An excavation method for soft surrounding rock tunnel construction based on real-time monitoring

Abstract

The invention relates to the technical field of tunnel excavation, and in particular to an excavation method for soft surrounding rock tunnel construction based on real-time monitoring, comprising the following steps: S1, performing advance support on a tunnel arch; S2, obtaining a design radius of the tunnel, determining an upper step height based on the design radius and a rock mass longitudinal wave velocity, and performing excavation and support on the upper step; step S3, determining an excavation sequence on the left and right sides of a lower step; S4, excavating and supporting an upper step and a lower step on one side according to the determined excavation sequence; S5, excavating and supporting the lower step on the other side and an upper step; S6, preliminarily judging a stable state of the surrounding rock; step S7, adjusting a single excavation amount of a tunnel cyclic excavation based on the stable state of the surrounding rock, and excavating the tunnel in a repeated cycle; the invention improves construction efficiency and shortens construction period by performing excavation and adjusting and optimizing excavation and support parameters by staggering upper and lower steps.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel excavation, and in particular to an excavation method for soft surrounding rock tunnel construction based on real-time monitoring. Background Art

[0002] As an important part of transportation and water conservancy projects, tunnel construction has always been valued by relevant personnel. This is mainly because the tunnel construction process is affected by a variety of external conditions and factors, and is therefore relatively difficult. Therefore, how to ensure the safety and stability of the tunnel construction process is a key factor in ensuring the smooth construction of water conservancy projects. The excavation link is a very important link in the tunnel construction process. For this link, how to choose a suitable excavation method is of great significance to speeding up the progress of tunnel construction and ensuring the quality of tunnel construction.

[0003] For the coal and gas outburst section, if the surrounding rock of this section is identified as carbonaceous mudstone plus pulverized coal seam through design, the self-stability of the surrounding rock is very poor. If full-section excavation is used, the coal cannot be sealed in time, the coal seam is exposed for a long time, and there is a possibility of pulverized coal sliding in the mandrel. At the same time, the increase in the amount of explosives will cause greater vibration, increasing the inducement of gas outburst.

[0004] Chinese patent application publication number CN116517573A discloses a tunnel excavation method, comprising the following steps: 1) construction preparation: preparing the manpower, material resources and technical support required in the entire construction process; 2) construction measurement: the staff carries out construction layout and specific measurement and marking according to the content of the construction drawings; 3) drilling and blasting operations: including tunnel excavation, drilling and blasting; 4) ventilation and smoke exhaust; 5) slag discharge: real-time slag discharge; 6) anchor rod driving: the corresponding anchor rod should be made in advance before anchor rod driving; 7) steel mesh (arch frame) installation: the corresponding steel mesh (arch frame) should be prepared in advance before the steel mesh (arch frame) is installed; 8) sprayed concrete support: the preparation materials of concrete should be prepared before spraying concrete. This method can effectively excavate and construct the water diversion tunnel of a hydropower station in a geological environment where the surrounding rock is mostly Class III and IV, and a small part is Class V, improve the safety of the surrounding rock during the construction process, reduce construction hazards, and ensure the construction quality and construction period. It can be seen from this that the above-mentioned tunnel excavation did not take into account the poor self-stability of the surrounding rock in tunnel excavation of Class V and above surrounding rock. When the full section is used, the risk of sliding and collapse is high due to the long-term exposure of the section for arch installation, the excavation efficiency is low and the construction progress is affected. Summary of the invention

[0005] To this end, the present invention provides an excavation method for soft surrounding rock tunnel construction based on real-time monitoring, so as to overcome the problems of slow progress and low excavation efficiency in the prior art of soft surrounding rock construction.

[0006] To achieve the above object, the present invention provides an excavation method for soft surrounding rock tunnel construction based on real-time monitoring, comprising:

[0007] Step S1, obtaining the basic geological conditions of the tunnel and performing advance support on the tunnel arch, wherein the basic geological conditions include surrounding rock classification and basic quality indicators of surrounding rock;

[0008] Step S2, obtaining the design radius of the tunnel, determining the height of the upper step based on the design radius and the longitudinal wave velocity of the rock mass, and performing excavation and support of the upper step;

[0009] Step S3, after the upper step support is completed, the surrounding rock parameters on the left and right sides of the upper step are obtained for comparison, and the excavation order on the left and right sides of the lower step is determined based on the comparison result;

[0010] Step S4, determining the first excavation step of the single-side lower step according to the determined excavation sequence, during the excavation of the single-side lower step, drilling holes on the upper step and the single-side lower step at the same time and adopting a synchronous blasting strategy, and after blasting, excavating the upper step and the single-side lower step at the same time and performing support;

[0011] Step S5, after step S4 is completed, drilling holes on the lower step and the upper step on the other side at the same time and adopting a synchronous blasting strategy, after blasting, excavating the upper step and the lower step on one side at the same time, and supporting them;

[0012] Step S6, after the excavation of the lower step is completed, the tunnel perimeter convergence and vault settlement are measured, and regression analysis is performed on the collected vault settlement and perimeter convergence data to predict the maximum displacement value umax of the vault settlement and perimeter convergence, as well as the time D required to reach convergence, and preliminarily judge the stability of the surrounding rock;

[0013] Step S7, adjusting the single excavation amount of the tunnel cyclic excavation based on the stable state of the surrounding rock, so as to repeat the steps S3 to S6 and cyclically excavate the tunnel;

[0014] Among them, the single excavation volume includes the single excavation volume of the lower step and the single excavation volume of the upper step.

[0015] Furthermore, in step S1, the advance support process includes:

[0016] An advance small guide tube is set on the top arch face, and the preset range of the advance small guide tube is 120° within the arch top;

[0017] Adjust the range of the advance small guide tube based on the thickness of the tunnel layer rock;

[0018] After completing the overlapping of the advance small ducts, the arch crown advance surrounding rock grouting reinforcement is carried out.

[0019] Further, in step S2, determining the upper step height includes:

[0020] Obtain rock mass longitudinal wave velocity and design radius before and after advance support;

[0021] Calculate the support coefficient based on the rock mass longitudinal wave velocity before and after advanced support;

[0022] Determine the height of the upper step according to the support coefficient and the tunnel design radius;

[0023] Among them, the upper step height is the distance between the bottom surface of the upper step and the top of the tunnel.

[0024] Furthermore, the step S2 further includes:

[0025] The initial excavation amount of the upper step is determined according to the upper step height and the length of the advance support, wherein the initial excavation amount of the upper step is less than or equal to the upper step height.

[0026] Furthermore, in step S2, the step of excavating the upper step includes:

[0027] Determine the blasthole position, and determine the blasthole position on the tunnel face based on the measured tunnel section data to locate the opening and drilling;

[0028] Determine the vertical depth of the borehole based on the unevenness of the face rock, the design radius and the initial excavation amount;

[0029] The charging, networking, blasting, mucking and supporting are carried out in sequence, wherein the spacing of the supporting arches is less than or equal to 1 / 7 of the tunnel design radius.

[0030] Further, in step S3, determining the excavation order of the left and right sides of the lower step includes:

[0031] Obtain the surrounding rock parameters on the left and right sides of the upper step, including the density of the surrounding rock and the flatness of the surrounding rock section;

[0032] Determine the surrounding rock weakness values ​​corresponding to the left and right sides of the upper step based on the surrounding rock parameters;

[0033] Compare the rock weakness values ​​of the surrounding rocks on the left and right sides, and determine the side corresponding to the smaller rock weakness value as the single-side lower step to be excavated first, and determine the side corresponding to the larger rock weakness value as the other side lower step to be excavated subsequently.

[0034] Furthermore, in the step S3, it also includes determining the initial single excavation amount of the lower step cyclic excavation and the excavation difference of the lower steps on both sides based on the settlement amount per unit time of the arch.

[0035] Furthermore, in the step S6, the surrounding rock stability parameter is determined based on the predicted maximum displacement value umax and the time D required to reach convergence.

[0036] Further, in the step S7, the single excavation amount of the tunnel cyclic excavation is adjusted based on the surrounding rock stability parameter, wherein the adjusted single excavation amount of the lower step is determined according to the surrounding rock stability parameter and the initial single excavation amount.

[0037] Further, in step S6, the regression analysis includes:

[0038] Obtain the tunnel perimeter convergence value and vault settlement at several time points;

[0039] A first regression curve of perimeter convergence is established based on the relationship between the tunnel perimeter convergence value and time, and a second regression fitting curve of vault settlement is established based on the relationship between the vault settlement amount and time;

[0040] Determine the maximum displacement value u1 of the peripheral convergence according to the first regression curve, and determine the maximum displacement value u2 of the arch sinking according to the second regression fitting curve;

[0041] The maximum value of u1 and u2 is taken as the maximum displacement value umax, and the corresponding time required to reach convergence is D.

[0042] Compared with the prior art, the beneficial effect of the present invention lies in that the excavation method for soft surrounding rock tunnel construction based on real-time monitoring of the present invention uses an excavation gantry to complete the upper step and the lower step left (or right) simultaneous drilling, charging, delayed detonation, and mucking, and excavation is staggered at two different positions in the front and rear, and timely support is provided in sections to form a support whole, shortening the operation cycle time, and the excavation and support of various parts are staggered and advanced in parallel along the longitudinal direction of the tunnel, which speeds up the construction progress and ensures construction safety and quality.

[0043] Furthermore, the excavation method for soft surrounding rock tunnel construction based on real-time monitoring of the present invention is convenient for flexibly and timely switching of construction procedures and adjusting of construction methods when geological conditions change. It can adapt to different spans and various cross-sectional forms, and the initial support procedure is easy to operate.

[0044] Furthermore, the excavation method for soft surrounding rock tunnel construction based on real-time monitoring of the present invention staggers the excavation on the left and right sides on the basis of step excavation, which is conducive to the stability of the excavation working face. When the surrounding rock deformation is large or sudden, the closing time can be adjusted as soon as possible under the premise of ensuring safety and meeting the clearance requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a flow chart of an excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to an embodiment of the present invention;

[0046] Figure 2 This is an overall schematic diagram of the excavation process of first excavating the left side of the lower step according to an embodiment of the present invention;

[0047] Figure 3 It is an engineering schematic diagram of the blasthole position of an embodiment of the present invention;

[0048] Figure 4 It is a logic decision diagram of the excavation method when the left side of the lower step is excavated first in an embodiment of the present invention;

[0049] In the figure: 1, peripheral eye; 2, auxiliary eye; 3, groove eye; 4, bottom plate eye. DETAILED DESCRIPTION

[0050] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0052] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the drawings. This is merely for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0053] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] By way of explanation, the following definitions are clear to those skilled in the art:

[0055] Surrounding rock: Surrounding rock refers to the rock mass within the range of stress redistribution around the tunnel after excavation, or refers to the part of the rock mass that affects the stability of the tunnel after excavation (the rock mass here refers to the general term for soil and rock mass).

[0056] Surrounding rock classification refers to dividing an infinite rock mass sequence into a finite number of categories with different degrees of stability based on indicators such as rock mass integrity and rock strength, that is, classifying some surrounding rocks with similar stability into one category, and dividing all surrounding rocks into several categories. Tunnel surrounding rocks are divided into six levels, namely Ⅰ, Ⅱ, Ⅲ, Ⅳ, Ⅴ, Ⅵ.

[0057] The basic quality index of surrounding rock is also called the basic quality index of rock mass BQ.

[0058] See also Figure 1 As shown, it is a flow chart of an excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to an embodiment of the present invention. An embodiment of the present invention provides an excavation method for soft surrounding rock tunnel construction based on real-time monitoring, comprising:

[0059] Step S1, obtaining the basic geological conditions of the tunnel and performing advance support on the tunnel arch, wherein the basic geological conditions include surrounding rock classification and basic quality indicators of surrounding rock;

[0060] Step S2, obtaining the design radius of the tunnel, determining the height of the upper step based on the design radius and the longitudinal wave velocity of the rock mass, and performing excavation and support of the upper step;

[0061] Step S3, after the upper step support is completed, the surrounding rock parameters on the left and right sides of the upper step are obtained for comparison, and the excavation order on the left and right sides of the lower step is determined based on the comparison result;

[0062] Step S4, determining the first excavation step of the single-side lower step according to the determined excavation sequence, during the excavation of the single-side lower step, drilling holes on the upper step and the single-side lower step at the same time and adopting a synchronous blasting strategy, and after blasting, excavating the upper step and the single-side lower step at the same time and performing support;

[0063] Step S5, after step S4 is completed, drilling holes on the lower step and the upper step on the other side at the same time and adopting a synchronous blasting strategy, after blasting, excavating the upper step and the lower step on one side at the same time, and supporting them;

[0064] Step S6, after the excavation of the lower step is completed, the tunnel perimeter convergence and vault settlement are measured, and regression analysis is performed on the collected vault settlement and perimeter convergence data to predict the maximum displacement value umax of the vault settlement and perimeter convergence, as well as the time D required to reach convergence, and preliminarily judge the stability of the surrounding rock;

[0065] Step S7, adjusting the single excavation amount of the tunnel cyclic excavation based on the stable state of the surrounding rock, so as to repeat the steps S3 to S6 and cyclically excavate the tunnel;

[0066] Among them, the single excavation volume includes the single excavation volume of the lower step and the single excavation volume of the upper step.

[0067] The excavation method of the present invention uses an excavation platform to complete the upper step and the lower step left (or right) simultaneous drilling, charging, delayed detonation, and mucking. The excavation is staggered at two different positions in the front and rear, and the parts are supported in time to form a support whole, shortening the operation cycle time. The excavation and support of each part are staggered and advanced in parallel along the longitudinal direction of the tunnel, which speeds up the construction progress and ensures the construction safety and quality.

[0068] Specifically, in step S1, if the surrounding rock classification in the basic geological conditions of the tunnel obtained is grade IV, V or VI, or the basic quality index of the surrounding rock is less than or equal to 280, it is necessary to perform advance support on the tunnel arch to increase the stability of the tunnel.

[0069] Specifically, in step S1, the advance support process includes:

[0070] An advance small guide tube is set on the top arch face, and the preset range of the advance small guide tube is 120° within the arch top;

[0071] Adjust the range of the advance small guide tube based on the thickness of the tunnel layer rock;

[0072] After completing the overlapping of the advance small ducts, the arch crown advance surrounding rock grouting reinforcement is carried out.

[0073] During implementation, when the thickness of the layered rock formations in the tunnel is greater than or equal to 0.1m, it is determined that there is no need to adjust the range of the advance small duct, and the range of the advance small duct is maintained at the 120° range of the arch; when the thickness of the layered rock formations in the tunnel is less than 0.1m or there is no layered rock formation, it is determined that the range of the advance small duct needs to be adjusted, and the adjusted range of the advance small duct increases by 8% to 15% on the preset range of the advance small duct.

[0074] In a specific embodiment, there is no layered rock formation in the tunnel, and an advance small duct Φ42×4mm, 4.5m long, with an external insertion angle of 5°~10°, an annular spacing of 35cm, a longitudinal overlap length of not less than 1.5m is set at the top arch face, and the arch crown is reinforced by advance grouting of the surrounding rock. The initial grouting pressure is 0.1MPa, and the maximum pressure does not exceed 0.3MPa. The range of the advance small duct is 130° within the arch crown.

[0075] Specifically, see Figure 2-Figure 4 As shown, in step S2, the upper step is first excavated, wherein determining the height of the upper step includes:

[0076] Obtain rock mass longitudinal wave velocity and design radius before and after advance support;

[0077] Calculate the support coefficient based on the rock mass longitudinal wave velocity before and after advanced support;

[0078] Determine the height of the upper step according to the support coefficient and the tunnel design radius;

[0079] Among them, the upper step height is the distance between the bottom surface of the upper step and the top of the tunnel.

[0080] The present invention generally adopts the upper and lower steps and the left and right staggered excavation method for the lower step. The construction sequence is to first blast and excavate the upper step. After the excavation is completed, the initial support structure is installed. After the excavation and support of the upper step are completed, the lower step on the side with better surrounding rock stability is excavated first, and holes are drilled and blasted on one side of the lower step and the upper step at the same time. After the excavation and support of one side of the lower step and the upper step are completed, the other side of the lower step and the upper step are excavated and supported. The excavation of the upper step and the single-sided lower step is repeated in this way, forming the main tunnel excavation method of the present invention.

[0081] It is understandable that, since advance support can effectively prevent the instability of the tunnel working face, the effectiveness of advance support can be evaluated by detecting the longitudinal wave velocity of the rock mass before and after the advance support, thereby guiding the determination of the upper step height.

[0082] During implementation, the longitudinal wave velocity V1 of the rock mass is measured before the advance support, and the longitudinal wave velocity V2 of the rock mass is measured again after the advance support is completed. The support coefficient α is the ratio of the longitudinal wave velocity V2 of the rock mass measured again after the advance support is completed to the longitudinal wave velocity V1 of the rock mass before the advance support, that is, α=V2 / V1. Then, the upper step height H1 is based on the product of the support coefficient α, the tunnel design radius R and the empirical coefficient β, that is, H1=α×R×β, wherein the empirical coefficient β is between 0.8 and 0.9, and preferably, β is 0.85.

[0083] In a specific embodiment, the longitudinal wave velocity V1 of the rock mass before the advance support is measured to be 2400 km / s, and the longitudinal wave velocity V2 of the rock mass is measured again after the advance support is completed to be 2450 km / s. The design radius R of the tunnel is 3.5 meters, and the value of β is 0.85. At this time, the calculated upper step height H1 is about 3 meters.

[0084] Specifically, the step S2 further includes:

[0085] The initial excavation amount of the upper step is determined according to the upper step height and the length of the advance support, wherein the initial excavation amount of the upper step is less than or equal to the upper step height.

[0086] It can be understood that the initial excavation volume of the upper step is an indicator for considering the staggered distance between the upper and lower steps. Since the upper step is excavated first and the lower step is excavated later, the staggered excavation effect can be effectively achieved, and the risk of the arch falling off during the initial support is avoided through the staged excavation of the lower step, further effectively taking into account the excavation efficiency and excavation safety, which is suitable for tunnel construction with soft surrounding rock.

[0087] In implementation, based on the strength of the initial support of the upper step and the risk assessment of arch falling, and within the range of the upper step advance support, the initial excavation volume of the upper step is 85% to 100% of the upper step height or 70% to 90% of the upper step advance support length, whichever is smaller. Preferably, the initial excavation volume of the upper step is 90% of the upper step height and 80% of the upper step advance support length, whichever is smaller.

[0088] Specifically, in step S2, the step of excavating the upper step includes:

[0089] Determine the blasthole position, and determine the blasthole position on the tunnel face based on the measured tunnel section data to locate the opening and drilling;

[0090] Determine the vertical depth of the borehole based on the unevenness of the face rock, the design radius and the initial excavation amount;

[0091] The charging, networking, blasting, slag removal and support are carried out in sequence, wherein the spacing of the support arches is less than or equal to 1 / 7 of the tunnel design radius.

[0092] In implementation, tunnel section data include the degree of unevenness of the face rock and the degree of consistency of the rock hole position excavation, wherein the degree of unevenness of the face rock is calculated based on the average value of the rock unevenness fluctuation of the face surface of the tunnel section within a preset area relative to the ideal plane, the larger the value of the degree of unevenness of the face rock, the better the stability of the face, the degree of consistency of the rock hole position excavation can be determined based on the ratio of the excavation diameter of the ideal rock hole and the actual excavation diameter, the larger the ratio, the closer the actual excavation diameter is to the excavation diameter of the ideal rock hole, indicating that the face stability is good and the risk of collapse is small, so the blasthole position can be adjusted based on the blasting design according to the stability of the face reflected by the tunnel section data, when the degree of unevenness of the face rock or the degree of consistency of the rock hole position excavation is greater, there is no need to adjust the position of the designed blasthole, and when the degree of unevenness of the face rock or the degree of consistency of the rock hole position excavation is lower than the corresponding threshold, the blasthole position of the blasting design is encrypted, and the weak vibration blasting method is used for blasting, which can reduce the disturbance to the surrounding rock.

[0093] Preferably, the threshold corresponding to the concavity of the face rock is generally 0.1 to 0.25 meters, and the threshold corresponding to the consistency of the rock hole position excavation is generally between 0.6 and 0.8, which can better characterize the stability of the surrounding rock of the face.

[0094] In implementation, the vertical depth of the drill hole is related to the size of the excavation face (design radius). If the blasthole is too deep, the clamping effect of the surrounding rocks will be greater, and the instability of the surrounding rock after blasting will also increase. For the surrounding rock that is weak, such as Class V surrounding rock, the blasthole depth should not be too deep. The depth coefficient of the drill hole is determined according to the unevenness of the rock on the face. The depth coefficient = (design radius + unevenness of the rock on the face) / design radius, and the vertical depths of the peripheral holes and bottom plate holes are defined as depth coefficient × depth coefficient × initial excavation volume, and the vertical depths of other holes are depth coefficient × initial excavation volume.

[0095] Specifically, during the support process, the layout interval of the support arch should be less than or equal to 1 / 7 of the tunnel design radius to obtain a more stable support effect.

[0096] In a specific embodiment, see Figure 3 As shown, for the tunnels designed and identified as carbonaceous mudstone plus pulverized coal seams, the design radius is 3.5 meters. According to the blasting design approved by relevant parties after the blasting test, 21 peripheral holes are arranged on the face. After testing, since the unevenness of the face rock can be controlled within 0.1 meters, it is adjusted to 24 peripheral holes with a spacing of 0.40 meters, 4 sections of detonators are used, and the charge of each hole is 0.3Kg; 12 auxiliary holes, 0.6m spacing, 2 sections of detonators are used, and the charge of a single hole is 0.6Kg; 28 slot holes, 0.4m to 0.6m spacing, 1 section of detonators are used; 9 bottom plate holes, 0.7m spacing, 3 sections of detonators are used. Set the initial excavation volume to 3 meters, then the vertical depth of the peripheral holes and bottom plate holes is 3.2 meters deep, and the other holes are 3.1 meters deep. The drilling adopts YT-28 air drill, and the blasthole diameter is 42mm. The charging, detonator networking, blasting and mucking are carried out according to the specifications. After mucking is completed and after the risk elimination treatment, the surrounding rock is sealed with sprayed concrete and the initial support is carried out. Preferably, the arch frame adopts I20b I-beam with a spacing of 50cm. The units are connected by high-strength bolts. When the steel frame is connected longitudinally, the tape that has been threaded and lubricated in the previous cycle is untied, and the sleeve is connected through the steel pipe pre-welded on the steel frame. The end of the steel bar is wrapped and the Φ8 steel mesh is installed; 2 3-meter-long Φ32 self-propelled hollow anchor rods are set on both sides of the arch waist and the upper step 50cm above the bottom as the shoulder and foot locking anchor rods, along the 270° range of the arch steel support, with a spacing of 1.5m and a length of 6m; the initial grouting pressure is 0.1MPa, and the maximum pressure does not exceed 0.3MPa. The construction system anchor rod. Withdraw the temporary support and spray C20 concrete mixed with airtight agent with a thickness of 20cm. It is understandable that the above implementation does not limit the present invention, and those skilled in the art can set and adjust corresponding processes and parameters according to specific tunnel conditions, which will not be described in detail here.

[0097] Specifically, in step S3, determining the excavation order of the left and right sides of the lower step includes:

[0098] Obtain the surrounding rock parameters on the left and right sides of the upper step, including the density of the surrounding rock and the compactness of the surrounding rock section;

[0099] Determine the surrounding rock weakness values ​​corresponding to the left and right sides of the upper step based on the surrounding rock parameters;

[0100] Compare the rock weakness values ​​of the surrounding rocks on the left and right sides, and determine the side corresponding to the smaller rock weakness value as the single-side lower step to be excavated first, and determine the side corresponding to the larger rock weakness value as the other side lower step to be excavated subsequently.

[0101] In the implementation, the surrounding rock parameters on the left and right sides of the upper step tunnel arch are obtained to calculate the surrounding rock weakness values ​​on the left and right sides of the upper step respectively, which is calculated using the following formula (1):

[0102] Z = (ρA / ρ1) 2 + (H1 / HA) 2 (1)

[0103] Among them, Z is the weakness value of the surrounding rock, ρ1 is the density of the surrounding rock on one side, ρA is the average density of the surrounding rock on both sides, H1 is the density of the surrounding rock section on one side, and HA is the average density of the surrounding rock section on both sides.

[0104] Among them, the cross-sectional density of the surrounding rock is obtained by using the same knocking force to knock a preset length of a pin of a set size from the surrounding rock surface into the surrounding rock layer, and obtaining the height of the surrounding rock loss around the pin as the cross-sectional density of the surrounding rock. If the pin on one side cannot be nailed into the surrounding rock, the cross-sectional density of the surrounding rock on that side is set to the preset length; if the pins on both sides cannot be nailed into the surrounding rock, the surrounding rock loss volume around the pin is recorded as the cross-sectional density of the surrounding rock on that side.

[0105] Under the guidance of formula (1), the magnitude of the surrounding rock weakness value can characterize the stability of the surrounding rock. The larger the surrounding rock weakness value, the weaker the surrounding rock on the corresponding side. Therefore, by comparing the surrounding rock weakness values ​​of the left and right sides, the side with better surrounding rock stability can be determined. The better side is used as the side to be excavated first. During the excavation of this side, the other side maintains the existing state, which can maintain the stability of the surrounding rock to the greatest extent, improve the excavation stability of the surrounding rock, and reduce the risk of collapse.

[0106] Specifically, in the step S3, it also includes determining the initial single excavation amount of the lower step cyclic excavation and the excavation difference of the lower steps on both sides based on the settlement amount per unit time of the arch.

[0107] In implementation, the preset initial single excavation amount of the lower step cycle excavation is 2 times the support arch spacing. The first reference value is determined by measuring the arch settlement of the upper step per unit time at the preset time after the support is completed and comparing it with the preset settlement standard value. The calculated value of the initial single excavation amount is determined according to the product of the first reference value and the preset initial single excavation amount, wherein the first reference value = preset settlement standard value / arch settlement of the upper step per unit time. Preferably, the preset time after the support is completed is within 1 hour, and the arch data collected around one hour after the support is completed is obtained to determine the arch settlement of the upper step per unit time, thereby calculating the initial single excavation amount. The preset settlement standard value ranges from 2cm to 5cm, and the preferred value is 3cm.

[0108] Specifically, the excavation difference of the lower steps on both sides is generally set to twice the initial single excavation amount. After determining the initial single excavation amount, the first excavated side of the lower step and the upper step are excavated until the difference in excavation distance with the later excavated side of the lower step reaches the excavation difference of the lower steps on both sides. Then the excavation of the upper step and the single-sided lower step is cyclically performed so that after each cycle of excavation, the two sides of the lower step always maintain the set excavation difference. It can be understood that the excavation width of the lower steps on both sides is generally taken as the central axis of the tunnel to divide the left and right lower steps, which will not be elaborated here.

[0109] Specifically, during the excavation of the lower steps on both sides, the upper step and the lower step on one side are excavated simultaneously. At this time, the lower step on one side uses the initial single excavation amount of the lower step cycle excavation as the single excavation amount of the lower step on one side in one excavation, and the upper step uses 1 / 2 of the initial single excavation amount as the single excavation amount of the upper step. That is, taking the left lower step as an example of excavating the left lower step first, after the upper step completes the initial excavation amount of the upper step, the upper step and the left lower step are excavated simultaneously. At this time, the excavation amount of the upper step is 1 / 2 of the initial single excavation amount, and the excavation amount of the left lower step is the initial single excavation amount; after completing the single excavation of the left lower step and the upper step, it is determined whether the left and right lower steps have reached the excavation difference. If the excavation difference has not been reached, the left lower step and the upper step are excavated again until the excavation difference is reached, and then the right lower step and the upper step are excavated single-time, and the left lower step and the upper step are excavated single-time.

[0110] Specifically, in step S6, the surrounding rock stability parameter is determined based on the predicted maximum displacement value umax and the time D required to reach convergence.

[0111] In implementation, the maximum displacement value umax and the time D required to reach convergence can both evaluate the stability of the surrounding rock. Generally speaking, the larger the maximum displacement value umax and the longer the time D required to reach convergence, the worse the stability of the surrounding rock.

[0112] As a better implementation method, the surrounding rock stability parameter W is determined by formula (2);

[0113] W=umax / umax0×e^(D / D0) (2)

[0114] Among them, umax0 is the maximum acceptable displacement value, D0 is the minimum convergence time of the historical tunnel, and preferably, umax0 is 10 cm and D0 is 10 hours.

[0115] Specifically, in step S6, the regression analysis includes:

[0116] Obtain the tunnel perimeter convergence value and vault settlement at several time points;

[0117] A first regression curve of perimeter convergence is established based on the relationship between the tunnel perimeter convergence value and time, and a second regression fitting curve of vault settlement is established based on the relationship between the vault settlement amount and time;

[0118] Determine the maximum displacement value u1 of the peripheral convergence according to the first regression curve, and determine the maximum displacement value u2 of the arch sinking according to the second regression fitting curve;

[0119] The maximum value of u1 and u2 is taken as the maximum displacement value umax, and the corresponding time required to reach convergence is D.

[0120] In implementation, the method of using regression analysis is not limited to the above implementation, as long as it can accurately predict the maximum displacement value umax and the time D required to reach convergence, it all falls within the protection scope of the present invention and will not be repeated here.

[0121] Specifically, in step S7, the single excavation amount of the tunnel cyclic excavation is adjusted based on the surrounding rock stability parameter, wherein the adjusted single excavation amount of the lower step is determined according to the surrounding rock stability parameter and the initial single excavation amount.

[0122] In the implementation, by comparing the surrounding rock stability parameter with the stability parameter threshold, if the surrounding rock stability parameter is greater than the stability parameter threshold, it is determined that the stability of the surrounding rock is poor, and the single excavation amount of the tunnel cycle excavation needs to be reduced; if the surrounding rock stability parameter is less than or equal to the stability parameter threshold, it is determined that the surrounding rock is stable and there is no need to adjust the single excavation amount of the tunnel cycle excavation. Here, the stability parameter threshold W0 can be calculated based on the surrounding rock stability parameter calculated when the umax value is 120% of umax0 and the D value is 2 times of D0. A better distinction reference can be obtained.

[0123] Specifically, the adjusted single excavation amount of the lower step is calculated based on the product of the reference coefficient determined by the surrounding rock stability parameter and the initial single excavation amount. The reference coefficient is calculated based on the ratio of the stability parameter threshold W0 to the surrounding rock stability parameter W, and the adjusted single excavation amount of the lower step is the product of the reference coefficient and the initial single excavation amount.

[0124] Example:

[0125] The first section of the North Main Canal of a water supply project is 10.3 km long. There are three construction branch tunnels and one entrance in the 0+000~10+300 section of the Shuida Bridge Tunnel in this section, namely 1#, 2#, and 3# construction branch tunnels. The length and bottom slope of the branch tunnels are L=587.411m, 663.082m, and 685.804m, respectively, and the bottom slope i=37.94%, 32.45%, and 34.46%; the main tunnel is a pressure-free circular tunnel, with a clearance of 2.7×2.7m after lining, and the lining thickness corresponds to different surrounding rock types IV, IV high external head (or V), and V high external head, respectively 0.4, 0.5, and 0.8m. After research and summary, the excavation and support of the coal and gas outburst section at the entrance of the Shuidaqiao tunnel was developed and applied by the excavation method of the present invention. After calculation, the height of the upper step was taken as 2.1 meters, the initial excavation volume of the upper step was 2.1 meters, and the layout interval of the support arch was 0.35 meters. After judgment, the left side of the lower step of the surrounding rock was excavated first, and the initial single excavation volume was 0.7 meters. The excavation difference of the lower steps on the left and right sides was 1.4 meters. By optimizing the excavation construction process, the gas outburst or collapse that may occur in the full-section construction was avoided. The time was shortened from 35 days (20m) in the first cycle of the test section to an average of 15 days (15m) after the fourth cycle, which accelerated the construction progress and greatly saved the construction period.

[0126] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for excavating a soft surrounding rock tunnel based on real-time monitoring, characterized in that: include: Step S1, obtaining the basic geological conditions of the tunnel and performing advance support on the tunnel arch, wherein the basic geological conditions include surrounding rock classification and basic quality indicators of surrounding rock; Step S2, obtaining the design radius of the tunnel, determining the height of the upper step based on the design radius and the longitudinal wave velocity of the rock mass, and performing excavation and support of the upper step; Step S3, after the upper step support is completed, the surrounding rock parameters on the left and right sides of the upper step are obtained for comparison, and the excavation order of the left and right sides of the lower step is determined based on the comparison result; Step S4, determining the first excavation step of the single-side lower step according to the determined excavation sequence, during the excavation of the single-side lower step, drilling holes on the upper step and the single-side lower step at the same time and adopting a synchronous blasting strategy, and after blasting, excavating the upper step and the single-side lower step at the same time and performing support; Step S5, after step S4 is completed, drilling holes on the lower step and the upper step on the other side at the same time and adopting a synchronous blasting strategy, after blasting, excavating the upper step and the lower step on one side at the same time, and supporting them; Step S6, after the excavation of the lower step is completed, the tunnel perimeter convergence and vault settlement are measured, and regression analysis is performed on the collected vault settlement and perimeter convergence data to predict the maximum displacement value umax of the vault settlement and perimeter convergence, as well as the time D required to reach convergence, and preliminarily judge the stability of the surrounding rock; Step S7, adjusting the single excavation amount of the tunnel cyclic excavation based on the stable state of the surrounding rock, so as to repeat the steps S3 to S6 and cyclically excavate the tunnel; The single excavation volume includes the single excavation volume of the lower step and the single excavation volume of the upper step; In step S1, the advance support process includes: An advance small guide tube is set on the top arch face, and the preset range of the advance small guide tube is 120° within the arch top; Adjust the range of the advance small guide tube based on the thickness of the tunnel layer rock; After the overlap of the advance small pipe is completed, the arch crown advance surrounding rock grouting reinforcement is carried out; In step S2, determining the upper step height includes: Obtain rock mass longitudinal wave velocity and design radius before and after advance support; Calculate the support coefficient based on the rock mass longitudinal wave velocity before and after advanced support; Determine the height of the upper step according to the support coefficient and the tunnel design radius; The upper step height is the distance between the bottom of the upper step and the top of the tunnel.

2. The excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to claim 1 is characterized in that: The step S2 further comprises: The initial excavation amount of the upper step is determined according to the upper step height and the length of the advance support, wherein the initial excavation amount of the upper step is less than or equal to the upper step height.

3. The excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to claim 2 is characterized in that: In step S2, the step of excavating the upper step includes: Determine the blasthole position, and determine the blasthole position on the tunnel face based on the measured tunnel section data to locate the opening and drilling; Determine the vertical depth of the borehole based on the unevenness of the face rock, the design radius and the initial excavation amount; The charging, networking, blasting, mucking and supporting are carried out in sequence, wherein the spacing of the supporting arches is less than or equal to 1 / 7 of the tunnel design radius.

4. The excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to claim 3 is characterized in that: In step S3, determining the excavation order of the left and right sides of the lower step includes: Obtain the surrounding rock parameters on the left and right sides of the upper step, including the density of the surrounding rock and the flatness of the surrounding rock section; Determine the surrounding rock weakness values ​​corresponding to the left and right sides of the upper step based on the surrounding rock parameters; Compare the rock weakness values ​​of the surrounding rocks on the left and right sides, and determine the side corresponding to the smaller rock weakness value as the single-side lower step to be excavated first, and determine the side corresponding to the larger rock weakness value as the other side lower step to be excavated subsequently.

5. The excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to claim 1 is characterized in that: In the step S3, it also includes determining the initial single excavation amount of the lower step cyclic excavation and the excavation difference of the lower steps on both sides based on the settlement amount per unit time of the arch.

6. The excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to claim 5 is characterized in that: In step S6, the surrounding rock stability parameter is determined based on the predicted maximum displacement value umax and the time D required to reach convergence.

7. The excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to claim 6 is characterized in that: In step S7, the single excavation amount of the tunnel cyclic excavation is adjusted based on the surrounding rock stability parameter, wherein the adjusted single excavation amount of the lower step is determined according to the surrounding rock stability parameter and the initial single excavation amount.

8. The excavation method for soft surrounding rock tunnel construction based on real-time monitoring according to claim 1 is characterized in that: In step S6, the regression analysis includes: Obtain the tunnel perimeter convergence value and vault settlement at several time points; A first regression curve of perimeter convergence is established based on the relationship between the tunnel perimeter convergence value and time, and a second regression fitting curve of vault settlement is established based on the relationship between the vault settlement amount and time; Determine the maximum displacement value u1 of the peripheral convergence according to the first regression curve, and determine the maximum displacement value u2 of the arch sinking according to the second regression fitting curve; The maximum value of u1 and u2 is taken as the maximum displacement value umax, and the corresponding time required to reach convergence is D.

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