Steel rolling deep foundation pit group combined support parallel construction method

Abstract

The invention relates to a steel rolling deep foundation pit group combined support parallel construction method. The method comprises the steps that firstly, a foundation pit group is divided into a heating furnace area, a rolling mill electric room area, a rough rolling area, a finish rolling area and a slag sluice area; step 2, respectively determining a support form for each area, wherein a slope ratio method is adopted for a rolling mill electric room area for sloping; the heating furnace area, the rough rolling area and the finish rolling area are supported by adopting a slope ratio method and soil nailing wall anchor cable combination; the cinder sluice area is supported in a combined mode of large excavation or soil unloading and Larsen steel sheet pile inner supporting, and a differentiated combined supporting system is formed. Thirdly, parallel excavation is synchronously carried out on all the areas; and 4, establishing a whole-process monitoring and early warning system, and starting a graded emergency plan when monitoring data exceeds a threshold value. The deep foundation pit group construction problem is solved, so that deep foundation pit construction safety and quality are guaranteed, the construction period is shortened, the overall construction period requirement is met, and cost is saved.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy, specifically to a method for parallel construction of combined support for deep foundation pits in steel rolling mills. Background Technology

[0002] According to the existing steel rolling production process, raw materials are processed in a heating furnace, then initially rolled on a roughing mill, and subsequently rolled a second time on a finishing mill before entering subsequent processing steps. The heating furnace and main rolling line are the absolute key points in the construction of the entire steel rolling plant. At the same time, the foundations of the heating furnace and main rolling line equipment are large in size and complex in structure, which are also the major challenges in the project construction. If the construction problems of the deep foundation pits in the heating furnace and main rolling line areas cannot be properly resolved, it will have a significant impact on the overall project schedule and the commissioning of subsequent equipment.

[0003] According to industry data, modern steel rolling mills generally adopt a continuous process of "heating furnace → roughing rolling → finishing rolling," resulting in large-volume and highly complex equipment foundations: the excavation depth of the heating furnace foundation reaches 8.6-8.8 meters, and the excavation depth of the roughing / finishing rolling zone foundation is 5-16.5 meters, forming a large-scale deep foundation pit complex (with a single project's earthwork exceeding 390,000 cubic meters). Such deep foundation pit projects present the following problems: 1. Complex geological conditions: The construction area generally contains loose Quaternary sediments, and the water content of the silt and silt layers is close to the liquid limit. The soil has low shear strength and is prone to landslides and collapses. 2. Spatial interference: There is a height difference of 12-18 meters between equipment foundations, underground pipe corridors, and slag flushing ditches. Traditional sequential construction methods result in a construction delay rate of up to 35%. 3. Accumulation of safety risks: The deep foundation pit group covers an area of ​​over 20,000 square meters, the construction impact coefficient of adjacent foundation pits reaches 0.7, and the settlement control value of surrounding buildings and structures must be ≤3mm / d.

[0004] The construction methods currently commonly used in the industry have the following technical defects: 1. The support system is too simple: 83% of the projects use slope excavation or single soil nailing wall support, which cannot meet the needs of excavation with a large drop of 8.6-16.5 meters; The application rate of sheet pile support is less than 15%, and a combined support system has not been formed. Typical case: Due to improper selection of support methods, a foundation pit collapse accident occurred at a steel plant project, resulting in direct economic losses exceeding 20 million yuan; 2. Inefficient construction organization: The sequential construction mode resulted in a more than 40% extension of the critical path construction period; Traditional methods result in equipment utilization rates of less than 60%, with idle machinery costs accounting for 12% of total costs. An important project was delayed by 82 days due to an unreasonable construction sequence. 3. Inadequate safety control: The monitoring frequency is less than 50% of the standard requirement, resulting in delayed detection of potential hazards; The emergency response plan is poorly operable, and the accident handling efficiency is less than 40%. Industry accident statistics show that deep foundation pit engineering accidents account for 28% of metallurgical construction accidents.

[0005] The above-mentioned deep foundation pit operations are highly dangerous, and the deep foundation pit group occupies a large area with an earthwork excavation volume of 390,000 cubic meters. 3 The project has tight deadlines, and the facilities such as equipment foundations, underground pipe corridors, and slag flushing ditches are intertwined and vary in height. It is difficult to ensure the construction progress and quality of the deep foundation pit group using traditional construction methods. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies and provide a parallel construction method for combined support of deep foundation pits in steel rolling mills, solving the problems of poor adaptability of support systems, inefficient construction organization, and lagging safety control.

[0007] To solve the above-mentioned technical problems, the present invention is implemented as follows: A parallel construction method for combined support of deep foundation pits for steel rolling mills, characterized by comprising the following steps: Step 1: Based on the arrival sequence of process equipment, divide the foundation pit group into the heating furnace area, rolling mill electrical room area, roughing rolling area, finishing rolling area, and slag flushing ditch area; Step 2: Determine the support method for each area: the slope method is used for the electrical room area of ​​the rolling mill; the "slope method + soil nail wall anchor cable" combination support is used for the heating furnace area, roughing rolling area and finishing rolling area; the "large excavation or soil unloading + Larssen steel sheet pile internal support" combination support is used for the slag flushing ditch area, forming a differentiated combination support system; Step 3: After the construction of each support system is completed, parallel excavation shall be carried out simultaneously in each area in accordance with the principles of "support first, then excavation; shallow first, then deep; layered and segmented; and over-excavation is strictly prohibited". Step 4: Establish a full-process monitoring and early warning system to monitor the deformation of the foundation pit, the groundwater level and the settlement of surrounding buildings and structures in real time. When the monitoring data exceeds the threshold, the graded emergency plan will be activated.

[0008] The parallel construction method for combined support of deep foundation pits for steel rolling mills is characterized in that: the support forms include: In areas with an excavation depth of 5-8.8m, a slope ratio method combined with soil nailing wall composite support is adopted, with a slope ratio of 1:0.75-1:1, and a first-level / second-level slope platform is set up; In areas with an excavation depth of 9-16.5m, a steel sheet pile + internal support system is adopted, with an embedment depth of ≥7m and three horizontal supports are set.

[0009] The parallel construction method for combined support of deep foundation pits for steel rolling mills is characterized in that: the parallel excavation includes: Level 1 parallel operation: The foundation pit support of the heating furnace area and the foundation excavation of the rolling mill electrical room are carried out simultaneously; Secondary parallel operation: The secondary slope support of the roughing / finishing zone of the main rolling line and the steel sheet pile construction of the slag flushing ditch are carried out simultaneously; Three-level parallel operations: equipment foundation construction and underground utility tunnel laying are carried out simultaneously.

[0010] The parallel construction method for combined support of deep foundation pits for steel rolling mills is characterized in that: the support system comprises: Soil nailing wall support parameters: φ130 steel bar soil nails spaced 2000mm, length 12-15m, equipped with MS1: φ150 steel strand anchor cable, anchoring section 8-11m; Steel sheet pile support parameters: Larsen IV type steel sheet piles, length 12-15m, 400mm×400mm H-beam steel walers, three φ609×16mm steel pipe supports; Slope ratio parameters: Level 1 slope excavation depth 4-4.5m, Level 2 slope excavation depth 4.5-5.5m, intermediate platform width 1-1.5m.

[0011] The aforementioned parallel construction method for combined support of deep foundation pits for steel rolling mills is characterized in that: the three-level parallel construction includes: Prioritize construction in the heating furnace area: employ the slope method combined with soil nailing wall support, and simultaneously excavate the electrical room slope; Relay construction in the main rolling zone: the secondary slope excavation in the roughing zone and the soil nailing wall anchor cable support in the finishing zone are carried out in an alternating manner; Simultaneous construction of slag ditch areas: East-west slag ditch adopts large-scale excavation + steel sheet pile support, and north-south slag ditch implements soil unloading + steel sheet pile composite support. Construction intervals in each area are controlled to be ≤15m to form a continuous working face.

[0012] The parallel construction method for combined support of deep foundation pits for steel rolling mills is characterized in that: the whole-process monitoring and early warning system includes: Monitoring point layout: Displacement monitoring points are set up every 20m on the slope of the foundation pit, and settlement observation points are set up every 50m on the surrounding buildings and structures; Monitoring frequency: twice a day during the excavation stage, once a day during the support stage, and increased to four times a day during heavy rain. Warning thresholds: horizontal displacement rate ≥3mm / d, settlement rate ≥2mm / d, groundwater level drop ≥1m / d; Emergency Response: A yellow alert will be activated when the monitored value reaches 80% of the alarm threshold, and a red alert will be activated and construction will be suspended when the value reaches 100%.

[0013] The parallel construction method for combined support of deep foundation pits for steel rolling mills is characterized in that: the graded emergency response plan includes: Level 1 Response (Instability of Enclosure Structure): Immediately backfill with counter-pressure and initiate dual-liquid grouting reinforcement; Level II Response (Pit Bottom Heave): Add dewatering well points and implement surcharge preloading; Level 3 response (surrounding settlement): Follow up with grouting on the affected buildings and structures; Emergency resource depot: 500m 3 Emergency supplies included sandbags, three double-liquid grouting machines, and 200 tons of cement.

[0014] The beneficial effects of this invention are as follows: As can be seen from the above technical solution, this application provides a parallel construction method for combined support of deep foundation pits for steel rolling. By using "differentiated combined support", high-risk deep areas (-16.5m) and shallow areas (-5m) are treated differently: in the deep area, 12m-15m Larssen IV type steel sheet piles are used with three φ609×16mm steel pipe internal supports to form a rigid support shell. The measured maximum horizontal displacement is 0.12%H, which is lower than the standard limit of 0.15%H for Class I environment. In the shallow area, a composite support of "slope ratio method + soil nail wall anchor cable" is used. The soil nail length is 12m-15m and a locking force of 120kN is applied, which increases the slope safety factor to 1.42, which is 32% higher than that of pure slope excavation. The full-process monitoring and early warning system collects deformation and water level data in real time at a frequency of twice a day. When the displacement rate reaches 3 mm / d, a yellow warning is activated, realizing a closed loop of "sensing-analysis-handling". This can control sudden dangers in the bud stage and avoid serious accidents such as collapses and sudden surges.

[0015] Traditional sequential construction requires a series of operations: "support completion → excavation → structure → backfilling," with a total construction period of approximately 150 days. This method utilizes a "three-level parallel" organizational logic: the first level of parallelism advances the heating furnace area and the rolling mill electrical room area simultaneously; the second level of parallelism constructs the roughing / finishing mill secondary slopes and the slag flushing trench sheet piles in parallel; and the third level of parallelism immediately inserts equipment foundation and pipe gallery operations after the foundation handover, with each zone's work surface spaced ≤15m apart, forming a continuous flow. Field measurements show that the critical path time was reduced from 98 days to 63 days, a reduction of 35%.

[0016] If a diaphragm wall is used for the slag flushing trench of the main rolling line, which is 16.5m deep and 97m wide, 18,000 m³ of concrete will be required. 3 The original steel reinforcement cost 2600 tons, with a support cost of approximately 42 million yuan. After switching to a system of "soil unloading + Larssen sheet piles + steel pipe internal bracing," concrete usage was reduced by 85% and steel usage by 60%. Under the same stiffness, the support cost dropped to 28 million yuan, saving 14 million yuan, a reduction of 33%. In shallow areas, internal bracing was eliminated, replaced by a slope method + soil nailing walls, saving 1200 tons of steel bracing and reducing the amount of excavation work by 11,000 m². 3 The overall cost will decrease by another 8%.

[0017] By combining zoned precipitation with on-demand well sealing, the total precipitation was reduced by 30%, and the groundwater level drop was controlled to 0.5m-0.8m below the pit bottom. The maximum settlement of surrounding roads was reduced from 38mm to 19mm, which is 20mm below the municipal warning value. Interception ditches were installed at the top of the slope, and blind ditches and collection wells were installed at the bottom of the pit. During the rainstorm period, muddy wastewater was reused after sedimentation, and the SS emission concentration was <50mg / L, meeting the green steel plant standards. Parallel operations shortened the exposure time, and the average online dust monitoring value was 0.18mg / m³. 3 This reduces costs by 40% compared to sequential construction, significantly lowering the risk of environmental fines and community complaints. Attached Figure Description

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments: Figure 1 This is a schematic diagram showing the distribution of various regions in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection claimed in this application. like Figure 1 As shown: A parallel construction method for combined support of deep foundation pits for steel rolling mills includes the following steps: Step 1: Determine the excavation design approach; The underground equipment foundations and underground structures in the heating furnace area and main rolling line area are complex, with varying designed burial depths and excavation depths all exceeding 5 meters, classifying them as deep foundation pits and posing significant risks. Furthermore, the stable groundwater level within the construction area is approximately -1 meter, with abundant water volume. The underground soil consists entirely of Quaternary and Tertiary loose sediments, primarily composed of alluvial and diluvial deposits forming brownish-yellow and grayish-yellow silt, silty clay, and silty sand. Each soil layer has high water content and is close to the liquid limit of the soil, especially the silt and silty sand layers, which exhibit poor soil properties and mechanical indicators, making them highly susceptible to landslides and subsequent foundation pit collapse.

[0020] Based on the actual site conditions and the equipment arrival schedule, a handover plan for the equipment foundations in each area was determined. Different types of foundation pit support were adopted to form a combined overall support scheme, and parallel construction was carried out in each area: the excavation for foundation pit support in the heating furnace area was carried out simultaneously and in parallel with the excavation for the primary slope support of the rolling mill electrical room and the main rolling line; the excavation for the secondary slope support of the roughing and finishing rolling areas and the excavation for the sheet pile support of the slag flushing trench within the main rolling line were carried out simultaneously and in parallel. This provided working surfaces for subsequent construction, accelerated the construction progress, and improved construction efficiency. Step 2: Determine the support method; Based on the environmental grade and support structure safety grade of the foundation pit specified in the current national standards, the deep foundation pit grade is first determined, and then the excavation and support methods are determined according to the deep foundation pit grade as follows: the excavation depth of the main rolling mill electrical room is -5.0m, and the slope method is used for construction; the excavation depth of the heating furnace is -8.6m to -8.8m, the excavation depth of the roughing rolling zone is -10.0m, and the excavation depth of the finishing rolling zone is -9.0m, and the slope method + soil nailing wall support is used; the excavation depth of the main rolling line slag flushing trench is -10.7m to 16.3m, and steel sheet pile support is used.

[0021] Step 3: Construction sequence design; Step 3.1: Based on the basic design and actual site conditions, organize and prepare a specialized construction plan for earthwork excavation. Step 3.2: Organize expert review and conduct a briefing on the earthwork excavation plan and quality; Step 3.3: Determine the location for earthwork stockpiling, plan the transportation route, level the site, lay temporary roads, and prepare dust suppression measures; Step 3.4: Surveying and setting out; Determine the location of the deep foundation pit and mark the excavation opening line with lime; Step 3.5: Dewatering; Based on the groundwater conditions, before excavating the deep foundation pit, dewatering should be carried out in the wells to lower the groundwater level to at least 0.5m above the bottom of the foundation pit before excavation can begin. Dewatering can only be stopped and the wells sealed after the equipment foundation construction is completed. Step 3.6: The excavation of the foundation pit support in the heating furnace area and the excavation of the primary slope support of the rolling mill electrical room and the main rolling line are carried out simultaneously and in parallel. The excavation of the secondary slope support in the roughing and finishing rolling areas and the excavation of the steel sheet pile support in the slag flushing ditch within the main rolling line are carried out simultaneously and in parallel. Step 3.6.1: Excavation of the deep foundation pit in the heating furnace area; As a key part of the project, the heating furnace area, with its equipment arriving first, requires priority construction to facilitate timely foundation handover. The excavation depth in this area is -8.6m to -8.8m, employing a slope ratio method combined with soil nailing wall support. The slope ratio is 1:1, with a first-level slope excavation depth of 4m and a second-level slope excavation depth of 4m-5m. The intermediate platform width is 1.5m. The soil nailing wall anchor cable support uses 5 soil nails (φ130 reinforced soil nails, C20@2000, L=12.00m) + 1 anchor cable (MS1: φ150 2 bundles of φs15.2 steel strands@2000, free section 7.0m, anchored section 8.0m, locking value 120kN). The anchor cable waist beam uses 18B channel steel. The surface layer is covered with a φ250*250 single-layer steel mesh and shotcrete C20, 80mm thick. The working surface for foundation construction is 1000~2000mm, and a water interception ditch is set at the top of the slope and a drainage ditch is set at the bottom of the slope.

[0022] Step 3.6.2: Excavation of the deep foundation pit for the rolling mill electrical room; The excavation depth of the rolling mill electrical room is -5.0m, and the entire support is provided by slope excavation with a slope ratio of 1:0.75. The foundation construction working surface is 1000mm. A water retaining wall is set at the top of the slope, and a drainage ditch is set at the bottom of the slope as appropriate according to the weather and rainfall conditions.

[0023] Step 3.6.3: Deep foundation pit excavation in the main rolling line area (roughing rolling area and finishing rolling area) After the deep foundation pit of the rolling mill electrical room is excavated, a two-stage slope with soil nailing and anchor cable support will be adopted. The slope ratio is 1:0.75, the excavation depth of the first-stage slope is 4.5m, the excavation depth of the second-stage slope is 4.5m-5.5m, and the width of the intermediate platform is 1.0m. The soil nailing and anchor cable support uses 5 soil nails (φ130 steel soil nails, C18 / 20@2000, L=12.00m / 15.00m) + 1 anchor cable (MS1: φ150 2 bundles of φs15.2 steel strands@2000, free section 4.0m, anchored section 11.0m, locking value 120kN). The anchor cable waist beam is made of 18B channel steel. The surface layer is covered with φ6@250*250 single-layer steel mesh, and shotcrete C20, 60mm thick. The foundation construction working surface is 1000mm wide. A water-retaining sill is set at the top of the slope, and a drainage ditch is set at the bottom of the slope as appropriate according to the weather and rainfall conditions.

[0024] Step 3.6.4: Excavation of deep foundation pit for slag flushing ditch The initial elevations on both sides of the main rolling line slag flushing trench (east-west direction) are -10.7m and -12.1m, with the deepest point in the center reaching approximately -14.8m. A combination of open excavation and Larssen sheet pile support is planned. Excavation will first proceed to the designed main rolling line elevations of -9.0m and -10.0m, followed by sheet pile support. The sheet piles will be 12m long Larssen IV type (400mm wide, 170mm high, 16.1mm thick), with the pile top elevation at the open excavation base elevation (-9.0m and -10.0m), and an embedment depth greater than 7m. The sheet pile walers will be made of 400mm×400mm×13mm×24mm H-beams, and the brackets will be made of [16a channel steel, installed every 3 meters and welded to the sheet piles. Internal bracing will also use 400mm×400mm×13mm×24mm H-beams, spaced 6m apart.

[0025] The north-south slag-filling ditch starts at a depth of -14.8m and ends at -16.2m. Construction will utilize a combination of excavation and sheet pile support. Excavation will begin at an elevation of -5.0m from the main motor span, proceeding to -8.0m. The excavation slope ratio for excavation is 1:0.75, and the distance from the toe of the excavation slope to the sheet pile support is ≥12m. The sheet piles will be 15m long Larsen IV type (400mm wide, 170mm high, 16.1mm thick), with the pile top elevation at the excavation base elevation (-8.0m) and an embedment depth of 6.8m. The sheet pile walers will be 2H700X300 double-section steel walers, with brackets made of [16a channel steel, installed every 3 meters and welded to the sheet piles. The internal support uses three ∅609X16 steel pipe supports, with the center elevations of the steel pipe supports being -8.4m, -10.9m, and -13.9m respectively, and arranged at a spacing of 6m.

[0026] Step 3.7: Bottom trimming; Deep foundation pits are excavated mechanically, and to prevent disturbance of the foundation soil, the bottom 20-30cm above the pit bottom is trimmed manually. Step 4: Develop an emergency response plan; Emergency plans should be developed and targeted and operable measures should be taken to address situations such as lateral deformation of underground retaining walls exceeding alarm values, water seepage in retaining walls, quicksand at the bottom of pits, piping, heave at the bottom of pits, over-excavation of soil at the bottom of pits, road cracking or collapse, and settlement, tilting, and deformation of adjacent buildings and underground pipelines. Step 5: Excavate the deep foundation pit Once the above four steps are completed, deep foundation pit excavation can be carried out according to the construction procedures described in step 3. The excavation principles are "support before excavation, shallow before deep, layered excavation, over-excavation strictly prohibited, and gradual advancement". The deep foundation pit group itself and the surrounding environment must be monitored throughout the entire process before, during and after excavation to ensure safety.

[0027] The construction process design method for the ultra-large deep foundation pit group in the hot rolling mill plate processing area proposed in this invention addresses the entire process, from excavation design concept, determination of support form, construction procedure design, emergency plan preparation, and deep foundation pit excavation. It solves the impact of complex surrounding environment, complex geological conditions, and complex relationships between foundation pits on the construction of the deep foundation pit group in the plate processing area, prevents collapse accidents during the excavation of the deep foundation pit group, and avoids settlement, tilting, and other accidents of surrounding buildings and roads due to the excavation of the deep foundation pit group. Under the premise of ensuring the safety of the foundation pit itself and the surrounding environment, it improves construction efficiency and shortens the construction period.

[0028] This invention employs a combination of various foundation pit support schemes, including graded slope using the slope ratio method, soil nailing wall support, and steel sheet pile support. This solves the problem of large-scale, deep foundation pit excavation caused by different burial depths of equipment foundations and complex underground structures, and saves on support costs.

[0029] Reasonably divide the area and arrange the construction procedures of each area using a parallel construction method to ensure that the critical path schedule of this project meets the needs of on-site foundation handover and equipment installation.

[0030] The technical problem to be solved by this invention is to solve the problem of deep foundation pit group construction by adopting a variety of support design methods, rationally arranging the construction sequence, and carrying out parallel construction based on the project's geological conditions, design drawings, and on-site requirements, thereby ensuring the safety and quality of deep foundation pit construction, shortening the construction period, meeting the overall construction period requirements, and saving costs.

[0031] The above are merely embodiments provided in this application and are not intended to limit this application. Although this application has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A parallel construction method for combined support of deep foundation pits for steel rolling mills, characterized in that... It includes the following steps: Step 1: Based on the arrival sequence of process equipment, divide the foundation pit group into the heating furnace area, rolling mill electrical room area, roughing rolling area, finishing rolling area, and slag flushing ditch area; Step 2: Determine the support method for each area: the slope method is used for the electrical room area of ​​the rolling mill; the "slope method + soil nail wall anchor cable" combination support is used for the heating furnace area, roughing rolling area and finishing rolling area; the "large excavation or soil unloading + Larssen steel sheet pile internal support" combination support is used for the slag flushing ditch area, forming a differentiated combination support system; Step 3: After the construction of each support system is completed, parallel excavation shall be carried out simultaneously in each area in accordance with the principles of "support first, then excavation; shallow first, then deep; layered and segmented; and over-excavation is strictly prohibited". Step 4: Establish a full-process monitoring and early warning system to monitor the deformation of the foundation pit, the groundwater level and the settlement of surrounding buildings and structures in real time. When the monitoring data exceeds the threshold, the graded emergency plan will be activated.

2. The parallel construction method for combined support of deep foundation pits for steel rolling mills according to claim 1, characterized in that: The support methods include: In areas with an excavation depth of 5-8.8m, a slope ratio method combined with soil nailing wall composite support is adopted, with a slope ratio of 1:0.75-1:1, and a first-level / second-level slope platform is set up; In areas with an excavation depth of 9-16.5m, a steel sheet pile + internal support system is adopted, with an embedment depth of ≥7m and three horizontal supports are set.

3. The parallel construction method for combined support of deep foundation pits for steel rolling mills according to claim 1, characterized in that: The parallel excavation includes: Level 1 parallel operation: The foundation pit support of the heating furnace area and the foundation excavation of the rolling mill electrical room are carried out simultaneously; Secondary parallel operation: The secondary slope support of the roughing / finishing zone of the main rolling line and the steel sheet pile construction of the slag flushing ditch are carried out simultaneously; Three-level parallel operations: equipment foundation construction and underground utility tunnel laying are carried out simultaneously.

4. The parallel construction method for combined support of deep foundation pits for steel rolling mills according to claim 2, characterized in that: The support system includes: Soil nailing wall support parameters: φ130 steel bar soil nails spaced 2000mm, length 12-15m, equipped with MS1: φ150 steel strand anchor cable, anchoring section 8-11m; Steel sheet pile support parameters: Larsen IV type steel sheet piles, length 12-15m, 400mm×400mm H-beam steel walers, three φ609×16mm steel pipe supports; Slope ratio parameters: Level 1 slope excavation depth 4-4.5m, Level 2 slope excavation depth 4.5-5.5m, intermediate platform width 1-1.5m.

5. The parallel construction method for combined support of deep foundation pits for steel rolling mills according to claim 3, characterized in that: The three-level parallel construction includes: Prioritize construction in the heating furnace area: employ the slope method combined with soil nailing wall support, and simultaneously excavate the electrical room with slope protection. Relay construction in the main rolling zone: the secondary slope excavation in the roughing zone and the soil nailing wall anchor cable support in the finishing zone are carried out in an alternating manner; Simultaneous construction of slag ditch areas: East-west slag ditch adopts large-scale excavation + steel sheet pile support, and north-south slag ditch implements soil unloading + steel sheet pile composite support. Construction intervals in each area are controlled to be ≤15m to form a continuous working face.

6. The parallel construction method for combined support of deep foundation pits for steel rolling mills according to claim 1, characterized in that: The whole-process monitoring and early warning system includes: Monitoring point layout: Displacement monitoring points are set up every 20m on the slope of the foundation pit, and settlement observation points are set up every 50m on the surrounding buildings and structures; Monitoring frequency: twice a day during the excavation stage, once a day during the support stage, and increased to four times a day during heavy rain. Warning thresholds: horizontal displacement rate ≥3mm / d, settlement rate ≥2mm / d, groundwater level drop ≥1m / d; Emergency Response: A yellow alert will be activated when the monitored value reaches 80% of the alarm threshold, and a red alert will be activated and construction will be suspended when the value reaches 100%.

7. The parallel construction method for combined support of deep foundation pits for steel rolling mills according to claim 1, characterized in that: The tiered emergency response plan includes: Level 1 Response (Instability of Enclosure Structure): Immediately backfill with counter-pressure and initiate dual-liquid grouting reinforcement; Level II Response (Pit Bottom Heave): Add dewatering well points and implement surcharge preloading; Level 3 response (surrounding settlement): Follow up with grouting on the affected buildings and structures; Emergency resource depot: 500m 3 Emergency supplies included sandbags, three double-liquid grouting machines, and 200 tons of cement.

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