阅读说明：本技术 一种富水砂层地质条件下盾构始发施工方法 (Shield starting construction method under water-rich sand layer geological condition ) 是由 胡国伟 李刚柱 俞南均 孙伯乐 邹科 淡永航 王鹏飞 汪晓 史邢凯 赵昕龙 李晓 于 2020-03-25 设计创作，主要内容包括：本发明属于隧道施工技术领域,具体涉及一种富水砂层地质条件下盾构始发施工方法。该工法在富水粉砂地层盾构始发施工中,采取三轴搅拌桩进行端头加固并施作一圈复搅止水帷幕阻水,RJP超高压旋喷桩进行剩余50cm“夹心层”的加固处理,然后坑外打设群井降水控制水位,在降水施工前先进行降水试验,采用Aquifertest软件和泰斯曲线法进行参数计算分析和配线拟合验证可否达到降水效果,配合局部水平注浆对洞门渗漏点进行补强,始发时洞圈内反压黏土和快干水泥反压止水,以确保盾构机安全的进出洞。为解决富水砂层等类似极差地质条件下盾构始发接收安全风险问题提供了良好借鉴,经济、社会效益显著,应用前景十分良好。(The invention belongs to the technical field of tunnel construction, and particularly relates to a shield launching construction method under a water-rich sand layer geological condition. In the construction method, during shield launching construction of a water-rich silt stratum, a triaxial stirring pile is adopted to reinforce the end and apply a circle of re-stirring waterproof curtain for water blocking, an RJP ultrahigh-pressure jet grouting pile is used for reinforcing the residual 50cm of a sandwich layer, then a group well is drilled outside a pit to control the water level, a precipitation test is carried out before precipitation construction, Aquifest software and a Tess curve method are adopted to carry out parameter calculation analysis and wiring fitting verification to verify whether the precipitation effect can be achieved, local horizontal grouting is matched to reinforce a leaking point of a tunnel portal, and back pressure clay and quick-drying cement in the tunnel ring are used for back pressure water blocking during launching so as to ensure that a shield machine can safely enter and exit the tunnel. The method provides a good reference for solving the problem of shield starting and receiving safety risks under similar extremely poor geological conditions such as water-rich sand layers and the like, and has remarkable economic and social benefits and very good application prospect.)

1. A shield launching construction method under the geological condition of a water-rich sand layer is characterized in that a triaxial mixing pile is adopted for end reinforcement and a circle of repeated mixing waterproof curtain water blocking is carried out, an RJP high-pressure jet grouting pile is added between a triaxial mixing pile reinforcement area and an underground continuous wall for reinforcement, and then a dewatering well is arranged outside a pit for dewatering control water level; carrying out precipitation test before precipitation construction of a precipitation well, and adopting pumping test software and a Tess curve method to carry out parameter calculation analysis and wiring fitting verification to verify whether the precipitation effect can be achieved or not; reinforcing the leakage point of the tunnel portal by matching with local horizontal grouting, and stopping water by back pressure clay and quick-drying cement in the tunnel portal during starting.

2. The shield starting construction method under the geological condition of the water-rich sand layer as claimed in claim 1, wherein the reinforcement range of the triaxial mixing pile is as follows:

a planar reinforcement range; the longitudinal direction is the shield tunneling direction of 11.5m, and the transverse direction is the area between the left side and the right side of the shield tunnel outline by 3 m;

a facade reinforcement range; the area between 3.0m above the top of the outer diameter of the shield tunnel and the ground is a weak reinforcing area, and the area between 3.0m above the top of the outer diameter of the shield tunnel and 3.0m below the bottom of the outer diameter of the shield tunnel is an strong reinforcing area.

3. The shield launching construction method under the geological condition of the water-rich sand layer as claimed in claim 1, wherein the construction method of the RJP high-pressure jet grouting pile is as follows:

high-pressure rotary spraying; firstly, starting an air compressor in a no-load mode, starting a high-pressure pump in the no-load mode after the air compressor is normally operated, and simultaneously supplying air and water into holes to enable the air quantity and the pump pressure to be increased to specified values; starting a grouting pump after wind and water are smooth, starting grouting after the pump amount and the pump pressure are normal, lifting a grouting pipe after cement slurry flows out of a spray head, and spraying grouting from bottom to top;

when the deep layer is sprayed in a rotary mode, the slurry is sprayed firstly, and then the rotating and lifting are carried out; when a grouting pipe is removed in jet grouting, lifting and rotation are stopped, and meanwhile, slurry feeding is stopped, so that the air quantity and the water quantity are reduced, and finally, the machine is stopped; the hole section for spraying and grouting is connected with the front section in an overlapping mode when the spraying and grouting are continued after the disassembly is finished, and the overlapping length is larger than or equal to 300;

measuring pressure, flow and slurry discharge parameters during rotary spraying, and recording item by item; when the slurry outflow amount is more than 40 percent of the grouting amount or the slurry does not flow at all, the rotary spraying is continued after the maintenance;

in the rotary spraying process, whether the nozzle is partially or completely blocked is checked, and the rotary spraying is carried out again after the nozzle is blocked and the pipe is pulled and cleaned;

pulp replenishing; and after the injection grouting operation is finished, timely supplementing and irrigating with cement paste with the mass ratio of water to ash being 1: 1.

4. The shield launching construction method under the geological condition of the water-rich sand layer as claimed in claim 2, wherein the construction steps of the triaxial mixing pile comprise:

1) spraying, stirring and sinking; before the guniting stirring sinking, checking whether a guniting system is normal, and then starting to prepare cement paste; starting a stirrer motor, pumping cement slurry by a mortar pump at the same time, and keeping the outlet pressure of the mortar pump between 0.4 and 0.6 MPa; when the guniting is started, the stirrer starts to stir and sink until the designed depth is reached, and the sinking speed is controlled by the gear of the pile machine;

2) spraying, stirring and rising; when the stirring of the stirrer sinks to the designed pile length standard, the stirrer starts to lift and stir until the hole opening;

3) repeatedly stirring, sinking and rising; when the mixer is lifted to the elevation of the orifice, the construction processes of spraying, stirring, sinking and spraying, stirring and rising are repeated again, and the construction of the pile is finished when the mixing pile is lifted to the orifice again;

4) shifting; after the two-time spraying and the two-time stirring, the stirring machine is moved away from the constructed pile position, then is moved to the next pile position, and the corresponding construction process is repeated to complete the construction of other pile holes.

5. The shield launching construction method under the geological condition of the water-rich sand layer as claimed in claim 3, wherein the diameter of the RJP high-pressure rotary jet grouting pile is phi 1200mm, the mass ratio of water to ash of cement paste is 1:1, the pressure of the cement paste is 40MPa, the pressure of main air is 0.8MPa, and the flow of the main air is 6m³Min, high-pressure clear water flow rate of 60L/min, cement consumption of 810kg/m³The lifting speed is 120mm/min, the flow rate of cement slurry is 150L/min, the pressure of high-pressure clean water is 20Mpa, the pile-forming angle error is controlled within 1/200, the diameter of the clean water nozzle is phi 2.4mm, the diameter of the slurry nozzle is phi 3.7mm, and the rotating speed of a drill bit is 6 r/min.

6. The shield launching construction method under the geological condition of the water-rich sand layer as claimed in claim 1, wherein the well depth of the dewatering well is set to 24m, the dewatering well is arranged at the junction of the end well enclosure and the stirring pile reinforcement, the dewatering wells are arranged at two sides of the shield machine entering the reinforced soil along the shield advancing direction, the dewatering wells are arranged at the junction side of the shield reinforcement body and the undisturbed soil, after all the dewatering wells are constructed, water is tried to be pumped, and the dewatering effect is checked.

7. The shield starting construction method under the geological condition of the water-rich sand layer as claimed in claim 3, wherein hole guiding is carried out before RJP high-pressure jet grouting pile construction, and during hole guiding, the error between a hole forming center and a pile position center is ensured to be less than 50mm, and the error of perpendicularity is less than 1/200.

8. The shield starting construction method under the geological condition of the water-rich sand layer as claimed in claim 1, wherein the horizontal grouting method comprises the following steps:

1) after the end reinforcement is finished and before the shield starts, firstly, horizontal hole probing is carried out at the starting tunnel portal, the depth of the horizontal hole probing is 2.5m, the water stopping effect of the reinforcement body is checked, horizontal grouting is carried out after water leakage occurs, cement paste and water glass slurry are adopted, and the mixing volume ratio of the cement paste to the water glass slurry is 1: 1;

2) grouting when the designed depth is reached during drilling, and grouting immediately if sand and water are produced during drilling; repeating the steps until the final hole is designed; the overall grouting sequence is from the annular direction to the middle, from the bottom to the top and from the edge to the middle;

3) grouting pressure is 2-4 MPa; when the ground runs or bulges on site, grouting is stopped immediately;

4) finishing grouting standard; and when the grouting pressure reaches the design value, stopping grouting after 10 minutes of grouting.

9. The shield starting construction method under the geological condition of the water-rich sand layer as claimed in claim 1, wherein 4 rows of the triaxial mixing pile reinforcing bodies adjacent to the underground continuous wall and the outermost row of the triaxial mixing pile reinforcing bodies are connected in a sealing mode to form a water-repeat-prevention curtain.

Technical Field

The invention belongs to the technical field of tunnel construction, and particularly relates to a shield launching construction method under a water-rich sand layer geological condition.

Background

After the shield is initiated and arrives at the portal and is broken, the end soil body is exposed, the stress balance state of the end stratum is broken, the soil body structure, the acting load and the stress are changed, and the potential slippage damage of the end soil body is possible. For soil bodies with short self-stabilization time, such as loose sandy soil, silt and saturated soft clay, end reinforcement is very necessary.

According to different stratum conditions, the common reinforcing modes of the interval end head include plain pile reinforcing, high-pressure injection method, freezing method, plain pile and horizontal grouting reinforcing and the like. And (4) reinforcing the plain piles, wherein the plain pile reinforcing construction is suitable for soil layers mainly containing clay, poor water and small water content. And (4) reinforcing by a freezing method, wherein the freezing method is suitable for constructing the stratum mainly including a sand layer, silt and a soil layer with large water content. If the freezing method is adopted for end reinforcement, the influence of the deformation of the side wall of the end of the station with frozen soil expansion exists, and meanwhile, the construction cost is very high and is limited by the surface conditions. The reinforcing method is suitable for a soil layer formed by combining a clay layer and a weathered rock layer of the tunnel, namely the clay layer is poor in water and small in water content.

As for the shield project in China, the safety risks including water burst and sand gushing at the tunnel portal, instability of the stratum at the end and the like are extremely high in the shield starting and receiving construction of the water-rich silt stratum, and the technical difficulty is high.

The water-rich sand layer has soft soil layer, high underground water level, poor mechanical property and strong water permeability. The types of underground water are mainly divided into diving water and confined water, the water level burial depth is generally 1.40-2.00 m, and the water level is higher. During shield starting construction of the water-rich silt stratum, the occurrence probability of various disaster accidents including water burst and sand burst at the tunnel portal, instability of the stratum at the end and the like is high. During the starting process, the control ensures that the tunnel portal is not flooded with water and gushed with sand, and the stratum at the end becomes a serious difficulty of the engineering.

Disclosure of Invention

An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.

In order to achieve the purpose, the invention provides a shield launching construction method under the geological condition of a water-rich sand layer, which adopts a three-shaft stirring pile to reinforce the end and apply a circle of re-stirring water-stopping curtain water resistance, adds an RJP high-pressure jet grouting pile between a three-shaft stirring pile reinforcing area and an underground continuous wall for reinforcement, and then drills a precipitation well outside a pit to control the water level; carrying out precipitation test before precipitation construction of a precipitation well, and adopting pumping test software and a Tess curve method to carry out parameter calculation analysis and wiring fitting verification to verify whether the precipitation effect can be achieved or not; reinforcing the leakage point of the tunnel portal by matching with local horizontal grouting, and stopping water by back pressure clay and quick-drying cement in the tunnel portal during starting.

Specifically, the reinforcing range of the triaxial mixing pile is as follows:

a planar reinforcement range; the longitudinal direction is the shield tunneling direction of 11.5m, and the transverse direction is the area between the left side and the right side of the shield tunnel outline by 3 m;

a facade reinforcement range; the area between 3.0m above the top of the outer diameter of the shield tunnel and the ground is a weak reinforcing area, and the area between 3.0m above the top of the outer diameter of the shield tunnel and 3.0m below the bottom of the outer diameter of the shield tunnel is an strong reinforcing area. The cement mixing amount of the weak reinforcing area is 7 percent, the cement mixing amount of the strong reinforcing area is 20 percent, and the drill bit of the weak reinforcing area is accelerated quickly.

Further, the construction method of the RJP high-pressure jet grouting pile comprises the following steps:

1) high-pressure rotary spraying; firstly, starting an air compressor in a no-load mode, starting a high-pressure pump in the no-load mode after the air compressor is normally operated, and simultaneously supplying air and water into holes to enable the air quantity and the pump pressure to be increased to specified values; starting a grouting pump after wind and water are smooth, starting grouting after the pump amount and the pump pressure are normal, lifting a grouting pipe after cement slurry flows out of a spray head, and spraying grouting from bottom to top;

2) when the deep layer is sprayed in a rotary mode, the slurry is sprayed firstly, and then the rotating and lifting are carried out; when a grouting pipe is removed in jet grouting, lifting and rotation are stopped, and meanwhile, slurry feeding is stopped, so that the air quantity and the water quantity are reduced, and finally, the machine is stopped; the hole section for spraying and grouting is connected with the front section in an overlapping mode when the spraying and grouting are continued after the disassembly is finished, and the overlapping length is larger than or equal to 300;

3) measuring pressure, flow and slurry discharge parameters during rotary spraying, and recording item by item; when the slurry outflow amount is more than 40 percent of the grouting amount or the slurry does not flow at all, the rotary spraying is continued after the maintenance;

4) in the rotary spraying process, whether the nozzle is partially or completely blocked is checked, and the rotary spraying is carried out again after the nozzle is blocked and the pipe is pulled and cleaned;

5) pulp replenishing; and after the injection grouting operation is finished, timely supplementing and irrigating with cement paste with the mass ratio of water to ash being 1: 1.

Further, the construction steps of the triaxial mixing pile comprise:

1) spraying, stirring and sinking; before the guniting stirring sinking, checking whether a guniting system is normal, and then starting to prepare cement paste; starting a stirrer motor, pumping cement slurry by a mortar pump at the same time, and keeping the outlet pressure of the mortar pump between 0.4 and 0.6 MPa; when the guniting is started, the stirrer starts to stir and sink until the designed depth is reached, and the sinking speed is controlled by the gear of the pile machine;

2) spraying, stirring and rising; when the stirring of the stirrer sinks to the designed pile length standard, the stirrer starts to lift and stir until the hole opening;

3) repeatedly stirring, sinking and rising; when the mixer is lifted to the elevation of the orifice, the construction processes of spraying, stirring, sinking and spraying, stirring and rising are repeated again, and the construction of the pile is finished when the mixing pile is lifted to the orifice again;

4) shifting; after the two-time spraying and the two-time stirring, the stirring machine is moved away from the constructed pile position, then is moved to the next pile position, and the corresponding construction process is repeated to complete the construction of other pile holes.

Further, the diameter of the RJP high-pressure jet grouting pile is phi 1200mm, the mass ratio of water to ash of cement paste is 1:1, the pressure of the cement paste is 40MPa, the pressure of a main air is 0.8MPa, and the flow of the main air is 6m³Min, high-pressure clear water flow rate of 60L/min, cement consumption of 810kg/m³The lifting speed is 120mm/min, the flow rate of cement slurry is 150L/min, the pressure of high-pressure clean water is 20Mpa, the pile-forming angle error is controlled within 1/200, the diameter of the clean water nozzle is phi 2.4mm, the diameter of the slurry nozzle is phi 3.7mm, and the rotating speed of a drill bit is 6 r/min.

Furthermore, the well depth of the dewatering well is set to be 24m, the dewatering well is arranged at the reinforced junction of the end well enclosure and the stirring pile, the dewatering well is arranged on the two sides of the shield machine entering the reinforced soil along the shield advancing direction, the dewatering well is arranged on the side of the junction of the shield reinforced body and the original soil, after all the dewatering wells are constructed, trial pumping is carried out, and the dewatering effect is checked.

Specifically, a hole is led before the RJP high-pressure jet grouting pile is constructed, and during hole leading, the error between a hole forming center and a pile position center is ensured to be less than 50mm, and the error of perpendicularity is less than 1/200.

Further, the horizontal grouting method comprises the following steps:

1) after the end reinforcement is finished and before the shield starts, firstly, horizontal hole probing is carried out at the starting tunnel portal, the depth of the horizontal hole probing is 2.5m, the water stopping effect of the reinforcement body is checked, horizontal grouting is carried out after water leakage occurs, cement paste and water glass slurry are adopted, and the mixing volume ratio of the cement paste to the water glass slurry is 1: 1;

2) grouting when the designed depth is reached during drilling, and grouting immediately if sand and water are produced during drilling; repeating the steps until the final hole is designed; the overall grouting sequence is from the annular direction to the middle, from the bottom to the top and from the edge to the middle;

3) grouting pressure is 2-4 MPa; when the ground runs or bulges on site, grouting is stopped immediately;

4) finishing grouting standard; and when the grouting pressure reaches the design value, stopping grouting after 10 minutes of grouting.

Furthermore, 4 rows of the triaxial mixing pile reinforcing bodies close to the underground continuous wall and the outermost ring of the triaxial mixing pile reinforcing bodies are connected in a sealing mode to form a repeat-stirring-preventing water curtain.

The quality control key points of the RJP high-pressure jet grouting pile are as follows:

1. the elevation of the nearby ground and underground pipelines is monitored in the construction process, when the variation value of the elevation is larger than +/-10 mm, the construction is suspended, and the construction is carried out after the pressure parameters are adjusted according to actual conditions. 2. When the slurry is prepared, the water-cement ratio is strictly controlled according to the design and cannot be changed randomly. During the rotary spraying process, the mud should be prevented from settling and the concentration should be reduced. No wet or out-of-date cement must be used. When the slurry is conveyed to a slurry suction barrel after the slurry is stirred, a screen is required for filtering, and the diameter of a filtering screen hole is preferably smaller than the diameter of 1/2 of the nozzle. 3. At the beginning, high-pressure water is sent first, then cement paste and compressed air are sent, and in general, the compressed air can be sent for 30s later. And (3) rotating and spraying at the bottom of the pile for 1min, and then rotating, lifting and spraying at the same time. 4. When spraying, the preset spraying pressure is reached, and the grouting pipe is gradually lifted after the spraying amount. When a fault occurs in the middle, the lifting and the rotary spraying are stopped to prevent the pile from being interrupted, and meanwhile, the detection is immediately carried out to remove the fault; if the designed diameter of the pile body is influenced by insufficient slurry injection, rechecking is carried out. 5. In the rotary spraying process, when the slurry amount is more than 40% of the grouting amount or no slurry is discharged at all, the reason should be found out, and the rotary spraying parameters are adjusted or the diameter of the nozzle is changed. The project needing to enlarge the reinforcing range or improve the strength can adopt the repeated spraying measures, namely, firstly spraying clear water once and then spraying cement paste once or twice. 6. The rotation and the lifting of the drill rod are required to be continuous without interruption, the drill rod is required to be kept to have the lap joint length of 50-100 cm when the long drill rod is disassembled or the rotary spraying is continued, and the lap joint length is required to be increased if the time is too long, so that the pile breakage is avoided. 7. In the rotary spraying process, if the rotary spraying is interrupted due to the mechanical failure, the rotary spraying is performed again after the rotary spraying is performed again until the designed elevation of the pile bottom is reached. 8. After the grouting material is sprayed to the height of the pile, the grout pipe is quickly pulled out, and the pipeline is washed by clear water to prevent solidification and blockage. 9. The jet grouting depth, diameter, overlap distance, compressive strength and water permeability should meet the design requirements.

The end precipitation quality control key points are as follows:

1. the dredging well adopting the slurry wall protection and the forward circulation drilling for pore forming adopts an air compressor to wash the well, the working time is not less than 2 hours, and the water after well washing is clear without visible sand grains. 2. The filter material of the dewatering well is preferably backfilled by coarse sand, and the top surface of the filter material column is filled with cohesive soil.

The quality control key points of the triaxial cement mixing pile are as follows:

1. the construction of the triaxial cement mixing pile adopts a two-spraying and two-stirring process. In order to avoid blocking the pipe during the first drilling, the drilling can be carried with slurry, the slurry spraying amount is less than 1/2 of the total amount, and the underwater drilling is strictly forbidden. The first drilling and the first drilling are carried out by adopting low-gear operation uniformly, and one gear can be increased during repeated stirring. The normal piling time of each pile is not less than 40 minutes. 2. In order to ensure the quality of the pile end, the pile top and the pile body of the cement mixing pile, the first drill lifting and cement spraying should stay at the bottom of the pile for 30 seconds to grind the pile end, the rest cement is completely sprayed into the pile body in the lifting process, and the pile head is ground at the top of the pile for 30 seconds. 3. When the construction finds that the guniting amount is insufficient, the pile is required to be rebuilt and stirred again according to the requirement, and the guniting amount of the re-spraying is not less than the design amount. If power failure and mechanical failure cause occur, the interruption depth should be recorded in time when the guniting is interrupted. And (5) taking a supplementary spraying treatment measure within 12 hours, and filling the supplementary spraying condition into a construction record. The post-spraying overlapping section is larger than 100cm, and pile-repairing measures are adopted after 12 hours. 4. During construction, the guniting time and the guniting stopping time should be strictly controlled. Each pile needs continuous operation after drilling, and the grouting is not interrupted. The drill rod lifting operation is strictly forbidden under the condition that the slurry is not sprayed. The grout in the grout storage tank is not less than 50kg of the grout added for one pile. If the amount of the stored grout is less than the weight, the construction of the next pile cannot be carried out. 5. The lifting speed is not suitable to be too fast, and the sinking of the peripheral foundation caused by vacuum negative pressure, hole wall collapse and the like is avoided. 6. The monitoring frequency of the adjacent station and the shield tunnel is increased in the construction process, and if abnormal conditions occur, the construction is stopped in time, and the construction can be continued after measures are taken.

Compared with the prior art, the invention has the advantages that:

according to the shield starting construction method under the geological condition of the water-rich sand layer, the safety risk of the shield starting stage is effectively controlled by adopting comprehensive measures, the RJP high-pressure rotary jet pile is additionally arranged between the underground continuous wall and the three-axis stirring pile, underground water is effectively cut off, meanwhile, the construction process of horizontal supplementary grouting is used, the weak link of easy water leakage at the underground continuous wall is strengthened, the safety and controllability of the stratum and the tunnel face in the shield starting construction stage are ensured, and the loss caused by settlement of the stratum at the end, water gushing and sand gushing is avoided. The construction speed of the triaxial mixing pile is high, and the water stopping effect is obvious after the pile is formed; the mechanical automation control is realized, and the operation procedure is simple; the labor investment is less, and the construction cost is low; and the triaxial mixing pile can be constructed after the groove is excavated, a mud pit is not needed on site, and the safety and civilization of the construction site are guaranteed. The RJP high-pressure rotary jet pile construction method carries out cutting twice to destroy the soil layer, increases the cutting depth and increases the diameter of a consolidation body. Compared with a freezing method or other traditional shield launching processes, the method has the advantages of safety, high quality, cost saving, construction period shortening and the like. The method provides a good reference for solving the problem of shield starting and receiving safety risks under similar extremely poor geological conditions such as water-rich sand layers and the like, and has remarkable economic and social benefits and very good application prospect.

Drawings

Fig. 1 is a schematic plan view of reinforcement of end soil.

Fig. 2 is a schematic longitudinal section view of end soil body reinforcement.

FIG. 3 is a RJP pile construction parameter table.

Fig. 4 is a horizontal grouting hole site layout.

In the figure: 1. shaft, 2, station enclosure structure, 3, RJP high-pressure jet grouting pile reinforcement, 4, underground continuous wall, 5, waterproof curtain, 6, triaxial mixing pile reinforcement, 601, strong reinforcement area, 602, weak reinforcement area, 7, shield body, 8 and sleeve.

Detailed Description

The embodiments of the present invention will be further described with reference to the accompanying drawings.

A shield launching construction method under the geological condition of a water-rich sand layer is characterized in that a three-shaft stirring pile is adopted to reinforce an end head and apply a circle of stirring water-stopping curtain water blocking, an RJP high-pressure jet grouting pile is added between a three-shaft stirring pile reinforcing area and an underground continuous wall for reinforcing, then a precipitation well is drilled outside a pit to control the water level for precipitation, a precipitation test is carried out before precipitation construction, water pumping experiment software and a Tess curve method are adopted to carry out parameter calculation analysis and wiring fitting verification to judge whether the precipitation effect can be achieved, local horizontal grouting is matched to reinforce a portal leakage point, and back pressure clay and quick-drying cement water stopping are carried out in a tunnel circle during launching.

Construction process flow

Three-shaft stirring pile, re-stirring waterproof curtain construction → RJP high-pressure jet grouting pile seam treatment → end well point dewatering construction → horizontal exploratory hole and grouting → sealing water-stopping measure in tunnel door → shield launching.

1.1 construction of three-axis mixing pile

1. Reinforcement scope

A planar reinforcement range; the longitudinal direction is the shield tunneling direction of 11.5m, and the transverse direction is the area between the left side and the right side of the shield tunnel outline by 3 m;

a facade reinforcement range; the area between 3.0m above the top of the outer diameter of the shield tunnel and the ground is a weak reinforcing area, and the area between 3.0m above the top of the outer diameter of the shield tunnel and 3.0m below the bottom of the outer diameter of the shield tunnel is an strong reinforcing area. As shown in fig. 2.

2. Construction process of mixing pile

1) Spraying, stirring and sinking; before the guniting stirring subsides, whether the guniting system is normal or not is checked, and then the preparation of cement paste is started. The motor of the stirring machine is started, the mortar pump pumps cement slurry, the outlet pressure of the mortar pump is kept between 0.4 and 0.6Mpa, when the mortar spraying is started, the stirring machine starts to stir and sink until the designed depth, and the sinking speed is controlled by the gear of the pile machine.

2) Spraying, stirring and rising; when the mixer is mixing down to the design pile length standard, the mixer begins to lift the mixing up to the orifice.

3) Repeatedly stirring, sinking and rising; when the mixer is lifted to the elevation of the orifice, the construction processes of guniting, stirring and sinking and guniting, stirring and rising are repeated again, and the construction of the pile is finished after the stirring pile is lifted to the orifice again.

4) Cleaning and shifting; after the two-time spraying and the two-time stirring, the stirring machine is moved away from the constructed pile position, then is moved to the next pile position, and the corresponding construction procedure is repeated. After the last pile is constructed every day, the slurry pump is washed by clean water to clean residual cement slurry and soft soil of the stirring head in all pipelines.

1.2RJP high-pressure jet grouting pile construction

The water stopping effect of the traditional high-pressure jet grouting pile is general, the basic principle of the RJP (rodnjet pile) construction method is the same as that of other high-pressure jet grouting, the structure of a soil layer is damaged by the function of jetting fluid at ultrahigh pressure, soil particles damaged by the soil particles are mixed with slurry and stirred, and a solidified body is formed in the stratum after solidification. However, the strengthening mechanism of the RJP construction method is different from that of common rotary spraying, and mainly comprises the steps of cutting twice to destroy a soil layer, wherein the first time is to cut the soil layer for the first time by the composite spraying fluid of ultrahigh pressure water and air at the upper section, and the second time is to cut the soil layer for the second time on the basis of the first cutting by the composite spraying fluid of ultrahigh pressure slurry and air at the lower section in the lifting process, so that the cutting depth is increased, and the diameter of a consolidation body is increased.

The technical process of the RJP high-pressure jet grouting pile comprises the following steps

1. Lead hole

(1) Because the bulge construction RJP possibly exists in the underground diaphragm wall construction at the end, hole leading is carried out, and professional equipment is adopted for hole leading.

(2) Because the quality of the formed holes has great influence on RJP construction, the construction must be carried out according to technical parameters, the error between the centers of the formed holes and the center of the pile position is ensured to be less than 50mm, and the error of perpendicularity is less than 1/200.

2. RJP construction step

(1) High-pressure rotary spraying:

① when rotary grouting, the start sequence of the equipment should be noticed, the air compressor is started in no-load mode, the high-pressure pump is started in no-load mode after normal operation, air and water are simultaneously supplied into the hole, the air quantity and the pump pressure are gradually increased to specified values, the grouting pump is started after the air and the water are smooth, grouting is started after the pump pressure is normal, and the grouting pipe is lifted after cement slurry flows out of the spray nozzle to spray the grouting from bottom to top.

② when deep rotary jetting, the pile should be rotated and lifted after the slurry is jetted, there is time for jet at the pile end to ensure the quality of the pile end, when the grouting pipe needs to be removed during jet grouting, the lifting and rotation should be stopped, the slurry feeding should be stopped at the same time, the air quantity and water quantity are gradually reduced, finally the machine is stopped, the hole section for jet grouting is overlapped with the front section when the jet grouting is continued after the disassembly, the overlapping length is larger than or equal to 300, and the disjunction of the consolidation body is prevented.

③ the rotary spraying process includes measuring pressure, flow rate and slurry discharge, and recording the measured parameters one by one as required, finding out the reason and taking relevant measures when the slurry discharge is 40% higher than the grouting amount or no slurry discharge is produced, and then continuing the rotary spraying process.

④ during the rotary spraying process, the nozzle is partially or completely blocked, otherwise, the rotary spraying process is carried out again after the pipe drawing cleaning.

⑤ and after the injection grouting operation is finished, the grout generally shrinks in different degrees due to the water precipitation effect of the grout, so that a recess appears at the top of the consolidation body, and the grout with the water cement ratio of 1:1 needs to be used for grouting in time.

(2) Stirring cement paste:

① the water cement ratio is prepared according to the design requirement during the process of rotary spraying to prevent the cement slurry from settling and separating, which results in reduced concentration.

② after construction, the grouting pipe is taken out immediately, the grouting pump and the grouting pump are cleaned thoroughly, and no residual cement slurry is left in the pump.

1.3 end precipitation

1. Dewatering well plane arrangement

And foundation reinforcement is arranged at the shield door of the end well. In order to reduce the risk of leakage of the tunnel portal caused by underground water as much as possible, the shield entry and exit precipitation wells are generally arranged according to the following modes:

1) the dewatering well is arranged at the reinforced junction of the end well enclosure and the stirring pile (close to reinforcement but avoiding reinforcement), so that possible lap joint leakage between the reinforcement and the foundation pit enclosure is prevented.

2) Along the shield structure advancing direction, arrange the precipitation well at the shield structure machine entering soil stabilization side, prevent in the shield structure advancing direction because the higher water pressure difference of shield structure door inside and outside, lead to water, soil along the shield structure machine outer fringe to the tunnel portal seepage.

3) The dewatering well is arranged at the boundary side of the shield reinforcing body and the undisturbed soil, and a waterproof curtain is formed through the dewatering well, so that the water and soil loss of the undisturbed soil to the reinforcing body side due to higher water content and sand content is reduced.

2. Depth of dewatering well

And (4) setting a dewatering well as an emergency construction measure in the range of the portal in combination with the design requirement. The shield dewatering well depth is set to be 24 m.

3. Dewatering well operation

And after all dewatering wells are constructed, trial pumping is carried out, and dewatering effect is checked. According to similar engineering experience, only from precipitation effect analysis, the longer the similar soil layer open type precipitation time, the larger the water level depth is, and the relatively obvious water-bearing layer unsteady flow time effect is. If the surrounding environment protection requirement does not exist, the opening time of the dewatering well is about 3-5 days before the shield enters and exits the hole, and the shield stops after the shield enters and exits the hole. Therefore, in a region with a complex surrounding environment, the monitoring frequency of the surrounding environment is enhanced after the precipitation is started, the starting time and the starting number of the precipitation wells are dynamically controlled according to the monitoring result, the precipitation is stopped when necessary, and a solution is negotiated.

2.4 horizontal borehole and grouting

After the end reinforcement is finished and before the shield starts, firstly, horizontal hole probing is carried out at the starting tunnel portal, the depth of the horizontal hole probing is 2.5m, the water stopping effect of the reinforcement body is determined, if water leakage occurs, horizontal grouting is carried out, cement paste and water glass double-grout are adopted, the mixing ratio is 1, and the mixing ratio is 1. Can carry out stagnant water fast high-efficient. Hole site placement as shown in fig. 4, for a total of 19 grouting holes.

Drilling and grouting are sequentially carried out on each hole according to the design sequence, and the principle is as follows: when drilling, grouting is carried out when the designed depth is reached every time, and when sand exists, sand is discharged and water is injected no matter how long the sand exists. And repeating the steps until the final hole is designed. The overall grouting sequence: first, the ring direction, the middle, the bottom to the top and the side to the middle.

Grouting pressure: the grouting is compaction reinforcement grouting, the grouting pressure is 2-4 MPa, ground monitoring needs to be enhanced in the grouting process, the grouting pressure is adjusted according to monitoring data, field observation is enhanced, and grouting is stopped immediately when ground grout leakage or obvious uplift is found;

and (5) finishing grouting standard: when the grouting pressure reaches the design value, the grouting lasts for 10 minutes and can be actually adjusted according to the field.

1.4 sealing and water-stopping measures in hole ring

When the water is started, water is usually leaked from the lower part of the hole ring and gushes. The common engineering adopts clay to backfill the lower part of the hole ring to stop water, but has no strength in the later period. Therefore, the method is optimized for the problem, cement is laid on the lower portion in the tunnel ring, the water burst and sand burst conditions during starting can be effectively prevented, and the cement has certain strength after solidification, so that the starting posture of the shield is good, and the starting safety is ensured.

According to the shield launching construction method under the geological condition of the water-rich sand layer, the connection between the triaxial mixing pile reinforcing area and the underground continuous wall cannot be very tight, and the water stopping effect cannot be guaranteed, so that the RJP high-pressure jet grouting pile is added between the triaxial mixing pile reinforcing area and the underground continuous wall for reinforcement, and compared with a common high-pressure jet grouting pile, the RJP high-pressure jet grouting pile is ultrahigh-pressure jet, and the reinforcement effect is better.

Horizontal exploratory holes are formed in the position of the tunnel portal before starting, the horizontal exploratory holes can determine the water stopping effect of the reinforcing body, if water leakage occurs, double-liquid slurry can be adopted for horizontal grouting, and water stopping can be performed quickly and efficiently.

When the water is started, water is usually leaked from the lower part of the hole ring and gushes. The common engineering adopts clay to backfill the lower part of the hole ring to stop water, but has no strength in the later period. Therefore, the problem is optimized, cement is laid on the lower portion in the tunnel ring, the water burst and sand burst conditions during starting can be effectively prevented, and the cement has certain strength after solidification, so that the starting posture of the shield is good.

The method of the invention brings the following benefits:

1. economic benefits

The RJP high-pressure jet grouting pile is additionally arranged between the underground diaphragm wall and the triaxial mixing pile, underground water is effectively cut off, meanwhile, a horizontal supplementary grouting construction process is used, the weak link that the underground diaphragm wall is easy to leak water is strengthened, safety and controllability of stratum and a tunnel face in the shield starting construction stage are ensured, and losses caused by end stratum settlement, water burst and sand gushing are avoided. The construction method saves a large amount of manpower, material resources, financial resources and construction period investment caused by end stratum settlement, water gushing and sand gushing, and has direct economic benefit of 100 ten thousand yuan and remarkable economic benefit.

2. Social benefits

The RJP high-pressure jet grouting pile is additionally arranged between the underground diaphragm wall and the triaxial mixing pile, underground water is effectively cut off, meanwhile, a horizontal supplementary grouting construction process is used, the weak link that the underground diaphragm wall is easy to leak water is strengthened, safety and controllability of stratum and a tunnel face in the shield starting construction stage are ensured, and losses caused by end stratum settlement, water burst and sand gushing are avoided. The starting process has no water burst and sand burst, the shield machine has good posture, the smooth starting of the shield is ensured, the owner gives high evaluation, and good social benefit is obtained.