CN118814819A - A construction method for reducing excavation settlement - Google Patents

Abstract

The invention relates to the field of soil improvement, and discloses a construction method for reducing excavation settlement, comprising the following steps: step 1, constructing retaining piles around a foundation pit and close to one side of an existing structure; step 2, excavating a foundation pit, drilling an i-th horizontal anchor hole on the upper part of the retaining pile, the horizontal anchor holes are arranged in sequence from top to bottom, and a hollow anchor rod is inserted into the i-th horizontal anchor hole, a grouting piece is provided at the end of the hollow anchor rod, and a grouting hole is opened on the grouting piece; step 3, sealing the anchor hole, reserving a grouting pipe, and performing the first grouting between the hollow anchor rod and the side wall of the horizontal anchor hole through the grouting pipe; step 4, after the slurry of the first grouting is solidified, pressure grouting is performed from the hollow anchor rod until the slurry pressure reaches the design pressure; step 5, repeating step 2-step 4 until the construction of i hollow anchor rods is completed, so as to reduce the settlement of the existing structure.

Description

A construction method for reducing excavation settlement

Technical Field

The invention relates to the field of excavation, and in particular to a construction method for reducing excavation settlement.

Background Art

Deep foundation pits have the characteristics of wide excavation range and great depth. During the excavation process, they often cause excessive settlement of surrounding buildings, resulting in safety accidents such as building tilting, damage and collapse. At present, the traditional practice is to set retaining piles between the foundation pit retaining structure and the building to play a deformation partition role, which has a better effect when the ground conditions outside the pit are soil layers.

However, foundation pit excavation itself will cause changes in the rock and soil stress structure. For some soils with high water content, the soil on the side of the existing structure will be disturbed during the construction of retaining piles, causing the existing structure to tilt on one side, and then causing the existing structure to sink on one side, further leading to safety accidents.

Summary of the invention

The present invention aims to provide a construction method for reducing excavation settlement and reducing the settlement of built structures.

To achieve the above object, the present invention adopts the following technical solution: a construction method for reducing excavation settlement, comprising the following steps:

Step 1: construct retaining piles around the foundation pit near the existing structure;

Step 2: excavate the foundation pit, drill the i-th horizontal anchor hole on the upper part of the retaining pile, the horizontal anchor holes are arranged in sequence from top to bottom, insert a hollow anchor rod into the i-th horizontal anchor hole, a grouting piece is provided at the end of the hollow anchor rod, and a grouting hole is opened on the grouting piece;

Step 3: seal the anchor hole, reserve a grouting pipe, and perform the first grouting between the hollow anchor rod and the side wall of the horizontal anchor hole through the grouting pipe;

Step 4: After the slurry of the first grouting solidifies, pressure grouting is performed from the hollow anchor until the slurry pressure reaches the design pressure;

Step 5: Repeat steps 2 to 4 until the construction of i hollow anchor rods is completed.

The beneficial effects of this program are:

1. In the prior art, the function of the anchor rod on the retaining pile is usually to provide tension to the retaining pile to prevent the retaining pile from overturning. Therefore, the setting direction of the anchor rod is usually inclined downward, and the anchor rod penetrates into the bedrock to find the fulcrum;

The main function of the central control anchor in this scheme is to strengthen the strength of the soil around the existing structure by grouting, reduce the disturbance of the soil around the existing structure caused by foundation pit excavation, and thus reduce the settlement of the existing structure; i is the total number of horizontal anchor holes set on the retaining piles, and the first horizontal anchor hole is set at the top.

2. By setting the hollow anchor rod horizontally, the grouting slurry can quickly approach the existing structure, so that the soil at the end of the hollow anchor rod and the slurry can combine, thereby strengthening the soil strength and preventing the existing structure from settling.

3. The existing hollow anchor rods are usually provided with multiple grouting holes at different positions, so that the grout can enter the soil from various positions of the hollow anchor rod for bonding and strengthening, thereby strengthening the connection strength between the hollow anchor rod and the soil;

The main purpose of this scheme is to transport the slurry to the area close to the existing structure through the hollow anchor rod, and to strengthen the soil strength in this area to prevent the settlement of the existing structure. Generally speaking, since the grouting position is at the hole mouth of the anchor hole, the closer to the anchor hole, the greater the slurry pressure, and the larger the range of the slurry diffusion in the soil, and the farther away from the anchor hole, the slurry pressure is released, and the smaller the range of the slurry diffusion in the soil. Therefore, the hollow anchor rod in this scheme does not have multiple grouting holes at different positions, and only a grouting hole is set at the end of the central control anchor rod, so that the position where the slurry is injected into the anchor hole is changed to the end of the hollow anchor rod, that is, the position closest to the existing structure. The slurry diffuses in this area first and combines with the soil to strengthen, and then the slurry flows back through the space between the central control anchor rod and the side wall of the anchor hole, and finally fills all the space.

4. After the first grouting, the slurry solidifies and reaches a certain strength to form solidified slurry. Due to the shrinkage of the slurry, some tiny gaps will be formed around the hollow anchor rod. If these gaps are not treated, they may affect the fixing effect and bearing capacity of the hollow anchor rod. At this time, a second pressure grouting can effectively fill these gaps and improve the adhesion between the anchor rod and the surrounding medium. At the same time, the pressure grouting slurry itself has almost no strength at the beginning, but under the pressure of the pressure grouting, it drives the solidified slurry to diffuse in the soil. The solidified slurry can squeeze and disturb the soil, and cooperate with the pressure grouting to spread to a farther range, which increases the range of the strengthened soil, improves the strengthening effect, and thus reduces the settlement of the built structure.

Furthermore, the grouting member and the side wall of the horizontal anchor hole are clearance-matched.

Furthermore, the grouting part is an elliptical hollow sphere, which includes a reflux part, a partition part and a front end part which are connected in sequence. The reflux part is connected to the hollow anchor rod, the outer surface of the reflux part faces the retaining pile, the cross-sectional radius of the partition part is larger than the hollow anchor rod, the partition part and the side wall of the horizontal anchor hole are gap-matched, the outer surface of the front end part faces the deep soil layer, and the grouting holes include a reflux grouting hole and an end grouting hole. The reflux grouting hole is arranged on the reflux part, and the end grouting hole is arranged on the front end part.

Furthermore, the diameter of the reflux grouting hole is less than 5 mm.

Furthermore, the circumferential gap between the grouting member and the horizontal anchor hole is less than 6 mm.

Furthermore, in step 2, when the horizontal anchor hole is drilled to the bedrock position or the edge of the built structure, the drilling is stopped, and the calculation formula for the length of the horizontal anchor hole is:

Li≤Di;

Li ≥ L(i+1);

When D(i+1)>Li-△hi/tanθ, L(i+1)=Li-△hi/tanθ;

Li - the length of the i-th horizontal anchor hole from top to bottom;

Di - horizontal distance from the inlet end of the i-th horizontal anchor hole to the bedrock;

△hi-the height difference between the i-th horizontal anchor hole and the i+1-th horizontal anchor hole;

θ - Angle between the sliding surface and the horizontal plane.

Furthermore, in step 2, a margin is left between the end of the center control anchor rod and the bottom of the anchor hole;

In step 3, the first grouting is performed at a pressure of 0.3-0.5 MPa, and the slurry cannot pass through the reflux grouting hole under the pressure of the first grouting, or the flow rate of the reflux grouting hole is less than the designed flow rate;

In step 4, when the slurry strength of the first grouting reaches more than 5 MPa, push the end of the hollow anchor rod to the bottom of the anchor hole, and then carry out pressure grouting. The design pressure is 4-5 MPa. The slurry passes through the reflux grouting hole and the end grouting hole under the pressure of pressure grouting, and stabilizes the pressure for more than 2 minutes after reaching the design pressure.

Furthermore, a plurality of prestressed anchor cables are provided at the lower part of the retaining pile from top to bottom, and the inclination angles of the prestressed anchor cables increase successively from top to bottom.

This solution also has the following effects:

1. In this scheme, by controlling the aperture of the return grouting hole, it is ensured that the slurry cannot pass through the return grouting hole under the pressure of the first grouting or the flow rate of the return grouting hole is less than the designed flow rate;

At the design flow rate, at the end of the first grouting, the slurry cannot fill the interior of the grouting part, that is, during pressure grouting, the slurry can pass through the center control anchor, the grouting part and the end grouting hole in sequence;

Then, the slurry is directly injected into the bottom of the anchor hole through pressure grouting, where it spreads and combines with the soil.

Specifically, since the partition of the grouting piece and the gap between the side wall of the anchor hole are matched, and when the grouting piece enters the anchor hole, the slag in the anchor hole fills the gap, it is difficult for the slurry to flow back from the gap between the partition and the side wall of the anchor hole; since the slurry has filled the space between the hollow anchor rod and the side wall of the anchor hole during the first grouting, the difficulty of the slurry to flow back from the space between the hollow anchor rod and the side wall of the anchor hole is further increased.

Therefore, the slurry at the bottom of the anchor hole can only diffuse into the soil on one side of the built structure under the action of pressure, thereby strengthening the strength of the soil around the built structure and preventing the built structure from settling.

2. The core purpose of this scheme is to strengthen the soil near the built structure by grouting. Therefore, the diffusion effect of the grouting position in the soil is much higher than that in the rock. Therefore, when the horizontal anchor hole is drilled to the bedrock position, drilling needs to be stopped to ensure the grouting effect.

3. Connect the ends of hollow anchor rods at different heights into a grouting center line to indicate the scope and area of grouting. The soil usually deforms along the sliding surface. The inclination angle of the grouting center line is greater than the inclination angle of the sliding surface. Grouting can be used to simultaneously reinforce the soil above and below the sliding surface, thereby increasing the integrity and strength of the soil and effectively reducing soil deformation.

4. To prevent the slurry in the first grouting from completely blocking the return grouting hole, so that during pressure grouting, the slurry cannot pass through the return grouting hole and cannot cooperate with the solidified slurry to achieve the effect of expanding the grouting range by secondary grouting;

In this scheme, before the first grouting, a margin is left between the end of the center control anchor rod and the bottom of the anchor hole, and before pressure grouting, the end of the hollow anchor rod is pushed to the bottom of the anchor hole to separate the reflux grouting hole and the solidified slurry, thereby unblocking the reflux grouting hole and ensuring that the effect of expanding the grouting range of the secondary grouting (pressure grouting) is achieved.

5. The prestressed anchor cable includes a free section and an anchoring section. The anchoring section is anchored into the hard rock layer in the soil, and the end of the free section away from the anchoring section is the prestressed tensioning end. Since the two prestressed cables of the same anchoring unit are set at the same height, that is, the prestressed tensioning ends are at the same height, the greater the difference in the inclination angles of the two prestressed anchor cables, the farther the distance between the anchoring sections, the smaller the overlap of the anchoring ranges of the two prestressed anchor cables, the larger the total anchoring range of the two prestressed anchor cables, and the better the anchoring effect.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a flow chart of an embodiment;

FIG2 is a schematic diagram of the retaining pile structure of an embodiment;

FIG3 is a schematic diagram of the end of the hollow anchor rod in step 2 of the embodiment;

FIG4 is a schematic diagram of the end of the hollow anchor rod in step three of the embodiment;

FIG. 5 is a schematic diagram of the end of the hollow anchor rod in step 4 of the embodiment.

DETAILED DESCRIPTION

The following is further described in detail through specific implementation methods:

The figure marks in the drawings of the specification include: built structure 1, retaining piles 2, hollow anchor rods 3, grouting parts 4, return flow part 41, partition part 42, front end part 43, return flow grouting hole 44, end grouting hole 45, prestressed anchor cable 5, solidified slurry 6, rock-soil boundary line 71, and sliding surface 72.

Example

The embodiment is basically as shown in FIG1: a construction method for reducing excavation settlement, which is suitable for mountain terrain and the working conditions where there is an existing structure 1 near the foundation pit, as shown in FIG2, the terrain includes bedrock and soil, and the flow chart is shown in FIG1, including the following steps:

Step 1: construct retaining piles 2 around the foundation pit near the side of the built structure 1;

Step 2: excavate the foundation pit and drill the i-th horizontal anchor hole (i=1, 2, 3, 4, 5) on the upper part of the retaining pile 2. The horizontal anchor holes are arranged in sequence from top to bottom, i is the total number of horizontal anchor holes arranged on the retaining pile 2, the first horizontal anchor hole is arranged at the top, and the height difference between the horizontal anchor holes is △h. When the horizontal anchor hole is drilled to the bedrock position or the edge of the built structure 1, the drilling is stopped. In this embodiment, the edge of the built structure 1 is defined as: 5 meters away from the edge of the foundation of the built structure 1, which is usually calculated based on the plan drawings of the built structure 1 and the retaining pile 2.

The calculation formula for the length of the horizontal anchor hole is:

Li≤Di;

Li ≥ L(i+1);

When D(i+1)>Li-△hi/tanθ, L(i+1)=Li-△hi/tanθ;

Li - the length of the i-th horizontal anchor hole from top to bottom;

Di - horizontal distance from the inlet end of the i-th horizontal anchor hole to the bedrock;

△hi-the height difference between the ith horizontal anchor hole and the i+1th horizontal anchor hole. In this embodiment, △hi is always equal to △h;

θ - the angle between the horizontal plane and the sliding surface 72 shown in FIG2 (when the landslide moves, an interface is formed between it and the parent body and slides down along it, which is called the sliding surface 72);

A hollow anchor rod 3 is inserted into the horizontal anchor hole. As shown in FIG3 , a grouting piece 4 is provided at the end of the hollow anchor rod 3. The grouting piece 4 and the side wall of the horizontal anchor hole are gap-matched. The grouting piece 4 is an elliptical hollow sphere. The long diameter of the elliptical hollow sphere is horizontally arranged. The grouting piece 4 includes a reflux portion 41, a partition 42 and a front end portion 43 connected in sequence. Among them, the partition 42 is a part of the elliptical hollow sphere with the largest vertical height. The cross-sectional radius of the partition 42 is larger than the hollow anchor rod 3. The partition 42 and the side wall of the horizontal anchor hole are gap-matched. The circumferential gap between the grouting piece 4 and the horizontal anchor hole is small. The diameter of the reflux portion 41 is 6 mm, and in this embodiment, it is specifically 5 mm. The reflux portion 41 is connected and communicated with the hollow anchor rod 3. The outer surface of the reflux portion 41 faces the retaining pile 2, and the outer surface of the front end portion 43 faces the deep soil layer. The grouting holes include a reflux grouting hole 44 and an end grouting hole 45. The reflux grouting hole 44 is circumferentially opened on the reflux portion 41. The diameter of the reflux grouting hole 44 is 4 mm. The end grouting hole 45 is circumferentially opened on the front end portion 43. A margin is left between the front end portion 43 and the bottom of the anchor hole. In this embodiment, the margin is 100 mm. The margin in the figure is only for reference, and the actual value shall prevail.

Step 3: seal the anchor hole, reserve the inlet at the left end of the hollow anchor rod and a grouting pipe, as shown in FIG4 , perform the first grouting between the hollow anchor rod 3 and the side wall of the horizontal anchor hole through the grouting pipe at a pressure of 0.3-0.5 MPa, and the slurry cannot pass through the return grouting hole 44 under the pressure of the first grouting or the flow rate of the return grouting hole 44 is less than the design flow rate;

Step 4: When the slurry strength of the first grouting reaches more than 5 MPa, as shown in FIG5 , the end of the hollow anchor rod 3 is pushed to the bottom of the anchor hole, that is, the remaining amount in step 2 becomes zero, and the return portion 41 of the grouting member 4 is separated from the solidified slurry 6 formed by the first grouting;

Then, pressure grouting is performed, and the design pressure is 4-5 MPa. The grout passes through the return grouting hole 44 and the end grouting hole 45 under the pressure of pressure grouting. After reaching the design pressure, the pressure is stabilized for more than 2 minutes, and pressure grouting is performed from the hollow anchor rod 3 until the grout pressure reaches the design pressure.

Step 5: Repeat step 2 to step 4 until the construction of five hollow anchor rods 3 is completed;

Step 6: construct a prestressed anchor cable 5 at the bottom of the retaining pile 2;

As shown in FIG2 , a plurality of prestressed anchor cables 5 are provided at the lower part of the retaining pile 2 from top to bottom. The ends of the prestressed anchor cables 5 pass through the rock-soil boundary 71 and enter the bedrock. The left side of the rock-soil boundary 71 is the bedrock, and the right side is the soil. The inclination angle α of the prestressed anchor cables 5 increases from top to bottom.

The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and/or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims (8)

1. The construction method for reducing the excavation settlement amount is characterized by comprising the following steps of:

Step one, constructing a guard pile at one side, close to a built structure, of the periphery of a foundation pit;

step two, excavating a foundation pit, namely drilling an ith horizontal anchor hole in the upper part of the guard pile, wherein the horizontal anchor holes are sequentially arranged from top to bottom, inserting a hollow anchor rod into the ith horizontal anchor hole, arranging a grouting piece at the end part of the hollow anchor rod, and arranging a grouting hole on the grouting piece;

step three, sealing the anchor hole, reserving a grouting pipe, and grouting for the first time between the hollow anchor rod and the side wall of the horizontal anchor hole through the grouting pipe;

Fourthly, performing pressure grouting in the hollow anchor rod after the grout subjected to primary grouting is solidified until the pressure of the grout reaches the design pressure;

And fifthly, repeating the second step and the fourth step until the construction of the i hollow anchor rods is completed.

2. A construction method for reducing excavation settlement as set forth in claim 1, wherein: the grouting piece is in clearance fit with the side wall of the horizontal anchor hole.

3. A construction method for reducing excavation settlement as set forth in claim 2, wherein: the grouting piece is an oval hollow sphere, the grouting piece comprises a backflow part, a separation part and a front end part, the backflow part is connected with a hollow anchor rod, the outer surface of the backflow part faces the guard pile, the radius of the section of the separation part is larger than that of the hollow anchor rod, the separation part and the side wall of a horizontal anchor hole are in clearance fit, the outer surface of the front end part faces the deep side of a soil layer, the grouting hole comprises a backflow grouting hole and an end grouting hole, the backflow grouting hole is formed in the backflow part, and the end grouting hole is formed in the front end part.

4. A construction method for reducing excavation settlement as set forth in claim 3, wherein: the aperture of the reflux grouting hole is smaller than 5mm.

5. A construction method for reducing excavation settlement as set forth in claim 2, wherein: the circumferential clearance between the grouting piece and the horizontal anchor hole is smaller than 6mm.

6. A construction method for reducing excavation settlement as set forth in claim 1, wherein: in the second step, when the horizontal anchor hole drills to the bedrock position or the edge of the built structure, stopping drilling, wherein the calculation formula of the length of the horizontal anchor hole is as follows:

Li≤Di；

Li≥L(i+1)；

when D (i+1) > Li- Δhi/tan θ, L (i+1) =li- Δhi/tan θ;

li-length of the ith horizontal anchor hole from top to bottom;

The horizontal distance from the inlet end of Di-ith horizontal anchor hole to bedrock;

the difference in height between the Delhi-ith horizontal anchor hole and the (i+1) th horizontal anchor hole;

Angle of theta-sliding surface to horizontal.

7. A construction method for reducing excavation settlement as set forth in claim 1, wherein:

In the second step, a margin is reserved between the end part of the central control anchor rod and the bottom of the anchor hole;

in the third step, the first grouting is carried out at the pressure of 0.3-0.5mpa, and the flow rate of the slurry which cannot pass through the reflow grouting holes or the reflow grouting holes under the pressure of the first grouting is smaller than the design flow rate;

And step four, pushing the end part of the hollow anchor rod to the bottom of the anchor hole after the strength of the slurry for the first grouting reaches more than 5mpa, then performing pressure grouting, wherein the design pressure is 4-5mpa, and the slurry passes through the reflow grouting hole and the end part grouting hole under the pressure of the pressure grouting, so that the pressure is stabilized for more than 2 minutes after the design pressure is reached.

8. A construction method for reducing excavation settlement as set forth in claim 1, wherein: the lower part of the guard pile is provided with a plurality of pre-stress anchor cables from top to bottom, and the inclination angles of the pre-stress anchor cables are sequentially increased from top to bottom.