A sinking method of a deep clay layer sinking well

Abstract

The application belongs to the technical field of bridge engineering, and particularly relates to a sinking well sinking construction method for deep clay layer, which comprises the following steps: S1, before sinking well construction, according to design drawings, the clay at the position of the sinking well in the sinking well construction area is replaced by sand piles to form a sand pile area, wherein the diameter of the sand pile is greater than the thickness of the sinking well wall; S2, the sinking well is placed in the sand pile area, and the soil in the well shaft is taken by using a high-pressure rotary jet grouting mode to realize the orderly sinking of the sinking well. The application can solve the problems of sudden sinking and slow sinking in the sinking process of the sinking well, and effectively improve the soil taking efficiency in the well shaft.

Description

Technical Field

[0001] This invention relates to the field of bridge engineering technology, and in particular to a method for sinking caissons in deep clay layers. Background Technology

[0002] Caissons, due to their large size and deep sinking depth, are often used for the foundations of long-span bridges. In the southeastern coastal areas and river estuaries of my country, there are deep layers of silt and clay. Caisson foundations need to penetrate these deep clay layers to reach the bearing stratum with good load-bearing capacity, ensuring the long-term stability of the bridge foundation.

[0003] During the sinking process of a caisson in a deep clay layer, on the one hand, the caisson is prone to sudden sinking during the process of raising the height and pouring concrete for the well wall due to the weak bearing capacity of the surface clay. On the other hand, due to the strong cohesion of the clay in the depths, the clay around the caisson is prone to adsorb onto the well wall, making it difficult for the caisson to sink. In addition, water-rich clay has great rheological and thixotropic properties, making it difficult to remove the hard plastic clay inside the well shaft and resulting in low soil breaking efficiency.

[0004] The Oujiang North Estuary Bridge, constructed between 2016 and 2020, involved tower and south anchorage caissons that pierced through thick clay layers and entered a pebble layer as the bearing stratum. To address the weak bearing capacity of the surface silt, small-diameter short sand piles were used for foundation replacement to prevent sudden sinking of the caissons during the initial sinking process. To address the issue of clay adhering to the caisson walls at deeper depths, air curtain measures were employed to prevent stagnation during later sinking stages. For soil removal from within the caissons, a combination of circulating drilling rigs, sludge suction machines, and grab buckets was used. However, during construction, sudden and stagnation of the caissons still occurred, resulting in low soil removal efficiency and a long construction period.

[0005] In the prior art, patent CN 122106107 A discloses a drag-reducing isolation layer and construction method for caissons. The isolation layer consists of sand piles installed at the bottom of the outer wall of the caisson and the partition wall. The sand piles form a sand sleeve below the step of the outer wall of the caisson to reduce lateral resistance. The sand piles also form a sand sleeve between the inner side of the caisson cutting edge and the soil to reduce end resistance. The outer edges of the continuous sand wall formed by the sand piles extend more than 5 cm beyond the outer edges of the cutting edge surface on both sides. The diameter of the sand piles is 50 cm-150 cm. The method involves cutting the small-diameter sand piles with the cutting edge to allow the sand in the piles to wrap around the cutting edge and form an isolation layer. However, in actual construction, the caisson wall is generally thick. Sand piles of this size can only form a sand sleeve within a local area of ​​the cutting edge, and even a slight tilt can cause the cutting edge to deviate beyond the sand pile. This method has high construction requirements and limited sinking effect.

[0006] In view of this, it is necessary to design a method for sinking caissons in deep clay layers to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a method for sinking caissons in deep clay layers to solve the problems of sudden sinking and stagnation during the sinking process, and to effectively improve the soil extraction efficiency inside the caisson.

[0008] To achieve the above-mentioned objectives, this invention provides a method for sinking caissons in deep clay layers, comprising the following steps: S1. Before the construction of the caisson, according to the design drawings, the clay at the location of the caisson in the construction area is replaced with sand piles to form a sand pile area, wherein the diameter of the sand piles is greater than the thickness of the caisson wall. S2. Place the caisson in the sand pile area and use high-pressure jet grouting to remove soil from the caisson shaft to achieve orderly sinking of the caisson.

[0009] As a further improvement of the present invention, in step S1, the difference between the diameter of the sand pile and the thickness of the caisson wall is 25-50% of the thickness of the caisson wall.

[0010] As a further improvement of the present invention, in step S1, the sand in the sand pile is medium-fine sand with a particle size of 0.25-0.5mm.

[0011] As a further improvement of the present invention, in step S1, the location of the caisson includes the location of the caisson sidewall and the location of the partition wall when a partition wall is provided inside the caisson.

[0012] As a further improvement of the present invention, after the caisson sinks to a certain height below the clay layer, a clay dispersant is injected into the outer periphery of the caisson wall.

[0013] As a further improvement of the present invention, if the caisson tilts to one side during the sinking process, the amount of clay dispersant used on the tilted side shall be reduced.

[0014] As a further improvement of the present invention, if the caisson tilts to one side during the sinking process, the amount of clay removed from the tilted side is reduced.

[0015] As a further improvement of the present invention, the sand pile construction adopts a rotary drilling rig to form the hole, wherein the upper part of the hole body is protected by a steel casing and the lower part of the hole body is protected by a low-density mud slurry.

[0016] As a further improvement of the present invention, the center of the caisson wall coincides with the center of the sand pile.

[0017] As a further improvement of the present invention, the bottom elevation of the sand pile is the same as the bottom elevation of the caisson.

[0018] The beneficial effects of this invention are: 1. This invention, based on design drawings, replaces the clay in the caisson construction area with sand piles, ensuring the sand pile diameter is greater than the caisson wall thickness. On one hand, the sand piles enhance the bearing capacity, addressing the issue of weak surface clay bearing capacity. On the other hand, the caisson's sinking is transformed from within the clay layer to within the sand piles, improving its smoothness. Furthermore, during sinking, sand layers form on both sides of the caisson, reducing contact between the clay and the caisson, preventing clay adsorption on the well wall from affecting the sinking effect. This effectively solves the problems of sudden and delayed sinking of the caisson in the clay layer.

[0019] 2. Based on the use of sand piles to replace clay and form sand layers on both sides of the caisson during the sinking process, the present invention uses high-pressure jet grouting of water to remove soil inside the caisson. This can make full use of the looseness of sand, and with the high-pressure jet grouting, the clay surrounding the caisson can be quickly stripped off, effectively improving the soil removal efficiency and allowing the caisson to sink in an orderly manner. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the caisson sinking construction.

[0021] Figure 2 This is a schematic diagram of the sand pile layout.

[0022] Figure 3 This is a schematic diagram of the caisson sinking construction.

[0023] Figure Labels 10. Caisson; 11. Partition wall; 20. Sand pile; 31. High-pressure jet grouting device; 32. High-pressure jet grouting soil breaking area; 41. Clay dispersant pipeline; 42. Clay dispersant. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0026] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0027] like Figures 1-3As shown, the present invention provides a method for sinking caissons in deep clay layers, comprising the following steps: S1. Before the construction of caisson 10, according to the design drawings, the clay at the location of caisson 10 in the construction area of ​​caisson 10 is replaced with sand piles 20 to form a sand pile 20 area. The diameter of the sand piles 20 is greater than the thickness of the caisson wall. S2. Place the caisson 10 in the sand pile 20 area and use high-pressure jet grouting to remove soil from the well shaft to achieve the orderly sinking of the caisson 10.

[0028] For example, in step S1, the location of the caisson 10 includes the location of the side wall of the caisson 10 and the location of the partition wall 11 when a partition wall 11 is provided inside the caisson 10. Figure 2 As shown in this example, the caisson 10 is provided with two perpendicularly intersecting partition walls 11. When the sand piles 20 are used for replacement, the clay in the area where the caisson 10 is located and the partition walls 11 are located is replaced with sand piles 20, and the diameter of the sand piles 20 is made larger than the thickness of the caisson 10 wall and the thickness of the partition walls 11, so as to replace the sinking of the caisson 10 in the clay with the sinking in the sand piles 20.

[0029] The sand in the sand pile 20 is medium-fine sand with a particle size of 0.25-0.5mm. This medium-fine sand has good dispersibility, facilitating the sinking of the caisson 10 within the sand pile 20. Simultaneously, the difference between the diameter of the sand pile 20 and the wall thickness of the caisson 10 is 25-50% of the wall thickness. This allows the sand pile 20 to isolate the surface of the caisson 10 from the clay, reducing the clay's adsorption effect on the well wall and preventing stagnation. The limited diameter of the sand pile 20 avoids construction difficulties and waste caused by an excessively large diameter, while also preventing insufficient diameter from affecting the replacement effect between the sand pile 20 and the clay. This would prevent the sand pile 20 from providing sufficient bearing capacity and failing to form an isolation layer between the caisson 10 and the clay during sinking, thus ensuring the orderly sinking of the caisson 10. This ensures that the caisson 10 remains within the sand pile 20 range during the sinking process, even with a slight tilt allowed by construction, preventing sudden or stagnation.

[0030] The center of the well wall of caisson 10 coincides with the center of sand pile 20, that is, the center of the well wall around caisson 10 coincides with the center of sand pile 20, and the center of partition wall 11 coincides with the center of sand pile 20, so that the sand in sand pile 20 is evenly distributed around the well wall of caisson 10.

[0031] The bottom elevation of sand pile 20 is the same as the bottom elevation of caisson 10.

[0032] For example, in the construction of sand pile 20, a rotary drilling rig is used to form the hole, wherein the upper part of the hole is protected by a steel casing, the lower part of the hole is protected by low-density mud, and the sand pile 20 is poured using the tremie pipe method.

[0033] For example, the high-pressure jet grouting method for soil removal involves extending the high-pressure jet grouting device 31 below the elevation of the cutting edge of the caisson 10. High-pressure jet grouting uses clean water to agitate the clay beneath the cutting edge, triggering rheological changes. Combined with a sludge suction machine, this achieves efficient soil removal from the caisson, reducing the bearing capacity of the soil beneath the cutting edge and preventing settling. The high-pressure jet grouting breaking area 32 during the process is as follows: Figure 3 As shown.

[0034] For the caisson 10 that sinks directly in the clay layer, the silt in the clay layer has great rheological and thixotropic properties, and it will adhere tightly to the surface of the caisson 10. If the high-pressure jet grouting method is used directly, the soil removal effect is poor. The present invention uses sand piles 20 to replace the clay so that a sand layer is formed on both sides of the caisson 10 during the sinking process. Then, the high-pressure jet grouting method is used in the well to remove soil. It can make full use of the looseness of the sand. Combined with the high-pressure jet grouting, the clay around the caisson 10 is quickly stripped off, which effectively improves the soil removal efficiency and allows the caisson 10 to sink in an orderly manner.

[0035] If the caisson 10 tilts to one side during the sinking process, reduce the amount of clay removed from the tilted side to avoid exacerbating the tilting phenomenon.

[0036] As the depth increases, the interstitial pressure of the clay gradually increases, leading to increased clay hardness and enhanced adhesion. In this example, after the caisson 10 sinks to a certain height below the clay layer, clay dispersant 42 is injected into the outer perimeter of the caisson wall to reduce the clay's adsorption and prevent settling. The use of clay dispersant 42 should consider the sinking posture of the caisson 10. If the caisson 10 tilts to one side during sinking, the amount of clay dispersant 42 used on the tilted side should be reduced to prevent further tilting. Figure 1 and Figure 3 As shown, after deep drilling is carried out on the outer edge of the caisson 10, a clay dispersant pipeline 41 is laid, and the clay dispersant 42 is sprayed on the outer periphery of the caisson 10 through the clay dispersant pipeline 41.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for sinking caissons in deep clay layers, characterized in that, Includes the following steps: S1. Before the construction of the caisson, according to the design drawings, the clay at the location of the caisson in the construction area is replaced with sand piles to form a sand pile area, wherein the diameter of the sand piles is greater than the thickness of the caisson wall. S2. Place the caisson in the sand pile area and use high-pressure jet grouting to remove soil from the caisson shaft to achieve orderly sinking of the caisson.

2. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: In step S1, the difference between the diameter of the sand pile and the thickness of the caisson wall is 25-50% of the thickness of the caisson wall.

3. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: In step S1, the sand in the sand pile is medium-fine sand with a particle size of 0.25-0.5mm.

4. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: In step S1, the location of the caisson includes the location of the caisson sidewall and the location of the partition wall when there is a partition wall inside the caisson.

5. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: After the caisson has sunk to a certain height below the clay layer, clay dispersant is injected into the outer perimeter of the caisson wall.

6. The method for sinking caissons in deep clay layers according to claim 5, characterized in that: If the caisson tilts to one side during the sinking process, reduce the amount of clay dispersant used on the tilted side.

7. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: If the caisson tilts to one side during the sinking process, reduce the amount of clay removed from the tilted side.

8. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: The sand pile construction uses a rotary drilling rig to form the hole, with a steel casing for the upper part of the hole and a low-density mud slurry for the lower part of the hole.

9. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: The center of the caisson wall coincides with the center of the sand pile.

10. The method for sinking caissons in deep clay layers according to claim 1, characterized in that: The bottom elevation of the sand pile is the same as the bottom elevation of the caisson.

Images