CN113089655A - Construction method in three-pipe rotary spraying pile pit in flowing water environment - Google Patents

Abstract

The invention discloses a construction method in a three-pipe rotary spraying pile pit in a flowing water environment, which comprises the steps of construction preparation, pile position lofting, drainage ditch excavation, drainage system construction, drilling machine in place, slurry configuration, drilling and pipe insertion, rotary spraying lifting, rotary spraying pile construction in the pit, compaction grouting, well patching and the like. The construction equipment is simple, has strong maneuverability and occupies less land; the construction requirement of low clear height can be met, the machine is constructed in the limited space from the pit bottom to the upper tunnel support, and the movement of the excavated foundation soil surface is not hindered. The construction machine has the advantages of small vibration, low noise, high speed and convenient operation. Can be simultaneously and alternately constructed with the earth excavation and the peripheral foundation structure. In a flowing water environment, compared with the traditional double-pipe method, the pile diameter and concretion calculus rate of the pile formed by the method are good in quality and high in construction efficiency.

Description

Construction method in three-pipe rotary spraying pile pit in flowing water environment

Technical Field

The invention relates to a construction method in a rotary jet grouting pile pit.

Background

In the construction of deep foundation pit, in order to guarantee the stability of the side slope of the low pit and increase the weight of the soil mass at the bottom of the pit to balance the floating force generated by confined water when the ultra-deep area of the foundation pit is excavated, high-pressure rotary spraying piles are generally adopted to reinforce the ultra-deep area and the surrounding soil mass, so that the solidified soil mass and the engineering pile group piles form a whole, the conventional rotary spraying pile process firstly reinforces the bottom of the pit before the earth excavation or after a part of the upper soil excavation, and the underground water level is relatively balanced and stable. However, in the construction process, due to sudden adjustment of a design scheme or due to the requirement of construction period and investment on optimization of a construction scheme for synchronous cross construction of reinforcement and excavation, the reinforcement of an ultra-deep area does not have construction conditions before a pit, and the construction of reinforcing and stopping water by using a jet grouting pile needs to be carried out at the bottom of the pit. Because the high-pressure jet grouting pile enters the pit for operation, the peripheral supporting height is limited, the mechanical construction is greatly influenced by the dense engineering piles in the pit, meanwhile, the high-pressure jet grouting pile in the traditional process is greatly influenced by the complexity of geological conditions in an ultra-deep area of a large-scale deep foundation pit, particularly the thickness of a sand layer, and the influence of underground water precipitation seepage (flowing water), the underground water seepage can dilute and even take away jet grouting liquid before the slurry is initially set, the effective cementation cannot be realized, and the pile forming quality of the jet grouting pile and the water stopping effect of the enclosure structure are difficult to ensure.

Disclosure of Invention

The invention aims to provide a construction method in a three-pipe rotary spraying pile pit in a flowing water environment, which is convenient to construct and good in construction effect.

The technical solution of the invention is as follows:

a construction method in a three-pipe rotary spraying pile pit in a flowing water environment is characterized by comprising the following steps: comprises the following steps:

preparation for construction

(1) Leveling the field: clearing all barriers in a construction area, backfilling and tamping a low-lying part of a field by using viscous soil materials, and excavating a drainage ditch with the width of 1m and the depth of 1.5m along the periphery of the outer side of the construction area to be used as a slurry drainage ditch; excavating a waste slurry pool and a slurry discharge ditch from a construction hole to the slurry pool outside a construction range according to the actual condition of a construction site;

(2) cement: P.O42.5 ordinary portland cement is adopted; each batch of cement is qualified by the field entry retest and the factory quality certification is obtained;

(3) water: the pH value is between 5 and 10;

(4) indoor mix proportion test: designing and adjusting several mixing ratios according to different water contents according to the spraying amount required by design or the condition of a field soil sample, air-drying or drying and crushing the soil sample collected on the field indoors, sieving a powdery soil sample with a sieve of 2-5 mm, stirring according to the designed spraying amount and the water-cement ratio, maintaining and performing mechanical tests to determine the construction spraying amount;

(5) pile testing: preparing cement slurry according to construction spraying amount and water cement ratio determined by indoor tests, driving a plurality of test piles at a test working point, adjusting the spraying amount of a reinforcing material according to a pile test result, and determining construction process parameters such as lifting speed of a rotary spraying pile drilling machine, rotation speed of a stirring shaft, spraying pressure, a slurry stopping surface and the like;

(6) installation and debugging of equipment: reasonably arranging and installing a complete set of equipment required by the construction of the three-pipe high-pressure jet grouting pile according to the construction site condition, respectively checking whether various equipment of a gas system, a slurry system and a water system normally operate or not, checking whether pipelines are smooth or not, and testing whether a monitoring instrument is complete and intact or not; after the process is ensured to be correct, the next process can be carried out;

pile position lofting

Firstly, a total station is adopted to discharge a control pile according to the pile number of a high-pressure jet grouting pile, then a steel tape and a hemp thread are used to transfer the pile position of the discharged jet grouting pile according to the pile distance, a small bamboo stick is used for marking, a lime mark is scattered, the pile driver is ensured to be accurately positioned, and the displacement deviation of the center of a pile hole is less than 50 mm;

(III) digging drainage ditch, building drainage system

In order to reduce the influence of water level disturbance on the pile forming quality of the high-pressure jet grouting pile in the pit, pumping water to a precipitation well in a construction area is suspended when the peripheral jet grouting pile is constructed; reducing water pumping within the range of 15-20 m of the precipitation influence radius of an outer pipe well at the periphery of a construction area, and controlling the water pumping amount, wherein the water level is controlled to be preferably 500mm below a construction surface; the water level of the dewatering well outside the range of 20 meters on the periphery is deepened; meanwhile, a drainage ditch with the depth of 1 meter and the width of 1.5 meters is dug along the periphery of the construction area, a water pump is adopted for open drainage, and a digging machine is arranged for cleaning the drainage ditch in time;

introducing waste slurry into a sedimentation tank through a drainage ditch according to the amount of slurry return generated in the construction process of the jet grouting pile;

(IV) drill setting

Moving the rotary jet grouting pile driver to a specified pile position, aligning a vertical shaft turntable with a hole position, leveling a drilling machine, calibrating the pile driver by using a horizontal ruler and a positioning measuring hammer, wherein a guide frame and a drill rod are vertical to the ground, and the verticality deviation of the drill rod is not more than 1-1.5%; in order to ensure the pile position to be accurate, a positioning card is required to be used, and the pile position centering error is not more than 50 mm;

(V) slurry preparation

When the pile machine is shifted, mixing cement paste according to the mix proportion determined by the design; firstly, adding water into a barrel, pouring cement and an admixture into the barrel, starting a stirrer to stir for 10-20 minutes, then screwing off a valve at the bottom of the stirring barrel, putting the first screen with the aperture of 0.8mm, filtering, flowing into a slurry pool, pumping into a second screen with the aperture of 0.8mm through a slurry pump, filtering for the second time, flowing into the slurry barrel, and standing by when grouting;

in order to prevent the cement grout from being separated, a slow stirring device is arranged in the grout storage barrel and needs to be continuously stirred until the grout is sprayed;

during guniting, cement paste is conveyed into a nozzle of the rotary vibration drilling machine through a rubber pipe and is finally ejected. The cement slurry is stored for not more than 4h, otherwise, the cement slurry is treated as waste slurry;

(VI) drilling cannula

And starting the drilling machine, rotating and drilling at the same time, and stopping drilling after reaching the designed elevation. The pipe inserting and the drilling are combined into a whole, and the pipe inserting operation is completed simultaneously when the drilling is completed. In the pipe inserting process, jetting high-pressure water to cut a soil body for reaming: starting the drilling machine, and simultaneously starting a high-pressure clean water pump to deliver water with the water pressure of 25-30 Mpa, so that the drill rod is vibrated along the guide frame and is sunk in the jet cutting reaming;

observing that the working current is not greater than a rated value until the designed elevation of the pile bottom;

parameters such as drilling speed, the section number and the length of a drill rod and the like are recorded in the drilling process, and the drilling depth is ensured to meet the design requirement; in order to avoid the inclination of the drill hole, the perpendicularity of the drill rod needs to be checked at any time in the process of positioning and drilling the drill, and the inclination is found and corrected in time so as to ensure that the inclination of the drill hole is within a design allowable range; drilling at a slow speed, and preventing the hole from inclining by adopting a guide device; firstly, pilot drilling is carried out in each section of construction area, and if drilling cannot be carried out or is slow, holes can be led in advance; after guiding, inserting a PVC pipe with the diameter of 150mm into the orifice;

(VII) lifting by rotary jetting

Stopping drilling after the guniting pipe sinks to reach the designed depth, stopping rotating without stopping, closing the high-pressure clean water pump and the water conveying pipe, connecting the high-pressure grout pipe and the air pressure pipe, starting a high-pressure grouting pump and an air compressor, controlling the grout pressure to be 20-25 Mpa and the air pressure to be not less than 0.7Mpa, controlling the pressure, the flow and the air quantity by using an instrument, and checking whether each construction parameter meets the design requirement;

firstly, high-pressure slurry is sent, and compressed air can be sent for 30s later; the guniting pipe sits at the bottom in situ for guniting for 30s, the guniting pipe rotates while guniting, and the lifting device is started after the orifice is normally guniting;

after the cement paste and the pile end soil are fully stirred, the grouting pipe is lifted in a reverse uniform-speed rotation mode while the cement paste is sprayed, the spraying rotation speed is 15r/min, the lifting speed is 8-16 cm/min, and the air volume is 10m³The spraying amount is 120L/min, and the cement doping amount is 45-50% of the volume weight of the soil body;

when the lifting of the rotary jet grouting pipe is close to the pile top, starting from 1.0m below the pile top, slowly lifting and rotary jetting, carrying out rotary jetting for a plurality of seconds, then slowly lifting upwards for 0.5m until the pile top stops on a grout surface, closing a high-pressure slurry pump, stopping the delivery of cement grout, rotatably lifting the rotary jet grouting pipe out of the ground, and closing a drilling machine;

in the jet grouting construction, the upper spray rod needs to be disassembled, the lower spray rod continues to spray, and the spray can be stopped when the lower spray rod is required to be higher than the wellhead device by more than 500 mm; the pile body is re-sprayed and lapped for more than 500mm when the guniting is continued so as to ensure the vertical continuity of the anti-seepage body;

if the spraying is stopped in case of a fault in the spraying process, the spraying needs to be recovered as soon as possible, and the spray rod needs to descend by 200-500 mm when the spraying is recovered;

various technological parameters of the rotary spraying operation system are controlled according to preset requirements, and the record of rotary spraying time, pulp consumption, pulp bleeding condition, pressure change and the like is made at any time;

(eighth) flushing machine

After the injection construction is finished, the grouting pipe and other equipment are washed clean by clear water to prevent solidification and blockage; the cement slurry can not remain in the pipe and the machine, the slurry is generally changed into clear water to be sprayed on the ground, so that the slurry in a slurry pump, a grouting pipe and a hose can be completely removed, and the soil adhered to the head of the guniting pipe is cleaned;

(nine) drill rig Displacement

Moving the pile machine to carry out construction of the next pile; repeating the step (four) to the step (nine);

(ten) recharging slurry

After the high-pressure sprinkling irrigation is finished, due to the fact that the volume of the cement slurry in the hole shrinks in the solidification process, and meanwhile, the slurry in the hole leaks to a certain extent to the periphery of the hole wall, the surface of the slurry in the hole sinks for a period of time, the slurry is continuously back-poured into the sprayed hole, and the grouting effect is kept until the slurry in the hole does not sink any more; the recharging slurry is filled by adopting high-spraying slurry-discharging static pressure of adjacent holes;

(eleven) constructing the jet grouting piles in the pit from outside to inside to form a closed ring by adopting ring construction, firstly constructing high-pressure jet grouting piles on the outer side of the periphery, and constructing inner jet grouting piles after the jet grouting piles on the outer side are initially set; the jet grouting pile adopts pile position jumping operation at intervals, the distance is controlled to be more than 2m, and after 24 hours, adjacent pile positions are constructed;

(twelfth) compacting grouting

Engineering piles and upright piles in a construction area are constructed on the natural ground, the joint parts of the high-pressure jet grouting piles, the engineering piles and the upright piles cannot be tightly lapped, after the jet grouting piles are constructed, the positions of the engineering piles are excavated, and holes are led by a geological drilling machine and compacted and grouted for reinforcement while being tightly attached to the engineering piles and the upright piles; the grouting slurry adopts P.O42.5 ordinary portland cement, the water cement ratio is 0.5-0.6, the grouting pressure is 0.3-0.6 Mpa, and the cement dosage is 100-150 kg/m;

(thirteen) well repairing

During construction of the jet grouting pile, a part of the downcomer well is blocked due to penetration of cement slurry, the cement slurry is used for filling and blocking in time after construction is finished, and well repairing is carried out at a proper position according to actual conditions on site; different from the construction on the ground, the water head pressure difference is small, and the holes cannot be formed at the periphery in a dynamic seepage state, so that the bentonite is used for making slurry and protecting the walls to form the holes;

(fourteen) calculating the cement consumption according to the requirements of design drawings; after the material enters the field, sampling and retesting are carried out according to related requirements, and unqualified materials are strictly forbidden to be put into engineering use; meanwhile, the materials qualified in the retest are reported and tested to the supervision unit in time.

The construction interval time of two adjacent piles is not less than 24h, and the distance between two adjacent piles is not less than 2 m; the distance between the injection hole and the high-pressure grouting pump is not more than 50m, and the actual hole position, the actual hole depth, underground obstacles in each drilling hole, the situation that the underground obstacles do not accord with geotechnical engineering investigation reports and the like are recorded in detail;

when the slurry is prepared, the water-cement ratio is strictly controlled according to the design and cannot be changed randomly; during the rotary spraying process, the mud is prevented from precipitating, and the concentration is reduced; no wet or out-of-date cement must be used. When the slurry is conveyed to a slurry suction barrel after the slurry is stirred, a screen is needed for filtering, and the diameter of a filtering screen hole is preferably smaller than the diameter of 1/2 of the nozzle;

high-pressure water is firstly sent when the pipe is inserted, the high-pressure water is closed when the pipe is lifted, cement paste is firstly sent, and compressed air can be sent for 30s later;

after spraying for 30s while rotating the bottom of the pile, rotating, lifting and spraying while spraying;

when spraying, the grouting pipe is gradually lifted after the preset spraying pressure and the preset spraying amount are reached. The rotation and lifting of the drill rod must be continuous without interruption, and the overlap length of the drill rod is not less than 50cm when the long drill rod is disassembled or the rotary spraying is continued, so that the pile breakage is avoided; if the designed diameter of the pile body is influenced by insufficient slurry injection, rechecking is carried out;

in the rotary spraying process, the phenomenon that the slurry outflow amount is less than 20% of the grouting amount is normal, if the slurry outflow amount exceeds 20% or the slurry does not flow at all, reasons should be found out, and rotary spraying parameters are adjusted or the diameter of a nozzle is changed;

and drilling at a low speed and a low bit pressure at the interface of the soft soil layer and the hard soil layer. Finding out the deviation of the drilled hole, backfilling clay in time, and drilling at low speed and low bit pressure after flushing;

in the rotary spraying process, if the rotary spraying is interrupted due to the failure of a machine, the lifting and the rotary spraying are stopped to prevent the pile from being interrupted, and meanwhile, the inspection is immediately carried out to remove the failure; drilling again to the designed elevation of the pile bottom, and then performing rotary spraying again;

when the guniting port reaches the height of the pile top, continuously guniting and lifting by 0.5m to ensure the quality of the pile top;

after the grouting material is sprayed to the height of the pile, the grout pipe is quickly pulled out, and the pipeline is washed by clear water to prevent solidification and blockage;

quality inspection: after the construction of the jet grouting pile is finished for 28 days, the construction quality of the project is checked through core drilling and sampling;

when the jet grouting pile is constructed, attention should be paid to avoid constructed engineering piles and upright piles, and when the position of the jet grouting pile conflicts with the engineering pile, the jet grouting pile is constructed closely to the engineering pile;

closely monitoring the water level and the water pumping quantity of the peripheral dewatering well during construction, keeping the dynamic stability of the hydraulic force and ensuring the pile forming quality of the jet grouting pile;

the rotary spraying pile is constructed according to the sequence of firstly outer, then inner and closed ring, the inner rotary spraying pile can be constructed after the peripheral pile body reaches initial setting, so that the side soil resistance effect and the influence of the dynamic seepage of the peripheral underground water on the inner pile during the inner construction are reduced.

The construction equipment is simple, has strong maneuverability and occupies less land; the construction requirement of low clear height can be met, the machine is constructed in the limited space from the pit bottom to the upper tunnel support, and the movement of the excavated foundation soil surface is not hindered. The construction machine has the advantages of small vibration, low noise, high speed and convenient operation. Can be simultaneously and alternately constructed with the earth excavation and the peripheral foundation structure. In a flowing water environment, compared with the traditional double-pipe method, the pile diameter and concretion calculus rate of the pile formed by the method are good in quality and high in construction efficiency. In a flowing water environment, compared with the traditional triple-pipe method lifting rotary spraying, the construction water is reduced, and the slurry flow concentration is greatly improved, so that the adverse effect caused by underground water is weakened, and the pile body quality is improved; compared with a double-high-pressure new two-pipe method, the method saves cement, reduces waste slurry discharge and environmental pollution, and has low construction cost and excellent construction effect. The method can meet the construction requirements of sensitive construction areas, the construction process can effectively control the uplift of the ground of the substrate and the influence on the existing supports and engineering pile bodies on the periphery, the reinforcement diameter can be freely selected, and the reinforcement range can be freely selected within 5-360 degrees. And by adopting the measure of externally discharging and internally controlling precipitation, the influence of the underground water level disturbance on the pile forming quality can be effectively reduced.

The construction in the three-pipe rotary-spraying pile pit in the flowing water environment is suitable for fine-particle soil layers such as silt, cohesive soil, loess, sand soil and the like, and can be used for foundation reinforcement treatment of existing buildings and newly-built buildings, deep foundation pit water-stopping curtains, slope soil-retaining or water-retaining, foundation pit bottom or ultra-deep region reinforcement, prevention of piping and uplift, underground large-diameter pipeline enclosure and reinforcement, soil layer reinforcement or seepage-proofing reinforcement of subway engineering and other underground engineering post construction in the pit under flowing water seepage, and water stopping and reinforcement in special environments (narrow space, limited high altitude and complex surrounding environment). When the method is used for treating foundation engineering with erosive property and gushed water in large-particle-size stratums such as artificially backfilled rock blocks, cobbles, gravels and the like or underground water, the applicability of the method is determined by tests.

The construction in the three-pipe rotary spraying pile pit in the flowing water environment is based on the process technology of a double-pipe method and a triple-pipe method. Drilling and inserting a pipe into a whole by a double-pipe method, and conveying cement slurry to lower the pipe at low pressure (0.5-1.0 MPa) during drilling; during lifting, two media of high-pressure cement slurry (20-40 MPa) and air (0.7-0.8 MPa) are simultaneously sprayed to cut the surrounding soil body, and the two media are stirred and mixed with the soil body to form a reinforced body. Because of the adoption of the direct cutting of the grout, the influence range of the grouting consolidation body is not stable enough, and the discreteness of the pile diameter of the consolidation body and the pile strength is large, under the condition of flowing water with large flow rate of underground water, the grout is difficult to stay, so that the low calculus rate and the small pile diameter of the consolidation body are easily caused.

After drilling by a triple tube method, discharging tubes by low-pressure water jet (0.5-1.0 MPa) during tube insertion; three media of high-pressure water (30-50 MPa), air (0.5-0.8 MPa) and cement slurry (0.2-0.8 MPa) are simultaneously sprayed during lifting, the soil body is punched by high-pressure water flow jet flow and air flow coaxial jet flow, then the cement slurry is injected into the ground to be cut and crushed at lower pressure and mixed with the ground to be solidified in the soil, and a larger consolidation body is formed. Although the cutting capacity of slurry flow can be improved by high-pressure water of a triple pipe method, a large amount of construction water can aggravate the damage of underground water, the effective concentration of mixed slurry is reduced, the gelation and consolidation of a mixture are not facilitated, the slurry in a flowing water-rich stratum can become thinner and can be quickly lost, and an effective consolidated body cannot be formed.

The construction in the three-pipe rotary spraying pile pit in the flowing water environment refers to the principle of triple-pipe high-pressure water cutting hole forming and double-pipe high-pressure cement slurry cutting consolidation, when the triple-pipe high-pressure rotary spraying pile is mechanically arranged on the bottom surface of a foundation pit, the inner periphery of the pit is subjected to precipitation and earth excavation or continuous construction operation of a foundation structure, 2 times of cutting destruction is carried out on a soil body by using high-pressure jet flow in the dynamic seepage environment, and the three-pipe rotary spraying pile pit is mixed, stirred and consolidated to form the rotary spraying pile. During construction, soil with a certain thickness is reserved at the bottom of a pit to serve as an operation surface, drilling and pipe insertion are combined into a whole and completed simultaneously, and high-pressure water is firstly sprayed during pipe insertion to cut a soil body and expand the hole; after drilling to the designed treatment depth, closing the high-pressure water pipe, communicating slurry and the air pipe, jetting high-pressure water slurry flow wrapping compressed air to the surrounding soil body through the rod end nozzle at high pressure, simultaneously, lifting the drill rod (spray rod) at a certain speed while rotating, secondarily cutting and damaging the soil body structure within a certain range by the high-pressure jet flow, forcibly mixing the soil body structure with the solidified slurry, and forming a solidified body with certain performance and shape in the soil body after solidification.

High-pressure water is firstly used for cutting and reaming, so that the construction efficiency of secondary cutting and pore forming of slurry flow is improved, and the double-pipe method is favorable for ensuring the pile-forming aperture; the water pipe is closed during lifting, so that the construction water consumption is reduced, and the scouring and dilution of slurry caused by the dynamic seepage of underground water are weakened; compared with the old three-pipe method, the high-pressure slurry flow injection method has high slurry flow concentration and large flow, and effectively ensures the pile forming and meshing quality of the pile body.

The rotary jet grouting pile for construction in the pit is constructed by adopting a ring from outside to inside to form a closed ring, so that the penetration of cement paste to a non-reinforced area during the subsequent construction of a central area is effectively blocked, the lateral soil squeezing effect in a reinforced area is reduced, and the influence of the flowing water seepage flow at the periphery of the reinforced area on the consolidation of the pile forming slurry in the central area is also reduced. The construction precipitation adopts external drainage and internal control, the precipitation depth and the water pumping amount are controlled in a construction area, the hydraulic dynamic stability is kept, and clear drainage ditches are arranged outside the construction area along the periphery of the construction area to drain mud and surface water gushing so as to reduce the influence of water level disturbance on the pile forming quality of the high-pressure jet grouting pile.

The present invention will be further described with reference to the following examples.

Detailed Description

A construction method in a three-pipe rotary spraying pile pit in a dynamic water environment comprises the following steps:

preparation for construction

(1) Leveling the field: clearing all barriers in a construction area, backfilling and tamping a low-lying part of a field by using viscous soil materials, and excavating a drainage ditch with the width of 1m and the depth of 1.5m along the periphery of the outer side of the construction area to be used as a slurry drainage ditch; excavating a waste slurry pool and a slurry discharge ditch from a construction hole to the slurry pool outside a construction range according to the actual condition of a construction site;

(2) cement: P.O42.5 ordinary portland cement is adopted; each batch of cement is qualified by the field entry retest and the factory quality certification is obtained;

(3) water: the pH value is between 5 and 10;

(4) indoor mix proportion test: designing and adjusting several mixing ratios according to different water contents according to the spraying amount required by design or the condition of a field soil sample, air-drying or drying and crushing the soil sample collected on the field indoors, sieving a powdery soil sample with a sieve of 2-5 mm, stirring according to the designed spraying amount and the water-cement ratio, maintaining and performing mechanical tests to determine the construction spraying amount;

(5) pile testing: preparing cement slurry according to construction spraying amount and water cement ratio determined by indoor tests, driving a plurality of test piles at a test working point, adjusting the spraying amount of a reinforcing material according to a pile test result, and determining construction process parameters such as lifting speed of a rotary spraying pile drilling machine, rotation speed of a stirring shaft, spraying pressure, a slurry stopping surface and the like;

(6) installation and debugging of equipment: reasonably arranging and installing a complete set of equipment required by the construction of the three-pipe high-pressure jet grouting pile according to the construction site condition, respectively checking whether various equipment of a gas system, a slurry system and a water system normally operate or not, checking whether pipelines are smooth or not, and testing whether a monitoring instrument is complete and intact or not; after the process is ensured to be correct, the next process can be carried out;

pile position lofting

Firstly, a total station is adopted to discharge a control pile according to the pile number of a high-pressure jet grouting pile, then a steel tape and a hemp thread are used to transfer the pile position of the discharged jet grouting pile according to the pile distance, a small bamboo stick is used for marking, a lime mark is scattered, the pile driver is ensured to be accurately positioned, and the displacement deviation of the center of a pile hole is less than 50 mm;

(III) digging drainage ditch, building drainage system

In order to reduce the influence of water level disturbance on the pile forming quality of the high-pressure jet grouting pile in the pit, pumping water to a precipitation well in a construction area is suspended when the peripheral jet grouting pile is constructed; reducing water pumping within the range of 15-20 m of the precipitation influence radius of an outer pipe well at the periphery of a construction area, and controlling the water pumping amount, wherein the water level is controlled to be preferably 500mm below a construction surface; the water level of the dewatering well outside the range of 20 meters on the periphery is deepened; meanwhile, a drainage ditch with the depth of 1 meter and the width of 1.5 meters is dug along the periphery of the construction area, a water pump is adopted for open drainage, and a digging machine is arranged for cleaning the drainage ditch in time;

introducing waste slurry into a sedimentation tank through a drainage ditch according to the amount of slurry return generated in the construction process of the jet grouting pile;

(IV) drill setting

Moving the rotary jet grouting pile driver to a specified pile position, aligning a vertical shaft turntable with a hole position, leveling a drilling machine, calibrating the pile driver by using a horizontal ruler and a positioning measuring hammer, wherein a guide frame and a drill rod are vertical to the ground, and the verticality deviation of the drill rod is not more than 1-1.5%; in order to ensure the pile position to be accurate, a positioning card is required to be used, and the pile position centering error is not more than 50 mm;

(V) slurry preparation

When the pile machine is shifted, mixing cement paste according to the mix proportion determined by the design; firstly, adding water into a barrel, pouring cement and an admixture into the barrel, starting a stirrer to stir for 10-20 minutes, then screwing off a valve at the bottom of the stirring barrel, putting the first screen with the aperture of 0.8mm, filtering, flowing into a slurry pool, pumping into a second screen with the aperture of 0.8mm through a slurry pump, filtering for the second time, flowing into the slurry barrel, and standing by when grouting;

in order to prevent the cement grout from being separated, a slow stirring device is arranged in the grout storage barrel and needs to be continuously stirred until the grout is sprayed;

during guniting, cement paste is conveyed into a nozzle of the rotary vibration drilling machine through a rubber pipe and is finally ejected. The cement slurry is stored for not more than 4h, otherwise, the cement slurry is treated as waste slurry;

(VI) drilling cannula

And starting the drilling machine, rotating and drilling at the same time, and stopping drilling after reaching the designed elevation. The pipe inserting and the drilling are combined into a whole, and the pipe inserting operation is completed simultaneously when the drilling is completed. In the pipe inserting process, jetting high-pressure water to cut a soil body for reaming: starting the drilling machine, and simultaneously starting a high-pressure clean water pump to deliver water with the water pressure of 25-30 Mpa, so that the drill rod is vibrated along the guide frame and is sunk in the jet cutting reaming;

observing that the working current is not greater than a rated value until the designed elevation of the pile bottom;

parameters such as drilling speed, the section number and the length of a drill rod and the like are recorded in the drilling process, and the drilling depth is ensured to meet the design requirement; in order to avoid the inclination of the drill hole, the perpendicularity of the drill rod needs to be checked at any time in the process of positioning and drilling the drill, and the inclination is found and corrected in time so as to ensure that the inclination of the drill hole is within a design allowable range; drilling at a slow speed, and preventing the hole from inclining by adopting a guide device; firstly, pilot drilling is carried out in each section of construction area, and if drilling cannot be carried out or is slow, holes can be led in advance; after guiding, inserting a PVC pipe with the diameter of 150mm into the orifice;

(VII) lifting by rotary jetting

Stopping drilling after the guniting pipe sinks to reach the designed depth, stopping rotating without stopping, closing the high-pressure clean water pump and the water conveying pipe, connecting the high-pressure grout pipe and the air pressure pipe, starting a high-pressure grouting pump and an air compressor, controlling the grout pressure to be 20-25 Mpa and the air pressure to be not less than 0.7Mpa, controlling the pressure, the flow and the air quantity by using an instrument, and checking whether each construction parameter meets the design requirement;

firstly, high-pressure slurry is sent, and compressed air can be sent for 30s later; the guniting pipe sits at the bottom in situ for guniting for 30s, the guniting pipe rotates while guniting, and the lifting device is started after the orifice is normally guniting;

after the cement paste and the pile end soil are fully stirred, the grouting pipe is lifted in a reverse uniform-speed rotation mode while the cement paste is sprayed, the spraying rotation speed is 15r/min, the lifting speed is 8-16 cm/min, and the air volume is 10m³The spraying amount is 120L/min, and the cement doping amount is 45-50% of the volume weight of the soil body;

when the lifting of the rotary jet grouting pipe is close to the pile top, starting from 1.0m below the pile top, slowly lifting and rotary jetting, carrying out rotary jetting for a plurality of seconds, then slowly lifting upwards for 0.5m until the pile top stops on a grout surface, closing a high-pressure slurry pump, stopping the delivery of cement grout, rotatably lifting the rotary jet grouting pipe out of the ground, and closing a drilling machine;

in the jet grouting construction, the upper spray rod needs to be disassembled, the lower spray rod continues to spray, and the spray can be stopped when the lower spray rod is required to be higher than the wellhead device by more than 500 mm; the pile body is re-sprayed and lapped for more than 500mm when the guniting is continued so as to ensure the vertical continuity of the anti-seepage body;

if the spraying is stopped in case of a fault in the spraying process, the spraying needs to be recovered as soon as possible, and the spray rod needs to descend by 200-500 mm when the spraying is recovered;

various technological parameters of the rotary spraying operation system are controlled according to preset requirements, and the record of rotary spraying time, pulp consumption, pulp bleeding condition, pressure change and the like is made at any time;

(eighth) flushing machine

After the injection construction is finished, the grouting pipe and other equipment are washed clean by clear water to prevent solidification and blockage; the cement slurry can not remain in the pipe and the machine, the slurry is generally changed into clear water to be sprayed on the ground, so that the slurry in a slurry pump, a grouting pipe and a hose can be completely removed, and the soil adhered to the head of the guniting pipe is cleaned;

(nine) drill rig Displacement

Moving the pile machine to carry out construction of the next pile; repeating the step (four) to the step (nine);

(ten) recharging slurry

After the high-pressure sprinkling irrigation is finished, due to the fact that the volume of the cement slurry in the hole shrinks in the solidification process, and meanwhile, the slurry in the hole leaks to a certain extent to the periphery of the hole wall, the surface of the slurry in the hole sinks for a period of time, the slurry is continuously back-poured into the sprayed hole, and the grouting effect is kept until the slurry in the hole does not sink any more; the recharging slurry is filled by adopting high-spraying slurry-discharging static pressure of adjacent holes;

(eleven) constructing the jet grouting piles in the pit from outside to inside to form a closed ring by adopting ring construction, firstly constructing high-pressure jet grouting piles on the outer side of the periphery, and constructing inner jet grouting piles after the jet grouting piles on the outer side are initially set; the jet grouting pile adopts pile position jumping operation at intervals, the distance is controlled to be more than 2m, and after 24 hours, adjacent pile positions are constructed;

(twelfth) compacting grouting

Engineering piles and upright piles in a construction area are constructed on the natural ground, the joint parts of the high-pressure jet grouting piles, the engineering piles and the upright piles cannot be tightly lapped, after the jet grouting piles are constructed, the positions of the engineering piles are excavated, and holes are led by a geological drilling machine and compacted and grouted for reinforcement while being tightly attached to the engineering piles and the upright piles; the grouting slurry adopts P.O42.5 ordinary portland cement, the water cement ratio is 0.5-0.6, the grouting pressure is 0.3-0.6 Mpa, and the cement dosage is 100-150 kg/m;

(thirteen) well repairing

During construction of the jet grouting pile, a part of the downcomer well is blocked due to penetration of cement slurry, the cement slurry is used for filling and blocking in time after construction is finished, and well repairing is carried out at a proper position according to actual conditions on site; different from the construction on the ground, the water head pressure difference is small, and the holes cannot be formed at the periphery in a dynamic seepage state, so that the bentonite is used for making slurry and protecting the walls to form the holes;

(fourteen) calculating the cement consumption according to the requirements of design drawings; after the material enters the field, sampling and retesting are carried out according to related requirements, and unqualified materials are strictly forbidden to be put into engineering use; meanwhile, the materials qualified in the retest are reported and tested to the supervision unit in time.

The construction interval time of two adjacent piles is not less than 24h, and the distance between two adjacent piles is not less than 2 m; the distance between the injection hole and the high-pressure grouting pump is not more than 50m, and the actual hole position, the actual hole depth, underground obstacles in each drilling hole, the situation that the underground obstacles do not accord with geotechnical engineering investigation reports and the like are recorded in detail;

when the slurry is prepared, the water-cement ratio is strictly controlled according to the design and cannot be changed randomly; during the rotary spraying process, the mud is prevented from precipitating, and the concentration is reduced; no wet or out-of-date cement must be used. When the slurry is conveyed to a slurry suction barrel after the slurry is stirred, a screen is needed for filtering, and the diameter of a filtering screen hole is preferably smaller than the diameter of 1/2 of the nozzle;

high-pressure water is firstly sent when the pipe is inserted, the high-pressure water is closed when the pipe is lifted, cement paste is firstly sent, and compressed air can be sent for 30s later;

after spraying for 30s while rotating the bottom of the pile, rotating, lifting and spraying while spraying;

when spraying, the grouting pipe is gradually lifted after the preset spraying pressure and the preset spraying amount are reached. The rotation and lifting of the drill rod must be continuous without interruption, and the overlap length of the drill rod is not less than 50cm when the long drill rod is disassembled or the rotary spraying is continued, so that the pile breakage is avoided; if the designed diameter of the pile body is influenced by insufficient slurry injection, rechecking is carried out;

in the rotary spraying process, the phenomenon that the slurry outflow amount is less than 20% of the grouting amount is normal, if the slurry outflow amount exceeds 20% or the slurry does not flow at all, reasons should be found out, and rotary spraying parameters are adjusted or the diameter of a nozzle is changed;

and drilling at a low speed and a low bit pressure at the interface of the soft soil layer and the hard soil layer. Finding out the deviation of the drilled hole, backfilling clay in time, and drilling at low speed and low bit pressure after flushing;

in the rotary spraying process, if the rotary spraying is interrupted due to the failure of a machine, the lifting and the rotary spraying are stopped to prevent the pile from being interrupted, and meanwhile, the inspection is immediately carried out to remove the failure; drilling again to the designed elevation of the pile bottom, and then performing rotary spraying again;

when the guniting port reaches the height of the pile top, continuously guniting and lifting by 0.5m to ensure the quality of the pile top;

after the grouting material is sprayed to the height of the pile, the grout pipe is quickly pulled out, and the pipeline is washed by clear water to prevent solidification and blockage;

quality inspection: after the construction of the jet grouting pile is finished for 28 days, the construction quality of the project is checked through core drilling and sampling;

when the jet grouting pile is constructed, attention should be paid to avoid constructed engineering piles and upright piles, and when the position of the jet grouting pile conflicts with the engineering pile, the jet grouting pile is constructed closely to the engineering pile;

closely monitoring the water level and the water pumping quantity of the peripheral dewatering well during construction, keeping the dynamic stability of the hydraulic force and ensuring the pile forming quality of the jet grouting pile;

the rotary spraying pile is constructed according to the sequence of firstly outer, then inner and closed ring, the inner rotary spraying pile can be constructed after the peripheral pile body reaches initial setting, so that the side soil resistance effect and the influence of the dynamic seepage of the peripheral underground water on the inner pile during the inner construction are reduced.

Claims (2)

1. A construction method in a three-pipe rotary spraying pile pit in a flowing water environment is characterized by comprising the following steps: comprises the following steps:

preparation for construction

(1) Leveling the field: clearing all barriers in a construction area, backfilling and tamping a low-lying part of a field by using viscous soil materials, and excavating a drainage ditch with the width of 1m and the depth of 1.5m along the periphery of the outer side of the construction area to be used as a slurry drainage ditch; excavating a waste slurry pool and a slurry discharge ditch from a construction hole to the slurry pool outside a construction range according to the actual condition of a construction site;

(2) cement: P.O42.5 ordinary portland cement is adopted; each batch of cement is qualified by the field entry retest and the factory quality certification is obtained;

(3) water: the pH value is between 5 and 10;

(4) indoor mix proportion test: designing and adjusting several mixing ratios according to different water contents according to the spraying amount required by design or the condition of a field soil sample, air-drying or drying and crushing the soil sample collected on the field indoors, sieving a powdery soil sample with a sieve of 2-5 mm, stirring according to the designed spraying amount and the water-cement ratio, maintaining and performing mechanical tests to determine the construction spraying amount;

(5) pile testing: preparing cement slurry according to construction spraying amount and water cement ratio determined by indoor tests, driving a plurality of test piles at a test working point, adjusting the spraying amount of a reinforcing material according to a pile test result, and determining construction process parameters such as lifting speed of a rotary spraying pile drilling machine, rotation speed of a stirring shaft, spraying pressure, a slurry stopping surface and the like;

(6) installation and debugging of equipment: reasonably arranging and installing a complete set of equipment required by the construction of the three-pipe high-pressure jet grouting pile according to the construction site condition, respectively checking whether various equipment of a gas system, a slurry system and a water system normally operate or not, checking whether pipelines are smooth or not, and testing whether a monitoring instrument is complete and intact or not; after the process is ensured to be correct, the next process can be carried out;

pile position lofting

Firstly, a total station is adopted to discharge a control pile according to the pile number of a high-pressure jet grouting pile, then a steel tape and a hemp thread are used to transfer the pile position of the discharged jet grouting pile according to the pile distance, a small bamboo stick is used for marking, a lime mark is scattered, the pile driver is ensured to be accurately positioned, and the displacement deviation of the center of a pile hole is less than 50 mm;

(III) digging drainage ditch, building drainage system

In order to reduce the influence of water level disturbance on the pile forming quality of the high-pressure jet grouting pile in the pit, pumping water to a precipitation well in a construction area is suspended when the peripheral jet grouting pile is constructed; reducing water pumping within the range of 15-20 m of the precipitation influence radius of an outer pipe well at the periphery of a construction area, and controlling the water pumping amount, wherein the water level is controlled to be preferably 500mm below a construction surface; the water level of the dewatering well outside the range of 20 meters on the periphery is deepened; meanwhile, a drainage ditch with the depth of 1 meter and the width of 1.5 meters is dug along the periphery of the construction area, a water pump is adopted for open drainage, and a digging machine is arranged for cleaning the drainage ditch in time;

introducing waste slurry into a sedimentation tank through a drainage ditch according to the amount of slurry return generated in the construction process of the jet grouting pile;

(IV) drill setting

Moving the rotary jet grouting pile driver to a specified pile position, aligning a vertical shaft turntable with a hole position, leveling a drilling machine, calibrating the pile driver by using a horizontal ruler and a positioning measuring hammer, wherein a guide frame and a drill rod are vertical to the ground, and the verticality deviation of the drill rod is not more than 1-1.5%; in order to ensure the pile position to be accurate, a positioning card is required to be used, and the pile position centering error is not more than 50 mm;

(V) slurry preparation

When the pile machine is shifted, mixing cement paste according to the mix proportion determined by the design; firstly, adding water into a barrel, pouring cement and an admixture into the barrel, starting a stirrer to stir for 10-20 minutes, then screwing off a valve at the bottom of the stirring barrel, putting the first screen with the aperture of 0.8mm, filtering, flowing into a slurry pool, pumping into a second screen with the aperture of 0.8mm through a slurry pump, filtering for the second time, flowing into the slurry barrel, and standing by when grouting;

in order to prevent the cement grout from being separated, a slow stirring device is arranged in the grout storage barrel and needs to be continuously stirred until the grout is sprayed;

during guniting, the cement paste is delivered into a spray pipe of the rotary vibration drilling machine through a rubber pipe and is finally ejected; the cement slurry is stored for not more than 4h, otherwise, the cement slurry is treated as waste slurry;

(VI) drilling cannula

Starting a drilling machine, rotating and drilling at the same time, and stopping drilling after reaching the designed elevation; the pipe inserting and the drilling are combined into a whole, and the pipe inserting operation is completed simultaneously when the drilling is completed; in the pipe inserting process, jetting high-pressure water to cut a soil body for reaming: starting the drilling machine, and simultaneously starting a high-pressure clean water pump to deliver water with the water pressure of 25-30 Mpa, so that the drill rod is vibrated along the guide frame and is sunk in the jet cutting reaming;

observing that the working current is not greater than a rated value until the designed elevation of the pile bottom;

parameters such as drilling speed, the section number and the length of a drill rod and the like are recorded in the drilling process, and the drilling depth is ensured to meet the design requirement; in order to avoid the inclination of the drill hole, the perpendicularity of the drill rod needs to be checked at any time in the process of positioning and drilling the drill, and the inclination is found and corrected in time so as to ensure that the inclination of the drill hole is within a design allowable range; drilling at a slow speed, and preventing the hole from inclining by adopting a guide device; firstly, pilot drilling is carried out in each section of construction area, and if drilling cannot be carried out or is slow, holes can be led in advance; after guiding, inserting a PVC pipe with the diameter of 150mm into the orifice;

(VII) lifting by rotary jetting

Stopping drilling after the guniting pipe sinks to reach the designed depth, stopping rotating without stopping, closing the high-pressure clean water pump and the water conveying pipe, connecting the high-pressure grout pipe and the air pressure pipe, starting a high-pressure grouting pump and an air compressor, controlling the grout pressure to be 20-25 Mpa and the air pressure to be not less than 0.7Mpa, controlling the pressure, the flow and the air quantity by using an instrument, and checking whether each construction parameter meets the design requirement;

firstly, high-pressure slurry is sent, and compressed air can be sent for 30s later; the guniting pipe sits at the bottom in situ for guniting for 30s, the guniting pipe rotates while guniting, and the lifting device is started after the orifice is normally guniting;

after the cement paste and the pile end soil are fully stirred, the grouting pipe is lifted in a reverse uniform-speed rotation mode while the cement paste is sprayed, the spraying rotation speed is 15r/min, the lifting speed is 8-16 cm/min, and the air volume is 10m³The spraying amount is 120L/min, and the cement doping amount is 45-50% of the volume weight of the soil body;

when the lifting of the rotary jet grouting pipe is close to the pile top, starting from 1.0m below the pile top, slowly lifting and rotary jetting, carrying out rotary jetting for a plurality of seconds, then slowly lifting upwards for 0.5m until the pile top stops on a grout surface, closing a high-pressure slurry pump, stopping the delivery of cement grout, rotatably lifting the rotary jet grouting pipe out of the ground, and closing a drilling machine;

in the jet grouting construction, the upper spray rod needs to be disassembled, the lower spray rod continues to spray, and the spray can be stopped when the lower spray rod is required to be higher than the wellhead device by more than 500 mm; the pile body is re-sprayed and lapped for more than 500mm when the guniting is continued so as to ensure the vertical continuity of the anti-seepage body;

if the spraying is stopped in case of a fault in the spraying process, the spraying needs to be recovered as soon as possible, and the spray rod needs to descend by 200-500 mm when the spraying is recovered;

various technological parameters of the rotary spraying operation system are controlled according to preset requirements, and the record of rotary spraying time, pulp consumption, pulp bleeding condition, pressure change and the like is made at any time;

(eighth) flushing machine

After the injection construction is finished, the grouting pipe and other equipment are washed clean by clear water to prevent solidification and blockage; the cement slurry can not remain in the pipe and the machine, the slurry is generally changed into clear water to be sprayed on the ground, so that the slurry in a slurry pump, a grouting pipe and a hose can be completely removed, and the soil adhered to the head of the guniting pipe is cleaned;

(nine) drill rig Displacement

Moving the pile machine to carry out construction of the next pile; repeating the step (four) to the step (nine);

(ten) recharging slurry

After the high-pressure sprinkling irrigation is finished, due to the fact that the volume of the cement slurry in the hole shrinks in the solidification process, and meanwhile, the slurry in the hole leaks to a certain extent to the periphery of the hole wall, the surface of the slurry in the hole sinks for a period of time, the slurry is continuously back-poured into the sprayed hole, and the grouting effect is kept until the slurry in the hole does not sink any more; the recharging slurry is filled by adopting high-spraying slurry-discharging static pressure of adjacent holes;

(eleven) constructing the jet grouting piles in the pit from outside to inside to form a closed ring by adopting ring construction, firstly constructing high-pressure jet grouting piles on the outer side of the periphery, and constructing inner jet grouting piles after the jet grouting piles on the outer side are initially set; the jet grouting pile adopts pile position jumping operation at intervals, the distance is controlled to be more than 2m, and after 24 hours, adjacent pile positions are constructed;

(twelfth) compacting grouting

Engineering piles and upright piles in a construction area are constructed on the natural ground, the joint parts of the high-pressure jet grouting piles, the engineering piles and the upright piles cannot be tightly lapped, after the jet grouting piles are constructed, the positions of the engineering piles are excavated, and holes are led by a geological drilling machine and compacted and grouted for reinforcement while being tightly attached to the engineering piles and the upright piles; the grouting slurry adopts P.O42.5 ordinary portland cement, the water cement ratio is 0.5-0.6, the grouting pressure is 0.3-0.6 Mpa, and the cement dosage is 100-150 kg/m;

(thirteen) well repairing

During construction of the jet grouting pile, a part of the downcomer well is blocked due to penetration of cement slurry, the cement slurry is used for filling and blocking in time after construction is finished, and well repairing is carried out at a proper position according to actual conditions on site; different from the construction on the ground, the water head pressure difference is small, and the holes cannot be formed at the periphery in a dynamic seepage state, so that the bentonite is used for making slurry and protecting the walls to form the holes;

(fourteen) calculating the cement consumption according to the requirements of design drawings; after the material enters the field, sampling and retesting are carried out according to related requirements, and unqualified materials are strictly forbidden to be put into engineering use; meanwhile, the materials qualified in the retest are reported and tested to the supervision unit in time.

2. The construction method in the three-pipe rotary spraying pile pit in the dynamic water environment as claimed in claim 1, which is characterized in that: the construction interval time of two adjacent piles is not less than 24h, and the distance between two adjacent piles is not less than 2 m; the distance between the injection hole and the high-pressure grouting pump is not more than 50m, and the actual hole position, the actual hole depth, underground obstacles in each drilling hole, the situation that the underground obstacles do not accord with geotechnical engineering investigation reports and the like are recorded in detail;

when the slurry is prepared, the water-cement ratio is strictly controlled according to the design and cannot be changed randomly; during the rotary spraying process, the mud is prevented from precipitating, and the concentration is reduced; no use of damp or outdated cement; when the slurry is conveyed to a slurry suction barrel after the slurry is stirred, a screen is needed for filtering, and the diameter of a filtering screen hole is preferably smaller than the diameter of 1/2 of the nozzle;

high-pressure water is firstly sent when the pipe is inserted, the high-pressure water is closed when the pipe is lifted, cement paste is firstly sent, and compressed air can be sent for 30s later;

after spraying for 30s while rotating the bottom of the pile, rotating, lifting and spraying while spraying;

when in injection, the grouting pipe is gradually lifted after the preset injection pressure and the preset injection amount are reached; the rotation and lifting of the drill rod must be continuous without interruption, and the overlap length of the drill rod is not less than 50cm when the long drill rod is disassembled or the rotary spraying is continued, so that the pile breakage is avoided; if the designed diameter of the pile body is influenced by insufficient slurry injection, rechecking is carried out;

in the rotary spraying process, the phenomenon that the slurry outflow amount is less than 20% of the grouting amount is normal, if the slurry outflow amount exceeds 20% or the slurry does not flow at all, reasons should be found out, and rotary spraying parameters are adjusted or the diameter of a nozzle is changed;

drilling at a low speed and a low bit pressure on a soft and hard soil layer interface; finding out the deviation of the drilled hole, backfilling clay in time, and drilling at low speed and low bit pressure after flushing;

in the rotary spraying process, if the rotary spraying is interrupted due to the failure of a machine, the lifting and the rotary spraying are stopped to prevent the pile from being interrupted, and meanwhile, the inspection is immediately carried out to remove the failure; drilling again to the designed elevation of the pile bottom, and then performing rotary spraying again;

when the guniting port reaches the height of the pile top, continuously guniting and lifting by 0.5m to ensure the quality of the pile top;

after the grouting material is sprayed to the height of the pile, the grout pipe is quickly pulled out, and the pipeline is washed by clear water to prevent solidification and blockage;

quality inspection: after the construction of the jet grouting pile is finished for 28 days, the construction quality of the project is checked through core drilling and sampling;

when the jet grouting pile is constructed, attention should be paid to avoid constructed engineering piles and upright piles, and when the position of the jet grouting pile conflicts with the engineering pile, the jet grouting pile is constructed closely to the engineering pile;

closely monitoring the water level and the water pumping quantity of the peripheral dewatering well during construction, keeping the dynamic stability of the hydraulic force and ensuring the pile forming quality of the jet grouting pile;

the rotary spraying pile is constructed according to the sequence of firstly outer, then inner and closed ring, the inner rotary spraying pile can be constructed after the peripheral pile body reaches initial setting, so that the side soil resistance effect and the influence of the dynamic seepage of the peripheral underground water on the inner pile during the inner construction are reduced.