A construction method for deep foundation pit cutoff wall

Abstract

A method for constructing a deep foundation pit water cutoff wall includes guide wall construction, plain pile construction, reinforced concrete pile construction, and grouting molding. In guide wall construction, a positioning template is set along the guide line where the water cutoff wall is to be set, with the distance between the center point of the plain pile position and the center point of the reinforced concrete pile position being less than the sum of the radii of the two. The positioning template is poured with concrete to reserve the positions of the plain pile and the reinforced concrete pile positions to form a continuous guide wall. In plain pile construction, a hole is drilled at the plain pile position of the positioning template with a drill rig, and then the plain pile is poured with concrete. In reinforced concrete pile construction, after the plain pile has initially set, a hole is drilled at the reinforced concrete pile position of the positioning template with a drill rig, and a steel cage is placed in the hole and concrete is poured. In grouting molding, a grouting hole pipe is set at the center point where the plain pile and the reinforced concrete pile intersect, and grouting is performed through the grouting hole pipe to fill the hole between the plain pile and the reinforced concrete pile. The advantage of the present invention is that it can effectively eliminate the mud skin interlayer between the two piles.

Description

Technical Field

[0001] The invention relates to a construction method of a deep foundation pit cutoff wall, in particular to a construction method of a cutoff wall composed of piles. Background Art

[0002] A certain project involved a deep foundation pit located near the Yangtze River. The quality of the interlocking piles' interlocking was crucial to the safety of the foundation pit and the personnel and equipment within it. If a thick mud layer formed between the two piles, sidewall piping would likely occur, leading to backflow into the foundation pit and preventing normal construction. Therefore, it was necessary to focus on and address the thickness of the interlocking pile mud layer. After consultation and discussion with the construction company, design company, survey company, and supervision company, it was determined that a post-grouting anti-seepage construction method, using a deep foundation pit water interception mother-and-child interlocking pile interface, would be adopted to address the potential pit seepage problem. Summary of the Invention

[0003] The invention provides a deep foundation pit cutoff wall construction method, which can effectively eliminate the mud skin interlayer appearing between two pile bites.

[0004] The technical solution for achieving the purpose of the present invention is a method for constructing a deep foundation pit cutoff wall, which includes guide wall construction, plain pile construction, reinforced concrete pile construction, and grouting molding;

[0005] The guide wall construction is to set up a positioning template along the guide line where the cutoff wall needs to be set up. The positioning template is composed of a plurality of plain pile positions and steel bar pile positions. A steel bar pile position is provided between two adjacent plain pile positions, and the distance between the center point of the plain pile position and the center point of the steel bar pile position is less than the sum of the radii of the two. The positioning template is poured with concrete to reserve the positions of the plain pile position and the steel bar pile position to form a continuous guide wall.

[0006] The pile construction comprises drilling holes in the pile positions of the positioning template with a drill and then pouring concrete into the piles.

[0007] The reinforced concrete pile construction is as follows: after the pile is initially set, a drilling machine is used to drill holes in the reinforced concrete pile positions of the positioning template, and a steel cage is placed in the hole and concrete is poured;

[0008] The grouting molding comprises setting a grouting hole pipe at the center point where the plain pile and the reinforced concrete pile intersect, and providing a filter hole on the surface of the grouting hole pipe. Within one to three weeks after the reinforced concrete pile is poured, the muddy water in the grouting hole pipe is pumped out, and then grouting is performed through the grouting hole pipe to fill the hole between the plain pile and the reinforced concrete pile.

[0009] The construction of deep foundation pit cutoff wall is completed through the above steps.

[0010] Furthermore, in the template positioning, the diameter of the plain pile is 80-95% of the diameter of the steel bar pile.

[0011] Furthermore, during the construction of the plain piles, the strength of the concrete used to cast the plain piles is no more than 3 MPa within 72 hours.

[0012] Furthermore, during the grouting process, the grouting pressure is less than 1.2 MPa and the grouting flow rate is less than 2.4 m 3 / h.

[0013] Furthermore, during the grouting process, the grouting hole tube includes a large head tube and a small tube arranged inside the large head tube, and filtering holes are provided on the surface of the small tube.

[0014] Furthermore, during the construction of the reinforced concrete pile, a detachable elastic positioning frame is provided on the positioning template. The elastic positioning frame includes positioning piles and a positioning frame. The positioning frame is composed of multiple small parts. The positioning piles are directly connected to the positioning template, and the positioning frame is connected to the positioning piles through elastic parts.

[0015] After the drill bit drills the reinforced concrete pile hole through the positioning template, a positioning pile is installed at the corresponding position of the positioning template, and the positioning pile and the small component are connected through an elastic component. Multiple small components are spliced ​​into a positioning frame, and the distance between the inner edge of the positioning frame and the edge of the drill rod is 2 cm.

[0016] The advantage of the present invention is that by arranging the grouting hole pipe, a vertical straight belt without mud skin appears from the upper end to the lower end of the pile at the bite of the two piles. In the early stage, mud and water are introduced into it through the grouting hole pipe, and grouting is carried out through the grouting hole pipe in the later stage to squeeze out the mud and water around it, thereby effectively eliminating the mud skin interlayer between the two piles. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the positioning template structure of the present invention.

[0018] Figure 2 It is a schematic diagram of the guide wall structure of the present invention.

[0019] Figure 3 Schematic diagram of the grouting hole pipe structure.

[0020] Figure 4 This is a schematic diagram of the elastic positioning frame structure.

[0021] As shown in the figure, there are positioning template 1, plain pile position 2, steel pile position 3, grouting hole tube 4, filter hole 5, large head tube 41, small tube 42, elastic positioning frame 6, positioning pile 61, positioning frame 62, small component 621, and elastic component 63. DETAILED DESCRIPTION

[0022] A deep foundation pit cutoff wall construction method includes guide wall construction, plain pile construction, reinforced concrete pile construction, and grouting molding;

[0023] The guide wall construction is to set the positioning template 1 along the wire where the cutoff wall needs to be set, such as Figure 1 The positioning template 1 is composed of a plurality of plain pile positions 2 and steel bar pile positions 3. A steel bar pile position 3 is provided between two adjacent plain pile positions 2. The distance between the center point of the plain pile position 2 and the center point of the steel bar pile position 3 is less than the sum of the radii of the two. The positioning template 1 is poured with concrete to reserve the positions of the plain pile position and the steel bar pile position to form a continuous guide wall (such as Figure 2 As shown), the diameter of the plain pile position 2 on the guide wall is 20mm to 40mm larger than the diameter of the plain pile, the diameter of the steel pile position 3 is 20mm to 40mm larger than the diameter of the steel pile, the concrete strength of the plain pile is not less than C15, and the concrete strength of the steel pile is not less than C20. Preferably, in the positioning template, the diameter of the plain pile position is 80-95% of the diameter of the steel pile position;

[0024] The described pile construction is to use a drilling rig to drill holes in the pile positions of the positioning template, and then use concrete to cast the piles. Preferably, during the described pile construction process, the strength of the concrete used to cast the piles is no more than 3Mpa within 72 hours. It is super slow-setting concrete. The slow-setting time is determined by performing a pile test on site according to the specific conditions of the project and the type of drilling rig selected to measure the slow-setting time of the sub-pile concrete. It is determined based on the single pile construction time Tb and Ta respectively, and the slow-setting time of the sub-pile concrete is calculated according to the following formula: T = k (2Tb + Ta) where T is the slow-setting time (initial setting time) of the sub-pile concrete; k is the influence coefficient of unforeseen factors, k = 1.20; Tb, Ta are the time required for the construction of the sub-pile and mother piles.

[0025] Concrete slump: In order to meet the needs of underwater concrete pouring and prevent "pipe burst", the concrete slump is generally 160mm~180mm.

[0026] During pile drilling, mud is used to protect the hole wall from collapse. The following requirements should be met regarding the mud pool and slurry preparation: a sedimentation tank and a slurry preparation tank should be installed. The tank volume should match the volume of the borehole and the two should be connected. A 0-20m sedimentation tank should be located between the hole opening and the sedimentation tank, with several sand filters installed along the way. A sand filter should also be installed at the sedimentation tank opening. To protect the mud and prevent sand from entering the hole during circulation, a sand filter cover should be installed in the slurry preparation tank to prevent sand from entering the mud pump pipeline.

[0027] During the hole cleaning process for raw piles, the first hole cleaning is carried out after the hole is formed. The drilling speed is slowed down by the drill rig and a double-bottomed slag drill bit is used to remove all suspended sediments. After the hole cleaning is completed and the self-inspection is passed, the various parameters of the pile hole are measured together with the supervising engineer using logging instruments.

[0028] The second hole cleaning must be carried out before pouring concrete. When cleaning the hole, use a 3PN mud pump with a flow rate of 120m3 / h to clear the sediment at the bottom of the hole. Replace the mud and add new mud in time until all indicators are qualified. The water head in the hole must be maintained during the hole cleaning process to prevent the hole from being overdone. The method of deepening the drilling depth must not be used instead of cleaning the hole. 3min-5min after the hole cleaning is completed, use a standard measuring rope to measure the thickness of the sediment under the supervision of the supervising engineer, and check that the sediment thickness is not greater than 30mm. If it exceeds the standard, the hole must be cleaned again. Regularly re-measure the accuracy of the measuring rope scale position, and a spare measuring rope should be available. At the end of the hole, check that the pile end has reached the design elevation, and effective measures should be taken to solve problems such as pile body leakage and deviated hole.

[0029] The reinforced concrete pile construction is as follows: after the pile is initially solidified, a drilling rig is used to drill holes in the reinforced concrete pile positions of the positioning template, and a steel cage is placed in the hole and concrete is poured. Preferably, during the reinforced concrete pile construction process, a detachable elastic positioning frame 6 is provided on the positioning template, and the elastic positioning frame 6 includes a positioning pile 61 and a positioning frame 62. The positioning frame 62 is composed of multiple small parts 621. The positioning pile 61 is directly connected to the positioning template, and the positioning frame 62 is connected to the positioning pile 61 through an elastic part 63.

[0030] After the drill bit drills the reinforced concrete pile hole through the positioning template, a positioning pile 61 is installed at the corresponding position of the positioning template, and the positioning pile 61 and the small component 621 are connected by the elastic component 63. A plurality of small components 621 are spliced ​​into a positioning frame 62. The distance between the inner edge of the positioning frame 62 and the edge of the drill rod is 2 cm. During the drilling process, if the drill bit deviates, the drill rod will also deviate accordingly. As the drill bit drills deeper, the probability of the drill bit being deflected by the different strengths of the plain concrete on both sides increases. When the drill bit deflects, the drill rod will be deflected. When the deviation exceeds about 1 cm, the drill rod will squeeze the corresponding side of the positioning frame 62. The operator can easily find the deviation of the drill rod and judge whether the drill bit is drilling in a certain direction. The drilling direction can be adjusted in real time during the drilling process to prevent the drill bit from drilling in a deviated manner, resulting in the reinforced concrete pile and one of the plain piles not intersecting, thereby forming a large area of ​​permeable holes. After using this device, the accuracy of the intersection of the reinforced concrete pile and the plain piles on both sides reaches more than 98%, and the deviation distance is less than 1.78 cm.

[0031] When cleaning reinforced concrete pile holes, the first cleaning should be carried out after the hole is formed and before the steel cage is hoisted. The second cleaning must be carried out after the steel cage is lowered and before the concrete is poured. Other operation requirements are the same as the key points for cleaning the holes of plain piles.

[0032] The reinforcement cage of reinforced concrete piles is made and placed. A high-pressure grouting pipe is set at each interface where the reinforcement cage corresponds to the adjacent sub-piles away from the foundation pit. Single-valve grouting holes are evenly distributed along the length of the pile from bottom to top to facilitate the grouting construction after the concrete of the mother and child piles has finally set. When lowering the reinforcement cage, it should be aligned with the center of the hole position and lowered slowly and gradually by using positive and negative rotation. It should be fixed immediately after it reaches the designed elevation. During the lowering process, the reinforcement cage should be aligned with the hole position when it is hoisted into the hole to ensure that it is vertical, gently, and slowly lowered into the hole. After entering the hole, it should be lowered slowly and not rotated left and right. If an obstacle is encountered, the lowering should be stopped, the cause should be identified and handled, and it is strictly forbidden to lift and drop suddenly or forcefully. Pay attention to check and check whether the position and elevation of the high-pressure grouting pipe at the interface where the adjacent sub-piles of the mother pile reinforcement cage are away from the foundation pit are accurate.

[0033] Concrete pouring for reinforced concrete piles: Set up guide tubes and funnels. Prepare several sets of rigid guide tubes with an inner diameter of 300mm. The middle section of the guide tube is generally 2m to 2.5m long, with the lower section extended to approximately 6m. The guide tube connections should be straight, reliable, and airtight, and a watertight test should be performed. The water pressure during the watertight test should be no less than 1.5 times the water depth in the hole and no less than 1.5 times the maximum internal pressure that the guide tube walls and welds can withstand during concrete pouring. Leaks detected during the water pressure test should be repaired or replaced. A funnel should be installed at the top of the guide tube. A guide tube no longer than 0.5m can be welded to the bottom of the funnel. The depth of the guide tube into the hole must be carefully measured. After installation, the bottom of the guide tube should be approximately 0.5m from the pile bottom. The guide tube joint should have a locking device, and the funnel should be installed at the top of the guide tube. For underwater concrete pouring, pour underwater concrete as soon as possible after the pile hole has been inspected and accepted. The slump of underwater concrete should be controlled between 160mm and 180mm. The baffle used in the conduit should be of appropriate size and installed correctly, generally above the water surface. The hole should be tightly covered before pouring concrete to prevent concrete from falling into the hole and contaminating the mud.

[0034] In the grouting forming, a grouting hole pipe 4 is set at the center point where the plain pile and the reinforced concrete pile intersect, and a filtering hole 5 is provided on the surface of the grouting hole pipe 4. Within one to three weeks after the reinforced concrete pile is poured, the mud and water in the grouting hole pipe 4 are extracted, and the mud and water at the interface between the plain pile and the reinforced concrete pile enter the grouting hole pipe 4 through the filtering hole 5. During the mud and water extraction process, because the surfaces of the plain pile and the reinforced concrete pile have been initially solidified, as long as the extraction pressure is well controlled, the structure of the surface of the plain pile and the reinforced concrete pile will not be destroyed, that is, the mud and water outside the plain pile and the reinforced concrete pile will not enter the grouting hole pipe 4, and only the mud and water between the plain pile and the reinforced concrete pile will be extracted into the grouting hole pipe 4, and then grouting is performed through the grouting hole pipe 4 to fill the hole formed after the mud skin interlayer between the plain pile and the reinforced concrete pile is extracted with cement. Preferably, in the grouting forming process, the grouting pressure is less than 1.2Mpa, and the grouting flow rate is less than 2.4m 3 / h, in the grouting process, the grouting hole pipe 4 includes a large head pipe 41 and a small tube 42 arranged in the large head pipe 41, and a filter hole 5 is provided on the surface of the small tube 42. The large head pipe 41 can facilitate the extraction and grouting of mud and water. The small tube 42 is arranged along the plain pile and the reinforced concrete pile. The filter hole 5 on the small tube 42 is used to introduce the mud and water into the small tube 42 by the extraction pressure in the early stage, and discharge it through the small tube 42. After the hole is formed between the plain pile and the reinforced concrete pile, it is filled with cement;

[0035] The construction of deep foundation pit cutoff wall is completed through the above steps.

Claims

1. A method for constructing a deep foundation pit cutoff wall, characterized by: The construction methods include guide wall construction, plain pile construction, reinforced concrete pile construction, and grouting molding; The guide wall is constructed by setting a positioning template along the cutoff wall guide line. The positioning template is composed of a plurality of plain pile positions and reinforced concrete pile positions. A reinforced concrete pile position is provided between two adjacent plain pile positions, and the distance between the center point of the plain pile position and the center point of the reinforced concrete pile position is less than the sum of the radii of the two. The positioning template is poured with concrete to reserve the positions of the plain pile position and the reinforced concrete pile position to form a continuous guide wall. The pile construction comprises the following steps: drilling holes in the pile positions of the positioning template with a drill, and then pouring concrete into the piles; The reinforced concrete pile construction is as follows: after the pile is initially set, a drilling machine is used to drill holes in the reinforced concrete pile positions of the positioning template, and a steel cage is placed in the hole and concrete is poured; The grouting molding comprises setting a grouting hole pipe at the center point where the plain pile and the reinforced concrete pile intersect, and providing a filter hole on the surface of the grouting hole pipe. Within one to three weeks after the reinforced concrete pile is poured, the muddy water in the grouting hole pipe is pumped out, and then grouting is performed through the grouting hole pipe to fill the hole between the plain pile and the reinforced concrete pile. The construction of deep foundation pit cutoff wall is completed through the above steps; During the grouting process, the grouting hole tube includes a large head tube and a small tube arranged inside the large head tube, and filtering holes are provided on the surface of the small tube; During the construction of the reinforced concrete pile, a detachable elastic positioning frame is provided on the positioning template. The elastic positioning frame includes positioning piles and a positioning frame. The positioning frame is composed of a plurality of small parts. The positioning piles are directly connected to the positioning template, and the positioning frame is connected to the positioning piles through elastic parts. After the drill bit drills into the reinforced concrete pile position through the positioning template, the positioning pile is installed at the corresponding position of the positioning template, and the positioning pile and the small component are connected through the elastic component. Multiple small components are spliced ​​into a positioning frame, and the distance between the inner edge of the positioning frame and the edge of the drill rod is 2 cm.

2. A deep foundation pit cutoff wall construction method according to claim 1, characterized in that: In the positioning template, the diameter of the plain pile is 80%-95% of the diameter of the reinforced concrete pile.

3. The method for constructing a deep foundation pit cutoff wall according to claim 1, wherein: During the construction of the plain piles, the strength of the concrete used to cast the plain piles is no more than 3 MPa within 72 hours.

4. A deep foundation pit cutoff wall construction method according to claim 1, characterized in that: During the grouting process, the grouting pressure is less than 1.2 MPa and the grouting flow rate is less than 2.4 m 3 / h.

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