Offshore area vertical shaft three-circle freezing construction method

Abstract

The application discloses a kind of offshore area vertical shaft three-circle freezing construction method, comprising the following steps: S1: surveying the hydrogeological condition of vertical shaft wellbore construction site;S2: determine the construction position of vertical shaft wellbore, the soil layer around wellbore is frozen by three-circle freezing construction method, the construction method of three-circle freezing is the construction method of using construction main freezing circle, inner freezing circle and outer freezing circle, wherein, main freezing circle is located outside wellbore, inner freezing circle is located inside wellbore, outer freezing circle is located outside main freezing circle;S3: construction wellbore.The construction method of the application can solve the problem of extremely complex hydrogeological condition of nearshore saline stratum, very close to the sea, large groundwater flow rate, large hydraulic gradient in wellbore excavation area, high salinity and difficult freezing by using the construction method of construction main freezing circle, inner freezing circle and outer freezing circle, reducing the adverse effects of salinity on freezing effect, and increasing the safety of offshore vertical shaft construction.

Description

Technical Field

[0001] This invention belongs to the field of mining construction, and in particular relates to a method for freezing construction of vertical shafts. Background Technology

[0002] The freezing method involves drilling a hole in the aquifer and inserting a steel pipe, then introducing circulating liquid nitrogen to freeze the surrounding soil, forming a hard frozen crust. This not only ensures ground stability but also acts as a water barrier, allowing for the excavation of deep foundation pits. This method has been used in some mining shaft projects in my country.

[0003] However, in coastal areas, groundwater resources are abundant, water flow is rapid, and the strata have high salinity. For example, in some areas of southeastern coastal my country, the groundwater salinity is 1-5%, and the average seawater salinity is 3.5-5.0%, which significantly impacts the construction of vertical shafts using the freezing method. The presence of strata salt lowers the soil freezing temperature, greatly prolongs the freezing wall contact time, and reduces the strength of the frozen soil. When water flow and salt are present simultaneously, construction becomes even more difficult, and conventional freezing methods are often insufficient to meet the construction requirements.

[0004] Therefore, finding an engineering measure that allows for safe construction after reinforcement of saline and high water content strata has become a problem that must be addressed in the construction of vertical shafts in the common water-rich and soft soil strata in coastal areas. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a three-ring freezing construction method for vertical shafts in near-shore areas. This construction method can solve the problems of being very close to the sea, having high groundwater flow velocity, large hydraulic gradient in the shaft excavation area, high salinity, and high freezing difficulty, and reduce the adverse effects of salinity on the freezing effect.

[0006] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0007] A method for constructing a three-ring freezing system for a vertical shaft in a nearshore area includes the following steps:

[0008] S1: Investigate the hydrogeological conditions at the construction site of the vertical shaft;

[0009] S2: Determine the construction location of the vertical shaft and use the three-ring freezing construction method to freeze the soil layer around the shaft. The three-ring freezing construction method is to construct a main freezing ring, an inner freezing ring, and an outer freezing ring. The main freezing ring is located outside the shaft, the inner freezing ring is located inside the shaft, and the outer freezing ring is located outside the main freezing ring.

[0010] S3: Construction shaft.

[0011] In the above-mentioned three-ring freezing construction method for vertical shafts in nearshore areas, the preferred method is to determine the freezing depth of the main freezing ring, inner freezing ring, and outer freezing ring based on hydrogeological conditions. The freezing depth of the main freezing ring satisfies the following relationship:

[0012] ;

[0013] Where Hz is the freezing depth of the main freezing zone, in meters; Ha is the depth of the weakly permeable layer, in meters, and the permeability coefficient K of the weakly permeable layer satisfies: 10 -5 ≤K<10 -4 The unit is cm / s, and the permeability q satisfies: 1≤q<10, and the unit is Lu; For the ultra-deep depth, we take 25m;

[0014] The freezing depth of the outer freeze zone satisfies the following relationship:

[0015] ;

[0016] Where Hw is the freezing depth of the outer freezing zone, in meters; Hb is the depth of the intermediate permeable layer, in meters, and the permeability coefficient K of the intermediate permeable layer satisfies: 10 -4 ≤K<10 -2 The unit is cm / s, and the permeability q satisfies: 10≤q<100, and the unit is Lu; For additional depth, take 5-10m;

[0017] The freezing depth of the inner freeze zone satisfies the following relationship:

[0018] Hn = Hw;

[0019] Where Hn is the freezing depth of the inner freeze zone, in meters, meaning the freezing depth of the inner freeze zone is equal to the freezing depth of the outer freeze zone.

[0020] When determining the freezing depth of the main freezing zone, inner freezing zone, and outer freezing zone, this invention takes into account the permeability of the rock strata and determines different freezing depths according to the different permeability of the rock strata, thus ensuring the freezing effect while saving costs.

[0021] In the above-mentioned three-ring freezing construction method for vertical shafts in nearshore areas, the preferred method is to determine the diameters of the main freezing ring, inner freezing ring, and outer freezing ring using the three-ring freezing construction method, as follows:

[0022] Diameter of the outer freezing zone R w The following relationship must be satisfied:

[0023] ;

[0024] in:

[0025] R 1 represents the maximum excavation diameter of the wellbore in alluvial deposits and bedrock, in meters.

[0026] Q f The allowable deviation rate of the freezing holes in the alluvial layer and bedrock section;

[0027] h 0 represents the freezing depth of the wellbore, in meters (m).

[0028] Diameter of the main freezing zone R z =Diameter of the outer freezing zone R w -1;

[0029] Diameter of the inner freezing zone R n =Net diameter of wellbore R -0.5.

[0030] In the above-mentioned three-ring freezing construction method for vertical shafts in nearshore areas, the preferred method is to determine the number of boreholes for the main freezing ring, inner freezing ring, and outer freezing ring using the three-ring freezing construction method, as follows: First, determine the hole spacing, then consider the diameters of the main freezing ring, inner freezing ring, and outer freezing ring to determine the number of boreholes; wherein, the hole spacing of the main freezing ring is controlled at 1.3-1.5m, the hole spacing of the outer freezing ring is 100-125% of that of the main freezing ring, and the hole spacing of the inner freezing ring is 60-75% of that of the main freezing ring.

[0031] In the above-mentioned three-ring freezing construction method for vertical shafts in nearshore areas, the preferred method is that the number of boreholes in the main freezing ring, inner freezing ring, and outer freezing ring meets the following distribution rule: more boreholes are distributed on the side closer to the seawater, and fewer boreholes are distributed on the side farther from the seawater, so that the number of boreholes on the side closer to the seawater is 1.5-2.5 times the number of boreholes on the side farther from the seawater.

[0032] The above-mentioned settings for the number of boreholes, borehole spacing, and borehole distribution fully consider the application scenarios of the three-ring freezing construction method of the present invention. In conjunction with the three-ring freezing construction method, the freezing method construction of vertical shafts can be better realized.

[0033] In the above-mentioned three-ring freezing construction method for vertical shafts in nearshore areas, the preferred method is to determine the freezing technical parameters of the main freezing ring, inner freezing ring, and outer freezing ring as follows:

[0034] The borehole deviation rate of each frozen zone shall be controlled to be no more than 3‰, the inward deviation shall be no more than 200mm, and the maximum hole spacing at the end of the hole shall be 1.8m.

[0035] The average temperature of the frozen wall is -8℃, the brine temperature during the active freezing period is -26 to -28℃, and the brine temperature during the maintenance freezing period is -20 to -22℃.

[0036] The thickness of the frozen wall satisfies the following relationship:

[0037] ;

[0038] in:

[0039] E This refers to the thickness of the frozen wall.

[0040] R a The inner radius of the frozen wall;

[0041] [σ] is the allowable stress of frozen soil, [σ]=σ / K0, σ is the ultimate compressive strength of frozen soil, and K0 is the safety factor;

[0042] The value is 2 when using the third strength theory and 3 when using the fourth strength theory.

[0043] p It is a permanent ground pressure.

[0044] In the above-mentioned three-ring freezing construction method for vertical shafts in nearshore areas, preferably, multiple temperature measuring holes are arranged outside the outer freezing ring, which are respectively arranged at different positions outside the outer freezing ring and have different depths.

[0045] In the above-mentioned three-ring freezing construction method for vertical shafts in nearshore areas, the preferred step S1, which involves investigating the hydrogeological conditions at the construction site of the vertical shaft, includes the following steps: investigating the lithology and rock mass characteristics of the rock mass at different depths at the construction site of the vertical shaft by drilling hydrological boreholes; conducting pumping tests at different depths at the construction site of the vertical shaft in conjunction with the drilling construction technology; and dividing the different depths at the construction site of the vertical shaft into different types of aquifer groups based on the drilling logs and pumping test data.

[0046] Among the above-mentioned three-ring freezing construction methods for vertical shafts in nearshore areas, the preferred method is to use the three-ring freezing construction method for drilling construction, with the following steps in sequence: construction preparation → drilling site foundation construction and temporary construction → drilling rig installation and positioning → mud preparation → normal drilling → inclination measurement, inclination correction and depth measurement → casing installation → pressure test → borehole acceptance.

[0047] Among the above-mentioned three-ring freezing construction methods for vertical shafts in nearshore areas, the preferred method is to use the following steps during freezing construction: construction preparation → foundation construction → equipment placement and pipeline and trench installation → pressure testing and insulation wrapping → brine preparation → trial operation of clean water and brine system → filling with medium and trial operation → normal operation of freezing → monitoring and surveillance → trial excavation → formal excavation and lining → maintenance freezing → shutdown → freezing acceptance.

[0048] More specifically, the above-mentioned method for three-ring freezing construction of vertical shafts in nearshore areas may include the following steps:

[0049] S1: Exploration of the vertical shaft's hydrogeology: By drilling hydrogeological boreholes, the lithology and characteristics of the rock mass at different depths of the vertical shaft are investigated. Combined with drilling construction techniques, pumping tests are conducted at different depths of the vertical shaft. Based on the drilling logs and pumping test data, the different depths of the vertical shaft are divided into different types of aquifer groups.

[0050] S2: Determination of freezing method: Considering the geological conditions of the near-shore area of ​​the vertical shaft, in order to ensure the effective thickness and strength of the frozen wall, realize the excavation of the shaft as soon as possible, and enable the continuous excavation and lining construction of the shaft, and after comprehensive analysis of the expansion of the frozen soil and the shaft excavation speed, the construction scheme of three-ring freezing is adopted based on the principle that the frozen wall can ensure continuous and safe excavation and lining construction when the shaft is excavated to each level.

[0051] S3: Determination of freezing depth: It is determined based on hydrogeological conditions. The depth of the main freezing zone of the vertical shaft is 25 meters below the depth of the weakly permeable layer, and the depths of the outer and inner freezing zones are the depths of the medium permeable layer.

[0052] S4: Determination of freezing technical parameters.

[0053] S5: Main freezing hole arrangement ring, outer freezing hole arrangement ring and inner freezing hole arrangement ring: Arranging the main freezing hole arrangement ring, outer freezing hole arrangement ring and inner freezing hole arrangement ring can reduce the influence of hydraulic gradient on the freezing ring; the main freezing hole ring and outer freezing hole ring isolate the influence of external seawater seepage on the well excavation area, and the inner freezing hole ring can freeze the influence of internal flowing water on freezing in the well excavation area, thus better ensuring the freezing effect.

[0054] S6: Determining the number of boreholes for the main freezing zone, outer freezing zone, and inner freezing zone. Unevenly distributed boreholes are used, with a larger number of boreholes in the main freezing zone, outer freezing zone, and inner freezing zone in nearshore areas to better ensure construction safety.

[0055] S7: Frozen tube structure design.

[0056] S8: Temperature measurement hole design: In order to accurately grasp the changes in the freezing temperature field, three temperature measurement holes can be designed.

[0057] S9: Freezing and refrigeration system design.

[0058] S10: Freezing Drilling Construction Method: The freezing drilling construction steps are as follows: construction preparation → (drilling site foundation construction, temporary construction) → drilling rig installation and positioning → mud preparation → normal drilling → inclination measurement, inclination correction, and depth measurement → casing installation → pressure test → borehole acceptance.

[0059] S11: Freezing Construction Process: The freezing construction steps are as follows: construction preparation → foundation construction → equipment placement and pipeline and trench installation → pressure testing and insulation wrapping → brine preparation → trial operation of clean water and brine system → filling medium and trial operation → freezing and normal operation → monitoring and surveillance → trial excavation → formal excavation and lining → maintenance freezing → shutdown → freezing acceptance.

[0060] In tidal-affected areas, groundwater is influenced by tides, resulting in a significant hydraulic gradient. Therefore, when carrying out engineering construction in nearshore areas, it is necessary to fully consider the unique local hydrogeological conditions, especially the large hydraulic gradient, and take effective protective measures to ensure the safety and stability of the project. For nearshore construction scenarios, this invention proposes a three-ring freezing construction method for vertical wells in nearshore areas. This method employs a construction approach with a main freezing ring, an inner freezing ring, and an outer freezing ring. These three rings reduce the impact of the large hydraulic gradient of nearshore groundwater on the freezing ring itself. The frozen body formed by the main freezing ring can resist erosion from groundwater in weakly permeable strata, ensuring well stability. The inner freezing ring, located inside the well, strengthens the freezing intensity within the well, reducing erosion from high-salinity groundwater from the coast and maintaining the safety of well construction. The outer freezing ring blocks groundwater from seeping in from medium-permeability strata, helping to maintain the entire freezing system. The three rings work synergistically to form a reliable triple protection mechanism, improving the overall construction reliability.

[0061] Overall, for high-salt and high-water-content strata along the coast, this invention employs three freezing zones—main, outer, and inner—working together. The main and outer freezing zones isolate the impact of external seawater seepage on the well excavation area, while the inner freezing zone freezes the impact of high-salt flowing water inside the well excavation area. The synergistic effect of the inner freezing zone and the main and outer freezing zones ensures a better freezing effect.

[0062] Compared with the prior art, the advantages of the present invention are as follows:

[0063] The three-ring freezing construction method for nearshore vertical shafts of the present invention utilizes a construction approach that employs a main freezing ring, an inner freezing ring, and an outer freezing ring. This method can solve the problems of extremely complex hydrogeological conditions in nearshore saline strata, proximity to the sea, high groundwater flow velocity, large hydraulic gradient in the shaft excavation area, high salinity, and high freezing difficulty. It also reduces the adverse effects of salinity on the freezing effect and increases the safety of nearshore vertical shaft construction. Attached Figure Description

[0064] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0065] Figure 1 The diagram shows the construction plan of the three-ring freezing method for nearshore vertical shaft construction, as illustrated in this example.

[0066] Figure 2 This is a flowchart of the freezing borehole construction process of the present invention.

[0067] Figure 3 This is a flowchart of the freezing construction process of the present invention.

[0068] Legend

[0069] 1. Hydrogeological borehole; 2. Inner freezing zone; 3. Inner freezing zone borehole; 4. Well shaft; 5. Main freezing zone; 6. Main freezing zone borehole; 7. Outer freezing zone; 8. Outer freezing zone borehole; 9. Temperature measuring hole #1; 10. Temperature measuring hole #2; 11. Temperature measuring hole #3. Detailed Implementation

[0070] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0071] It should be noted that when a component is described as being "fixed to, attached to, connected to or connected to" another component, it can be directly fixed to, attached to, connected to or connected to the other component, or it can be indirectly fixed to, attached to, connected to or connected to the other component through other intermediate connectors.

[0072] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0073] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0074] Example:

[0075] like Figure 1The diagram shows a construction plan of the three-ring freezing method for a nearshore vertical shaft, as illustrated in this embodiment. The method involves constructing a main freezing ring 5, an inner freezing ring 2, and an outer freezing ring 7. First, the lithology and characteristics of the rock mass at different depths of the shaft are investigated using hydrogeological borehole 1. The main freezing ring 5 is obtained through freezing construction using multiple main freezing ring boreholes 6. The outer freezing ring 7 is obtained through freezing construction using multiple outer freezing ring boreholes 8. The inner freezing ring 2 is obtained through freezing construction using multiple inner freezing ring boreholes 3. To accurately monitor the changes in the freezing temperature field, three temperature measuring holes were designed: No. 1 (temperature measuring hole 9), No. 2 (temperature measuring hole 10), and No. 3 (temperature measuring hole 11).

[0076] The nearshore vertical shaft three-ring freezing construction method of this embodiment includes the following steps:

[0077] Step S1: Investigate the hydrogeological conditions at the shaft construction site. Drill hydrographic boreholes to investigate the lithology and characteristics of the rock mass at different depths at the shaft construction site. Combined with drilling techniques, conduct pumping tests at different depths at the shaft construction site. Based on the drilling logs and pumping test data, the different depths at the shaft construction site are divided into different types of aquifer groups, as shown in Table 1 below.

[0078] Table 1: Hydrogeological conditions at the shaft construction site

[0079]

[0080] The formula for calculating the seepage coefficient in a pumping test is as follows:

[0081] Pressure-bearing complete well:

[0082] ;

[0083] Complete unsubmerged well:

[0084] ;

[0085] In the formula:

[0086] K The aquifer permeability coefficient (m / d);

[0087] Q The flow rate of the pumping well (m³) 3 / d);

[0088] s w The drawdown of the water level in the pumping well (m);

[0089] M Thickness of the confined aquifer (m);

[0090] R yRadius of influence (m);

[0091] H The thickness of the unconfined aquifer (m);

[0092] h The thickness of the unconfined aquifer after pumping (m);

[0093] r w The radius of the pumping well is (m).

[0094] The pumping test results of this embodiment are shown in Table 2 below.

[0095] Table 2: Results of Pumping Test

[0096]

[0097] The proposed intake well borehole is divided into the following four engineering rock groups from top to bottom:

[0098] Loose sedimentary rock formation, 0.00-45.20m in depth, 45.20m thick. Medium permeability layer, mainly composed of sand and clay. Topped with backfill.

[0099] The bedrock weathering zone consists of rock assemblages ranging from 45.20 to 72.69 m in length and 27.49 m in thickness. It is a weakly permeable layer, composed from top to bottom of strongly weathered, moderately weathered, and slightly weathered zones of metagabbro.

[0100] The upper metagabbro group, 72.69-802.04m in length and 729.35m in thickness, is a slightly permeable layer. The main lithology is metagabbro (originally named plagioclase amphibolite), and the lithographic series belongs to the Luanjiazhai Unit of the Malianzhuang Sequence (Ar3) of the Neoarchean. ν Ml).

[0101] The lower part consists of a metagabbro interbedded with fine-grained granite, ranging from 802.04 to 1065.09 m in length and 263.05 m in thickness. It is a slightly permeable layer, with the main lithology being metagabbro, interspersed with several monzogranite veins (or quartz veins).

[0102] Step S2: Confirming the freezing method. Considering the geological conditions of the nearshore area of ​​the vertical shaft, in order to ensure the effective thickness and strength of the frozen wall, realize the excavation of the shaft as soon as possible, and enable continuous excavation and lining construction of the shaft, and based on a comprehensive analysis of the expansion of the frozen soil and the shaft excavation speed, a three-ring freezing construction scheme is adopted, with the principle that the frozen wall can guarantee continuous and safe excavation and lining construction when the shaft is excavated to each level.

[0103] Step S3: Determination of freezing depth. The freezing depths of the main freezing zone, inner freezing zone, and outer freezing zone are determined based on hydrogeological conditions. The freezing depth of the main freezing zone satisfies the following relationship:

[0104] ;

[0105] Where Hz is the freezing depth of the main freezing zone, in meters; Ha is the depth of the weakly permeable layer, in meters, and the permeability coefficient K of the weakly permeable layer satisfies: 10 -5 ≤K<10 -4 The unit is cm / s, and the permeability q satisfies: 1≤q<10, and the unit is Lu; For the ultra-deep depth, we'll use approximately 25m.

[0106] The freezing depth of the outer freeze zone satisfies the following relationship:

[0107] ;

[0108] Where Hw is the freezing depth of the outer freezing zone, in meters; Hb is the depth of the intermediate permeable layer, in meters, and the permeability coefficient K of the intermediate permeable layer satisfies: 10 -4 ≤K<10 -2 The unit is cm / s, and the permeability q satisfies: 10≤q<100, and the unit is Lu; For additional depth, take 5-10m;

[0109] The freezing depth of the inner freeze zone satisfies the following relationship:

[0110] Hn = Hw;

[0111] Where Hn is the freezing depth of the inner freeze zone, in meters, meaning the freezing depth of the inner freeze zone is equal to the freezing depth of the outer freeze zone.

[0112] Based on the above limitations, this embodiment determines the depth of the main freezing zone of the ventilation shaft to be 96.60m, the depth of the outer freezing zone to be 55m, and the depth of the inner freezing zone to be 55m.

[0113] Step S4: Determining the freezing technical parameters.

[0114] Based on the geological conditions of the wellbore, the freezing parameters are determined as follows:

[0115] 1. The borehole deviation rate of each frozen zone shall be controlled to be no more than 3‰, the inward deviation shall be no more than 200mm, and the maximum hole spacing at the end of the hole shall be 1.80m.

[0116] 2. The average temperature of the frozen wall is -8℃, the brine temperature during the active freezing period is -26 to -28℃, and the brine temperature during the maintenance freezing period is -20 to -22℃.

[0117] 3. The thickness of the frozen wall satisfies the following relationship:

[0118] ;

[0119] in:

[0120] E This refers to the thickness of the frozen wall.

[0121] R a The inner radius of the frozen wall;

[0122] [σ] is the allowable stress of frozen soil, [σ]=σ / K0, σ is the ultimate compressive strength of frozen soil, and K0 is the safety factor;

[0123] The value is 2 when using the third strength theory and 3 when using the fourth strength theory.

[0124] p It is a permanent ground pressure.

[0125] The thickness of the frozen wall of the well is taken as 2.30m.

[0126] Step S5: Determine the diameters of the main freezing zone, outer freezing zone, and inner freezing zone.

[0127] The diameter of the outer freezing zone is calculated based on the drilling and blasting method used in the bedrock section:

[0128] ;

[0129] In the formula:

[0130] R 1 represents the maximum excavation diameter of the wellbore in alluvial deposits and bedrock, in meters;

[0131] Q f The allowable deviation rate of the freezing holes in the alluvial layer and bedrock section;

[0132] h 0 represents the freezing depth of the wellbore, in meters (m).

[0133] Diameter of the main freezing zone R z =Diameter of the outer freezing zone R w -1;

[0134] Diameter of the inner freezing zone R n =Net diameter of wellbore R -0.5.

[0135] Based on the calculation results, the diameter of the outer freezing zone is 11.40m; the diameter of the main freezing zone is 10.40m; and the diameter of the inner freezing zone is 6m.

[0136] Step S6: Determine the number of holes for the main freezing zone, outer freezing zone, and inner freezing zone.

[0137] When using the three-ring freezing construction method, the number of boreholes for the main freezing ring, inner freezing ring, and outer freezing ring is determined as follows: First, determine the hole spacing, then consider the diameters of the main freezing ring, inner freezing ring, and outer freezing ring to determine the number of boreholes. Specifically, the borehole spacing in the main freezing ring is controlled at 1.3-1.5m, the borehole spacing in the outer freezing ring is 100-125% of that in the main freezing ring, and the borehole spacing in the inner freezing ring is 60-75% of that in the main freezing ring. The arrangement of the boreholes in the main freezing ring, inner freezing ring, and outer freezing ring follows this distribution pattern: more boreholes are distributed on the side closer to seawater, and fewer boreholes are distributed on the side farther from seawater, so that the number of boreholes on the side closer to seawater is 1.5-2.5 times the number of boreholes on the side farther from seawater.

[0138] In this embodiment, to cope with the influence of a large hydraulic gradient, the optimal spacing of the freezing holes in the main freezing zone should be controlled at approximately 1.3-1.5m. Therefore, the spacing at the nearshore end is approximately 1.3m, while at the offshore end, where the hydraulic gradient is relatively smaller, the spacing is approximately 2.6m. Compared to the main freezing zone, the hole spacing in the outer freezing zone is approximately 100-125% of that in the main freezing zone. Therefore, the spacing at the nearshore end is approximately 1.56m, and at the offshore end, it is approximately 3.12m. Compared to the main freezing zone, the hole spacing in the inner freezing zone is approximately 60-75% of that in the main freezing zone. Therefore, the spacing at the nearshore end is approximately 0.8m, and at the offshore end, it is approximately 1.6m.

[0139] like Figure 1 As shown, the specific distribution is as follows: there are 12 holes near the sea surface of the outer freezing zone, with a hole spacing of 1.56m; there are 5 holes far offshore of the outer freezing zone, with a hole spacing of 3.1m.

[0140] There are 14 holes near the main freezing zone, with a hole spacing of 1.3m; there are 5 holes far from the main freezing zone, with a hole spacing of 2.63m.

[0141] There are 13 holes in the nearshore area of ​​the inner freezing zone, with a hole spacing of 0.8m; there are 5 holes in the offshore area of ​​the inner freezing zone, with a hole spacing of 1.54m.

[0142] Step S7: Design of the freezing tube structure.

[0143] A φ108×5mm seamless steel pipe is placed below the freezing hole, and the coupling is a φ121×6mm seamless steel pipe.

[0144] Step S8: Temperature sensing port design.

[0145] To accurately monitor the changes in the freezing temperature field, three temperature measuring holes were designed, using φ108×5mm seamless steel pipes connected by external couplings, with the couplings being φ121×6mm seamless steel pipes.

[0146] Temperature measuring hole #1 is located above the outer side of the main surface of the outer freezing ring, 1m away from the diameter of the freezing hole array, and at a depth of 90m; temperature measuring hole #2 is located to the left of the outer side of the main surface of the outer freezing ring, 1m away from the diameter of the freezing hole array, and at a depth of 45m; temperature measuring hole #3 is located below the outer side of the main surface of the outer freezing ring, 1m away from the diameter of the freezing hole array, and at a depth of 45m.

[0147] Step S9: Design of the freezing and refrigeration system.

[0148] 1. The calculation of the wellbore cooling capacity is shown in Table 3 below.

[0149] Parameter selection: 1) Cooling coefficient of the freezing tube: 250 kcal / h; 2) Cooling loss coefficient: 1.15.

[0150] Table 3: Wellbore Cooling Capacity Calculation Table

[0151]

[0152] 2. Selection and quantity of refrigeration units.

[0153] A freezing station is set up in the air intake shaft. The selection and quantity of the refrigeration unit are shown in Table 4 below.

[0154] Table 4: Refrigeration Unit Configuration Table

[0155]

[0156] 3. Selection of auxiliary equipment.

[0157] The selection and quantity of auxiliary equipment are shown in Table 5 below.

[0158] Table 5: Selection and Quantity of Auxiliary Equipment

[0159]

[0160] 4. Brine system design.

[0161] 1) Total brine circulation volume: The flow rate of each orifice is 12m³. 3 / h, the total brine flow rate of the intake well is 372m³ / h. 3 / h. The specific gravity of the saline solution is taken as 1.26.

[0162] 2) Selection of liquid supply pipe: Use Ф60×5mm polyethylene plastic liquid supply pipe.

[0163] 3) Brine main pipe and distribution ring: According to the total brine flow rate, the air intake well is made of Ф299×8mm seamless steel pipe, one for outgoing and one for returning.

[0164] 4) Selection of brine pump: 10Sh-9 (Q=468m) is selected. 3 Two water pumps of type H=30m, N=55KW (one in use, one on standby).

[0165] 5. Cooling water system design.

[0166] 1) Total cooling water circulation volume: 300m³ 3 / h, two 10SH-13A cooling water circulating pumps are selected (one spare) (Q=342m 3 / h, H=22.2m, N=37KW).

[0167] 2) Fresh water replenishment: 30m³ 3 / h, two 200QJ32-26 / 2 type water pumps are selected (one in use and one on standby) (Q=32m 3 / h, H=26m, N=4KW).

[0168] Step S10: Freeze drilling construction method, such as Figure 2 As shown.

[0169] 1. Construction preparation.

[0170] After the construction preparation personnel arrived on site, they completed organizational, material, and technical preparations within the planned preparation period. They completed the construction of the drilling site foundation, mud pump room, inclination measurement room, slurry supply and drainage system, freezing station, power distribution room, and other temporary production and living facilities for the freezing construction, as well as water and power supply, according to the construction layout, thus creating conditions for the freezing construction and meeting the construction requirements.

[0171] 2. Drilling construction method.

[0172] 1) DZJ-500 / 1000 drilling rigs were used for construction, equipped with TBW-850 / 50 mud pumps. JDT-5 gyroscopes were used for borehole inclination measurement, enabling inclination measurement without lifting the drill bit. JDT-3K gyroscopes were used for orientation, along with a retractable guide vane and a 5LZ146-7.0 screw drill for inclination correction.

[0173] 2) Drilling site construction: First, measure the site area from the center of the well shaft, level the site, lay and compact the 3:7 lime-soil layer (350mm thick), pour 300mm thick C30 concrete on top of the 3:7 lime-soil layer, and reserve the drilling position and build mud circulation trench.

[0174] 3) Determine the borehole location: Using the center of the wellbore as a reference, determine the borehole location. The borehole location should be clearly marked using a stake-and-pile method.

[0175] 4) Drilling rig installation: Proceed according to the equipment installation requirements and ensure proper mud preparation facilities are in place. Connect water and electricity, install nighttime lighting, inspect drilling tools, and complete all necessary preparations.

[0176] 5) Drilling: A heavy-duty drilling tool consisting of an 89mm drill rod, a 159mm weight rod, and 171.4mm and 190.5mm roller cone drill bits is used. The drilling mud is used for wall protection in a rotary drilling method and the operation is carried out in shifts.

[0177] 3. The mud preparation is shown in Table 6.

[0178] Table 6: Mud Performance Parameters

[0179]

[0180] When constructing in sandy soil layers, a certain amount of soil-powder slurry should be prepared before drilling to prevent the soil layer from collapsing. Dosage: 15% soil powder, 5% soda ash (based on the amount of soil powder). Slurry properties: viscosity 22-24s, specific gravity 1.1-1.15.

[0181] During drilling in clay layers, due to the significant mud formation and relatively stable wellbore, it is necessary to improve the lubricity of the mud and reduce water loss to prevent drill bit sticking. Dosage method: 0.5% broad-spectrum wall-protecting agent, 1% sulfonated lignite resin. Properties: Viscosity 18s, specific gravity 1.05-1.10 g / cm³. 3 .

[0182] During construction in bedrock weathered zones, the risk of collapse and significant leakage is high. Therefore, it is necessary to increase the mud viscosity and specific gravity to reduce water loss and strengthen wellbore protection. Dosage method: 1.5% broad-spectrum wall-protecting agent, 1% sulfonated lignite resin. Performance: Viscosity 20s, specific gravity 1.10 g / cm³. 3 Water loss ≤8mL.

[0183] When constructing in bedrock formations, where the formation is relatively stable, to prevent rockfalls and drill bit sticking, as well as rock powder settling and jamming, it is essential to ensure the mud carries rock effectively, allowing rock powder to settle promptly, maintaining low solids content, minimal water loss, and good lubricity. Dosage method: 1% broad-spectrum wall-protecting agent, 1% sulfonated lignite resin. Properties: Viscosity 18s, specific gravity 1.05-1.1 g / cm³. 3 8-10 mL of water is lost.

[0184] Step S11: Freeze the construction process, such as Figure 3 As shown.

[0185] 1. Construction Preparation

[0186] After the construction preparation personnel move into the site, they complete organizational, material, and technical preparations within the planned preparation period.

[0187] 2. Infrastructure

[0188] The installation of the freezing station includes the installation of the brine system and the cooling water system. According to the overall design of the freezing station, the installation procedure of equipment first and then pipelines and the technical requirements of the construction drawings are required to install the three major circulation systems separately, and pressure test and inspection are required in accordance with the "Code for Acceptance of Quality of Coal Mine Tunneling Engineering" (GB50213-2010).

[0189] Before installation, the equipment, pressure vessels, and valves of the freezing station must be cleaned and pressure tested. The brine system piping uses 20# low-carbon seamless steel pipes (GBT / 8163-2008), and the brine tank is equipped with an automatic liquid level alarm device. After the freezing station piping passes the pressure test, the low-temperature piping and the brine piping within the station are insulated and wrapped.

[0190] 3. Construction of freezing trenches and installation of freezing equipment

[0191] After the borehole is completed, the freezing trench is constructed and the freezing devices are installed. After installation, the trench must be cleaned to ensure it is clean and easy to operate. A brine flow detection device and a freezing device flow control device should be installed in the trench to allow for timely monitoring and adjustment of the brine flow of each freezing device. A circuit temperature detection probe should be installed at the head of each freezing device to check its normal operation, and a venting device should also be installed. After the brine system passes pressure testing, the brine pipeline should be insulated according to design requirements.

[0192] 4. Prepare saline solution

[0193] Prepare the brine according to the designed specific gravity. When preparing the brine, prevent foreign objects from getting in, so as not to clog the freezer and affect the normal freezing operation of the well.

[0194] Once all the above procedures are completed, the medium (fluorine) charging trial run can be carried out. During the trial run, the operating parameters of each system should be carefully adjusted, and the brine flow rate of each freezer should be tested and adjusted to ensure that the brine flow rate of the freezer meets the design requirements.

[0195] 5. Normal operation, equipment maintenance and monitoring.

[0196] During the freezing period, all operating parameters must be controlled according to the designed number of machines to be started. Strict monitoring and detection must be carried out on the water level of the hydrological well, the water level of the reference well, the temperature of the temperature measuring well, the temperature of the well wall during the shaft excavation, and the observation of the displacement of the frozen wall, so as to provide a reliable basis for the shaft excavation construction.

Claims

1. A method for constructing a vertical shaft in a nearshore area using a three-ring freezing method, characterized in that, Includes the following steps: S1: Investigate the hydrogeological conditions at the construction site of the vertical shaft; S2: Determine the construction location of the vertical shaft and use the three-ring freezing construction method to freeze the soil layer around the shaft. The three-ring freezing construction method is to construct a main freezing ring, an inner freezing ring, and an outer freezing ring. The main freezing ring is located outside the shaft, the inner freezing ring is located inside the shaft, and the outer freezing ring is located outside the main freezing ring. S3: Construction shaft; When using the three-ring freezing method, the freezing depths of the main freezing ring, inner freezing ring, and outer freezing ring are determined based on hydrogeological conditions. The freezing depth of the main freezing ring satisfies the following relationship: ； Where Hz is the freezing depth of the main freezing zone, in meters; Ha is the depth of the weakly permeable layer, in meters, and the permeability coefficient K of the weakly permeable layer satisfies: 10 -5 ≤K<10 -4 The unit is cm / s, and the permeability q satisfies: 1≤q<10, and the unit is Lu; For the ultra-deep depth, we take 25m; The freezing depth of the outer freeze zone satisfies the following relationship: ； Where Hw is the freezing depth of the outer freezing zone, in meters; Hb is the depth of the intermediate permeable layer, in meters, and the permeability coefficient K of the intermediate permeable layer satisfies: 10 -4 ≤K<10 -2 The unit is cm / s, and the permeability q satisfies: 10≤q<100, and the unit is Lu; For additional depth, take 5-10m; The freezing depth of the inner freeze zone satisfies the following relationship: Hn = Hw; Wherein, Hn is the freezing depth of the inner freeze zone, in meters, that is, the freezing depth of the inner freeze zone is equal to the freezing depth of the outer freeze zone. When using the three-ring freezing method, the diameters of the main freezing ring, inner freezing ring, and outer freezing ring are determined as follows: Diameter of the outer freezing zone R w The following relationship must be satisfied: ； in: R 1 represents the maximum excavation diameter of the wellbore in alluvial deposits and bedrock, in meters. Q f The allowable deviation rate of the freezing holes in the alluvial layer and bedrock section; h 0 represents the freezing depth of the wellbore, in meters (m). Diameter of the main freezing zone R z =Diameter of the outer freezing zone R w -1; Diameter of the inner freezing zone R n =Net diameter of wellbore R -0.5; When using the three-ring freezing method, the freezing technical parameters of the main freezing ring, inner freezing ring, and outer freezing ring are determined as follows: The borehole deviation rate of each frozen zone shall be controlled to be no more than 3‰, the inward deviation shall be no more than 200mm, and the maximum hole spacing at the end of the hole shall be 1.8m. The average temperature of the frozen wall is -8℃, the brine temperature during the active freezing period is -26 to -28℃, and the brine temperature during the maintenance freezing period is -20 to -22℃. The thickness of the frozen wall satisfies the following relationship: ； in: E This refers to the thickness of the frozen wall. R a The inner radius of the frozen wall; [σ] is the allowable stress of frozen soil, [σ]=σ / K0, σ is the ultimate compressive strength of frozen soil, and K0 is the safety factor; The value is 2 when using the third strength theory and 3 when using the fourth strength theory. p It is a permanent ground pressure.

2. The nearshore vertical shaft three-ring freezing construction method according to claim 1, characterized in that, When using the three-ring freezing construction method, the number of boreholes for the main freezing ring, inner freezing ring, and outer freezing ring is determined as follows: First, determine the hole spacing, then consider the diameters of the main freezing ring, inner freezing ring, and outer freezing ring to determine the number of boreholes; the hole spacing for the main freezing ring is controlled at 1.3-1.5m, the hole spacing for the outer freezing ring is 100-125% of that for the main freezing ring, and the hole spacing for the inner freezing ring is 60-75% of that for the main freezing ring.

3. The nearshore vertical shaft three-ring freezing construction method according to claim 2, characterized in that, The arrangement of boreholes in the main freezing zone, inner freezing zone, and outer freezing zone follows the following distribution pattern: more boreholes are distributed on the side closer to the seawater, and fewer boreholes are distributed on the side farther from the seawater, so that the number of boreholes on the side closer to the seawater is 1.5-2.5 times the number of boreholes on the side farther from the seawater.

4. The nearshore vertical shaft three-ring freezing construction method according to any one of claims 1-3, characterized in that, Multiple temperature measuring holes are arranged outside the outer freezing ring, at different positions on the outside of the outer freezing ring, and at different depths.

5. The nearshore vertical shaft three-ring freezing construction method according to any one of claims 1-3, characterized in that, In step S1, the hydrogeological conditions of the shaft construction site are investigated by the following steps: the lithology and rock mass characteristics of the rock mass at different depths of the shaft construction site are investigated by drilling hydrological boreholes; pumping tests are conducted at different depths of the shaft construction site in combination with drilling construction technology; and the shaft construction site is divided into different types of aquifer groups based on the drilling log and pumping test data.

6. The method for constructing a three-ring freezing system for a vertical shaft in nearshore areas according to any one of claims 1-3, characterized in that, When using the three-ring freezing construction method for drilling, the steps are as follows: construction preparation → drilling site foundation construction and temporary building construction → drilling rig installation and positioning → mud preparation → normal drilling → inclination measurement, inclination correction and depth measurement → casing installation → pressure test → borehole acceptance.

7. The nearshore vertical shaft three-ring freezing construction method according to any one of claims 1-3, characterized in that, When using the three-ring freezing construction method, the steps are as follows: construction preparation → foundation construction → equipment placement and pipeline and trench installation → pressure testing and insulation wrapping → brine preparation → trial operation of clean water and brine system → filling medium and trial operation → normal operation of freezing → monitoring and surveillance → trial excavation → formal excavation and lining → maintenance freezing → shutdown → freezing acceptance.

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