Three-circle freezing construction method for vertical shaft in offshore area

Abstract

The invention discloses a three-circle freezing construction method for a vertical shaft in an offshore area. The three-circle freezing construction method comprises the following steps that S1, hydrogeological conditions at the construction position of the vertical shaft are surveyed; s2, the construction position of the shaft of the vertical shaft is determined, a soil layer around the shaft is frozen in a three-circle freezing construction mode, the three-circle freezing construction mode is a construction mode of constructing a main freezing circle, an inner freezing circle and an outer freezing circle, the main freezing circle is located outside the shaft, the inner freezing circle is located inside the shaft, and the outer freezing circle is located outside the shaft; the outer freezing ring is located outside the main freezing ring; and S3, constructing the shaft. According to the construction method, the construction mode of constructing the main freezing ring, the inner freezing ring and the outer freezing ring is adopted, and the problems that the hydrogeological conditions of an offshore salt-bearing stratum are extremely complex, the offshore salt-bearing stratum is very close to the sea, the flow velocity of underground water is large, the hydraulic gradient of a shaft excavation area is large, the salt content is high and the freezing difficulty is large can be solved; the adverse effect of the salt-containing effect on the freezing effect is reduced, and the construction safety of the offshore vertical shaft is improved.

Description

Technical Field

[0001] The invention belongs to the field of mine construction, and in particular relates to a vertical shaft freezing construction method. Background Art

[0002] The freezing method of construction refers to drilling a hole into the water-bearing soil layer, inserting a steel pipe, and introducing circulating liquid nitrogen to freeze the surrounding strata to form a hard frozen soil shell. It not only ensures the stability of the strata, but also acts as a water barrier, allowing deep foundation pit excavation. Some mining shaft projects in my country can be constructed using this method.

[0003] However, in coastal areas, groundwater resources are abundant, water flows fast, and the strata have high salinity. For example, the groundwater salinity in some areas of southeastern coastal areas of my country is 1-5%, and the average salt content of seawater is 3.5-5.0%, which will have a great impact on the construction of the vertical shaft freezing method. The presence of stratum salt causes the freezing temperature of the soil to decrease, the freezing wall handover time is greatly extended, and the presence of salt causes the strength of frozen soil to decrease. When water flow and salt exist at the same time, the construction is more difficult, and conventional freezing schemes are difficult to meet the construction requirements.

[0004] Therefore, finding an engineering measure that can be safely constructed after the salt-containing and high-water-content strata are reinforced has become a problem that must be faced in the construction of vertical shafts in water-rich soft soil layers that are common in coastal areas. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings and defects mentioned in the above background technology and provide a three-circle freezing construction method for a vertical shaft in a near-shore area. The construction method can solve the problems of being very close to the sea, having a high groundwater flow rate, a large hydraulic gradient in the shaft excavation area, a high salt content and great difficulty in freezing, thereby reducing the adverse effects of the salt effect on the freezing effect.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is: A three-circle freezing construction method for a vertical shaft in an offshore area comprises the following steps: S1: Survey the hydrogeological conditions at the shaft construction site; S2: Determine the construction position of the shaft, and freeze the soil layer around the shaft using a three-circle freezing construction method. The three-circle freezing construction method is to use a main freezing circle, an inner freezing circle, and an outer freezing circle. The main freezing circle is located outside the shaft, the inner freezing circle is located inside the shaft, and the outer freezing circle is located outside the main freezing circle. S3: Construction shaft.

[0007] In the above-mentioned three-circle freezing construction method for offshore vertical shafts, preferably, when the three-circle freezing construction method is used, the freezing depths of the main freezing circle, the inner freezing circle and the outer freezing circle are determined according to the hydrogeological conditions, wherein the freezing depth of the main freezing circle satisfies the following relationship: ; Among them, Hz is the freezing depth of the main freezing zone, in meters; Ha is the depth of the weak permeable layer, in meters, and the seepage coefficient K of the weak permeable layer satisfies: 10 -5 ≤K<10 -4 , unit is cm / s, water permeability q satisfies: 1≤q<10, unit is Lu; For ultra-deep, take 25m; The freezing depth of the outer freezing circle satisfies the following relationship: ; Where Hw is the freezing depth of the outer freezing zone, in meters; Hb is the depth of the medium permeable layer, in meters, and the seepage coefficient K of the medium permeable layer satisfies: 10 -4 ≤K<10 -2 , unit is cm / s, water permeability q satisfies: 10≤q<100, unit is Lu; For extra super depth, 5-10m is taken; The freezing depth of the inner freezing circle satisfies the following relationship: Hn = Hw; Among them, Hn is the freezing depth of the inner freezing circle, in m, that is, the freezing depth of the inner freezing circle is equal to the freezing depth of the outer freezing circle.

[0008] The present invention takes into account the permeability of the rock layer when determining the freezing depths of the main freezing circle, the inner freezing circle and the outer freezing circle, and determines different freezing depths according to the different permeabilities of the rock layers, thereby ensuring the freezing effect while saving costs.

[0009] In the above-mentioned offshore vertical shaft three-circle freezing construction method, preferably, when using the three-circle freezing construction method, the diameters of the main freezing circle, the inner freezing circle and the outer freezing circle are determined in the following manner: Diameter of outer freezing zone R w Satisfies the following relationship: ; in: R 1 is the maximum excavation diameter of the wellbore in alluvial layer and bedrock, in m; Q f Allowable deflection rate of frozen holes in alluvial layer and bedrock section; h0 is the freezing depth of the wellbore, in m; Diameter of the main freezing circle R z =Outer freezing zone diameter R w -1; Diameter of the inner freezing circle R n = Net diameter of wellbore R -0.5.

[0010] In the above-mentioned three-circle freezing construction method for vertical shafts in offshore areas, preferably, when the three-circle freezing construction method is used for construction, the number of drill holes in the main freezing circle, the inner freezing circle and the outer freezing circle is determined in the following manner: first determine the hole spacing, and then consider the diameters of the main freezing circle, the inner freezing circle and the outer freezing circle to determine the number of drill holes; wherein, the drilling spacing of the main freezing circle is controlled at 1.3-1.5m, the drilling spacing of the outer freezing circle is 100-125% of that of the main freezing circle, and the drilling spacing of the inner freezing circle is 60-75% of that of the main freezing circle.

[0011] In the above-mentioned three-circle freezing construction method for a vertical shaft in the offshore area, preferably, the arrangement of the number of drill holes in the main freezing circle, the inner freezing circle and the outer freezing circle satisfies the following distribution rule: more drill holes are distributed on the side close to the sea water, and fewer drill holes are distributed on the side far from the sea water, so that the number of drill holes on the side close to the sea water is 1.5-2.5 times the number of drill holes on the side far from the sea water.

[0012] The above-mentioned setting method of the number of drilling holes, hole spacing and hole distribution method fully considers the use scenario of the three-circle freezing construction method of the present invention. With the three-circle freezing construction method, the freezing construction of the vertical shaft can be better realized.

[0013] In the above-mentioned offshore vertical shaft three-circle freezing construction method, preferably, when the three-circle freezing construction method is used for construction, the freezing technical parameters of the main freezing circle, the inner freezing circle and the outer freezing circle are determined in the following manner: The drilling deviation rate of each freezing circle is controlled to be no more than 3‰, the inward deviation is no more than 200mm, and the maximum hole spacing of the final hole is 1.8m; The average temperature of the freezing wall is -8°C, the brine temperature during the active freezing period is -26 to -28°C, and the brine temperature during the maintenance freezing period is -20 to -22°C; The thickness of the frozen wall satisfies the following relationship: ; in: E is the thickness of the frozen wall; R a is 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, K0 is the safety factor; is the coefficient. When the third strength theory is used, the value is 2; when the fourth strength theory is used, the value is 3; p For permanent pressure.

[0014] In the above-mentioned three-circle freezing construction method for a vertical shaft in offshore areas, preferably, a plurality of temperature measuring holes are arranged outside the outer freezing circle, which are respectively arranged at different positions outside the outer freezing circle and have different depths.

[0015] In the above-mentioned three-circle freezing construction method for a vertical shaft in offshore areas, preferably, in step S1, investigating the hydrogeological conditions at the vertical shaft construction site includes the following steps: investigating the lithology and rock characteristics of the rock mass at different depths at the vertical shaft construction site by drilling hydrological holes, conducting pumping tests at different depths at the vertical shaft construction site in combination with the drilling construction technology, and dividing the different depths at the vertical shaft construction site into different types of aquifer groups based on the drilling catalog and pumping test data.

[0016] In the above-mentioned three-circle freezing construction method for vertical shafts in offshore areas, it is preferred that the three-circle freezing construction method is used for drilling construction, and the 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, depth measurement → pipe lowering → pressure test → drilling acceptance.

[0017] In the above-mentioned three-circle freezing construction method for vertical shafts in offshore areas, it is preferred that the three-circle freezing construction method is used for freezing construction, and the steps are as follows: construction preparation → foundation construction → equipment placement and pipeline and trench installation → pressure test insulation wrapping → brine preparation → clean water and brine system trial operation → medium filling, trial operation → freezing normal operation → monitoring, supervision → trial excavation → formal excavation → maintenance freezing → shutdown → freezing acceptance.

[0018] The above-mentioned offshore vertical shaft three-circle freezing construction method may more specifically include the following steps: S1: Survey the hydrogeology of the shaft: The lithology and rock mass characteristics of the rock mass at different depths of the shaft are surveyed by drilling hydrological holes, and pumping tests are conducted at different depths of the shaft in combination with the drilling construction technology. Different depths of the shaft are divided into different types of aquifer groups based on the drilling log and pumping test data.

[0019] S2: Determination of freezing method: In view of the geological conditions of the offshore area of ​​the vertical shaft, in order to ensure the effective thickness and strength of the frozen wall, to realize the excavation of the shaft as soon as possible and to enable continuous excavation and masonry construction of the shaft, and after a comprehensive analysis of the expansion of frozen soil and the shaft excavation speed, the principle is that the frozen wall can ensure continuous and safe excavation and masonry construction when the shaft is excavated to each level, a three-circle freezing construction plan is adopted.

[0020] S3: Determination of freezing depth: It is determined according to the hydrogeological conditions. The depth of the main freezing zone of the vertical shaft is 25 meters below the depth of the weak permeable layer, and the depths of the outer freezing zone and the inner freezing zone are the depth of the medium permeable layer.

[0021] S4: Determination of freezing technical parameters.

[0022] S5: Main freezing hole arrangement circle, outer freezing hole arrangement circle and inner freezing hole arrangement circle: The arrangement of the main freezing hole arrangement circle, the outer freezing hole arrangement circle and the inner freezing hole arrangement circle can reduce the influence of hydraulic gradient on the freezing circle; the main freezing hole circle and the outer freezing hole circle isolate the influence of external seawater seepage on the wellbore excavation area, and the inner freezing hole circle can freeze the influence of internal flowing water in the wellbore excavation area on freezing, thereby better ensuring the freezing effect.

[0023] S6: Determination of the number of holes drilled in the main freezing circle, outer freezing circle and inner freezing circle. Arrange the number of holes unevenly, and arrange more holes in the main freezing circle, outer freezing circle and inner freezing circle in the offshore area to better ensure construction safety.

[0024] S7: Freezing pipe structure design.

[0025] S8: Temperature measuring hole design: In order to accurately grasp the changes in the freezing temperature field, three temperature measuring holes can be designed.

[0026] S9: Freezing refrigeration system design.

[0027] S10: Frozen drilling construction method: The frozen drilling construction steps are construction preparation → (drilling site foundation construction, temporary construction) → drilling rig installation and positioning → mud preparation → normal drilling → inclination measurement, inclination correction, depth measurement → pipe lowering → pressure test → drilling acceptance.

[0028] S11: Freezing construction process: The freezing construction steps are construction preparation → foundation construction → equipment placement and pipeline and trench installation → pressure test insulation wrapping → brine preparation → clean water and brine system trial operation → medium filling, trial operation → freezing normal operation → monitoring and supervision → trial excavation → formal excavation and masonry → maintenance freezing → shutdown → freezing acceptance.

[0029] In the tidal influence area, groundwater is affected by the tide and its hydraulic gradient is large. Therefore, when carrying out engineering construction in offshore areas, it is necessary to fully consider the local special hydrogeological conditions, especially the large hydraulic gradient, and take effective protective measures to ensure the safety and stability of the project. In view of the construction scene in the offshore area, the present invention proposes a three-circle freezing construction method for the offshore vertical shaft, which adopts the construction method of the main freezing circle, the inner freezing circle and the outer freezing circle. The main freezing circle, the outer freezing circle and the inner freezing circle can reduce the influence of the large hydraulic gradient of offshore groundwater on the freezing circle. The frozen body formed by the main freezing circle can resist the erosion of groundwater from weak permeable strata and ensure the stability of the wellbore. The inner freezing circle is located inside the wellbore, which can strengthen the freezing strength inside the wellbore, reduce the erosion of the high-salt groundwater on the inside of the wellbore by the sea, and maintain the safety of the wellbore construction. The outer freezing circle blocks the groundwater from the medium permeable stratum from infiltrating from the outside, which is conducive to maintaining the entire freezing system. The three circles work together to form a reliable triple protection mechanism and improve the overall construction reliability.

[0030] In general, for high-salt and high-water content strata at the seaside, the present invention adopts three main and outer freezing circles to cooperate with each other. The main freezing circle and the outer freezing circle isolate the influence of external seawater seepage on the wellbore excavation area, and the inner freezing circle can freeze the freezing influence of high-salt flowing water inside the wellbore excavation area. The inner freezing circle works synergistically with the main and outer freezing circles to better ensure the freezing effect.

[0031] Compared with the prior art, the advantages of the present invention are: The three-circle freezing construction method for offshore vertical shafts of the present invention utilizes the construction method of constructing a main freezing circle, an inner freezing circle and an outer freezing circle, which can solve the problems of extremely complex hydrogeological conditions in offshore saline strata, close proximity to the sea, high groundwater flow rate, large hydraulic gradient in the shaft excavation area, high salt content and great difficulty in freezing, reduce the adverse effects of salt effects on the freezing effect, and increase the safety of offshore vertical shaft construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 It is a construction plan view of the three-circle freezing construction method for the offshore vertical shaft of an embodiment.

[0034] Figure 2 The present invention is a flow chart of the freeze drilling construction.

[0035] Figure 3 It is the freezing construction flow chart of the present invention.

[0036] Legend 1. Hydrogeological hole; 2. Inner freezing circle; 3. Inner freezing circle drilling hole; 4. Wellbore; 5. Main freezing circle; 6. Main freezing circle drilling hole; 7. Outer freezing circle; 8. Outer freezing circle drilling hole; 9. 1# temperature measuring hole, 10. 2# temperature measuring hole; 11. 3# temperature measuring hole. DETAILED DESCRIPTION

[0037] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0038] It should be noted that when an element is described as being "fixed, fixed, connected or connected to" another element, it can be directly fixed, fixed, connected or connected to the other element, or it can be indirectly fixed, fixed, connected or connected to the other element through other intermediate connectors.

[0039] Unless otherwise defined, all the professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0040] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0041] Example: like Figure 1 As shown, it is a construction plan of the three-circle freezing construction method of the offshore vertical shaft of the embodiment, wherein the construction method of the main freezing circle 5, the inner freezing circle 2 and the outer freezing circle 7 is adopted. First, the lithology and rock mass characteristics of the rock mass at different depths of the vertical shaft are surveyed through the hydrogeological hole 1. The main freezing circle 5 is obtained by freezing construction through multiple main freezing circle boreholes 6, the outer freezing circle 7 is obtained by freezing construction through multiple outer freezing circle boreholes 8, and the inner freezing circle 2 is obtained by freezing construction through multiple inner freezing circle boreholes 3. In order to accurately grasp the changes in the freezing temperature field, three temperature measuring holes are designed, namely, the 1# temperature measuring hole 9, the 2# temperature measuring hole 10 and the 3# temperature measuring hole 11.

[0042] The offshore vertical shaft three-circle freezing construction method of this embodiment includes the following steps: Step S1: Survey the hydrogeological conditions at the shaft construction site, survey the lithology and rock mass characteristics of the rock mass at different depths at the shaft construction site by drilling hydrological holes, and conduct pumping tests at different depths at the shaft construction site in combination with the drilling construction process. According to the drilling log 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.

[0043] Table 1: Hydrogeological conditions at the shaft construction site

[0044] The calculation formula of seepage coefficient of pumping test is as follows: Complete pressurized well: ; Diving Complete Well: ; Where: K is the permeability coefficient of the aquifer (m / d); Q is the pumping well flow rate (m 3 / d); s w is the water level drawdown in the pumping well (m); M is the thickness of the confined aquifer (m); R y is the impact radius (m); H is the thickness of the phreatic aquifer (m); h is the thickness of the unconfined aquifer after pumping (m); r w is the radius of the pumping well (m).

[0045] The pumping test of this embodiment is shown in Table 2 below.

[0046] Table 2: Pumping test results

[0047] The proposed air intake well borehole is divided into the following four engineering rock groups from top to bottom: Loose sedimentary rock group, 0.00-45.20m, thickness 45.20m. Medium permeable layer, mainly composed of sand and clay. The top is backfill.

[0048] The bedrock weathering zone group is 45.20-72.69m and 27.49m thick. The weakly permeable layer is composed of the strong weathering zone, medium weathering zone and slightly weathering zone of the gabbro from top to bottom.

[0049] The upper metagabbro group is 72.69-802.04m thick and 729.35m thick. The micro-permeable layer is mainly composed of metagabbro (formerly known as amphibolite), and the rock spectrum belongs to the Luanjiazhai unit of the Neoarchean Malianzhuang sequence (Ar3 ν Ml).

[0050] The lower part is a group of metagabbro intercalated with fine-grained granite, 802.04-1065.09m, with a thickness of 263.05m. The micro-permeable layer is mainly composed of metagabbro, with many diorite veins (or quartz veins) interspersed.

[0051] Step S2: The freezing method is confirmed. In view of the geological conditions of the offshore area of ​​the vertical shaft, in order to ensure the effective thickness and strength of the frozen wall, to achieve the shaft excavation as soon as possible, and to enable continuous excavation and masonry construction of the shaft, and after a comprehensive analysis of the expansion of frozen soil and the shaft excavation speed, the principle is that the frozen wall can ensure continuous and safe excavation and masonry construction when the shaft is excavated to each level, and a three-circle freezing construction plan is adopted.

[0052] Step S3: Determination of freezing depth. The freezing depths of the main freezing zone, the inner freezing zone and the outer freezing zone are determined according to the hydrogeological conditions, wherein the freezing depth of the main freezing zone satisfies the following relationship: ; Among them, Hz is the freezing depth of the main freezing zone, in meters; Ha is the depth of the weak permeable layer, in meters, and the seepage coefficient K of the weak permeable layer satisfies: 10 -5 ≤K<10 -4 , unit is cm / s, water permeability q satisfies: 1≤q<10, unit is Lu; For ultra-deep, take about 25m; The freezing depth of the outer freezing circle satisfies the following relationship: ; Where Hw is the freezing depth of the outer freezing zone, in meters; Hb is the depth of the medium permeable layer, in meters, and the seepage coefficient K of the medium permeable layer satisfies: 10 -4 ≤K<10 -2 , unit is cm / s, water permeability q satisfies: 10≤q<100, unit is Lu; For extra super depth, 5-10m is taken; The freezing depth of the inner freezing circle satisfies the following relationship: Hn = Hw; Among them, Hn is the freezing depth of the inner freezing circle, in m, that is, the freezing depth of the inner freezing circle is equal to the freezing depth of the outer freezing circle.

[0053] According to the above limitations, this embodiment determines that the main freezing zone depth of the wind shaft is 96.60m, the outer freezing zone depth is 55m, and the inner freezing zone depth is 55m.

[0054] Step S4: Determination of freezing technical parameters.

[0055] According to the wellbore engineering geological conditions, the freezing parameters are determined as follows: 1. The drilling deviation rate of each freezing circle is controlled to be no more than 3‰, the inward deviation is no more than 200mm, and the maximum hole spacing of the final hole is 1.80m.

[0056] 2. The average temperature of the freezing wall is -8°C, the brine temperature during the active freezing period is -26 to -28°C, and the brine temperature during the maintenance freezing period is -20 to -22°C.

[0057] 3. The thickness of the frozen wall satisfies the following relationship: ; in: E is the thickness of the frozen wall; R a is 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, K0 is the safety factor; is the coefficient. When the third strength theory is used, the value is 2; when the fourth strength theory is used, the value is 3; p For permanent pressure.

[0058] The thickness of the frozen wall of the wellbore is 2.30m.

[0059] Step S5: Determine the diameters of the main freezing circle, the outer freezing circle and the inner freezing circle.

[0060] The diameter of the outer freezing zone is calculated based on the drilling and blasting method used in the bedrock section: ; Where: R 1 is the maximum excavation diameter of the shaft in alluvial layer and bedrock, m; Q f Allowable deflection rate of frozen holes in alluvial layer and bedrock section; h 0 is the freezing depth of the wellbore, m; Diameter of the main freezing circleR z =Outer freezing zone diameter R w -1; Diameter of the inner freezing circle R n = Net diameter of wellbore R -0.5.

[0061] According to 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.

[0062] Step S6: Determine the number of holes drilled in the main freezing circle, the outer freezing circle, and the inner freezing circle.

[0063] When using the three-circle freezing construction method, the number of drill holes in the main freezing circle, inner freezing circle and outer freezing circle is determined in the following way: first determine the hole spacing, then consider the diameters of the main freezing circle, inner freezing circle and outer freezing circle, and determine the number of drill holes; among them, the drilling spacing of the main freezing circle is controlled at 1.3-1.5m, the drilling spacing of the outer freezing circle is 100-125% of the main freezing circle, and the drilling spacing of the inner freezing circle is 60-75% of the main freezing circle. The arrangement of the number of drill holes in the main freezing circle, inner freezing circle and outer freezing circle meets the following distribution law: more drill holes are distributed on the side close to the seawater, and fewer drill holes are distributed on the side far from the seawater, so that the number of drill holes on the side close to the seawater is 1.5-2.5 times the number of drill holes on the side far from the seawater.

[0064] In this embodiment, in order to cope with the influence of the larger hydraulic gradient, the optimal opening spacing of the freezing holes of the main freezing circle should be controlled at about 1.3-1.5m, so the freezing spacing at the nearshore end is about 1.3m, and the hydraulic gradient at the offshore end is relatively small, so the freezing spacing at the offshore end is about 2.6m. Compared with the main freezing circle, the drilling spacing of the outer freezing circle is about 100-125% of the main freezing circle, so the freezing spacing at the nearshore end is about 1.56m, and the freezing spacing at the offshore end is about 3.12m. Compared with the main freezing circle, the drilling spacing of the inner freezing circle is about 60-75% of the main freezing circle, so the freezing spacing at the nearshore end is about 0.8m, and the freezing spacing at the offshore end is about 1.6m.

[0065] like Figure 1 As shown, the specific distribution is as follows: there are 12 holes in the outer freezing circle near the sea, and the spacing between the holes in the outer freezing circle is 1.56m; there are 5 holes in the outer freezing circle far sea, and the spacing between the holes in the outer freezing circle is 3.1m.

[0066] There are 14 holes in the main freezing circle near the coast, and the spacing between the holes is 1.3m; there are 5 holes in the main freezing circle far offshore, and the spacing between the holes is 2.63m.

[0067] There are 13 holes in the nearshore area of ​​the inner freezing circle, and the spacing between the holes is 0.8m; there are 5 holes in the farshore area of ​​the inner freezing circle, and the spacing between the holes is 1.54m.

[0068] Step S7: freezing pipe structure design.

[0069] A φ108×5mm seamless steel pipe is placed under the freezing hole, and the coupling is a φ121×6mm seamless steel pipe.

[0070] Step S8: Temperature measuring hole design.

[0071] In order to accurately grasp the changes in the freezing temperature field, three temperature measuring holes are designed, φ108×5mm seamless steel pipes, external couplings are connected, and the couplings are φ121×6mm seamless steel pipes.

[0072] The 1# temperature measuring hole is arranged above the outer main surface of the outer freezing circle, 1m away from the hole diameter of the freezing holes and 90m deep; the 2# temperature measuring hole is arranged on the left side of the outer main surface of the outer freezing circle, 1m away from the hole diameter of the freezing holes and 45m deep; the 3# temperature measuring hole is arranged below the outer main surface of the outer freezing circle, 1m away from the hole diameter of the freezing holes and 45m deep.

[0073] Step S9: Freeze the refrigeration system design.

[0074] 1. The calculation of wellbore cooling capacity is shown in Table 3.

[0075] Parameter selection: 1) Freezing pipe heat dissipation coefficient: 250 kcal / h; 2) Cooling loss coefficient: 1.15.

[0076] Table 3: Wellbore cooling capacity calculation table

[0077] 2. Selection and quantity of freezers.

[0078] A freezing station is set up in the air inlet shaft, and the type and quantity of freezers are shown in Table 4 below.

[0079] Table 4: Refrigerator configuration table

[0080] 3. Selection of auxiliary equipment.

[0081] After calculation, the selection and quantity of auxiliary equipment are shown in Table 5 below.

[0082] Table 5: Selection and quantity of auxiliary equipment

[0083] 4. Brine system design.

[0084] 1) Total brine circulation volume: single hole flow rate is 12m3 / h, the total brine flow rate of the air inlet well is 372m 3 / h. The specific gravity of the brine is 1.26.

[0085] 2) Liquid supply pipe selection: Use Ф60×5mm polyethylene plastic liquid supply pipe.

[0086] 3) Brine main pipe and distribution collecting ring: According to the total flow of brine, Ф299×8mm seamless steel pipes are used for the air inlet well, one for going and one for returning.

[0087] 4) Brine pump selection: 10Sh-9 (Q=468m 3 , H=30m, N=55KW) type water pumps 2 sets (1 in use and 1 as spare).

[0088] 5. Cooling water system design.

[0089] 1) Total cooling water circulation volume: 300m 3 / h, select 2 10SH-13A cooling water circulation pumps (1 spare) (Q=342m 3 / h, H=22.2m, N=37KW).

[0090] 2) New water replenishment: 30m 3 / h, select 2 200QJ32-26 / 2 water pumps (1 for use and 1 for backup) (Q=32m 3 / h, H=26m, N=4KW).

[0091] Step S10: Freeze the drilling construction method, such as Figure 2 shown.

[0092] 1. Construction preparation.

[0093] After the construction preparation personnel enter the site, they will complete the organizational preparation, material preparation, and technical preparation within the planned preparation period. According to the construction plan, the drilling site foundation, mud pump room, inclinometer room, slurry supply and drainage system construction, freezing station, power distribution room and other temporary production projects and temporary living projects, as well as water supply and power supply, will be completed for the frozen construction according to the construction plan, creating conditions for the frozen construction and meeting the construction requirements.

[0094] 2. Drilling construction method.

[0095] 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, which enabled inclination measurement without lifting the drill. JDT-3K gyroscope orientation, a liftable guide while drilling, and 5LZ146-7.0 screw drill were used for inclination correction.

[0096] 2) Drilling site construction: First, measure the site range from the center of the wellbore and level the site, lay and compact the 37-gray soil in layers (350mm thick), pour C30 concrete 300mm thick on the top of the 37-gray soil, and reserve drilling positions and build mud circulation trenches.

[0097] 3) Determine the hole position: Determine the hole position based on the center of the wellbore. Use the stake method to set up obvious marks at the drilling hole position.

[0098] 4) Drilling rig installation: Install the equipment according to the installation requirements and equip the mud facilities. Connect water and electricity, install nighttime lighting, check the drilling tools, and make all preparations.

[0099] 5) Drilling: Use a weighted drilling tool consisting of a φ89mm drill rod, a φ159mm weighted rod, and φ171.4mm and φ190.5mm roller drill bits, a rotary drilling mud wall protection method, and a continuous working mode in shifts.

[0100] 3. The mud preparation is shown in Table 6.

[0101] Table 6: Mud performance parameters

[0102] During the construction of sandy soil layer, in order to prevent the sandy soil layer from collapsing, a certain amount of soil powder slurry is added before drilling. Dosage method: 15% soil powder, 5% soda ash. Mud properties: viscosity 22-24s, specific gravity 1.1-1.15.

[0103] During the construction of clay layer, due to the serious mud formation in clay layer, the well wall is relatively stable. In order to prevent sticking to the drill, the lubricity of mud should be improved and the water loss should be reduced. Dosage method: 0.5% broad-spectrum wall protector, 1% sulfonated lignite resin. Performance: viscosity is 18s, specific gravity is 1.05-1.10g / cm 3 .

[0104] During construction in the weathered zone of bedrock, since the weathered zone is prone to collapse and the leakage is large, it is necessary to increase the viscosity and specific gravity of the mud, reduce the water loss, and strengthen the protection of the well wall. Dosage method: 1.5% broad-spectrum wall protector, 1% sulfonated lignite resin. Performance: viscosity is 20s, specific gravity is 1.10g / cm 3 , water loss ≤8mL.

[0105] During construction in bedrock formations, the formation is relatively stable. If there is a phenomenon of falling blocks, and to prevent sticking of drills and rock powder precipitation and drilling jams, it is necessary to ensure that the mud carries the rock normally, the rock powder can be precipitated in time, the solid content is low, the water loss is small, and the lubricity is good. Dosage method: 1% broad-spectrum wall protector, 1% sulfonated lignite resin. Performance: viscosity 18s, specific gravity 1.05-1.1g / cm 3 , water loss 8-10mL.

[0106] Step S11: Freeze the construction process, such as Figure 3 shown.

[0107] 1. Construction preparation After the construction preparation personnel enter the site, they will complete the organizational preparation, material preparation, and technical preparation within the planned preparation period.

[0108] 2. Infrastructure 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 three circulation systems shall be installed separately according to the installation procedure of equipment first and pipeline later and the technical requirements of the construction drawings, and pressure testing, inspection and acceptance shall be carried out in accordance with the requirements of "Code for Quality Acceptance of Coal Mine Shaft and Tunnel Engineering" (GB50213-2010).

[0109] The freezing station equipment, pressure vessels and valves must be cleaned and pressure tested before installation. The brine system pipelines use 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 pipelines pass the pressure test, the low-temperature pipelines and the brine pipelines in the station are insulated and wrapped.

[0110] 3. Freezing trench construction and freezer installation After the drilling is completed, the freezing trench construction and freezer installation are carried out. After the freezer is installed, the trench should be cleaned to ensure that the trench is clean and easy to operate. The brine flow detection and freezer flow control devices should be installed in the trench to detect and adjust the brine flow of each freezer on time. The loop temperature detection probe should be installed on the freezer head to detect whether the freezer is operating normally, and a venting device should be installed. After the brine system passes the pressure test, the brine pipeline should be insulated and wrapped according to the design requirements.

[0111] 4. Prepare salt water Prepare brine according to the designed specific gravity. When preparing brine, prevent foreign matter from mixing in, so as to avoid clogging the freezer and affecting the normal freezing construction of the wellbore.

[0112] After the above processes are completed, the medium (fluorine) filling test operation can be carried out. During the test operation, the operating parameters of each system should be carefully debugged, and the brine flow of each freezer should be tested and adjusted to ensure that the brine flow of the freezer meets the design requirements.

[0113] 5. Normal operation, equipment maintenance and testing monitoring During the freezing period, various operating parameters must be controlled according to the designed number of units to be started, and strict inspection and monitoring must be carried out on the water level of the hydrological hole, the water level of the reference well, the temperature of the temperature measuring hole, the temperature of the well wall during well excavation, and the observation of the frozen wall displacement, so as to provide a reliable basis for the well excavation construction.

Claims

1. A three-circle freezing construction method for a vertical shaft in an offshore area, characterized in that: The following steps are involved: S1: Survey the hydrogeological conditions at the shaft construction site; S2: Determine the construction position of the shaft, and freeze the soil layer around the shaft using a three-circle freezing construction method. The three-circle freezing construction method is to use a main freezing circle, an inner freezing circle, and an outer freezing circle. The main freezing circle is located outside the shaft, the inner freezing circle is located inside the shaft, and the outer freezing circle is located outside the main freezing circle. S3: Construction shaft.

2. The offshore vertical shaft three-circle freezing construction method according to claim 1 is characterized in that: When the three-circle freezing construction method is used for construction, the freezing depths of the main freezing circle, the inner freezing circle and the outer freezing circle are determined according to the hydrogeological conditions. The freezing depth of the main freezing circle satisfies the following relationship: ； Among them, Hz is the freezing depth of the main freezing zone, in meters; Ha is the depth of the weak permeable layer, in meters, and the seepage coefficient K of the weak permeable layer satisfies: 10 -5 ≤K<10 -4 , unit is cm / s, water permeability q satisfies: 1≤q<10, unit is Lu; For ultra-deep, take 25m; The freezing depth of the outer freezing circle satisfies the following relationship: ； Where Hw is the freezing depth of the outer freezing zone, in meters; Hb is the depth of the medium permeable layer, in meters, and the seepage coefficient K of the medium permeable layer satisfies: 10 -4 ≤K<10 -2 , unit is cm / s, water permeability q satisfies: 10≤q<100, unit is Lu; For extra super depth, 5-10m is taken; The freezing depth of the inner freezing circle satisfies the following relationship: Hn = Hw; Among them, Hn is the freezing depth of the inner freezing circle, in m, that is, the freezing depth of the inner freezing circle is equal to the freezing depth of the outer freezing circle.

3. The offshore vertical shaft three-circle freezing construction method according to claim 1 is characterized in that: When using the three-circle freezing construction method, the diameters of the main freezing circle, the inner freezing circle, and the outer freezing circle are determined in the following way: Diameter of outer freezing zone R w Satisfies the following relationship: ； in: R 1 is the maximum excavation diameter of the wellbore in alluvial layer and bedrock, in m; Q f Allowable deflection rate of frozen holes in alluvial layer and bedrock section; h 0 is the freezing depth of the wellbore, in m; Diameter of the main freezing circle R z =Outer freezing zone diameter R w -1; Diameter of the inner freezing circle R n = Net diameter of wellbore R -0.

5.

4. The offshore vertical shaft three-circle freezing construction method according to claim 1 is characterized in that: When the three-circle freezing construction method is used for construction, the number of drill holes in the main freezing circle, inner freezing circle and outer freezing circle is determined in the following manner: first determine the hole spacing, then consider the diameters of the main freezing circle, inner freezing circle and outer freezing circle to determine the number of drill holes; among them, the drilling spacing of the main freezing circle is controlled at 1.3-1.5m, the drilling spacing of the outer freezing circle is 100-125% of that of the main freezing circle, and the drilling spacing of the inner freezing circle is 60-75% of that of the main freezing circle.

5. The offshore vertical shaft three-circle freezing construction method according to claim 4 is characterized in that: The arrangement of the number of drilling holes in the main freezing circle, inner freezing circle and outer freezing circle meets the following distribution rule: there are more drilling holes on the side close to the sea water and fewer drilling holes on the side far from the sea water, so that the number of drilling holes on the side close to the sea water is 1.5-2.5 times the number of drilling holes on the side far from the sea water.

6. The offshore vertical shaft three-circle freezing construction method according to claim 1 is characterized in that: When using the three-circle freezing construction method, the freezing technical parameters of the main freezing circle, inner freezing circle and outer freezing circle are determined as follows: The drilling deviation rate of each freezing circle is controlled to be no more than 3‰, the inward deviation is no more than 200mm, and the maximum hole spacing of the final hole is 1.8m; The average temperature of the freezing wall is -8°C, the brine temperature during the active freezing period is -26 to -28°C, and the brine temperature during the maintenance freezing period is -20 to -22°C; The thickness of the frozen wall satisfies the following relationship: ； in: E is the thickness of the frozen wall; R a is 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, K0 is the safety factor; is the coefficient. When the third strength theory is used, the value is 2; when the fourth strength theory is used, the value is 3; p For permanent pressure.

7. The offshore vertical shaft three-circle freezing construction method according to any one of claims 1 to 6, characterized in that: A plurality of temperature measuring holes are arranged outside the outer freezing circle, which are respectively arranged at different positions outside the outer freezing circle and have different depths.

8. The offshore vertical shaft three-circle freezing construction method according to any one of claims 1 to 6, characterized in that: In step S1, the investigation of the hydrogeological conditions at the vertical shaft construction site includes the following steps: investigating the lithology and rock characteristics of the rock mass at different depths at the vertical shaft construction site by drilling hydrological holes, conducting pumping tests at different depths at the vertical shaft construction site in combination with the drilling construction technology, and dividing the different depths at the vertical shaft construction site into different types of aquifer groups based on the drilling catalog and pumping test data.

9. The offshore vertical shaft three-circle freezing construction method according to any one of claims 1 to 6, characterized in that: When using the three-circle freezing construction method for drilling construction, the 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, depth measurement → pipe lowering → pressure test → drilling acceptance.

10. The offshore vertical shaft three-circle freezing construction method according to any one of claims 1 to 6, characterized in that: When using the three-circle freezing construction method for freezing construction, the steps are as follows: construction preparation → foundation construction → equipment placement and pipeline and trench installation → pressure test insulation wrapping → brine preparation → clean water and brine system trial operation → medium filling, trial operation → freezing normal operation → monitoring and supervision → trial excavation → formal excavation and masonry → maintenance freezing → shutdown → freezing acceptance.

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