Road and bridge pile foundation construction technology

Abstract

The invention discloses a road and bridge pile foundation construction technology, and belongs to the field of road and bridge pile foundation construction. S2, pile position lofting is carried out; a round pit is dug in the pile position, the pit bottom is filled with clay, the center of a drilled hole is marked, and the pile casing is hoisted into the pit to be buried; s4, drilling after a drilling machine is in place; s5, hole forming inspection and hole cleaning are carried out; s6, manufacturing and placing a reinforcement cage: manufacturing the reinforcement cage in sections, connecting joints of the reinforcement cage by adopting a sleeve, and vertically hoisting the manufactured reinforcement cage into the drill hole by adopting two-point hoisting; s7, underwater concrete is poured through a guide pipe method; and S8, the pile casing is pulled out, and pile forming detection is conducted. By the adoption of the road and bridge pile foundation construction technology, the problems that in the existing road and bridge pile foundation construction process, the pile casing embedding precision is low, the drilling adaptability is weak, the reinforcement cage installation is unstable, the pile forming treatment is simple, and the technology adaptability is poor can be solved.

Description

Technical Field

[0001] This invention relates to the field of road and bridge pile foundation construction technology, and in particular to a road and bridge pile foundation construction process. Background Technology

[0002] As the foundational load-bearing structure of bridges and roads, the construction quality of road and bridge pile foundations directly determines the stability and service life of the overall project.

[0003] Currently, conventional pile foundation construction techniques in the industry have many shortcomings: During casing installation, low center positioning accuracy and poor verticality control easily lead to subsequent borehole deviation and borehole wall collapse; during drilling operations, there is a lack of standards for adjusting the drilling speed according to different geological conditions, and insufficient operational standardization of rotary drilling or impact drilling easily causes problems such as irregular pile diameter and borehole wall tilting; during the hoisting of the reinforcing steel cage, deformation is prone to occur, and the reliability of joint connections is insufficient; the tremie pipe is not fully tested before use, resulting in quality defects such as grout leakage, pile breakage, and mud inclusion during concrete pouring; pile treatment only involves simple removal of laitance, insufficient compaction of the backfill around the pile, and the testing methods are limited, making it difficult to comprehensively investigate hidden defects in the pile body. Furthermore, for sites with thick soft soil and complex geology, conventional techniques lack effective site pretreatment solutions, further exacerbating construction quality fluctuations, resulting in low pile foundation qualification rates, high subsequent maintenance costs, and an inability to meet the high requirements of modern road and bridge engineering for construction accuracy and reliability. Summary of the Invention

[0004] The purpose of this invention is to provide a construction process for road and bridge pile foundations, which solves the problems of low accuracy of casing installation, weak adaptability to drilling, unstable installation of steel reinforcement cage, simple pile treatment, and poor process adaptability in the existing road and bridge pile foundation construction process.

[0005] To achieve the above objectives, the present invention provides a road and bridge pile foundation construction process, comprising the following steps: Step S1, Site leveling: Before the drilling rig is in place, use an excavator to remove the soft soil layer on the original ground, level the entire site and compact it to serve as the drilling rig's working platform, and make the site hard. Step S2, Pile location layout: Calculate the pile foundation coordinates based on the data provided in the construction drawings, and after verification, use a total station to lay out the pile locations; Step S3, casing installation: dig a circular pit at the pile location, fill the bottom of the pit with clay and mark the center of the borehole, and hoist the casing into the pit for installation; Step S4, drilling after the drilling rig is in place: accurately determine the position of the drilling rig by measuring the pile position, adjust the drill rod to keep it vertical, conduct the first pile test drilling according to the construction drawings, and then carry out the drilling operation. Step S5, Hole Formation Inspection and Cleaning: After the hole reaches the design elevation, check the hole depth, hole diameter, hole wall verticality, and sediment thickness. After the inspection is completed, clean the hole. Step S6, Rebar cage fabrication and placement: The rebar cage is fabricated in sections, and the joints of the rebar cage are connected by sleeves. The fabricated rebar cage is vertically lifted into the borehole using a two-point lifting method. Step S7, underwater concrete pouring using the tremie pipe method: determine the concrete mix ratio, prepare the concrete slurry, and lower the tremie pipe into the borehole for continuous concrete pouring; Step S8, Removal of casing and pile inspection: After the concrete curing is completed, the casing is removed, the pile is treated, and the quality is inspected.

[0006] Preferably, in step S1, if the soft soil on the site is thick and not hard enough, a 60cm thick layer of weathered material is laid on the site surface and leveled and compacted.

[0007] Preferably, in step S3, the casing is made of steel and is welded from steel plates, flat steel hoops, and angle steel ribs. When installing the casing, first dig a circular pit at the pile location that is 20cm to 40cm larger than the outer diameter of the casing. Fill the bottom of the pit with 50cm thick clay and compact it in layers. Then, mark the center position of the borehole at the bottom of the pit using the positioning control stakes. Then, hoist the casing into the pit, find the center position of the casing, fix it at the top of the casing with a crosshair, move the casing so that the center of the casing coincides with the center of the borehole, and check with a spirit level or plumb bob to ensure that the casing is vertical. After that, backfill the casing symmetrically and evenly with clay of the optimal moisture content, compact it in layers to achieve the optimal density.

[0008] Preferably, during the layered compaction process, the center position and verticality of the casing are checked after each layer is compacted. After leveling, a plumb bob is hung up and the casing is checked again. Any deviations are corrected immediately. The top of the casing is 0.3m above the ground. Reinforcing ribs and lifting lugs are welded to the top of the casing, and a water outlet is opened. During the drilling process, the casing is checked for any displacement or sinking, and any issues are addressed promptly.

[0009] Preferably, in step S4, a rotary drilling rig or an impact drilling rig is used for drilling operations, and the drilling operations are carried out continuously in shifts. When drilling with a rotary drilling rig, monitor the actual working position of the borehole, the position of each advance, and the depth of the hole. When drilling, first place the drill bucket on the ground and use the weight of the drill bucket and pressure as the drilling power. When the drill bucket is squeezed and filled with drill cuttings, lift it to the surface and use a loader to load the drill cuttings into a muck truck and transport it off-site for disposal. During the drilling process, control the advance speed according to the geological conditions. When drilling with an impact drill, check the pile diameter, planar position, and vertical axis inclination. Ensure the hole position is accurate. Drill slowly at the beginning and accelerate after the drill bit has fully entered the stratum. Check the hole quality every 4-6 meters.

[0010] Preferably, in step S5, the hole formation inspection standards are: hole depth and hole diameter ≥ design specifications, drilling inclination error ≤ 1%, and sediment thickness conforming to design specifications.

[0011] Preferably, in step S6, the allowable deviations for the fabrication and hoisting of the reinforcing steel cage are: main bar spacing ±0.5d; stirrup spacing ±20mm; reinforcing bar spacing ±0.5d; cage diameter ±20mm; cage verticality ±1%; and the length of the reinforcing steel cage below the foundation bottom ±100mm.

[0012] Preferably, a two-point lifting method is used: the large hook of the crane is horizontally lifted at a position away from both ends of the steel reinforcement cage, and then the small hook lifts the lifting end of the steel reinforcement cage, so that the steel reinforcement cage is lifted; during the lifting, square timber or steel sections are used to assist in lifting the top and bottom of the steel reinforcement cage.

[0013] Preferably, in step S7, the guide pipe undergoes watertightness, pressure resistance, and joint tensile tests before use. When the guide pipe is lowered into the hole, its position is centered, its axis is straight, and it is steadily lowered without getting caught on the reinforcing steel skeleton or colliding with the hole wall. After the concrete pouring begins, it is carried out continuously to shorten the interval time for removing the guide pipe. During the pouring process, a sounding hammer is used to detect the position of the concrete surface in the hole and adjust the burial depth of the guide pipe in a timely manner. The burial depth of the guide pipe is controlled between 2m and 6m.

[0014] Preferably, in step S8, the pile forming process involves: using a combination of mechanical and manual methods to remove the laitance layer at the top of the pile and chiseling away any excess concrete to ensure the pile top elevation meets design requirements; cleaning the concrete residue and rust from the surface of the pre-reserved reinforcing bars at the pile head and adjusting the spacing and verticality of the reinforcing bars; removing loose soil, debris, and uncured concrete around the pile body; filling and compacting any holes or gaps around the pile with fine aggregate concrete of the same grade; and backfilling and compacting the annular pit left after removing the casing with graded sand and gravel in layers. Pile testing: A general survey of the pile foundation is conducted using the low-strain reflected wave method to detect defects such as broken piles, mud inclusions, and diameter reduction in the pile body. For pile foundations with complex geology or questionable low-strain test results, a supplementary ultrasonic transmission method is used for re-inspection. The sound wave propagation velocity is measured point by point through pre-embedded sonic logging tubes to determine the location and extent of defects. 1% to 3% of the total number of piles are selected according to design requirements, and the vertical compressive bearing capacity is tested using the high-strain method. The loading rate is strictly controlled during the test, and the load-settlement curve is recorded. The test data is compiled, and a test report is issued.

[0015] Therefore, the present invention employs the above-mentioned road and bridge pile foundation construction technology, which has the following beneficial effects: 1. The casing is installed with high precision. Through the process of compacting the clay at the bottom of the pit, positioning with cross lines, and verifying the layered compaction, combined with the top reinforcing bars and lifting lug design, the casing is effectively prevented from shifting or sinking, ensuring that the borehole center is consistent with the pile position. 2. Strong adaptability to drilling, with clear operating procedures and quality control points for rotary drilling and impact drilling. Adjusting the drilling speed according to different geological conditions, and matching the first pile test drilling process to reduce problems such as borehole wall collapse and pile diameter deviation. 3. The steel reinforcement cage is installed stably, using sleeve connection, two-point lifting, and auxiliary protection with square timber / section steel. All dimensional deviations are strictly controlled to ensure the verticality and connection reliability of the steel reinforcement cage, thereby improving the load-bearing performance of the pile foundation. 4. Comprehensive quality assurance for pile formation: Standardized procedures for pile head treatment and pile perimeter backfilling prevent lateral deformation of the pile body. A combination of low-strain inspection, ultrasonic re-inspection, and high-strain bearing capacity testing enables dual verification of pile defects and bearing capacity. 5. The process is highly adaptable, with weathered material paving schemes designed for soft soil and thick soil. It is compatible with different drilling equipment and geological conditions, with a clear operation process and strong operability, which improves construction efficiency and reduces rework rate. It is suitable for various road and bridge pile foundation projects.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the steps of an embodiment of a road and bridge pile foundation construction process according to the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0019] It should be noted that the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0020] Similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] like Figure 1 As shown, the road and bridge pile foundation construction process of the present invention includes the following steps: Step S1, Leveling the site: Due to the large turning radius, tall drill rod, and heavy weight of rotary drilling rigs, an 8-meter-wide operating platform is required during operation. Before the rig is positioned, an excavator is used to remove the soft soil layer from the original ground, level the entire site, and compact it to serve as the drilling platform. The site must be firm enough to prevent the rig from sinking or tilting. If the soft soil is thick and not firm enough, a 60cm-thick layer of weathered material is laid on the surface and leveled and compacted to ensure the safety of the drilling operation.

[0024] Step S2, pile location layout: The pile foundation coordinates were calculated based on the data provided in the drawings, and the layout was carried out after verification. An imported Leica total station was used for the layout, and four protective piles were laid out around the perimeter. These were reinforced and protected with concrete to facilitate checking the pile center position during pile driving and after hole formation. Leveling points were set up on the protective piles and pile foundation casing according to the control pile elevation to check the depth after hole formation.

[0025] All cast-in-place piles are laid out under a control network. Only after the pile foundation layout and measurement are completed and self-inspected to ensure accuracy can the inspection report be filled out. The supervising engineer must then conduct an on-site acceptance inspection. Only after the supervising engineer has reviewed and signed off on the inspection can the next procedure proceed. After the concrete is poured, any portion of the cast-in-place pile exceeding the design height is removed. Leveling points are established based on the control pile points, and the pile top elevation is continuously monitored to ensure it remains within the allowable error range, thus meeting design and construction requirements.

[0026] Step S3, casing installation: Before drilling, a casing must be accurately installed at the determined pile location to fix the drilling position; isolate surface water; increase the water head in the well to increase the hydrostatic pressure; stabilize the soil at the wellhead and protect the borehole wall from collapse to facilitate drilling. The casing is made of steel, welded from 3mm steel plates, 4mm×30mm flat steel hoops, and 40mm×4mm angle steel ribs. The casing is 2m high, and its inner diameter is 30-40cm larger than the designed pile diameter. The casing installation method is as follows: When installing the steel casing, first dig a circular pit at the pile location that is 20cm to 40cm larger than the outer diameter of the casing. Fill the bottom of the pit with about 50cm of clay and compact it in layers. Then, mark the center position of the borehole at the bottom of the pit using the positioning control stakes. Next, hoist the casing into the pit, find the center position of the casing, and fix it at the top of the casing with a crosshair. Move the casing so that the center of the casing coincides with the center of the borehole. At the same time, use a spirit level or plumb bob to check that the casing is vertical. After that, backfill the casing symmetrically and evenly with clay of the optimal moisture content, and compact it in layers to achieve the optimal density. During compaction, prevent the casing from tilting.

[0027] During layered compaction, the center position and verticality of the casing should be checked after each layer is compacted. After leveling, a plumb bob should be used to check again, and any deviations should be corrected immediately. The top of the casing should be about 0.3m above the ground, and reinforcing ribs and lifting lugs should be welded to the top, along with a water outlet. During drilling, the casing should be frequently checked for displacement or subsidence, and any issues should be addressed promptly.

[0028] Mud preparation: The drilling mud preparation and storage tanks, drilling mud recovery and sedimentation tanks, and cuttings storage tanks should be rationally arranged, and the capacity of the mud tanks should meet the needs of mud circulation. Based on the properties of bentonite and the requirements for soil wall protection, the mud mix ratio and required quantity should be determined, and mud performance tests should be conducted. The density of the drilling mud for entry into the borehole can be 1.05–1.15 g / cm³. 3 When encountering silty sand layers or geological conditions, the concentration can be adjusted to 1.3 g / cm. Specific indicators are shown in Table 1, the mud performance index table.

[0029] Table 1 Mud Performance Indicators

[0030] Step S4, Drilling after the drilling rig is in place: Before positioning the drilling rig, check its performance and condition to ensure it is working properly. Accurately determine the rig's location using the surveyed pile positions and ensure its stability. After manually coarsely leveling to ensure the drill rod is basically vertical, the automatic control system can be used to maintain the drill rod's vertical position.

[0031] According to the design drawings, a test drill shall be conducted for the first pile. A test pile report shall be completed based on the bearing stratum determined by the test pile and the accuracy of the geological data, serving as the basis for formal construction. Large-scale construction of rotary-dug pile foundations can only commence after the first pile has passed the test pile acceptance inspection.

[0032] Drilling: 1. Rotary drilling rig Before drilling, the drill rod needs to be adjusted vertically. During drilling, the drill bucket is first brought to the ground, and the initial position of the drill bit is recorded. The actual working position of the borehole, the position of each advance, and the hole depth are monitored to guide the drilling operation. When opening the hole, the drill bucket's own weight and pressure serve as the drilling power. Once the drill bucket is filled with drill cuttings, it is lifted to the surface and loaded onto a muck truck using a loader for disposal off-site to prevent pollution.

[0033] During drilling, the drilling speed should be controlled according to geological conditions: when drilling from hard to soft strata, the drilling speed can be appropriately increased; when soft strata become hard strata, the speed should be reduced; in strata prone to diameter reduction, the number of hole sweeps should be increased appropriately to prevent diameter reduction; high-speed drilling should be used for hard plastic layers to improve drilling efficiency; for sand layers, slow-speed drilling should be used, and the mud density and viscosity should be appropriately increased; if a pebble layer is encountered during actual construction, the following measures should be taken: for pebble layers with smaller particle sizes, a bucket drill bit should be used for slow drilling; for pebble layers with larger particle sizes, a conical auger drill bit should be used, followed by switching to a bucket drill bit for cleaning, and this process should be repeated until the pebble layer is penetrated. Drill cuttings should be promptly transported off the site and disposed of at a suitable location to meet environmental protection requirements.

[0034] 2. Impact drill Before the drilling rig is in place, all preparatory work before drilling should be checked, including the inspection and maintenance of the main tools and equipment; the base and top of the drilling rig should be stable after installation, and there should be no displacement or sinking during drilling, otherwise it should be dealt with in time.

[0035] Drilling operations should be carried out continuously in shifts. Detailed drilling records should be filled out for each shift, and the drilling progress and precautions for the next shift should be explained during shift handover. Drilling mud should be frequently tested and inspected; any deviations should be corrected immediately. Changes in the geological formation should be closely monitored. At points of geological change, cuttings samples should be collected, identified, and recorded in the log, then compared with the geological profile.

[0036] The hole position must be accurate when drilling. Drilling should be done slowly, and the speed should be increased only after the drill bit has fully entered the formation.

[0037] The deviation between the wire rope of the punch and the center of the steel casing should not exceed 2cm. The cone head should be raised and lowered smoothly, and should not collide with the casing or the hole wall. High strokes should not be used too often during drilling to avoid disturbing the hole wall and causing hole collapse, hole enlargement or drill jamming accidents.

[0038] When drilling for cuttings removal, removing soil by retrieving the drill bit, or stopping drilling for any reason, the specified water level and required relative density and viscosity of the drilling mud must be maintained in the borehole. When dealing with borehole accidents or stopping drilling for any reason, the drill bit must be removed from the borehole.

[0039] After each slag removal or when restarting drilling after a stoppage for any reason, the stroke should be gradually increased from a low stroke to the normal stroke to avoid jamming.

[0040] If the geological conditions are found to be inconsistent with the original drilling data during the construction process, the design, supervision and other units should be notified immediately for timely handling.

[0041] When encountering boulders during drilling, you can throw in boulders or pebbles of similar hardness and use high-stroke impact or alternating high and low-stroke impact to break up the large boulders and squeeze them into the borehole wall.

[0042] During the drilling process, the pile diameter, planar position, and vertical axis inclination should be checked frequently, and any deviations should be corrected immediately.

[0043] During the drilling process, the drilling quality is checked every 4 to 6 meters. When the depth approaches the design depth, the drilling depth is accurately controlled, and a record is made of the depth of entry into the bearing layer.

[0044] During the construction process, drilling records should be kept carefully, accurately, and promptly, and reports should be filled out.

[0045] Step S5, Hole inspection and cleaning: After the hole reaches the design elevation, the hole depth, hole diameter, hole wall verticality, and sediment thickness are checked. Before the test, test tools and measuring ropes are prepared.

[0046] Inspection standards: Hole depth and diameter shall not be less than the design specifications; drilling inclination error shall not exceed 1%; sediment thickness shall meet the design specifications.

[0047] Step S6, Fabrication and Placement of the Reinforcing Steel Frame: 1. Reinforcing cage fabrication All reinforcing bars used should have a manufacturing date, product certificate, and quality certificate, and should be used only after passing inspection. Before fabrication, the main reinforcing bars should be straightened, and oil and debris should be removed from their surfaces.

[0048] When fabricating the reinforcing cage, cages shorter than 18m are fabricated in one section. Cages longer than 18m but less than 40m are fabricated in two sections. Sleeve connections are used at the joints to ensure that 50% of the joints are staggered within a single plane. Reinforcing cage assembly is carried out uniformly on a hardened platform, with spacing strictly controlled according to drawings and specifications to ensure the cage is straight.

[0049] The ultrasonic testing tubes should be pre-embedded and spot-welded to the pile reinforcement according to the design requirements of the drawings, ensuring that the position of the testing tubes is accurate and the length is not less than the pile length L + 100cm. The testing joints and bottoms should be sealed well, and measures should be taken at the top to prevent mortar and debris from clogging the pipes.

[0050] The allowable deviations for the fabrication and hoisting of the reinforcing steel cage are as follows: main bar spacing ±0.5d; stirrup spacing ±20mm; reinforcing bar spacing ±0.5d; cage diameter ±20mm; cage verticality ±1%; and the length of the reinforcing steel cage below the foundation bottom ±100mm.

[0051] Store the fabricated reinforcing cages in designated locations. During storage, place wooden planks under the cages to ensure they are 50cm off the ground. Arrange each cage segment in sequence for easy loading and transport to the pile locations. A tag should be attached to each segment indicating the pier number, pile number, and segment number. When connecting two reinforcing bars within the same cage, use mechanical connection. During connection, place the reinforcing bars on a separate processing platform to ensure the axes of the two welded bars are aligned. Before formal connection, inspect the completed test pieces. Only after passing inspection can large-scale connection construction proceed.

[0052] 2. Lower the steel cage To prevent deformation during rebar cage installation, a two-point lifting method is used. The 25T crane's large hook is used to horizontally lift the cage from 3 meters away from both ends, and then the smaller hook lifts the lifting end of the cage. During hoisting, square timber or steel sections must be used as support at the top and bottom to prevent individual rebars from being stressed and deformed. Afterward, the 25T crane's large hook is released, and the rebar cage is checked for straightness; any bends are straightened.

[0053] After the cage enters the borehole, a designated person should observe its verticality from a distance and direct its slow, proper lowering. During the lowering process, a designated person should support the cage and adjust its direction appropriately, strictly preventing it from colliding with the borehole wall. When the cage is lowered to the last reinforcing stirrup, two steel sections should be passed through the bottom of the reinforcing stirrup to ensure the cage is aligned vertically and then connected.

[0054] During the connection process, the quality and length of the mechanical connection must be strictly controlled. After the connection is completed, slightly lift the steel reinforcement cage to remove the temporary supports, and then slowly lower the cage. Repeat this process until the design elevation is reached.

[0055] In addition, to prevent the steel cage from falling during construction, the stirrups used to fix the steel cage must be welded firmly, and the wire ropes and lifting rings of the crane must be carefully inspected before construction.

[0056] Method for positioning the top of the reinforcing bars: Calculate the design elevation of the top of the reinforcing cage based on the on-site measurement of the top elevation of the casing. After the last section of the reinforcing cage is positioned according to the design elevation, welding is performed on the positioning reinforcing bars. The specific shape of the positioning bars is a closed hook, with the lower part welded to the main reinforcing bars. The positioning reinforcing bars are cut off after the concrete is poured.

[0057] The top of the frame is positioned by calculating the length of the positioning ribs based on the measured borehole elevation, and the positioning ribs are welded only after repeated verification. Then, two parallel channel steels are inserted under the top lifting ring at the top of the positioning rib frame; two guide steel pipes are placed symmetrically around the reinforcing cage, with their bottoms clamped to the reinforcing cage's reinforcing hoops and their tops welded to the casing. The upward movement of the reinforcing cage is controlled by the channel steel pressed under the drilling rig.

[0058] Step S7: Underwater concrete is poured using the tremie pipe method. Underwater concrete pouring employs the tremie pipe method. The tremie pipe joints are bayonet type, 300mm in diameter, 10mm thick, and each section is 2m long. Before use, the tremie pipe must undergo watertightness, pressure resistance, and joint tensile strength tests. Before pouring concrete, the pouring equipment, such as storage hoppers, chutes, and funnels, must be prepared. When lowering the tremie pipe into the borehole, its position must be centered and its axis straight, and it must be lowered steadily to prevent it from getting caught on the reinforcing steel frame or colliding with the borehole wall.

[0059] The underwater concrete is designed to a strength grade of C30, with a water-cement ratio of 0.5–0.6 and a slump of 18–22 cm. P.O42.5 cement is used, with medium sand as fine aggregate and well-graded artificial crushed stone as coarse aggregate. The maximum particle size of the crushed stone should not exceed 25 mm. The addition of appropriate amounts of water-reducing retarder and fly ash should be determined through testing. The initial setting time should be no less than 6 hours. An HZ50 type mixing plant should be used for mixing, with a capacity of 7m³. 3 Concrete mixer trucks transport concrete to the site. When the concrete is close to the top of the pile, it is poured out using a bucket to raise the height of the funnel.

[0060] After the second cleaning of the borehole to ensure the sediment layer thickness at the bottom meets specifications, concrete pouring can only proceed after all pre-pouring inspection records have been completed and confirmed by the supervising engineer. When pouring the first batch of concrete, the distance from the bottom of the tremie pipe to the bottom of the borehole should be controlled at 40cm, and the tremie pipe should be embedded in the concrete to a depth of at least 1m. Once concrete pouring begins, it should be continuous, and the interval between tremie pipe removals should be minimized. During pouring, the position of the concrete surface inside the borehole should be frequently probed with a sounding hammer, and the embedment depth of the tremie pipe should be adjusted accordingly. The embedment depth of the tremie pipe should ideally be controlled between 2m and 6m. When the concrete surface approaches the bottom of the reinforcing steel cage, the following measures should be taken to prevent the reinforcing steel cage from floating: ① Keep the guide pipe buried at a slightly greater depth and slow down the pouring speed to reduce the impact force of the concrete.

[0061] ②When the concrete in the hole has penetrated 1m to 2m into the reinforcing cage, the guide pipe should be raised appropriately to reduce the embedment depth of the guide pipe and increase the embedment depth of the lower part of the reinforcing cage.

[0062] To ensure the quality of the pile top, an additional 1 meter or more of concrete was poured on top. A designated person was responsible for filling out the underwater concrete pouring record. After all concrete pouring was completed, the steel casing was removed, and the site was cleaned.

[0063] Technical requirements for underwater concrete construction: (1) The amount of concrete poured in the first batch should be sufficient to meet the initial burial depth of the conduit (≥1.0m) and the need to fill the bottom of the conduit.

[0064] (2) During the first filling, the distance from the bottom of the guide pipe to the bottom of the hole is generally 20-40cm. A storage trough and a funnel are set at the top of the guide pipe, and the bottom of the funnel must not be lower than the opening of the casing.

[0065] (3) When the concrete mixture is transported to the pouring site, its uniformity and slump should be checked. If it does not meet the requirements, it should be mixed a second time. If it still does not meet the requirements after the second mixing, it shall not be used.

[0066] (4) After the first batch of concrete mixture falls, the concrete should be poured continuously.

[0067] (5) During the grouting process, especially in tidal areas and areas with pressurized groundwater, attention should be paid to maintaining the water pressure inside the borehole.

[0068] (6) During the infusion process, the embedment depth of the catheter should be controlled between 2 and 6 m.

[0069] (7) During the grouting process, the position of the concrete surface inside the well should be measured frequently, and the burial depth of the guide pipe should be adjusted in a timely manner.

[0070] (8) To prevent the steel reinforcement cage from floating, the pouring speed should be reduced when the top surface of the poured concrete is about 1m away from the bottom of the steel reinforcement cage. When the concrete mixture rises to more than 4m above the bottom of the cage, the tremie pipe should be raised so that its bottom is more than 2m above the bottom of the cage, and the normal pouring speed can be resumed.

[0071] (9) The top elevation of the grouting pile should be more than 1m higher than the design elevation to ensure the concrete strength. The excess part must be removed before splicing the pile, and the remaining pile head should not have a loose layer.

[0072] (10) When the pouring is almost finished, the amount of concrete poured should be checked to determine whether the measured pouring height of the concrete is correct.

[0073] (11) When using a full casing for underwater concrete pouring, once the concrete surface enters the casing, the bottom of the casing should always be below the concrete surface. As the guide pipe is raised, the casing should be gradually pulled up. The pouring height of the concrete inside the casing should not only take into account the height that the guide pipe and casing will be raised, but also the decrease in the concrete surface caused by pulling up the casing, so as to ensure that the embedment depth of the guide pipe and the bottom surface of the casing are lower than the concrete surface. Pour and drain water simultaneously to keep the water level inside the casing stable and prevent it from becoming too high, which could cause back-perforation.

[0074] (12) During the grouting process, the water or mud overflowing from the hole should be diverted to a suitable location for treatment and should not be discharged at will, so as to avoid polluting the environment and rivers.

[0075] Step S8, Removal of casing and pile inspection: After the concrete curing is completed, the casing is removed, the pile is treated, and the quality is inspected.

[0076] Pile preparation: Mechanical and manual methods are used to remove the laitance layer at the top of the pile and remove any excess concrete to ensure the pile top elevation meets design requirements; concrete residue and rust are cleaned from the surface of the pre-reserved reinforcing bars at the pile head, and the spacing and verticality of the reinforcing bars are adjusted; loose soil, debris, and uncured concrete around the pile are removed, and if there are holes or gaps around the pile, they are filled and compacted with fine aggregate concrete of the same grade; the annular pit left after removing the casing is backfilled and compacted in layers with graded sand and gravel. Pile testing: A general survey of the pile foundation is conducted using the low-strain reflected wave method to detect defects such as broken piles, mud inclusions, and diameter reduction in the pile body. For pile foundations with complex geology or questionable low-strain test results, a supplementary ultrasonic transmission method is used for re-inspection. The sound wave propagation velocity is measured point by point through pre-embedded sonic logging tubes to determine the location and extent of defects. 1% to 3% of the total number of piles are selected according to design requirements, and the vertical compressive bearing capacity is tested using the high-strain method. The loading rate is strictly controlled during the test, and the load-settlement curve is recorded. The test data is compiled, and a test report is issued.

[0077] Special geological construction: 1. Caves (1) This embodiment contains a cave. Encountering karst caves is not uncommon during bridge pile foundation construction. As a hidden underground structure, they pose significant challenges to construction. Improper handling can lead to accidents such as drill bit loss, hammer jamming, hammer burial, grout leakage, and borehole collapse, even threatening the operational safety of the bridge. Therefore, it is crucial to fully understand the development patterns, basic morphology, size, thickness and integrity of the roof strata, and shape of the filling material within the karst caves encountered at the bridge pile locations, and to take prudent measures to ensure the smooth progress of construction.

[0078] Based on geological exploration and the surrounding geological conditions, the caves in this embodiment mainly take the following three forms: The first type: The soil cavities in the overburden layer are generally filled with material, but not densely, and the cavities are generally not large. The second type: small caves in bedrock, with no filling material inside, or with filling material but not dense, i.e. small cavities; The third type: large caves in bedrock, with no filling material inside, or with filling material but not dense, i.e., large cavities.

[0079] ① For the first two situations, the construction should adopt the conventional method of karst cave treatment, that is, after the top of the cave is broken through, clay, gravel, and a whole bag of cement are poured in, then compacted by flushing and pressing, and flushed again after solidification.

[0080] ② For relatively small, enclosed karst caves, grouting measures should be taken to provide the conditions for drilling through the cave. If there is no filling material inside the cave, crushed stone or dry sand should be filled first, and then grouting should be performed; if the filling material is in a soft plastic state, grouting should be performed directly for consolidation.

[0081] ③ If there is no filling material in the karst cave and sand needs to be filled in, select a suitable hole, insert and fix a steel casing, connect the sand injection pipe to the steel casing, and inject sand before grouting. Use an air compressor to pressurize the dry sand in. To prevent high pressure inside the cave from hindering sand injection, use other holes as pressure relief holes. Stop when the calculated filling volume is reached and the pressure stabilizes.

[0082] ④ For some solution channels, solution grooves, small fissures, etc., when drilling, you can put in rubble, clay, or even a whole bag of cement to block them and protect the wall, so as to prevent the mud from being lost and allow the borehole to pass through the karst area smoothly.

[0083] ⑤ For the third scenario, construction requires first filling and reinforcing the karst cave, filling the soil and cave with cement and fly ash slurry, and then drilling after 7 days. For a small number of cases with poor overburden geology, thick gravel layers, and where leakage of grout could cause the borehole to collapse, steel casings are used for wall protection.

[0084] 2. Collapsed hole The steel casing is only 1-2 meters high and sits on a layer of gravel and pebbles. When it impacts the sinkhole, the sudden leakage of grout causes a sharp drop in the water head, destabilizing the gravel and pebbles layer and forming a funnel-shaped collapse hole.

[0085] (1) Methods to prevent borehole collapse ① During construction, the steel casing can be placed on the sub-clay layer, and then the hole can be drilled by impact, which can also avoid hole collapse.

[0086] ②Replenish water promptly if grout leakage is detected.

[0087] (2) Methods for handling collapsed holes ① When the hole depth is not large, the entire hole can be backfilled with clay, and after a period of time, the impermeable layer of the steel casing can be buried deep before drilling can be restarted.

[0088] ② When the drilling depth is large, the steel casing can be placed on the sub-clay layer at the lower edge of the flared end of the collapsed hole, and clay can be backfilled around the casing, compacted, and then the hole can be re-drilled.

[0089] 3. Inclined hole A slanted hole is caused by a tilted rock surface or the presence of protruding rocks, causing the drill bit to slide down the softer, lower part. The solution is to backfill with rubble or pour underwater concrete. After it has gained strength, use a short stroke and tighten the rope repeatedly to impact the hole until it is aligned correctly. An excessively long stroke will result in an out-of-round hole, causing a slanted hole; a stroke of 1–4 meters is generally recommended.

[0090] 4. Grouting at the bottom of the pile (1) After the borehole of the bored pile is completed, the sonic logging pipe is used as the grouting pipe, and the grouting pipe is set up to meet the requirements of the grouting process.

[0091] (2) Concrete pouring: After the grouting pipe comes into contact with the ground, the pipe opening is sealed to prevent foreign objects from entering and blocking the grouting pipe. Concrete is poured to form a pile, and grouting is carried out after 7 days of curing.

[0092] (3) Water injection: Before grouting, inject clean water to open the grout flow pipe and make the grouting smooth. At this time, the injection pressure is 3 MPa. After the pipeline is opened (i.e. when the pressure drops), stop the water injection in time and prepare for the grouting work.

[0093] (4) Grout preparation: Cement-based grout is used, with cement grade P.S32.5 and a water-cement ratio of 0.6:1. High-efficiency water-reducing agent is added.

[0094] (5) Grouting: The amount of grout injected at the bottom of each pile is about 2.0 cubic meters, and the grouting pressure is stable at about 3 MPa. When grouting, first seal one grouting pipe and start injecting from the other. When the injection volume reaches the requirement, seal the hole that is being grouted and inject from the other hole until the grouting is completed. When the amount of grouting cement is not less than 80% of the design requirement and the pump pressure reaches 3 MPa, and grout leakage occurs, the grouting work can be stopped.

[0095] (6) While performing high-pressure grouting, keep grouting records and observe the amount of pile top lifting.

[0096] (7) Each pile must be grouted at once, and the grouting interval between the grouting pipes of the same pile shall not exceed 12 hours.

[0097] (8) Grouting shall not be carried out when there are other pile foundation operations within 5m around the pile foundation that requires grouting.

[0098] (9) The curing period after grouting is more than 15 days.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A construction process for road and bridge pile foundations, characterized in that: The method comprises the following steps: Step S1, site leveling: before the rig is positioned, the soft soil layer of the original site is removed using an excavator, the whole site is leveled and rammed to serve as a construction operation platform for the rig, and the site is made hard; Step S2, pile position lofting: pile foundation coordinates are calculated according to data provided by construction drawings, and after checking, pile position lofting is performed using a total station; Step S3, casing embedding: a circular pit is dug at the pile position, clay is filled at the pit bottom and the drilling center is marked, and the casing is hoisted into the pit and embedded; Step S4, drilling after the rig is positioned: the position of the rig is accurately determined through the measured pile position, the drill rod is adjusted to keep it vertical, the first pile is trial drilled according to the construction drawings, and drilling operation is performed after the trial drilling; Step S5, hole inspection and hole cleaning: after the hole reaches the design elevation, the hole depth, hole diameter, hole wall perpendicularity and sediment thickness are inspected, and the hole is cleaned after the inspection is completed; Step S6, steel reinforcement cage manufacturing and placing: the steel reinforcement cage is manufactured in sections, the steel reinforcement cage joints adopt sleeve connection, and the manufactured steel reinforcement cage is hoisted vertically into the drilling hole using two-point lifting; Step S7, underwater concrete pouring using the guide pipe method: the concrete proportioning is determined to prepare concrete slurry, and the guide pipe is hoisted into the drilling hole to continuously pour concrete; Step S8, casing pulling out and pile quality detection: after the concrete curing is completed, the casing is pulled out, and the quality of the pile is detected after the pile is processed.

2. The road-bridge pile foundation construction process according to claim 1, characterized in that: In step S1, if the site soft soil is thick and the hardness is not enough, 60cm-thick weathered material is laid on the site surface and leveled and rolled.

3. The road-bridge pile foundation construction process according to claim 1, characterized in that: In step S3, the casing adopts a steel casing, which is welded from a steel plate, a flat steel hoop and an angle steel rib; when the casing is embedded, a circular pit with a diameter 20cm-40cm larger than the outer diameter of the casing is first dug at the pile position, 50cm-thick clay is filled at the pit bottom and is layered and rammed; the center position of the drilling hole is marked on the pit bottom through the positioning of the control pile; then the casing is hoisted into the pit, the center position of the casing is found, the cross line is determined at the top of the casing, the casing is moved so that the center of the casing coincides with the center position of the drilling hole, and the casing is checked using a level or a plumb bob so that the casing is vertical; thereafter, clay with the optimal water content is backfilled symmetrically and uniformly around the casing, which is layered and rammed to achieve the optimal compactness.

4. The road-bridge pile foundation construction process according to claim 3, characterized in that: When the layered ramming is performed, the center position and the perpendicularity of the casing are checked after each layer is rammed, the plumb bob is hung again after the filling is leveled, and the deviation is immediately corrected; the top of the casing is 0.3m higher than the ground, reinforcing ribs and lifting lugs are welded at the top of the casing, and a water outlet is opened; During the drilling process, whether the casing deviates and sinks is checked and timely treated.

5. The road-bridge pile foundation construction process according to claim 1, characterized in that: In step S4, rotary drilling or impact drilling is used for drilling operation, and the drilling operation is continuously performed in shifts; During the rotary drilling, the actual working position, the position of each footage and the hole depth position are monitored, the drill bucket is first landed on the ground, the self-weight of the drill bucket and the pressure are used as the drilling power, the drill bucket is lifted out of the ground after being squeezed and filled with drilling slag, the drilling slag is loaded into a slag transport vehicle using a loader and transported to the outside for disposal, and the footage speed is controlled according to the geological conditions during the drilling process; During the impact drilling, the pile diameter size, the plan position and the vertical axis inclination are checked, the hole position is accurate, the drilling is slowly performed when the hole is opened, the drilling is accelerated after the drill bit completely enters the stratum, and the hole quality is checked every 4-6m.

6. The road-bridge pile foundation construction process according to claim 1, characterized in that: In step S5, the hole inspection criteria are: hole depth, hole diameter ≥ design requirements, drilling inclination error ≤ 1%, and sediment thickness meets design requirements.

7. The road-bridge pile foundation construction process according to claim 1, characterized in that: In step S6, the allowable deviation for the production and hoisting of the steel reinforcement cage is: main reinforcement spacing ± 0.5d; stirrup spacing ± 20mm; reinforcement spacing ± 0.5d; cage diameter ± 20mm; cage verticality ± 1%; the length of the steel reinforcement cage below the pile cap bottom is ± 100mm.

8. The road-bridge pile foundation construction process according to claim 7, characterized in that: Two-point lifting is adopted, the crane hook is horizontally lifted at a position away from the two ends of the steel reinforcement cage, then the small hook lifts the lifting end of the steel reinforcement cage, and the steel reinforcement cage is lifted; during hoisting, the top and bottom of the steel reinforcement cage are assisted by wooden boards or steel when being lifted.

9. The road-bridge pile foundation construction process according to claim 1, characterized in that: In step S7, the guide pipe is subjected to water tightness, pressure bearing and joint tensile tests before use. When the guide pipe is hoisted into the hole, its position is centered, the axis is straight, it is steadily sunk, and it does not get stuck with the steel reinforcement cage or collide with the hole wall; after the concrete pouring starts, the interval time for removing the guide pipe is shortened, the position of the concrete surface in the hole is detected by a depth probe during the pouring process, the depth of the guide pipe is adjusted in time, and the depth of the guide pipe is controlled at 2m-6m.

10. The road-bridge pile foundation construction process according to claim 1, characterized in that: In step S8, pile processing: the pile top floating layer is removed by mechanical and manual methods, the over-poured part of the concrete is chiseled off, and the pile top elevation meets the design requirements; the concrete residue and rust on the surface of the reserved steel reinforcement at the pile head are cleaned, and the spacing and verticality of the steel reinforcement are adjusted; the floating soil, sundries and un-solidified concrete around the pile body are removed, if there are holes or gaps around the pile, the same grade of fine stone concrete is used for filling and compaction; the annular pit left after the removal of the pile casing is backfilled and tamped in layers with graded sand and gravel; Pile detection: the pile foundation is surveyed by the low-strain reflected wave method to detect whether there are defects such as broken pile, mud inclusion and reduced diameter in the pile body; for pile foundations with complex geology or doubtful low-strain detection results, ultrasonic transmission method is used for re-inspection, the sound wave propagation speed is measured point by point through the pre-buried acoustic measuring pipe to determine the defect position and degree; according to the design requirements, 1%-3% of the total number of piles are extracted, the vertical compressive bearing capacity is detected by the high-strain method, the loading rate is strictly controlled during detection, and the load-settlement curve is recorded; the detection data is sorted out, and a detection report is issued.

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