CN111101951A - Vertical freezing construction method for comprehensive pipelines such as urban subway underpass high-voltage cable and the like - Google Patents
Vertical freezing construction method for comprehensive pipelines such as urban subway underpass high-voltage cable and the like Download PDFInfo
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- CN111101951A CN111101951A CN201911258957.5A CN201911258957A CN111101951A CN 111101951 A CN111101951 A CN 111101951A CN 201911258957 A CN201911258957 A CN 201911258957A CN 111101951 A CN111101951 A CN 111101951A
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
- E21D9/00—Tunnels or galleries, with or without linings; Methods or apparatus for making thereof; Layout of tunnels or galleries
- E21D9/001—Improving soil or rock, e.g. by freezing; Injections
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Abstract
The invention discloses a vertical freezing construction method for comprehensive pipelines such as urban subway down-passing high-voltage cables, comprising the following steps of: firstly, preparing construction and constructing fender piles around a pipeline; secondly, drilling construction and freezing station installation; thirdly, actively freezing and maintaining freezing; fourthly, constructing a fender post structure after excavation of the foundation pit, dewatering and freezing; fifthly, cutting off and plugging the freezing pipe, performing melt-down grouting, and finishing construction; the vertical freezing construction method of the comprehensive pipeline such as the urban subway underpass high-voltage cable has safe and reliable construction and high economic benefit, the vertical freezing enables the enclosure structure diaphragm wall gap to form a waterproof plate, and provides conditions for deep foundation pit excavation and precipitation, wherein the frozen wall can bear certain water and soil pressure in the foundation pit excavation process; the underground water is not polluted in the freezing process; and the protection reliability for the 220KV electric power pull tube is high, and the influence caused by the movement and the modification of the pipeline is avoided.
Description
Technical Field
The invention relates to the technical field of subway construction methods, in particular to a vertical freezing construction method for a comprehensive pipeline such as a high-voltage cable for urban subway underpass.
Background
Along with the development of economy, the construction scale of urban subways is gradually enlarged, and the adoption of a proper subway construction method is an important factor for determining the construction speed and the construction quality of the subways. The subway construction method is limited by construction low-level characteristics and construction environment, for example, the construction of a deep foundation pit enclosure structure is greatly influenced by urban comprehensive pipelines, the excavation depth of a general station foundation pit is large, and the quality of the construction of the enclosure structure is related to the problems of settlement of the ground surface around the foundation pit, inclination of buildings, seepage, stable excavation of the foundation pit and the like, particularly in a section with more urban comprehensive pipelines; the vertical freezing method construction is an effective means for solving the difficult problem of unclosed construction of the deep foundation pit enclosure water-stop structure in a water-rich stratum, can effectively prevent the foundation pit from water inrush disasters, and improves stratum characteristics and construction environment; however, the freezing method adopted in the current deep foundation pit construction has the problems of long period, low temperature influence on the pipeline, great influence of foundation pit precipitation on the freezing wall and the like.
In areas with more comprehensive pipeline influences, especially when the pipeline is buried deeply, the pipeline is high in importance degree and cannot be changed or is difficult to change, due to the fact that the lower portion of the pipeline of the enclosure structure is closed, a gap exists in the excavation process in the geology with sand and pebbles, the lower portion of the pipeline is complex in geology, the underground water amount is large, and accidents are prone to occurring in the excavation process of a foundation pit.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a vertical freezing construction method for comprehensive pipelines such as urban subway underpass high-voltage cables.
In order to achieve the purpose, the invention is realized by the following technical scheme:
a vertical freezing construction method for comprehensive pipelines such as urban subway underpass high-voltage cables comprises the following steps:
firstly, preparing construction and constructing fender piles around a pipeline;
secondly, drilling construction and freezing station installation;
thirdly, actively freezing and maintaining freezing;
fourthly, constructing a fender post structure after excavation of the foundation pit, dewatering and freezing;
fifthly, cutting off and plugging the freezing pipe, performing melt-down grouting and finishing construction.
Preferably, the construction preparation and the surrounding pile construction of the pipeline comprises pipeline positioning, pile foundation placement by excavating the pipeline, steel protecting cylinders with freezing holes, positioning protecting cylinders, backfilling and tamping, steel protecting cylinders fixing and surrounding pile construction of the pipeline.
Preferably, the drilling construction and freezing station installation comprises freezing construction preparation, vertical freezing hole drilling and freezing station installation and brine pipeline connection.
Preferably, 24-27 freezing holes are arranged at the joint of each structure, and the flow rate of single-hole brine in each freezing hole is 4-6 m during active freezing3/h。
Preferably, the step of enclosing pile structure construction after excavation of the foundation pit and precipitation freezing is that excavation of the foundation pit is more than the water level, precipitation of the foundation pit is analyzed to influence freezing, freezing measures are enhanced if influence exists, excavation is carried out below the water level of the foundation pit if influence does not exist, and then enclosing pile structure construction is carried out.
Preferably, the process parameters of the pile foundation construction around the pipeline are that a safe distance of 1.8-2.2 m is reserved around the pipeline, and after the pipeline is proved, the pile foundation is added within the safe distance range after the pile casing is embedded; the positioning error of the pile casing is not more than 5cm, and a construction space of 30cm +/-5 cm of the grid steel frame is reserved; the bottom of the positioning protective cylinder is embedded at least 0.5m deeper than the pipeline, and the protective cylinder is fixed; and the top of the backfilled pile casing is fixed by adopting reinforced concrete.
Preferably, when the freezing holes are constructed, the maximum distance between the formed holes is not more than 1.2m, and the distance between the freezing holes on the periphery of the wall of the working well and the wall of the working well is not more than 0.5 m; the pressure resistance of the freezing pipe and the temperature measuring pipe is not lower than 0.8 MPa.
Preferably, the melting and sinking grouting is carried out in cooperation with tunnel deformation monitoring, the freezing hole is used as a melting and sinking grouting hole, the grouting sequence is carried out from bottom to top, the melting and sinking grouting mainly adopts cement-water glass double grout, cement single grout is used as an auxiliary material, a small amount of uniform grouting is carried out for multiple times, and the grouting pressure is not more than 0.5 MPa.
Compared with the prior art, the invention has the following advantages:
according to the vertical freezing construction method for the comprehensive pipelines such as the high-voltage cable penetrating through the urban subway, the enclosing structure below the pipeline is sealed in a water stop mode by vertical freezing, and the gap in the excavation process is supported by the grid steel frame, so that the efficient freezing effect can be achieved, and the in-situ protection of 220KV power lines and the safe excavation of a deep foundation pit can be realized;
the invention relates to a vertical freezing construction method of comprehensive pipelines such as a high-voltage cable for passing through a city subway, which adopts a saline water vertical freezing method to form a freezing wall at a gap of an enclosure structure below a power pipeline, adopts an open excavation method to accurately position the pipeline position, sets a steel casing to supplement and perfect the enclosure structure, accurately positions a freezing hole and protects construction safety measures, and combines a grid steel frame to support a soil body below the pipeline in the excavation process and combines foundation pit dewatering and vertical freezing to perform foundation pit waterless excavation; the construction method can adapt to severe geological conditions such as sand pebbles and the like, and the situation that the gaps of the enclosure water stop structure are discontinuous due to the in-situ protection of the power line in the foundation pit; the method is particularly suitable for the conditions that the pipeline is deeper in buried depth, the importance degree of the pipeline is high, and the pipeline cannot be changed or is difficult to change;
the vertical freezing construction method of the comprehensive pipeline such as the urban subway underpass high-voltage cable has safe and reliable construction and high economic benefit, the vertical freezing enables the enclosure structure diaphragm wall gap to form a waterproof plate, and provides conditions for deep foundation pit excavation and precipitation, wherein the frozen wall can bear certain water and soil pressure in the foundation pit excavation process; the underground water is not polluted in the freezing process; and the protection reliability for the 220KV electric power pull tube is high, and the influence caused by the movement and the modification of the pipeline is avoided.
Drawings
Fig. 1 is a schematic process flow diagram of a vertical freezing construction method of a comprehensive pipeline for urban subway under-crossing high-voltage cables and the like.
Detailed Description
The invention aims to provide a vertical freezing construction method for comprehensive pipelines such as urban subway underpass high-voltage cables, and the like, which is realized by the following technical scheme:
a vertical freezing construction method for comprehensive pipelines such as urban subway underpass high-voltage cables comprises the following steps:
firstly, preparing construction and constructing fender piles around a pipeline;
secondly, drilling construction and freezing station installation;
thirdly, actively freezing and maintaining freezing;
fourthly, constructing a fender post structure after excavation of the foundation pit, dewatering and freezing;
fifthly, cutting off and plugging the freezing pipe, performing melt-down grouting and finishing construction.
Preferably, the construction preparation and the pile surrounding construction of the pipeline comprise pipeline positioning, pipeline excavation and pile foundation placement, freezing hole steel casing, positioning casing, backfilling and tamping, steel casing fixing and pile surrounding construction of the pipeline;
preferably, the drilling construction and the freezing station installation comprise freezing construction preparation, vertical freezing hole drilling and freezing station installation, and brine pipeline connection;
preferably, the process parameters in the active freezing and the maintenance freezing are as follows:
the active freezing time is 30 +/-2 days, the maintenance freezing is carried out for 60 +/-2 days, the lowest salt water temperature is-25 to-28 ℃, the average temperature of the frozen soil wall is not higher than-10 ℃, and the temperature near the interface between the frozen soil wall and the diaphragm wall of the working well is not higher than-5 ℃ when the tunnel entrance is opened;
preferably, 24-27 freezing holes are arranged at the joint of each structure, and the flow rate of single-hole brine in each freezing hole is 4-6 m during active freezing3/h；
Preferably, the step of constructing the fender post structure after excavation of the foundation pit and precipitation freezing is that the foundation pit is excavated to a position above the water level, the foundation pit is subjected to precipitation, the influence of the precipitation on freezing is analyzed, if the influence exists, the freezing measure is enhanced, if the influence does not exist, excavation is carried out below the water level of the foundation pit, and then the fender post structure construction is carried out;
preferably, the process parameters of the pile foundation construction around the pipeline are that a safe distance of 1.8-2.2 m is reserved around the pipeline, and after the pipeline is proved, the pile foundation is added within the safe distance range after the pile casing is embedded; the positioning error of the pile casing is not more than 5cm, and a construction space of 30cm +/-5 cm of the grid steel frame is reserved; the bottom of the positioning protective cylinder is embedded at least 0.5m deeper than the pipeline, and the protective cylinder is fixed; backfilling compaction degree meets pile foundation construction requirements (the backfilled soil adopts loess or yellow clay, the optimal water content is confirmed before construction, if the backfilled soil can not meet the optimal water content requirement, lime or cement is adopted for improvement, a layer is compacted every 30-50 cm through backfilling layer by layer, the backfilling compaction coefficient is not less than 0.95), and the top of the pile casing is fixed by reinforced concrete after backfilling;
preferably, when the freezing holes are constructed, the maximum distance between the formed holes is not more than 1.2m, and the distance between the freezing holes on the periphery of the wall of the working well and the wall of the working well is not more than 0.5 m; the pressure resistance of the freezing pipe and the temperature measuring pipe is not lower than 0.8 MPa;
the freezing pipe is put into the drill hole and is firstly arranged, when welding is carried out, a welding seam is full, after the freezing pipe is put, an inclinometer is used for measuring the inclination, the depth of the freezing hole is measured again, the freezing pipe is pressed and tested for leakage after the length and the inclination of the freezing pipe are qualified, the pressure for testing the leakage of the freezing hole is controlled to be 0.7-1.0 MPa, and the pressure is stable for 15 minutes and is not changed, so that the pressure test is qualified;
preferably, the melting and sinking grouting is carried out in cooperation with tunnel deformation monitoring, a freezing hole is used as a melting and sinking grouting hole, the grouting sequence is carried out from bottom to top, the melting and sinking grouting mainly adopts cement-water glass double grout, cement single grout is used as an auxiliary material, a small amount of uniform grouting is carried out for multiple times, and the grouting pressure is not more than 0.5 MPa;
the volume ratio of cement paste to water glass solution in the cement-water glass double-liquid slurry is 1: 0.8 to 1.2; wherein the water-cement ratio of the cement paste is 1: 0.8 to 1.2; preferably, the water glass solution is prepared by diluting B35-B40 water glass with 1-2 times of water by volume.
The invention is further described with reference to specific examples.
Examples
The 1 st wind pavilion of the R1 # line Dayanzhuang station of the south Ji subway and the A entrance are positioned at the northwest corner of the intersection of the Shixi road and the Qilu road. Is an oversized special-shaped foundation pit, and the excavation area of the foundation pit is about 3000m2The maximum excavation depth is 15m, and the average excavation depth is12 m. The water level in the pit is reduced by 8 m. The peripheral pipelines are numerous, and the 220KV power pipeline and the 10KV power pipeline mainly influence the construction of auxiliary structures of the Dayangzhuang station. The building enclosure is influenced by a 220KV electric power pull pipe, the lower part of a pipeline of the building enclosure is closed, a gap exists, and due to complex geology and large underground water amount, accidents are easy to happen in the excavation process of a foundation pit, the vertical freezing construction method of the comprehensive pipelines such as the urban subway underpass high-voltage cables is adopted for construction, and as shown in figure 1, the vertical freezing construction method specifically comprises the following steps:
firstly, preparing construction and constructing fender piles around a pipeline;
construction preparation, pipeline positioning, digging a pipeline, placing a pile foundation and a freezing hole steel casing, positioning the casing, backfilling and tamping, fixing the steel casing, and constructing surrounding piles around the pipeline;
the pipeline treatment construction stage before freezing comprises:
1) accurately positioning the pipeline, strictly prohibiting mechanical excavation of the excavated pipeline, and adopting a manual excavation mode at the periphery of the pipeline;
2) embedding the pile casing to go deep under the pipeline, positioning the pile casing to be firmly fixed, and constructing underground constructions such as a surrounding structure of the pipeline, a freezing hole and the like after the completion. Embedding a protection cylinder and a pipeline and making a heat insulation measure;
3) installing the pipeline observation protective cylinder, facilitating the visual observation of the pipeline condition and preventing the occurrence of an accident condition;
4) making pipeline bottom crossing and pipeline safety marks on site;
5) making a pipeline emergency disposal scheme, and staring at by electric power professionals in the construction process;
the process for constructing the surrounding fender piles of the pipeline comprises the following steps:
before construction, a Luoyang shovel is adopted to perform penetration detection on a soil layer of the casing, and the penetration depth is greater than the pipeline buried depth by 2 m;
reserving a safety distance of about 2 meters around the periphery of the pipeline, adding a pile foundation within the range of 2 meters after the pipeline is proved and a pile casing is buried, wherein the positioning error of the pile casing is not more than 5 centimeters, and reserving a construction space of 30 centimeters of a grid steel frame; the bottom of the positioning pile casing is embedded at least 0.5m deeper than the pipeline, the pile casing is fixed, then the backfilling compactness meets the construction requirement of the pile foundation, and the top of the backfilled pile casing is fixed by adopting reinforced concrete;
the equipment construction process strictly prohibits the protective cylinder from being excessively collided, and the displacement deformation condition of the protective cylinder is monitored in real time;
secondly, drilling construction and freezing station installation;
preparing for freezing construction, drilling a vertical freezing hole, installing a freezing station, and connecting a brine pipeline;
1. freezing pipe, temperature measurement pipe and feed pipe specification:
the freezing pipe is connected with a No. 20 high-quality carbon structural steel pipe with the diameter of 108 multiplied by 5mm by butt welding with an outer sleeve, and the material of the outer sleeve is the same as that of the pipe; the diameter of the liquid supply pipe is 48 multiplied by 4.5mm high-quality carbon structural steel; the diameter phi of the vertical temperature measuring tube outside the hole ring is 60X 5 mm;
2. drilling equipment type selection:
selecting 1 MGL-135D type drilling machine, wherein the power of each motor is 30 kw; the steel sleeve is pulled out after the freezing pipe is lowered down by using a steel sleeve retaining wall with the diameter of 168mm, the guide wall reinforced concrete flanging is broken by using a total concrete excavator, the position which can not be excavated is drilled by using a diamond core drill with the diameter of 200mm, and the drilling is measured by using the light of a theodolite.
2 BW-200/50 slurry pumps are selected, the flow rate is 200L/min, and the power of each motor is 14.5 kw.
3. Freeze hole quality requirement
And arranging the freezing holes according to the construction reference points and the freezing hole construction drawing. The hole site deviation should not be larger than 50 mm. The drilling depth of the freezing hole is required to ensure that the freezing pipe can be lowered to the designed depth.
The deviation rate of the drilled holes is controlled to be within 1 percent, the maximum distance between the formed holes is not more than 1.2m, and the distance between the freezing holes on the periphery of the working well wall and the well wall is not more than 0.5 m.
The pressure resistance of the freezing pipe and the temperature measuring pipe is not lower than 0.8 MPa.
4. Freezing hole drilling and freezer installation
1) Fixing a drilling machine according to the design position of the freezing hole, drilling holes by using a phi 200mm core drill, and using a three-wing drill bit during normal drilling;
2) in order to ensure the drilling precision, the drilling of the hole opening section is a key, when the hole is drilled for 10m before drilling, the verticality of a drill rod needs to be checked repeatedly, the position of a drilling machine is adjusted, and pressure reduction drilling is adopted;
3) the freezing pipe is arranged in the drill hole before being put into the drill hole, and a welding seam is full during welding, so that the freezing pipe is ensured to have enough strength, and the freezing pipe is prevented from being broken during pipe drawing; after the freezing pipe is put, measuring the inclination by using an inclinometer, and measuring the depth of the freezing hole again; after the length and the deflection of the freezing pipe are qualified, pressing and leakage testing are carried out, the leakage testing pressure of the freezing hole is controlled to be 0.7-1.0 MPa, and the pressure is qualified when the pressure is stable for 15 minutes and is not changed;
4) after the freezing pipe is installed, blocking the pipe orifice by a wooden plug and the like so as to prevent foreign matters from falling into the freezing pipe;
5) a liquid supply pipe is arranged in the freezing pipe, the bottom end of the liquid supply pipe is connected with a bracket with the height of 0.3m, and then a removing claw, a loop claw and a freezing pipe end cover are installed;
6) the construction method and requirements of the temperature measuring hole are the same as those of the freezing hole, and brine with the specific gravity of 1.26-1.265 is filled in the lower temperature measuring pipe.
5. Freezing refrigeration system installation
5.1 model selection and pipeline design of freezing refrigeration equipment for shield tunnel entrance engineering
1) Two sets of YSLGF300 type refrigerating units (one of which is a standby unit) are selected, when the temperature of brine is-28 ℃ and the temperature of cooling water is 26 ℃, the maximum refrigerating capacity is 86000kcal/h, and the total power of a motor of the refrigerating unit is 103 kw;
2) one 200S42A brine circulating pump is selected, and the flow rate is 198m3H, lift 43m, motor power 37 kw;
3) 1 cooling water circulating pump with the flow rate of 100m IS selected from IS125-100-3H, the lift is 20m, and the total power of the motor is 11 kw; a DBNL3-50 type cooling tower 3, the motor power is12 kw;
4) salt settingOne water tank with volume of 6m3；
5) The saline water main pipe and the liquid collecting and distributing pipe are seamless steel pipes with the diameter of 159 multiplied by 5mm, and the high-pressure rubber pipes are used for connecting the liquid collecting and distributing pipe and the cleat;
6) a welded pipe for a cooling water pipe, and thermometers are arranged on a water inlet pipe and a water outlet pipe of the refrigerator;
7) a pressure gauge, a temperature sensor and a control valve are arranged on the brine pipeline of the return circuit and the brine pipeline;
8) a valve is arranged between the liquid distribution ring and the freezer so as to control the flow of brine of the freezer;
9) the connection of the freezers adopts a series-parallel connection mode, and the number of the freezers in each group is 3;
10) the cooling water consumption for freezing construction is 15m3The maximum total electricity consumption is about 165 kw;
11) others
(1) Refrigerating machine oil: n46 refrigerator oil is selected;
(2) refrigerant: r22 refrigerant is selected;
(3) a refrigerant agent: using a calcium chloride solution as freezing circulating brine, wherein the specific gravity of the brine is 1.260-1.265;
5.2 freezing station arrangement and equipment installation: the equipment in the freezing station mainly comprises a power distribution cabinet, a freezing unit, a brine tank, a brine pump, a clean water pump, a cooling tower, a clean water tank and the like, and is according to the equipment use instruction;
5.3 connecting line, installation heat preservation and test instrument:
the saline water and the cooling water pipeline are paved on a ground pipe frame and connected with a flange; the thermometer, the pressure gauge and the flowmeter are arranged according to the standard; the saline pipe is tested for leakage and cleaned, then is insulated by polystyrene foam plastic, the thickness of the insulation layer is 50mm, the outer surface of the insulation layer is wrapped by a plastic film, and the connection of the liquid collecting and distributing ring and the freezing pipe is realized by a high-pressure rubber pipe with the pressure resistance of 1 MPa.
The evaporator and low-temperature pipeline of the refrigerating unit are insulated by soft foam plastic insulating material, and the brine tank and the brine main pipe are insulated by polystyrene foam plastic with the thickness of 50 mm.
5.4 dissolving calcium chloride and filling fluorine and oil in machine set
Firstly, the fresh water of about 1/4 is injected into the brine tank, then the pump is started to circulate and solid calcium chloride is added step by step until the brine concentration reaches the design requirement. Impurities are removed when dissolving calcium chloride.
The filling of the unit with fluorine and the filling of the refrigerator are carried out according to the requirements of the operating instruction of the equipment. Firstly, leak detection and nitrogen flushing of a refrigerating system are carried out, and after the system is ensured to be free of leakage, fluorine is refilled and oil is added.
Thirdly, actively freezing and maintaining freezing;
the freezing process parameters are as follows:
establishing a freezing station on the ground, wherein the positive freezing time is 30 +/-2 days, maintaining and freezing for 60 +/-2 days, the lowest salt water temperature is-25 to-28 ℃, the average temperature of the frozen soil wall is not higher than-10 ℃, and the temperature near the interface between the frozen soil wall and the underground diaphragm wall of the working well is not higher than-5 ℃ when the tunnel entrance is opened; freezing holes with the number of 24-27 are arranged at the joint of each structure, and the flow of single-hole brine in the freezing holes is 4-6 m when the freezing holes are actively frozen3H; the outer diameter of the freezing pipe is 108mm, and 5-10 temperature measuring holes are arranged at the relative weak position of the freezing wall;
the water is vertically frozen in the gap of the enclosure structure to form a continuous freezing wall, so that the underground water is blocked, the water gushing and sand gushing risks are reduced, and compared with the traditional chemical slurry water stopping measures, the water stopping method has no pollution to underground water resources; compared with the traditional strong precipitation foundation pit, the foundation pit saves water resources, is clean in construction process, and does not generate raise dust and construction waste.
1. Test run and active freeze of freezing system
Debugging and trial running are carried out after the equipment is installed, and during trial running, various state parameters such as pressure, temperature and the like are adjusted at any time, so that the unit runs under the technical parameter conditions related to process specifications and design requirements; in the freezing process, detecting the temperature of brine, the flow of brine and the expansion condition of a frozen earth wall at regular time, adjusting the operation parameters of a freezing system if necessary, entering active freezing after the freezing system operates normally, and actively freezing until the freezing meets the design requirements;
detecting the change condition of the ambient temperature of the pipeline in the freezing process, wherein the temperature is not lower than-20 ℃;
the change condition of the freezing wall temperature is analyzed in real time after the dewatering well is started, so that the temperature of the freezing wall is prevented from rising;
the dewatering well can be started to dewater after the cross ring of the freezing wall;
and monitoring the freezing process for 24 hours, and making emergency plans such as freezing equipment and the like.
2. Borehole and maintenance freeze
After the actually measured temperature of the frozen soil wall reaches a design value, a plurality of exploration holes are drilled on the wall of a working well close to the tunnel portal by using 38mm diamond coring, and the shield portal can be opened after the situation that the frozen soil wall and the wall of the well are completely frozen is judged. When the hole is drilled, tools such as a wooden plug and the like are prepared to prevent water from being discharged from the drilled hole. And stopping freezing after the shield tunneling machine enters the tunnel.
Fourthly, constructing a fender post structure after excavation of the foundation pit, dewatering and freezing;
excavating the foundation pit to be above the water level, dewatering the foundation pit, analyzing influence of dewatering on freezing, strengthening freezing measures if the influence is influenced, excavating below the water level of the foundation pit if the influence is not influenced, and then constructing a fender post structure; wherein, when the foundation pit is excavated, the foundation pit is firstly supported and then excavated, and each layer of earthwork near the freezing wall is not more than 2 meters;
under the condition that the excavation condition of a foundation pit is met, the water pumping amount is reduced as much as possible, wherein the position of a water pumping pump is 2-5 meters away from the base and the bottom of the freezing wall, so that the influence of water flow on the freezing wall is reduced;
after excavation, grid reinforcing steel bars are manufactured immediately, the exposure time of the freezing wall is reduced, and heat insulation measures are additionally arranged, so that the influence of concrete water heating and external heat on the freezing wall is reduced.
Mechanical vibration excavation is forbidden, and 2m earthwork around the freezing wall is excavated manually;
fifthly, cutting off and plugging the freezing pipe, performing melt-down grouting and finishing construction.
The method is characterized in that the melting and sinking grouting is carried out in cooperation with tunnel deformation monitoring, freezing holes are used as melting and sinking grouting holes, and grouting is carried out from bottom to top. The melting and depositing grouting adopts cement-water glass double-liquid cement as a main material, single-liquid cement slurry as an auxiliary material, a small amount of the single-liquid cement slurry is used for assisting, the grouting pressure is not more than 0.5Mpa, and the grouting range is the whole freezing area. The cement-water glass double-liquid-slurry ratio is that the volume ratio of cement slurry to water glass solution is 1: 1, wherein the water-cement ratio of cement paste is 1: 1, diluting the water glass solution by adding 1-2 times of water into B35-B40 of water glass.
The melting and sinking grouting equipment adopts a plunger or piston double-liquid grouting pump, can simultaneously convey two media or independently convey one medium, and is provided with accurate metering instruments such as grouting pressure, grouting flow and the like, the grouting flow range is about 0L/min-70L/min, and a mixer is arranged during the injection of double-liquid grout, and the grout is uniformly mixed before entering the stratum.
A vertical freezing construction method for a comprehensive pipeline such as a high-voltage cable penetrating under an urban subway can ensure the construction safety of a deep foundation pit under the geological conditions of pipelines and sand pebbles, has high vertical freezing process efficiency and good effect, has little influence on the surrounding environment, meets the construction conditions under the field working conditions, and can solve the safety risk of a notch of the deep foundation pit under the pipeline conditions; compared with the traditional power line relocation, the method has the advantages that the social electricity demand is not influenced, the relocation cost with high cost is not generated, and the total construction period can be reduced.
As the 220KV high-voltage cable is arranged above the No. 1 wind pavilion of the poplar station and the foundation pit at the entrance A, the enclosure structure cannot be completely closed. The geological conditions of the foundation pit are complex, a pebble layer and a silt layer exist on the base, the excavation depth is deep, underground water is abundant, and the adaptability of the vertical grouting process in a sandy pebble stratum is poor. By combining the reasons and the actual situation on site, the comprehensive construction method mainly based on vertical salt water freezing is more beneficial to the safety of the foundation pit, and the construction process is safe and reliable. The method has the advantages of achieving remarkable effect actually, ensuring the safety of the power pipeline, ensuring the safety of the foundation pit and reducing the influence and related cost of the changed power.
Claims (8)
1. A vertical freezing construction method for comprehensive pipelines such as urban subway underpass high-voltage cables is characterized in that: the method comprises the following steps:
firstly, preparing construction and constructing fender piles around a pipeline;
secondly, drilling construction and freezing station installation;
thirdly, actively freezing and maintaining freezing;
fourthly, constructing a fender post structure after excavation of the foundation pit, dewatering and freezing;
fifthly, cutting off and plugging the freezing pipe, performing melt-down grouting and finishing construction.
2. The vertical freezing construction method of the comprehensive pipelines such as the urban subway under-crossing high-voltage cables and the like according to claim 1, characterized in that: the construction preparation and the construction of the surrounding piles of the pipeline comprise pipeline positioning, pile foundation placement by excavating the pipeline, freezing hole steel pile casing, positioning pile casing, backfilling and tamping, fixing steel pile casing and the construction of the surrounding piles of the pipeline.
3. The vertical freezing construction method of the comprehensive pipelines such as the urban subway under-crossing high-voltage cables and the like according to claim 1, characterized in that: the drilling construction and the freezing station installation comprise freezing construction preparation, vertical freezing hole drilling and freezing station installation, and brine pipeline connection.
4. The vertical freezing construction method of the comprehensive pipelines such as the urban subway under-crossing high-voltage cables and the like according to claim 1, characterized in that: freezing holes with the number of 24-27 are arranged at the joint of each structure, and the flow of single-hole brine in the freezing holes is 4-6 m when the freezing holes are actively frozen3/h。
5. The vertical freezing construction method of the comprehensive pipelines such as the urban subway under-crossing high-voltage cables and the like according to claim 1, characterized in that: the steps of excavation of foundation pit and precipitation freezing back fender pile structure construction do, excavation of foundation pit to above the water level, foundation pit precipitation, analysis precipitation are to freezing influence, if influence then strengthen freezing measure, if do not influence then excavate below the foundation pit water level, then carry out fender pile structure construction.
6. The vertical freezing construction method of the comprehensive pipelines such as the urban subway under-crossing high-voltage cables and the like according to claim 1, characterized in that: the process parameters of the construction of the pile foundation at the periphery of the pipeline are that a safe distance of 1.8-2.2 m is reserved at the periphery of the pipeline, and the pile foundation is added within the safe distance range after the pipeline is proved and the pile casing is embedded; the positioning error of the pile casing is not more than 5cm, and a construction space of 30cm +/-5 cm of the grid steel frame is reserved; the bottom of the positioning protective cylinder is embedded at least 0.5m deeper than the pipeline, and the protective cylinder is fixed; and the top of the backfilled pile casing is fixed by adopting reinforced concrete.
7. The vertical freezing construction method of the comprehensive pipelines such as the urban subway under-crossing high-voltage cables and the like according to claim 1, characterized in that: when the freezing holes are constructed, the maximum distance between the formed holes is not more than 1.2m, and the distance between the freezing holes on the periphery of the working well wall and the well wall is not more than 0.5 m; the pressure resistance of the freezing pipe and the temperature measuring pipe is not lower than 0.8 MPa.
8. The vertical freezing construction method of the comprehensive pipelines such as the urban subway under-crossing high-voltage cables and the like according to claim 1, characterized in that: the method is characterized in that the melting and sinking grouting is carried out in cooperation with tunnel deformation monitoring, a freezing hole is used as a melting and sinking grouting hole, the grouting sequence is carried out from bottom to top, the melting and sinking grouting mainly adopts cement-water glass double grout, cement single grout is used as an auxiliary material, a small amount of uniform grouting is carried out for multiple times, and the grouting pressure is not more than 0.5 MPa.
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