CN111733827A - Construction method of deep foundation pit protection in the complex environment of adjacent high-speed railways under silt geology - Google Patents

Abstract

A construction method for deep foundation pit protection in a station yard under a complex environment of silt geology adjacent to a high-speed railway. It includes steps such as construction preparation, construction of enclosure piles, support at the top of the foundation pit and preliminary excavation, chiseling of existing concrete structures, manual continued excavation, and concrete back sealing. Effect of the invention: the protection construction method of concrete bored piles and rotary spray piles in traditional foundation pits is changed into a protection construction method of concrete bored piles and steel caissons, wherein the concrete bored piles mainly play the role of shear resistance, and the steel caisson plays the role of shear resistance. Waterproof and sand control effect, thus forming a protection system for the entire deep foundation pit. During the excavation process, the protection system of concrete bored piles and steel caisson not only ensures the stability and safety of the foundation pit, but also prevents the underground water and sand gushing when the groundwater pressure is too high, causing the settlement of the existing line and ensuring the safety of the business line. Safety.

Description

Construction method of deep foundation pit protection in the complex environment of adjacent high-speed railways under silt geology

technical field

The invention belongs to the technical field, and in particular relates to a protection construction method for a deep foundation pit in a station yard under a complex environment of silt geology adjacent to a high-speed railway.

Background technique

For the construction of deep foundation pits near the existing high-speed rail complex environment and silt geology, the foundation pit protection generally adopts the protection construction method of concrete bored piles and rotary spray piles. In high-speed rail stations, there are usually complex geological conditions and underground In the case of many concrete structures, due to the soft soil and abundant groundwater, the high-pressure jetted piles sometimes cannot reach the expected pile bottom elevation, making it difficult to achieve the effect of a water-stop curtain. In addition, it is possible that water gushing and sand gushing may occur during the excavation process, resulting in settlement of the existing line. Therefore, the above-mentioned protective construction method can hardly meet the operational safety requirements of the existing high-speed railway during the construction process under such conditions. In addition, if a small foundation pit such as an elevator shaft needs to be set up in the foundation pit, if the small foundation pit continues to be excavated, it is very likely that there will be landslides, quicksand, groundwater backflow, etc., thus affecting the progress and safety of the construction.

SUMMARY OF THE INVENTION

In order to solve the above problems, the purpose of the present invention is to provide a construction method for the protection of deep foundation pits in stations adjacent to high-speed rail complex environments with silt geology.

In order to achieve the above-mentioned purpose, the construction method for the protection of deep foundation pits in the adjacent high-speed rail complex environment silt geology provided by the present invention comprises the following steps in order:

1) Before construction, according to the geological conditions and considering the safety of the high-speed railway business line, steel casings and steel caissons for bored piles shall be prefabricated, and a mud tank shall be set up on the side of the deep foundation pit to be constructed;

2) According to the design requirements, a percussion drill is used to form holes at the edge of the deep foundation pit to be constructed, and multiple drilling holes are formed at intervals by means of mud wall protection. A section of steel casing is set on the side wall of the borehole, and so on until the design depth of the concrete bored pile is reached, and then a steel cage is placed in each borehole provided with a steel casing, and then the Concrete is poured into the hole, and after the concrete is solidified and reaches the design strength, a plurality of concrete bored piles are made as foundation pit enclosure piles;

3) Manually chisel off the pile head of the above-mentioned concrete bored pile, then carry out crown beam construction at the upper end of the concrete bored pile of the chiseled pile head, and at the same time of crown beam construction, multiple steel plates are pre-buried in the crown beam at intervals. inner side;

4) When excavating the soil body inside the concrete bored pile, when digging down to 1m from the top of the concrete bored pile, the two ends of the multiple horizontal supports are respectively welded to the corresponding pair of steel plates on the crown beam; Continue to excavate the soil to the position of the existing concrete structure;

5) Use a breaker to chisel the existing concrete structure to the base elevation of the main foundation pit, thereby forming the main foundation pit;

6) Lower the steel caisson to the bottom surface of the main foundation pit, and position it precisely at the position of the small foundation pit, and then manually continue to excavate the soil inside the steel caisson. The steel caisson will gradually sink while excavating the soil. Until the lower end of the steel caisson reaches the base elevation of the small foundation pit, a small foundation pit is formed, and the steel caisson serves as a protective structure for the small foundation pit;

7) Use the sky pump truck to pour concrete to seal the bottom of the main foundation pit and the small foundation pit to ensure that there is no water and sand gushing underground, and then pour the cushion in other positions, thus completing the construction process of the protection system for the entire deep foundation pit.

In step 1), the thickness of the steel casing is 6mm, the height is 250cm, and the inner diameter is 100cm; the mud box is welded by steel plates with a length of 6m, a width of 2m, and a thickness of 15mm; to make.

In step 2), the diameter of the concrete bored pile is 0.8m, the distance between the piles is 1.0m, and the length of the pile is 6-18m.

In step 3), the height of the chiseled pile head is 1 meter; the height of the crown beam is 1 meter, the width is 0.8 meters, the reinforced concrete structure is adopted, the thickness of the protective layer is 40mm, the concrete adopts C30 concrete, and the main reinforcement adopts HRB400Φ22 steel bar.

In step 4), a steel pipe with a diameter of 50 cm is used for the lateral support; the soil is excavated in a segmented, layered, symmetrical, balanced, and time-limited manner, with a layered thickness of 3.5 meters and a length of 6 meters.

The construction method for the protection of deep foundation pits in stations under silt geology in a complex environment adjacent to a high-speed railway provided by the present invention has the following beneficial effects:

1. Change the protection construction method of concrete bored piles and rotary spray piles in the traditional foundation pit to the protection construction method of concrete bored piles and steel caissons, in which the concrete bored piles mainly play the role of shear resistance, and the steel caisson plays the role of waterproof and sand prevention. function, thus forming a protection system for the entire deep foundation pit.

2. During the excavation process, the protection system of concrete bored piles and steel caisson not only ensures the stability and safety of the foundation pit, but also prevents the underground water and sand gushing out when the groundwater pressure is too large, causing the settlement of the existing lines and ensuring the business operation. line safety.

Description of drawings

FIG. 1 is a flowchart of a construction method for deep foundation pit protection in a station yard under a complex environment of silt geology near a high-speed rail provided by the present invention.

2 is a plan view of a deep foundation pit when the construction method for protecting a deep foundation pit in a station yard under a complex environment of silt geology provided by the present invention is adopted.

3 is a side view of the deep foundation pit when the construction method for the protection of the deep foundation pit in the station yard under the complex environment of the silt geology provided by the present invention is adopted.

Detailed ways

In the reconstruction project of a railway engineering station, the site is located in a complex geological environment with many underground concrete structures, soft soil and abundant groundwater. In order to ensure the construction safety and the operation safety of the existing business line, the applicant has carried out the construction of the deep foundation pit by using the deep foundation pit protection construction method of the nearby high-speed railway complex environment silt geology provided by the present invention, effectively preventing landslides, quicksand , the impact of groundwater inversion and other conditions on the project, to ensure the progress and safety of the construction.

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in Figures 1 to 3, the construction method for the protection of deep foundation pits in stations under silt geological conditions adjacent to high-speed rail complex environments provided by the present invention includes the following steps in order:

1) Before construction, according to the geological conditions and considering the safety of the high-speed rail line, prefabricated steel casings and steel caisson 4 for bored piles, and set up a mud tank on one side of the deep foundation pit 1 to be constructed; The thickness of the cylinder is 6mm, the height is 250cm, and the inner diameter is 100cm; the mud tank is welded by steel plates with a length of 6m, a width of 2m and a thickness of 15mm; the steel caisson 4 is welded by the template of the abandoned bridge pier.

2) According to the design requirements, a percussion drill is used to form holes at the edge of the deep foundation pit 1 to be constructed, and multiple holes are formed at intervals by means of mud wall protection. A section of steel casing is set on the side wall of the borehole, and so on, until the design depth of the concrete bored pile 2 is reached, and then a reinforcement cage is placed in each borehole provided with the steel casing, and then Concrete is poured in the borehole, and after the concrete is solidified and reaches the design strength, a plurality of concrete bored piles 2 are made as foundation pit enclosure piles; in the present invention, the diameter of the concrete bored piles 2 is 0.8m, The pile spacing is 1.0m, and the pile length is 6-18m; when drilling, use a small stroke to open the hole. After entering the normal drilling state, use a medium and large stroke of 4-5m, and the maximum stroke does not exceed 6m. During the drilling process, it should be timely. Ballast. Pay attention to stratum changes, take ballast samples at the strata changes to judge the geological type, compare it with the geological profile provided by the design, make relevant records, and adjust the drilling process in time according to the geological conditions. The joints of the main reinforcement of the reinforcement cage are double-sided lap welding, the number of joints on each section does not exceed 50%, and the connection between the reinforcement stirrups and the main reinforcement is fully welded. The hole cleaning adopts the pumping method, and the mud pump of the impact drilling rig is used to continuously suck the slag for about 5 minutes to 15 minutes to remove the drilling slag at the bottom of the hole. After the reinforcement cage and the conduit are installed, the conduit is used for secondary hole cleaning, so that the mud index in the borehole and the thickness of the sediment at the bottom of the hole after hole cleaning meet the design and specification requirements. When cleaning the hole and discharging the slag, pay attention to maintaining the water head in the hole to prevent collapse. Concrete is poured immediately after the secondary hole cleaning is completed.

3) Manually chisel off the pile head of the above-mentioned concrete bored pile 2, then carry out crown beam construction on the upper end of the concrete bored pile 2 from which the pile head is chiseled, and pre-embed a plurality of steel plates in the crown beam at an interval distance during the crown beam construction. on the inside of the beam. In the present invention, the height of the chiseled pile head is 1 meter; the height of the crown beam is 1 meter, the width is 0.8 meters, the reinforced concrete structure is adopted, the thickness of the protective layer is 40mm, the concrete adopts C30 concrete, and the main reinforcement adopts HRB400Φ22 steel bar.

4) Excavate the soil inside the concrete bored pile 2, and when the excavation reaches 1m from the top of the concrete bored pile 2, the two ends of the multi-channel lateral supports 3 are respectively welded to the corresponding pair of the crown beams. On the steel plate; continue to excavate the soil to the existing concrete structure position, such as the existing retaining wall foundation or pipe pile cap; in the present invention, the transverse support 3 adopts a steel pipe with a diameter of 50cm. The soil is excavated in sections, layers, symmetry, balance and time limit. The layer thickness is 3.5 meters and the length is 6 meters. The excavation should be completed within 9 hours;

5) Use a breaker to chisel the existing concrete structure to the base elevation of the main foundation pit, thereby forming the main foundation pit;

6) Lower the steel caisson 4 to the bottom surface of the main foundation pit, and accurately position it at the position of the small foundation pit, and then manually continue to excavate the soil inside the steel caisson 4. While excavating the soil, the steel caisson 4 will gradually Sinking until the lower end of the steel caisson 4 reaches the base elevation of the small foundation pit, thereby forming a small foundation pit, and the steel caisson 4 serves as a protective structure for the small foundation pit;

7) Use the sky pump truck to pour concrete to seal the bottom of the main foundation pit and the small foundation pit to ensure that there is no water and sand gushing underground, and then pour the cushion at other positions, thus completing the construction process of the protection system of the entire deep foundation pit 1.

Claims (5)

1. A protection construction method for a deep foundation pit of a station yard under a high-speed rail complex environment sludge geology is characterized by comprising the following steps: the construction method comprises the following steps in sequence:

1) before construction, according to geological conditions and in consideration of the safety of a high-speed rail business line, prefabricating a steel casing and a steel caisson (4) for a bored pile, and arranging a mud box at one side of a deep foundation pit (1) to be constructed;

2) according to design requirements, a percussion drill is adopted at the edge of a deep foundation pit (1) to be constructed to form holes, a plurality of drill holes are formed at intervals in a mud retaining wall mode, one distance is drilled every time, the drill holes are checked and cleaned, then a section of steel retaining cylinder is arranged on the side wall of each drill hole, the operation is repeated until the design depth of a concrete drilling pile (2) is reached, then a steel reinforcement cage is placed in each drill hole provided with the steel retaining cylinder, concrete is poured into the drill holes, and a plurality of concrete drilling piles (2) are manufactured after the concrete is solidified and reaches the design strength to serve as foundation pit retaining piles;

3) manually chiseling off the pile head of the concrete bored pile (2), then performing crown beam construction on the upper end of the concrete bored pile (2) chiseled off the pile head, and embedding a plurality of steel plates on the inner side surface of the crown beam at intervals during the crown beam construction;

4) excavating a soil body on the inner side of the concrete bored pile (2), and when the soil body is excavated to a position 1m away from the top of the concrete bored pile (2), respectively welding two ends of a plurality of transverse supports (3) on a pair of corresponding steel plates on the crown beam; continuously excavating the soil body to the position of the existing concrete structure;

5) chiseling the existing concrete structure to the base elevation of the main foundation pit by using a breaking hammer, thereby forming the main foundation pit;

6) the steel caisson (4) is placed on the bottom surface of the main foundation pit and accurately positioned at the position of the small foundation pit, then the soil body is continuously excavated inside the steel caisson (4) manually, the steel caisson (4) is gradually sunk while the soil body is excavated until the lower end of the steel caisson (4) reaches the base elevation of the small foundation pit, so that the small foundation pit is formed, and the steel caisson (4) is used as a protective structure of the small foundation pit;

7) and (3) utilizing the pump truck to pour concrete to seal the bottom of the main foundation pit and the small foundation pit, ensuring that no water gushing and sand gushing phenomenon exists underground, and then pouring other position cushion layers, thereby completing the construction process of the protection system of the whole deep foundation pit (1).

2. The protection construction method for the deep foundation pit of the underground station yard adjacent to the high-speed rail complex environment sludge geology according to claim 1, which is characterized in that: in the step 1), the thickness of the steel casing is 6mm, the height of the steel casing is 250cm, and the inner diameter of the steel casing is 100 cm; the mud box is formed by welding steel plates with the length of 6m, the width of 2m and the thickness of 15 mm; the steel caisson (4) is formed by welding waste pier templates.

3. The protection construction method for the deep foundation pit of the underground station yard adjacent to the high-speed rail complex environment sludge geology according to claim 1, which is characterized in that: in the step 2), the pile diameter of the concrete bored pile (2) is 0.8m, the pile spacing is 1.0m, and the pile length is 6-18 m.

4. The protection construction method for the deep foundation pit of the underground station yard adjacent to the high-speed rail complex environment sludge geology according to claim 1, which is characterized in that: in the step 3), the height of the chiseled pile head is 1 meter; the height of the crown beam is 1 meter, the width of the crown beam is 0.8 meter, the crown beam is of a reinforced concrete structure, the thickness of a protective layer is 40mm, the concrete is C30 concrete, and the main reinforcement is HRB400 phi 22 steel bars.

5. The protection construction method for the deep foundation pit of the underground station yard adjacent to the high-speed rail complex environment sludge geology according to claim 1, which is characterized in that: in the step 4), a steel pipe with the diameter of 50cm is adopted as the transverse support (3); the soil body adopts the excavation mode of segmentation, layering, symmetry, balance, time limit, and the layering thickness is 3.5 meters, and the length is 6 meters.

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