Construction method for foundation treatment of large-volume cast-in-place beam support in large-scale shallow karst cave area

Abstract

The present application belongs to the field of bridge engineering technology, and discloses a large-scale cast-in-place beam support foundation treatment construction method in a large-scale shallow karst cave area, including: geological survey and program planning, using geological radar for comprehensive scanning, formulating foundation reinforcement treatment and karst cave treatment plans; foundation treatment, including removing original soil, replacing gravel cushion layer, pouring concrete cushion layer and preloading of site; karst cave treatment, formulating a comprehensive treatment plan according to the type, size, filling condition and surrounding environment of the karst cave; support erection and preloading, including support erection and support preloading; construction monitoring, monitoring foundation settlement, support deformation and displacement of surrounding structures. The present invention combines the results of geological survey and radar data analysis to accurately evaluate the impact of karst caves on foundation stability, formulate a reasonable foundation treatment plan, and effectively protect the hole wall and prevent collapse by taking different treatment measures for shallow karst caves and deep karst caves, thereby significantly improving the bearing capacity and stability of the foundation.

Description

Technical Field

[0001] The present application relates to the technical field of bridge engineering, and specifically to a construction method for treating the foundation of a large-volume cast-in-situ beam support in a large-scale shallow karst cave area. Background Art

[0002] In recent years, my country has stepped up efforts to build transportation in remote areas, and the number of newly built expressways in various places in the southwest has increased. At the same time, the probability of newly built expressways crossing with existing high-speed rail lines is increasing. Prefabricated beams cannot meet the requirements of crossing, and traditional portal support technology has many problems such as railway-related safety risks. Large-tonnage swivel bridges are increasingly appearing on cross-line bridges. The installation accuracy of large-tonnage ball joints is difficult to control, and the stability of large-tonnage swivel beams is difficult to control. The geological landforms in the southwest are mostly karst geological landforms, with abundant underground karst development. It is difficult to make holes for pile foundations, and it is easy to get stuck, drop the drill, and be unable to clean the cavity fillings, resulting in the problem of being unable to make holes in the end. The presence of caves and karst gaps can easily cause bridge collapse. The quality of karst geological drilling, the quality of cast-in-place beam support foundation treatment in shallow cave areas, and the quality of large-tonnage ball joint installation accuracy control largely determine the success or failure of the project.

[0003] The document with the prior art publication number CN116219888A provides a construction method for the foundation treatment of the full-span bracket for cast-in-place beam construction, comprising the following steps: step 1, pouring foundation concrete; step 2, assembling high-density polyethylene PP boards on the surface of the foundation concrete, wherein an anti-slip layer is provided between the high-density polyethylene PP boards and the foundation concrete; step 3, erecting the full-span bracket on the high-density polyethylene PP boards. Due to the high strength of the high-density polyethylene PP boards, the depth of the foundation replacement treatment of the cast-in-place beam full-span bracket can be reduced by fully paving the high-density polyethylene PP boards, thereby greatly reducing the cost of the foundation replacement treatment, saving foundation treatment time, and increasing the overall strength of the full-span bracket foundation, ultimately achieving the purpose of improving the project quality, saving construction period, and reducing construction costs.

[0004] Although the above-mentioned existing technical solutions can achieve relevant beneficial effects through the existing technical structures, they still have the following defects: 1. The existing technical construction solutions cannot adapt to the large-volume cast-in-place beam support foundation treatment in a large-scale shallow karst cave area, and the presence of karst caves and karst gaps can easily cause bridge collapse. 2. Traditional geological survey methods, such as drilling and pit exploration, can intuitively obtain underground geological conditions, but have problems such as high cost, low efficiency, and limited coverage, especially for large-scale and complex karst cave distribution, it is difficult to conduct comprehensive and accurate detection.

[0005] In view of this, we propose a construction method for large-volume cast-in-place beam support foundation treatment in large-scale shallow cave areas. Summary of the invention

[0006] 1. Technical problems to be solved.

[0007] The purpose of this application is to provide a large-volume cast-in-place beam support foundation treatment construction method in a large-scale shallow cave area, which solves the technical problems raised in the above-mentioned background technology, realizes the combination of geological survey and radar data analysis results, more accurately evaluates the impact of caves on foundation stability, and formulates a more scientific and reasonable foundation treatment plan. By taking different treatment measures for shallow caves and deep caves, the hole wall is effectively protected to prevent collapse, ensure the smooth progress of drilling operations, reduce construction risks, enhance foundation stability, and significantly improve the bearing capacity and stability of the foundation; ensure the safety of important surrounding structures.

[0008] 2. Technical solution.

[0009] The technical solution of the present application provides a construction method for foundation treatment of large-volume cast-in-place beam supports in a large-scale shallow karst cave area, comprising the following steps.

[0010] S1. Geological survey and program planning: Use geological radar to conduct a comprehensive scan of a large area of ​​shallow karst caves. The scanning range should cover the entire project impact area and accurately identify the distribution, scale, depth and filling of shallow karst caves. According to the geological survey results and combined with construction requirements, formulate a detailed foundation reinforcement treatment plan and karst cave treatment plan.

[0011] S2. Foundation treatment: including removal of original soil, replacement of gravel cushion, pouring of concrete cushion and pre-compression of site.

[0012] Removing original soil: within the cast-in-place range of the main bridge support, remove the original surface fill soil to ensure that the treatment area is clean and free of impurities.

[0013] Replacement of gravel cushion layer: Use 50cm thick gravel cushion layer for replacement and compact it with heavy roller to ensure that the compaction degree is greater than 90% to increase the bearing capacity of the foundation to fa≥130kPa (the specific value can be adjusted according to the actual situation).

[0014] Pour concrete cushion: Pour a 20cm thick C20 concrete cushion on top of the gravel cushion to ensure a flat surface and prevent rainwater from soaking and softening the support foundation.

[0015] Site preloading: Select representative areas (such as 20x30m) for preloading tests, use the most unfavorable load of 130kPa (the specific value can be adjusted according to actual conditions) for graded loading, monitor the settlement, and ensure that the settlement during the construction period does not exceed 10mm. When preloading a large area, set up fixed observation points and regularly observe the impact on surrounding buildings to ensure safety. Conduct a detailed analysis of the preloading test data, evaluate the reinforcement effect, and adjust the relevant parameters for large-area treatment.

[0016] S3. Cave treatment: A comprehensive treatment plan is formulated based on factors such as the type, size, filling conditions and surrounding environment of the cave. This includes shallow cave treatment and deep cave treatment. Shallow caves are treated by backfilling and compaction with stone, spanning with cover plates, grouting reinforcement and other methods; deep caves are reinforced by drilling grouting and drilling blasting. Safety monitoring and environmental protection work must be strengthened during the treatment process to ensure the safety and stability of the project.

[0017] S4. Scaffold erection and pre-stressing: including scaffold erection and scaffold pre-stressing.

[0018] Scaffolding: Build full-hall scaffolding according to design requirements. The scaffolding range must cover the horizontal projection range of the beam and extend one meter outward. Ensure that the scaffolding has sufficient rigidity, strength and stability to meet construction requirements.

[0019] Pre-stressing of the support: Before pouring concrete, pre-stress the support, and the pre-stressing weight shall not be less than 1.1 times of the structural load and construction load. Measure the elastic deformation and inelastic deformation of the support so as to adjust the elevation and reserve deformation value when the box beam is erected. Make sure that the support is fully stable (the cumulative settlement does not exceed 2mm for three consecutive days, and the pre-stressing time is not less than seven days) before pouring the beam.

[0020] S5. Construction monitoring: During the construction process, the settlement of the foundation, deformation of the support, displacement of the surrounding structures, etc. are continuously monitored, and abnormal conditions are monitored to ensure construction safety. Once an abnormality is found, the emergency plan is immediately activated and corresponding measures are taken to deal with it.

[0021] As an optional solution of the present invention, geological survey and program planning include geological radar scanning and data analysis.

[0022] Geological radar scanning: According to the terrain planning of large-volume cast-in-place beam support foundation in a large-scale shallow karst cave area, obtain the topographic map and plan the route of drone radar scanning. Use geological radar equipment to conduct a comprehensive scan of the shallow karst cave area to obtain the reflection image data of the underground structure; including the following steps.

[0023] (1) Topographic map acquisition: Use drone aerial photography or satellite remote sensing technology to obtain high-precision topographic maps of large-scale shallow cave areas. Topographic maps contain detailed information such as contour lines, landform features, and water system distribution to facilitate subsequent topographic analysis and planning.

[0024] (2) UAV radar scanning route planning: Based on the topographic map, identify potential karst cave development areas and key scanning areas. Plan the flight route of the UAV radar scanning to ensure full coverage of shallow karst cave areas, and focus on areas with complex terrain and strong karst development. Set a reasonable flight altitude, speed and scanning angle to obtain high-quality radar reflection image data.

[0025] (3) Implementation of geological radar scanning: Select geological radar equipment suitable for cave detection, such as the GPR (Ground Penetrating Radar) system. Ensure that the equipment is in good working condition and check the connection and performance of components such as antennas, cables, and power supplies. Set up survey line markers on the planned scanning route to ensure that the drone or ground exploration vehicle can accurately scan along the survey line. Arrange ground control points at key locations for subsequent data processing and correction. Start the drone and perform radar scanning along the planned route. Monitor the scanning process in real time to ensure the continuity and stability of data collection.

[0026] Data analysis: The radar data is processed and analyzed by GPRMax geological radar data processing and analysis software to identify the specific location, shape, scale and filling of the cave. Special attention is paid to the depth, size and boundary of the cave, as well as the presence of filling and its nature. The following steps are included.

[0027] Data import: Import the raw data collected by the geological radar equipment into GPRMax or compatible data processing software. These data usually include time series echo signals, which record the reflection of radar waves in underground media.

[0028] Preprocessing: Before data analysis, the data is preprocessed, including noise removal, filtering, and gain adjustment, to improve the data quality and signal-to-noise ratio.

[0029] Model building: In the data analysis stage, the model of the underground medium is inverted based on the geological radar data. The simulation function of GPRMax is used to assist in this process, and the model parameters are continuously adjusted to fit the actual data.

[0030] Data processing and analysis: Import the collected radar data into professional data processing software, such as GPRMax. Perform data preprocessing, including denoising, filtering, gain adjustment, etc., to improve data quality and signal-to-noise ratio. Use GPRMax or the data analysis tools integrated with it to conduct in-depth analysis of the preprocessed radar data. This includes using specific algorithms and tools to identify the location, morphology, scale and filling of caves. Pay special attention to the depth, size and boundaries of the caves, as well as whether there are fillings and their properties. GPRMax provides specialized tools or scripts to handle these tasks, or users may need to write custom scripts to implement specific analysis functions. Based on the geological radar scanning results, draw a cave distribution map to clarify the spatial distribution and morphological characteristics of the caves. Combined with the results of geological surveys, evaluate the impact of caves on foundation stability, including cave scale, filling conditions, surrounding rock stability, etc.

[0031] Result visualization: Display the analysis results in the form of graphics or images to intuitively understand the characteristics of the cave. This includes generating two-dimensional radar images or three-dimensional underground structure models. Based on the analysis results, interpret the characteristics of the cave and write a report. This includes describing the location, size, shape, depth, filling condition of the cave, and evaluating its impact on foundation stability.

[0032] In this technical solution, reasonable suggestions are made for the design and construction of large-volume cast-in-place beam support foundations based on the scanning results and terrain planning. In view of the special conditions of the karst cave area, corresponding foundation treatment plans and construction measures are formulated to ensure the safety and stability of the project.

[0033] As an optional solution of the present invention, data processing and analysis include the following contents.

[0034] Data collation: Extract key information from the data obtained from geological radar scanning, including reflection intensity, signal propagation time, etc. Use professional software to process radar data to identify the location, shape, scale and filling of the cave.

[0035] Draw a cave map: Use a geographic information system (GIS) or mapping software to draw a cave map on a topographic map based on the radar data. Use different colors or shapes to represent caves of different sizes or types to ensure that the diagram is clear.

[0036] Assess the spatial distribution characteristics of caves: Analyze the spatial distribution pattern of caves, such as concentration, dispersion or clustering. Consider the relationship between caves and natural features such as topography and water systems.

[0037] Assess cave morphology: Describe the shape of the cave, such as round, oval, or other irregular shapes. Measure the dimensions of the cave, including length, width, and height.

[0038] Assess cave filling: Determine if there is any filling material, such as soil, gravel, or other materials, in the cave. Assess the properties of the filling material, such as density, moisture content, and mechanical properties.

[0039] Assess the stability of surrounding rock: Check the rock type and structure around the cave and assess its stability. Consider the degree of development of rock cracks, joints and fault distribution.

[0040] Comprehensively evaluate the impact of caves on foundation stability: Combine the spatial distribution, morphological characteristics, filling conditions and surrounding rock stability of caves to evaluate their potential impact on foundation stability. Consider issues such as uneven settlement and reduced foundation bearing capacity that may be caused by caves.

[0041] Foundation stability index S f The assessment is based on multiple characteristics of the cave.

[0042] S f =w1*D+w2*A c +w3*V f +w4*S c ; Among them, S f is the foundation stability index, which is a comprehensive indicator used to quantify the stability of the foundation, taking into account multiple characteristics of the cave. w1 is the weight assigned to the spatial distribution characteristics of the cave, reflecting the importance of this characteristic on the foundation stability. D is the spatial distribution index of the cave, which quantifies the spatial distribution pattern of the cave, such as the degree of concentration, dispersion or grouping. w2 is the weight assigned to the morphological characteristics of the cave, reflecting the influence of the cave morphology on the foundation stability. c is the area or size of the cave, representing the size of the cave, usually related to the diameter or size of the cave. w3 is the weight assigned to the cave filling, reflecting the influence of the nature and volume of the filling on the foundation stability. f is the volume of the filling material, which may affect the effect of the cave on the stability of the foundation. w4 is the weight assigned to the stability of the surrounding rock, reflecting the influence of the stability of the surrounding rock on the overall stability of the foundation. c The surrounding rock stability coefficient is used to evaluate the stability of the surrounding rock, which may be based on the ratio of the shear strength and shear stress of the surrounding rock. These weights w1, w2, w3 and w4 need to be determined according to actual conditions and professional knowledge, and they reflect the importance of different factors in the comprehensive evaluation.

[0043] Formulate foundation treatment plan: According to the assessment results, formulate corresponding foundation treatment plan, such as grouting reinforcement, foundation replacement or pile foundation construction. Consider the feasibility, cost and construction period of the foundation treatment plan.

[0044] As an optional solution of the present invention, the support erection includes the following contents.

[0045] The erection of the scaffolding must be carried out strictly in accordance with the construction drawings and technical requirements to ensure that the scaffolding structure meets the load-bearing requirements of the bridge.

[0046] Select qualified steel, wood or composite materials as the main components of the bracket to ensure that the material quality meets national standards and engineering requirements.

[0047] The support range should cover the horizontal projection range of the beam body and extend at least one meter outward to increase the stability and safety of the support. Through reasonable structural design, material selection and connection methods, ensure that the support has sufficient rigidity, strength and stability to withstand various loads during construction, including structural loads, construction loads and possible dynamic loads. Pay attention to the verticality, horizontality and tightness of the connection parts of the support to avoid tilting, twisting or loosening. At the same time, do a good job of foundation treatment at the bottom of the support to ensure that the support foundation is solid and reliable.

[0048] As an optional solution of the present invention, the bracket pre-stressing includes the following contents.

[0049] By pre-stressing to simulate the stress state of the beam after casting, the bearing capacity and stability of the support are tested, and the elastic and inelastic deformations of the support are measured at the same time, providing a basis for the elevation adjustment and reserved deformation value when erecting the box beam formwork.

[0050] The preload weight should be no less than 1.1 times the structural load and construction load to ensure the safety of the support under extreme conditions.

[0051] Load pre-compression materials (such as sandbags, water tanks, etc.) in stages and monitor the deformation of the support. Pause for a while after each stage of loading, and then proceed to the next stage of loading after the deformation of the support stabilizes.

[0052] The graded loading of the pre-pressed material can be achieved by setting multiple loading stages i, with the loading weight W in each stage i is a ratio of the total preload weight: W i = (i / n) × W; W = 1.1 × (W str +W con ), where W is the preload weight, simulating the total load after the beam is poured, including 1.1 times of the structural load and construction load. str W is the structural load, which refers to the weight of the beam itself and the load it will bear during expected use. con Construction load refers to the load temporarily applied to the support during the construction process, such as workers, equipment, etc. i is the weight of each loading stage, when loading the pre-pressed material in stages, the weight of each loading stage. n is the total number of loading stages, the number of stages into which the pre-pressed material is divided during the pre-pressing process.

[0053] During the preloading process, the elastic and inelastic deformation of the support are measured regularly. The elastic deformation will recover after unloading, while the inelastic deformation is permanent. These data are crucial for adjusting the box girder formwork elevation and reserved deformation value.

[0054] The elastic deformation δe and the inelastic deformation δp can be calculated by the following formula: e =δ 加载 −δ 卸载 ; δp = δ 加载 −δ e ; Among them, δ e is the elastic deformation, which is the reversible deformation of the bracket after loading and the deformation that can be recovered after unloading. p is the inelastic deformation, the irreversible deformation of the bracket after loading, that is, the permanent deformation. 加载 Deformation after loading: the total deformation of the bracket measured after loading the pre-compression material. 卸载 Deformation after unloading: The deformation of the bracket measured after unloading the pre-compression material.

[0055] Continuously monitor the settlement of the support. When the cumulative settlement does not exceed 2mm for three consecutive days and the preloading time is not less than seven days, the support can be considered to be sufficiently stable and meet the conditions for pouring the beam.

[0056] After confirming that the support is stable, gradually unload the preloading material. According to the deformation data measured during the preloading process, adjust the box beam formwork elevation and reserved deformation value to ensure that the line shape and elevation of the beam body after pouring meet the design requirements.

[0057] According to the deformation data measured during the preloading process, adjust the box beam formwork elevation H 调整 And the reserved deformation value ΔH: ΔH=H 原始 −δ p ΔH=δ e +K 安 ×δp; where H is adjusted to the adjusted box girder formwork elevation, which is the adjusted box girder formwork elevation based on the inelastic deformation. 原始 K is the original formwork elevation, which is the box beam formwork elevation set before preloading. ΔH is the reserved deformation value, which is calculated based on the elastic deformation and inelastic deformation, and is used to ensure that the line shape and elevation of the beam body meet the design requirements after pouring. 安 is the safety factor, a coefficient greater than 1, used to consider additional safety margin when calculating the reserved deformation value.

[0058] In this technical solution, through scientific design, careful construction and strict monitoring, the safety and stability of the support can be ensured, laying a solid foundation for the high-quality casting of the beam.

[0059] As an optional solution of the present invention, during the site preloading process, in order to effectively control the loading rate, monitor the settlement, and evaluate the reinforcement effect and determine the relevant parameters for large-area treatment, the following contents are included.

[0060] 1. Loading plan: Loading is carried out over five days, with uniform loading every day. Such a loading rate is intended to steadily increase the foundation pressure and avoid foundation instability caused by excessive loading. During the loading process, the loading amount is strictly controlled to ensure that the daily loading amount is accurate. If loading cannot be carried out as planned due to special circumstances (such as weather, equipment failure, etc.), the subsequent loading plan should be adjusted in time to ensure that the total loading amount and loading time meet the design requirements.

[0061] 2. Settlement observation: A fixed observation point shall be set in the center of the test area. The point shall be selected in a representative location to accurately reflect the settlement of the entire area. The observation point shall be stable and reliable to ensure that it will not be displaced or damaged during the observation process.

[0062] Settlement observations are conducted twice a day, in the morning and evening, to obtain more comprehensive settlement data. After each observation, the observation data, including observation time, observation value, weather conditions, etc., should be recorded in time for subsequent data analysis.

[0063] If the settlement on a given day exceeds 2 cm, loading should be stopped immediately for one day to prevent the foundation from being damaged by excessive settlement. Loading can only be continued after the settlement becomes stable (usually when the settlement for two consecutive days is less than a certain set value, such as 0.5 cm).

[0064] 3. Data analysis: Observe continuously for one month, collect and organize all settlement observation data.

[0065] Perform preliminary data processing, such as calculating average settlement, maximum settlement, settlement rate and other indicators. Evaluate the reinforcement effect of the foundation by analyzing the settlement data. Focus on whether the settlement trend is stable and whether the settlement is within the allowable range.

[0066] If it is found that the foundation reinforcement effect is not good or there are safety hazards, the reinforcement plan should be adjusted or remedial measures should be taken in time.

[0067] According to the settlement data of the test area and the reinforcement effect evaluation results, the relevant parameters of large-scale treatment are determined. The parameters include loading rate, total loading amount, preloading time, foundation treatment depth, etc. The determination of parameters should fully consider geological conditions, engineering requirements, economic benefits and other factors to ensure the scientificity and feasibility of the large-scale treatment plan.

[0068] 4. Adjustment and optimization: During the entire preloading process, timely summarize the experience and lessons learned to provide reference and reference for similar projects. Feedback the test results and data analysis results to the design unit and construction unit, and make necessary adjustments and optimizations to the design and construction plans based on the feedback.

[0069] Ensure the smooth progress of the site preloading process and the effective evaluation of the reinforcement effect, and provide strong support for subsequent large-scale treatment.

[0070] 5. When preloading a large area, especially when such operations are carried out near railways, it is crucial to ensure the safety and stability of the railway. Fixed observation points must be set up near the railway to regularly observe the impact on the railway. The detection plan should be submitted to the relevant railway departments for approval. Monitoring alarm value: lateral displacement>3mm / d, cumulative>30mm; ground settlement 25mm, change rate above 3mm / d. When the monitoring value reaches the above limit or the change rate of the monitoring value suddenly increases or maintains a high rate for three consecutive days, an alarm should be issued in time, and all parties should be asked to pay attention, analyze the reasons, and deal with them in time.

[0071] As an optional solution of the present invention, large-area pre-pressing specifically includes the following contents.

[0072] 1. Setting of observation points: Fixed observation points should be set up along the railway, especially in the sections adjacent to or potentially affected by the preloading area. The observation points should be selected at representative locations, such as bridge piers, roadbed slopes, and sensitive areas of track geometry changes. The number and distribution of observation points should be reasonably determined based on the importance of the railway and the scope of the preloading area. Ensure that the impact of preloading activities on the railway can be fully reflected. Stable observation devices, such as displacement meters and settlement observation piles, should be installed at the observation points to accurately measure lateral displacement and ground settlement.

[0073] 2. Regular observation: According to the progress of preloading activities and the requirements of the railway management department, a reasonable observation frequency should be established. Observe twice a day (once in the morning and once in the evening). In the early stage of preloading or when the railway is greatly affected, the number of observations can be appropriately increased. The two main indicators to be observed are lateral displacement and ground settlement. Lateral displacement reflects the lateral stability of the railway structure, and ground settlement reflects the compression deformation of the foundation. After each observation, the observation data should be recorded in time, including observation time, observation value, weather conditions, etc., and the corresponding change curve should be drawn for subsequent analysis.

[0074] 3. Approval of the testing plan: Prepare a detailed testing plan based on the specific circumstances of the preloading activities and the requirements of the railway management department. The plan should include the setting of observation points, observation methods, observation frequency, data recording and processing methods, alarm mechanism, etc. Submit the testing plan to the relevant railway departments for approval. During the approval process, full communication with the railway management department is required to ensure the rationality and feasibility of the testing plan.

[0075] 4. Alarm mechanism: Set reasonable alarm values ​​according to the requirements of the railway management department and the actual situation of the project. For example, the lateral displacement is greater than 3mm / d or the cumulative displacement is greater than 30mm, the ground settlement reaches 25mm and the rate of change is above 3mm / d, etc. When the monitoring value reaches the above alarm limit or the rate of change of the monitoring value suddenly increases or maintains a high rate for three consecutive days, the alarm process should be started immediately. First, notify the on-site person in charge and the railway management department; secondly, organize relevant personnel to review and analyze the monitoring data; finally, take corresponding emergency measures according to the analysis results. After the alarm, the preloading activities should be stopped or adjusted immediately to prevent further impact on the railway. At the same time, organize experts to conduct a safety assessment of the railway structure and formulate corresponding reinforcement or repair plans based on the assessment results.

[0076] 5. Summary and feedback: During the entire preloading process, observation data and monitoring results should be summarized regularly to evaluate the impact of preloading activities on the railway. At the same time, the monitoring results and evaluation reports should be fed back to the railway management department and relevant units in a timely manner so that the construction plan can be adjusted in time and necessary protective measures can be taken.

[0077] As an optional solution of the present invention, construction monitoring ensures that the project is carried out safely and smoothly during the construction process, including the following contents.

[0078] 1. Foundation settlement monitoring: Evaluate the stability of the foundation under construction loads, promptly detect and deal with abnormal foundation settlement, and prevent adverse effects on the superstructure. Set up settlement observation points on the foundation, regularly measure and record settlement data, and analyze settlement trends. If the settlement rate is found to be abnormally accelerated or the settlement exceeds the design allowable value, construction should be stopped immediately, the cause should be found, and reinforcement measures should be taken.

[0079] 2. Support deformation monitoring: Ensure the stability and safety of the support system during construction and prevent safety accidents caused by support deformation. Install deformation monitoring equipment, such as stress sensors and displacement meters, at key parts of the support to monitor support deformation in real time. Once it is found that the support deformation exceeds the allowable range, measures should be taken immediately to strengthen the support and redesign the support plan if necessary.

[0080] 3. Monitoring of geological condition changes: Understand the changes in geological conditions in the construction area and prevent construction safety problems caused by changes in geological conditions. Monitor changes in geological conditions through geological exploration, in-situ tests and other means, combined with geological observations during the construction process. If geological anomalies such as karst caves and soil caves are found, construction should be stopped immediately and a special treatment plan should be formulated to ensure construction safety.

[0081] 4. Monitoring of groundwater changes: Prevent groundwater changes from causing adverse effects on foundations, foundation pits, etc., to ensure construction safety. Set up groundwater level observation wells, measure groundwater levels regularly, and analyze groundwater change trends. If abnormal groundwater level rises or falls, the cause should be immediately identified, and measures such as drainage, precipitation, or recharging should be taken to keep the groundwater level stable.

[0082] 5. Monitoring of displacement of surrounding structures: Assess the impact of construction on surrounding structures to prevent damage or collapse of surrounding structures due to construction. Set up displacement observation points on surrounding structures, measure and record displacement data regularly. If abnormal displacement of surrounding structures is found, construction should be stopped immediately, the cause should be analyzed, and reinforcement or protective measures should be taken.

[0083] 6. Monitoring of meteorological and environmental factors: Understand the meteorological and environmental conditions in the construction area to prevent construction safety accidents caused by bad weather. Obtain meteorological information in the construction area through weather stations or weather forecasts, including rainfall, wind speed, temperature, humidity, etc. Before bad weather comes, protective measures should be taken in advance, such as reinforcing temporary facilities, to ensure construction safety.

[0084] 3. Beneficial effects.

[0085] One or more technical solutions provided in the technical solution of this application have at least the following technical effects or advantages.

[0086] 1. By combining geological survey and radar data analysis results, the present invention can more accurately evaluate the impact of caves on foundation stability, including the size of the caves, the properties of the filling materials, and the stability of the surrounding rocks, so as to formulate a more scientific and reasonable foundation treatment plan.

[0087] 2. According to the distribution of karst caves, the layout and construction plan of large-volume cast-in-place beam support foundation can be optimized to avoid inappropriate construction operations in the karst cave area, reduce construction difficulty and cost, and improve construction efficiency and safety.

[0088] 3. Through the joint application of drones and geological radar, large areas can be covered efficiently, reducing the input of manpower and material resources, while quickly obtaining high-precision topographic maps and underground structure information to improve resource utilization efficiency. The data analysis results are intuitively displayed in the form of graphics or images, which makes it easier for decision makers to quickly understand the characteristics of caves and the stability of foundations, providing strong data support for project decisions.

[0089] 4. Potential problems can be discovered in time. Through continuous monitoring of key parameters such as foundation settlement, support deformation, and displacement of surrounding structures, potential problems or abnormal conditions in the construction process can be discovered in time, providing the possibility for timely response measures. It can improve the quality of the project. Construction monitoring helps control deformation and displacement during the construction process and ensure that the geometric dimensions and linear shapes of the structure meet the design requirements.

[0090] 5. By strictly following the design requirements to set up the full-height bracket and extending it to one meter outside the horizontal projection range of the beam body, the risk of collapse during construction is effectively prevented, ensuring the safety of construction personnel and on-site equipment. Through bracket preloading, the actual construction load can be simulated to cause the bracket to deform accordingly, and the non-elastic deformation part is eliminated during the preloading process, thereby avoiding unpredictable settlement during subsequent concrete pouring and improving the stability of the structure.

[0091] 6. By taking different treatment measures for shallow and deep caves, the hole wall is effectively protected to prevent collapse, ensure the smooth progress of drilling operations, reduce construction risks, enhance foundation stability, and significantly improve the bearing capacity and stability of the foundation, ensuring the safety of important surrounding structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 This is a flow chart of the construction method for large-volume cast-in-place beam support foundation treatment in a large-scale shallow cave area in this application. DETAILED DESCRIPTION

[0093] The present application is further described in detail below in conjunction with the accompanying drawings.

[0094] In the karst area of ​​Guangxi, the karst development level of the site is comprehensively judged based on the surface karst development density, linear karst rate, cave rate and unit water inflow. The hole rate of the drilling hole in the bridge location area is 54.2%, the linear karst rate of the drilling hole is 1% to 49.1%, the karst development of the drilling hole is weak to strong, and the karst development of the construction site is moderate. The existence of caves and karst gaps can easily cause bridge collapse. Therefore, the end bearing piles of the bridge pile foundation shall not fall in the caves and karst gaps. During the construction process, the caves with larger cave heights should be pre-grouted (or filled with sand (gravel) and then grouting) or pre-cast with concrete treatment or steel pipes should be lowered to the rock surface to form holes to the caves. Backfill with clay, expansive soil, cement, and stone flakes, and make a construction plan to prevent construction-induced karst collapse. When the caves with smaller cave heights are rushed to the caves, the caves are backfilled with stone flakes, fragments, clay blocks, bagged cement concrete, etc. In the sections with strong karst development, measures should be taken to prevent quality accidents caused by cement slurry loss during concrete pouring. The key point of large-volume cast-in-place beam construction in large-scale shallow karst cave areas is to effectively treat the support foundation. Before foundation treatment, geological radar scanning is carried out to clarify the distribution of shallow karst caves, accurately replace filling and grouting to meet the needs of support construction.

[0095] Reference Figure 1 The embodiment of the present application provides a large-volume cast-in-place beam support foundation treatment construction method for a large-scale shallow cave area, including the following steps.

[0096] S1. Geological survey and scheme planning: Use geological radar to conduct a comprehensive scan of a large area of ​​shallow karst caves. The scanning range should cover the entire project impact area and accurately identify the distribution, scale, depth and filling of shallow karst caves. According to the results of geological survey and combined with construction requirements, formulate detailed foundation reinforcement treatment plan and karst cave treatment plan. Comprehensive scanning helps to more accurately identify the distribution of karst caves and provide comprehensive and detailed data support for scheme planning. At the same time, when formulating the plan, factors such as geological conditions, construction requirements and construction period constraints should be fully considered to ensure the rationality and feasibility of the plan.

[0097] S2. Foundation treatment: including removal of original soil, replacement of gravel cushion, pouring of concrete cushion and pre-compression of site.

[0098] Removing original soil: within the cast-in-place range of the main bridge support, remove the original surface fill soil to ensure that the treatment area is clean and free of impurities.

[0099] Replacement of gravel cushion layer: Use 50cm thick gravel cushion layer for replacement and compact it with heavy roller to ensure that the compaction degree is greater than 90% to increase the bearing capacity of the foundation to fa≥130kPa (the specific value can be adjusted according to the actual situation).

[0100] Pour concrete cushion: Pour a 20cm thick C20 concrete cushion on top of the gravel cushion to ensure a flat surface and prevent rainwater from soaking and softening the support foundation.

[0101] Site preloading: Select representative areas (such as 20x30m) for preloading tests, use the most unfavorable load of 130kPa (the specific value can be adjusted according to actual conditions) for graded loading, monitor the settlement, and ensure that the settlement during the construction period does not exceed 10mm. When preloading a large area, set up fixed observation points and regularly observe the impact on surrounding buildings to ensure safety. Conduct a detailed analysis of the preloading test data, evaluate the reinforcement effect, and adjust the relevant parameters for large-area treatment.

[0102] S3. Cave treatment: A comprehensive treatment plan is formulated based on factors such as the type, size, filling conditions and surrounding environment of the cave. This includes shallow cave treatment and deep cave treatment. Shallow caves are treated by backfilling and compaction with stone, spanning with cover plates, grouting reinforcement and other methods; deep caves are reinforced by drilling grouting and drilling blasting. Safety monitoring and environmental protection work must be strengthened during the treatment process to ensure the safety and stability of the project.

[0103] S4. Scaffold erection and pre-stressing: including scaffold erection and scaffold pre-stressing.

[0104] Scaffolding: Build full-hall scaffolding according to design requirements. The scaffolding range must cover the horizontal projection range of the beam and extend one meter outward. Ensure that the scaffolding has sufficient rigidity, strength and stability to meet construction requirements.

[0105] Pre-stressing of the support: Before pouring concrete, pre-stress the support, and the pre-stressing weight shall not be less than 1.1 times of the structural load and construction load. Measure the elastic deformation and inelastic deformation of the support so as to adjust the elevation and reserve deformation value when the box beam is erected. Make sure that the support is fully stable (the cumulative settlement does not exceed 2mm for three consecutive days, and the pre-stressing time is not less than seven days) before pouring the beam.

[0106] S5. Construction monitoring: During the construction process, the settlement of the foundation, deformation of the support, displacement of the surrounding structures, etc. are continuously monitored, and abnormal conditions are monitored to ensure construction safety. Once an abnormality is found, the emergency plan is immediately activated and corresponding measures are taken to deal with it.

[0107] Further, geological survey and program planning, including geological radar scanning and data analysis.

[0108] Geological radar scanning: According to the terrain planning of large-volume cast-in-place beam support foundation in a large-scale shallow karst cave area, obtain the topographic map and plan the route of drone radar scanning. Use geological radar equipment to conduct a comprehensive scan of the shallow karst cave area to obtain the reflection image data of the underground structure; including the following steps.

[0109] (1) Topographic map acquisition: Use drone aerial photography or satellite remote sensing technology to obtain high-precision topographic maps of large-scale shallow cave areas. Topographic maps contain detailed information such as contour lines, landform features, and water system distribution to facilitate subsequent topographic analysis and planning.

[0110] (2) UAV radar scanning route planning: Based on the topographic map, identify potential karst cave development areas and key scanning areas. Plan the flight route of the UAV radar scanning to ensure full coverage of shallow karst cave areas, and focus on areas with complex terrain and strong karst development. Set a reasonable flight altitude, speed and scanning angle to obtain high-quality radar reflection image data.

[0111] (3) Implementation of geological radar scanning: Select geological radar equipment suitable for cave detection, such as the GPR (Ground Penetrating Radar) system. Ensure that the equipment is in good working condition and check the connection and performance of components such as antennas, cables, and power supplies. Set up survey line markers on the planned scanning route to ensure that the drone or ground exploration vehicle can accurately scan along the survey line. Arrange ground control points at key locations for subsequent data processing and correction. Start the drone and perform radar scanning along the planned route. Monitor the scanning process in real time to ensure the continuity and stability of data collection.

[0112] Data analysis: The radar data is processed and analyzed by GPRMax geological radar data processing and analysis software to identify the specific location, shape, scale and filling of the cave. Special attention is paid to the depth, size and boundary of the cave, as well as the presence of filling and its nature. The following steps are included.

[0113] Data import: Import the raw data collected by the geological radar equipment into GPRMax or compatible data processing software. These data usually include time series echo signals, which record the reflection of radar waves in underground media.

[0114] Preprocessing: Before data analysis, the data is preprocessed, including noise removal, filtering, and gain adjustment, to improve the data quality and signal-to-noise ratio.

[0115] Model building: In the data analysis stage, the model of the underground medium is inverted based on the geological radar data. The simulation function of GPRMax is used to assist in this process, and the model parameters are continuously adjusted to fit the actual data.

[0116] Data processing and analysis: Import the collected radar data into professional data processing software, such as GPRMax. Perform data preprocessing, including denoising, filtering, gain adjustment, etc., to improve data quality and signal-to-noise ratio. Use GPRMax or the data analysis tools integrated with it to conduct in-depth analysis of the preprocessed radar data. This includes using specific algorithms and tools to identify the location, morphology, scale and filling of caves. Pay special attention to the depth, size and boundaries of the caves, as well as whether there are fillings and their properties. GPRMax provides specialized tools or scripts to handle these tasks, or users may need to write custom scripts to implement specific analysis functions. Based on the geological radar scanning results, draw a cave distribution map to clarify the spatial distribution and morphological characteristics of the caves. Combined with the results of geological surveys, evaluate the impact of caves on foundation stability, including cave scale, filling conditions, surrounding rock stability, etc.

[0117] Result visualization: Display the analysis results in the form of graphics or images to intuitively understand the characteristics of the cave. This includes generating two-dimensional radar images or three-dimensional underground structure models. Based on the analysis results, interpret the characteristics of the cave and write a report. This includes describing the location, size, shape, depth, filling condition of the cave, and evaluating its impact on foundation stability.

[0118] In this technical solution, reasonable suggestions are made for the design and construction of large-volume cast-in-place beam support foundations based on the scanning results and terrain planning. In view of the special conditions of the karst cave area, corresponding foundation treatment plans and construction measures are formulated to ensure the safety and stability of the project.

[0119] Furthermore, data processing and analysis include the following contents.

[0120] Data collation: Extract key information from the data obtained from geological radar scanning, including reflection intensity, signal propagation time, etc. Use professional software to process radar data to identify the location, shape, scale and filling of the cave.

[0121] Draw a cave map: Use a geographic information system (GIS) or mapping software to draw a cave map on a topographic map based on the radar data. Use different colors or shapes to represent caves of different sizes or types to ensure that the diagram is clear.

[0122] Assess the spatial distribution characteristics of caves: Analyze the spatial distribution pattern of caves, such as concentration, dispersion or clustering. Consider the relationship between caves and natural features such as topography and water systems.

[0123] Assess cave morphology: Describe the shape of the cave, such as round, oval, or other irregular shapes. Measure the dimensions of the cave, including length, width, and height.

[0124] Assess cave filling: Determine if there is any filling material, such as soil, gravel, or other materials, in the cave. Assess the properties of the filling material, such as density, moisture content, and mechanical properties.

[0125] Assess the stability of surrounding rock: Check the rock type and structure around the cave and assess its stability. Consider the degree of development of rock cracks, joints and fault distribution.

[0126] Comprehensively evaluate the impact of caves on foundation stability: Combine the spatial distribution, morphological characteristics, filling conditions and surrounding rock stability of caves to evaluate their potential impact on foundation stability. Consider issues such as uneven settlement and reduced foundation bearing capacity that may be caused by caves.

[0127] Foundation stability index S f The assessment is based on multiple characteristics of the cave.

[0128] Sf =w1*D+w2*A c +w3*V f +w4*S c ; Among them, S f is the foundation stability index, which is a comprehensive indicator used to quantify the stability of the foundation, taking into account multiple characteristics of the cave. w1 is the weight assigned to the spatial distribution characteristics of the cave, reflecting the importance of this characteristic on the foundation stability. D is the spatial distribution index of the cave, which quantifies the spatial distribution pattern of the cave, such as the degree of concentration, dispersion or grouping. w2 is the weight assigned to the morphological characteristics of the cave, reflecting the influence of the cave morphology on the foundation stability. c is the area or size of the cave, representing the size of the cave, usually related to the diameter or size of the cave. w3 is the weight assigned to the cave filling, reflecting the influence of the nature and volume of the filling on the foundation stability. f is the volume of the filling material, which may affect the effect of the cave on the stability of the foundation. w4 is the weight assigned to the stability of the surrounding rock, reflecting the influence of the stability of the surrounding rock on the overall stability of the foundation. c The surrounding rock stability coefficient is used to evaluate the stability of the surrounding rock, which may be based on the ratio of the shear strength and shear stress of the surrounding rock. These weights w1, w2, w3 and w4 need to be determined based on actual conditions and professional knowledge, and they reflect the importance of different factors in the comprehensive evaluation. Each component in the formula should be quantified based on detailed geological survey data and professional analysis. It can provide a comprehensive view to help engineers and decision makers understand the potential impact of caves on foundation stability and formulate corresponding foundation treatment plans accordingly.

[0129] Formulate foundation treatment plan: According to the assessment results, formulate corresponding foundation treatment plan, such as grouting reinforcement, foundation replacement or pile foundation construction. Consider the feasibility, cost and construction period of the foundation treatment plan.

[0130] Furthermore, the scaffolding erection includes the following contents.

[0131] The erection of the scaffolding must be carried out strictly in accordance with the construction drawings and technical requirements to ensure that the scaffolding structure meets the load-bearing requirements of the bridge.

[0132] Select qualified steel, wood or composite materials as the main components of the bracket to ensure that the material quality meets national standards and engineering requirements.

[0133] The support range should cover the horizontal projection range of the beam body and extend at least one meter outward to increase the stability and safety of the support. Through reasonable structural design, material selection and connection methods, ensure that the support has sufficient rigidity, strength and stability to withstand various loads during construction, including structural loads, construction loads and possible dynamic loads. Pay attention to the verticality, horizontality and tightness of the connection parts of the support to avoid tilting, twisting or loosening. At the same time, do a good job of foundation treatment at the bottom of the support to ensure that the support foundation is solid and reliable.

[0134] Furthermore, the stent preloading includes the following contents.

[0135] By pre-stressing to simulate the stress state of the beam after casting, the bearing capacity and stability of the support are tested, and the elastic and inelastic deformations of the support are measured at the same time, providing a basis for the elevation adjustment and reserved deformation value when erecting the box beam formwork.

[0136] The preload weight should be no less than 1.1 times the structural load and construction load to ensure the safety of the support under extreme conditions.

[0137] Load pre-compression materials (such as sandbags, water tanks, etc.) in stages and monitor the deformation of the support. Pause for a while after each stage of loading, and then proceed to the next stage of loading after the deformation of the support stabilizes.

[0138] The graded loading of the pre-pressed material can be achieved by setting multiple loading stages i, with the loading weight W in each stage i is a ratio of the total preload weight: W i = (i / n) × W; W = 1.1 × (W str +W con ), where W is the preload weight, simulating the total load after the beam is poured, including 1.1 times of the structural load and construction load. str W is the structural load, which refers to the weight of the beam itself and the load it will bear during expected use. con Construction load refers to the load temporarily applied to the support during the construction process, such as workers, equipment, etc. i is the weight of each loading stage, when loading the pre-pressed material in stages, the weight of each loading stage. n is the total number of loading stages, the number of stages into which the pre-pressed material is divided during the pre-pressing process.

[0139] During the preloading process, the elastic and inelastic deformation of the support are measured regularly. The elastic deformation will recover after unloading, while the inelastic deformation is permanent. These data are crucial for adjusting the box girder formwork elevation and reserved deformation value.

[0140] The elastic deformation δe and the inelastic deformation δp can be calculated by the following formula: e =δ 加载 −δ卸载 ; δp = δ 加载 −δ e ; Among them, δ e is the elastic deformation, which is the reversible deformation of the bracket after loading and the deformation that can be recovered after unloading. p is the inelastic deformation, the irreversible deformation of the bracket after loading, that is, the permanent deformation. 加载 Deformation after loading: the total deformation of the bracket measured after loading the pre-compression material. 卸载 Deformation after unloading: The deformation of the bracket measured after unloading the pre-compression material.

[0141] Continuously monitor the settlement of the support. When the cumulative settlement does not exceed 2mm for three consecutive days and the preloading time is not less than seven days, the support can be considered to be sufficiently stable and meet the conditions for pouring the beam.

[0142] After confirming that the support is stable, gradually unload the preloading material. According to the deformation data measured during the preloading process, adjust the box beam formwork elevation and reserved deformation value to ensure that the line shape and elevation of the beam body after pouring meet the design requirements.

[0143] According to the deformation data measured during the preloading process, adjust the box beam formwork elevation H 调整 And the reserved deformation value ΔH: ΔH=H 原始 −δ p ΔH=δ e +K 安 ×δp; where H is adjusted to the adjusted box girder formwork elevation, which is the adjusted box girder formwork elevation based on the inelastic deformation. 原始 K is the original formwork elevation, which is the box beam formwork elevation set before preloading. ΔH is the reserved deformation value, which is calculated based on the elastic deformation and inelastic deformation, and is used to ensure that the line shape and elevation of the beam body meet the design requirements after pouring. 安 is the safety factor, a coefficient greater than 1, used to consider additional safety margin when calculating the reserved deformation value.

[0144] In this technical solution, through scientific design, careful construction and strict monitoring, the safety and stability of the support can be ensured, laying a solid foundation for the high-quality casting of the beam.

[0145] Furthermore, during the site preloading process, in order to effectively control the loading rate, monitor the settlement, and evaluate the reinforcement effect and determine the relevant parameters for large-area treatment; the following contents are included.

[0146] 1. Loading plan: Loading is carried out over five days, with uniform loading every day. Such a loading rate is intended to steadily increase the foundation pressure and avoid foundation instability caused by excessive loading. During the loading process, the loading amount is strictly controlled to ensure that the daily loading amount is accurate. If loading cannot be carried out as planned due to special circumstances (such as weather, equipment failure, etc.), the subsequent loading plan should be adjusted in time to ensure that the total loading amount and loading time meet the design requirements.

[0147] 2. Settlement observation: A fixed observation point shall be set in the center of the test area. The point shall be selected in a representative location to accurately reflect the settlement of the entire area. The observation point shall be stable and reliable to ensure that it will not be displaced or damaged during the observation process.

[0148] Settlement observations are conducted twice a day, in the morning and evening, to obtain more comprehensive settlement data. After each observation, the observation data, including observation time, observation value, weather conditions, etc., should be recorded in time for subsequent data analysis.

[0149] If the settlement on a given day exceeds 2 cm, loading should be stopped immediately for one day to prevent the foundation from being damaged by excessive settlement. Loading can only be continued after the settlement becomes stable (usually when the settlement for two consecutive days is less than a certain set value, such as 0.5 cm).

[0150] 3. Data analysis: Observe continuously for one month, collect and organize all settlement observation data.

[0151] Perform preliminary data processing, such as calculating average settlement, maximum settlement, settlement rate and other indicators. Evaluate the reinforcement effect of the foundation by analyzing the settlement data. Focus on whether the settlement trend is stable and whether the settlement is within the allowable range. If it is found that the foundation reinforcement effect is not good or there are safety hazards, the reinforcement plan should be adjusted in time or remedial measures should be taken.

[0152] According to the settlement data of the test area and the reinforcement effect evaluation results, the relevant parameters of large-scale treatment are determined. The parameters include loading rate, total loading amount, preloading time, foundation treatment depth, etc. The determination of parameters should fully consider geological conditions, engineering requirements, economic benefits and other factors to ensure the scientificity and feasibility of the large-scale treatment plan.

[0153] 4. Adjustment and optimization: During the entire preloading process, timely summarize the experience and lessons learned to provide reference and reference for similar projects. Feedback the test results and data analysis results to the design unit and construction unit, and make necessary adjustments and optimizations to the design and construction plans based on the feedback. Ensure the smooth progress of the site preloading process and the effective evaluation of the reinforcement effect, and provide strong support for subsequent large-scale treatment.

[0154] 5. When preloading a large area, especially when such operations are carried out near railways, it is crucial to ensure the safety and stability of the railway. Fixed observation points must be set up near the railway to regularly observe the impact on the railway. The detection plan should be submitted to the relevant railway departments for approval. Monitoring alarm value: lateral displacement>3mm / d, cumulative>30mm; ground settlement 25mm, change rate above 3mm / d. When the monitoring value reaches the above limit or the change rate of the monitoring value suddenly increases or maintains a high rate for three consecutive days, an alarm should be issued in time, and all parties should be asked to pay attention, analyze the reasons, and deal with them in time.

[0155] Furthermore, large-area preloading specifically includes the following contents.

[0156] 1. Setting of observation points: Fixed observation points should be set up along the railway, especially in the sections adjacent to or potentially affected by the preloading area. The observation points should be selected at representative locations, such as bridge piers, roadbed slopes, and sensitive areas of track geometry changes. The number and distribution of observation points should be reasonably determined based on the importance of the railway and the scope of the preloading area. Ensure that the impact of preloading activities on the railway can be fully reflected. Stable observation devices, such as displacement meters and settlement observation piles, should be installed at the observation points to accurately measure lateral displacement and ground settlement.

[0157] 2. Regular observation: According to the progress of preloading activities and the requirements of the railway management department, a reasonable observation frequency should be established. Observe twice a day (once in the morning and once in the evening). In the early stage of preloading or when the railway is greatly affected, the number of observations can be appropriately increased. The two main indicators to be observed are lateral displacement and ground settlement. Lateral displacement reflects the lateral stability of the railway structure, and ground settlement reflects the compression deformation of the foundation. After each observation, the observation data should be recorded in time, including observation time, observation value, weather conditions, etc., and the corresponding change curve should be drawn for subsequent analysis.

[0158] 3. Approval of the testing plan: Prepare a detailed testing plan based on the specific circumstances of the preloading activities and the requirements of the railway management department. The plan should include the setting of observation points, observation methods, observation frequency, data recording and processing methods, alarm mechanism, etc. Submit the testing plan to the relevant railway departments for approval. During the approval process, full communication with the railway management department is required to ensure the rationality and feasibility of the testing plan.

[0159] 4. Alarm mechanism: Set reasonable alarm values ​​according to the requirements of the railway management department and the actual situation of the project. For example, the lateral displacement is greater than 3mm / d or the cumulative displacement is greater than 30mm, the ground settlement reaches 25mm and the rate of change is above 3mm / d, etc. When the monitoring value reaches the above alarm limit or the rate of change of the monitoring value suddenly increases or maintains a high rate for three consecutive days, the alarm process should be started immediately. First, notify the on-site person in charge and the railway management department; secondly, organize relevant personnel to review and analyze the monitoring data; finally, take corresponding emergency measures according to the analysis results. After the alarm, the preloading activities should be stopped or adjusted immediately to prevent further impact on the railway. At the same time, organize experts to conduct a safety assessment of the railway structure and formulate corresponding reinforcement or repair plans based on the assessment results.

[0160] 5. Summary and feedback: During the entire preloading process, observation data and monitoring results should be summarized regularly to evaluate the impact of preloading activities on the railway. At the same time, the monitoring results and evaluation reports should be fed back to the railway management department and relevant units in a timely manner so that the construction plan can be adjusted in time and necessary protective measures can be taken.

[0161] Furthermore, the shallow cave treatment includes the following contents.

[0162] (1) To treat shallow karst caves, especially soil caves, the steel casing follow-up method is adopted. The steel casing can effectively protect the hole wall and prevent collapse, while ensuring the smooth progress of drilling.

[0163] (2) For shallow caves where the foundation piles are located in a single-layer or small-layer shallow cave area and the cave height is less than 3m, when the drilling hole is about 1m away from the cave top, the stroke should be reduced and the cave top should be gradually penetrated by a short-stroke rapid impact method to prevent the drill from getting stuck or the hole wall from collapsing due to excessive stroke.

[0164] (3) Before drilling to the top of a shallow cave, sufficient small pieces of stone and clay mixture should be prepared in advance. Repeated pounding and plugging can effectively fill the cave space and improve the stability of the foundation. Before drilling to the top of a shallow cave below the surface and above the groundwater level, sufficient small pieces of stone (stone diameter 10-20cm), clay (clay made into balls or cakes, diameter 15-20cm) and cement should be prepared in advance. Depending on the size of the cave, a mixture of stone and clay is backfilled and repeatedly pounded to plug the leak. The ratio of stone to clay mixture is 4:1.

[0165] (4) When there are important structures within 10m of the soil cave, the soil cave is large and has a certain degree of connectivity. To ensure the safety of surrounding structures, the soil cave should be pre-treated, including interception, anti-seepage and plugging. The surface water should be intercepted to prevent it from seeping into the soil cave area. The groundwater should be treated to prevent it from seeping into the soil cave area. Leakage plugging measures should be taken to ensure that there is no leakage in the soil cave area to prevent the soil cave from further expanding or the formation of new soil caves. For shallow soil caves and collapses formed by surface water, the soft soil should be excavated first, and then backfilled and compacted with block or slab concrete.

[0166] (5) For shallow karst soil caves, they can be dug up or blasted to reveal the top. If there is collapsed soft soil in the cave, it should be dug out and filled with boulders, stone slabs, sand, etc., and then covered with clay soil and compacted.

[0167] (6) For caves with a burial depth of less than 10 meters, small caves, empty caves or semi-filled caves, bored pile construction technology can be used to drill holes. The geological conditions can be directly observed and flexibly handled according to the actual situation.

[0168] (7) When using an impact drill to drill a hole, the inner diameter of the steel casing should be 20 to 40 cm larger than the diameter of the drill bit; the thickness of the casing should be 1 / 130d to 1 / 150d, and not less than 10 mm; the top surface of the casing should be 2 m higher than the construction water level or groundwater level, and should also meet the height requirements of the mud surface in the hole. In dry land or when building an island, it should also be 0.5 m higher than the construction ground. This ensures that the casing can be smoothly lowered and play a protective role.

[0169] (8) The depth of the steel casing buried in the ground is controlled within 15m to protect the soft cover layer. When the surface soil layer is relatively soft and the karst caves are strongly developed, the steel casing should be fully inserted into the rock and is not allowed to fall on the inclined rock surface; if the lower soil layer is relatively hard and dense and there are no karst caves, the steel casing should enter the dense soil layer at least 0.5m.

[0170] (9) The steel casing follow-up method adopts the segmented joint vibration method, which is to connect and extend the steel casing by vibrating it with a vibrating hammer while drilling, or directly insert the casing from the top of the hole when it is determined to enter the rock surface. At the same time, the welding between the segments should be dense and leak-proof to ensure the smooth follow-up of the casing and the stability of the hole wall.

[0171] (10) The deviation between the center of the top surface of the steel casing and the designed pile position shall not exceed 5 cm, and the inclination shall not exceed 1%. Ensure the quality of pile formation and construction safety.

[0172] Furthermore, deep cave treatment includes the following contents.

[0173] (1) For caves with a burial depth greater than 10m and a cave height less than 5m.

[0174] (1.1) In the case of a single cave without filling or semi-filling, the repeated punching method of stone and clay is adopted. By continuously adding stone and clay, the impact force of the punching machine is used to squeeze the materials into the cave, filling the cave space and enhancing the stability of the foundation. In addition, it is also possible to consider pouring a certain amount of low-grade concrete to reinforce the cave. After pouring concrete, punching operations are carried out to ensure that the cave is fully filled and reinforced.

[0175] (1.2) In the case of beaded caves, due to their complex shape and strong connectivity, cave grouting technology can be used in advance within a range of 0.5-1.0m around the center of the pile foundation. By injecting cement slurry or other suitable grouting materials, the gaps between the caves are filled to form a solid curtain to prevent the caves from causing adverse effects on the pile foundation construction.

[0176] (2) For caves with a burial depth greater than 10m and a cave height greater than 5m.

[0177] (2.1) In the case of backfill, it is necessary to select appropriate backfill materials according to the nature of the backfill. If the backfill is stone and relatively hard, then the backfill material should be mainly soil to make full use of its bearing capacity. If the backfill is soil and relatively soft, then the backfill material should be mainly stone to enhance the stability of the foundation. If there is serious leakage during the backfill process, it means that there may be large cavities or cracks inside the cave. At this time, it is necessary to throw stone, clay and cement to the bottom of the hole, and pour C20 underwater concrete to reinforce the hole wall and the bottom of the cave.

[0178] (2.2) In the case of a single cave without filling material, the method of backfilling with stone and clay is adopted. Since there is no supporting structure inside the cave, it is necessary to backfill the cave space with stone mainly to form a solid support body. At the same time, it is also possible to consider filling with concrete or using grouting technology to further reinforce the cave.

[0179] (2.3) When the height of the beaded caves or hollows exceeds 8m, more stringent and effective treatment measures are required because the caves are large in scale, highly connected and have a more significant impact on pile foundation construction. In addition to the cave grouting technology, the rotary spray curtain technology can also be considered for treatment. The rotary spray curtain technology forms a solid curtain wall around the cave by spraying cement slurry or other grouting materials at high pressure, effectively isolating the connection between the cave and the pile foundation construction area, ensuring construction safety and engineering quality. The cave grouting technology or rotary spray curtain technology can be used in advance within a range of 0.5-1.0m around the center of the pile foundation for treatment.

[0180] In this technical solution, deep cave treatment needs to select appropriate treatment methods and measures according to the specific conditions of the cave and construction conditions. Through scientific and reasonable design and construction, it can ensure that the cave is fully filled and reinforced, thereby ensuring the safety and stability of pile foundation construction.

[0181] Furthermore, construction monitoring ensures that the project is carried out safely and smoothly during the construction process. Through the monitoring results of foundation settlement, support deformation, geological condition change, groundwater change, surrounding structure displacement and meteorological environmental factors, abnormal conditions are monitored and abnormal conditions in the construction process are identified in time. Including the following contents.

[0182] 1. Foundation settlement monitoring: Evaluate the stability of the foundation under construction loads, promptly detect and deal with abnormal foundation settlement, and prevent adverse effects on the superstructure. Set up settlement observation points on the foundation, regularly measure and record settlement data, and analyze settlement trends. If the settlement rate is found to be abnormally accelerated or the settlement exceeds the design allowable value, construction should be stopped immediately, the cause should be found, and reinforcement measures should be taken.

[0183] 2. Support deformation monitoring: Ensure the stability and safety of the support system during construction and prevent safety accidents caused by support deformation. Install deformation monitoring equipment, such as stress sensors and displacement meters, at key parts of the support to monitor support deformation in real time. Once it is found that the support deformation exceeds the allowable range, measures should be taken immediately to strengthen the support and redesign the support plan if necessary.

[0184] 3. Monitoring of geological condition changes: Understand the changes in geological conditions in the construction area and prevent construction safety problems caused by changes in geological conditions. Monitor changes in geological conditions through geological exploration, in-situ tests and other means, combined with geological observations during the construction process. If geological anomalies such as karst caves and soil caves are found, construction should be stopped immediately and a special treatment plan should be formulated to ensure construction safety.

[0185] 4. Monitoring of groundwater changes: Prevent groundwater changes from causing adverse effects on foundations, foundation pits, etc., to ensure construction safety. Set up groundwater level observation wells, measure groundwater levels regularly, and analyze groundwater change trends. If abnormal groundwater level rises or falls, the cause should be immediately identified, and measures such as drainage, precipitation, or recharging should be taken to keep the groundwater level stable.

[0186] 5. Monitoring of displacement of surrounding structures: Assess the impact of construction on surrounding structures to prevent damage or collapse of surrounding structures due to construction. Set up displacement observation points on surrounding structures, measure and record displacement data regularly. If abnormal displacement of surrounding structures is found, construction should be stopped immediately, the cause should be analyzed, and reinforcement or protective measures should be taken.

[0187] 6. Monitoring of meteorological and environmental factors: Understand the meteorological and environmental conditions in the construction area to prevent construction safety accidents caused by bad weather. Obtain meteorological information in the construction area through weather stations or weather forecasts, including rainfall, wind speed, temperature, humidity, etc. Before bad weather comes, protective measures should be taken in advance, such as reinforcing temporary facilities, to ensure construction safety.

[0188] In response to possible abnormal situations, a detailed emergency plan should be prepared in advance to clarify the emergency response process, responsible persons and response measures. Once an abnormal situation is discovered, the emergency plan should be immediately activated and forces should be quickly organized to deal with it to prevent the situation from escalating.

[0189] In this technical solution, construction monitoring is an important means to ensure construction safety and quality. Through comprehensive and continuous monitoring and timely abnormal handling measures, construction safety accidents can be effectively prevented.

[0190] The present invention can more accurately evaluate the impact of caves on foundation stability and formulate a more scientific and reasonable foundation treatment plan by scanning with geological radar and combining geological survey and radar data analysis results. Through the joint application of unmanned aerial vehicles and geological radars, a large area can be efficiently covered, manpower and material resources can be reduced, and high-precision topographic maps and underground structure information can be quickly obtained to improve resource utilization efficiency. The data analysis results are intuitively displayed in the form of graphics or images, which is convenient for decision makers to quickly understand the characteristics of caves and the stability of foundations, and provide strong data support for project decisions. Potential problems can be discovered in time. Through continuous monitoring of key parameters such as foundation settlement, support deformation, and displacement of surrounding structures, potential problems or abnormal conditions in the construction process can be discovered in time, which provides the possibility of taking countermeasures in time. By discovering and handling abnormal conditions in time, quality problems caused by improper construction can be avoided and the overall quality of the project can be improved. By strictly setting up full-hall supports in accordance with design requirements and extending them to one meter outside the horizontal projection range of the beam body, the risk of collapse during the construction process is effectively prevented, and the safety of construction personnel and on-site equipment is guaranteed. By preloading the support, the actual construction load can be simulated, causing the support to deform accordingly, and the non-elastic deformation part is eliminated during the preloading process, thereby avoiding unpredictable settlement during subsequent concrete pouring and improving the stability of the structure. By taking different treatment measures for shallow and deep caves, the hole wall is effectively protected to prevent collapse, ensuring the smooth progress of drilling operations, reducing construction risks, enhancing foundation stability, and significantly improving the bearing capacity and stability of the foundation. The safety of surrounding important structures is ensured.

[0191] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A large-volume cast-in-place beam support foundation treatment construction method for a large-scale shallow karst cave area, characterized in that: The following steps are involved: S1. Geological survey and program planning: Use geological radar to conduct a comprehensive scan of the entire project impact area to accurately identify the distribution, scale, depth and filling conditions of shallow karst caves; formulate foundation reinforcement treatment plans and karst cave treatment plans based on the geological survey results and construction requirements; S11. Geological radar scanning: According to the terrain planning of the cast-in-place beam support foundation, obtain the topographic map, plan the route of the drone radar scanning, use the geological radar equipment to conduct a comprehensive scan, and obtain the reflection image data of the underground structure; S12, data analysis: processing and analyzing radar data to identify the specific location, shape, scale and filling of the cave; S121, data import: import the raw data collected by the geological radar equipment into the GPRMax data processing software; S122, preprocessing: preprocessing the data, including noise removal, filtering and gain adjustment, to improve the quality and signal-to-noise ratio of the data; S123, model building: invert the model of underground media based on geological radar data, assist with the simulation function of GPRMax, and fit the actual data by continuously adjusting the model parameters; S124, Data processing and analysis: Import the collected radar data into professional data processing software for data preprocessing; use GPRMax to conduct in-depth analysis of the preprocessed radar data; identify the location, shape, scale and filling of the cave; Includes the following: Data collation: Extract key information from the data obtained from geological radar scanning; use professional software to process radar data to identify the location, shape, size and filling of caves; Draw a cave distribution map: Use the Geographic Information System (GIS) to draw a cave distribution map on the topographic map based on radar data; Assess the spatial distribution characteristics of caves: Analyze the spatial distribution pattern of caves, including whether they are concentrated, dispersed or clustered; Assess the morphological characteristics of the cave: describe the morphology of the cave and measure the size of the cave; Assess cave filling: determine whether there is filling in the cave; assess the nature of the filling; Assess the stability of surrounding rock: Check the rock type and structure around the cave, assess its stability, and consider the degree of development of rock cracks, joints, and fault distribution; Comprehensively evaluate the impact of karst caves on foundation stability: Combine the spatial distribution, morphological characteristics, filling conditions and surrounding rock stability of karst caves to evaluate their potential impact on foundation stability; foundation stability index S f Combine multiple characteristics of caves to evaluate: S f =w1*D+w2*A c +w3*V f +w4*S c ; Among them, S f is the foundation stability index, which is used to quantify the stability of the foundation; w1 is the weight of the spatial distribution characteristics of the cave; D is the spatial distribution index of the cave, which quantifies the spatial distribution pattern of the cave; w2 is the weight of the morphological characteristics of the cave; A c is the area or size of the cave; w3 is the weight of the cave filling condition; V f is the volume of the filling; w4 is the weight of the surrounding rock stability; S c is the surrounding rock stability coefficient; Formulate foundation treatment plan: According to the assessment results, formulate corresponding foundation treatment plan, including grouting reinforcement, foundation replacement or pile foundation construction; S125. Result visualization: Display the analysis results in the form of graphics or images; S2. Foundation treatment: including removal of original soil, replacement of gravel cushion, pouring of concrete cushion and pre-compression of site; S3. Cave treatment: Develop a comprehensive treatment plan based on the cave's type, size, filling conditions and surrounding environmental factors; specifically include: S31, shallow cave treatment; S32, deep cave treatment; S4, Scaffold erection and preloading: including scaffold erection and scaffold preloading; Scaffolding installation: erect full-hall scaffolding according to design requirements, with the scaffolding covering the horizontal projection range of the beam and extending one meter outward; Pre-stressing the support: Before pouring concrete, pre-stress the support; measure the elastic deformation and inelastic deformation of the support so as to adjust the elevation and reserve deformation value when erecting the box beam formwork; ensure that the beam body can be poured only after the support is fully stable; S5. Construction monitoring: During the construction process, the foundation settlement, support deformation and displacement of surrounding structures are continuously monitored, and abnormal conditions are monitored.

2. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 1 is characterized by: Step S2 includes the following steps: S21. Removal of original soil: within the cast-in-place range of the main bridge support, remove the original surface fill soil to ensure that the treatment area is clean and free of impurities; S22, gravel cushion replacement: Use a 50cm thick gravel cushion for replacement and compact it with a heavy roller to ensure that the compaction degree is greater than 90% to improve the bearing capacity of the foundation; S23, pouring concrete cushion: pour a 20cm thick C20 concrete cushion on top of the gravel cushion to ensure a smooth surface; S24. Site preloading: Select representative areas for preloading tests, adopt the most unfavorable load for graded loading, monitor the settlement, and ensure that the settlement during the construction period does not exceed 10mm; when preloading a large area, set up fixed observation points, regularly observe the impact on surrounding buildings, and conduct a detailed analysis of the preloading test data.

3. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 1 is characterized by: Step S11 includes the following steps: S111. Topographic map acquisition: Use satellite remote sensing technology to obtain high-precision topographic maps; topographic maps contain detailed contour lines, landform features and water system distribution information; S112, UAV radar scanning route planning: Based on the topographic map, identify potential karst cave development areas and key scanning areas; plan the flight route of the UAV radar scanning; set the flight altitude, speed and scanning angle to obtain high-quality radar reflection image data; S113. Implementation of geological radar scanning: Select geological radar equipment suitable for cave detection, start the drone, and perform radar scanning according to the planned route.

4. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 1 is characterized in that: The stent preloading is performed by loading the preloading material in stages and monitoring the deformation of the stent; the staged loading of the preloading material is achieved by setting a plurality of loading stages i, and the loading weight W of each stage is i W i = (i / n) × W; W=1.1×(W str +W con ), where W is the preload weight, simulating the total load after the beam is poured; W str W is the structural load, which refers to the weight of the beam itself and the load it will bear in expected use; con W is the construction load, which refers to the load temporarily applied to the support during the construction process; i is the loading weight at each stage; n is the total number of loading stages; During the preloading process, the elastic and inelastic deformations of the stent were measured regularly; The elastic deformation δe and the inelastic deformation δp are calculated by the following formula: δ e =δ 加载 −δ 卸载 ; δp = δ 加载 −δ e ; Among them, δ e is the elastic deformation, which is the reversible deformation of the bracket after loading; δ p is the inelastic deformation; δ 加载 is the deformation after loading; δ 卸载 is the deformation after unloading; Continuously monitor the settlement of the support. When the cumulative settlement does not exceed 2mm for three consecutive days and the preloading time is not less than seven days, the support is considered to be sufficiently stable and ready for pouring the beam.

5. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 4 is characterized in that: After confirming that the support is stable, gradually unload the preloading material, adjust the box beam formwork elevation and reserved deformation value according to the deformation data measured during the preloading process, and ensure that the line shape and elevation of the beam body after pouring meet the design requirements; according to the deformation data measured during the preloading process, adjust the box beam formwork elevation H 调整 And the reserved deformation value ΔH: ΔH=H 原始 −δ p ΔH=δ e +K 安 ×δp; where H is adjusted to the adjusted box girder formwork elevation; H 原始 is the original formwork elevation, the box girder formwork elevation set before preloading; ΔH is the reserved deformation value; K 安 is the safety factor.

6. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 1 is characterized by: Step S31 includes the following steps: S311. To treat shallow karst caves, including earth caves, the steel casing follow-up method is adopted; S312. For shallow karst caves with a single layer or a few layers and a cave height of less than 3m, when the hole is drilled to about 1m from the cave top, the cave top is gradually penetrated by a short-stroke rapid impact method to prevent the drill from getting stuck or the hole wall from collapsing due to excessive stroke; S313. Before drilling to the top of the shallow cave, fill the cave with a mixture of slabs of stone and clay according to the size of the cave, and repeatedly pound and seal the leaks. The ratio of the mixture of slabs of stone and clay is 4:

1. S314. When there are important structures within 10m of the earth cave, the earth cave is large and has a certain degree of connectivity, and the earth cave is pre-treated, including interception, anti-seepage and plugging, to intercept surface water and prevent surface water from seeping into the earth cave area; S315. For shallow karst caves, dig them open or blast them to expose the top, then fill them with rocks, slabs and sand, and then cover them with clay soil and tamp them down; S316. For caves with a burial depth of less than 10 meters, small cave bodies, empty or semi-filled caves, bored pile construction technology is used to drill holes.

7. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 1 is characterized by: Step S32 includes the following steps: S321: For caves with a burial depth greater than 10m and a cave height less than 5m, different treatment methods are adopted according to the specific situation: S3211. In the case of a single cave without filling or semi-filling, a repeated punching method of stone and clay is used. By continuously adding stone and clay, the impact force of the punching machine is used to squeeze the materials into the cave, filling the cave space and enhancing the stability of the foundation. S3212: In the case of beaded karst caves, the karst cave grouting technology is used in advance within the range of 0.5-1.0m around the center of the pile foundation. The gaps between the karst caves are filled by injecting cement slurry to form a solid curtain to prevent the karst caves from causing adverse effects on the pile foundation construction. S322: For caves with a burial depth greater than 10m and a cave height greater than 5m, different treatment methods are adopted according to the specific situation: S3221. In case of filling, select appropriate backfill material according to the nature of the filling; S3222: In the case of a single cave without filling material, backfilling with stone and clay is used; S3223: When the height of beaded caves or cavities exceeds 8m, use rotary jet curtain technology to treat them.

8. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 6 is characterized by: The follow-up method for steel casing adopts the segmented splicing and vibration method, which is to connect and lengthen the steel casing by vibrating it with a vibrating hammer while drilling.

9. The method for treating the foundation of a large volume cast-in-situ beam support in a large-scale shallow karst cave area according to claim 1 is characterized by: Step S5 includes the following contents: Foundation settlement monitoring: Set up settlement observation points on the foundation, regularly measure and record settlement data, analyze settlement trends, and promptly detect and handle abnormal foundation settlement; Bracket deformation monitoring: Install deformation monitoring equipment at key parts of the bracket to monitor the bracket deformation in real time; Monitoring of geological condition changes: Monitoring of geological condition changes through geological exploration and in-situ testing combined with geological observations during construction; Groundwater change monitoring: set up groundwater level observation wells, regularly measure groundwater levels, and analyze groundwater change trends; Displacement monitoring of surrounding structures: Set up displacement observation points on surrounding structures, measure and record displacement data regularly, and promptly detect abnormal displacement of surrounding structures; Monitoring of meteorological environmental factors: Obtain meteorological information of the construction area through the meteorological station.

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