are set, and when the pile diameter ≥ 1.5m, 4 inspection pipes are set.

10. A construction method for a super-thick permeable sand layer pile foundation according to claim 1, characterized in that, The specific content of the said Step 10 is as follows: Step 10.1: After the pouring starts, it needs to be carried out continuously, and the continuous pouring time of the concrete for the same pile is not greater than the initial setting time of the concrete; Step 10.2: During the pouring process, it is necessary to prevent the concrete mixture from overflowing from the top of the funnel or falling into the bottom of the hole outside the funnel. During the pouring process, it is necessary to pay attention to observing the drop of the 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 in a timely manner; Step 10.3: During the pouring process, when the concrete in the conduit is not full and contains air, the subsequent concrete should be poured slowly to prevent the formation of a high-pressure air bag in the conduit.

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