CN-120719670-B - Advanced support construction method for foundation pit excavation of silt and pebble soil layer

CN120719670BCN 120719670 BCN120719670 BCN 120719670BCN-120719670-B

Abstract

The invention discloses a construction method for advanced support of foundation pit excavation of a silt and pebble soil layer, and belongs to the technical field of foundation pit engineering. Aiming at the problems that a soil body is easy to be eroded to form a cavity by hanging a foundation pit on a silt and pebble soil layer, and the foundation pit is easy to be unstable when the gradient is large, the method comprises the steps of firstly constructing an external retaining wall, connecting steel bars and an internal retaining wall steel wire net of the foundation pit, excavating corresponding grooves, synchronously manufacturing supporting structures, using different materials (undisturbed soil/cement soil and concrete of the same level by spraying anchors) when the grooves are backfilled, arranging foam plates/inflatable air bags on the inner side of the retaining wall steel wire net, excavating the foundation pit in layers after the backfilling materials reach 70% of design strength, connecting and fixing anchor rods by using a middle steel wire net after the retaining wall steel wire net is exposed, and spraying the concrete. The invention can improve the collapse resistance of the foundation pit and the structural strength of the sprayed concrete, and effectively improve the supporting safety.

Inventors

LIN NAN
TAO AILIN
YANG WENBIAO

Assignees

中国十七冶集团有限公司

Dates

Publication Date: 20260505
Application Date: 20250815

Claims (4)

1. The advanced support construction method for the excavation of the foundation pit in the silt and pebble soil layer is characterized by comprising the following steps of: S1, measuring lofting and trench excavation, namely lofting a foundation pit excavation edge line through measuring equipment, excavating a rear retaining wall trench (7) and a connecting steel bar trench (5) corresponding to a rear retaining wall (1) at a position where the excavation edge of the foundation pit is outwards 5-10 m and construction is not affected, excavating a retaining wall steel wire mesh trench (4) along the position of the foundation pit excavation edge line, wherein the depth of the rear retaining wall trench (7) is consistent with the foundation pit excavation design depth, the distance between adjacent rear retaining wall trenches (7) is controlled to be 5-10 m, the connecting steel bar trench (5) is perpendicular to the long side of the rear retaining wall trench (7), the distance between the center line of each outermost connecting steel bar trench (5) and the short side of the nearest rear retaining wall trench (7) is not more than 1m, the excavation depth of the connecting steel bar trench (5) is upwards 0.5m, or the length of the retaining wall trench (4) is consistent with the steel wire mesh trench (7) of the same group, or the length of the retaining wall trench (7) is more than the corresponding to the steel wire mesh trench (7) of each end of the rear retaining wall trench (7) and the depth of the retaining wall trench (4); S2, manufacturing steel bars and a steel wire mesh structure, wherein in the groove excavation process, a rear retaining wall steel bar cage (8), connecting steel bars (6) and retaining wall steel wire meshes (2) are synchronously manufactured, the rear retaining wall steel bar cage (8) is rectangular, the retaining wall steel wire meshes (2) are double-layer steel wire meshes, the distance between the two layers of steel wire meshes is 3-5 cm, the top 5cm range of the retaining wall steel wire meshes (2) is inwards bent for 90 degrees to form retaining wall steel wire mesh bearing surfaces (2-1), the bottom 5cm range is inwards bent for 135 degrees to form retaining wall steel wire mesh ends (2-2), and the connecting steel bars (6) are arranged in two layers; s3, reinforcing corners of the foundation pit, namely continuously arranging retaining wall steel wire nets (2) at the inner and outer corners of the foundation pit to form L-shaped retaining wall steel wire nets (2) at the two sides of the L-shaped retaining wall steel wire nets are respectively connected with rear retaining wall steel reinforcement cages (8) corresponding to the corners; S4, hanging the reinforcement structure, namely hanging the manufactured rear retaining wall reinforcement cage (8) and the connecting reinforcement (6) into the corresponding rear retaining wall groove (7) and the connecting reinforcement groove (5) integrally; S5, backfilling the grooves, namely, firstly backfilling the connecting reinforced grooves (5), backfilling by adopting cement soil stirring materials if original soil at the positions of the connecting reinforced grooves (5) is silt soil, backfilling by adopting original soil if the original soil is not silt soil, backfilling the rear retaining wall grooves (7) by adopting cement soil stirring materials, and finally backfilling the retaining wall steel wire mesh grooves (4), placing foam plates or inflatable air bags at the positions of the retaining wall steel wire meshes (2) close to the inner sides of the foundation pits, enabling the retaining wall steel wire meshes (2) to cling to the rear soil, and backfilling the retaining wall steel wire mesh grooves (4) by adopting concrete of the same level as the spraying anchors of the side slopes of the foundation pits; s6, excavating the foundation pit in a layered manner, namely after the backfill material intensities of the rear retaining wall groove (7), the connecting reinforcement groove (5) and the retaining wall steel wire mesh groove (4) reach 70% of the design intensity, excavating the foundation pit in a layered manner along the side line of the foundation pit, stopping mechanical operation when excavating to a position which is 0.3m close to the side line of the foundation pit, adopting manual excavation, adopting mechanical excavation to excavate a blank area which is not provided with the retaining wall steel wire mesh (2) to the side line of the foundation pit, and adopting manual excavation in a range which is 0.5m away from the edge of the retaining wall steel wire mesh (2), and timely removing a foam plate or an inflatable airbag on the inner side of the retaining wall steel wire mesh (2) in the excavation process; S7, hanging the net to connect with the sprayed concrete, namely after the adjacent retaining wall steel wire nets (2) on the same layer are exposed along with excavation, connecting the adjacent retaining wall steel wire nets (2) by using a middle steel wire net (3), wherein the lap joint length of the middle steel wire net (3) and the retaining wall steel wire nets (2) is not less than 1m, the connecting mode is welding or binding, and fixing anchor rods (9) are driven into the bottom of the middle steel wire net (3), so that the middle steel wire nets (3) and the retaining wall steel wire nets (2) are tightly attached to the rear soil body, and the concrete is sprayed to the outer surfaces of the middle steel wire nets (3) and the retaining wall steel wire nets (2) until the concrete thickness reaches the design thickness; And S8, circularly constructing, namely repeating the step S6 and the step S7, and continuously excavating downwards in layers after finishing the construction of other parts of the same layer of the foundation pit, and repeating the construction steps until the foundation pit is excavated to the designed depth.
2. The advanced support construction method for the excavation of the foundation pit of the silt and pebble soil layer, which is characterized in that the length of the rear retaining wall groove (7) is 7 m, and the width of the rear retaining wall groove is 1 m.
3. The advanced support construction method for foundation pit excavation of silt and pebble soil layers is characterized in that the rear retaining wall reinforcement cages (8) and the retaining wall steel wire nets (2) are manufactured in a layering mode, the heights of the rear retaining wall reinforcement cages (8) and the retaining wall steel wire nets (2) of each layer are 2 meters, the rear retaining wall reinforcement cages (8) and the retaining wall steel wire nets (2) are layered and stacked to the slope top height of the foundation pit according to the depth of the foundation pit, the upper and lower adjacent rear retaining wall reinforcement cages (8) are connected into a whole in a binding or welding mode, and retaining wall steel wire net ends (2-2) of the upper retaining wall steel wire nets (2) vertically fall on retaining wall steel wire net bearing surfaces (2-1) of the lower retaining wall steel wire nets (2).
4. The advanced support construction method for the excavation of the foundation pit of the silt and pebble soil layer is characterized in that the connecting steel bars (6) are fixedly connected with the rear retaining wall steel reinforcement cage (8), and the connecting steel bars (6) are fixedly connected with the retaining wall steel wire mesh (2) in a welding mode.

Description

Advanced support construction method for foundation pit excavation of silt and pebble soil layer Technical Field The invention relates to the technical field of foundation pit engineering, in particular to a construction method for advanced support of foundation pit excavation of a silt and pebble soil layer. Background When the hanging net guniting operation is adopted in foundation pit supporting construction, the guniting at the bottom of the excavation operation surface is easy to wash out sludge or pebbles at the bottom of the reinforcing steel bar net, so that the reinforcing steel bar net falls off and is caked at the bottom of the foundation pit, a cavity is easy to form at the bottom of the combined position of the reinforcing steel bar net and the foundation pit, and the quality of foundation pit supporting cannot be effectively ensured. When the foundation pit slope is large due to construction red line limitation and short slope releasing distance of the mucky soil layer, the mucky soil bearing capacity is insufficient, and foundation pit instability is easy to occur. In order to ensure the safety of excavation and support of the foundation pit with silt and pebble soil layers, the invention provides a construction method for advanced support of excavation of the foundation pit with silt and pebble soil layers, and the safety of the support of the foundation pit is improved by implementing advanced protection on the silt and pebble soil layers. Disclosure of Invention The invention aims to provide a construction method for advanced support of foundation pit excavation of a silt and pebble soil layer, which aims to solve the problems in the background technology. The technical scheme of the invention for realizing the purpose is that the advanced support construction method for the excavation of the foundation pit of the silt and pebble soil layer comprises the following steps: S1, measuring lofting and trench excavation, namely lofting a foundation pit excavation edge line through measuring equipment, excavating a rear retaining wall trench and a connecting steel bar trench corresponding to a rear retaining wall at a position which is 5-10 meters outwards from the excavation edge of the foundation pit and does not affect construction, and excavating a retaining wall steel wire mesh trench along the position of the foundation pit excavation edge line, wherein the depth of the rear retaining wall trench is consistent with the design depth of the foundation pit excavation, the distance between adjacent rear retaining wall trenches is controlled to be 5-10 meters, the connecting steel bar trench is perpendicular to the long side of the rear retaining wall trench, the distance between the adjacent connecting steel bar trenches is 2+/-0.3 meter, the horizontal distance between the center line of each outermost connecting steel bar trench and the short side of the nearest rear retaining wall trench is not more than 1 meter, the excavation depth of the connecting steel bar trench is 0.5 meter upwards from the design bottom elevation of the foundation pit excavation, and the width of the steel wire mesh trench is 0.5 meter, the length of the retaining wall trench is consistent with the rear retaining wall trench of the same group, or the length of the steel wire mesh trench is 1 meter and remains symmetric, and the depth of the retaining wall trench is consistent with the rear retaining wall trench; S2, manufacturing a steel bar and a steel wire mesh structure, namely synchronously manufacturing a rear retaining wall steel bar cage, connecting steel bars and retaining wall steel wire meshes in the groove excavation process, wherein the rear retaining wall steel bar cage is rectangular, the retaining wall steel wire meshes are double-layer steel wire meshes, the distance between the two layers of steel wire meshes is 3-5 cm, the top 5cm range of the retaining wall steel wire meshes is inwards bent for 90 degrees to form retaining wall steel wire mesh bearing surfaces, and the bottom 5cm range is inwards bent for 135 degrees to form retaining wall steel wire mesh ends; S3, reinforcing corners of the foundation pit, namely continuously arranging retaining wall steel wire nets at the yin and yang corners of the foundation pit to form L-shaped retaining wall steel wire nets at the two sides of the L-shaped retaining wall steel wire nets, and connecting the retaining wall steel wire nets with rear retaining wall steel bar cages corresponding to the corners respectively; s4, hanging the reinforcement structure, namely hanging the manufactured rear retaining wall reinforcement cage and the connecting reinforcement into the corresponding rear retaining wall groove and the connecting reinforcement groove; S5, backfilling the connecting reinforced grooves, wherein if the original soil at the position of the connecting reinforced grooves is silt soil, backfilling by adopting cement soil stirring materials, if the or