Underground station high-precision continuous open caisson construction method based on earth cutting and sedimentation coupling

Abstract

The invention discloses an underground station high-precision continuous open caisson construction method based on earth cutting and sedimentation coupling, which comprises the following steps: 1, dividing a to-be-built underground station into an odd number of open caisson sections along the length direction of the to-be-built underground station, and numbering all the open caisson sections in sequence; 2, all the open caisson sections with the odd numbers serve as open caisson sections for first-stage construction to be constructed in advance; 3, all the remaining open caisson sections with the even numbers serve as open caisson sections for second-stage construction, and construction is conducted after the open caisson sections for first-stage construction are completed; and 4, connecting sections between every two adjacent open caisson sections are constructed. According to the method, high-precision control over the perpendicularity in the open caisson construction process is achieved, the construction requirement of a continuous open caisson method ultra-deep station is met, the method is simple, safe and reliable, industrial technical progress is promoted, and good economic and social benefits are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of open caisson construction, and particularly to a high-precision continuous open caisson construction method for an underground station based on the coupling of excavation and settlement. Background Art

[0002] As a new type of green and low-carbon underground station construction technology, the continuous open caisson method has been increasingly widely applied to urban rail underground stations in soft soil areas. The so-called continuous open caisson method means that the open caisson structure is first fabricated in sections on the ground, then pressed in batches in situ and sunk to the designated position, and finally connected to form the overall station.

[0003] During the construction process of the continuous open caisson method, in order to ensure the accurate connection of the elevation of the previous open caisson and the subsequent open caisson, it is crucial to strictly control the verticality of a single open caisson. Currently, the pressed open caisson construction method is usually adopted in open caisson construction, and the verticality can be controlled within 1 / 500. However, with the continuous in-depth development of rail transit construction, the buried depth of rail transit stations is increasing day by day, and transfer stations with a buried depth exceeding 30m emerge in an endless stream. The existing verticality control accuracy of open caisson construction can no longer fully meet the strict requirements for errors when the previous and subsequent open caissons of ultra-deep stations are connected.

[0004] The excavation method is a key factor in controlling the verticality of the open caisson during the construction process. Currently, methods such as basin excavation and stepped excavation are usually adopted. The removal of soil during excavation will cause stress redistribution of the surrounding soil, which will in turn cause settlement, and unreasonable settlement will conversely affect the sinking attitude and excavation effect of the open caisson. The conventional excavation methods do not fully consider the mutual influence and coupling relationship between excavation and settlement, making it difficult to achieve high-precision control of the verticality and overall construction quality during the open caisson construction process.

[0005] Therefore, how to achieve high-precision control of the verticality during the open caisson construction process and meet the construction requirements of ultra-deep stations using the continuous open caisson method has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the present invention provides a high-precision continuous open caisson construction method based on the coupling of excavation and settlement. The achieved purpose is to achieve high-precision control of the verticality during the open caisson construction process, meet the construction requirements of ultra-deep stations using the continuous open caisson method, the method is simple, safe and reliable, promotes the technological progress of the industry, and has good economic and social benefits.

[0007] To achieve the above purpose, the present invention discloses a high-precision continuous open caisson construction method for an underground station based on the coupling of excavation and settlement, including the following construction steps:

[0008] Step 1: Along the length direction of the to-be-built underground station, divide the to-be-built underground station into an odd number of caisson segments, and sequentially number all the caisson segments.

[0009] Step 2: Take all the caisson segments with odd numbers as the caisson segments for the first-phase construction and construct them first.

[0010] Step 3: Take the remaining caisson segments with even numbers as the caisson segments for the second-phase construction and construct them after the completion of the caisson segments for the first-phase construction.

[0011] Step 4: Construct the connection section between every two adjacent caisson segments.

[0012] Preferably, the net distance between every two adjacent caisson segments is not less than 2 meters, and the longitudinal intervals of all the caisson segments are equal.

[0013] The aspect ratio of the length to the width of each caisson segment is not greater than 2, and the aspect ratio of the height to the width is not greater than 2.5.

[0014] Preferably, among all the caisson segments, one of the two caisson segments located at the ends is the station end well of the to-be-built underground station.

[0015] Preferably, in Step 2 and Step 3, the construction process of each caisson segment includes the following steps:

[0016] Step A1: Construct the press-sinking coupling pile foundation of the corresponding caisson segment and pour the caisson cushion layer.

[0017] Step A2: Pour the caisson cutting edge, side wall and frame column of the lowest layer structure of the corresponding caisson segment, and install the sinking assistance device on the side wall.

[0018] Step A3: After each layer structure of the corresponding caisson segment reaches the design strength, under the action of the friction-reducing slurry and the sinking assistance device, sink it to the specified elevation.

[0019] Step A4: Inject water into the part of the corresponding caisson segment that has completed sinking, and excavate the soil.

[0020] Step A5: Remove the sinking assistance device, and sequentially complete the caisson side wall, frame column and middle plate frame beam of each layer structure of the corresponding caisson segment from the lowest layer structure where the soil excavation has been completed upwards, and install the corresponding sinking assistance device, and repeat Step A3 and Step A4 until the production, sinking and soil excavation of the uppermost layer structure of the corresponding caisson segment are completed.

[0021] Step A6: Pour the bottom-sealing concrete, floor slab and the remaining main structure, and backfill with soil.

[0022] More preferably, in step A3, during the first sinking process of each caisson segment, the sinking assistance device used is a press-in type sinking assistance system;

[0023] Each press-in type sinking assistance system includes a press-in device, a steel bracket, a steel strand, and a press-sinking coupled pile foundation. Each press-in operation adopts lift control, that is, the press-in height is a fixed value each time, ensuring that the corresponding caisson blade foot always lands at the same elevation position of the soil layer.

[0024] Preferably, in step A4, the soil within each caisson segment is excavated in an underwater layered and segmented manner, specifically as follows:

[0025] Step A4.1: Set 1 longitudinal beam and 2 cross beams within the corresponding caisson segment to divide the internal space of the corresponding caisson segment into 9 construction zones;

[0026] Step A4.2: Use 2 excavation equipment to carry out excavation construction synchronously, and always ensure axisymmetric excavation according to the longitudinal direction during the excavation construction process;

[0027] The specific excavation process is as follows: First, excavate the construction zone in the middle of the corresponding caisson segment, and then excavate the construction zones on both sides of the middle construction zone;

[0028] Among them, each construction zone is divided into several rectangular excavation units, and excavation is carried out along a spiral path;

[0029] The excavation sequence of the spiral path is: starting from the rectangular excavation unit at the center of each construction zone, excavate each rectangular excavation unit in a spiral-shaped divergent path on the plane until all the rectangular excavation units within the corresponding construction zone are excavated;

[0030] More preferably, several soil settlement monitoring points are arranged around each caisson segment;

[0031] Several soil settlement monitoring points are used to monitor the change of ground settlement around the corresponding caisson segment during the construction stage in real time, and the collected data are all sent to the control center;

[0032] Each excavation equipment is an intelligent excavation robot;

[0033] The excavation speed v of each intelligent excavation robot is coupled with the ground settlement control value S and is adjusted in real time through the control center.

[0034] More preferably, the excavation speed v of each intelligent excavation robot is calculated by the following formula:

[0035]

[0036] Where: v is the excavation speed, with the unit of m 3 / min;

[0037] t is the construction time, and the initial time is 0;

[0038] v 0 is the initial excavation speed, with the unit of m 3 / min. When the soil within the corresponding caisson segment is silt, v 0 is 0.5 m 3 / min to 1.0 m 3 / min. When the soil within the corresponding caisson segment is cohesive soil, v 0 is 1.0 m 3 / min to 1.5 m 3 / min. When the soil within the corresponding caisson segment is sandy soil, v 0 is 0.8 / min to 1.2 m 3 / min;

[0039] K is the correction factor. When the soil within the corresponding caisson segment is silt, K is 0.8. When the soil within the corresponding caisson segment is cohesive soil, K is 0.9. When the soil within the corresponding caisson segment is sandy soil, K is 0.85;

[0040] S is the measured value of soil settlement, with the unit of mm;

[0041] S 0 is the initial settlement control value of the soil, with the unit of mm, which is related to the surrounding environmental protection level. It takes 10 mm for the first level, 15 mm for the second level, and 20 mm for the third level.

[0042] During the excavation process, according to the real-time ground settlement monitoring data S and the above formula, the excavation speed v is adjusted dynamically in real time to ensure that the settlement of the surrounding ground surface is within the control range during the whole excavation process.

[0043] More preferably, the size of each rectangular excavation unit is determined by the following formula:

[0044]

[0045] Where: a and b are the side lengths of the rectangular excavation unit on the plan, with the unit of m;

[0046] k is the soil layer correction coefficient. When the soil within the corresponding caisson segment is silt, k is 0.8. When the soil within the corresponding caisson segment is cohesive soil, k is 0.9. When the soil within the corresponding caisson segment is sandy soil, k is 0.85;

[0047] v0 is the initial excavation speed, with the unit of m 3 / min. When the soil within the corresponding sectional segment of the open caisson is silt, v 0 is 0.5 m 3 / min to 1.0 m 3 / min. When the soil within the corresponding sectional segment of the open caisson is cohesive soil, v 0 is 1.0 m 3 / min to 1.5 m 3 / min. When the soil within the corresponding sectional segment of the open caisson is sandy soil, v 0 is 0.8 / min to 1.2 m 3 / min;

[0048] L and W are respectively the length and width of the corresponding construction sub - area on the plan, with the unit of m;

[0049] h is the thickness of the earthwork excavated each time, with the unit of m, and the value ranges from 0.5 m to 1.5 m;

[0050] λ is the soil settlement correction coefficient, which is related to the surrounding environmental protection level. It takes 0.8 for the first - level, 0.9 for the second - level, and 1.0 for the third - level.

[0051] Advantages of the present invention:

[0052] The present invention realizes high - precision control of the verticality during the open caisson construction process, meets the construction requirements of ultra - deep stations using the continuous open caisson method, has a simple method, is safe and reliable, promotes the technological progress of the industry, and has good economic and social benefits.

[0053] The following will further illustrate the concept, specific structure and technical effects generated by the present invention with reference to the drawings, so as to fully understand the purpose, features and effects of the present invention. Description of the Drawings

[0054] Figure 1 Shows the plan layout of an underground station to be built with 5 sectional segments of open caissons in an embodiment of the present invention.

[0055] Figure 2 Shows the schematic diagram of constructing the press - sinking coupled pile foundation and pouring the open caisson cushion in an embodiment of the present invention.

[0056] Figure 3 Shows the schematic diagram of pouring the open caisson blade foot, side wall and frame columns of the lowest - layer structure of the sectional segment of the open caisson, and installing the sinking - assisting device on the side wall in an embodiment of the present invention.

[0057] Figure 4 Shows the schematic diagram of the lowest - layer structure of the sectional segment of the open caisson sinking to the specified elevation in an embodiment of the present invention.

[0058] Figure 5 Schematic diagram showing water injection into the lowest layer structure where the open caisson is sunk in sections and excavation of the soil mass in an embodiment of the present invention.

[0059] Figure 6 Schematic plan view of the excavation path of the open caisson in sections in an embodiment of the present invention.

[0060] Figure 7 Schematic diagram showing the final completed state of any open caisson section in an embodiment of the present invention. Detailed implementation manners

[0061] Embodiment

[0062] As Figures 1 to 7 shown, a high-precision continuous open caisson construction method for an underground station based on the coupling of excavation and settlement includes the following construction steps:

[0063] As Figure 1 shown, Step 1: Along the length direction of the underground station to be built, divide the underground station to be built into an odd number of open caisson sections, and sequentially number all the open caisson sections;

[0064] Step 2: Take all the open caisson sections with odd numbers as the open caisson sections for the first-phase construction and construct them first;

[0065] Step 3: Take the remaining open caisson sections with even numbers as the open caisson sections for the second-phase construction and construct them after the completion of the open caisson sections in the first-phase construction;

[0066] Step 4: Construct the connection section between every two adjacent open caisson sections.

[0067] In some embodiments, the net distance between every two adjacent open caisson sections is not less than 2 meters, and the longitudinal distances of all the open caisson sections are equal;

[0068] The aspect ratio of the length to the width of each open caisson section is not greater than 2, and the aspect ratio of the height to the width is not greater than 2.5.

[0069] In some embodiments, among all the open caisson sections, one of the two open caisson sections at the ends is the station end well of the underground station to be built.

[0070] In some embodiments, in Step 2 and Step 3, the construction process of each open caisson section includes the following steps:

[0071] As Figure 2 shown, Step A1: Construct the press-sinking coupling pile foundation of the corresponding open caisson section and pour the caisson cushion;

[0072] As Figure 3As shown, in step A2, pour the cutting edge, side wall and frame columns of the lowest layer structure of the corresponding caisson section, and install sinking aids on the side wall;

[0073] As Figure 4 shown, in step A3, after each layer of structure of the corresponding caisson section reaches the design strength, under the action of the friction-reducing slurry and sinking aids, sink it to the specified elevation;

[0074] As Figure 5 shown, in step A4, inject water into the part of the corresponding caisson section that has completed sinking, and excavate the soil;

[0075] As Figure 7 shown, in step A5, remove the sinking aids, and successively complete the caisson side wall, frame columns and middle plate frame beams of each layer structure of the corresponding caisson section from the lowest layer structure where the soil excavation has been completed upwards, and install the corresponding sinking aids, and repeat step A3 and step A4 until the production, sinking and soil excavation of the topmost layer structure of the corresponding caisson section are completed;

[0076] Step A6, pour the bottom sealing concrete, floor slab and the remaining main structure, and backfill with soil.

[0077] In some embodiments, in step A3, during the first sinking process of each caisson section, the sinking aids used are all press-in type sinking systems;

[0078] Each press-in type sinking system includes a press-in device, a steel corbel, a steel strand and a press-sinking coupling pile foundation. Each press-in uses lift control, that is, the press-in height is a fixed value each time, to ensure that the corresponding cutting edge of the caisson always falls on the same elevation position of the soil layer.

[0079] The reason for adopting the above technical means is that: the geological conditions are complex and changeable, the soil layer distribution is uneven, and the downward pressure applied by each press-sinking system on the plane needs to be dynamically adjusted according to the pressing depth and soil layer conditions.

[0080] In some embodiments, in step A4, the soil in each caisson section is excavated by the underwater layered and segmented method, specifically:

[0081] Step A4.1, set 1 longitudinal beam and 2 cross beams in the corresponding caisson section, and divide the internal space of the corresponding caisson section into 9 construction zones;

[0082] Step A4.2, use 2 excavating equipments to carry out excavation construction synchronously, and always ensure axisymmetric excavation according to the longitudinal direction during the excavation construction; Axisymmetric excavation according to the longitudinal direction can ensure the stability of the caisson attitude during the excavation process.

[0083] The specific excavation process is as follows: First, excavate the construction area in the middle of the corresponding sectional caisson, and then excavate the construction areas on both sides of the middle construction area;

[0084] Among them, each construction area is divided into several rectangular excavation units, and a spiral path is used for excavation;

[0085] As Figure 6 shown, the excavation sequence of the spiral path is: starting from the rectangular excavation unit at the center of each construction area, excavate each rectangular excavation unit in turn along a spiral path diverging outward on the plane until the excavation of all rectangular excavation units in the corresponding construction area is completed;

[0086] Based on the coupling effect of sinking attitude control and surrounding soil settlement, the present invention further divides a single construction area into several rectangular excavation units and uses a spiral path for excavation. The excavation path starts from the center of the construction area and diverges outward in a spiral shape.

[0087] In some embodiments, several soil settlement monitoring points are arranged around each sectional caisson;

[0088] The several soil settlement monitoring points are used to monitor the change of the surrounding ground settlement of the corresponding sectional caisson during the construction stage in real time, and the collected data are all sent to the control center;

[0089] Each excavation device is an intelligent excavation robot;

[0090] The excavation speed v of each intelligent excavation robot is determined by coupling with the ground settlement control value S and is adjusted in real time through the control center.

[0091] In some embodiments, the excavation speed v of each intelligent excavation robot is calculated by the following formula:

[0092]

[0093] where: v is the excavation speed, with the unit of m 3 / min;

[0094] t is the construction time, and the initial time is 0;

[0095] v 0 is the initial excavation speed, with the unit of m 3 / min. When the soil in the corresponding sectional caisson is silt, v 0 is 0.5 m 3 / min to 1.0 m 3 / min. When the soil in the corresponding sectional caisson is cohesive soil, v 0 is 1.0 m 3 / min to 1.5 m 3 / min. When the soil within the corresponding caisson segment is sandy soil, v 0 is from 0.8 / min to 1.2 m 3 / min;

[0096] K is the correction factor. When the soil within the corresponding caisson segment is silt, K is 0.8; when the soil within the corresponding caisson segment is cohesive soil, K is 0.9; when the soil within the corresponding caisson segment is sandy soil, K is 0.85;

[0097] S is the measured value of soil settlement, with the unit of mm;

[0098] S 0 is the initial soil settlement control value, with the unit of mm, which is related to the surrounding environmental protection level. It takes 10 mm for the first level, 15 mm for the second level, and 20 mm for the third level.

[0099] During the excavation process, according to the real-time ground settlement monitoring data S and the above formula, the excavation speed v is adjusted dynamically in real time to ensure that the surrounding surface settlement is within the control range during the whole excavation process.

[0100] In some embodiments, the size of each rectangular excavation unit is determined by the following formula:

[0101]

[0102] In the formula: a and b are the side lengths of the rectangular excavation unit on the plan, with the unit of m;

[0103] k is the soil layer correction coefficient. When the soil within the corresponding caisson segment is silt, k is 0.8; when the soil within the corresponding caisson segment is cohesive soil, k is 0.9; when the soil within the corresponding caisson segment is sandy soil, k is 0.85;

[0104] v 0 is the initial excavation speed, with the unit of m 3 / min. When the soil within the corresponding caisson segment is silt, v 0 is from 0.5 m 3 / min to 1.0 m 3 / min. When the soil within the corresponding caisson segment is cohesive soil, v 0 is from 1.0 m 3 / min to 1.5 m 3 / min. When the soil within the corresponding caisson segment is sandy soil, v 0 is from 0.8 / min to 1.2 m³ / min;

[0105] L and W are respectively the length and width of the corresponding construction area on the plan, with the unit of m;

[0106] h is the thickness of the earthwork excavated in a single operation, with the unit of m, and the value ranges from 0.5 m to 1.5 m;

[0107] λ is the soil settlement correction coefficient, which is related to the surrounding environmental protection level. It takes 0.8 for the first level, 0.9 for the second level, and 1.0 for the third level.

[0108] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field according to the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. A high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling; characterized in that: The construction steps include: Step 1: Divide the underground station to be constructed into an odd number of caisson sections along the length direction of the underground station to be constructed, and number all the caisson sections in sequence; Step 2, constructing all the caisson sections with odd numbers as the caisson sections of the first phase of construction first; Step 3, taking all the remaining caisson sections with even numbers as the caisson sections for the second phase of construction, and carrying out the construction after completing the caisson sections for the first phase of construction; Step 4: construct the connecting section between every two adjacent caisson sections.

2. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 1 is characterized in that: The net distance between every two adjacent caisson sections is not less than 2 meters, and the longitudinal spacing of all caisson sections is equal; The length-to-width ratio of each caisson section is not greater than 2, and the height-to-width ratio is not greater than 2.

5.

3. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 1 is characterized in that: Among all the caisson sections, one of the two caisson sections located at the ends is the station end well of the underground station to be built.

4. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 1 is characterized in that: In step 2 and step 3, the construction process of each caisson section includes the following steps: Step A1, constructing the pressure-sunk coupling pile foundation corresponding to the caisson sections and pouring the caisson cushion layer; Step A2, casting the caisson blade foot, side wall and frame column of the lowermost structure of the corresponding caisson segment, and installing a sinking aid device on the side wall; Step A3, after each layer structure of the corresponding caisson section reaches the designed strength, sinking is carried out under the action of the friction-reducing mud and the sinking-aiding device to a specified elevation; Step A4, injecting water into the part of the corresponding caisson section that has completed sinking, and excavating the soil; Step A5, dismantling the sinking aid device, and sequentially completing the caisson side walls, frame columns and middle plate frame beams of each layer of the corresponding caisson section from the bottom structure where the soil excavation has been completed, and installing the corresponding sinking aid device, and repeating steps A3 and A4 until the manufacturing, sinking and soil excavation of the top structure of the corresponding caisson section are completed; Step A6: pour the bottom concrete, base plate and the remaining main structure, and backfill with soil.

5. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 4 is characterized in that: In step A3, during the first sinking process, the sinking aid device used in each caisson section is a press-in sinking aid system; Each of the press-in type sinking-aiding systems includes a press-in device, a steel corbel, a steel strand and a press-in coupling pile foundation. Each press-in is controlled by a lift, that is, the press-in height is a fixed value each time, ensuring that the corresponding caisson blade always falls on the same elevation position of the soil layer.

6. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 1 is characterized in that: In step A4, the soil in each caisson section is excavated in an underwater layered and segmented manner, specifically: Step A4.1, arranging one longitudinal beam and two transverse beams in the corresponding caisson section, dividing the internal space of the corresponding caisson section into nine construction zones; Step A4.2, using two earth-moving devices to carry out excavation construction synchronously, and during the excavation construction process, always ensuring that the excavation is symmetrical along the longitudinal axis; The specific excavation process is as follows: first excavate the construction partition in the middle of the corresponding caisson section, and then excavate the construction partitions on both sides of the construction partition in the middle; Wherein, each of the construction zones is divided into a number of rectangular excavation units, and excavation is carried out using a spiral path; The excavation sequence of the spiral path is: starting from the rectangular excavation unit located at the center of each construction zone, each rectangular excavation unit is excavated in turn in a spiral outward path on the plane until the excavation of all the rectangular excavation units in the corresponding construction zone is completed.

7. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 6 is characterized in that: A number of soil settlement monitoring points are arranged around each of the caisson sections; The soil settlement monitoring points are used to monitor the changes of ground settlement around the corresponding caisson sections in real time during the construction phase, and the collected data are sent to the control center; Each of the excavation equipment is an intelligent excavation robot; The digging speed v of each of the intelligent digging robots is determined by coupling with the ground settlement control value S and is adjusted in real time by the control center.

8. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 7 is characterized in that: The digging speed v of each intelligent digging robot is calculated by the following formula: Where: v is the digging speed, unit is m 3 / min; t is the construction time, and the initial time is 0; v0 is the initial digging speed, in m 3 / min, when the soil in the corresponding caisson section is silt, v0 is 0.5m 3 / min to 1.0m 3 / min, when the soil in the corresponding caisson section is clay, v0 is 1.0m 3 / min to 1.5m 3 / min, when the soil in the corresponding caisson section is sand, v0 is 0.8 / min to 1.2m 3 / min; K is a correction factor. When the soil in the corresponding caisson section is silt, K is 0.8; when the soil in the corresponding caisson section is clay, K is 0.9; when the soil in the corresponding caisson section is sand, K is 0.85; S is the measured value of soil settlement, in mm; S0 is the initial settlement control value of soil, in mm, which is related to the surrounding environmental protection level. Level 1 is 10 mm, level 2 is 15 mm, and level 3 is 20 mm. During the excavation process, the excavation speed v is adjusted dynamically in real time according to the real-time ground settlement monitoring data S and the above formula to ensure that the surrounding surface settlement is within the control range during the entire excavation process.

9. The high-precision continuous caisson construction method for underground stations based on excavation and settlement coupling according to claim 6 is characterized in that: The size of each rectangular excavation unit is determined by the following formula: Where: a, b are the side lengths of the rectangular excavation unit on the plane, in m; k is the soil layer correction coefficient. When the soil in the corresponding caisson section is silt, k is 0.8; when the soil in the corresponding caisson section is clay, k is 0.9; when the soil in the corresponding caisson section is sand, k is 0.85; v0 is the initial digging speed, in m 3 / min, when the soil in the corresponding caisson section is silt, v0 is 0.5m 3 / min to 1.0m 3 / min, when the soil in the corresponding caisson section is clay, v0 is 1.0m 3 / min to 1.5m 3 / min, when the soil in the corresponding caisson section is sand, v0 is 0.8 / min to 1.2m 3 / min; L and W are the length and width of the corresponding construction zone on the plan, in meters; h is the thickness of earthwork excavated in a single operation, in meters, ranging from 0.5m to 1.5m; λ is the soil settlement correction coefficient, which is related to the surrounding environmental protection level. The first level is 0.8, the second level is 0.9, and the third level is 1.0.

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