CN112921998B - Cofferdam enclosure slope-making foundation pit excavation method suitable for deep sludge covering layer - Google Patents
Cofferdam enclosure slope-making foundation pit excavation method suitable for deep sludge covering layer Download PDFInfo
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- CN112921998B CN112921998B CN202110179171.5A CN202110179171A CN112921998B CN 112921998 B CN112921998 B CN 112921998B CN 202110179171 A CN202110179171 A CN 202110179171A CN 112921998 B CN112921998 B CN 112921998B
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- 238000009412 basement excavation Methods 0.000 title abstract 4
- 239000010802 sludge Substances 0.000 title abstract 2
- 238000010276 construction Methods 0.000 abstract 8
- 238000005192 partition Methods 0.000 abstract 8
- 230000002787 reinforcement Effects 0.000 abstract 2
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D19/00—Keeping dry foundation sites or other areas in the ground
- E02D19/02—Restraining of open water
- E02D19/04—Restraining of open water by coffer-dams, e.g. made of sheet piles
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D15/00—Handling building or like materials for hydraulic engineering or foundations
- E02D15/08—Sinking workpieces into water or soil inasmuch as not provided for elsewhere
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
- E02D5/22—Piles
- E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
- E02D5/46—Concrete or concrete-like piles cast in position ; Apparatus for making same making in situ by forcing bonding agents into gravel fillings or the soil
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02F—DREDGING; SOIL-SHIFTING
- E02F5/00—Dredgers or soil-shifting machines for special purposes
- E02F5/28—Dredgers or soil-shifting machines for special purposes for cleaning watercourses or other ways
Abstract
The invention discloses a cofferdam enclosure sloping foundation pit excavation method suitable for a deep sludge covering layer, which is characterized in that N partitions are segmented and divided along the length direction of a cofferdam body 1 between two cofferdam bodies 1, and the method comprises the following steps: step a, when stratum excavation construction of a (K-3) th partition is carried out, simultaneously starting dredging construction of the (K-2) th partition, ballast replacement back pressure construction of the (K-1) th partition and reinforcement body construction of the K th partition; and step b, after the step a is finished, simultaneously starting and implementing stratum excavation construction of the (K-2) th partition, dredging construction of the (K-1) th partition, ballast replacement back pressure construction of the K th partition and reinforcement body construction of the (K + 1) th partition.
Description
Technical Field
The invention relates to a construction method of a foundation pit in a water area, in particular to a cofferdam enclosure slope-making foundation pit excavation method suitable for a deep sludge covering layer.
Background
The earth-rock cofferdam is commonly used for projects such as water conservancy projects, underwater tunnels and the like, and the stability and the seepage-proofing performance of the earth-rock cofferdam are of great importance to the safety of the projects. The cofferdam is usually built on a deep covering layer of a riverbed, and the earth-rock cofferdam is built on the deep covering layer, so that the requirements on the anti-seepage system and the stability of a weir body of the cofferdam are high. Factors such as seepage damage of cofferdam foundation, too large subsidence or sliding can cause serious damage to the weir body, and serious threats are caused to construction safety and the quality of a main building body. The water area stratum has a deep silt overburden, the cofferdam construction is difficult to clean, and a lot of projects directly apply the earth-rock cofferdam structure on the deep silt overburden. The method brings great problems to the excavation of the deep foundation pit in the cofferdam, and the problem that how to ensure that the excavation of the deep foundation pit cannot cause the damage of the cofferdam on a deep silt stratum is urgently needed to be solved.
Some technical solutions to solve the problems are proposed in the prior art, such as a sludge riverbed combined cofferdam and a construction method thereof disclosed in chinese patent publication No. CN108035368A, and a composite temporary water retaining structure and a construction method combining a continuous wall and an earth-rock cofferdam in TRD method disclosed in publication No. CN 111501681A.
The construction method of the sludge riverbed combined cofferdam is disclosed in the publication No. CN108035368A, and the purposes of consolidation and seepage prevention can be achieved by adopting high-pressure jet grouting pile equipment to construct a first seepage-proof wall and a second seepage-proof wall. Although the method can improve the overall stability of the cofferdam, when the deep foundation pit is excavated in the cofferdam, the inner side of the cofferdam body (1) is unloaded, so that the cofferdam body (1) is greatly deformed inwards, the impervious wall is easily deformed and cracked greatly, and the integrity of the impervious wall is easily influenced.
Compared with other cofferdam structure forms, the earth-rock cofferdam structure provided by the publication number CN111501681A has advantages in construction period, investment and seepage-proofing effect, but the cofferdam is easy to deform greatly in the excavation process of a foundation pit in the cofferdam, and an internal seepage-proofing wall is damaged. Therefore, the method for excavating the inner slope foundation pit in the cofferdam of the thick silt stratum is convenient to construct and is an urgent problem to be solved in the similar cofferdam engineering.
Disclosure of Invention
The invention aims to: the cofferdam enclosure slope-making foundation pit excavation method suitable for the deep sludge covering layer is provided, the problems of deformation, settlement, lateral movement and the like of a cofferdam body after foundation pit excavation can be effectively solved, and the construction cost is reduced.
In order to achieve the purpose, the invention adopts the following technical scheme:
a cofferdam enclosure slope-making foundation pit excavation method suitable for a deep sludge covering layer is characterized in that N partitions are segmented and divided along the length direction of cofferdam bodies between two cofferdam bodies, and the method comprises the following steps:
step a, when stratum excavation construction of a (K-3) th partition is carried out, simultaneously starting dredging construction of the (K-2) th partition, ballast replacement back pressure construction of the (K-1) th partition and reinforcement body construction of the K th partition;
b, after the step a is finished, simultaneously starting and implementing stratum excavation construction of a (K-2) th partition, dredging construction of a (K-1) th partition, ballast replacement back pressure construction of the K th partition and reinforcement body construction of a (K + 1) th partition;
constructing a reinforcing body; carrying out stone throwing and silt squeezing at the toe of the inner sides of the two cofferdams of any partition to provide an operation surface for the construction of the high-pressure jet grouting pile, then carrying out the construction of the high-pressure jet grouting pile to form a reinforcement body of the partition at the toe, and constructing a primary drainage ditch after the reinforcement body of the partition has certain strength; the grain diameter of the stone slag adopted for the stone throwing and the silt squeezing is not more than 30cm, and the thickness is 20-30 cm;
and (3) filling and back pressure construction: the depth of the back pressure construction for replacing and filling any subarea slag is not less than the thickness of the sludge layer, and the width of the back pressure construction is not less than 0.5 time of the width of the cofferdam;
dredging construction: after the desilting construction is finished, finishing, driving a first anchor and spraying slurry on the stacking slope after the ballast replacement back-pressure construction to form a ballast back-pressure slope of the subarea;
and (3) excavating and constructing the stratum: and excavating the lower stratum of any subarea according to the design of the foundation pit, and correcting, driving a second anchor and spraying the slurry to the foundation pit slope in the underground excavation process to form the rock slope.
Preferably, in the construction of the reinforcing body in any partition, the width of the stone throwing and silt squeezing and the construction of the high-pressure jet grouting pile is not less than the thickness of the silt layer, and the depth of the construction of the high-pressure jet grouting pile is not less than the thickness of the silt layer.
Preferably, the pile diameter of the high-pressure jet grouting pile is not less than 800 mm.
As a preferable scheme, the stacking slopes of any two subareas after the filling and back pressure replacement construction are the same, and the range of the stacking slopes is 0.7: 1-1.5: 1.
As a preferred scheme, a secondary drainage ditch is built in any partition before the stratum excavation construction is carried out.
Preferably, the ballast replacement back pressure construction of any subarea is carried out after the strength of the formed reinforcing body of the subarea reaches 2 MPa.
Preferably, the first anchor depth is no less than the width of the ballast refill.
As a preferable scheme, when K =1, only the reinforcing body construction of the 1 st subarea is carried out; when K =2, after the reinforcing body construction of the 1 st subarea is finished, the reinforcing body construction of the 2 nd subarea and the stone slag replacement back pressure construction of the 1 st subarea are started; and when K =3, after the construction of the reinforcing body in the 2 nd partition is finished, starting the construction of the reinforcing body in the 3 rd partition, the construction of the ballast replacement back pressure in the 2 nd partition and the dredging construction in the 1 st partition.
As a preferable scheme, when K = N, after the construction of the reinforcing body of the N-1 th partition is finished, the construction of the reinforcing body of the N-th partition, the construction of the ballast replacement back pressure of the (N-1) th partition, the construction of the dredging of the (N-2) th partition and the construction of the stratum excavation of the (N-3) th partition are started;
after the construction of the reinforcing body (2) of the Nth partition is finished, the stone slag replacement back pressure construction of the Nth partition, the dredging construction of the (N-1) th partition and the stratum excavation construction of the (N-2) th partition are started;
after the ballast replacement back pressure construction of the Nth partition is finished, starting the stratum excavation construction of the (N-1) th partition and the dredging construction of the Nth partition;
and after the desilting construction of the Nth partition is finished, starting the stratum excavation construction of the Nth partition.
As a preferable scheme, the ballast adopted in the 1 st zone and the 2 nd zone needs to be transported outwards, and when K is more than or equal to 3, the ballast used in the K zone is filled with ballast material dug by the K-2 nd zone stratum.
The invention has the beneficial effects that:
the cofferdam enclosure slope-making foundation pit excavation method suitable for the deep sludge covering layer, disclosed by the invention, comprises the following steps of firstly, limiting deformation of a cofferdam body during excavation and unloading of surface sludge through a reinforcing body stable slope foot formed by riprap silt squeezing and high-pressure jet grouting piles, and avoiding large settlement and lateral displacement of the cofferdam; the foundation pit is excavated in a layered and segmented manner, a silt layer at the weir foot is replaced and filled with stone slag, the load and the anti-sliding force at the weir foot are increased, and the settlement and the lateral displacement of a cofferdam body caused by excavation unloading of the foundation pit are reduced; cleaning the sludge layer on the inner side by sections; finally, the stratum at the lower part of the sludge layer is excavated, and the excavated partial ballast is used for ballast exchange and back pressure of the weir foot, so that the cost can be reduced to a great extent.
Drawings
FIG. 1 is a schematic diagram of a cross section structure of deep foundation pit excavation according to the present invention;
FIG. 2 is a partial schematic view of FIG. 1 of the present invention;
fig. 3 is a schematic view of the layered excavation of fig. 1 of the present invention.
In the figure: 1. the cofferdam comprises a cofferdam body, 2 parts by weight, a reinforcing body, 2-1 parts by weight, a primary drainage ditch, 3 parts by weight, a ballast counter-pressure slope, 3-1 parts by weight, first anchoring bolts, 4 parts by weight, a rock slope, 4-1 parts by weight, a secondary drainage ditch, 4-2 parts by weight and second anchoring bolts.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
Referring to fig. 1-2, a cofferdam enclosure sloping foundation pit excavation method suitable for a deep sludge covering layer, which is to divide N partitions in a segmented manner along the length direction of a cofferdam body 1 between two cofferdam bodies 1, comprises the following steps:
step a, when stratum excavation construction of a K-3 th partition is carried out, dredging construction of a K-2 th partition, stone slag replacement back pressure construction of a K-1 th partition and reinforcement body construction of the K-3 th partition are started at the same time;
b, after the step a is finished, simultaneously starting and implementing stratum excavation construction of a (K-2) th partition, dredging construction of a K-1 th partition, stone slag replacement back pressure construction of the K-1 th partition and reinforcement body construction of a K +1 th partition;
constructing a reinforcing body; carrying out stone throwing and silt squeezing at the toe of the inner sides of the two cofferdams 1 of any partition to provide an operation surface for the construction of the high-pressure jet grouting pile, then carrying out the construction of the high-pressure jet grouting pile to form a reinforcing body 2 of the partition at the toe of the slope, and constructing a primary drainage ditch 2-1 after the reinforcing body 2 of the partition has certain strength; the grain diameter of the stone slag adopted for the stone throwing and the silt squeezing is not more than 30cm, and the thickness is 20-30 cm;
and (3) filling and back pressure construction: the depth of the back pressure construction of replacing and filling any subarea slag is not less than the thickness of the sludge layer, and the width of the back pressure construction is not less than 0.5 time of the width of the cofferdam 1;
dredging construction: after the desilting construction is finished, finishing, driving a first anchor 3-1 and spraying slurry on the stacking slope after the ballast replacement back pressure construction to form a ballast back pressure slope 3 of the subarea;
and (3) excavating and constructing the stratum: and (3) excavating the lower stratum of any partition according to the design of the foundation pit, and correcting, driving a second anchor (4-2) and spraying slurry to the foundation pit slope in the underground excavation process to form a rock slope 4.
In the construction of the reinforcing body in any subarea, the width of the construction of the riprap silt squeezing and the high-pressure jet grouting pile is not less than the thickness of the silt layer, and the depth of the construction of the high-pressure jet grouting pile is not less than the thickness of the silt layer.
The pile diameter of the high-pressure jet grouting pile is not less than phi 800 mm.
And after the replacement, filling and back pressure construction is carried out on any two subareas, the stacking gradient is the same, and the range of the stacking gradient is 0.7: 1-1.5: 1.
And (4) building a secondary drainage ditch 4-1 before the stratum excavation construction is carried out in any partition.
The ballast replacement back pressure construction of any one subarea is carried out after the strength of the formed reinforced body 2 of the subarea reaches 2 MPa.
The depth of the first anchor bolts 3-1 is not less than the width of the ballast replacement body.
Aiming at a specific excavation method, only constructing a reinforcing body in a 1 st subarea when K = 1; when K =2, after the construction of the reinforcing body in the 1 st subarea is finished, the construction of the reinforcing body in the 2 nd subarea and the construction of the ballast changing, filling and back pressure in the 1 st subarea are started, and the ballast used in the construction of the ballast changing, filling and back pressure in the 1 st subarea is transported from the outside; and when K =3, after the construction of the reinforcing body in the 2 nd subarea is finished, the construction of the reinforcing body in the 3 rd subarea, the construction of the ballast changing and filling back pressure in the 2 nd subarea and the construction of the dredging in the 1 st subarea are started, and the ballast used in the construction of the ballast changing and filling back pressure in the 2 nd subarea is transported from the outside.
Aiming at a specific excavation method, when K = N, after the construction of the reinforcing body of the (N-1) th partition is finished, the construction of the reinforcing body of the (N-1) th partition, the construction of the ballast replacement back pressure of the (N-1) th partition, the construction of the dredging of the (N-2) th partition and the construction of the stratum excavation of the (N-3) th partition are started;
after the construction of the reinforcing body (2) of the Nth partition is finished, the stone slag replacement back pressure construction of the Nth partition, the dredging construction of the (N-1) th partition and the stratum excavation construction of the (N-2) th partition are started;
after the ballast replacement back pressure construction of the Nth partition is finished, starting the stratum excavation construction of the (N-1) th partition and the dredging construction of the Nth partition;
and after the desilting construction of the Nth partition is finished, starting the stratum excavation construction of the Nth partition.
Aiming at a specific excavation method, the ballast adopted by the 1 st partition and the 2 nd partition needs to be transported outwards, and when K is more than or equal to 3, the ballast used by the K-th partition is changed, filled and back-pressed to construct by utilizing the ballast material excavated by the K-2 nd partition.
In the embodiment 1, 5 subareas are firstly divided into two cofferdam bodies 1, and only the reinforcing body construction of the 1 st subarea is firstly carried out;
after the 1 st subarea reinforcing body construction is finished, starting the 2 nd subarea reinforcing body construction and the 1 st subarea ballast replacement back pressure construction;
after the construction of the reinforcing body in the 2 nd partition is finished, starting the construction of the reinforcing body in the 3 rd partition, the construction of the ballast replacement back pressure in the 2 nd partition and the dredging construction in the 1 st partition;
after the construction of the reinforcing body of the 3 rd partition is finished, starting the construction of the reinforcing body of the 4 th partition, the construction of the 3 rd partition stone slag replacement back pressure, the construction of the 2 nd partition desilting and the construction of the 1 st partition stratum excavation;
after the construction of the reinforcing body in the 4 th partition is finished, starting the construction of the reinforcing body in the 5 th partition, the construction of the ballast replacement back pressure in the 4 th partition, the dredging construction in the 3 rd partition and the stratum excavation construction in the 2 nd partition;
after the construction of the reinforcing body of the 5 th partition is finished, the construction of stone ballast replacement back pressure of the 5 th partition, the construction of dredging of the 4 th partition and the construction of stratum excavation of the 3 rd partition are started;
after the rock ballast replacement back pressure construction of the 5 th partition is finished, the dredging construction of the 5 th partition and the stratum excavation construction of the 4 th partition are started;
and after the desilting construction of the 5 th partition is finished, carrying out stratum excavation construction of the 5 th partition.
Notably, to achieve flow overlap; and (3) generally starting and ending the stratum excavation construction of the (K-2) th partition, the dredging construction of the (K-1) th partition, the ballast replacement back pressure construction of the K th partition and the reinforcement body construction of the (K + 1) th partition at the same time. The method is finished at the same time, and the maintenance and transition time required by flowing water lapping is included.
It should be noted that in this embodiment, the ballast used in the 1 st partition and the 2 nd partition needs to be transported outside, and when K is greater than or equal to 3, the ballast used in the K-th partition is changed and filled with ballast material excavated from the stratum of the K-2 nd partition, so as to reduce cost and improve construction efficiency.
In this embodiment, the grain size of the stone residue used for the stone throwing and pressing should be not more than 30cm, and the thickness should be 20-30cm, specifically, the grain size grading is that the mass ratio of the grain size is less than 5% and less than 5% for less than 5cm, the mass ratio of the grain size is 5-10cm and less than 10%, the mass ratio of the grain size is 10-20cm and more than 65%, the mass ratio of the grain size is 20-25cm and less than 15%, and the mass ratio of the grain size is 25-30cm and less than 5%; the depth of the replacement, filling and back pressure construction of any subarea slag is not less than the thickness of the sludge layer, and the width of the construction is 0.6 times of the width of the cofferdam 1; the pile diameter of the high-pressure jet grouting pile is phi 800-; the ballast replacement back pressure construction of any one subarea is carried out after the strength of the formed reinforced body 2 of the subarea reaches 2 MPa.
In the case of the example 2, the following examples are given,
firstly 10 subareas are divided by two cofferdams 1,
step a, when stratum excavation construction of a (K-3) th partition is carried out, simultaneously starting dredging construction of the (K-2) th partition, ballast replacement back pressure construction of the (K-1) th partition and reinforcement body construction of the K th partition;
b, after the step a is finished, simultaneously starting and implementing stratum excavation construction of a (K-2) th partition, dredging construction of a (K-1) th partition, ballast replacement back pressure construction of the K th partition and reinforcement body construction of a (K + 1) th partition;
when K =1, only reinforcing body construction of the 1 st subarea is carried out; when K =2, after the reinforcing body construction of the 1 st subarea is finished, the reinforcing body construction of the 2 nd subarea and the stone slag replacement back pressure construction of the 1 st subarea are started; and when K =3, after the construction of the reinforcing body in the 2 nd partition is finished, starting the construction of the reinforcing body in the 3 rd partition, the construction of the ballast replacement back pressure in the 2 nd partition and the dredging construction in the 1 st partition.
When K =10, after the construction of the reinforcing body in the 9 th partition is finished, starting the construction of the reinforcing body in the 10 th partition, the construction of the ballast replacement back pressure in the 9 th partition, the construction of the dredging in the 8 th partition and the construction of the stratum excavation in the 7 th partition;
after the construction of the reinforcing body 2 in the 10 th partition is finished, the stone ballast replacement back pressure construction of the 10 th partition, the dredging construction of the 9 th partition and the stratum excavation construction of the 8 th partition are started;
after the ballast replacement back pressure construction of the 10 th partition is finished, starting the stratum excavation construction of the 9 th partition and the desilting construction of the 9 th partition;
and after the desilting construction of the 10 th partition is finished, starting the stratum excavation construction of the 10 th partition.
As a preferable scheme, when K is more than or equal to 3, the ballast used in the K-th subarea rock ballast replacement back pressure construction utilizes the ballast material excavated by the K-2 th subarea stratum.
In the embodiment, the grain size of the stone slag used for the stone throwing and the silt squeezing is not more than 30cm, and the thickness is 20-30cm, specifically, the grain size grading is that the mass ratio of the grain size is less than 10cm and less than 15%, the mass ratio of the grain size is more than 75% between 10cm and 20cm, and the mass ratio of the grain size is less than 15% between 20cm and 30 cm; the depth of the back pressure construction of replacing and filling any partition slag is not less than the thickness of the sludge layer, and the width of the back pressure construction is 0.7 times of the width distance of the cofferdam body 1; the pile diameter of the high-pressure jet grouting pile is phi 900 plus 1000mm, the stacking gradient of any two partitions subjected to the replacement filling back-pressure construction is the same, and the stacking gradient range is 1: 1; the ballast replacement back pressure construction of any one subarea is carried out after the strength of the formed reinforced body 2 of the subarea reaches 2 MPa.
In the present invention and all embodiments, K is a reference number of the kth partition which is obtained by segmenting and dividing N partitions along the length direction of the cofferdam 1 between the two cofferdams 1.
This cofferdam enclosure slope-making foundation pit excavation method suitable for deep silt overburden has a great deal of advantages, for example, first, foundation ditch excavation is little to the cofferdam influence, can guarantee the stability of cofferdam body: the silt layer at the weir foot is reinforced through the high-pressure jet grouting pile and the ballast replacement back pressure, so that the soil body is reinforced, the load at the weir foot can be improved, the excavation unloading influence is reduced, and the deformation of the cofferdam body can be effectively controlled. Secondly, the resources are fully utilized, and the cost is saved: the stone slag dug out by the foundation pit is utilized for replacing and filling the sludge, the outsourcing of materials is reduced, the transport distance is short, and the engineering cost is greatly reduced. Thirdly, the construction is simple, the mechanical investment is less, the operation is easy, and the operation on a deep sludge layer is convenient. Fourthly, the operation is performed in sections, and all the procedures can be performed in parallel and continuously, so that the construction period is shortened.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (10)
1. The utility model provides a cofferdam enclosure slope-making foundation pit excavation method suitable for deep silt overburden, carries out segmentation with cofferdam body (1) length direction and divides N subregion along two cofferdam bodies (1), its characterized in that includes following step:
step a, when stratum excavation construction of a (K-3) th partition is carried out, simultaneously starting dredging construction of the (K-2) th partition, ballast replacement back pressure construction of the (K-1) th partition and reinforcement body construction of the K th partition;
b, after the step a is finished, simultaneously starting and implementing stratum excavation construction of a (K-2) th partition, dredging construction of a (K-1) th partition, ballast replacement back pressure construction of the K th partition and reinforcement body construction of a (K + 1) th partition;
constructing a reinforcing body; carrying out stone throwing and silt squeezing at the toe of the inner sides of the two cofferdams (1) of any partition to provide an operation surface for the construction of the high-pressure jet grouting pile, then carrying out the construction of the high-pressure jet grouting pile to form a reinforcing body (2) of the partition at the toe of the slope, and constructing a primary drainage ditch (2-1) after the reinforcing body (2) of the partition has certain strength; the grain diameter of the stone slag adopted for the stone throwing and the silt squeezing is not more than 30cm, and the thickness is 20-30 cm;
and (3) filling and back pressure construction: the depth of the back pressure construction for replacing and filling any subarea slag is not less than the thickness of the sludge layer, and the width of the back pressure construction is not less than 0.5 time of the width of the cofferdam (1);
dredging construction: after the desilting construction is finished, finishing, driving a first anchor (3-1) and spraying slurry on the stacking slope after the ballast replacement back-pressure construction to form a ballast back-pressure slope (3) of the subarea;
and (3) excavating and constructing the stratum: and (3) excavating the lower stratum of any partition according to the design of the foundation pit, and correcting, driving a second anchor (4-2) and spraying slurry to the foundation pit slope in the excavation process to form the rock slope (4).
2. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to claim 1, which is characterized in that: in the construction of the reinforcing body in any subarea, the width of the construction of the riprap silt squeezing and the high-pressure jet grouting pile is not less than the thickness of the silt layer, and the depth of the construction of the high-pressure jet grouting pile is not less than the thickness of the silt layer.
3. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to claim 2, which is characterized in that: the pile diameter of the high-pressure jet grouting pile is not less than phi 800 mm.
4. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to claim 1, which is characterized in that: and after the replacement, filling and back pressure construction is carried out on any two subareas, the stacking gradient is the same, and the range of the stacking gradient is 0.7: 1-1.5: 1.
5. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to claim 1, which is characterized in that: and (4-1) constructing a secondary drainage ditch before the stratum excavation construction is carried out in any partition.
6. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to claim 1, which is characterized in that: the ballast replacement back pressure construction of any subarea is carried out after the strength of the formed reinforced body (2) of the subarea reaches 2 MPa.
7. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to claim 1, which is characterized in that: the depth of the first anchor bolt (3-1) is not less than the width of the ballast replacement body.
8. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to any one of claims 1 to 7, which is characterized in that: when K =1, only reinforcing body construction of the 1 st subarea is carried out; when K =2, after the reinforcing body construction of the 1 st subarea is finished, the reinforcing body construction of the 2 nd subarea and the stone slag replacement back pressure construction of the 1 st subarea are started; and when K =3, after the construction of the reinforcing body in the 2 nd partition is finished, starting the construction of the reinforcing body in the 3 rd partition, the construction of the ballast replacement back pressure in the 2 nd partition and the dredging construction in the 1 st partition.
9. The method for excavating cofferdam enclosure sloping foundation pit suitable for the deep sludge covering layer according to any one of claims 1 to 7, which is characterized in that: when K = N, after the construction of the reinforcing body of the (N-1) th subarea is finished, starting the construction of the reinforcing body of the (N) th subarea, the construction of the ballast replacement back pressure of the (N-1) th subarea, the dredging construction of the (N-2) th subarea and the stratum excavation construction of the (N-3) th subarea;
after the construction of the reinforcing body (2) of the Nth partition is finished, the stone slag replacement back pressure construction of the Nth partition, the dredging construction of the (N-1) th partition and the stratum excavation construction of the (N-2) th partition are started;
after the ballast replacement back pressure construction of the Nth partition is finished, starting the stratum excavation construction of the (N-1) th partition and the dredging construction of the Nth partition;
and after the desilting construction of the Nth partition is finished, starting the stratum excavation construction of the Nth partition.
10. The method for excavating cofferdam enclosure sloping foundation pit applicable to the deep sludge coverage as claimed in any one of claims 1-7, wherein when K is greater than or equal to 3, the ballast used in the K-th sub-area ballast replacement back-pressure construction utilizes the ballast material excavated from the K-2-th sub-area stratum.
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