Special-shaped freezing construction method suitable for shield butt joint asynchronous control frost heaving

Abstract

The invention provides a special-shaped freezing construction method suitable for shield butt joint asynchronous control frost heaving, and relates to the technical field of shield tunnel engineering.During shield butt joint freezing construction, an anterior shield and a posterior shield adopt asymmetric freezing, an anterior shield freezing pipe serves as a main freezing side, and a posterior shield freezing pipe serves as an auxiliary freezing side; and a freezing body formed by the previous shield freezing pipe completely envelops the butt joint position of the subsequent shield cutterhead. By designing an asymmetric special-shaped freezing hole arrangement form and combining the technical means of asynchronous freezing control, the forming time and range of a freezing wall and the bearing requirement can be effectively controlled, the requirements for shield butt joint and freezing hole drilling precision are effectively lowered, the shield butt joint frost heaving problem under a high-water-pressure strong permeable stratum is effectively restrained, and the construction efficiency is improved. The frost heaving effect on the shield body is reduced, the safety and stability of the shield shell are ensured, and safe and reliable frozen wall support is provided for subsequent butt joint excavation.

Description

Technical Field

[0001] The invention relates to a special-shaped freezing construction method suitable for shield butt joint asynchronous frost heave control, and relates to the technical field of shield tunnel engineering. Background Art

[0002] Building tunnels across rivers, lakes and seas has become the mainstream development trend today. At the same time, the distance of tunnels is also increasing. Often, one shield machine is unable to complete the excavation task. Therefore, underwater docking of shield machines has developed into one of the scientific and reasonable solutions, especially the underwater docking of ultra-large diameter shield machines has become a hot research topic.

[0003] In underwater shield docking projects, artificial freezing methods are often used to reinforce the ground at the docking point of two shield machines. However, during the formation and development of the frozen wall, the frozen soil produces frost heave, which causes a certain frost heave force to act on the shield. Due to the dismantling of the internal structure of the shield machine, the overall bearing capacity of the shield is reduced. Excessive frost heave force will cause the overall or partial instability of the shield, seriously endangering the safety of the shield structure. At the same time, during the thawing period, the more significant the frost heave effect, the more significant the accompanying thaw settlement effect. Excessive thaw settlement will cause the shield to "empty", which is extremely unfavorable to its own structure. Therefore, the frost heave effect cannot be ignored and plays a vital role in the success or failure of the project. On the premise of ensuring that the thickness of the frozen wall meets the design requirements, certain technical means need to be taken to suppress the frost heave effect.

[0004] In addition, the current super-large diameter shield has a huge cross-section. In order to improve the safety of the frozen wall, multiple circles of freezing pipes are often used for freezing operations, which means that a large number of freezing holes need to be constructed in the limited space soil, which undoubtedly greatly increases the difficulty of controlling the accuracy of the freezing hole construction. At the same time, the docking accuracy of super-large shield machines is often an important factor restricting the freezing design. The twisting and distance deviation of a few centimeters at the center of the shield will be reflected in the deviation of the upper and lower shield shell boundaries, which will have an adverse effect on the layout of the freezing pipes and the formation of the frozen wall.

[0005] At present, in shield docking projects, traditional technologies mostly adopt single-circle freezing pipes or double-row freezing pipes. Among them, single-circle freezing pipes are mostly applied to rock formations with a relatively high surrounding rock grade or soil layers with good grouting improvement effects. At this time, the main function of the frozen wall is water sealing to ensure that the adverse factors of water flow are not affected during the excavation process. Double-circle freezing pipes are often applicable to formations where the thickness of the frozen wall is small and the formation has been grouted and improved. At this time, the double-circle freezing pipes, as cold sources, simultaneously cool and freeze the soil mass, and the formed frozen wall can both bear the load and seal the water. In terms of the layout form of the freezing pipes, they often adopt a symmetrical layout, that is, the freezing pipes are arranged on both sides of the shield machines respectively, and the lengths of the freezing pipes are close to each other, and the shape of the formed frozen wall is approximately symmetrical. At the same time, the existing technology mostly adopts synchronous freezing construction control on both sides, that is, low-temperature brine within the same temperature range is circulated in the freezing pipes on both sides at the same time, and the soil layer outside the two shield machines starts to freeze synchronously.

[0006] For the technical methods introduced above, for the freezing reinforcement of large-diameter shield docking projects, the main deficiencies are as follows:

[0007] The deficiency of the symmetrical synchronous freezing method lies in that the effect of controlling frost heave is weak. After low-temperature brine is synchronously introduced into the freezing pipes on both sides, the soil mass around the freezing pipes freezes first, and then gradually completes the freezing circle to form a frozen closed body with a certain strength. At this time, the frozen soil strength formed around the freezing pipes is much greater than the unfrozen soil area between the two freezing pipes on both sides. The frost heave effect generated by the development of frozen soil will squeeze towards the unfrozen soil layer with lower strength and transfer the stress to the shield shell, endangering the safety of the shield structure. At the same time, this method has relatively high requirements for the docking accuracy of the shield and the drilling accuracy of the freezing holes. During the later construction of driving the freezing pipes, collisions are very likely to occur, resulting in damage to the freezing pipes and even the emergence of waste holes. And repairing holes also poses a great risk to the local stability of the shield shell, and there may not even be a reasonable space for hole repair.

[0008] In summary, it is necessary to design a freezing method that comprehensively considers the docking accuracy of the shield, the drilling accuracy of the freezing holes, and the influence of frost heave, so as to avoid the impact of the above problems on the safety of the frozen soil at the shield docking and the safety of the shield structure. Summary of the Invention

[0009] The present invention relates to a special-shaped freezing construction method suitable for asynchronous control of frost heave in shield docking. By designing an asymmetric special-shaped freezing hole layout form and combining technical means of asynchronous freezing control, it is possible to effectively control the formation time, scope, and bearing requirements of the frozen wall, effectively reduce the requirements for shield docking and the drilling accuracy of freezing holes, effectively inhibit the frost heave problem during shield docking in high-water-pressure and highly permeable formations, reduce the frost heave acting on the shield body, ensure the safety and stability of the shield shell, and provide a safe and reliable frozen wall support for subsequent docking excavation.

[0010] The present invention provides a special-shaped freezing construction method suitable for shield docking asynchronous control of frost heaving, including the following steps: during shield docking freezing construction, the advancing shield and the trailing shield adopt asymmetric freezing. The freezing pipes of the advancing shield serve as the main freezing side, and the freezing pipes of the trailing shield serve as the auxiliary freezing side. The frozen body formed by the freezing pipes of the advancing shield completely envelopes the docking position of the cutter head of the trailing shield.

[0011] Preferably, after the freezing condition is met on the side of the advancing shield, the surrounding soil of the advancing shield side is pre-cooled. When the drilling operation of the trailing shield is completed and the freezing condition is met, all the freezing pipes on the side of the advancing shield and the side of the trailing shield are simultaneously started for active freezing. The freezing temperature on the side of the advancing shield is always lower than the freezing temperature on the side of the trailing shield before the intersection. Pressure relief is carried out through the side of the trailing shield before the intersection.

[0012] Preferably, the freezing pipes of the advancing shield and the trailing shield are both arranged in a plum blossom pattern circumferentially.

[0013] Preferably, the row spacing of adjacent freezing pipes of the advancing shield is uniform.

[0014] Furthermore, the distance between the intersection points of each circle of freezing pipes on the side of the advancing shield and the shield shell satisfies:

[0015] D min ≤L i -L i+1 ≤D max ;

[0016] Wherein, L i is the distance from the intersection point of the i-th circle of freezing pipes of the advancing shield from the outside to the inside and the shield shell to the cutter head panel of the advancing shield. i is a positive integer, 1≤i<n, and n is the number of circles of freezing pipes of the advancing shield. L i+1 is the distance from the intersection point of the i-th circle of freezing pipes of the advancing shield from the outside to the inside and the shield shell to the cutter head panel of the advancing shield. D min represents the minimum construction distance, and D max represents the maximum construction distance.

[0017] Preferably, the length L a of the outermost circle of freezing pipes of the advancing shield satisfies the condition:

[0018]

[0019] In the formula, L 1 is the distance from the intersection point of the A-circle freezing pipes of the advancing shield and the shield shell to the cutter head panel of the advancing shield. The A-circle is the outermost circle of the advancing shield. L p is the distance between the cutter head panels after the two shields are completely docked. L q is the distance from the cutter head panel of the trailing shield to the rear partition of the bubble chamber. L 0 is the length of the end of the freezing pipe that does not participate in the circulating brine. θ aIndicates the angle between the axis of the freezing pipe in the A circle and the axis of the shield machine.

[0020] Furthermore, the length L of the freezing pipe in the middle circle of the leading shield machine b Meets the condition that:

[0021]

[0022] In the formula, L b Is the length of the freezing pipe in the B circle. The B circle is the freezing circle corresponding to the freezing holes in the middle circle of the leading shield machine. L 2 Is the distance between the intersection point of the freezing pipe in the B circle and the shield shell and the cutter head panel of the leading shield machine. L p Is the distance between the cutter head panels after the two shield machines are completely docked. L q Is the distance between the cutter head panel of the trailing shield machine and the rear baffle of the air chamber. L 0 Is the length of the end of the freezing pipe that does not participate in the circulating brine. θ b Is the angle between the axis of the freezing pipe in the B circle and the axis of the shield machine.

[0023] Furthermore, the length Lc of the freezing pipe in the C circle meets the condition that:

[0024]

[0025] In the formula, Lc is the length of the freezing pipe in the C circle. The C circle is the freezing circle corresponding to the freezing holes in the innermost circle of the leading shield machine. L 3 Is the distance between the intersection point of the freezing pipe in the C circle and the shield shell and the cutter head panel of the leading shield machine. L p Is the distance between the cutter head panels after the two shield machines are completely docked. L q Is the distance between the cutter head panel of the trailing shield machine and the rear baffle of the air chamber. L 0 Is the length of the end of the freezing pipe that does not participate in the circulating brine. θ c Is the angle between the axis of the freezing pipe in the C circle and the axis of the shield machine.

[0026] Preferably, there is a frost heave release channel between the freezing pipes of the leading shield machine and the freezing pipes of the trailing shield machine.

[0027] Preferably, the connecting line of the end points of each circle of freezing pipes of the trailing shield machine is parallel to the angle of the innermost circle of freezing pipes of the leading shield machine.

[0028] The beneficial effects of the present invention are:

[0029] The present invention relates to a special-shaped freezing construction method suitable for asynchronous control of frost heaving during shield docking. By designing an asymmetric special-shaped freezing hole layout form and combining technical means of asynchronous freezing control, it is possible to effectively control the formation time, scope, and bearing requirements of the freezing wall, effectively reduce the requirements for shield docking and freezing hole drilling accuracy, effectively inhibit the frost heaving problem during shield docking in high water pressure and highly permeable strata, reduce the frost heaving effect acting on the shield body, ensure the safety and stability of the shield shell, and provide a safe and reliable freezing wall support for subsequent docking excavation.

[0030] (1) The present invention adopts an asymmetric special-shaped freezing hole layout form, effectively reducing the requirements for shield docking and freezing hole drilling accuracy. It effectively solves the problems that the conventional symmetric layout of freezing pipes on both sides has high requirements for shield docking accuracy and drilling accuracy, and it is extremely easy to collide during the later freezing pipe drilling process, resulting in damage to the freezing pipes, and even the occurrence of waste holes. Moreover, there are also relatively large risks to the local stability of the shield shell when making up holes.

[0031] (2) Through the targeted design of the specific parameters of the asymmetric special-shaped freezing hole layout, the present invention can provide effective and practical engineering reference for existing shields, and has great significance for popularization.

[0032] (3) The present invention adopts an asynchronous control method, which is more beneficial for controlling the frost heaving effect. Because in the case of the symmetric layout of freezing pipes, the soil on both sides cools down simultaneously, and there is no obvious time difference in the formation of frozen soil. The frozen soil on both sides forms almost synchronously, showing symmetry, and the freezing pipes complete the intersection first. There is still unfrozen soil between the freezing pipes and the shield shell. At this time, a form of frozen soil wrapping unfrozen soil is formed. As the cooling capacity continues to be input, the unfrozen soil between the freezing pipes and the shield shell continues to freeze. At this time, the frost heaving effect generated cannot dissipate away from the shield shell due to the resistance of the external frozen soil, resulting in a continuous increase in the frost heaving force borne by the shield shell, threatening the shield shell structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings described herein are used to provide a further understanding of the present invention, and constitute a part of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0034] Figure 1 is the construction flow chart of asynchronous control of frost heaving of the present invention;

[0035] Figure 2 is the layout of freezing pipes for shield docking and the configuration diagram of the refrigeration system of the present invention;

[0036] Figure 3 is the schematic diagram of the spatial position of the freezing pipe layout on the rear shield side of the present invention;

[0037] Figure 4 is the 1 / 28 calculation model diagram of the present invention;

[0038] Figure 5 is the 60-day temperature nephogram of the present invention;

[0039] Figure 6 is the 67-day temperature nephogram of the present invention;

[0040] Figure 7 is the 71-day temperature nephogram of the present invention;

[0041] Figure 8 is the 75-day temperature nephogram of the present invention;

[0042] Figure 9 is the 90-day temperature nephogram of the present invention;

[0043] Figure 10 is the 120-day temperature nephogram of the present invention. Detailed implementation manners

[0044] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only a part of the implementation manners of the present invention, rather than all the implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0045] Example 1

[0046] Aiming at the main technical problems, the present invention designs a special-shaped freezing construction method applicable to shield docking asynchronous control of frost heave, reduces the docking accuracy and drilling accuracy, and at the same time combines asynchronous freezing control construction to effectively inhibit the frost heave effect, reduce the influence of the frost heave effect on the shield shell, and improve the safety of the excavation process of the docking project.

[0047] Among them, the special-shaped freezing refers to the asymmetric arrangement of freezing pipes on the leading shield and the trailing shield. During the shield docking freezing construction, the leading shield and the trailing shield adopt asymmetric freezing. The freezing pipes of the leading shield are used as the main freezing side, and the freezing pipes of the trailing shield are used as the auxiliary freezing side. The frozen body formed by the freezing pipes of the leading shield completely envelopes the docking position of the cutter head of the trailing shield.

[0048] The main technical route of the asynchronous construction of the present invention is as Figure 1As shown, after the preceding shield machine reaches the designated docking position, the internal structure disassembly starts, and at this time, the following shield continuously advances; after the following shield advances to the docking position, the disassembly of the preceding shield machine is completed, and the freezing pipe drilling operation of the preceding shield machine starts. At this time, the following shield can synchronously carry out the disassembly work; after the freezing pipe drilling operation of the preceding shield machine is completed, the soil pre-cooling starts. At this time, after the disassembly of the following shield is completed, the freezing pipe drilling operation is carried out; after the drilling of the following shield is completed, at this time, the preceding and following shields start synchronous cyclic freezing; according to the on-site monitoring results, the development of the frozen soil is judged. After it is determined through the test holes that the average temperature of the frozen soil and the thickness of the frozen curtain meet the design requirements, the excavation operation is carried out; after the excavation operation is completed, the freezing pipes are sealed, and the follow-up thaw settlement grouting is carried out.

[0049] Embodiment 2

[0050] The present invention specifically designs the arrangement form of the freezing pipes of two shield machines as follows:

[0051] As Figure 2 shown, three circles of freezing pipes are designed on each of the two shield machines. The circumferential spacing of the freezing pipe layout is adaptively designed according to the influence of the rib plates and other internal structures of the shield body. The hole spacing of a single circle of freezing holes is controlled between 1.1 m and 1.6 m. The present invention does not make other special descriptions here. In addition, in order to enhance the freezing effect and ensure that there is no conflict in the spatial position of the orifice blowout prevention device of the supporting sealing structure of the three circles of freezing pipes, the freezing pipes of the preceding shield and the following shield are both arranged in a plum blossom shape in the circumferential direction. For example, circle A and circle C are on the same axis, and circle B is located in the middle of them. Among them, circle A is the outermost circle of the freezing pipes of the preceding shield, circle B is the middle circle of the freezing pipes of the preceding shield, and circle C is the innermost circle of the freezing pipes of the preceding shield. The same is true for the following shield side.

[0052] Embodiment 3

[0053] Embodiment 3 makes further reasonable refinement settings on the basis of Embodiment 2.

[0054] Specifically, as the main freezing side, the length of the freezing pipes of the preceding shield machine should be reasonably designed. It should be noted here that the key point of the asymmetric freezing is to ensure that the frozen body formed by the freezing pipes of the preceding shield machine can completely envelope the docking position of the cutter head of the following shield machine, so as to ensure that even if there are slight deviations in the shield docking and drilling accuracy, it will not affect the implementation of the present invention, thereby reducing the influence of the shield docking accuracy and drilling accuracy, and having a wider applicability. Based on this, in the freezing pipe design of the present invention, taking the position of the diaphragm of the air bubble chamber of the following shield machine when the freezing side of the preceding pipe drills to the zero-error docking state of the shield as an example of the design, even when the docking accuracy does not reach the ideal state, this design has a large redundancy. In addition, in the above design example, it is not limited to the position of the diaphragm of the air bubble chamber of the following shield machine, and can be appropriately adjusted according to the actual situation of different embodiments.

[0055] Among them, the A - circle is the outermost circle of the freeze pipes of the advancing shield (the side far from the cutter head). Its spatial position is first used to control the thickness of the frozen curtain to reach the designed thickness H. Secondly, the row spacing between the three circles of freeze pipes affects the freezing time. Finally, fully considering the construction position of the anti - blowout device in the tunnel supporting the freeze pipes during construction. Based on the above three requirements, the included angle θ between the axis of the A - circle freeze pipes and the shield axis a should satisfy the condition: 20° ≤ θ a ≤ 25°. It should be noted here that the present invention gives an appropriate angle range rather than a specific value. However, the specific angle should be appropriately adjusted according to the above - mentioned three requirements in different embodiments. The design angles of the remaining rows of freeze pipes below are all considered in this regard.

[0056] The length L of the outermost - circle freeze pipes of the advancing shield a should satisfy the condition:

[0057]

[0058] (H - L 1 sinθ a )cosθ a ≤ v dp t;

[0059] In the formula, L 1 is the distance between the intersection point of the A - circle freeze pipes of the advancing shield and the shield shell and the cutter - head panel of the advancing shield. The A - circle is the outermost circle of the advancing shield. L p is the distance between the cutter - head panels after the two shields are fully docked. L q is the distance between the cutter - head panel of the trailing shield and the rear baffle of the air chamber. L 0 is the length of the end of the freeze pipes where brine cannot circulate, generally not more than 0.15 m. v dp is the average unilateral expansion speed of the frozen wall, with the unit of m / d; t is the freezing time, with the unit of d.

[0060] The B - circle freeze pipes are arranged in the middle of the advancing shield to ensure uniform row spacing between the three circles of freeze pipes. The included angle θ between the axis of the B - circle freeze pipes and the shield axis b should satisfy the condition: 15° ≤ θ b ≤ 20°. The length L of the B - circle freeze pipes b should satisfy the condition:

[0061]

[0062] In the formula, L 2 is the distance between the intersection point of the B - circle freeze pipes and the shield shell and the cutter - head panel of the advancing shield.

[0063] The C-ring freezing pipes are arranged in the innermost ring (close to the cutter head side) of the preceding shield tunneling machine. Their space directly affects the development of frozen soil above the excavation of the shield docking section. Considering the row spacing between the three rings of freezing pipes, the included angle θ between the axis of the C-ring freezing pipes and the axis of the shield tunneling machine c should meet the condition: 11° ≤ θ c ≤ 15°.

[0064] The length Lc of the C-ring freezing pipes should meet the condition:

[0065]

[0066] In the formula, L 3 is the distance between the intersection point of the C-ring freezing pipes and the shield shell and the cutter head panel of the preceding shield tunneling machine.

[0067] At the same time, considering the construction position of the anti-blowout device inside the tunnel supporting the freezing pipes, the distance between the intersection points of the three rings of freezing pipes and the shield shell should be controlled between D min ~D max where D min represents the minimum construction distance, and D max represents the maximum construction distance. D min usually takes the empirical value of 1 m, and D max takes the empirical value of 1.5 m. Therefore, further design is carried out for the distance between the intersection points of the three rings of freezing pipes on the side of the preceding shield tunneling machine and the shield shell:

[0068] D min ≤ L 1 - L 2 ≤ D max ;

[0069] D min ≤ L 2 - L 3 ≤ D max ;

[0070] In addition, ensure that the end hole spacing between the freezing pipes is controlled according to the specification requirements. Therefore, further design is carried out for the freezing pipes of the preceding shield tunneling machine:

[0071] d min ≤ (L 1 - L 2 ) sinθ a + L b sin(θ a - θ b ) ≤ d max ;

[0072] d min ≤ (L 2 - L 3 ) sinθ b + L csin(θ b - θ c ) ≤ d max ;

[0073] In the formula, d min represents the minimum allowable value of the end hole spacing of the freezing pipes with different lengths in the specification, and d max represents the maximum allowable value of the end hole spacing of the freezing pipes with different lengths in the specification. The freezing pipes of the trailing shield are used as the auxiliary freezing side, and its main function is to assist the leading shield side to complete the intersection of frozen soil development and jointly reduce the frozen soil temperature to the designed average temperature to meet the bearing requirements of the frozen wall.

[0074] Example 4

[0075] Based on Example 3, Example 4 designs the trailing shield to provide a frost heave release channel.

[0076] Specifically, in terms of frost heave control, to ensure that there is a frost heave release channel between the C-ring freezing pipes on the leading shield side and the freezing pipes of the trailing shield, the length of the freezing pipes of the trailing shield is further designed here. For example Figure 3 As shown, the connecting line of the end points of the three circles of freezing pipes D, E, and F is parallel to the central axis of the C-ring freezing pipes. Among them, the D-ring is the innermost circle of the freezing pipes of the trailing shield (close to the cutter head side), the E-ring is the middle circle of the freezing pipes of the trailing shield, and the F-ring is the outermost circle of the freezing pipes of the trailing shield (far from the cutter head side).

[0077] The same is true for the three circles of freezing pipes on the trailing shield side. The included angle θ between the axis of the innermost circle D of the freezing pipes of the trailing shield and the axis of the shield d should satisfy the condition: 10° ≤ θ d < θ c - 1°, and the length L of the C-ring freezing pipes d should satisfy the condition:

[0078]

[0079] L 4 - L q > X min ;

[0080] In the formula, L 4 is the distance between the intersection point of the D-ring freezing pipe and the shield shell and the cutter head panel of the trailing shield; X min is the minimum construction position of the in-tunnel anti-blowout device supporting the freezing pipes, which is adaptively matched according to the freezing pipes with different diameters.

[0081] The included angle θ between the axis of the middle circle E of the freezing pipes of the trailing shield and the axis of the shield e should satisfy the condition: θ d ≤ θ e ≤ 20°, and the length L of the E-ring freezing pipese The conditions that should be met are:

[0082] w 1 tanθ c =L d sinθ d ;

[0083]

[0084] Combining the above formulas, we can obtain:

[0085]

[0086] Where, L 5 w is the distance between the intersection of the E-circle freezing pipe and the shield shell and the rear shield cutterhead panel; 1 、w 2 、w 3 They are the projected lengths of the intersections of the parallel lines of the C circle freezing pipe and the D circle, E circle and F circle pipes on the shield.

[0087] The angle θ between the axis of the outermost ring F of the freezing pipe of the rear shield and the axis of the shield f The conditions that should be met are: e ≤θ f ≤25°, F ring freezing pipe length L f The calculation process is the same as above, and the conditions that should be met are:

[0088]

[0089] Where, L 6 The distance between the intersection of the F-circle freezing pipe and the shield shell and the rear shield cutterhead panel;

[0090] Similarly, considering the construction position of the blowout prevention device in the freezing pipe supporting hole and the final hole spacing, the three circles of freezing pipes of the subsequent shield are further designed:

[0091] D min ≤L 5 -L 4 ≤D max ;

[0092] D min ≤L 6 -L 5 ≤D max ;

[0093] d min ≤(L 5 -L 4 )sinθ e +L d sin(θ e -θ d )≤dmax ;

[0094] d min ≤(L 6 -L 5 )sinθ f +L e sin(θ f -θ e )≤d max ;

[0095] The above design is different from the conventional bilateral symmetric layout. The two symmetric freezing pipes have high requirements for the docking accuracy and drilling accuracy of the shield tunneling. During the subsequent installation process of the freezing pipes, collisions are likely to occur, resulting in damage to the freezing pipes and even the emergence of abandoned holes. At the same time, filling the holes also poses a great risk to the local stability of the shield shell. In addition, controlling the frost heaving effect is relatively weak and difficult. The asymmetric freezing pipe layout designed in the present invention reduces the docking accuracy and drilling accuracy, effectively inhibits the frost heaving effect, reduces the influence of the frost heaving effect on the shield shell, and improves the safety during the excavation process of the docking project.

[0096] Embodiment 5

[0097] The present invention requires a total of two sets of brine circulation systems. The first freezing system is connected to three circles of freezing pipes, namely, the A circle, B circle, and C circle, on the side of the leading shield tunneling. The second freezing system is connected to three circles of freezing pipes, namely, the D circle, E circle, and F circle, on the side of the trailing shield tunneling. The brine temperature is controlled uniformly. That is, after the trailing shield tunneling reaches the docking position and disassembling work is carried out, when the freezing construction conditions are met on the side of the leading shield tunneling, the freezing operation on the side of the leading shield tunneling can be started. To ensure that no drilling in frozen soil occurs during the drilling process on the side of the trailing shield tunneling, reduce the drilling risk, and improve the hole formation rate; at the same time, reduce the influence of the frost heaving effect on the shield structure, the present invention designs for the brine temperature and time, and combines finite element calculations for corroborative analysis. The specific implementation is as follows:

[0098] (1) Freezing construction of three circles of freezing holes on the side of the leading shield tunneling

[0099] After the freezing conditions are met on the side of the leading shield tunneling, start the active freezing on the side of the leading shield tunneling. At this time, the temperature of the circulating brine in the three rows of freezing pipes is controlled so that the brine temperature drops to 0 °C in 7 days and is maintained at this temperature until 60 days. It should be noted here that the specific number of days of maintenance should be adjusted adaptively according to the thickness of the frozen wall and the formation properties. The present invention does not make mandatory protection requirements here. The purpose is to pre-cool the soil around the leading shield tunneling, but not reach the freezing temperature.

[0100] (2) Circulate low-temperature brine on the sides of the leading shield tunneling and the trailing shield tunneling simultaneously after 60 days

[0101] After circulating 0℃ brine on the side of the leading shield for 60 days, the drilling operation on the side of the trailing shield is completed at this time, and the freezing condition is met. At this time, all the freezing pipes on the side of the leading shield and the side of the trailing shield are started for active freezing, and they are frozen together for 120 days. At this time, the brine temperature on the side of the leading shield drops from 0℃ to -18℃ in 5 days and to -28℃ in 15 days; the brine temperature on the side of the trailing shield drops from normal temperature to -18℃ in 7 days, to -24℃ in 15 days, and to -28℃ in 20 days; ensure that the brine temperature on the side of the leading shield is always lower than the brine temperature on the side of the trailing shield before the freezing of the leading shield and the trailing shield intersects, accelerate the development speed of the frozen soil on the side of the leading shield, and pressure relief can be carried out through the side of the trailing shield before the freezing of the leading shield and the trailing shield intersects, so as to achieve the effect of controlling frost heave.

[0102] Combined with finite element calculation, a specific analysis is carried out for the temperature field and frost heave effect. The temperature field calculation adopts a two-dimensional solid heat transfer transient analysis model considering the phase change process. For the convenience of calculation and without affecting the actual results, the model is simplified, and a 1 / 28 model (two groups of freezing pipes) is selected to carry out the calculation study, as Figure 4 shown. The calculation assumptions are as follows:

[0103] ① The soil layer is a single homogeneous material with isotropic properties;

[0104] ② The soil layer where the shield is located is assigned values according to the actual formation material properties;

[0105] ③ The influence of moisture migration is ignored;

[0106] ④ The brine temperature load is directly applied to the outer wall of the freezing pipe, and the temperature difference during the brine circulation process is not considered; ⑤ The phase change effect is considered during the calculation process;

[0107] ⑥ The brine temperatures on the side of the leading shield and the side of the trailing shield are strictly simulated according to the above specified requirements;

[0108] ⑦ The adverse influence of heat input on the inner surface of the shield is considered.

[0109] The calculation results at 60 days, 67 days, 71 days, 75 days, 90 days and 120 days are selected for analysis, as Figures 5 - 10。After 60 days of freezing on the side of the advancing shield tunneling machine, the pre-cooling of some soil within the designed frozen wall range has been achieved, and the temperature of the soil around the freezing pipes on the side of the advancing shield tunneling machine has dropped to around 0°C. At this time, the low-temperature brine circulation is started simultaneously for both the advancing and the trailing shield tunneling machines. On the 67th day, the frozen soil has formed around the B circle on the side of the advancing shield tunneling machine, and the temperature of the soil around the E circle on the side of the trailing shield tunneling machine has also dropped to near the soil freezing temperature, starting to form frozen soil. As the temperature continues to develop until the 71st day, the frozen soil mass continues to expand outwards. It can be clearly seen that the temperature of the soil in the middle between the advancing and the trailing shield tunneling machines is relatively high. Since the arrangement type of the freezing pipes is open-ended, the soil strength is relatively low at this time, with strong compressibility, and the frost heave can be released to the unfrozen soil, greatly reducing the frost heave pressure at the shield shell. On the 75th day, the frozen soil has connected around both the advancing and the trailing shield tunneling machines. At this time, the volume of the unfrozen soil is small, and the resulting frost heave effect is limited. Most of the pressure has been released through the rapid freezing process, achieving the effect of controlling the frost heave. At the same time, by combining the existing advanced grouting pipelines of the shield tunneling machine and the flushing ports at the cutter head for pressure relief operations, the frost heave pressure can be further effectively released.

[0110] Here, it can be foreseen that in the case of the symmetric freezing pipe arrangement, the soil on both sides cools down simultaneously, and there is no obvious time difference in the formation of frozen soil. The frozen soil on both sides forms almost synchronously, showing symmetry, and the frozen soil around the freezing pipes completes the connection first. There is still unfrozen soil between the freezing pipes and the shield shell. At this time, a form of frozen soil wrapping the unfrozen soil is formed. As the cooling capacity continues to be input, the unfrozen soil between the freezing pipes and the shield shell continues to freeze. At this time, the resulting frost heave effect cannot dissipate away from the shield shell due to the resistance of the external frozen soil, resulting in a continuous increase in the frost heave force borne by the shield shell, posing a threat to the shield shell structure. Therefore, compared with the symmetric freezing form and the traditional symmetric freezing form, the asymmetric freezing form is more beneficial for controlling the frost heave effect.

[0111] Continuing to develop until the 90th day and the 120th day, at this time, it enters the stage of temperature drop of the frozen soil mass, gradually reaching the designed average temperature, thickness and other bearing requirement design conditions of the frozen soil. During the process, the development of the frozen soil is continuously expanding outwards. Since the strength of the internal frozen soil is relatively high, the resulting frost heave effect will be compressed and released outwards, rather than acting on the internal frozen soil or even the shield body.

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A special-shaped freezing construction method suitable for shield butt joint asynchronous control of frost heave, characterized by: During the shield connection freezing construction, the leading shield and the following shield use asymmetric freezing, with the leading shield's freezing pipe serving as the main freezing side and the following shield's freezing pipe serving as the auxiliary freezing side. The frozen body formed by the leading shield's freezing pipe completely envelops the following shield's cutterhead connection position.

2. A special-shaped freezing construction method suitable for shield butt joint asynchronous control of frost heave according to claim 1, characterized in that: The distance between the intersection points of each circle of freezing pipes and the shield shell on the leading shield side meets the following requirements: D min ≤L i -L i+1 ≤D max ; Among them, L i L is the distance from the intersection of the i-th freezing pipe and the shield shell of the leading shield from the outside to the inside to the cutter head panel of the leading shield, i is a positive integer, 1≤i<n, n is the number of freezing pipes of the leading shield, L i+1 D is the distance from the intersection of the i+1th circle freezing pipe and the shield shell to the cutterhead panel of the leading shield from the outside to the inside, min Indicates the minimum construction distance, D max Indicates the maximum construction distance.

3. A special-shaped freezing construction method suitable for shield butt joint asynchronous control of frost heave according to claim 1, characterized in that: Length of the outermost freezing pipe of the first shield machine L a The conditions are: Where L1 is the distance between the intersection of the freezing pipe and the shield shell of the leading shield circle A and the cutterhead panel of the leading shield. Circle A is the outermost circle of the leading shield. p L is the distance between the cutterhead panels after two shield machines are fully connected. q is the distance between the rear shield cutterhead panel and the rear partition of the bubble chamber, L0 is the length of the freezing pipe end that does not participate in the circulating brine, θ a It represents the angle between the axis of the freezing pipe in circle A and the axis of the shield.

4. A special-shaped freezing construction method suitable for shield butt joint asynchronous control of frost heave according to claim 1, characterized in that: Length of freezing pipe in the middle ring of the first shield machine L b The conditions are: Where, L b is the length of the freezing pipe in circle B. Circle B is the freezing circle corresponding to the freezing holes in the middle circle of the first shield. L2 is the distance between the intersection of the freezing pipe in circle B and the shield shell and the cutter head panel of the first shield. p L is the distance between the cutterhead panels after two shield machines are fully connected. q is the distance between the rear shield cutterhead panel and the rear partition of the bubble chamber, L0 is the length of the freezing pipe end that does not participate in the circulating brine, θ b It is the angle between the axis of the freezing pipe in circle B and the axis of the shield.

5. The method for special-shaped freezing construction suitable for shield butt joint asynchronous control of frost heave according to claim 1, characterized in that: The length of the freezing pipe in circle C, Lc, meets the following conditions: Where Lc is the length of the freezing pipe in circle C, circle C is the freezing circle corresponding to the innermost freezing hole of the leading shield, L3 is the distance between the intersection of the freezing pipe in circle C and the shield shell to the cutterhead panel of the leading shield, and L p L is the distance between the cutterhead panels after two shield machines are fully connected. q is the distance between the rear shield cutterhead panel and the rear partition of the bubble chamber, L0 is the length of the freezing pipe end that does not participate in the circulating brine, θ c It is the angle between the axis of the C circle freezing pipe and the axis of the shield.

6. A special-shaped freezing construction method suitable for shield butt joint asynchronous control of frost heave according to claim 1, characterized in that: After the freezing conditions are met on the leading shield side, the soil around the leading shield side is pre-cooled. When the drilling operation of the rear shield is completed and the freezing conditions are met, all the freezing pipes on the leading shield side and the rear shield side are started at the same time for active freezing. The freezing temperature of the leading shield side is always lower than that of the rear shield side before the handover, and the pressure is relieved through the rear shield side before the handover.

7. The method for construction of special-shaped freezing applicable to shield machine docking and asynchronously controlling frost heave according to claim 1, characterized in that: The freezing pipes of both the leading shield and the trailing shield are arranged in a plum blossom shape in the circumferential direction.

8. The method for special-shaped freezing construction suitable for shield butt joint asynchronous control of frost heave according to claim 1, characterized in that: The spacing between adjacent freezing pipes of the advance shield is uniform.

9. The method for construction of special-shaped freezing applicable to shield machine docking and asynchronously controlling frost heave according to claim 1, characterized in that: There is a frost heave release channel between the freezing pipe of the preceding shield machine and the freezing pipe of the succeeding shield machine.

10. The method for construction of special-shaped freezing applicable to shield machine docking and asynchronously controlling frost heave according to claim 1, characterized in that: The connecting line of the end points of each circle of freezing pipes of the following shield is parallel to the angle of the innermost circle of freezing pipes of the preceding shield.

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