Composite foundation stress isolation structure adjacent to existing railway and construction method

Abstract

The invention discloses a stress isolation structure of a composite foundation adjacent to an existing railway and a construction method of the stress isolation structure, and active control of roadbed displacement of the existing railway is realized by constructing a composite barrier of rigid isolation piles and flexible cloth bag piles and combining a staged construction process matched with soil stress development. According to the technology, when the embankment is filled to half of the height, the cloth bag piles on the pile tops are activated, after filling is completed and stabilization is conducted, the cloth bag piles between the piles are activated, and a complete composite isolation wall is formed; and through stress transmission path construction and elastic wave verification, the integrity of the isolation system is ensured. On-site application shows that the process can effectively limit the horizontal displacement of the existing line roadbed, the maximum displacement value is effectively reduced compared with a traditional method, deformation distribution is uniform, the safety and reliability of adjacent business line construction are greatly improved, and meanwhile extra cost caused by later reinforcement is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of foundation construction, in particular to a composite foundation stress isolation structure and construction method close to an existing railway. BACKGROUND

[0002] In the field of railway construction, it is common but challenging to construct new projects adjacent to existing operating lines. When constructing a new roadbed next to an existing railway, the lateral earth pressure generated by the new embankment filling will squeeze the existing roadbed, causing it to displace horizontally, which may affect the track geometry and pose a safety risk to train operation.

[0003] Traditional construction methods usually use single isolation piles or continuous walls as protective measures, but due to their single structure and fixed construction timing, they cannot adapt to the dynamic development of soil stress during the filling process of the new roadbed. Especially in soft soil conditions, the cooperative performance of the isolation structure and the surrounding soil is poor, making it difficult to prevent shallow soil from sliding along the pile body, resulting in poor displacement control of the existing roadbed, which often requires additional post-construction reinforcement measures, increasing engineering costs and project risk. SUMMARY

[0004] The present application aims to provide a composite foundation stress isolation structure and construction method close to an existing railway, which realizes active control of the displacement of the existing roadbed by constructing a composite barrier of rigid isolation piles and flexible bag piles, and combining a phased construction process that matches the development of soil stress.

[0005] To achieve the above purpose, the technical solution adopted by the present application is as follows: a composite foundation stress isolation structure close to an existing railway, comprising: continuous concrete isolation piles arranged along the junction of the new railway and the existing railway; bag piles arranged at the top of the isolation piles, which are composed of water-permeable geotextile bags filled with cement-improved soil, forming a hoop structure at the top end of the isolation piles; inter-pile bag piles arranged at the midpoint of adjacent isolation piles, which, together with the surrounding compacted soil, form a continuous flexible belt that works together with the rigid isolation piles to form an integrated composite isolation wall; and static pressure pipe piles arranged on the side of the new railway, the top of which is connected to a double-layer double-direction reinforced raft slab.

[0006] On the other hand, the present application proposes a construction method for a composite foundation stress isolation structure close to an existing railway, comprising: construction preparation and measurement and setting out, including laying temporary reference points and setting out the axis of the isolation piles on site; based on the results of measurement and setting out, forming continuous concrete piles by isolating pile hole forming and concrete pouring; After the completion of the isolation pile construction, the new line foundation bottom layer treatment and raft construction are carried out, the gravel cushion is laid and the static pressure pipe pile is constructed, the first stage embankment filling is carried out on the raft to half of the design total height, then the construction is suspended, the top bag pile construction is carried out on the top of the isolation pile; After the embankment filling is resumed to the design elevation and is stabilized, the position preparation of the inter-pile top bag pile is carried out at the midpoint of the adjacent isolation piles, the inter-pile top bag pile is formed based on the prepared position, and the composite isolation wall is closed; The additional load is applied through the horizontal displacement monitoring data, the stress transmission path of the isolation pile and the top bag pile is constructed, then the elastic wave test is carried out on the composite isolation wall, and the integrity and long-term performance are verified.

[0007] Preferably, the construction preparation and measurement and lofting include: When the temporary reference point is laid out, the area far away from the mechanical walking route and with stable geological conditions is selected, the three-dimensional coordinate error is controlled within ±3mm through multiple back-and-forth measurement and adjustment calculation; After the main axis is lofted, the center position of each isolation pile is measured and lofted at a three-meter interval along the line direction, and a mark is set at the midpoint of the connecting line of the adjacent two isolation piles; After the pile position marking is completed, the site is leveled, the 0.5m soft soil on the surface is excavated and removed, the graded gravel is backfilled in layers, and the compaction is carried out until the characteristic value of the ground bearing capacity reaches more than 150kPa.

[0008] Preferably, the isolation pile hole forming and concrete pouring include: When the hole is drilled, the vertical state of the drill rod is monitored in real time through the electronic inclination sensor, the hole diameter is one meter, the deviation is ±20mm, and the depth penetrates the upper soft soil layer and enters the hard soil layer by not less than two meters; The hole cleaning adopts the air-lift reverse circulation mode, the thickness of the hole bottom sediment is controlled to be less than 50mm, the mud specific gravity is less than 1.15, and the sand content is lower than 2%; After the steel reinforcement cage is lowered, it is fixed on the hole mouth casing through the four positioning steels welded at the top; When the underwater concrete is poured, the guide pipe is kept buried at a depth of 2 to 6 meters, and the pouring is carried out to be 50cm above the design elevation of the pile top.

[0009] Preferably, the new line foundation bottom layer treatment and raft construction include: The 50cm thick graded gravel cushion is laid, the maximum particle size of the gravel is not more than 50mm, the silt content is lower than 5%, and the compaction coefficient K is greater than or equal to 0.95; The static pressure pipe pile adopts the prestressed high-strength concrete pipe pile with an outer diameter of 500mm and a wall thickness of 100mm, and the pile pressing force is terminated when the design requirement final pressure value is reached; After the pile head treatment, the 50cm thick raft steel reinforcement is bound, and the double-layer and double-direction reinforcement is adopted.

[0010] Preferably, the embankment is first constructed to half the total design height on the raft, and then the construction of pile-top bag piles on the top of the isolation piles is performed, including: The filling is performed using Group A or Group B fillers, with a loose thickness of 30 cm per layer and a compaction degree K≥0.90, and the filling is stopped when the height reaches half of the total design height; A guide hole is drilled above the top of the isolation piles using a high-pressure grouting device, a permeable geotextile bag filled with cement-modified soil is sent to the bottom of the hole, and a high-pressure fluid is injected to inflate the bag, with an initial diameter of 0.3 meters expanding to 0.4 meters; The relationship between the volume increment of the inflated bag and the volume strain of the surrounding soil is analyzed to quantify the strength improvement of the soil caused by the compaction effect.

[0011] Preferably, the position preparation for the inter-pile bag pile in the middle of the adjacent isolation piles is performed, including: The same filler type, loose thickness, and compaction process as in the first stage are maintained when the embankment filling is resumed; The filling is performed to the design elevation, and then a settlement period of 7 to 14 days is entered, and when the settlement rate is less than 0.5 mm / day for consecutive days, the surface at the middle point between the piles is cleaned; The distance between the middle point mark and the two side isolation piles is reviewed to ensure that it is located in the middle, and the vertical alignment of the guide pipe of the high-pressure grouting device with the mark point is adjusted.

[0012] Preferably, the inter-pile bag pile is formed based on the prepared position, so that the composite isolation wall is closed, including: A permeable geotextile bag filled with cement-modified soil mixture is sent underground to the same depth as the pile-top bag pile; The pressure of the high-pressure pump is controlled to allow the bag to inflate smoothly under the radial constraint of the surrounding soil; The change in void ratio caused by the inflation of the bag is analyzed to calculate the shear strength improvement effect; The construction of adjacent inter-pile bag piles is spaced 24 hours apart to allow the soil stress to be preliminarily adjusted, and all inter-pile bag piles and compacted soil together form a continuous flexible belt, which forms an overall composite wall with the rigid isolation piles.

[0013] Preferably, the stress transmission path of the isolation piles and the bag piles is constructed, including: Two rows of horizontal displacement monitoring points are symmetrically arranged at the shoulder position on the top surface of the embankment, the probe is buried to a depth that penetrates the soft soil layer and enters the hard soil layer, the monitoring frequency is once every 2 hours, and the monitoring lasts for 7 days; A depth-displacement curve is drawn to identify the position of the soil shear slip surface; If the slip surface is close to the embankment slope toe and develops towards the existing line, temporary loading is applied on the ground projection area above the pile-top bag pile, with a load weight of 10%-15% of the weight of the overlying soil, and the loading lasts for 48 hours, and after the load is removed, the displacement rate is continuously monitored to verify the displacement rate slowing effect.

[0014] Preferably, the elastic wave test on the composite isolation wall comprises: The micro-vibration points are arranged on the surface of the new area along the axis of the isolation pile at an interval of one meter; High-sensitivity seismic detectors are arranged at the same position on the existing line side; Transient impact is applied to each vibration point, and the propagation time, waveform and energy attenuation of the wave are recorded; The average wave velocity of the elastic wave passing through the composite isolation wall is calculated, and the deviation is less than 10% compared with the theoretical calculation value based on the area proportion of the concrete pile, the bag pile and the compacted soil, so as to determine that the integrity of the composite isolation wall meets the requirements.

[0015] Preferably, the first-stage filling of the embankment on the raft plate to half of the designed total height is suspended, and the pile-top bag pile construction is performed on the top of the isolation pile, and the method further comprises: The cement content of the cement modified soil is 8% during the bag pile construction; The embankment filling process is always symmetrically performed from the center of the embankment to the two side slopes; When the pile-top bag pile and the inter-pile bag pile jointly act, a hoop structure is formed at the top end of the isolation pile through the compacting effect, the shear resistance of the pile-top area is enhanced, and the shallow soil body is prevented from sliding upward along the isolation pile.

[0016] Compared with the prior art, the method has the beneficial effects that: The method realizes the active control of the displacement of the existing line embankment by constructing the composite barrier of the rigid isolation pile and the flexible bag pile, and combining the phased construction process matching the stress development of the soil body. The pile-top bag pile is activated when the embankment is filled to half of the height, the inter-pile bag pile is activated after the filling is completed and stabilized, and a complete composite isolation wall is formed. The integrity of the isolation system is ensured through the stress transmission path construction and the elastic wave verification. The field application shows that the method can effectively limit the horizontal displacement of the existing line embankment, the maximum displacement value is effectively reduced compared with the traditional method, the deformation distribution is uniform, the safety and reliability of the construction adjacent to the operating line are greatly improved, and the additional cost caused by the later reinforcement is avoided. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a schematic diagram of the composite foundation stress isolation structure adjacent to the existing railway of the application; Figure 2 It is a flowchart of the foundation isolation construction process adjacent to the operating line of the application.

[0018] In the figure: 1, isolation pile; 2, pile-top bag pile; 3, inter-pile bag pile; 4, static pressure pipe pile; 5, reinforced raft plate. DETAILED DESCRIPTION

[0019] The following description is used to disclose the present application to enable a person skilled in the art to implement the present application. The preferred embodiments in the following description are only as examples, and other obvious modifications can be conceived by those skilled in the art.

[0020] As shown in Figure 1 The present application proposes a composite foundation stress isolation structure adjacent to an existing railway, which comprises: continuous concrete isolation piles 1 arranged along the junction of the newly built railway and the existing railway; pile top bag piles 2 arranged at the top of the isolation piles, which are composed of water permeable geotextile bags filled with cement modified soil, forming a hoop structure at the top end of the isolation piles; inter-pile bag piles 3 arranged at the midpoint of adjacent isolation piles, which together with the surrounding compacted soil form a continuous flexible belt, and work together with the rigid isolation piles to form an integral composite isolation wall; and static pressure pipe piles 4 arranged on the side of the newly built railway, the top of which is connected to a double-layer double-direction reinforced raft 5.

[0021] The present application proposes a composite foundation stress isolation structure adjacent to an existing railway and a construction method as shown in Figure 2 The present application proposes a composite foundation stress isolation structure adjacent to an existing railway and a construction method as shown in Construction preparation and measurement and setting out, including arranging temporary reference points on site and setting out the axis of the isolation piles; specifically including: when arranging temporary reference points, selecting an area far from the mechanical walking route and with stable geological conditions, controlling the three-dimensional coordinate error within ±3mm through multiple round-trip measurements and adjustment calculations; after setting out the main axis, measuring and setting out the center position of each isolation pile at a three-meter interval along the line direction, and setting a mark at the midpoint of the connecting line of the adjacent two isolation piles; after completing the pile position marking, the site is leveled, the 0.5m soft soil on the surface is excavated, and graded gravel is backfilled in layers, and compacted to a surface bearing capacity characteristic value of more than 150kPa. A high-precision spatial reference and an operation surface with sufficient bearing capacity are provided for subsequent processes, ensuring the stable positioning of large machinery and the verticality of drilling, thereby ensuring the accuracy of isolation pile hole positioning and the straightness of the overall linear shape from the source.

[0022] Based on the results of measurement and setting out, the isolation pile hole is formed and the concrete is poured to form a continuous concrete pile; specifically including: when drilling, the vertical state of the drill rod is monitored in real time through an electronic inclination sensor, the drilling diameter is one meter, the deviation is ±20mm, and the depth penetrates the upper soft soil layer and enters the hard soil layer by not less than two meters; the hole cleaning adopts air-lift reverse circulation mode, the thickness of the hole bottom sediment is controlled to be less than 50mm, the mud specific gravity is less than 1.15, and the sand content is less than 2%; after the reinforcement cage is lowered, it is fixed on the hole mouth casing through four positioning steels welded at the top; when pouring underwater concrete, the guide pipe is kept buried to a depth of 2 to 6 meters, and poured to 50cm above the design elevation of the pile top.

[0023] The verticality, hole cleaning and reinforcement cage positioning accuracy of the isolation pile are ensured, the continuity and integrity of the pile body concrete are effectively guaranteed, and a rigid barrier with sufficient embedded depth and structural strength is formed, providing a reliable bearing foundation for the overall stability of the subsequent composite isolation wall.

[0024] After the completion of the isolation pile construction, the new line base layer treatment and raft construction are carried out, the gravel cushion is laid and the static pressure pipe pile is constructed, specifically including: laying a 50 centimeter thick graded gravel cushion, the maximum particle size of the gravel is not more than 50 millimeters, the silt content is less than 5%, and the compaction coefficient K is greater than or equal to 0.95; the static pressure pipe pile adopts a prestressed high-strength concrete pipe pile with an outer diameter of 500 millimeters and a wall thickness of 100 millimeters, and the pile pressing force is terminated when it reaches the design requirement final pressure value; after the pile head treatment, a 50 centimeter thick raft steel bar is bound, and double-layer double-direction reinforcement is adopted. A uniform and stable bearing layer is formed, effectively dispersing the upper embankment load and inhibiting uneven settlement; the synergistic effect of the static pressure pipe pile and the raft significantly improves the foundation bearing capacity, providing a flat and high-strength foundation support surface for the subsequent embankment filling and bagged pile construction, and ensuring the stable transmission of the upper structure load to the isolation pile system.

[0025] After the first stage of embankment filling to half of the design total height on the raft, the pile top bagged pile construction is carried out on the top of the isolation pile; specifically including: filling with A or B group fillers, each layer with a loose paving thickness of 30 centimeters and a compaction degree K greater than or equal to 0.90, and stopping when the filling height reaches half of the design total height; using high-pressure grouting equipment to drill a guide hole directly above the top of the isolation pile, sending a permeable geotextile bag filled with cement modified soil to the bottom of the hole, injecting high-pressure fluid to make the bag expand, and the initial diameter of 0.3 meters expands to 0.4 meters; by analyzing the relationship between the volume increment of the bag expansion and the volume strain of the surrounding soil, the soil strength improvement caused by the compaction effect is quantified. The cement content of 8% is used in the bagged pile construction; the embankment filling process is always symmetrically carried out from the center of the embankment to the two side slopes; when the pile top bagged pile and the inter-pile bagged pile work together, a hoop structure is formed at the top of the isolation pile through the compaction effect, enhancing the shear resistance of the pile top area and preventing the shallow soil from sliding upward along the isolation pile.

[0026] At the key stage of embankment filling, the pile top bagged pile is activated, the compaction and compaction effect of which significantly improves the density and shear strength of the soil at the top of the isolation pile, forming an effective hoop constraint structure, inhibiting the lateral sliding tendency of the shallow soil of the new embankment towards the existing line, and achieving effective control of the deformation source.

[0027] After the embankment is restored to the design elevation and stabilized, the position of the bagged pile between the adjacent isolation piles is prepared at the midpoint, which specifically includes: maintaining the same filler type, loose paving thickness and compaction process as in the first stage during the restoration of embankment filling; after filling to the design elevation, enter the settlement period for 7 to 14 days, when the settlement rate is less than 0.5 mm / day for consecutive days, clean the surface of the midpoint position between the piles; review the distance between the midpoint mark and the two side isolation piles to ensure that it is in the middle, and adjust the vertical alignment of the high-pressure grouting equipment guide pipe to the mark point.

[0028] By settlement stability period judgment and positioning, it is ensured that the bagged pile between the piles is constructed after the embankment deformation tends to be stable, and it is ensured that the bagged pile is located in the optimal position between the isolation piles, which creates precise geometric conditions for the subsequent formation of continuous and uniform composite isolation wall, and effectively avoids the structural weak plane caused by improper timing or positioning deviation.

[0029] Based on the prepared position, the bagged pile between the piles is formed to close the composite isolation wall; specifically including: sending the permeable geotextile bag filled with cement modified soil mixture into the ground, with the same depth as the bagged pile on the pile top; control the pressure of the high-pressure pump to make the bag expand smoothly under the radial constraint of the surrounding soil; analyze the change of void ratio caused by the bag expansion, and calculate the shear strength improvement effect; the construction interval of adjacent bagged piles between piles is 24 hours, so that the soil stress is preliminarily adjusted, and all the bagged piles between the piles and the compacted soil body together form a continuous flexible belt, and form an overall composite wall with the rigid isolation pile.

[0030] The flexible connection between the rigid isolation piles is realized, and a continuous closed composite isolation wall is formed; through controllable expansion and time sequence construction, the compaction effect is uniformly expanded in the plane, which significantly improves the overall lateral deformation resistance of the wall, effectively blocks the flow path of the soil between the isolation pile gaps, and enhances the integrity and barrier effect of the structure.

[0031] Additional loads are applied through horizontal displacement monitoring data to build a stress transfer path for the isolation pile and the bagged pile, which specifically includes: symmetrically arranging two rows of horizontal displacement monitoring points at the shoulder position on the top surface of the embankment, the probe is buried to a depth that penetrates the soft soil layer into the hard soil layer, the monitoring frequency is once every 2 hours, and the monitoring lasts for 7 days; draw a depth-displacement curve to identify the position of the soil shear slip surface; if the slip surface is close to the embankment slope toe and develops towards the existing line, temporarily pile up a load on the ground projection area above the bagged pile on the pile top, the load weight is 10%-15% of the weight of the overlying soil, and the load lasts for 48 hours. Continue to monitor after removing the load to verify the displacement rate slowing effect.

[0032] By real-time monitoring to identify potential sliding trends, controllable additional loads are used to actively induce stress redistribution, which promotes the cooperative stress of the isolation pile and the bagged pile, optimizes the stress transfer path inside the composite wall, effectively suppresses the lateral displacement development of the deep soil, and improves the overall stability and anti-deformation ability of the structural system.

[0033] Then the composite isolation wall is tested by elastic wave to verify the integrity and long-term performance, specifically including: along the isolation pile axis on the surface of the new area, a micro excitation point is arranged at an interval of one meter; high-sensitivity seismometers are arranged at the same position on the existing line side; a transient impact is applied to each excitation point, and the propagation time, waveform and energy attenuation of the wave are recorded; the average wave velocity of the elastic wave passing through the composite isolation wall is calculated, and compared with the theoretical calculation value based on the area ratio of concrete piles, bag piles and compacted soil, and the deviation is less than 10%, the integrity of the composite isolation wall is determined to meet the requirements.

[0034] The non-destructive quantitative verification of the structural integrity and uniformity of the composite isolation wall is realized, the consistency of the measured wave velocity and the theoretical value is used to judge the cooperative working effect of the rigid pile and the flexible belt, and the wall body is ensured to have no obvious weak area or gap, which provides a reliable basis for evaluating the long-term service performance and engineering safety.

[0035] In order to more clearly illustrate the specific steps of the composite foundation stress isolation structure and construction method close to the existing railway, the following will be further described in combination with specific embodiments: Step 1: Construction preparation and measurement and setting out This step lays the spatial and environmental foundation for all subsequent engineering activities, and its core task is to convert the design on the drawing into accurate physical coordinates on site, and to create safe and stable site conditions for large-scale mechanical operations.

[0036] 1.1 According to the high-level control points provided by the survey department, a set of stable temporary reference points are laid out on the construction site using high-precision total stations. These reference points are selected in places far from the future heavy machinery walking route and with relatively stable geological conditions to prevent them from moving during construction. Through multiple round-trip measurements and adjustment calculations, the three-dimensional coordinate error of each reference point is ensured to be less than ±3mm. This set of reference points forms the framework of the entire construction area, and all subsequent local setting out work will rely on it.

[0037] 1.2 Taking the temporary reference points established in step 1.1 as the starting data, the first main axis is set out according to the plan position of the isolation pile axis in the design file. The setting out content includes the starting point, ending point and intermediate key turning points of the isolation pile belt. These points are fixed with concrete markers buried in the ground and equipped with protective covers. The setting out of the main axis determines the overall trend of the isolation pile belt.

[0038] 1.3 After the main axis is confirmed, the precise center position of each isolation pile is measured and placed along the line direction according to the design specified center distance of isolation piles (e.g. 3.0 meters) using polar coordinate method. Each pile position is vertically nailed into the ground with a steel bar whose top is painted red, and a small concrete pier is poured around it to fix and protect it. At the same time, in order to accurately position the subsequent bag pile, an auxiliary marker is also set at the ground projection point directly above each isolation pile, and a marker is also set at the midpoint of the line connecting the two adjacent isolation piles. These marker points form a dense two-dimensional grid, ensuring the absolute accuracy of the later pile position.

[0039] 1.4 After completing all pile position marking, the site is leveled for construction operations. Remove surface vegetation, construction waste and all obstacles. For sections with soft layers (such as silt soil) or accumulated water on the surface, they need to be treated by replacement. The specific method is to remove 0.5 meters thick soft soil on the surface, then backfill graded gravel or gravel in layers, each layer not more than 30 centimeters thick, and use a vibrating roller to repeatedly compact until the surface bearing capacity characteristic value reaches more than 150 kPa. The completed work surface should be flat, solid, and have a certain transverse slope to facilitate drainage. At this time, the rotary drilling rig can be put into place. After the equipment is placed stably, the total station instrument needs to be used again to check whether the drill rod center coincides with the pile position center placed in step 1.3, and the whole preparation work is completed after the confirmation, providing reliable guarantee for the hole forming operation of the isolation pile.

[0040] Step two: Isolation pile hole forming and concrete pouring This step is the key process of materializing the isolation pile in the design under the precise conditions created in step one. Its goal is to form a series of high-strength concrete piles with a diameter of 1.0 meters and a depth sufficient to anchor in stable soil layers, forming a rigid framework to resist lateral pressure.

[0041] 2.1 Use the rotary drilling rig that has been calibrated and placed in step 1.4 to drill down from the surface at the set speed and drilling pressure. During the drilling process, the vertical state of the drill rod is monitored in real time through the electronic inclination sensor in the drilling rig cab. Once a deviation trend is found, it is immediately corrected by adjusting the hydraulic jacks of the drilling rig legs. The drilling diameter is strictly controlled at 1.0 meters with an allowable deviation of ±20 millimeters. The drilling speed is adjusted according to different soil layers, and slow drilling is preferred in soft clay layers to reduce disturbance to the hole wall, and fast drilling is required in sand layers to prevent collapse. The drilling depth needs to penetrate the upper soft and saturated clay layer and enter the lower hard soil layer (such as dense silty clay or sand) with good engineering properties not less than 2.0 meters, to ensure that the pile body has sufficient anchoring force to resist overturning.

[0042] 2.2 When the drill bit reaches the design bearing layer required in step 2.1 and reaches the predetermined depth, stop drilling. Start the hole cleaning program, use gas lift reverse circulation to completely discharge the drill cuttings, sediment and high sand content mud at the bottom of the hole. During the hole cleaning process, continuously supplement the qualified new mud into the hole to maintain the water head pressure of the hole wall and prevent the hole from collapsing. The quality of hole cleaning is determined by measuring the thickness of the sediment at the bottom of the hole. When the sediment thickness is less than 50 mm, and the specific gravity of the returned mud is less than 1.15 and the sand content is less than 2%, it is determined that the hole cleaning is qualified.

[0043] 2.3 After the hole cleaning is qualified, immediately lower the reinforcement cage. The reinforcement cage is pre-made in a special place, the main reinforcement uses HRB400 grade threaded steel, and the stirrup uses HPB300 grade round steel. Its specifications, length, reinforcement arrangement and welding quality have been inspected and accepted by the supervisor. When lowering, use a crawler crane to lift it smoothly through multiple point slings to avoid distortion. After the reinforcement cage is aligned with the center of the hole, it is slowly lowered. During the lowering process, its perpendicularity is observed at all times, and forced ramming is strictly prohibited. When the reinforcement cage is lowered to the design elevation, use the four positioning steels welded at the top of the reinforcement cage to firmly fix it on the casing at the hole, to prevent it from floating up due to buoyancy during subsequent concrete pouring.

[0044] 2.4 After the reinforcement cage is fixed, install a steel guide pipe with a diameter of 250 mm. The guide pipe is composed of multiple sections connected by flanges and rubber gaskets to ensure the interface is sealed. The bottom of the guide pipe is 30 to 50 cm away from the bottom of the hole. Then underwater concrete pouring is carried out. The concrete uses C30 commercial concrete with a slump of 180 to 220 mm, which has good fluidity and workability. The first batch of concrete must be poured to ensure that the initial burial depth of the guide pipe is not less than 1.0 meters to isolate the contact between the mud and the concrete. Thereafter, continuous pouring is maintained, the rising height of the concrete surface is measured at any time, and the guide pipe is lifted accordingly to always keep the depth of the guide pipe embedded in the concrete within the safe range of 2 to 6 meters. Pouring continues until the concrete liquid level is 50 cm higher than the design elevation of the pile top. The over-poured part will be removed later to ensure the integrity and compactness of the pile head concrete.

[0045] Step three: New line foundation treatment and raft construction This step shifts the focus of work to the new line side, and under the protection of the isolation barrier established in step two, starts to build the bearing foundation of the new roadbed itself.

[0046] 3.1 In the design of the new line embankment, first of all, the surface is cleaned, and then a layer of graded gravel cushion with a thickness of 50 cm is laid. The maximum particle size of the gravel is not more than 50 mm, and the clay content is less than 5%. After laying the cushion, a vibrating roller with a self-weight of not less than 20 tons is used for rolling, and the rolling frequency is not less than 6 times until the compaction coefficient K≥0.95. The main role of this layer of cushion is to diffuse the concentrated stress from the upper static pressure pipe pile and prevent it from penetrating into the underlying soft soil layer. At the same time, it provides a flat and solid working platform for the pile driver, avoiding the inclination of the machinery during construction.

[0047] 3.2 On the graded gravel cushion completed in step 3.1, the static pressure pipe pile construction is carried out according to the design pile layout. Pre-stressed high-strength concrete pipe piles (PHC piles) with an outer diameter of 500 mm and a wall thickness of 100 mm are selected. The static pressure pile driver is used to press the pipe pile into the soil one section at a time through the hydraulic system. During the pile pressing process, the size and trend of the pile pressing force are closely monitored. When the pile pressing force reaches the design final pressure value, or the pile length meets the design depth and the pile pressing force grows steadily, the pile pressing is terminated. The static pressure construction almost does not produce vibration and noise, which is crucial for the existing railway in operation, and can minimize the impact on the track geometry of the existing line.

[0048] 3.3 After all the static pressure pipe piles in a construction section are completed and the pile integrity is confirmed by low-strain dynamic testing, the pile head treatment is carried out. A special pile cutter is used to neatly cut off the part of the pile head that is above the design elevation, so that all the pile tops are kept at the same level. Then, the raft steel reinforcement is tied. The raft is 50 cm thick and uses double-layer double-direction reinforcement, with a tie bar supporting between the upper and lower reinforcement nets to ensure the accurate position of the reinforcement. The connection of the reinforcement uses welding or mechanical connection, and the joint position is staggered according to the regulations to ensure the overall bending resistance of the raft.

[0049] 3.4 After the reinforcement net is accepted, the formwork is set up. The formwork uses a shaped steel form, which is firm and tightly jointed to prevent concrete leakage. Then the raft concrete is poured, with a grade of C30. The pouring is carried out in a segmented and layered manner, from one end to the other end, using an inserted vibrator to ensure that the concrete is dense and free of honeycomb and pitted surface. After pouring, the second surface is promptly finished, then covered with double-layer geotextile and watered for maintenance, with a maintenance time of not less than 7 days. The role of the raft is to effectively disperse the huge load from the upper embankment to the numerous pipe piles below, forming a composite foundation that works together. With the completion of the raft, the foundation framework of the new embankment is basically formed, and its weight begins to be transmitted to the deep soil through the raft and pipe piles, thereby generating an initial lateral thrust on the isolation pile.

[0050] Step four: First-stage embankment filling and pile-top bag pile construction This step opens the dynamic interaction process of new embankment load application and protection system strengthening. When the new embankment bears about half of the total load, the first flexible reinforcement measure is activated, aiming to deal with the current stage of soil deformation requirements, embodying the "load-response" synchronous design concept.

[0051] 4.1 After the completion of the raft top surface in step 3.4, embankment filling is started. Choose A or B group fillers (such as sandy soil or gravel soil) that meet the specification requirements, and the maximum particle size of the filler shall not exceed 2 / 3 of the compaction thickness. The filling adopts horizontal layering method, and the loose paving thickness of each layer is strictly controlled within 30 cm. Use bulldozers for rough leveling, and use graders for fine leveling, and then use vibrating rollers above 22 tons for rolling. Rolling follows the principle of "light first, heavy later, slow first, fast later, and both sides first, middle later", generally rolling 6 to 8 times, until the compaction degree reaches the standard (K≥0.90) of the embankment below the subgrade through the sand filling method or nuclear density instrument detection.

[0052] 4.2 According to the method of step 4.1, continue the cycle of layered filling, leveling and rolling. During the filling process, it is always symmetrically carried out from the center of the embankment to the two side slopes to maintain the balance of the foundation stress and prevent uneven settlement. When the cumulative filling height reaches half of the designed total height, the filling work is temporarily suspended. At this time, the additional stress generated by the new embankment has transmitted a considerable part to the surrounding soil, the lateral earth pressure on the isolation pile has reached 60% to 70% of its final value, and the plastic deformation zone of the soil has been preliminarily expanded.

[0053] 4.3 After the embankment is filled to half the height, a bagged pile is constructed above the top of each isolation pile using high-pressure grouting equipment. Before construction, a guide hole is drilled at the pile top mark using a small drill, with a depth slightly greater than the design depth of the bagged pile. Then, a permeable geotextile bag filled with cement modified soil (cement content about 8%) is sent to the bottom of the hole through a recyclable conduit. Then, high-pressure water or cement slurry is pumped into the bag to make the bag expand radially under the constraint of the surrounding soil. The initial diameter of the bag is 0.3 meters, and the expanded diameter can reach 0.4 meters, forming a short and thick columnar body.

[0054] 4.4 The expansion of the bagged pile is a typical undrained shear process, which will produce a strong compaction effect on the surrounding soil. This effect can be quantitatively analyzed by the concept of soil volume strain. Assuming that the volume occupied by the bagged pile after expansion is , and the volume of the hole before expansion is , then the volume increment . This volume increment must be given up by the surrounding soil, causing it to compress. If the affected soil is considered as a cylindrical body with the bag as the center and the radius as , then its average volume strain is: ; wherein is the effective length of the bag pile. This positive value of directly reflects the degree of forced compression of the soil mass. The larger it is, the more the soil void ratio is reduced, and the more the dry density and shear strength of the soil are increased. The formation of such a strongly compacted soil ring at the top of the isolation pile is equivalent to adding a hoop at the top of the rigid pile, greatly enhancing the shear capacity of the pile top region and effectively preventing the tendency of the shallow soil mass to slide upward along the isolation pile. After the construction of the bag pile at the top of all the isolation piles is completed, the load application process of the new embankment will continue, creating conditions for the introduction of the second flexible reinforcement measure.

[0055] Step Five: Final Stage of Embankment Filling and Preparation of Bag Pile Positions between Piles This step takes over from the construction state of the previous stage and pushes the load application process of the new embankment to its end, allowing the entire foundation system to reach its final stress balance under design operating conditions.

[0056] 5.1 After completing the construction of the bag pile at the top of all the isolation piles in Step 4.4, resume the embankment filling work. Continue to follow the cycle of layer filling, paving, flattening, and rolling established in Step 4.1, gradually increasing the embankment layer by layer. All parameters such as filling type, loose paving thickness, compaction technology, etc. remain completely consistent with the first stage to ensure uniformity of the overall performance of the embankment. It is particularly important to note that when approaching the final layers of filling near the design elevation, height control must be strengthened, and precise leveling instruments must be used for measurement to ensure that the final formed embankment top surface strictly meets the design requirements of the longitudinal and transverse sections of the line, avoiding local overfilling or underfilling.

[0057] 5.2 When the embankment is filled to the design elevation, stop all rolling work of heavy machinery, allowing the new embankment to enter a natural settlement period under its own weight. This period usually lasts for 7 to 14 days, and its purpose is to allow the excess pore water pressure in the soil to dissipate and the primary consolidation settlement to be completed. During this period, periodic monitoring is carried out through settlement observation boards placed on the surface of the embankment, and when the settlement rate for consecutive days is less than a certain threshold (e.g., 0.5 mm / day), it is considered that the embankment has stabilized. At this time, the lateral soil pressure generated by the new embankment also reaches its maximum value and the distribution pattern is relatively fixed, and no longer changes dramatically.

[0058] 5.3 The stability of the roadbed is a prerequisite for proceeding with the next stage of construction. Because the construction of the inter-pile bag piles itself generates new disturbances, if this is carried out before the roadbed itself is stable, the superposition of old and new disturbances may lead to unpredictable consequences. Therefore, it is necessary to wait for the system to reach a relatively static equilibrium point. At this point, the isolation piles bear the maximum lateral thrust from the newly constructed area, while the existing roadbed is effectively blocked.

[0059] 5.4 Using the midpoint mark between two adjacent isolation piles pre-laid out in step 1.3, clean the surface of the area. Check the surface for cracks or depressions caused by previous settlement. If there is slight unevenness, a thin layer of sand can be laid to level it. Then, move the high-pressure grouting equipment to the designated position and adjust the guide pipe to align it vertically with the marked point. At the same time, check the distance between this point and the isolation piles on both sides to ensure that it is in the exact center. After the preparation work is completed, the forming operation of the bag piles between the piles can begin.

[0060] Step Six: Formation of Bag Piles Between Piles and Closure of Composite Isolation Wall This step involves filling the gaps between isolation piles under the condition that the stress field of the newly built roadbed is highly stable, transforming the discrete rigid pile body into a continuous and integral composite wall.

[0061] 6.1 Starting from the construction site prepared in step 5.4, permeable geotextile bags filled with cement-modified soil mixture are inserted into the ground through a conduit. The insertion depth must be the same as the depth of the geotextile bag pile at the top of the pile in step 4.3, ensuring that both form a reinforcement layer on the same horizontal plane, thus creating a continuous, three-dimensional reinforcement zone. Subsequently, a high-pressure pump is started to inject high-pressure fluid (clean water or thin cement slurry) into the geotextile bag, causing the geotextile bag to expand laterally under the radial constraint of the surrounding soil.

[0062] 6.2 The expansion of the ductwork exerts a strong compressive effect on the surrounding undisturbed soft soil. This compression alters the physical state of the soil, transforming it from a loose to a dense state. To quantify this process, the void ratio of the soil can be introduced. The concept. The initial void ratio is... After compaction, the porosity decreases to The decrease in porosity With volumetric strain There is a direct relationship: ; As can be seen from the formula in step 4.4, It is determined by the volume increase of the bag as it expands. The larger the value, the denser the soil becomes. According to Terzaghi's effective stress principle, the shear strength of soil... Its effective normal stress and internal friction angle Concerning: ; wherein is the effective cohesion. The densification of the soil mass is usually accompanied by an increase of and .

[0063] 6.3 After the formation of the bagged pile in each pile space, move the equipment to the next pile space and repeat the operations of steps 6.1 and 6.2. All the bagged piles in pile spaces are sequentially constructed. It is worth noting that, since the construction of each bagged pile will affect the soil mass in its adjacent area, the construction time of adjacent piles should be spaced a certain time (such as 24 hours) to allow the soil stress to be preliminarily adjusted to avoid excessive superposition effect. Ultimately, all the bagged piles in pile spaces and the soil mass they densify together form a continuous flexible belt which is tightly "woven" between the rigid isolation piles.

[0064] 6.4 By now, the entire isolation protection system has achieved complete spatial closure. The "skeleton" composed of concrete isolation piles and the "filling body" composed of bagged piles and their densified soil mass work together to form a composite wall with strong integrity and reasonable stiffness distribution. This wall not only has high bending and shear resistance, but also effectively blocks the seepage path between the new construction area and the existing area, reducing the risk of soil loss caused by seepage erosion. The lateral pressure of the new roadbed is effectively blocked by this continuous composite wall, and its deformation is limited to a very small range.

[0065] Step Seven: Construction of Stress Transmission Path of Isolation Pile and Bagged Pile This step is a key process of actively constructing and optimizing the internal mechanical conduction path of the structure. It uses the time window of soil consolidation to guide and solidify the transmission direction of new roadbed load to the deep stable stratum through specific intervention measures, while ensuring that the stress distribution inside the isolation protection system reaches the optimal state.

[0066] 7.1 Immediately after the completion of all pile space bagged pile construction in step six, symmetrically arrange two rows of horizontal displacement monitoring points on the new roadbed top surface along the longitudinal direction of the line at the shoulder position. These monitoring points use high-precision inclinometers or optical fiber sensors, and the probe depth needs to penetrate the entire soft soil layer and enter the lower hard soil layer. The monitoring frequency is set to every 2 hours for 7 days.

[0067] 7.2 Organize the data of horizontal displacement change with depth collected in step 7.1 to draw a complete depth-displacement curve. By analyzing the shape of the curve, the approximate position of the soil shear slip surface (i.e. the displacement mutation) can be identified. If the slip surface is found to be close to the toe of the new roadbed and has a tendency to develop towards the existing line, it indicates that the restraining force at the top of the isolation wall still has room for improvement.

[0068] 7.3 The core of the reinforcement plan is to apply a controlled, short-term additional load on top of the pile-top bag piles in some critical sections. The specific operation is to use small weight blocks (such as precast concrete blocks) to temporarily pile up on the ground outside the shoulder, directly opposite the ground projection area of the pile-top bag pile, with a pile-up weight of about 10%-15% of the weight of the overlying soil in that area, lasting 48 hours. This additional load will generate a downward vertical stress increment . According to the stress diffusion theory in soil mechanics, in homogeneous soil, this stress will spread to the surrounding area at a certain angle. For the pile-top bag pile and its compacted soil directly below it, will significantly increase its confining pressure, thereby further increasing the shear strength of the soil , expressed by the formula: ; where is the original effective normal stress, The addition of directly improves

[0069] 7.4 After 48 hours, remove the additional load and continue to monitor soil displacement. It is usually observed that the displacement rate slows down significantly and the depth-displacement curve tends to flatten. This indicates that through this active intervention, the stress transfer path at the top of the isolation and protection system has been successfully reshaped and strengthened, making it more effective in converting lateral thrust into downward pressure and transmitting it to the deep stable soil.

[0070] Step Eight: Integrity Verification and Long-term Performance Prediction of Composite Isolation Wall This step goes beyond traditional site cleanup and data archiving, elevating it to a scientific, field test-based system performance evaluation. It aims to verify, through a non-destructive method, whether the completed composite isolation wall truly achieves the designed overall cooperative performance, and makes a preliminary judgment on its long-term service ability.

[0071] 8.1 After the settlement of the new embankment has stabilized, select a representative section of the isolation and protection zone (length not less than 50 meters) and, on the ground surface on one side (newly built area), lay out a series of micro-vibration points along the axis of the isolation pile at intervals of 1.0 meters. Each vibration point uses a small mass drop hammer or electromagnetic vibrator to produce a controllable energy, spectrum-concentrated transient impact.

[0072] 8.2 On the other side (existing line side), at the same positions, lay out a set of high-sensitivity seismic detectors for receiving elastic wave signals through the composite isolation wall. When an impact is applied at one vibration point on the newly built side, the detector array will record the wave propagation time, wave shape and energy attenuation.

[0073] 8.3 Process the collected waveform data and calculate the average wave velocity of the elastic wave from the new side to the existing side If the composite isolation wall is well combined and has high integrity, because the concrete pile, bag pile and compacted soil jointly constitute a continuous and high stiffness barrier, the elastic wave will quickly pass through, The value is high. On the contrary, if there is obvious void or weak connection, the wave propagation path will become tortuous, and a large amount of energy will be scattered and absorbed, resulting in Significant reduction, and the waveform appears distorted.

[0074] 8.4 Compare the measured Value with the theoretically calculated value based on design parameters and material properties. The theoretical calculation can use the equivalent medium model, which regards the composite wall as a kind of isotropic homogeneous material, and the equivalent longitudinal wave velocity Can be estimated by the mixing law: ; Where Is the area ratio of the first Kind of component (such as concrete pile, bag pile, compacted soil) in the cross section, Is its respective longitudinal wave velocity. If the deviation of the measured From Is less than 10%, it is determined that the integrity of the composite isolation wall meets the design requirements. This test result together with all the construction records constitutes the most core technical evidence in the completion file, which not only proves the immediate quality of the project, but also provides valuable benchmark data for future possible maintenance and evaluation.

[0075] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application. The scope of protection required by the present application is defined by the appended claims and their equivalents.

Claims

1. A stress isolation structure of a composite ground foundation in close proximity to an existing railway, characterized by, The application relates to a continuous concrete isolation pile and a construction method thereof. The continuous concrete isolation pile comprises a continuous concrete isolation pile arranged at the junction of a newly-built railway and an existing railway; a cloth bag pile arranged at the top of the isolation pile, the cloth bag pile being composed of a water-permeable geotextile bag filled with cement-improved soil, and forming a hoop structure at the top end of the isolation pile; an inter-pile cloth bag pile arranged at the midpoint of adjacent isolation piles, the inter-pile cloth bag pile and the surrounding compacted soil body jointly forming a continuous flexible belt, and working together with the rigid isolation pile to form an integral composite isolation wall body; and a static pressure pipe pile arranged on the side of the newly-built railway, and the top of the static pressure pipe pile being connected with a double-layer and double-direction reinforced raft slab.

2. A construction method for the stress isolation structure of a composite foundation in close proximity to an existing railway as claimed in claim 1, characterized by, The application relates to a continuous concrete isolation pile and a construction method thereof. The construction preparation and measurement lofting comprises the following steps: arranging temporary reference points and lofting the axis of the isolation pile on the site; forming the continuous concrete pile based on the result of the measurement lofting and concrete pouring; after the completion of the construction of the isolation pile, carrying out the base layer treatment and raft construction of the newly-built line, laying a gravel cushion, and constructing the static pressure pipe pile, and then stopping the first-stage embankment filling to the half of the total design height, and carrying out the construction of the cloth bag pile at the top of the isolation pile; after the embankment filling is restored to the design elevation and is stabilized, carrying out the position preparation of the inter-pile cloth bag pile at the midpoint of adjacent isolation piles, and forming the inter-pile cloth bag pile based on the prepared position, so that the composite isolation wall is closed; 3. The construction method according to claim 2, characterized in that, applying an additional load through the horizontal displacement monitoring data, constructing the stress transmission path of the isolation pile and the cloth bag pile, and then carrying out the elastic wave test on the composite isolation wall to verify the integrity and long-term performance. The construction preparation and measurement lofting comprises the following steps: when the temporary reference points are arranged, a region far away from the mechanical walking route and having stable geological conditions is selected, and through multiple back-and-forth measurements and adjustment calculation, the three-dimensional coordinate error is controlled to be within + / - 3mm; after the main axis is lofted, the center position of each isolation pile is measured and lofted at a three-meter interval along the line direction, and a mark is arranged at the midpoint of the connecting line of the adjacent two isolation piles; 4. The construction method according to claim 2, characterized in that, after the pile position marking is completed, the site is leveled, the 0.5m soft soil on the surface is excavated, the graded gravel is backfilled in layers, and the characteristic value of the ground bearing capacity is compacted to be higher than 150kPa. The isolation pile hole forming and concrete pouring comprises the following steps: when the hole is drilled, the vertical state of the drill rod is monitored in real time through an electronic inclination sensor, the hole diameter is one meter, the deviation is + / - 20mm, and the depth penetrates the upper soft soil layer and enters the hard soil layer by not less than two meters; the hole cleaning adopts the air-lift reverse circulation mode, the thickness of the hole bottom sediment is controlled to be less than 50mm, the mud specific gravity is less than 1.15, and the sand content is lower than 2%; after the steel reinforcement cage is lowered, the four positioning steels welded at the top end are fixed on the hole mouth casing; 5. The construction method according to claim 2, characterized in that, when the underwater concrete is poured, the guide pipe is kept to be buried to a depth of 2-6 meters, and the pouring is carried out to be higher than the design elevation of the pile top by 50cm. The newly-built line base layer treatment and raft construction comprises the following steps: a 50cm-thick graded gravel cushion is laid, the maximum particle size of the gravel is not higher than 50mm, the silt content is lower than 5%, and the compaction coefficient K is greater than or equal to 0.95; the static pressure pipe pile adopts a prestressed high-strength concrete pipe pile with an outer diameter of 500mm and a wall thickness of 100mm, and the pile pressing force is terminated when the design requirement final pressure value is reached; after the pile head is treated, the 50cm-thick raft slab steel bars are bound, and the double-layer and double-direction reinforced raft slab is adopted.

6. The construction method according to claim 2, characterized in that, The first-stage filling of the embankment is suspended when the embankment is filled to half of the total design height, and the pile-top bag pile construction is carried out on the top of the isolation pile, including: The filling is performed by using A group or B group fillers, each layer has a loose laying thickness of 30 cm, the compaction degree K is greater than or equal to 0.90, and the filling is suspended when the filling height reaches half of the total design height; A high-pressure grouting equipment is used to drill a guide hole above the top of the isolation pile, a permeable geotextile bag filled with cement modified soil is sent to the bottom of the hole, a high-pressure fluid is injected to make the bag swell, and the initial diameter of 0.3 m is expanded to 0.4 m; The relationship between the volume increment of the bag swelling and the volume strain of the surrounding soil is analyzed, and the strength improvement of the soil caused by the compaction effect is quantified.

7. The construction method according to claim 2, characterized in that, The inter-pile bag pile position preparation is performed at the midpoint of the adjacent isolation pile, including: The same filler type, loose laying thickness and compaction process as in the first stage are maintained when the embankment filling is resumed; The embankment filling is performed to the design elevation, and then a settlement period of 7 to 14 days is entered, and when the settlement rate is less than 0.5 mm / day for consecutive days, the surface of the midpoint position between piles is cleaned; The distance between the midpoint mark and the two side isolation piles is reviewed to ensure that it is located in the middle, and the vertical alignment of the high-pressure grouting equipment guide pipe with the mark point is adjusted.

8. The construction method according to claim 2, characterized in that, The inter-pile bag pile is formed based on the prepared position, so that the composite isolation wall is closed, including: The permeable geotextile bag filled with cement modified soil mixture is sent underground, and the depth is the same as that of the pile-top bag pile; The pressure of the high-pressure pump is controlled to make the bag swell smoothly under the radial constraint of the surrounding soil; The change of the void ratio caused by the bag swelling is analyzed, and the shear strength improvement effect is calculated; The construction interval of adjacent inter-pile bag piles is 24 hours, so that the soil stress is preliminarily adjusted, and all the inter-pile bag piles and the compacted soil together form a continuous flexible belt, which forms an overall composite wall with the rigid isolation pile.

9. The construction method according to claim 2, characterized in that, The stress transmission path of the isolation pile and the bag pile is constructed, including: Two rows of horizontal displacement monitoring points are symmetrically arranged at the shoulder position on the top surface of the embankment, the probe is buried to a depth penetrating the soft soil layer into the hard soil layer, the monitoring frequency is once every 2 hours, and the monitoring lasts for 7 days; A depth-displacement curve is drawn to identify the position of the soil shear slip surface; If the slip surface is close to the embankment slope foot and develops towards the existing line, temporary loading is applied in the ground projection area above the pile-top bag pile, the loading weight is 10%-15% of the weight of the overlying soil, and the loading lasts for 48 hours, and after removing the load, the monitoring is continued to verify the displacement rate slowing effect.

10. The construction method according to claim 2, characterized in that, The elastic wave test of the composite isolation wall is performed, including: Miniature excitation points are arranged on the ground surface in the new area along the axis of the isolation pile at an interval of one meter; High-sensitivity seismic detectors are arranged at the same position on the existing line side; Transient impact is applied to each excitation point, and the propagation time, wave shape and energy attenuation of the wave are recorded; The average wave velocity of the elastic wave passing through the composite isolation wall is calculated, and compared with the theoretically calculated value based on the area ratio of the concrete pile, the bag pile and the compacted soil, and when the deviation is less than 10%, it is determined that the integrity of the composite isolation wall meets the requirements.

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