阅读说明：本技术 塌陷性土质深基坑支护方法 (Support method for collapse soil deep foundation pit ) 是由 杨景伟 李春波 敖及辉 于 2021-09-18 设计创作，主要内容包括：本发明公开了一种塌陷性土质深基坑支护方法,包括如下步骤：沿基坑设计位置的边线设置多个钻孔灌注桩；在基坑四周等间距设置多个水泥搅拌桩；采用高压旋喷工艺设置锚索,在锚索锚入前在钻杆的钻头处固定有一锚索组件,在钻杆钻进时,所述锚索组件的锚索随之一起锚入土层内；所述锚索组件包括两个间隔设置且中部带有穿孔的锚固盘以及至少两根头部固定安装在两锚固盘之间的锚索,在每根锚索上均套有一PE软管,在每个锚索的头部均安装有一移除式锚具,所述移除式锚具固定在两锚固盘之间,在外力作用下,所述锚索能够从移除式锚具内脱落；张拉锚索；开挖土方；锚索回收。(The invention discloses a support method for a collapse soil deep foundation pit, which comprises the following steps: arranging a plurality of cast-in-situ bored piles along the side line of the designed position of the foundation pit; arranging a plurality of cement mixing piles at equal intervals around the foundation pit; an anchor cable is arranged by adopting a high-pressure rotary spraying process, an anchor cable component is fixed at a drill bit of the drill rod before the anchor cable is anchored, and the anchor cable of the anchor cable component is anchored into the soil layer along with the anchor cable when the drill rod drills; the anchor cable assembly comprises two anchor disks which are arranged at intervals and provided with through holes in the middle and at least two anchor cables of which the heads are fixedly arranged between the two anchor disks, a PE hose is sleeved on each anchor cable, a removable anchor is arranged at the head of each anchor cable and fixed between the two anchor disks, and the anchor cables can fall off from the removable anchors under the action of external force; tensioning the anchor cable; excavating earthwork; and (6) recovering the anchor cable.)

1. A support method for a collapse soil deep foundation pit is characterized by comprising the following steps: s1, site investigation; s2, arranging a plurality of cast-in-situ bored piles (2) along the side line of the designed position of the foundation pit; s3, arranging a plurality of cement mixing piles (1) at equal intervals around the foundation pit, wherein the cement mixing piles (1) form a closed waterproof curtain around the foundation pit; s4, arranging an anchor cable at a soil layer between two adjacent cast-in-situ bored piles (2) by adopting a high-pressure jet grouting process, determining the position of an anchor hole before the anchor cable is anchored, then arranging a drilling machine, adjusting the angle of a drill rod, fixing an anchor cable assembly (4) at a drill bit of the drill rod, and anchoring the anchor cable (43) of the anchor cable assembly (4) into the soil layer along with the drill rod when the drill rod is drilled; the anchor cable assembly (4) comprises two anchor disks (41) which are arranged at intervals and provided with through holes in the middle and at least two anchor cables (43) of which the heads are fixedly installed between the two anchor disks (41), a PE hose (42) is sleeved on each anchor cable (43), a removable anchor (44) is installed at the head of each anchor cable (43), the removable anchor (44) is fixed between the two anchor disks (41), and the anchor cables (43) can fall off from the removable anchor (44) under the action of external force; s5, pouring a crown beam (3) on the cast-in-situ bored pile (2); s6, tensioning the arranged anchor cable (43); s7, excavating earthwork to form a foundation pit, and pouring a concrete cushion layer in the foundation pit; and S8, when earth is backfilled to the anchor head, rotating and pulling each anchor cable to enable the anchor cable to fall off from the removable anchor device, so that the anchor cable is recovered.

2. The method for supporting the deep foundation pit with the collapse soil as claimed in claim 1, wherein a reinforcing cage (46) is further welded and fixed on the anchoring disc (41) close to the anchoring section, the reinforcing cage (46) comprises a plurality of vertical ribs vertically fixed on the anchoring disc (41) and spiral ribs fixed outside the vertical ribs, and each anchor cable penetrates through the reinforcing cage (46) and is fixed on the reinforcing cage through iron wires; and the drill rod penetrates through the reinforcing cage and then is sleeved on the middle through holes of the two anchoring discs.

3. A method for supporting a deep foundation pit in a collapsible soil according to claim 1 or 2, wherein a plurality of screws (45) are further fixed between the two anchor disks (41) of each anchor cable assembly (4).

4. The method for supporting a deep foundation pit with collapsible soil according to claim 1, wherein the drill rod is a hollow spiral drill pipe, a nozzle is arranged at the bottom of the drill bit, two nozzles are arranged on the side wing, the cement slurry is filtered in the stirring tank, then introduced into the drill rod by a high-pressure pump through a high-pressure guide pipe and sprayed outwards from each nozzle of the drill bit, and the soil body on the peripheral side is synchronously cut in the cement slurry spraying process; the drill bit is gradually pushed forward under the driving of power until reaching the designed depth and diameter to form an anchor body.

5. The support method for the collapsed soil deep foundation pit according to claim 4, wherein the cement paste is prepared by mixing and stirring ordinary portland cement and water, the doping amount of the anchor body cement is 20%, and the water cement ratio is 0.5-0.7.

6. The support method for the collapsed soil deep foundation pit according to claim 4, wherein the speed is increased by no more than 30cm/min, the rotation speed is no less than 20 revolutions per minute, and the slurry flow is no less than 50L/min during the construction of the anchor body; the pressure of anchor body jet grouting stirring should be 20Mpa to 25 Mpa.

7. A method for supporting a deep foundation pit with collapsible soil according to claim 1, 2, 4, 5 or 6, wherein the excavation of earth is carried out in layers, the thickness of each layer is not more than 2m, and the prestressed rotary-spraying anchor cable on the upper layer has to be maintained for more than 7 days and tensioned and locked when the soil on the lower layer is excavated.

8. The method for supporting a deep foundation pit with collapsible soil according to claim 1, 2, 4, 5 or 6, wherein before the anchor hole is positioned, the soil layer on the surface of the cast-in-situ bored pile needs to be cleaned, and after a side slope is excavated on one side of the cast-in-situ bored pile, the side slope is netted and sprayed with grout; when the anchor hole is positioned, positioning hole positions according to the elevation and the horizontal distance required by design, and marking by using self-spraying paint; and after the marking is finished, drilling a drill positioning inclined hole at the marked position.

Technical Field

The invention relates to a foundation pit supporting process, in particular to a method for supporting a collapse soil deep foundation pit.

Background

With the development of urban building industry, deep foundation pit engineering is widely applied to underground space technology, complex soil layer enclosure technology, high-pressure jet grouting anchor cable construction technology and the like. The distance between the foundation pit wall and the surrounding existing buildings (roads) becomes smaller and smaller, and the key of the project is how to ensure the stability of the foundation pit, the safety of the existing buildings (roads) and the structures of the proposed buildings and the safety of operators in the construction process. The high-pressure rotary spraying anchor cable is a novel anchor cable structure formed by combining a large-diameter cement soil pile body with a traditional anchor cable, holes are formed in a soil body according to a certain angle by using a rotary spraying drilling machine, cement slurry is sprayed, the anchor cable is fully stirred and subjected to physical and chemical reactions, so that the cement and the soil body interact to finally form an anchoring body, the construction mode is less in disturbance to the stratum during construction, the influence on the surrounding environment is very weak, and the high-pressure rotary spraying anchor cable is particularly suitable for foundation pit engineering with important buildings at the periphery. In the existing construction, when a high-pressure jet grouting anchor cable process is adopted to support a pile foundation, the anchor cable is usually anchored in a soil layer and cannot be recovered, and the construction cost is high. Meanwhile, for collapsible soil, the hole collapse phenomenon is easily caused in the anchoring process by adopting a mode of firstly excavating earthwork and then anchoring.

Disclosure of Invention

Aiming at the defects of the prior art, the technical problems to be solved by the invention are as follows: how to provide a collapse soil deep foundation pit supporting method which has the advantages of simple construction process, firm foundation pit supporting structure and low construction cost.

In order to solve the technical problems, the invention adopts the following technical scheme:

a support method for a collapse soil deep foundation pit is characterized by comprising the following steps: s1, site investigation; s2, arranging a plurality of cast-in-situ bored piles along the side line of the designed position of the foundation pit; s3, arranging a plurality of cement mixing piles at equal intervals around the foundation pit, wherein the cement mixing piles form a closed waterproof curtain around the foundation pit; s4, arranging an anchor cable at a soil layer between two adjacent cast-in-situ bored piles by adopting a high-pressure jet grouting process, determining the position of an anchor hole before the anchor cable is anchored, arranging a drilling machine, adjusting the angle of a drill rod, fixing an anchor cable assembly at a drill bit of the drill rod, and anchoring the anchor cable of the anchor cable assembly into the soil layer when the drill rod is drilled; the anchor cable assembly comprises two anchor disks which are arranged at intervals and provided with through holes in the middle and at least two anchor cables of which the heads are fixedly arranged between the two anchor disks, a PE hose is sleeved on each anchor cable, a removable anchor is arranged at the head of each anchor cable and fixed between the two anchor disks, and the anchor cables can fall off from the removable anchors under the action of external force; s5, pouring a crown beam on the cast-in-situ bored pile; s6, tensioning the arranged anchor cable; s7, excavating earthwork to form a foundation pit, and pouring a concrete cushion layer in the foundation pit; and S8, when earth is backfilled to the anchor head, rotating and pulling each anchor cable to enable the anchor cable to fall off from the removable anchor device, so that the anchor cable is recovered. Like this, during the construction, adopt to set up earlier and bore the bored concrete pile and consolidate the soil layer, then form the stagnant water curtain with cement mixing pile around the foundation ditch, prevent that outside groundwater from infiltrating the foundation ditch, then anchor into the anchor rope and further increase the steadiness of foundation pile after, carry out the earthwork excavation again, this construction mode can be to the soil layer in advance the reinforcement, excavation again after the dimension is steady, when the soil layer excavation, can not cause the hole phenomenon of collapsing, foundation ditch supporting construction is stable. When the anchor rope is anchored, the anchor rope and the drill rod are synchronously anchored, so that the problems of hole collapse, blockage of the slurry return pipe and the like can be further reduced, the occurrence probability of quality diseases is practically reduced, and the overall construction quality level is improved. Meanwhile, the anchor cable assembly is provided with a plurality of anchor cables, the anchor cables can be anchored in at one time, the anchoring force is effectively improved, the end parts of the anchor cables are fixed on the removable anchor device, and the anchor cable assembly can fall off from the anchor device under the action of external force and is recycled after being drawn out. Before the anchor rope was retrieved, pour the concrete cushion, the concrete cushion forms a whole with the drilling bored concrete pile to after the anchor rope was retrieved, also can not influence the pile foundation and strut the steadiness to some extent. The hoses sleeved on the anchor cables can prevent the anchor cables from being solidified with cement paste, and the anchor cables can be pulled out under small external force. The anchor disc can fix the removable anchor, and meanwhile, when the drill rod rotates, the anchor cable cannot rotate along with the drill rod and is wound on the drill rod.

Furthermore, a reinforcing cage is welded and fixed on the anchoring disc close to the anchoring section, the reinforcing cage comprises a plurality of vertical ribs vertically fixed on the anchoring disc and spiral ribs fixed outside the vertical ribs, and each anchor cable penetrates through the reinforcing cage and is fixed on the reinforcing cage through an iron wire; and the drill rod penetrates through the reinforcing cage and then is sleeved on the middle through holes of the two anchoring discs. Like this, set up and consolidate the cage after, can effectively increase the intensity of anchor rope anchor tip, simultaneously, consolidate the cage and can also be used for fixing each anchor rope, avoid behind the jet grouting grout, the grout is in the same place each anchor rope extrusion, and it is inconvenient when the anchor rope is taken out in the later stage.

Furthermore, a plurality of screw rods are fixed between the two anchor plates of each anchor cable assembly. Like this, the screw rod can be fixed two anchor dishes and be a whole, increases the joint strength between the anchor dish.

Furthermore, the drill rod is a hollow spiral drill pipe, a nozzle is arranged at the bottom of the drill bit, two nozzles are arranged on the side wing, cement slurry is introduced into the drill rod through a high-pressure guide pipe by a high-pressure pump after being filtered in the stirring tank and is sprayed outwards from each nozzle of the drill bit, and soil on the peripheral side is synchronously cut in the cement slurry spraying process; the drill bit is gradually pushed forward under the driving of power until reaching the designed depth and diameter to form an anchor body. In the construction, the disturbance to the stratum is less, the influence to the surrounding environment is very weak, the mixture is sprayed to the soil body in a high-pressure rotary spraying mode, a cement soil pile body is further formed, and the cement and the soil body interact through a physical and chemical reaction, so that the bearing capacity required by the anchor cable is supplied to the anchoring section is finally formed.

Furthermore, the cement paste is prepared by mixing and stirring ordinary portland cement and water, the doping amount of the anchor body cement is 20%, and the water cement ratio is 0.5-0.7. Therefore, cement paste is stirred by the paste barrel, uniform stirring and proper water-cement ratio are guaranteed, meanwhile, the cement paste is stirred at any time, continuous operation is guaranteed, the cement paste is used in the specified time limit, the cement paste is sprayed to the soil body, and after physical and chemical reactions, the effect of a solidified body is achieved.

Furthermore, the speed is increased to be not more than 30cm/min during anchor body construction, the rotating speed is not less than 20 revolutions per minute, and the slurry flow is not less than 50L/min; the pressure of anchor body jet grouting stirring should be 20Mpa to 25 Mpa. Therefore, the pressure is controlled in the numerical range, and the guniting pressure, the drill rod rotation speed and the drill lifting speed are adjusted in the rotary guniting grouting process on the premise of not influencing the ground outside the foundation pit and not causing grout bleeding, so that the rotary guniting cylinder is ensured to be formed completely and uniformly; high-pressure grouting is carried out in the anchor cable hole, the advancing and retreating times of the jet grouting stirring of the expansion head is increased by two times compared with the pile body so as to ensure the diameter of the expansion head, the anchoring section and the diameter of the expansion head can meet the requirement of the design working condition, and the consolidation body is formed and has homogeneity.

Furthermore, when earth is excavated, layered excavation is needed, the layered thickness is not more than 2m, and when the lower layer soil is excavated, the prestressed rotary-spraying anchor cable on the upper layer needs to be maintained for more than 7 days and tensioned and locked. Therefore, the upper layer is firstly tensioned and locked, and meets the design requirements, mainly aiming at preventing the soil stress and the strength from being sharply reduced, so that the foundation pit side slope is locally damaged or integrally unstable and slides to collapse, and the safety of foundation pit construction can be ensured.

Further, before anchor hole positioning, cleaning a soil layer on the surface of the cast-in-situ bored pile, excavating a side slope on one side of the cast-in-situ bored pile, and then hanging a net on the side slope for guniting; when the anchor hole is positioned, positioning hole positions according to the elevation and the horizontal distance required by design, and marking by using self-spraying paint; and after the marking is finished, drilling a drill positioning inclined hole at the marked position. Therefore, in order to prevent the side slope surface soil layer from further weathering, peeling and sporadically dropping blocks, the net hanging guniting and the concrete spraying are adopted, so that a protective layer is formed on the side slope, and the safety of foundation pit construction can be achieved. In the construction process, the anchor hole position needs to be continuously monitored and controlled so as to avoid the influence of large obstacles on the hole forming quality and the guarantee of the construction period and ensure the smooth development of the building construction engineering.

Drawings

FIG. 1 is a schematic elevation structure of a foundation pit support in an embodiment;

FIG. 2 is an enlarged schematic end view of the cable bolt assembly according to an embodiment;

FIG. 3 is a schematic cross-sectional view of FIG. 2, taken along line 1-1;

fig. 4 is a schematic cross-sectional view of 2-2 in fig. 2.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

Example (b):

the support method for the collapsed soil deep foundation pit provided by the embodiment comprises the following steps: s1, site investigation; s2, arranging a plurality of cast-in-situ bored piles 2 along the side line of the designed position of the foundation pit (as shown in figure 1); s3, arranging a plurality of cement mixing piles 1 at equal intervals around the foundation pit, wherein the cement mixing piles 1 form a closed waterproof curtain around the foundation pit; s4, arranging an anchor cable at the soil layer between two adjacent cast-in-situ bored piles 2 by adopting a high-pressure jet grouting process, determining the position of an anchor hole before anchoring the anchor cable, then arranging a drilling machine, adjusting the angle of a drill rod, and fixing an anchor cable assembly 4 at the drill bit of the drill rod (as shown in figures 2-4), wherein when the drill rod drills, the anchor cable 43 of the anchor cable assembly 4 is anchored into the soil layer along with the drill rod; the anchor cable assembly 4 comprises two anchor disks 41 which are arranged at intervals and provided with through holes in the middle and at least two anchor cables 43 of which the head parts are fixedly arranged between the two anchor disks 41, a PE hose 42 is sleeved on each anchor cable 43, a removable anchor 44 is arranged at the head part of each anchor cable 43, the removable anchor 44 is fixed between the two anchor disks 41, and the anchor cables 43 can fall off from the removable anchor 44 under the action of external force; s5, pouring the crown beam 3 on the cast-in-situ bored pile 2; s6, tensioning the anchor cable 43; s7, excavating earthwork to form a foundation pit, and pouring a concrete cushion layer in the foundation pit; and S8, when earth is backfilled to the anchor head, rotating and pulling each anchor cable to enable the anchor cable to fall off from the removable anchor device, so that the anchor cable is recovered.

The removable anchor used in this embodiment is a prior art anchor, and its specific structure is disclosed in chinese patent application nos. 201520300678, 201320276172, and 2020222338054.

A reinforcing cage 46 is further welded and fixed on the anchoring disc 41 close to the anchoring section, the reinforcing cage 46 comprises a plurality of vertical ribs vertically fixed on the anchoring disc 41 and spiral ribs fixed outside the vertical ribs, and each anchor cable penetrates through the reinforcing cage 46 and is fixed on the reinforcing cage through iron wires; and the drill rod penetrates through the reinforcing cage and then is sleeved on the middle through holes of the two anchoring discs.

A plurality of threaded rods 45 are also secured between the anchor plates 41 of each cable bolt assembly 4.

The drill rod adopted in the embodiment is a hollow spiral drill pipe, the bottom of the drill bit is provided with a nozzle, the flank is provided with two nozzles, cement slurry is introduced into the drill rod by a high-pressure pump through a high-pressure guide pipe after being filtered in a stirring tank and is sprayed outwards from each nozzle of the drill bit, and soil on the peripheral side is synchronously cut in the cement slurry spraying process; the drill bit is gradually pushed forward under the driving of power until reaching the designed depth and diameter to form an anchor body. The cement paste is prepared by mixing and stirring ordinary portland cement and water, the doping amount of the anchor body cement is 20%, and the water cement ratio is 0.5-0.7.

When the anchor body is constructed, the speed is increased to be not more than 30cm/min, the rotating speed is not less than 20 revolutions per minute, and the slurry flow is not less than 50L/min; the pressure of anchor body jet grouting stirring should be 20Mpa to 25 Mpa.

When the earth is excavated, layered excavation is needed, the layered thickness is not more than 2m, and when the lower layer soil is excavated, the prestressed jet grouting anchor cable on the upper layer needs to have maintenance time of more than 7 days and is tensioned and locked.

Before anchor hole positioning, cleaning a soil layer on the surface of the cast-in-situ bored pile, excavating a side slope on one side of the cast-in-situ bored pile, and then hanging a net on the side slope for guniting; when the anchor hole is positioned, positioning hole positions according to the elevation and the horizontal distance required by design, and marking by using self-spraying paint; and after the marking is finished, drilling a drill positioning inclined hole at the marked position.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the technical solutions, and although the present invention has been described in detail by referring to the preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention can be made without departing from the spirit and scope of the technical solutions, and all the modifications and equivalent substitutions should be covered by the claims of the present invention.