Channel excavation support method for thick soft foundation containing block stones on the side of existing roads

Abstract

This application discloses a channel excavation and support method for deep, soft foundations containing boulders on the side of an existing road. The method comprises the following steps: Step S1: Based on the geophysical prospecting report of the underground environment of the plot to be excavated; Step S2: Based on the designed elevation of the site, the original ground is transformed into a flat surface that meets the requirements for foundation pit excavation by excavating high and filling low; Step S5: The boulders are excavated using a skipping method, with the excavation width selected based on the width affected by the construction of the grid retaining wall; Step S6: The east retaining wall foundation pit is excavated in sections with sloped sections, and the surface layer is supported by mesh sprayed concrete; Step S7: The foundation pit is excavated in sections to the bottom of the pit, and the sections are replaced and compacted in sections; Step S8: A plurality of cement mixing piles are arranged in a grid pattern along the road extension direction on the side adjacent to the road to form a cement pile mixing wall; Step S9: If boulders are encountered during the construction of the cement pile mixing wall, they are excavated and backfilled with clay to the construction platform elevation. This method can effectively control soil and foundation pit deformation.

Description

Technical Field

[0001] The present application relates to the technical field of road foundation pit excavation and support, and in particular to a channel excavation and support method applied to a thick soft foundation containing block stones on the side of an existing road. Background Art

[0002] Foundation pit engineering is a crucial structural element in large-scale construction projects, municipal engineering projects, and rail transit projects. It is often the controlling element of an entire construction project. Its importance determines the overall project's construction schedule, safety, cost effectiveness, and quality assurance.

[0003] In foundation pit projects, the simplest and most economical construction method is slope excavation, but slope excavation is limited by site conditions and the surrounding environment, and the amount of excavation and filling is large, which has certain requirements on the excavation depth.

[0004] To the west of the upcoming Zhongnan 23# drainage channel is the already constructed West Ring Island Road, which also features an elevated bridge. The existing West Ring Island Road and elevated bridge have high road grades and foundation bearing capacity. Given these historical road conditions, digging a new channel near the existing road using existing excavation and support methods can cause soil sliding, leading to instability of the pile foundations due to shear forces. This also places high safety requirements on load, strength, deformation, anti-seepage, and durability. This can easily cause changes in the surrounding groundwater level and stress field, leading to deformation of the surrounding soil and the collapse of one side of the road, impacting traffic safety and increasing construction costs.

[0005] Current regulations do not allow the dumping of boulders on the side of an existing road. If the side of the existing road contains thick silt, this problem can be addressed by using cement mixing piles, cast-in-place piles, high-pressure rotary jet piles, etc.

[0006] Cast-in-place piles have good bearing performance but are expensive. High-pressure rotary jet pile equipment occupies a small area and has strong adaptability but is expensive and causes great pollution to the environment. It is not used for special soils that cannot solidify the sprayed slurry.

[0007] Cement mixing piles are applicable to a wide range of soil types and have a large reinforcement depth, but are subject to equipment limitations and length restrictions. If the depth of the foundation pit exceeds 25m, there is a problem that the cement slurry is too thin to solidify, so cement mixing piles cannot be used in deeper foundation pits.

[0008] It is extremely difficult to carry out channel excavation and support under such conditions. The existing support methods have the following problems when used in this environment: first, it is difficult to ensure the protection of surrounding roads during soft foundation excavation and support, and it is impossible to avoid collapse or impact on surrounding buildings; second, there are a large number of boulders underground, and the boulders have a loose structure, and it is inevitable that the excavation and replacement of boulders will damage road driving safety; finally, the deep underground silt is in a plastic state, which makes trenching difficult and it is difficult to ensure the quality of the trench after excavation.

[0009] The technical treatment of the dumped rocks and thick silt in the excavation support of the construction channel on the side of the existing road has become a major problem in road design. Summary of the Invention

[0010] The present application provides a channel excavation and support method for a deep soft foundation containing boulders on the side of an existing road, which is used to solve the technical problems existing in the prior art that when excavating a drainage channel on the side of an existing road with soft foundation, the existing support method is difficult to ensure the protection of the surrounding roads during the excavation and support of the soft foundation, and it is difficult to avoid collapse or impact on surrounding buildings; the boulders layer structure in the soft foundation environment is loose, and it is inevitable that the road driving safety will be damaged due to the excavation and replacement of the boulders; the deep underground silt is in a fluid plastic state, which makes it difficult to form a trench and it is difficult to ensure the quality of the trench after excavation.

[0011] The present application provides a channel excavation and support method for a thick soft foundation containing block stones on the side of an existing road, comprising the following steps:

[0012] Step S1: Based on the geophysical prospecting report of the underground environment of the plot to be excavated, determine the structure of the rock layer at different depths, the thickness distribution of the rock layer, and the plane distribution of the rock layer. Use exploration drilling to obtain the deepest bottom elevation of the underground rock layer and the depth of the shallowest part.

[0013] Step S2: Based on the designed elevation of the site, the original ground is transformed into a flat site that meets the requirements for foundation pit excavation by cutting high and filling low. On the flat site, the east side slope of the foundation pit is constructed first, and after the east side drainage channel structure is completed, the west side is excavated.

[0014] Step S3: First, construct the pit bottom reinforcement piles, insert temporary columns, support steel sheet piles, and construct the first support when the foundation pit is excavated to 0.5m below the first support. When the foundation pit is excavated to the pit bottom, construct the cushion layer, gabion retaining wall foundation, and backfill the fertilizer trough to 1 / 4 of the wall height layer by layer;

[0015] Step S4: Remove the upper structure supporting the construction of the retaining wall, backfill the retaining wall to the designed elevation, remove the steel sheet piles, cut the temporary columns, and excavate the foundation pit on the west side to an elevation of 1.0m. Excavate and replace the boulders within the cement pile mixing wall area, and construct the mixing piles.

[0016] Step S5: The block excavation adopts the skipping construction method. The excavation width is selected according to the width of the grid retaining wall construction. The excavation length is less than 5m. After the block excavation is completed, clay is backfilled to the construction platform elevation, and then cement mixing piles are constructed. The thick block stone base layer is drilled using a hole-guiding device. After drilling, high-pressure jet grouting piles are used as a replacement.

[0017] Step S6: The east retaining wall foundation pit is excavated in sections with slope, and the surface layer is supported by mesh spraying concrete. When the excavation reaches the 0.00 elevation, riprap and silt removal are started. From the 0.00 elevation to the pit bottom, riprap and excavation are used to treat the silt. The treatment depth is not less than 2.5m. The foundation and structure of the east retaining wall are constructed. After the strength reaches the required level, the back of the wall is backfilled to the 0.00 elevation. The west retaining wall of the drainage channel is excavated in sections along the longitudinal direction of the drainage channel to the pit bottom elevation. The length of each section is ≤10m. The pit bottom is riprapped and replaced with silt for compaction.

[0018] Step S7: Excavate the foundation pit in sections to the bottom of the pit, and replace and compact the foundation pit in sections. During the replacement and compaction process, avoid damaging the existing retaining wall and pile parts. The areas around the existing retaining wall and pile parts should be evenly replaced and compacted symmetrically.

[0019] Step S8: Arranging multiple cement mixing piles in a lattice along the road extension direction on the side adjacent to the road to form a cement mixing pile wall, setting up multiple layers of cement mixing pile walls on the side adjacent to the road, and inserting seamless steel pipes by skipping piles at the first row of cement mixing piles;

[0020] Step S9: If boulders are encountered during the construction of the cement pile mixing wall, excavation is used to deal with them. After excavation, clay is backfilled to the construction platform elevation, and then cement mixing piles are constructed at the preset position. Drilling equipment is used for the thick and thick boulders in the foundation layer. After drilling, high-pressure rotary jet piles are installed in the drilled holes to replace the cement mixing piles. The passive area is replaced with boulders for reinforcement. Excavation and replacement are carried out in sections, and progress is made from far to near in the direction of the cement pile mixing wall until the support of the foundation pit is completed.

[0021] Preferably, the deepest bottom elevation of the rock layer is -9.5m, and the shallowest bottom elevation is -3m. The silt layer is relatively thick, with a maximum depth of 15m. The method provided in this application is particularly suitable for rock layer environments at this depth. In this environment, using the method provided in this application for support excavation can effectively achieve reliable support for the rock layer, preventing the rock layer from collapsing and causing danger or damage to surrounding existing buildings and roads.

[0022] Preferably, when leveling the site in step S2, the site is advanced slowly from far to near and from east to west. More preferably, the support is a steel support, which can better support the building on the side that has been constructed.

[0023] Preferably, when replacing and tamping in step S6, the foundation pit is expanded from the east side to the west side, and the paving and leveling work should be carried out by large-scale machinery, and individual uneven places should be leveled manually with fine stones and stone chips.

[0024] Preferably, the rock dumping and filling compaction operation in step S6 is performed using an excavator.

[0025] Preferably, the cement mixing pile installation method of step S8 includes the following steps:

[0026] Step S81: Measure and set out the pile positioning, transport the pile driving rig, aggregate hopper, mortar mixer, and mortar pump to the positioning point, align the drill bit with the pile position, with a deviation of no more than 20 mm and a vertical deviation of no more than 1% before drilling.

[0027] Step S82: Pre-stir and sink at the drill hole, stirring and sinking. After sinking to the designed reinforcement depth, stir the cement slurry according to the mix ratio, control the lifting speed of the mixing drill bit, spray the pile bottom continuously for 30 seconds, and then lift it to the stop surface while stirring. Spray the pile top continuously for 30 seconds, stir it four times and mix it twice, and then sink it to the reinforcement depth. Repeat the drilling head stirring movement of this step until it reaches 0.5m from the original ground, and then stop spraying.

[0028] Step S83: The drilling rig is moved and the construction steps S81 to S82 are repeated to construct the next cement mixing pile. After the construction is completed, the pile construction effect is tested on the 7th day after the pile is completed to check the pile diameter and slurry uniformity. If the inspection results of each pile meet the requirements, a composite foundation static load test is carried out on the 28th day after the pile is completed to determine whether each cement mixing pile meets the design requirements.

[0029] The cement mixing pile prepared by the above method starts to drill downwards towards the ground through the drill bit and sprays cement slurry while drilling to achieve full mixing of mud and soil, effectively improving the load-bearing reliability of the obtained cement mixing pile.

[0030] The beneficial effects of this application include:

[0031] 1) The channel excavation and support method provided in this application for deep soft foundation containing block rocks on the side of an existing road can effectively control the deformation of the soil and foundation pit, prevent the collapse of the existing road, and ensure the safe, rapid and low-cost excavation of the channel excavation foundation pit project with deep soft foundation containing block rocks on the side of the existing road by effectively treating the block rocks under the deep base.

[0032] 2) This application provides a channel excavation and support method for deep, soft foundations containing boulders on the sides of existing roads, offering excellent overall benefits. This method utilizes a passive zone excavation and replacement method, reducing large sections to smaller ones. Each unit of the foundation pit support project is constructed in sections and layers, increasing the safety and stability of the foundation pit and reducing construction risks. To ensure trench quality and prevent equipment overturning and silt slippage, cement mixing piles are used on both sides of the channel for reinforcement. Compared to existing cast-in-place piles, cement mixing piles are more affordable, reducing the cost by approximately 18% compared to commonly used bored cast-in-place piles. Compared to high-pressure jet grouting, cement mixing piles have a lower environmental impact. They offer a short construction period, reasonable project costs, minimal environmental pollution, wide compatibility with soil formations, and excellent anti-seepage performance. This method is highly applicable to existing roads and buildings in the surrounding area and can prevent road collapse caused by excavation on the side of the road. It is highly adaptable to various complex geological and hydrogeological environments, offers excellent deformation control, anti-seepage and water-stopping effects, and provides excellent foundation pit stability, making it highly applicable.

[0033] 3) The channel excavation and support method provided in this application is applied to deep soft foundations containing boulders on the side of an existing road. This method strictly adheres to the basic principles of "grooving and support, supporting first and then excavating, excavating in layers, and strictly prohibiting over-excavation." Excavation of the next layer of earthwork is not carried out until the upper layer of support is completed. This fully utilizes the temporal and spatial effects of the soil, controls pit top deformation, and minimizes disturbance to existing roads and viaducts.

[0034] 4) The channel excavation support method provided in this application is applied to the deep soft foundation containing boulders on the side of an existing road. This method has high overall rigidity and good stability. It uses a cement mixing wall composed of multiple cement mixing piles, which can not only play a good stress adjustment role, but also control excessive deformation of the rock and soil, and can also achieve the purpose of effective anti-seepage and water stopping. The cost of the cement mixing wall is only 60%-70% of the reinforced concrete underground continuous wall. The cement mixing piles are constructed at the same time, with high work efficiency and reliable quality. The cement mixing piles fully mix the cement slurry with the soil, increase the foundation strength, effectively prevent the deformation of the soft soil foundation, and achieve a reliable support effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the process flow of the channel excavation and support method for deep soft foundation containing block stones on the side of an existing road provided in this application;

[0036] Figure 2 This is a graph showing the horizontal displacement observation results of the support structure obtained by the support method provided in this application during observation of the test section of the embodiment of this application;

[0037] Figure 3 A graph showing the vertical displacement observation results of the support structure obtained by the support method provided in this application during observation of the test section of the embodiment of this application;

[0038] Figure 4 A graph showing the settlement observation results of the surrounding ground after the support structure is set according to the support method provided in this application during the test section of the embodiment of this application;

[0039] Figure 5 A graph showing the settlement observation results of the surrounding bridges after the support structure is set according to the support method provided in this application during the test section of the embodiment of this application;

[0040] Figure 6 Observation of the test section of the embodiment of this application. This application provides on-site construction photos of the support method, wherein a) is the excavation construction operation of the cement mixing pile platform at the elevation of 1.0 on the west side of the foundation pit; b) is the excavation and replacement of block stones at the elevation of the cement mixing pile platform on the west side of the foundation pit; c) is the drilling operation of the cement mixing pile construction after the excavation and replacement of block stones on the west side of the foundation pit; DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0042] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0043] The technical means that are not described in detail in this application and are not used to solve the technical problems of this application are all set according to the common knowledge in this field, and can be implemented in a variety of common knowledge settings. Example

[0044] See also Figure 1 , the method provided by this application comprises the following steps:

[0045] Step 1) Based on the geophysical prospecting report, rock layers at various depths were obtained within the excavation area. Preliminary determination indicated that these rocks primarily originated from the construction of the West Ring Island Road and the access road along the West Dike. The deepest rock layer revealed by the survey drilling was -9.5m in elevation, with the shallowest depth being -3m. The thickness and planar distribution of the rock layer were extremely uneven.

[0046] The geophysical prospecting report reveals that a large area of ​​rock layers within the excavation area is extremely uneven in depth and planar distribution, with the deepest bottom elevation being -9.5m and the shallowest being -3m. The silt layer is relatively deep, reaching a maximum depth of 15m. The method proposed in this application fully considers the impact of support methods on the bearing capacity of existing road and viaduct foundations.

[0047] Step 2) Based on the designed elevation of the site, the original ground is transformed into a flat site that meets the requirements of foundation pit excavation by digging high and filling low. When leveling the site, proceed slowly from far to near and from east to west.

[0048] Step 3) Each area should follow the order of constructing the east side slope of the foundation pit first, and then excavating the west side after the east side drainage channel structure is completed.

[0049] Step 4) First, construct the pit bottom reinforcement piles, insert temporary columns, and support the steel sheet piles;

[0050] Step 5) Excavate the foundation pit to 0.5m below the first support and construct the first support.

[0051] Step 6) Excavate the foundation pit to the bottom, construct the cushion layer, gabion retaining wall foundation, and backfill the fertilizer trough to 1 / 4 of the wall height.

[0052] Step 7) Remove the supports, construct the upper structure of the retaining wall, backfill the retaining wall to the designed elevation, pull out the steel sheet piles, and cut the temporary columns.

[0053] Step 8) The west side foundation pit is excavated to an elevation of 1.0, the rocks within the cement soil mixing wall are excavated and replaced, and mixing piles are constructed.

[0054] Step 9) The excavation of the rocks shall be carried out by skipping the trench. The excavation width shall be selected according to the width of the grid retaining wall construction. The excavation length shall be less than 5m. Clay backfill shall be carried out after the excavation of the rocks is completed.

[0055] Step 10) Excavate the east retaining wall foundation pit in sections with sloped sections, and support the surface with mesh and sprayed concrete. When excavation reaches the 0.00 elevation, begin dumping rocks and squeezing out silt. From the 0.00 elevation to the pit bottom, use a dumping and excavation method, with a treatment depth of no less than 2.5m.

[0056] Step 11) Construct the foundation and structure of the east retaining wall. Once the required strength is achieved, backfill the wall to the 0.00 elevation. Excavate the west retaining wall along the longitudinal direction of the drainage channel in sections, ≤10m in length, to the pit bottom elevation. Rockfill the pit bottom and compact it. During this replacement process, proceed from the east side of the foundation pit toward the west. Use large machinery for paving and leveling. Any uneven areas should be leveled manually with fine stone and stone chips.

[0057] Step 12) Stone throwing is carried out using an excavator. The foundation pit is excavated in sections to the bottom of the pit, and the sections are replaced and compacted. During the replacement and compaction process, attention should be paid to protecting the existing retaining walls and piles. The areas around the protected objects should be evenly replaced and compacted symmetrically.

[0058] Step 13) The road-side cement mixing wall is formed by arranging a plurality of cement mixing piles in a lattice structure, and the first row of cement mixing piles adjacent to the road side are skipped and inserted into seamless steel pipes.

[0059] Step 14) Measure and set out the pile positions, position the pile drill, and equip the aggregate hopper, mortar mixer, and mortar pump. Align the drill bit with the pile position, with a deviation of no more than 20 mm and a vertical deviation of no more than 1%.

[0060] Step 15) Pre-mix and sink, mixing and sinking, sink to the designed reinforcement depth, mix cement slurry according to the mix ratio, control the mixing and lifting speed, spray the bottom of the pile continuously for 30 seconds, lift to the slurry stopping surface while mixing, spray the top of the pile continuously for 30 seconds, mix four times and sink to the reinforcement depth, repeat the mixing, and stop spraying when it reaches 0.5m from the original ground.

[0061] Step 16) The drilling rig is moved and the above construction steps are repeated to construct the next pile. After 7 days of pile construction, the pile construction effect is tested to check the pile diameter and slurry uniformity. After 28 days of pile construction, a static load test of the composite foundation is carried out.

[0062] Step 17) If any boulders are encountered during cement pile wall construction, excavate them. Backfill with clay to the level of the construction platform before continuing with cement pile construction. For foundations containing thick boulders, drill holes using a borehole guide. After drilling, replace them with high-pressure jet grouting piles.

[0063] Step 18) Replace the passive area with stone blocks for reinforcement. Excavate and replace the stone blocks in sections, moving from far to near towards the cement mixing wall to ensure excavation stability.

[0064] Note: Horizontal segmented excavation ≤10m, vertical layered excavation ≤1m, over-excavation is strictly prohibited. Follow the principle of constructing the slope on the east side of the foundation pit first, and after the construction of the east side flood drainage channel structure is completed, excavate the west side. On the east side, cement mixing piles are set up to enclose the fill layer where the foundation pit slope is excavated. On the plane, the cement mixing piles should be designed in a grid-like distribution, which has a very good enclosure effect for liquefiable soil, and can also effectively limit the effect of shear strain, so it can be used as an enclosure wall. The cement soil grid as the enclosure wall must pass through the liquefied layer to ensure that it can be effectively driven into the low-compressibility soil layer and low-permeability soil layer below. Simply put, the bottom of the enclosure box must be a low-permeability and low-compressibility non-liquefied soil layer.

[0065] The above method has been used in the foundation pit support project of the "Hengqin New Area Sponge City Central and Southern Drainage Channel Foundation Pit" in 2019. The on-site construction photos of the test section are as follows: Figure 6 a~c).

[0066] 1. Surrounding environment of foundation pit to be started:

[0067] The drainage channel starts at the intersection of Huandao West Road and Hengqin Avenue. The starting point of the channel is located on the north side of Hengqin Avenue. The surrounding environment is as follows:

[0068] (1) The west side of the drainage channel is adjacent to the existing West Ring Island Road and is separated from the West Ring Island Road by a 12m wide green corridor. The minimum horizontal clearance between the channel bottom edge and the West Ring Island Road corridor edge is 28.8m.

[0069] (2) Rainwater pipes, water pipes and cable trenches are distributed within the pipeline corridor of Huandao West Road. The distance between the channel bottom edge and the nearest pipeline water pipe is 21m, and the distance between the channel excavation slope top line and the nearest pipeline water pipe is 3.7m.

[0070] (3) The east side of the flood drainage channel is adjacent to the Da Hengqin Real Estate and other plots. The Da Hengqin Real Estate plot has completed vacuum preloading treatment. The closest distance between the vacuum preloading treatment edge and the bottom edge of the flood drainage channel is 25m.

[0071] (4) The starting point of the Zhongnan 23# drainage channel is located on the north side of Hengqin Avenue. The channel bottom edge is 17.2m away from the edge of the Hengqin Avenue pipeline corridor and 9.5m away from the nearest sewage pipe.

[0072] (5) The drainage channel intersects with the No. 1 Bridge on Caihong Road, the No. 1 Bridge on Caixia Road and the No. 1 Bridge on Xiangjiang Road from south to north. Currently, the construction of the three bridges has been completed.

[0073] (6) The minimum horizontal distance between the drainage channel bottom edge and the main pier of the Hengqin Second Bridge South Approach Bridge is 54m, and the minimum clear distance from the Hengqin Second Bridge A Ramp Approach Bridge Pier is 32m. The excavation slope top line is closest to the edge of the Hengqin Second Bridge Approach Bridge Pier.

[0074] 2. Monitoring methods and standards:

[0075] The method of combining instrument observation with patrol inspection is adopted. According to the requirements of the "Technical Specifications for Monitoring of Construction Foundation Pit Engineering" (GB50497-2009) and other regulations, the monitoring items of this project are as follows:

[0076] (1) Horizontal and vertical displacement of the slope top; (2) Horizontal displacement of the support deep layer; (3) Support axial force monitoring; (4) Groundwater level; (5) Displacement, settlement and crack monitoring of buildings around the foundation pit; (6) Deformation of pipelines around the foundation pit.

[0077] 3. Monitoring frequency The monitoring frequency of the monitoring project should be determined based on the foundation pit type, different construction stages of the foundation pit and underground engineering, as well as changes in the surrounding environment, natural conditions and local experience.

[0078] (1) Initial measurement: A comprehensive measurement is carried out before excavation, and the measured values ​​are used as the benchmark for future monitoring. (2) During the formal excavation, each measuring point is measured once a day. If it is found that the deformation of a local measuring point is large or the deformation rate is large, an additional measurement should be made every day. (3) When a measuring point reaches the alarm value on a certain day, an alarm should be immediately triggered and measures should be taken in a timely manner. At the same time, the number of measurements should be increased, and even continuous monitoring should be carried out. (4) On-site monitoring will be carried out by combining scheduled observation and follow-up observation: the monitoring frequency can be appropriately adjusted according to the size of the changes in the monitoring data; when there is a sudden change in the monitoring data, the monitoring frequency will be increased to 2 to 3 times a day.

[0079] For this project, in the absence of data anomalies and signs of accidents, according to the above monitoring frequency requirements, the monitoring frequency shall be increased when any of the following situations occurs:

[0080] (1) Monitoring data reaches the alarm value. (2) Monitoring data changes significantly or at an accelerated rate. (3) There are unfavorable geological conditions that have not been discovered during the survey. (4) Construction that violates the design working conditions, such as excessively deep or long excavation or failure to add supports in time. (5) Large amounts of water accumulate in the foundation pit and its surroundings, long-term continuous rainfall, or leakage in municipal pipelines. (6) The ground load near the foundation pit suddenly increases or exceeds the design limit. (7) The support structure cracks. (8) The surrounding ground suddenly settles significantly or cracks severely. (9) The adjacent buildings suddenly settle significantly, unevenly, or crack severely. (10) Piping, leakage, or quicksand occur at the bottom or side walls of the foundation pit. (11) Construction is reorganized after an accident in the foundation pit project. (12) Other abnormal conditions that affect the safety of the foundation pit and the surrounding environment occur.

[0081] The current test section is as follows. According to the actual situation on site, "K0+180~K0+220", "K0+360~K0+400.766" and "K0+565.321~K0+605.000" were selected for construction according to the above method. The above three sections were monitored for foundation pit according to the existing method. The results are as follows: Figures 2 to 5 As shown. Figures 2 to 5 It can be seen that the foundation pit using the method provided in this application can effectively support the surrounding existing buildings. The horizontal displacement of the support structure is small, the observed settlement of the surrounding existing bridges is small, the vertical displacement of the support structure is small, and the surrounding ground settlement is also small.

[0082] Depend on Figure 5 It can be seen that the method provided by this application has the least impact on the settlement of surrounding existing bridges, which shows that this method is particularly suitable for foundation pit excavation and support in the environment of existing bridges.

[0083] Figures 2 to 5 The reference numerals S10~S52 and CJ10~58 are the numbers of the observation points.

[0084] S20 and S21 are located on the west side of the foundation pit of the test section K0+180~K0+220. The block excavation was completed before the Spring Festival, but the cement soil grid retaining wall was not constructed in time after the festival. In mid-February, there was heavy rain and rainwater for foot soaking could not be discharged in time, resulting in a deformation alarm. The deformation was stable in the later period. At present, the cement soil grid retaining wall of the foundation pit has been basically constructed, and part of it has been excavated to the bottom of the pit to complete the block stone replacement: there is no obvious abnormality in the monitoring data of other test sections, and there is no abnormality in the monitoring of the West Ring Island Road viaduct on the west side.

[0085] The main application in this invention

[0086] 1. Forming a cement soil anti-seepage curtain

[0087] The permeability coefficient of cement soil is smaller than that of natural soil, and its permeability is very small. It has good anti-seepage ability. In recent years, it has been widely used as an anti-seepage curtain in foundation pit excavation projects.

[0088] 2. Form cement soil retaining structure

[0089] In soft soil foundations with excavation depths of approximately 4-7m, cement-soil pile retaining walls formed using the deep mixing method can fully utilize the strength of the cement-soil to form a cement-soil gravity support structure. Furthermore, due to the cement-soil's anti-seepage properties, it can also serve as an anti-seepage curtain. However, the use of gravity cement-soil retaining walls presents certain difficulties when the site is narrow or the excavation depth is very deep.

[0090] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A channel excavation and support method for a thick soft foundation containing block stones on the side of an existing road, characterized in that: The following steps are involved: Step S1: Based on the geophysical prospecting report of the underground environment of the plot to be excavated, determine the structure of the rock layer at different depths, the thickness distribution of the rock layer, and the plane distribution of the rock layer. Use exploration drilling to obtain the deepest bottom elevation of the underground rock layer and the depth of the shallowest part. Step S2: Based on the designed elevation of the site, the original ground is transformed into a flat site that meets the requirements for foundation pit excavation by cutting high and filling low. On the flat site, the east side slope of the foundation pit is constructed first, and after the east side drainage channel structure is completed, the west side is excavated. Step S3: First, construct the pit bottom reinforcement piles, insert temporary columns, support steel sheet piles, and construct the first support when the foundation pit is excavated to 0.5m below the first support. When the foundation pit is excavated to the pit bottom, construct the cushion layer, gabion retaining wall foundation, and backfill the fertilizer trough to 1 / 4 of the wall height layer by layer; Step S4: Remove the upper structure supporting the construction of the retaining wall, backfill the retaining wall to the designed elevation, remove the steel sheet piles, cut the temporary columns, and excavate the foundation pit on the west side to an elevation of 1.0m. Excavate and replace the boulders within the cement pile mixing wall area, and construct the mixing piles. Step S5: The block excavation adopts the skipping construction method. The excavation width is selected according to the width of the grid retaining wall construction. The excavation length is less than 5m. After the block excavation is completed, clay is backfilled to the construction platform elevation, and then cement mixing piles are constructed. The thick block stone base layer is drilled using a hole-guiding device. After drilling, high-pressure jet grouting piles are used as a replacement. Step S6: The east retaining wall foundation pit is excavated in sections with slope, and the surface layer is supported by mesh spraying concrete. When the excavation reaches the 0.00 elevation, riprap and silt removal are started. From the 0.00 elevation to the pit bottom, riprap and excavation are used to treat the silt. The treatment depth is not less than 2.5m. The foundation and structure of the east retaining wall are constructed. After the strength reaches the required level, the back of the wall is backfilled to the 0.00 elevation. The west retaining wall of the drainage channel is excavated in sections along the longitudinal direction of the drainage channel to the pit bottom elevation. The length of each section is ≤10m. The pit bottom is riprapped and replaced with silt for compaction. Step S7: Excavate the foundation pit in sections to the bottom of the pit, and replace and compact the foundation pit in sections. During the replacement and compaction process, avoid damaging the existing retaining wall and pile parts. The areas around the existing retaining wall and pile parts should be evenly replaced and compacted symmetrically. Step S8: Arranging multiple cement mixing piles in a lattice along the road extension direction on the side adjacent to the road to form a cement mixing pile wall, setting up multiple layers of cement mixing pile walls on the side adjacent to the road, and inserting seamless steel pipes by skipping piles at the first row of cement mixing piles; Step S9: If boulders are encountered during the construction of the cement pile mixing wall, excavation is used to deal with them. After excavation, clay is backfilled to the construction platform elevation, and then cement mixing piles are constructed at the preset position. Drilling equipment is used for the thick and thick boulders in the foundation layer. After drilling, high-pressure rotary jet piles are installed in the drilled holes to replace the cement mixing piles. The passive area is replaced with boulders for reinforcement. Excavation and replacement are carried out in sections, and progress is made from far to near in the direction of the cement pile mixing wall until the support of the foundation pit is completed.

2. The channel excavation and support method for deep soft foundation containing block stones on the side of an existing road according to claim 1 is characterized in that: The deepest bottom elevation of the rock layer is -9.5m, and the shallowest bottom elevation is -3m. The silt layer is relatively thick, with the deepest reaching 15m.

3. The channel excavation and support method for a thick soft foundation containing block stones on the side of an existing road according to claim 1 is characterized in that: When leveling the site in step S2, the site is leveled slowly from far to near and from the east to the west.

4. The channel excavation and support method for a thick soft foundation containing block stones on the side of an existing road according to claim 1, characterized in that: When replacing and tamping in step S6, the foundation pit is expanded from the east side to the west side. The paving and leveling work should be carried out by large-scale machinery, and individual uneven places should be leveled manually with fine stones and stone chips.

5. The channel excavation and support method for deep soft foundation containing block stones on the side of an existing road according to claim 1 is characterized in that: In step S6, the rock dumping, filling and compaction operation is performed using an excavator.

6. The channel excavation and support method for a thick soft foundation containing block stones on the side of an existing road according to claim 1, characterized in that: The cement mixing pile installation method of step S8 comprises the following steps: Step S81: Measure and set out the pile positioning, transport the pile driving rig, aggregate hopper, mortar mixer, and mortar pump to the positioning point, align the drill bit with the pile position, with a deviation of no more than 20 mm and a vertical deviation of no more than 1% before drilling. Step S82: Pre-stir and sink at the drill hole, stirring and sinking. After sinking to the designed reinforcement depth, stir the cement slurry according to the mix ratio, control the lifting speed of the mixing drill bit, spray the pile bottom continuously for 30 seconds, and then lift it to the stop surface while stirring. Spray the pile top continuously for 30 seconds, stir it four times and mix it twice, and then sink it to the reinforcement depth. Repeat the drilling head stirring movement of this step until it reaches 0.5m from the original ground, and then stop spraying. Step S83: The drilling rig is moved and the construction steps S81 to S82 are repeated to construct the next cement mixing pile. After the construction is completed, the pile construction effect is tested on the 7th day after the pile is completed to check the pile diameter and slurry uniformity. If the inspection results of each pile meet the requirements, a composite foundation static load test is carried out on the 28th day after the pile is completed to determine whether each cement mixing pile meets the design requirements.

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