Double-layer steel casing caisson structure and construction method for water-rich soft soil layer connection construction

Abstract

The application discloses a double-layer steel casing well structure for pipe connection construction in water-rich soft soil layer and a construction method thereof. The structure comprises an outer-layer steel casing well, an inner-layer steel casing well and an inner-outer pipeline passage. The outer-layer steel casing well is arranged above an existing pipeline in a cylindrical shape and with a pipe connection point position as a center. The inner-layer steel casing well is sunk into the inner part of the outer-layer steel casing well and is seated on the existing pipeline. A groundwater isolation layer is arranged between the inner-layer steel casing well and the outer-layer steel casing well and between the inner-layer steel casing well and the existing pipeline. The soil in the well is excavated underwater, and the water level in the well is flush with the outside of the well. After the excavation is completed, concrete is poured between the inner and outer well walls, and grouting is carried out between the inner-layer steel casing well and the existing pipeline through pre-embedded grouting pipes to form a groundwater isolation layer at the bottom of the double-layer well. Then, the water level in the well is pumped out, personnel go down into the well to complete the pipe connection construction and the backfill construction in the well.

Description

Technical Field

[0001] This invention belongs to the field of pipeline construction technology, specifically relating to a double-layer steel casing caisson structure and construction method for connecting new pipelines to existing municipal pipelines in water-rich soft soil strata. Background Technology

[0002] In the process of upgrading and renovating municipal pipeline networks in large coastal cities in my country, it is common to encounter engineering application scenarios where new pipelines need to be connected to existing deep-buried pipelines. This involves creating T-shaped pipe joints on existing deep-buried pipelines to connect new pipelines upwards and link them to newly constructed shallow-buried pipelines. Depending on the burial depth of the existing pipeline, geological conditions, and environmental protection requirements of the surrounding foundation pit, the construction of the connection point can employ foundation pit support structures such as steel sheet piles or SMW (Surface Mount Welded) piles, or retaining structures such as steel casing caissons (or "riding wells").

[0003] Excavation pit support structures are generally characterized by large footprints, long construction periods, and high costs, making them unsuitable for land-constrained urban centers. Conventional steel-cased caissons (or "riding caissons") are also unsuitable for construction in water-rich soft soil strata with stringent environmental protection requirements. Because they can only be lowered above existing pipelines, the steel casing cannot effectively support the soil beneath the pipeline. After excavation, significant uplift of the soft soil at the bottom of the caisson leads to ground subsidence and substantial deformation of surrounding buildings. Furthermore, conventional steel-cased caissons cannot be tightly fitted to existing pipelines, resulting in large gaps that can cause soil and sand to surge in during construction, threatening the safety of workers inside. Moreover, in water-rich strata, conventional steel-cased caissons cannot isolate groundwater, requiring only temporary water level reduction through open-pit dewatering. This can lead to widespread ground subsidence in urban centers, affecting the safety of surrounding buildings. Additionally, continuous dewatering during construction compromises safety and reliability, failing to guarantee the safety of workers inside the caisson.

[0004] Chinese patent (201620679124.1) proposes a manhole with a steel casing device. An arched cutting edge is set at the bottom of the steel casing, allowing it to sit on the surface of the existing pipeline. This arched cutting edge can provide a certain degree of support for the sides and the soil below the pipeline. However, in practice, the arched cutting edge at the bottom makes sinking difficult, especially when the existing pipeline is buried at a deep depth. The steel casing pressed in from the ground cannot ensure that the arched cutting edge is precisely positioned above the existing pipeline, making construction difficult and failing to solve the groundwater problem. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a double-layer steel casing caisson structure and construction method for pipe connection construction in water-rich soft soil strata, so as to overcome the shortcomings of the prior art.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: On the one hand, a double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata is provided, which includes an outer steel casing caisson, an inner steel casing caisson, and inner and outer pipeline channels. The outer steel casing caisson is cylindrical and arranged above the existing pipeline with the pipe connection point as the center. The inner steel casing caisson is sunk into the interior of the outer steel casing caisson and sits on the existing pipeline. Groundwater isolation layers are provided between the inner and outer steel casing caissons and between the inner steel casing caisson and the existing pipeline.

[0007] As described above, the double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata includes a deep U-shaped groove at the bottom of the inner steel casing caisson, and a semi-circular shape at the top of the deep U-shaped groove with a radius slightly larger than that of the existing pipeline. The inner steel casing caisson sits on the existing pipeline through the deep U-shaped groove.

[0008] As described above, the double-layer steel casing caisson structure for the construction of the water-rich soft soil stratum includes a compaction grouting pipe pre-embedded on the inner surface of the inner steel casing caisson structure.

[0009] As described above, in the construction of a double-layer steel casing caisson structure for water-rich soft soil strata, a flexible rubber strip is provided on the surface of the deep U-shaped groove.

[0010] On the other hand, a method for constructing a double-layer steel casing caisson in water-rich soft soil strata is provided, comprising the following steps: S1. Construction of the outer steel casing caisson includes the following steps: S11. At the location of the proposed connection point of the existing pipeline, the outer steel casing caisson is pressed into the ground and sunk to the top of the existing pipeline, so that the bottom of the caisson is as close as possible to the top of the existing pipeline. During the sinking process, the reserved pipeline opening at the top of the caisson is sealed with a temporary cover plate. S12. Excavate the soil inside the well on the ground, and ensure that the groundwater level inside the well is level with the groundwater level outside the well during the excavation process; S13. After excavating the soil within a 180° radius of the top of the existing pipeline, accurately locate the position and elevation of the existing pipeline. S2. The deep U-shaped groove of the inner steel casing caisson is aligned with the center of the existing pipeline and pressed into the caisson to ensure that the existing pipeline can be accurately embedded in the deep U-shaped groove. S3. The groundwater barrier layer at the bottom of the construction caisson includes the following steps: S31. Pour underwater concrete between the inner and outer caissons to form a groundwater barrier between the inner and outer caissons. S32. Grouting is carried out on the soil between the inner steel casing caisson and the existing pipeline and the soil below the existing pipeline through the grouting pipe pre-embedded on the inner wall of the inner steel casing caisson to form a groundwater isolation layer between the inner steel casing caisson and the existing pipeline. S33. After the underwater concrete and compacted grouting body reach the design strength, test the groundwater level inside the well and observe the changes in the groundwater level outside the well. If the groundwater level inside the well decreases and the groundwater level outside the well also decreases synchronously, repeat steps S31 to S32 to strengthen the groundwater barrier layer. The strengthening measures include continuing to pour underwater concrete between the inner and outer caissons and performing secondary grouting reinforcement on the compacted grouting body inside the inner steel casing caisson until the groundwater level outside the well does not change when water is pumped out. At this point, the groundwater level inside the well is completely pumped out to prepare for the next process. S4. After the groundwater level in the well is pumped out, personnel will go down into the well to carry out well connection work, including the following steps: S41. Install T-shaped tee pipes on existing pipelines and install risers in the manholes; S42. The newly built shallow buried pipeline passes through the reserved pipeline opening at the top of the outer steel casing caisson and enters the caisson, and is connected to the riser inside the caisson; S43. After the takeover is completed, the caisson shall be backfilled as required.

[0011] The beneficial effects of the technical solution of this invention are: 1. The outer steel casing caisson sinks from the ground all the way to the top of the existing buried pipeline, reaching a relatively deep depth; the inner rectangular steel casing caisson sinks from the top of the existing pipeline until it is embedded above it, reaching a shallower depth. This relay sinking method of the inner and outer casings ensures high verticality and construction precision of the inner steel casing, allowing it to be accurately embedded above the existing pipeline.

[0012] 2. After the outer steel casing is lowered to the top of the existing pipeline, the existing pipeline can be excavated and exposed for precise positioning, which makes up for the inaccuracy of conventional ground geophysical exploration methods.

[0013] 3. The outer steel casing caisson adopts a circular cross-section structure with better stress distribution. On the one hand, it can reduce the deformation of the caisson structure and optimize the wall thickness of the caisson structure. On the other hand, it can reduce the disturbance to the soil during the sinking process. Combined with micro-disturbance sinking methods such as pipe-rolling method, it can further accelerate the construction speed and reduce the impact on the surrounding environment.

[0014] 4. The inner rectangular steel casing caisson adopts a rectangular cross-section structure with high space utilization. On the one hand, it can reduce the gap between the caisson wall and the existing pipeline, reduce the construction difficulty of the groundwater isolation layer of the compaction grouting at the bottom of the caisson, and improve the space utilization inside the caisson. On the other hand, it is easy to process the deep U-shaped groove on the short side, so that the groove fits the existing pipeline well.

[0015] 5. Through the deep U-shaped groove on the short side, the bottom of the inner rectangular steel casing caisson can be inserted under the existing pipeline, forming effective support for the soil under the pipeline and preventing the soft soil at the bottom of the caisson from bulging due to excavation and unloading.

[0016] 6. A groundwater isolation layer is set between the inner and outer steel casings, which can effectively isolate the hydraulic connection between the inside and outside of the well, ensuring that the precipitation inside the well does not affect the water level outside the well, thereby avoiding ground subsidence and deformation of surrounding buildings caused by the decrease of the groundwater level outside the well.

[0017] 7. The soil excavation process is completed by machinery on the ground. After the groundwater barrier layer is completed, personnel will enter the well to work only after the groundwater level in the well is pumped out. Moreover, after personnel enter the well, there is no need to continuously lower the groundwater level, which ensures the safety of construction personnel.

[0018] 8. Grouting reinforcement of the soil between the inner rectangular steel casing caisson and the existing pipeline, as well as the soil below the existing pipeline, can also serve as foundation reinforcement for the pipeline at the riser, avoiding uneven settlement of the pipeline due to the increased self-weight of the riser. Attached Figure Description

[0019] To further illustrate the above-mentioned objectives, structural features, and effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings.

[0020] Figure 1(a) is a plan view of the construction stage S1 of the preferred embodiment of the present invention; Figure 1(b) is a cross-sectional view of Figure 1(a) along section AA; Figure 1(c) is a cross-sectional view along BB of Figure 1(a); Figure 2(a) is a plan view of the construction stage S2 of the preferred embodiment of the present invention; Figure 2(b) is a cross-sectional view along section AA of Figure 2(a); Figure 2(c) is a cross-sectional view along BB of Figure 2(a); Figure 3(a) is a plan view of the construction stage S3 of the preferred embodiment of the present invention; Figure 3(b) is a cross-sectional view along section AA of Figure 3(a); Figure 3(c) is a cross-sectional view along BB of Figure 3(a); Figure 4(a) is a plan view of the construction stage S4 of the preferred embodiment of the present invention; Figure 4(b) is a cross-sectional view along section AA of Figure 4(a); Figure 4(c) is a cross-sectional view along BB of Figure 4(a); Figure 5 This is a three-dimensional view of the construction stage S2 of a preferred embodiment of the present invention; Figure 6 This is a three-dimensional view of the construction stage S4 of a preferred embodiment of the present invention; In the diagram: 1. Existing pipeline; 2. Outer steel casing caisson; 2a. Reserved pipeline opening; 3a. Groundwater level inside the caisson; 3b. Groundwater level outside the caisson; 4. Excavation face inside the caisson; 5. Inner steel casing caisson; 5a. Deep U-shaped groove; 6. Underwater concrete; 7. Compacting grouting pipe; 8. Compacting grouting reinforced body; 9a. Shallow buried pipeline; 9b. Riser inside the caisson; 9c. T-shaped tee pipe; 10. Backfill inside the caisson. Detailed Implementation

[0021] The terms “invention” and “the present invention” used in this specification are intended to broadly refer to all subject matter of this specification and any of the following patent claims. Statements containing these terms should not be construed as limiting the subject matter described herein or limiting the meaning or scope of any of the following patent claims. Furthermore, this specification does not attempt to describe or limit the subject matter covered by any claim of any particular component, paragraph, statement, or drawing of this application. The subject matter should be understood with reference to the entire specification, all drawings, and any of the following claims. The invention may have other embodiments and be practiced or implemented in other ways. Moreover, it should be understood that the wording and terminology used herein are for illustrative purposes and should not be considered limiting.

[0022] Details of the invention will now be discussed with reference to the accompanying drawings, which are illustrated by way of example only. In the drawings, similar features or components may be labeled using the same reference numerals.

[0023] The use of the terms "comprising," "having," and "including," and variations thereof, herein means to include the items listed herein and their equivalents and additional items. While reference may be made in the description of the drawings to directions such as above, below, upward, downward, backward, bottom, top, front, rear, etc., for convenience, reference is made relative to the drawings. These directions are not intended to literally accept or limit the invention in any form. Furthermore, terms such as "first," "second," "third," etc., are used herein for illustrative purposes and are not intended to indicate or imply importance or significance.

[0024] See Figures 1 to 12 Figure 6As shown, the double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata of the present invention includes an outer steel casing caisson 2, an inner steel casing caisson 5, and inner and outer pipeline channels. The outer steel casing caisson 2 is cylindrical and arranged above the existing pipeline 1 with the pipe connection point as the center. The outer steel casing caisson 5 is sunk above the existing pipeline 1, the existing pipeline 1 is exposed by excavation, the pipeline position and elevation are accurately located, and then the inner steel casing caisson 5 is sunk inside the outer steel casing caisson 2.

[0025] Furthermore, the top of the outer steel casing caisson 2 is provided with a circular reserved pipe opening 2a, and temporary sealing measures are taken to seal the opening during the sinking process.

[0026] See Figures 2(a), 2(b), 2(c) and Figure 5 As shown, the short side of the rectangular inner steel casing caisson 5 is perpendicular to the existing pipeline 1, while the long side is parallel to it. At the bottom of the short side, a deep U-shaped groove 5a is provided, with the radius of the semi-circular top of the groove 5a slightly larger than the radius of the existing pipeline 1. During the sinking of the inner steel casing caisson 5, the deep U-shaped groove 5a is aligned with the existing pipeline 1 to ensure that the existing pipeline 1 can be accurately embedded within the groove 5a after sinking. The long side of the caisson inserts below the existing pipeline 1, providing effective support to the soil beneath the pipeline. Furthermore, flexible rubber strips are installed on the surface of the deep U-shaped groove 5a at the bottom of the short side of the inner steel casing caisson 5 structure to prevent it from colliding with and damaging the existing pipeline 1 during the sinking process, while also playing a certain role in blocking water and sand.

[0027] Furthermore, a compaction grouting pipe 7 is pre-embedded on the inner surface of the inner steel casing caisson 5 structure.

[0028] Referring to Figures 3(a), 3(b), and 3(c), in water-rich strata, all excavation work following the sinking of the double-layer steel casing caisson is underwater excavation. Mechanical excavation is conducted on the surface, and personnel do not enter the caisson to ensure safety. After the inner steel casing caisson 5 is sunk, underwater concrete 6 is poured between the inner and outer casing caisson walls. Grouting is then performed between the inner steel casing caisson 5 and the existing pipeline 1 via pre-embedded compaction grouting pipes 7 to reinforce the soil between the inner steel casing caisson 5 and the existing pipeline 1, as well as the soil below the existing pipeline 1. Through these combined measures, a groundwater barrier layer is formed at the bottom of the inner and outer steel casings. Finally, the groundwater level 3a inside the caisson is pumped out, creating a dry working environment suitable for personnel to enter the caisson.

[0029] During the dewatering process inside the double-layered steel casing caisson, the groundwater level 3b outside the caisson is monitored simultaneously. If the groundwater level 3b outside the caisson also drops during dewatering, it indicates that there are still seepage channels in the groundwater barrier layer at the bottom of the steel casing. At this point, dewatering inside the caisson is stopped, and the groundwater barrier layer is reinforced a second time. The reinforcement measures include continuing to pour underwater concrete 6 between the inner and outer steel casing walls and performing secondary grouting through pre-embedded compaction grouting pipes 7. After the reinforcement measures are completed, test dewatering inside the caisson and monitoring of the groundwater level 3b outside the caisson continue. The groundwater level 3b outside the caisson remains unchanged when water is dewatered inside the caisson, at which point the groundwater level 3a inside the caisson is completely dewatered.

[0030] See Figures 4(a), 4(b), 4(c) and Figure 6 As shown, after the groundwater in the double-layer steel casing caisson is pumped out, personnel go down into the caisson to cut the existing pipe 1, install the T-tee pipe 9c, and install the riser pipe 9b inside the caisson. A newly constructed shallow-buried pipe 9a passes through the reserved pipe opening 2a at the top of the outer steel casing caisson and connects to the riser pipe 9b inside the caisson. After the connection is completed, the caisson is backfilled as required.

[0031] Accordingly, the present invention provides a construction method for a double-layer steel casing caisson structure, comprising the following steps: S1: Construction of the outer steel casing caisson 2, specifically including the following steps: S11: At the proposed connection point of the existing pipeline 1, the outer steel casing caisson 2 is pressed into the ground and lowered above the existing pipeline 1, so that the bottom of the caisson is as close as possible to the top of the existing pipeline 1. During the lowering process, the reserved pipeline opening 2a at the top of the caisson is sealed with a temporary cover plate.

[0032] S12: Excavate the soil inside the well on the ground, ensuring that the groundwater level 3a inside the well is level with the groundwater level 3b outside the well during the excavation process.

[0033] S13: After excavating the soil within a 180° range above the existing pipeline 1, accurately locate the position and elevation of the existing pipeline 1.

[0034] S2: Align the deep U-shaped groove 5a on the short side of the inner steel casing caisson 5 with the center of the existing pipe 1 and press it into the caisson, ensuring that the existing pipe 1 can be accurately embedded into the deep U-shaped groove 5a. A flexible rubber strip is installed on the surface of the deep U-shaped groove 5a to prevent it from colliding with and damaging the existing pipe 1 during the sinking process.

[0035] S3: Groundwater barrier layer at the bottom of the construction caisson, specifically including the following steps: S31: Pour underwater concrete 6 between the inner and outer caissons to form a groundwater barrier between the inner and outer caissons.

[0036] S32: Grouting is carried out on the soil between the inner steel casing caisson 5 and the existing pipeline 1 and the soil below the existing pipeline 1 through the pre-embedded compaction grouting pipe 7 on the inner wall of the inner steel casing caisson 5, forming a groundwater isolation layer between the inner steel casing caisson 5 and the existing pipeline 1.

[0037] S33: After the underwater concrete 6 and the compacted grouting solid 8 reach their design strength, test the water level 3a inside the well and observe the changes in the groundwater level 3b outside the well. If the groundwater level 3a inside the well decreases and the groundwater level 3b outside the well also decreases simultaneously, repeat steps S31~S32 to strengthen the groundwater barrier layer. The strengthening measures include continuing to pour the underwater concrete 6 between the inner and outer caissons and performing secondary grouting reinforcement on the compacted grouting solid 8 inside the inner steel casing caisson 5 until the groundwater level 3b outside the well does not change when water is pumped out. At this point, the groundwater level 3a inside the well is completely pumped out to prepare for the next process.

[0038] S4: After the groundwater level in the well is pumped out (3a), personnel will go down into the well to carry out well connection work, which includes the following steps: S41: Install a T-shaped tee pipe 9c on the existing pipe 1 and install a riser pipe 9b inside the well.

[0039] S42: The newly built shallow buried pipe 9a passes through the reserved pipe opening 2a at the top of the outer steel casing caisson and enters the caisson, and is connected to the riser 9b inside the caisson.

[0040] S43: After the takeover is completed, the caisson will be backfilled as required.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata, characterized in that, The system includes an outer steel casing caisson (2), an inner steel casing caisson (5), and internal and external pipeline channels. The outer steel casing caisson (2) is cylindrical and positioned above the existing pipeline (1) with the connection point as its center. The inner steel casing caisson (5) is submerged inside the outer steel casing caisson (2) and sits on the existing pipeline (1). Groundwater isolation layers are provided between the inner steel casing caisson (5) and the outer steel casing caisson (2), and between the inner steel casing caisson (5) and the existing pipeline (1). The bottom of the inner steel casing caisson (5) has a deep U-shaped groove (5a), and the top of the deep U-shaped groove (5a) has a radius slightly larger than that of the outer steel casing caisson (2). The inner steel casing caisson (5) sits on the existing pipe (1) through the deep U-shaped groove (5a) in a semi-circular radius of the existing pipe (1); the inner steel casing caisson (5) is pre-embedded with a compaction grouting pipe (7) on the inner surface of the structure; the surface of the deep U-shaped groove (5a) is provided with a flexible rubber strip; after the groundwater in the double-layer steel casing caisson is pumped out, personnel go down into the well to cut the existing pipe (1), install the T-shaped tee pipe (9c), install the well riser (9b), and the newly built shallow buried pipe (9a) passes through the reserved pipe opening (2a) at the top of the outer steel casing caisson (2) and enters the outer steel casing caisson (2), and is connected to the well riser (9b).

2. A method for constructing a double-layer steel casing caisson in water-rich soft soil strata, used for constructing the double-layer steel casing caisson structure as described in claim 1, characterized in that, Includes the following steps: S1. Construction of the outer steel casing caisson includes the following steps: S11. At the location of the proposed connection point of the existing pipeline, the outer steel casing caisson is pressed into the ground. The outer steel casing caisson sinks to above the existing pipeline, so that the bottom of the outer steel casing caisson is as close as possible to the top of the existing pipeline. During the sinking process, the reserved pipeline opening at the top of the outer steel casing caisson is sealed with a temporary cover plate. S12. Excavate the soil inside the well on the ground, and ensure that the groundwater level inside the well is level with the groundwater level outside the well during the excavation process; S13. After excavating the soil within a 180° radius of the top of the existing pipeline, accurately locate the position and elevation of the existing pipeline. S2. The deep U-shaped groove of the inner steel casing caisson is aligned with the center of the existing pipeline and pressed into the inner steel casing caisson to ensure that the existing pipeline can be accurately embedded in the deep U-shaped groove. S3. The groundwater barrier layer at the bottom of the construction caisson includes the following steps: S31. Pour underwater concrete between the inner steel casing caisson and the outer steel casing caisson to form a groundwater barrier layer between the inner steel casing caisson and the outer steel casing caisson. S32. Grouting is carried out on the soil between the inner steel casing caisson and the existing pipeline and the soil below the existing pipeline through the pre-embedded compaction grouting pipe on the inner wall of the inner steel casing caisson to form a groundwater isolation layer between the inner steel casing caisson and the existing pipeline. S33. After the underwater concrete and compacted grouting solids reach the design strength, test the groundwater level inside the well and observe the changes in the groundwater level outside the well. If the groundwater level inside the well decreases and the groundwater level outside the well also decreases synchronously, repeat steps S31 to S32 to strengthen the groundwater barrier layer. The strengthening measures include continuing to pour the underwater concrete between the inner steel casing caisson and the outer steel casing caisson, and performing secondary grouting reinforcement on the compacted grouting solids inside the inner steel casing caisson until the groundwater level outside the well does not change when water is pumped out. At this point, the groundwater level inside the well is completely pumped out to prepare for the next process. S4. After the groundwater level in the well is pumped out, personnel will go down into the well to carry out well connection work, including the following steps: S41. Install T-shaped tee pipes on existing pipelines and install risers in the manholes; S42. The newly built shallow buried pipeline passes through the reserved pipeline opening at the top of the outer steel casing caisson and enters the outer steel casing caisson, and is connected to the riser inside the caisson. S43. After the takeover is completed, the caisson shall be backfilled as required.

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