In this paper, the application of grouting method in shield tunnel crossing has been deeply discussed. Combined with the engineering example of shanghai metro line 4 shield advancing through Line 2 (already in operation), based on the investigation of engineering geological conditions, strict theoretical calculation is made and the construction scheme is determined. In the process of implementation, the weak interlayer between the two tunnels is reinforced by "subsection, ring jump, hole jump, single hole layered multi-high pressure split grouting technology"
Keywords: grouting; Shielding propulsion; Crossing; Has been operated; tunnel
Shanghai metro line 4 Zhang Yang Road Station-Pudian Road Tunnel is located under century avenue and Fushan Road, starting from Zhang Yang Road Station (next to Dongfang Road Station of Metro Line 2) in the north and reaching Pudian Road in the south, with a total length of 670m m. According to the provided line plan and longitudinal section, this section of tunnel crosses Metro Line 2 at the intersection of Weifang Road, Fushan Road and century avenue. In order to ensure the safety of this section of the tunnel and the operating subway line 2. In addition to the necessary measures required in the process of shield propulsion, the soft soil interlayer between short-distance tunnels must be reinforced.
1 reinforcement measures
In the process of shield propulsion, it will cause an uncertain amount of over-excavation (or under-excavation) and disturbance to the surrounding soil, thus causing a certain amount of settlement impact on the ground and underground structures near the tunnel axis. Metro Line 2 is located above the tunnel of Line 4, with the shortest distance of 1.045m, and the tunnel of Line 4 intersects with the tunnel of Line 2 in operation with a radius of 379.85 1m, which will increase the disturbance and overbreak of soil around the tunnel. Although synchronous grouting is strictly controlled in the process of propulsion, it is an inert slurry. Considering many unfavorable factors such as long setting time, low strength and instability of inert slurry, it is necessary to reinforce the soft soil interlayer between the two tunnels at close range after the shield successfully crosses Line 2. After many arguments, the feasibility, safety and controllability of the reinforcement construction are fully considered, and finally the double liquid grouting reinforcement is selected. Grouting reinforcement uses grouting holes on segments. Grouting reinforcement is carried out in four steps:
(1) After the shield construction of the tunnel, on the premise of ensuring that the grouting will not affect the shield propulsion, the tunnel is reinforced by double-liquid synchronous grouting. The concrete implementation is as follows: the grouting holes are reserved from the upper part of the tunnel in the 5 ~ 8 ring behind the shield tail for synchronous grouting, and the grouting holes are reserved from the lower part of the tunnel in the 10 ring behind the shield tail for synchronous grouting.
(2) In the process of synchronous grouting construction, in the construction section that has an influence on Metro Line 2, a proper amount of grouting pipe is embedded from the reserved grouting hole at the top of the tunnel within 90, and the embedded depth of grouting pipe is tentatively set at 3m. If the hole location is less than 3m away from the outer wall of metro line segment 2, the embedded grouting pipe depth is about 20cm away from the outer wall of metro line segment 2. After the embedded grouting pipe is driven, according to the monitoring data and actual requirements, it is ready to carry out tracking grouting reinforcement at any time, so as to achieve the purpose of protecting Metro Line 2 and play a certain role in rectifying the deviation when the deformation is large.
(3) During and after the synchronous grouting construction, the inert grout in the construction section that has an impact on Metro Line 2 is reinforced by displacement grouting (displacement grouting reinforcement is double liquid grouting), so that the inert grout is completely replaced, and the reinforcement scope of displacement grouting is 0.5m outside the section.
(4) After the tunnel replacement grouting construction is completed, the soft soil between the two tunnels in this section is reinforced by double liquid grouting. The reinforcement section is 34 1 ~ 45 1 ring of the down tunnel and 1 14 ~ 239 ring of the up tunnel. The construction scope is the soil above 5 reserved grouting holes at the top of the tunnel within 90 degrees below the center line of Metro Line 2. The reinforced soil should have good uniformity and low permeability coefficient, and the strength of the soil after grouting reinforcement should be ≥ 1.2MPa. After the two tunnels are advanced, according to the measured data, the reserved grouting holes can be opened for re-grouting in the parts with large deformation to control the deformation.
2 simulation experiment
Before the shield crosses Metro Line 2, two rows of deep settlement monitoring points are arranged on Fushan Road to simulate the settlement of the existing tunnel when the shield crosses Metro Line 2 and guide the construction parameters when the shield crosses Metro Line 2.
Due to the influence of the actual situation of the road surface in the simulated propulsion section, after consultation with the pipeline and road management departments, according to the principle of symmetry of the settlement tank, the points are arranged unilaterally from the tunnel axis. The specific locations are located at Z32 1, Z324, Z330, Z345, Z350 and Z355, with each row of 1 ~ 2 measuring points, and the depth of the measuring points is1.40m. The purpose of simulated propulsion is to test the actual effect of all active technical protection measures of shield propulsion and the synchronous grouting of inert slurry after shield propulsion. Double-liquid synchronous grouting, displacement grouting, soil reinforcement grouting and tracking grouting effect are adopted to guide the formal crossing construction. The main detection indicators are ground subsidence and vertical displacement of 1.4m soil layer above the shield.
The simulated propulsion length is 20m, the front influence zone is 20m, and the rear influence zone is 10m, * * * 50m.
When the shield is pushed into the simulation area, the measuring point has a continuous and slow lifting process before the shield is pushed through the deep monitoring point, and a continuous and slow settlement process after the shield is pushed through the deep monitoring point. When the cumulative settlement of points SC32 1, SC324 and SC330 changes from positive value to negative value, grouting and grouting construction will be started at the top of the tunnel in the above areas. When the cumulative settlement of SC345 is close to zero, grouting and grouting construction will be started at the top of the tunnel in the corresponding area of SC345. When there is an obvious trend of settlement acceleration at SC350 and SC355, grouting and grouting construction will be carried out at the top of the tunnel in the corresponding area of SC350 and SC355.
Grouting construction is based on the principle of small amount and multiple times. When the measuring point just emerges from the tail of the shield, the settlement speed of the measuring point is faster. Grout 1 ~ 2 times a day, and the grouting amount is 400L/ hole each time. After grouting for many times, the settlement speed of the measuring point slows down, and grouting is changed to once every 2 ~ 3 days, and the grouting amount is 400L/ hole each time; After the measuring point is stable, grouting construction will not be carried out.
According to the settlement observation records, after grouting and grouting, the observation point has obviously picked up, and settled again after a period of stability, but the settlement speed has obviously slowed down. Grouting construction should be carried out in several times, and after each grouting, the measuring point should be stable and slightly improved. The lifting amount of single grouting shall be controlled at 1.0 ~ 2.0 mm for many times, so as to achieve the purpose of stability.
According to the simulation results, the settlement of Metro Line 2 can be controlled within 3 ~ 4 mm by synchronous supplementary grouting when the tunnel segment is completely separated from the shield tail and its back auxiliary equipment, which creates favorable space-time effects for subsequent replacement grouting, soil reinforcement grouting and follow-up grouting. In the subsequent grouting construction, Metro Line 2 will gradually return to its original position.
3 key points of construction technology
(1) Selection and arrangement of grouting holes: This time, double grouting holes are arranged in the reserved holes of the upper tunnel 1 17 ~ 239 ring, the lower tunnel 34 1 ~ 45 ring, the standard and adjacent bid sections embedded parts1and embedded parts 4.
Firstly, the reserved hole is dredged by impact drill, and the grouting pipe vibration of 1.5m is inserted into the hole to the outside of the tunnel wall by displacement grouting; Grouting to reinforce soil and subsequent grouting: insert 1.0m grouting pipe into the tunnel and vibrate the wiring to the required depth outside the tunnel wall. Install the special blowout preventer immediately and connect the one-way ball valve to the grouting pipe for grouting. If there is slurry leakage or groundwater, first install the blowout preventer in the reserved hole, connect the one-way ball valve, and directly drive the grouted seamless steel pipe with leak-proof sealing ring into the grouting hole to the designed depth to prevent groundwater or slurry leakage.
(2) Construction technology. The construction process of synchronous grouting is shown in figure 1.
Construction process of replacement grouting, soil reinforcement grouting and subsequent grouting: determining the hole position → dredging the reserved hole → vibrating grouting pipe → placing the BOP → preparing slurry → grouting → pulling out the pipe → injecting closed slurry into the orifice → flushing the slurry pipe for replacement.
(3) Double-slurry ratio: In order to minimize the impact of grouting technology on the surrounding environment of Metro Line 2, through calculation and experiment, the slurry ratio with shrinkage less than 5% is selected as: liquid A is water: cement: fly ash: bentonite =100kg:100kg:. The second solution is 30-50kg of No.35 sodium silicate.
If grouting holes need to be opened several times for repeated grouting, after the completion of double-liquid grouting construction, an appropriate amount of sealing slurry is injected into the hole area to ensure that the grouting holes can be opened smoothly when grouting again.
(4) Construction technical parameters:
Grouting pressure: ≤ 0.5 MPa;
Grouting flow:10 ~15l/min;
Grouting quantity: 200 ~ 400 L/ hole (synchronous grouting and displacement grouting);
Initial setting time of double liquid slurry: 30 ~ 45s.
(5) In the process of slurry formation, transportation and grouting, synchronous grouting, tracking grouting and secondary displacement grouting are carried out. The grouting equipment is behind the shield machine, and the materials are transported into the tunnel by the battery truck, and grouting can be carried out at any time as needed.
During the construction of soil reinforcement and grouting in the crossing area, the shield propulsion has been completed, and it goes out through the reserved hole of rail transit line 4 of metro line 2. Due to the limited space in the subway tunnel, only the head openings at both ends of the subway station are connected to the ground, which brings difficulties to the transportation of construction equipment and materials. According to the specific situation, take the following measures:
(1) refining mixing: refining mixing is set, and liquid A and liquid B are prepared respectively according to the specific proportion of slurry and stored in refining storage barrels.
(2) slurry conveying by slurry conveying pipe: the prepared slurry A and slurry B are respectively conveyed into the tunnel through slurry conveying pipes.
(3) Mixing in the hole: Mix the liquid A and the liquid B conveyed through the slurry conveying pipe according to a certain proportion, and immediately inject them into the hole with grouting pump.
④ Grouting sequence: In order to reduce slurry leakage and grouting pressure, the construction shall be carried out in sections, with every 50 rings as a construction section, and each section shall be constructed in the form of one ring jumping three rings, and each ring shall be constructed with 2-3 holes with balanced stress. Displacement grouting is suitable for the construction of a ring separated by three rings. At the same time, adjust the grouting quantity and pressure according to the monitoring situation. After grouting, pull out the grouting pipe and close the orifice.
(6) Grouting pressure and flow control: the grouting pressure is controlled below 0.5MPa, and the grouting flow is controlled between 10 ~ 15l/min.
(7) Grouting quantity control: according to the monitoring data, adjust the grouting quantity within the range of 200 ~ 400 L/ hole, and control the grouting according to the specified lifting quantity in combination with the monitoring data. Displacement grouting grouting quantity is 400L/ hole, 2400L/ ring; At the same time, control the grouting pressure. Tracking grouting quantity depends on actual requirements. The grouting amount of double liquid grouting is adjusted according to the volume of each section of reinforced soil and soil to be reinforced. ④ and ⑤- 1 layer soil Ps value increased by about 1 times. According to the construction experience, the grouting amount is 20% of the reinforced soil volume (that is, the cement content is about 5.5%), and the grouting pressure is controlled at the same time. Each hole is divided into six grouting sections, one for each construction, and the grouting quantity of each grouting reinforcement section is as follows:
①5.6 ~ 6. 1m:0.276 m3； ②5. 1 ~ 5.6m:0.252 m3； ③4.6 ~ 5. 1m:0.229 m3； ④4. 1 ~ 4.6m:0.205 m3； ⑤3.6 ~ 4. 1m:0. 18 1m 3； ⑥3. 1 ~ 3.6m:0. 158 m3； The total amount of grout injected into each hole is 1.305438+0m3. ⑤-2 layer soil has a high Ps in undisturbed soil, so the amount of mud can be appropriately reduced during grouting.
(8) Selection of grouting time: In addition to the large deformation of the tunnel of Line 2, which needs to be corrected in time, the grouting time should be selected from 23: 00 to 6:00 the next morning when the subway line 2 is stopped, so as to ensure that the injected double grout has a certain solidification time and improve the reinforcement effect.
(9) Problems and solutions in engineering construction:
① Blowout prevention: The underground water outside the tunnel is very rich, and there is even confined water in some places. When dredging reserved holes and placing grouting pipe, special blowout preventers are adopted to prevent groundwater leakage and injection and ensure tunnel safety; At the same time, in the process of grouting, ensure that the initial setting time of the injected slurry meets the matching requirements, so that the slurry can solidify as soon as possible and reduce the leakage of groundwater and slurry.
② Slurry leakage: In concrete construction, after grouting pipe is inserted into the reserved grouting hole, there may be slurry leakage, slurry leakage and slurry leakage along the adjacent hole outside grouting pipe. Use special blowout preventer to prevent blowout and leak stoppage. After the construction, after the initial setting of the double slurry, pull out the grouting pipe, clean the orifice, seal it with a special cover, and clean up the site.
(3) The reserved hole of the adjacent block on the top wall is higher than the ground, which is not conducive to the construction. Solution: For the standard block and adjacent block with a certain distance from the bottom of the tunnel, the construction difficulties are solved by building a movable working platform on site.
4 Construction monitoring
Arrange measuring points in the tunnel and ground of Line 4 to track and monitor the whole grouting process and delay monitoring after grouting; An electronic level is set in the tunnel of Metro Line 2 for 24-hour real-time monitoring. In order to minimize the impact of grouting on the 4# line tunnel, the 2# line subway and the surrounding environment, the construction parameters and construction sequence are adjusted in time according to the measured data to realize information construction.
5 concluding remarks
In the construction of Shanghai subway, shield method is used to cross the completed and put into operation subway tunnel. Only Metro Line 2 of People's Square Station has crossed Metro 1# once before. But in the end, the crossing area is close to the station, and the crossing form is orthogonal, which has little influence on 1# line, and being close to the station provides very convenient conditions for rectification and reinforcement. However, the crossing area is located in the middle of the tunnel section far away from the station, with a large buried depth and poor soil quality, and the crossing form is a small angle arc oblique crossing. The influence distance on the tunnel is long, and the overbreak of earthwork in the arc section intensifies the disturbance to the soil and poses a great threat to the tunnel.
After repeated verification and demonstration, the above reinforcement and protection scheme is finally determined, and the effectiveness and feasibility of the scheme are verified by the simulation experiment section. The subway protection requirements put forward by Shanghai Metro Monitoring Company are: the cumulative deformation during tunnel construction should not exceed 3 mm, and the cumulative deformation within 1 year after construction should not exceed 5 mm. During the implementation, with our efforts and the assistance of relevant parties, the cumulative deformation during tunnel construction should be controlled within 2 mm, and the maximum measured cumulative deformation after completion 1 year is -2.3mm, which is far better than the protection requirements, and the project is successful.
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