Water-rich soft soil stratum connecting pipe construction double-layer steel casing open caisson structure and construction method

Abstract

The invention discloses a double-layer steel casing open caisson structure for pipe connection construction in a water-rich soft soil stratum.The structure comprises an outer-layer steel casing open caisson, an inner-layer steel casing open caisson, an inner-layer pipeline channel and an outer-layer pipeline channel, and the outer-layer steel casing open caisson is cylindrical and arranged above an existing pipeline with the pipe connection point position as the center; the inner-layer steel casing open caisson sinks into the outer-layer steel casing open caisson and is located on the existing pipeline, and underground water separation layers are arranged between the inner-layer steel casing open caisson and the outer-layer steel casing open caisson and between the inner-layer steel casing open caisson and the existing pipeline. A soil body in the open caisson is excavated underwater, and the water level in the well is flush with the outside of the well; after excavation is completed, concrete is poured between the well walls of the inner-layer open caisson and the outer-layer open caisson, grouting reinforcement is conducted between the inner-layer rectangular open caisson and the existing pipeline through pre-buried grouting pipes, and therefore an underground water separation layer is formed at the bottom of the double-layer open caisson; and after the water level in the well is completely pumped out, workers descend into the well to complete pipe connecting construction and backfilling 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. In this case, 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 and 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 installed at the bottom of the steel casing, allowing it to sit on the surface of the existing pipeline. This arched cutting edge provides some support to the sides of the pipeline and the soil below. 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 address the groundwater issue. 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 object, the present application is realized by the following technical scheme:

[0007] In one aspect, a double-layer steel casing caisson structure for water-rich soft soil layer pipe connection construction is provided, which comprises an outer layer steel casing caisson, an inner layer steel casing caisson and an inner-outer pipeline passage. The outer layer steel casing caisson is arranged above the existing pipeline in a cylindrical shape and centered at the pipe connection point. The inner layer steel casing caisson is sunk into the inner part of the outer layer steel casing caisson and seated on the existing pipeline. A groundwater isolation layer is arranged between the inner layer steel casing caisson and the outer layer steel casing caisson and between the inner layer steel casing caisson and the existing pipeline.

[0008] In the double-layer steel casing caisson structure for water-rich soft soil layer pipe connection construction, the bottom of the inner layer steel casing caisson is provided with a deep U-shaped notch. The top of the deep U-shaped notch is in a semicircular shape with a radius slightly larger than that of the existing pipeline. The inner layer steel casing caisson is seated on the existing pipeline through the deep U-shaped notch.

[0009] In the double-layer steel casing caisson structure for water-rich soft soil layer pipe connection construction, a compacting grouting pipe is pre-buried in the inner surface of the structure of the inner layer steel casing caisson.

[0010] In the double-layer steel casing caisson structure for water-rich soft soil layer pipe connection construction, a flexible rubber strip is arranged on the surface of the deep U-shaped notch.

[0011] In another aspect, a double-layer steel casing caisson construction method for water-rich soft soil layer pipe connection construction is provided, which is used to construct the double-layer steel casing caisson structure according to any one of the aspects, and comprises the following steps:

[0012] S1, constructing an outer layer steel casing caisson, comprising the following steps:

[0013] S11, pressing the outer layer steel casing caisson into the ground at the pipe connection point of the existing pipeline, sinking the caisson above the existing pipeline, and making the bottom of the caisson as close as possible to the top of the existing pipeline. During the sinking process, the reserved pipeline hole at the top of the caisson is temporarily covered and sealed.

[0014] S12, excavating the soil in the well body on the ground, and ensuring that the underground water level in the well is level with the underground water level outside the well during the excavation process.

[0015] S13, removing the soil within a 180° range of the top of the existing pipeline, and accurately positioning the position and elevation of the existing pipeline.

[0016] S2, aligning the deep U-shaped notch of the inner layer steel casing caisson with the center of the existing pipeline and pressing the caisson into the well, and ensuring that the existing pipeline can be accurately embedded in the deep U-shaped notch.

[0017] S3, the underground water isolation layer of the construction sinking well bottom, comprising the following steps:

[0018] S31, pouring underwater concrete between the inner and outer layer sinking wells to form the underground water isolation layer between the inner and outer layer sinking wells;

[0019] S32, through the grouting pipe pre-buried on the inner wall of the inner layer steel casing sinking well, the soil between the inner layer steel casing sinking well and the existing pipeline and the soil below the existing pipeline are grouted and reinforced to form the underground water isolation layer between the inner layer steel casing sinking well and the existing pipeline;

[0020] S33, after the underwater concrete and the compacted grouting body reach the design strength, the water level in the well is tested for water level reduction, and the change of the water level outside the well is observed, if the water level in the well is reduced, the water level outside the well is also reduced synchronously, then the steps of S31-S32 are repeated to strengthen the underground water isolation layer; the strengthening measures include continuously pouring underwater concrete between the inner and outer layer sinking wells, and secondary grouting and reinforcing the compacted grouting body inside the inner layer rectangular steel casing sinking well, until the water level outside the well does not change when pumping water in the well, at this time, the water level in the well is completely pumped out, and the next process is prepared;

[0021] S4, after the water level in the well is pumped out, personnel go down into the well for well pipe connection operation, comprising the following steps:

[0022] S41, a T-shaped three-way pipe interface is arranged on the existing pipeline, and a well vertical pipe is installed;

[0023] S42, the newly built shallow buried pipeline passes through the pipeline hole reserved at the top of the outer steel casing sinking well and is connected into the sinking well and connected with the well vertical pipe;

[0024] S43, after the pipe connection is completed, the sinking well is backfilled according to the requirements.

[0025] The beneficial effects of the technical scheme of the present application are:

[0026] 1. The outer layer steel casing sinking well is sunk from the ground to the top of the existing deep buried pipeline, and the sinking depth is deep; the inner layer rectangular steel casing sinking well is sunk from the top of the existing pipeline to be embedded above the existing pipeline, and the sinking depth is shallow. By using this inner and outer layer sinking well connection sinking mode, the sinking verticality and construction accuracy of the inner layer steel casing can be ensured to be high, so that the inner layer steel casing can be accurately embedded above the existing pipeline.

[0027] 2. After the outer layer steel casing is sunk to the top of the existing pipeline, the existing pipeline excavation exposure can be accurately positioned, which makes up for the defect of inaccurate positioning of conventional ground geophysical prospecting means.

[0028] 3. The outer layer steel casing caisson adopts a circular cross-section structure with good stress form, which can reduce the caisson structure deformation, optimize the caisson structure wall thickness, reduce the disturbance to the soil during the sinking process, and cooperate with the micro-disturbance sinking method such as the rocking pipe method, so as to further speed up the construction speed and reduce the influence on the surrounding environment.

[0029] 4. The inner layer rectangular steel casing caisson adopts a rectangular cross-section structure with high space utilization, which can reduce the gap between the well wall and the existing pipeline, reduce the construction difficulty of the underground water cutoff layer of the sinking bottom pressure grouting body, improve the space utilization rate in the well, and facilitate the processing of the deep U-shaped notch of the short side, so that the notch has high adhesion with the existing pipeline.

[0030] 5. Through the deep U-shaped notch of the short side, the inner layer rectangular steel casing caisson bottom can be inserted below the existing pipeline to form effective support for the soil below the pipeline, avoiding large uplift of the soft soil at the sinking bottom due to excavation unloading.

[0031] 6. The underground water cutoff layer is arranged between the inner and outer layer steel casings, which can effectively cut off the hydraulic connection between the inside and outside of the well, ensure that the well water level is not affected by the well water level, and avoid the ground subsidence and deformation of the surrounding buildings caused by the reduction of the water level outside the well.

[0032] 7. The soil excavation process is completed by machinery on the ground, and personnel can only work in the well after the underground water cutoff layer is constructed and the water level in the well is pumped out, and the personnel do not need to continuously reduce the underground water level after entering the well, which ensures the safety of the construction personnel.

[0033] 8. The soil grouting reinforcement between the inner layer rectangular steel casing caisson and the existing pipeline and below the existing pipeline can be used as the foundation reinforcement of the pipeline at the standpipe to avoid uneven settlement of the pipeline due to the increase of the self-weight of the standpipe. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to further illustrate the above-mentioned purposes, structural characteristics and effects of the present application, the present application will be described in detail below with reference to the drawings.

[0035] Fig. 1(a) is a plan layout of the preferred embodiment of the present application at the construction stage S1;

[0036] Fig. 1(b) is a cross-sectional view along A-A of Fig. 1(a);

[0037] Fig. 1(c) is a cross-sectional view along B-B of Fig. 1(a);

[0038] Fig. 2(a) is a plan layout of the preferred embodiment of the present application at the construction stage S2;

[0039] Fig. 2(b) is a cross-sectional view along A-A of Fig. 2(a);

[0040] Figure 2(c) is a cross-sectional view of Figure 2(a) along B-B;

[0041] Figure 3(a) is a plan view of the preferred embodiment of the present application at construction stage S3;

[0042] Figure 3(b) is a cross-sectional view of Figure 3(a) along A-A;

[0043] Figure 3(c) is a cross-sectional view of Figure 3(a) along B-B;

[0044] Figure 4(a) is a plan view of the preferred embodiment of the present application at construction stage S4;

[0045] Figure 4(b) is a cross-sectional view of Figure 4(a) along A-A;

[0046] Figure 4(c) is a cross-sectional view of Figure 4(a) along B-B;

[0047] Figure 5 Figure 5(a) is a three-dimensional view of the preferred embodiment of the present application at construction stage S2;

[0048] Figure 6 Figure 5(b) is a three-dimensional view of the preferred embodiment of the present application at construction stage S4;

[0049] In the drawings: 1 existing pipeline; 2 outer steel casing caisson; 2a reserved pipeline opening; 3a in-well groundwater level; 3b out-of-well groundwater level; 4 in-well excavation face; 5 inner steel casing caisson; 5a deep U-shaped slot; 6 underwater concrete; 7 compaction grouting pipe; 8 compaction grouting reinforcement; 9a shallow buried pipeline; 9b in-well riser; 9c T-shaped tee pipeline; 10 in-well backfill. DETAILED DESCRIPTION

[0050] The terms "application" and "the present application" used in the present specification are intended to refer broadly to all of the subject matter of this patent application. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of any patent claims below. Furthermore, the present specification shall not be interpreted as meaning that the only subject matter covered by this application is comprised of the specific components, paragraphs, statements, or figures used in the specification. The subject matter shall be interpreted in reference to the entire specification, all figures, and any patent claims below. The application can have other embodiments and be practiced or carried out in other ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

[0051] The details of the application will now be discussed with reference to the accompanying drawings, which illustrate only example embodiments of the application. In the drawings, like features or components can be labeled with the same reference numerals.

[0052] The use of "including", "has", "having" and "includes" and variations thereof herein is meant to encompass the items listed thereafter and equivalents and additional items. Although the terms such as above, below, upward, downward, front, back, bottom, top, rear, etc. can be used in this description to facilitate understanding of the concepts, these terms are used in relation to the drawings, as appropriate. These terms are not intended to literally recite or limit the application in any form. In addition, terms such as "first", "second", "third", etc. are used herein for illustrative purposes only and are not intended to signify importance or significance.

[0053] Referring to FIGS. 1 to Figure 6 The double-layer steel casing caisson structure for water-rich soft soil stratum connection construction of the present application includes an outer layer steel casing caisson 2, an inner layer steel casing caisson 5 and an inner-outer pipeline passage. The outer layer steel casing caisson 2 is cylindrical and arranged above the existing pipeline 1 with the connection point position as the center. The outer layer 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 positioned, and then the inner layer steel casing caisson 5 is sunk inside the outer layer steel casing caisson 2.

[0054] Further, the outer layer steel casing caisson 2 is provided with a circular reserved pipeline opening 2a at the top, which is temporarily blocked by blocking measures during the sinking process.

[0055] Referring to Figure 2(a) , 2(b) , 2(c) and Figure 5 The inner layer steel casing caisson 5 has a rectangular structure with the short side perpendicular to the existing pipeline 1 and the long side parallel to the existing pipeline 1. A deep U-shaped notch 5a is arranged at the bottom of the short side, and the radius of the semicircle at the top of the deep U-shaped notch 5a is slightly larger than the radius of the existing pipeline 1. When the inner layer steel casing caisson 5 is sunk, the deep U-shaped notch 5a is aligned with the existing pipeline 1 to ensure that the existing pipeline 1 can be accurately embedded in the deep U-shaped notch 5a after the sinking is completed. The long side of the caisson is inserted below the existing pipeline 1 to form effective support for the soil body below the pipeline.

[0056] Further, a flexible rubber strip is arranged on the surface of the deep U-shaped notch 5a at the bottom of the short side of the inner layer steel casing caisson 5 structure to avoid damage to the existing pipeline 1 caused by collision and contact during the sinking process, and also to play a certain water and sand blocking role.

[0057] Further, a compact grouting pipe 7 is embedded in the inner surface of the inner layer rectangular steel casing caisson 5 structure.

[0058] Referring to Figure 3(a) , 3(b)As shown in Figs. 3(c), in the water-rich stratum, the excavation construction after the sinking of the double-layer steel casing caisson is underwater excavation, and the mechanical excavation is performed on the ground surface without personnel entering the caisson to ensure the safety of the personnel. After the sinking of the inner-layer steel casing caisson 5, the underwater concrete 6 is poured between the inner and outer-layer steel casing caissons, and the pre-embedded pressure grouting pipe 7 is used to grout and reinforce the soil between the inner-layer rectangular steel casing caisson 5 and the existing pipeline 1 and the soil below the existing pipeline 1. Through the above-mentioned combined measures, the underground water isolation layer is formed at the bottom of the inner and outer-layer steel casings, and finally the underground water level 3a in the caisson is pumped out for 3a to form a dry working environment in which the personnel can work in the caisson.

[0059] During the process of pumping out the underground water in the double-layer steel casing caisson, the underground water level 3b outside the caisson is synchronously observed. If the underground water level 3b outside the caisson also decreases during the process of pumping out the underground water in the caisson, it indicates that there is still a water seepage channel in the underground water isolation layer at the bottom of the steel casing, at which time the pumping out of the underground water in the caisson is stopped, and the underground water isolation layer is reinforced for the second time. The reinforcement measures include continuously pouring the underwater concrete 6 between the inner and outer-layer steel casing caissons and performing the second grouting through the pre-embedded pressure grouting pipe 7. After the reinforcement measures are completed, the pumping out of the underground water in the caisson and the observation of the underground water level 3b outside the caisson are continued. Until the underground water level 3b outside the caisson does not change when the underground water in the caisson is pumped out, the underground water level 3a in the caisson is completely pumped out.

[0060] Referring to Figs. 4(c) and Figure 4(a) , 4(b) Figure 6 After the underground water in the double-layer steel casing caisson is pumped out, the personnel work in the caisson to cut the existing pipeline 1, install the T-shaped three-way pipeline 9c, and install the vertical pipeline 9b in the caisson. The newly-built shallow buried pipeline 9a penetrates the pre-embedded pipeline hole 2a at the top of the outer-layer steel casing caisson to enter the caisson and is connected with the vertical pipeline 9b in the caisson. After the connection is completed, the backfilling 10 in the caisson is completed according to the requirements.

[0061] Correspondingly, the application provides a construction method of a double-layer steel casing caisson structure, which comprises the following steps:

[0062] S1: constructing the outer-layer steel casing caisson 2, specifically comprising the following steps:

[0063] S11: pressing the outer-layer steel casing caisson 2 from the ground surface at the position of the existing pipeline 1 where the pipeline is to be connected, sinking the caisson above the existing pipeline 1, and making the bottom of the caisson as close as possible to the top of the existing pipeline 1. During the sinking process, the pre-embedded pipeline hole 2a at the top of the caisson is sealed by a temporary cover plate.

[0064] S12: performing the soil excavation in the caisson body on the ground surface, and ensuring that the underground water level 3a in the caisson is flush with the underground water level 3b outside the caisson during the excavation.

[0065] ​S13: After the top 180° of the existing pipeline 1 is removed, the position and elevation of the existing pipeline 1 are accurately positioned.

[0066] S2: The deep U-shaped notch 5a of the inner layer steel casing caisson 5 is aligned with the center of the existing pipeline 1 and pressed into the caisson, ensuring that the existing pipeline 1 can be accurately embedded in the deep U-shaped notch 5a. A flexible rubber strip is provided on the surface of the deep U-shaped notch 5a to avoid damage to the existing pipeline 1 caused by contact during the sinking process.

[0067] S3: The underground water isolation layer at the bottom of the caisson is constructed, including the following steps:

[0068] S31: Underwater concrete 6 is poured between the inner and outer layer caissons to form the underground water isolation layer between the inner and outer layer caissons.

[0069] S32: The soil between the inner layer steel casing caisson 5 and the existing pipeline 1 and the soil below the existing pipeline 1 are grouted and reinforced through the pre-buried pressure grouting pipe 7 on the inner wall of the inner layer steel casing caisson 5, forming the underground water isolation layer between the inner layer steel casing caisson 5 and the existing pipeline 1.

[0070] S33: After the underwater concrete 6 and the pressure grouting reinforcement 8 reach the designed strength, the underground water level 3a in the caisson is tested for lowering, and the change of the underground water level 3b outside the caisson is observed. If the underground water level 3a in the caisson decreases, the underground water level 3b outside the caisson also decreases synchronously, then the steps of S31-S32 are repeated to strengthen the underground water isolation layer; the strengthening measures include continuing to pour underwater concrete 6 between the inner and outer layer caissons, and performing secondary grouting and reinforcement of the pressure grouting reinforcement 8 inside the inner layer steel casing caisson 5, until the underground water level 3b outside the caisson does not change when pumping water in the caisson, at which time the underground water level 3a in the caisson is completely pumped out, preparing for the next process.

[0071] S4: After the underground water level 3a in the caisson is pumped out, personnel enter the caisson to perform the in-caisson pipe connection operation, including the following steps:

[0072] S41: A T-shaped pipe tee 9c is provided on the existing pipeline 1, and an in-caisson vertical pipe 9b is installed.

[0073] S42: A newly built shallow buried pipeline 9a is connected to the caisson through the pipeline hole 2a reserved at the top of the outer layer steel casing caisson and connected to the in-caisson vertical pipe 9b.

[0074] S43: After the pipe connection is completed, the in-caisson backfill 10 is performed as required.

[0075] The above merely preferred embodiments of the present application and are not intended to limit the embodiments and protection scope of the present application. Those skilled in the art should be able to understand that any equivalent substitutions and obvious changes made according to the present application description and drawings should be included in the protection scope of the present application.

Claims

1. A double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata, characterized in that, It 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 is arranged above the existing pipeline (1) with the connection point as the center. The inner steel casing caisson (5) is sunk into the interior of the outer steel casing caisson (2) and sits on the existing pipeline (1). A groundwater isolation layer is 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).

2. The double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata as described in claim 1, characterized in that, The bottom of the inner steel casing caisson (5) is provided with a deep U-shaped groove (5a). The top of the deep U-shaped groove (5a) is a semi-circle with a radius slightly larger than that of the existing pipe (1). The inner steel casing caisson (5) sits on the existing pipe (1) through the deep U-shaped groove (5a).

3. The double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata as described in claim 1, characterized in that, The inner surface of the inner steel casing caisson (5) is pre-embedded with a compaction grouting pipe (7).

4. The double-layer steel casing caisson structure for pipe connection construction in water-rich soft soil strata as described in claim 1, characterized in that, The surface of the deep U-shaped groove (5a) is provided with a flexible rubber strip.

5. A method for constructing a double-layer steel casing caisson in water-rich soft soil strata, comprising constructing the double-layer steel casing caisson structure as described in any one of claims 1 to 4, 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 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 water level in the well and observe the changes in the groundwater level outside the well. If the water level in the well decreases and the water 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 rectangular steel casing caisson until the water level outside the well does not change when water is pumped out. At this point, the water level in the well is completely pumped out to prepare for the next process. S4. After the water 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-type tee pipe interfaces on existing pipelines and install risers inside the manholes; S42. The newly built shallow buried pipeline passes through the pre-reserved pipeline opening at the top of the outer steel casing caisson and enters the caisson, and connects with the riser inside the caisson; S43. After the takeover is completed, the caisson shall be backfilled as required.

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