Research and excavation technology of composite shield in soft and hard uneven stratum?

The following is the research and excavation technology of composite shield in uneven soft and hard strata brought by Zhong Da Consulting, for your reference.

Aiming at the shield construction in the soft and hard uneven stratum between Yuexiu Park and Sanyuanli of Guangzhou Metro Line 2, the design idea of composite shield is put forward, the function and technical parameters of composite shield are studied, and the adaptability of cutter head and cutter to geology is analyzed. The principle, tunneling parameters and mode conversion technology of composite shield tunneling are studied, and the technical problems such as difficult tunneling, low efficiency, high cost and difficult control of stratum deformation in uneven soft and hard strata are solved. In order to effectively control the heading direction and shield posture, the reasons for the deviation of the heading direction of shield are analyzed, and the corresponding control methods are studied to prevent the segment from cracking and control the wrong platform. In order to prevent the phenomenon of "mud cake" and "water gushing" in the excavation of cohesive stratum, the corresponding muck improvement technology is studied. Through the study of synchronous grouting technology in annular gap of shield tail, reliable technical measures are taken and construction monitoring is strengthened. Change excavation parameters in time, control stratum deformation, and ensure the normal operation of Beijing-Guangzhou railway and the safety of adjacent buildings and structures.

1 Introduction

In this paper, the shield construction in Yuexiu Park-Sanyuanli (hereinafter referred to as Yuesan) section of Guangzhou Metro Line 2 is taken as the research object. The stratum is uneven in hardness and softness, in which moderately weathered rock (8) and slightly weathered rock (9) with high strength and good stability account for the majority, and the maximum uniaxial compressive strength of the rock is 78.2MPa. At the same time, the tunnel body also passes through unstable strata such as strongly weathered rock (7), completely weathered rock (6) (soil-like), residual soil layer (5) and fault fracture zone. And the stratum interface fluctuates greatly, and the rocks generally contain gravel, which seriously wears tools. See figure 1 for the geological profile and figure 2 for the statistics of each layer. Because of the existence of high viscous soil layer in the stratum, mud cake is easy to form in front of the cutter head during shield tunneling, which seriously affects the tunneling. At the same time, when crossing the water-rich fault fracture zone, water inrush may occur during construction.

The ground traffic is busy and buildings are dense in the crossing area of the third section of the tunnel in March. There is a 135 building above the tunnel, and the bottom of the pile foundation is only 0.56m away from the nearest tunnel. There are 3/kloc-0 buildings whose pile foundation is only 0.56 ~ 2.00 m away from the top of the tunnel. There are many types of pile foundations and different strata. The tunnel with a length of about 165m will cross the Guangzhou Railway Station 14 track, and the pile foundation of pedestrian bridge and the underground passage of post and telecommunications in the station are only 3 ~ 5 m away from the top of the tunnel.

In order to solve the technical problems such as difficulty in tunneling, low efficiency, high cost, and difficult control of tunneling direction and stratum deformation, it is necessary to study the composite shield and the conversion technology between tunneling methods, tunneling parameters and tunneling methods, as well as the corresponding attitude control technology, muck improvement technology and stratum deformation control technology.

Study on composite shielding

2. Functional design of1composite shield

It is the first time to use shield method in such a complex stratum in China, and it is also very rare in the world. However, only a few projects have not been well solved, such as CCL 1 Metro in Singapore, Porto Light Rail Tunnel in Portugal and Guangzhou Metro 1 Line of Japanese companies. When earth pressure or slurry shield is used in construction, some unstable uneven soft and hard strata with great strength difference are encountered, and the progress is slow, and many accidents such as stratum collapse and even building collapse occur. Therefore, it is of great significance to develop composite shield and its supporting technology which can adapt to the construction of complex and changeable uneven soft and hard strata, to ensure the safe, high-quality and efficient completion of the crossing project of the third bid section and to promote the improvement of shield method technology in China.

According to the geological and environmental conditions of the third section of the third lunar month, it is required that the shield machine must have the ability to crush rocks in various strata, control formation deformation, prevent water gushing, flexibly adjust posture and prevent mud cake on the cutter head. TBM and traditional shield cannot have these functions at the same time. Therefore, the design idea of composite shield is put forward, and the function design of composite shield is carried out by organically combining the rock breaking principle of hard rock boring machine with the principle of soft soil shield tunneling and stable working face [1 ~ 6]:

(1) In view of the problem of rock breaking in various strata, the shield machine must be equipped with a composite cutter head, so that rolling rock breaking and cutting rock breaking can be used separately or mixed, and hob and toothed cutter can be used interchangeably or mixed.

(2) In order to stabilize the working face and control the stratum deformation, the shield machine must be equipped with three modes: earth pressure balance, open mode and semi-open mode, and each mode can be interchanged to provide stable working face pressure as required; It is necessary to have the function of synchronous grouting to fill the annular space as soon as possible and control the groundwater loss.

(3) In order to prevent mud cake, the shield machine must be equipped with foam injection system, and the cutterhead has an inverted splayed opening, and foam is injected in front of the cutterhead, the soil chamber and the screw conveyor to improve the fluidity of the muck and facilitate the muck to enter the soil chamber.

(4) In order to prevent "water gushing", the shield machine must be equipped with a muck improvement system and two screw conveyors, so as to improve the watertightness of muck, prevent groundwater from flowing in and establish a "soil plug" effect.

(5) Aiming at the problem of heading direction control, the shield machine must be equipped with an automatic guiding system, a follow-up articulated device and a zone-controlled propulsion cylinder. Real-time indication and control of walking posture, flexible steering and rectification.

(6) In view of the wear problem of cutter head, cutter and unearthed mechanism, the shield machine must be equipped with muck improvement system and back-mounted cutter. Improve the fluidity of muck, and rationally allocate and safely replace tools according to the stratum conditions.

2.2 Design of main technical parameters of composite shield

(1) shield tail clearance

Shield tail clearance includes: theoretical minimum clearance, allowable segment assembly error, shield tail manufacturing error, shield tail structural deformation and shield tail sealing brush structural requirements, etc.

After calculation, the theoretical minimum clearance is b1=10 mm; Segmentation accuracy and assembly error: B2 = 5mm；; Manufacturing error of shield tail: b3 = 5mm；; Deformation of shield tail: b4 = 5mm；; Others: b5 = 5mm；; Installation of shield tail seal brush: b6=45mm. Total clearance of shield tail: b=75mm.

(2) Thrust

The external load of the shield is calculated according to the loose earth pressure at the maximum buried depth and the earth pressure generated when the height of the whole soil column is twice the diameter of the shield, and the maximum of the two is taken. Shield thrust should include: in the earth pressure balance mode, there are

The total thrust is calculated as follows: EPB mode 22478kN；; The TBM mode is 18422kN. According to the experience, when the shield turns uphill, the shield thrust is considered to be 1.5 times that of the straight horizontal section. In the third quarter, the actual thrust of shield machine is 342 10kN, which can meet the needs of shield machine.

(3) Torque

The torque when moving forward in soft soil includes: cutting torque, main bearing rotation torque caused by the dead weight of cutter head, rotation resistance torque caused by cutter head thrust, reaction torque caused by cutter head thrust, friction torque generated by sealing device, friction torque at the front end of cutter head, friction torque behind cutter head, shear torque of cutter head opening and disturbance torque in earth pressure cavity. The calculated total torque is 4475 kn m.

The torque when moving forward in hard rock includes: the rolling resistance torque of cutter head, the torque required for stone slag mixing, and other torques generated by overcoming the self-weight of cutter head. The calculated total torque is 2347 kn m.

The actual driving torque of the cutter head equipped with the shield machine in the third stage of March is 4500 kn·m, which is greater than the previous calculated value and meets the needs.

(4) The digging ability of the screw conveyor

The theoretical value of excavation capacity required for shield excavation is

Where: d is the tunneling diameter of the shield machine, Vmax is the maximum tunneling speed of the shield machine, and ζ is the loose coefficient of muck.

The calculated theoretical excavation amount is 238m3/h, and the actual excavation amount of shield crossing in the third section is 300m3/h, which meets the requirements.

(5) Calculation of shield tunneling speed

In hard rock area, the tunneling speed of shield machine per revolution is v 0 = 6 ~ 10mm/ revolution, the maximum speed is 6r/min, and the tunneling speed should be 60mm/min；; ; In soft soil area, the maximum propulsion speed of shield machine is the maximum design propulsion speed of propulsion cylinder, that is, 80mm/min.

2.3 Research and design of cutterhead cutter

Through mechanical analysis, a large number of data such as rock fracture angle, rolling notch, edge between rock notches, tool wear and damage are statistically analyzed. During the construction of Guangzhou Metro, the hob spacing and the relative height difference between hob, cutter and panel were optimized. The cutters for the third shield crossing are (1) 65438 double-edged hob and 6 double-edged center cutter, both of which are used for hard rock excavation. (2) There are 6 sun gear cutters and 8 spur gear cutters for soft soil excavation. They are back-mounted, and can be replaced by central gear cutters. The blade height is 140mm. (3) 64 knives and soft soil knives are installed on one side of the slag discharge port, which can also be used for scraping slag in hard rock excavation. The knife height is 140mm. (4) There are 32 arc scrapers, which are soft soil cutters around arc cutterheads and can also be used to scrape slag under hard rock excavation. (5) 1 profiling cutter: used to enlarge the tunnel section locally, with a stroke of 80 mm ..

3 tunnel mode conversion and attitude control technology

3. 1 Basic principle of driving mode

There are three tunneling modes of composite shield: open, semi-open and earth pressure balance.

(1) Open: a shield tunneling mode that does not need to keep any pressure in the earth cabin. When the stratum through which the shield passes has good stability, and the excavation has little impact on the surrounding environment or less groundwater, the open excavation method can be used for excavation.

(2) Semi-open: Although the tunnel face has a certain self-stabilizing ability, it cannot be completely self-stable, or there is a certain amount of groundwater in the tunnel face, so it is necessary to establish a certain pressure in the tunnel face to prevent groundwater from entering the soil bin and reduce soil erosion. In order to reduce the torque of cutter head rotation, it is only necessary to keep a small amount of muck (generally 1/2 ~ 2/3) in the soil chamber, and then inject compressed air or foam into the soil chamber to assist excavation. This is a semi-open mode.

(3) Earth pressure balance type: During shield excavation, the earth pressure and groundwater pressure on the excavation surface are balanced by the pressure generated by excavating the soil in the muck bin or filling auxiliary materials, so as to maintain the stability of the working face and avoid the surface subsidence caused by the collapse of tunnel face or excessive water loss in the stratum.

3.2 Tunnel Mode Conversion Technology

(1) Open to semi-open conversion

Mainly to ensure that the air pressure can be maintained in the slag chamber, and the height of slag in the slag chamber should be 2 ~ 3m higher than the upper part of the feed inlet of the screw conveyor. In the process of conversion, the rotating speed of the screw conveyor should be appropriately reduced to make the slag speed less than the slag cut by the driving speed, so that the height of the slag in the slag bin can be raised to the height required for air pressure balance, and then compressed air is injected into the slag bin to establish the required air pressure.

(2) the transformation from semi-open to open

The key is to reduce the pressure in the slag chamber as soon as possible and at the same time reduce the height of slag in the slag chamber. Therefore, it is necessary to improve the speed of the screw conveyor and increase the opening of the conveyor outlet to facilitate the discharge of slag.

(3) Open conversion to earth pressure balance type

The key is to establish the required earth pressure as soon as possible. In the process of conversion, it is generally to stop the slag discharge of the screw conveyor first, so that the cut slag can fill the space in the slag bin as soon as possible to maintain the stability of the working face and stratum. When the earth pressure in the slag chamber reaches the design earth pressure value, start the screw conveyor to discharge the soil and discharge the slag. Under the earth pressure balance mode, the slag discharge speed is balanced with the amount of slag cut by the excavation speed.

(4) The earth pressure balance type is changed to open type.

The key is to reduce the earth pressure in the slag chamber as soon as possible and increase the rotating speed of the screw conveyor, so as to improve the slag discharge speed, reduce the pressure in the slag chamber and reduce the torque required for the rotation of the cutter head, thereby increasing the rotating speed of the cutter head, reducing the total thrust, effectively increasing the driving thrust and improving the driving efficiency.

(5) Semi-open earth pressure balance conversion.

The main purpose is to prevent groundwater from infiltrating into the slag chamber and provide sufficient equilibrium pressure when the formation is unstable. Therefore, the space occupied by compressed air in the slag chamber must be replaced by muck. In the process of conversion, the slag discharge speed of the screw conveyor should be reduced to increase the pressure in the slag chamber, so that the air in the slag chamber can escape into the stratum, thus establishing the earth pressure balance tunneling mode.

(6) Earth pressure balance type to semi-open type.

Compressed air is mainly used to replace the muck in the upper part of the slag chamber, so in the process of replacing the air with muck, the slag discharge speed should match the sum of the amount of muck cut by the driving speed and the amount of compressed air injected.

3.3 Causes and Solutions of Course Deviation

The main factors affecting the parameters of shield tunneling direction deviating from straight line [6, 7]:

(1) shield machine's own factors. The image of the weight distribution of the shield machine is described as "top-heavy", and it is not enough to maintain the posture of the shield only by driving thrust and friction of the working face. Therefore, the shield itself tends to "bow its head". By increasing the thrust of the lower part of the shield, the shield can move forward smoothly.

(2) The influence of geological factors. During the construction, the main shield machine has the inertia of shifting to the softer side of the stratum due to the uneven hardness of the stratum in the section and the great change of thrust and torque. We should grasp the stratum distribution and the change of stratum interface in the heading face in advance, and make a preliminary heading parameter scheme.

(3) the operation level of personnel. Due to the different technical level and job responsibilities of operators, the heading direction often deviates greatly. Therefore, it is necessary to formulate strict operating procedures.

(4) The influence of the front body and tail of shield passing through the middle folding angle of articulated cylinder. Usually, the gap between the shield tail and the segment ring that has not separated from the shield tail is required to be uniform along the periphery, which is beneficial to the control and adjustment of the heading direction.

(6) Error of guidance system. For the error of control points, it is mainly through multi-level measurement and recheck to eliminate the error. According to the above deviation control method, the statistical data of shield construction deviation in the third interval is obtained, and the deviation of shield tunneling direction in the later period is effectively controlled, basically within the range of 50mm, as shown in Figure 3.

4 muck improvement technology

4. 1 The role of muck improvement

According to the experience at home and abroad, in shield construction, especially in uneven soft and hard strata, muck improvement is an indispensable and important technical means to ensure the safe, smooth and rapid shield construction. The specific functions are as follows: (1) The muck has a good earth pressure balance function, which is conducive to stabilizing the excavation face and controlling the surface subsidence; Make the sludge have better water-stopping performance and control groundwater loss; Make the cut muck enter the soil bin smoothly and quickly, which is beneficial to the smooth soil discharge of the screw conveyor; Can effectively prevent soil slag from adhering to the cutter head to generate mud cakes; It can prevent or reduce the gushing phenomenon when the screw conveyor unloads soil; It can effectively reduce the torque of cutter head and reduce the wear of cutter head, cutter and screw conveyor.

4.2 Sludge improvement technology under different geological conditions

(1) When excavating sandy cohesive soil and completely, strongly and moderately weathered argillaceous siltstone, it is mainly to stabilize the excavation surface, prevent the cutter head from producing mud cakes and reduce the cutter head torque. Generally, the method of injecting foam into the knife surface and the soil bin is used to improve the muck, and foam can be injected into the screw conveyor when necessary.

(2) The main purpose of excavation in hard rock area is to reduce the wear of cutter and screw conveyor and prevent water gushing. Generally, foam with high water content is injected into the front of cutter head, soil chamber and screw conveyor.

(3) When excavating in water-bearing strata such as water-rich areas by earth pressure balance, it is mainly to prevent water gushing, prevent water gushing and reduce cutter head torque. Generally, bentonite mud is injected into cutter head, soil chamber and screw conveyor to increase the bentonite injected into screw conveyor, which is beneficial to the formation of soil plug effect of screw conveyor.

(4) When driving in sandy soil stratum, it is mainly to keep the pressure balance in the soil bin, so as to stabilize the excavation face and control the settlement of the stratum. It is planned to inject foam into the cutter head and soil bin to improve the muck. The foam injection amount is determined according to the specific situation.

4.3 Foaming agent waste residue improvement technology

(1) Use of foaming agent

Foaming agent is usually prepared according to 1% ~ 6%, which is soluble in water. It can also be adjusted according to the particle gradation, uneven coefficient, driving speed, driving thrust and torque of the excavated soil.

(2) injecting foaming agent

Injection mode: semi-automatic operation mode and automatic operation mode can be selected for injection of foaming agent.

Injection rate: In general, the minimum injection rate of foam is 20%, and when the muck is sticky, the minimum injection rate of foam is not less than 30% to prevent mud cake or warehouse blockage. In the actual construction process, the injection amount of foam should be adjusted according to the observation of muck during excavation, and the most critical factors affecting the injection amount are the liquid limit, plastic limit and water content of soil. According to experience, when the viscosity index Ic=0.5, the soil is easier to improve. Viscosity index is calculated as follows

Ic=(wL-ws)/Ip(4)

Where wL is the liquid limit of soil, ws is the water content of soil, and Ip is the plasticity index.

4.4 Analysis on Improvement Effect of Dregs

When excavating residual soil layer or fully weathered rock layer, the waste residue is improved by adding foam. The typical characteristics of the excavation process are: the muck is in a plastic state with good fluidity, and the muck has obvious water luster, which is easy to catch by hand; The slag from the screw conveyor is continuously and evenly spread on the belt conveyor, and no mud cake and spherical muck are produced; In the muck, you can obviously smell the smell of foaming agent in the muck; The consistency of muck is generally 25 ~ 40mm.

Analysis: Because the improvement effect of muck is relatively good, the shield machine shows a typical soft soil excavation parameter state in the excavation process, that is, the torque is small, the excavation speed is high and stable, and the excavation efficiency is high.

5 strata deformation control technology

5. 1 Ground subsidence control technology for shield tunneling through Guangzhou Railway Station.

This section of tunnel crosses Guangzhou Railway Station 14 track. The schematic diagram of the relationship between the tunnel and the platform is shown in Figure 4.

In order to ensure the safety of train operation, it is required that when the shield passes, the rail surface settlement value should not exceed 10 mm, the horizontal height difference between the two rails should not exceed 4mm, and the maximum lifting amount should not exceed 10mm under any circumstances.

The strata in the station area where the shield passes are mainly moderately weathered and strongly weathered strata and hard plastic residual soil strata, with a length of about 160m and a buried depth of about 15m. Due to the poor self-stabilization ability of the excavation face, the construction principles are: correct mode, reasonable earth pressure, rapid excavation, synchronous grouting, timely reinforcement, close monitoring and rapid feedback.

(1) Main control technology of surface subsidence [8]

① Shield tunneling method: Through calculation, in order to meet the strict requirements of track and surface settlement, the earth pressure balance method is adopted for tunneling.

② Synchronous grouting: synchronous grouting must be adopted, and the grouting amount is 6.5m3/ ring; Grouting pressure: (2.5 ~ 3.0) × 105pa. When determining the grouting pressure, it will be adjusted in time according to the monitoring results of surface subsidence in order to avoid causing great disturbance to the stratum and make the surface not uplift.

③ Earth pressure: In order to ensure the stability of the excavation face, in theory, the earth pressure should be the sum of static earth pressure and water pressure, and allowance should be considered.

The earth pressure in the earth cabin shall be kept above 1.5× 105Pa. If the settlement value is too large during excavation, the earth pressure should be increased appropriately.

④ Driving speed: the driving speed is controlled at 5cm/min. In order to avoid causing great disturbance to the stratum and properly control the shield thrust, the surface uplift in front of the shield is controlled below 2mm.

⑤ Shield attitude control: the horizontal snake of shield is less than 10mm/ ring; Up and down control 5mm/ ring. Reduce unnecessary formation loss.

⑥ Controlling the loss of groundwater: The loss of groundwater can easily lead to the consolidation and settlement of strata, which will lead to the large-scale settlement of the surface, and the influence range is very large. Therefore, it is required to pay close attention to the water output of the working face. Once it is found that the muck is too thin, the water is too large or the groundwater gushes out of the working face, the door of the screw conveyor should be closed immediately to establish the air pressure balance or earth pressure balance mode.

⑦ Monitoring measurement and information feedback: CZ-8Y deformation monitor (self-recording connected pipe settlement monitor) is used to continuously and automatically monitor the track. According to the monitoring information, the excavation parameters are adjusted in time to reduce the disturbance of shield excavation to the stratum and the stratum loss when the shield tail passes, and effectively control the surface subsidence.

(2) Analysis of surface subsidence results

① The ground settlement of the right line is controlled in a small range, and the deformation is stable quickly. However, the construction of the left line disturbed the surface and the settlement increased. After that, due to the high pressure in the slag chamber, the surface slightly bulges.

(2) When the left tunnel just entered the station, due to the poor stability of the stratum, the corresponding stratum loss increased, and the maximum settlement was about 5 mm. Then, due to the large earth pressure in the soil chamber, the local surface slightly swelled; After pressure adjustment, the surface subsidence is about 2mm.

③ The maximum uplift of this section is 0.6mm and the maximum subsidence is 5.4mm, which ensures the safety of train operation and structures.

5.2 Ground Subsidence Control Technology for Shield Tunneling under Adjacent Buildings

Among the buildings affected by tunnel construction, there are 29 167# building piles passing through from below, only 0.6~2.0m away from the top of the tunnel. See fig. 5 for the relationship between the tunnel and the pile foundation of 167# building. How to accurately predict and control the influence of tunnel construction on pile foundation and take measures to protect the safety of buildings during construction is quite difficult. By adopting the correct tunneling method, reasonable tunneling parameters, synchronous grouting and other technologies, the construction monitoring is strengthened, and the tunneling parameters are changed in time according to the feedback information of deformation speed and deformation amount, and the building foundation is strengthened. The settlement duration curve of building measuring points is shown in Figure 6. The final settlement is controlled within 5mm, the settlement speed is controlled within 1mm/d, and the later settlement is very small. It shows that the construction parameters used in the study are reasonable, and the shield construction has little influence on the surrounding buildings, which ensures the safety of the shield passing through buildings such as 167# [9].

Synchronous grouting technology in annular space 6

Synchronous grouting method for annular gap of shield: synchronous grouting is carried out through synchronous grouting system and grouting pipe at the tail of shield, and the gap at the tail of shield is formed while the shield is advancing. Grout fills the gap at the tail of the shield in time, so that the surrounding rock mass can be supported in time, which can effectively prevent the rock mass from collapsing and control the surface subsidence. The stability of the stratum is poor, and the importance of synchronous grouting is more obvious when EPB mode is used for tunneling.

6. 1 grouting material test

After five field tests, the mortar mixture ratio was continuously adjusted and the test results were analyzed. It can be seen from the test data that the consistency, decantation rate and 1d strength of several groups of mortars tested earlier basically meet the requirements, but the fluidity of mortars does not meet the requirements, and the unit price of mortars is high, which is not conducive to reducing production costs [10].

According to the situation of the construction site, in order to meet the requirements of different stages of construction, after repeated tests and adjustments, the following three groups of slurry ratios are obtained, as shown in table 1.

6.2 Shield Annular Gap Grouting Technology

6.2. 1 Main technical parameters

(1) Selection of grouting materials

According to the field test of grouting materials, both synchronous grouting and instant grouting materials are cement mortar, as shown in table 1 [10,1].

(2) Selection of grouting parameters

Grouting pressure: According to the construction practice, the simultaneous grouting and immediate grouting pressure of the third section backing is controlled at 0. 1 ~ 0.3 MPa, and the secondary reinforcement grouting pressure is controlled at 0.3 ~ 0.5 MPa.

Grouting quantity: according to the empirical calculation formula of synchronous grouting in annular gap during shield construction;

Q=Vλ(5)

Where: V is the filling volume and λ is the grouting rate.

According to the calculation, the required grouting quantity for circumferential joint synchronous grouting is 5.65 ~ 7.82 m3/ ring. The grouting quantity of secondary reinforcement is determined according to the site conditions. According to the principle of pressure control, the grouting quantity of single hole is 2.42m3, and the grouting quantity of each circle is 7.3m3.

Grouting speed: It is determined by the performance of grouting pump and the single-ring grouting quantity, which should be adapted to the driving speed. Assuming that the driving speed is 1.5m/h, the single pump grouting speed should be controlled at 70 ~ 100 l/min. Secondary reinforcement grouting can be controlled at 10 ~ 25l/min.

6.2.2 Grouting system and construction technology

(1) grouting system

The synchronous (instant) grouting system is an automatic grouting system, which adopts two grouting pump, and is a fully hydraulic double-cylinder double-outlet piston grouting pump. After the slurry is prepared in the mixing station, it is transported to the grouting station by the mortar truck, pumped into the mortar storage tank (i.e. the mixing tank) through the hose, connected with the grouting pipeline, and grouted at a set pressure and flow rate. The grouting pipeline adopts a high-pressure hose with an inner diameter of 50mm and a common steel pipe with an outer diameter of 50mm, and the joint of the grouting hole is provided with a hoop pipe joint, a hoop gate valve and a pressure sensor. The grouting end standard also adopts the systematic automatic control program.

(2) Construction technology

In order to evenly fill the annular gap and prevent the lining from being unevenly biased, pressure grouting is carried out at four preset grouting holes at the tail of the shield at the same time, and a voltage divider is set at the outlet of each grouting hole to detect and control the grouting pressure and grouting quantity of each grouting hole, so as to obtain symmetrical and uniform grouting behind the segment.

(3) Treatment of slurry leakage phenomenon

Leakage of slurry at the tail of shield: generally, plugging method is adopted, and cotton yarn is used for plugging. Slurry leakage in tunnel face: Due to the stability of surrounding rock and other reasons, the gap between shield shell and rock face is too large, and slurry will leak into tunnel face along the outer wall of shield shell during grouting. In this case, it is necessary to inject bentonite isolation ring between shield shell and rock wall by using foam injection system to prevent grouting from flowing into tunnel face.

6.3 Influence of Annular Gap Grouting on Surface Settlement

Analysis of longitudinal ground settlement of (1) right-hand tunnel

YDK17694.5 ~ YDK17346 strata are mainly moderately weathered (8), with open excavation and instant grouting, in which YDK 1765 1 has a large surface subsidence, with the cumulative subsidence reaching 9.4. The main reason is that the grouting quantity is insufficient and the grouting filling rate is less than 1.

(2) Analysis of longitudinal surface subsidence of left tunnel.

In ZDK 17289 and ZDK 1798, water inrush occurred, and the surface subsidence increased obviously, with the maximum surface subsidence exceeding 50 mm The main reason is that the grouting quantity is insufficient, which can not effectively fill the gap between buildings, and the stratum shrinks towards the tunnel under the action of formation pressure.

7 conclusion

The research results of this paper expand the technical field of shield method, greatly broaden the geological scope of application of shield method and enrich the construction technology of tunnel shield method. It provides theoretical support and good experience cases for the application of shield method in complex geological tunnels in the future, which is conducive to promoting the further development of shield method technology in China.

The tunnel construction crossing Bid Section 3 has reached the best level at home and abroad, with the average machine hour utilization rate of 67% ~ 75%. The highest record of shield construction progress in China has been set twice-the average monthly excavation of a single shield is 236 and 33 1.4m, and the maximum monthly excavation is 405 and 562.5m When crossing Beijing-Guangzhou Railway, the ground settlement is controlled within 5.4mm and the track settlement is controlled within 2.3mm, which ensures the Beijing-Guangzhou Railway. Under the conditions of uneven soft and hard strata and complex linear, the deviation of tunnel axis is controlled within 39mm, which is within the design requirements.

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