A method for cross-chamber pre-hole post-wall ring pre-splitting shock attenuation excavation

Abstract

The application discloses a kind of cross caverns first hole then wall ring pre-splitting shock attenuation excavation methods, it is related to underground engineering cavern group excavation construction technical field, its steps are as follows: before main cavern high side wall is excavated to cross cavern elevation, first excavate cross cavern and complete lock mouth support;Ring pre-splitting blast hole is set along the contour line of main cavern side wall at the junction position, and continuous through pre-crack is formed after detonation;Main cavern high side wall is excavated in layers, and pre-crack is used as active vibration isolation barrier to block the propagation of blasting vibration wave to supported section;After through, the intersection section is reinforced support.The application forms pre-crack before large-scale blasting of main cavern, uses the discontinuity of medium to make stress wave reflection attenuation, actively reduces vibration energy from propagation path;First hole then wall makes cross cavern through and lock mouth in advance, avoids opening blasting under the condition of free surface;Combining layered excavation and staggered construction forms multiple protection, effectively avoids the vibration superposition of multiple parallel caverns and auxiliary hole vibration exceeds standard.

Description

Technical Field

[0001] This invention relates to the field of underground engineering cavern excavation and construction technology, specifically to a method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns, where the excavation is carried out before the walls are laid. Background Technology

[0002] Underground powerhouse systems typically consist of main and auxiliary powerhouses, main transformer tunnels, tailgate tunnels, and other main caverns, as well as auxiliary and intersecting caverns connected to the main caverns, such as busbar tunnels, traffic cable tunnels, and main transformer / traffic tunnels. Due to functional zoning and space utilization requirements, these intersecting caverns are mostly arranged perpendicular to the longitudinal axis of the main powerhouse, accessing from one or both sides of the high sidewalls of the main powerhouse, forming a dense cavern group structure. During the construction of such cavern groups, the sequence of excavation procedures directly affects the stability of the surrounding rock and the safety of the engineering structure.

[0003] In conventional construction practice, there are two main approaches to the excavation sequence at the intersection of the cross-section cavern and the high sidewall of the main plant. One approach is to first complete the main excavation of the large-section cavern of the main plant, and then excavate the cross-section cavern from the sidewall inwards after the high sidewall is fully formed. The other approach is to excavate the cross-section cavern from an adjacent cavern (such as the main transformer cavern) towards the main plant before the main plant is excavated to the corresponding elevation. Once the cross-section cavern is completed and its support is in place, the main plant excavation at that elevation level is then carried out.

[0004] While the latter approach embodies the "tunnel first, wall later" principle in its overall construction process, a significant challenge remains at the final connection between the cross-tunnel and the main plant's high sidewall: the blasting excavation of the last section of rock in the cross-tunnel inevitably runs adjacent to the plant's design boundary. If the vibration control during this blasting is inadequate, the resulting shockwaves will directly impact the unexcavated or newly exposed high sidewall surrounding rock, potentially causing longitudinal cracks, expanding loose zones, and even creating unfavorable structural surfaces. More critically, the high sidewall of the main plant often features a rock-wall crane beam. This structure demands extremely high integrity from the surrounding rock. Damage to the surrounding rock at the crane beam location due to blasting vibrations not only affects the crane beam's anchorage capacity but also poses safety hazards for subsequent concrete pouring and crane operation.

[0005] In existing technologies, vibration reduction at the junction of the cross-junction and the high sidewall of the main plant typically involves controlling the charge per explosion, shortening the cycle depth, and using smooth blasting. While these methods reduce blasting vibration intensity to some extent, the limited cross-sectional dimensions of the cross-junction, narrow drilling space, and difficulty in precisely controlling the angle and depth of the surrounding holes often result in inconsistent vibration reduction effects. Especially in the final few meters of the cross-junction entering the main plant sidewall, limited working conditions often prevent the placement of effective vibration-damping holes or pre-scrapers near the plant, causing vibration waves to be directly transmitted to the surrounding rock of the high sidewall. Furthermore, conventional interlocking supports are often implemented after the cross-junction excavation is completed, by which time the surrounding rock has already been affected by blasting vibrations, and the interlocking supports fail to fully realize their pre-reinforcement function.

[0006] For the reasons mentioned above, it is an urgent technical problem to be solved to develop a more effective vibration-damping excavation method for the special part where the cross-tunnel intersects with the high sidewall of the main plant without increasing the construction process and time burden. This method should ensure the forming quality of the cross-tunnel itself while protecting the integrity of the high sidewall of the main plant and the surrounding rock of the crane beam in the rock wall to the greatest extent. Summary of the Invention

[0007] The purpose of this invention is to provide a method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns, which solves the problems of surrounding rock damage and structural safety caused by blasting vibration at the intersection of the main cavern and the intersecting caverns by forming a complete system of intersecting cavern vibration-damping excavation construction method through the construction sequence of "cave first, wall later", circumferential pre-splitting blasting for vibration isolation, layered and zoned excavation, and staggered construction.

[0008] This invention is achieved through the following technical solution:

[0009] A method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns includes the following steps:

[0010] Before the main tunnel's high sidewall is excavated to the design elevation of the cross tunnel, the cross tunnel is excavated first and the lock support is completed.

[0011] At the junction of the cross chamber and the main chamber, a circumferential pre-splitting blasting hole is set along the outline of the high side wall of the main chamber. After the circumferential pre-splitting blasting hole is detonated, a continuous pre-splitting crack is formed.

[0012] The high sidewall of the main tunnel is excavated in layers. During the layered excavation process, the pre-cracks serve as an active vibration isolation barrier to block the propagation path of the blasting vibration waves generated by the blasting excavation of the high sidewall of the main tunnel towards the supported section of the cross tunnel.

[0013] After the intersecting chamber is connected to the main chamber, the intersection section is reinforced with support.

[0014] In this scheme, the method forms continuous pre-cracks on the outside of the entrance to the cross-tunnel before large-scale blasting excavation of the high sidewall of the main tunnel. The discontinuity of the medium at the pre-cracks causes reflection and transmission attenuation of the incident blasting stress waves, thereby actively and significantly reducing the vibration wave energy entering the supported area of ​​the cross-tunnel through the pre-cracks from the propagation path. This active vibration isolation mechanism effectively protects the already completed high-standard interlocking support structure and surrounding rock of the cross-tunnel from repeated disturbances during subsequent blasting of the main tunnel. Simultaneously, the "tunnel first, wall later" construction sequence adopted in this invention allows the cross-tunnel to be connected first and the interlocking support to be completed before the sidewall of the main tunnel is exposed, avoiding the need to construct the cross-tunnel before the high sidewall of the main tunnel is exposed. This invention addresses the inherent drawbacks of blasting cross-chamber openings under unfavorable conditions such as increased clamping effect, reduced borehole utilization, and increased risk of surrounding rock loosening and cracking. It improves blasting conditions at the cross-chamber openings by employing layered and zoned excavation, staggered construction of multiple cross-chambers, and active vibration isolation via circumferential pre-cracks. This provides multiple layers of protection in time and space, effectively avoiding the superposition of blasting vibrations during the construction of multiple parallel cross-chambers and the problem of excessive vibration during auxiliary borehole blasting. This is particularly beneficial for special structures highly sensitive to vibration, such as those with rock wall crane beams. Therefore, this method significantly reduces the risk of vibration damage during construction, ensuring the quality of the structure.

[0015] Furthermore, to further reduce the risk of blasting vibration damage to the supported structure of the cross chamber, the circumferential pre-splitting blasting holes are uniformly arranged along the outline of the intersection of the cross chamber and the main chamber. The hole spacing of the pre-splitting holes is 70-90cm, the hole depth is 2.5-6.0m, and the pre-splitting holes adopt a non-coupled interval charge structure with a linear charge density of 200-400g / m, so that the optimal attenuation effect is obtained throughout the entire propagation path from the vibration source to the protected object.

[0016] Furthermore, when the cross chamber is excavated first, it enters the main chamber at a predetermined distance, so that when the main chamber sidewall is excavated to the cross chamber position, the complete outline of the opening has been formed in advance and reinforced by locking. The cross chamber adopts a short advance, weak blasting, and multi-cycle excavation method to strictly control the range and degree of disturbance to the surrounding rock mass during the excavation of the cross chamber itself. After excavation, the system anchor bolts and shotcrete support are completed in a timely manner. After the cross chamber is excavated to the design cross section, the section of the opening within 1.5 times the diameter of the opening is reinforced to complete the locking construction, effectively suppressing the development of surrounding rock deformation in a harmful direction caused by stress redistribution.

[0017] Furthermore, in order to shorten the overall construction period of the cavern group and achieve a high degree of synergy between safety and efficiency, when there are multiple intersecting caverns arranged in parallel, the working faces of each intersecting cavern are staggered by a distance of not less than 30m along the longitudinal direction of the main cavern. The construction of the next cavern can only proceed after the excavation and support of the adjacent staggered cavern sections are completed.

[0018] Furthermore, the layered excavation of the high sidewall of the main tunnel adopts a combination of central slotting pre-splitting and reserved protective layer. The central slotting advances the protective layers on both sides by at least 30m, and the excavation working faces of the protective layers on both sides are staggered by no less than 30m. The protective layer is excavated after the central slotting, thereby achieving the unification of multiple objectives of vibration isolation protection of the already supported section of the intersecting tunnel, deformation control of the surrounding rock stability of the main tunnel wall, and vibration safety of special structures by the blasting of the high sidewall of the main tunnel.

[0019] Furthermore, when the high sidewall of the main chamber is excavated to the location of the intersecting chamber, according to the Sadovsky formula... The maximum single-blast charge is calculated and controlled, where V is the particle vibration velocity, Q is the maximum single-blast charge, R is the blast source distance, and K and α are the site coefficient and attenuation index calibrated through field blasting tests. The vibration isolation effect of the pre-crack is used as one of the input conditions for blasting parameter optimization. As each layer of excavation progresses and the effective vibration isolation area of ​​the pre-crack is gradually exposed, the field monitoring system acquires the vibration attenuation data after crossing the pre-crack in real time, continuously corrects and iteratively optimizes the calibration parameters, so that the maximum single-blast charge of each subsequent blasting cycle can be accurately calculated based on the latest acquired equivalent site coefficient and attenuation index. This maximizes the release of the single blasting scale and increases the advance per cycle while always ensuring the vibration safety of the supported section of the cross chamber.

[0020] Furthermore, after the intersecting chamber is connected to the main chamber, a deformation monitoring section is set up at the intersection to monitor the surrounding rock convergence and blasting vibration. The monitoring data is statistically analyzed regularly to evaluate the support effect and the stability of the surrounding rock. The monitoring frequency is dynamically adjusted according to the deformation rate, thereby constructing a full-process information monitoring system that runs through the entire intersection from excavation to long-term stability.

[0021] Furthermore, to ensure the construction safety of the supported cross-tunnel throughout the entire construction period, the interlocking support includes setting multiple rows of interlocking anchors or pipe roofs in the area outside the excavation line at the cross-tunnel entrance. The spacing between the interlocking anchors or pipe roofs is 0.3 to 1.0 m, the anchor length is 0.5 to 1 times the tunnel diameter, the top anchor is tilted upwards by 5 to 15°, and the side anchors are tilted outwards by 5 to 15°. When the set number of rows is reached, the tunnel face is covered with wire mesh and shotcrete to form an integral connection.

[0022] Furthermore, to further ensure construction safety throughout the entire construction period, when the main tunnel is equipped with a rock wall crane beam, the intersecting tunnels near the lower part of the rock wall crane beam are excavated first through the aforementioned steps. The pre-splitting depth of the circumferential pre-splitting blasting holes is not less than 6m and the pre-splitting cracks are ensured to be continuous. Before the concrete of the rock wall crane beam reaches the design strength, the excavation of adjacent tunnels within a 30m range is suspended.

[0023] Furthermore, the cross chamber is any one or more of the following: busbar tunnel, traffic cable tunnel, main transformer traffic tunnel, or tail gate traffic tunnel; the main chamber is the underground powerhouse main and auxiliary powerhouse tunnel or the main transformer tunnel.

[0024] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0025] 1. This invention forms a continuous pre-crack by setting circumferential pre-splitting blasting holes at the junction of the cross chamber and the main chamber. This pre-crack can effectively cut off or significantly reduce the propagation path of blasting vibration waves during the subsequent blasting of the high sidewall of the main chamber, reducing the disturbance of blasting vibration to the completed support structure and surrounding rock of the cross chamber. At the same time, the presence of the pre-crack causes the explosive stress wave to be reflected and refracted when it propagates to the pre-crack, resulting in a significant energy attenuation, thereby protecting the safety of the surrounding rock and support structure at the entrance section of the cross chamber.

[0026] 2. In this invention, the high sidewall of the main tunnel is excavated in layers using the method of "central groove pre-splitting and reserved protective layer". The central groove is at least 30m ahead of the protective layer, and the protective layers on both sides are staggered and follow up. This works in conjunction with the circumferential pre-splitting to reduce the impact of blasting vibration on the cross tunnel in both time and space dimensions.

[0027] 3. The present invention adopts a staggered construction sequence for multiple parallel intersecting caverns, with the construction positions of each intersecting cavern being staggered by a distance of not less than 30m along the longitudinal direction of the main cavern. This effectively avoids the vibration superposition effect when multiple intersecting caverns are blasted simultaneously, and reduces the risk of mutual interference and cumulative damage between adjacent caverns. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0029] Figure 1 This is a flowchart of the construction process of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0031] Example 1

[0032] This embodiment 1 provides a method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns, taking the construction of the intersection of the main and auxiliary powerhouses (main cavern) and the busbar tunnels (intersecting caverns) of a pumped storage power station as an example. The excavation dimensions of the main and auxiliary powerhouses of the power station are 171.8m × 24.5m × 54.7m (length × width × height), excavated in seven layers from top to bottom. The excavation span below the crane beam of the main powerhouse is 24.5m, and the span above the crane beam is 26m, with a total height of 54.7m. Four busbar tunnels are arranged in parallel between the main powerhouse and the main transformer tunnel. Each busbar tunnel is 40.0m long, with a bottom elevation of 346.0m and an excavation cross-section ranging from 7.3m × 7.5m (width × height) to 9.4m × 9.0m (width × height). The surrounding rock of the plant area is mainly of Class II to III, with local faults and alteration zones of Class IV to V.

[0033] like Figure 1 As shown, before excavating the high sidewall of the main plant to the design elevation of the busbar tunnel, a geological survey and determination of the surrounding rock type were first conducted in the busbar tunnel area. Based on the design drawings and geological survey data, the intersection angle between the busbar tunnel and the main plant was determined to be approximately 90°, with the surrounding rock type primarily classified as Class II to III. Based on the surrounding rock type, preliminary support and blasting parameters were determined: under Class II and III surrounding rock conditions, the cyclic advance of the busbar tunnel was controlled at 3.0–3.5 m; the length of the anchor bolts was 0.5–1 times the tunnel diameter, i.e., 4.5–6.0 m; the spacing between circumferential pre-splitting blasting holes was 70–90 cm, and the hole depth was 2.5–4.0 m.

[0034] Before the main plant's high sidewall is excavated to the design elevation of the busbar tunnel, the excavation of the busbar tunnel will begin from the direction of the main transformer tunnel. The busbar tunnel will be excavated in two layers. First, the upper layer (5.0m high) will be excavated, and after the upper layer is completed, the lower layer (4.0m high) will be excavated.

[0035] The upper-level excavation employed a self-made drilling platform combined with a YT-28 hand-held pneumatic drill for horizontal drilling and full-face blasting. Smooth blasting was used for the surrounding structural lines, with a blast hole spacing of 50cm. For Class II and III surrounding rock, the cyclic advance was 3.0–3.5m, and for Class IV surrounding rock, the cyclic advance was no more than 1.5m. After each excavation cycle, the excavated section was immediately supported by systematic anchor bolts and shotcrete.

[0036] After the upper layer of the busbar tunnel is excavated 2.0m into the main plant, the section of the tunnel extending 1.5 times the tunnel diameter (approximately 10.5m) from the tunnel entrance is reinforced with support to complete the interlocking construction. The interlocking support specifically includes: installing three rows of interlocking anchor bolts on the top edge outside the excavation line of the busbar tunnel entrance, with a row spacing of 1.0m. The first row is 0.5m from the designed structural surface of the high sidewall of the main plant. The interlocking anchor bolts are φ25 prestressed anchor bolts, 6.0m long, with a spacing of 1.0m. The top anchor bolts are tilted upwards at 10°, and the side anchor bolts are tilted outwards at 10°. After three rows of interlocking anchor bolts are installed, the tunnel face is reinforced with mesh and shotcrete. A φ8@15cm×15cm steel mesh is installed, and 15cm of C30 concrete is sprayed, connecting the rows of interlocking anchor bolts into a unified load-bearing system. For fractured surrounding rock sections, grouting pipe roofs are used instead of conventional anchor bolts for interlocking reinforcement.

[0037] After the lower layer is excavated and the upper layer is connected, the construction will proceed backward from the main plant to the main tunnel. Vertical drilling and stepped blasting will be carried out using YT-28 hand-held pneumatic drills. A 50cm protective layer will be reserved on the foundation surface, and horizontal drilling and smooth blasting will be carried out using hand-held pneumatic drills.

[0038] After the busbar tunnel's anchorage support is completed, circumferential pre-splitting blasting holes are installed at the junction of the busbar tunnel and the main powerhouse, along the outline of the high sidewall of the main powerhouse. The pre-splitting holes are evenly distributed along the intersection outline of the busbar tunnel and the main powerhouse, with the plane of the pre-splitting holes coinciding with the excavation outline of the high sidewall of the main powerhouse. The circumferential pre-splitting blasting holes are spaced 80cm apart, with a diameter of φ76mm and a depth of 3.0m (the smaller value is used for Class II and III surrounding rock, and 4.0–6.0m for Class IV and V surrounding rock). The pre-splitting holes employ a decoupled, spaced-charge structure, with a charge diameter of 32mm, a decoupling coefficient of approximately 2.4, an air gap length of 30–50cm, and a linear charge density of 250g / m³. Digital electronic detonators are used for sequential detonation, with the pre-splitting holes detonated before the subsequent main blasting holes on the sidewall of the main tunnel.

[0039] After the circumferential pre-splitting blasting is completed, a continuous pre-crack is formed between the busbar tunnel and the high sidewall of the main powerhouse. This pre-crack serves as an active vibration isolation barrier during subsequent large-scale blasting of the main tunnel sidewall. The discontinuity of the medium at the pre-crack causes the incident blasting stress wave to be reflected and attenuated through transmission, thereby significantly reducing the vibration wave energy that penetrates the pre-crack and enters the supported area of ​​the busbar tunnel.

[0040] After the circumferential pre-splitting blasting was completed, the high sidewalls of the main plant were excavated in layers. The high sidewalls of the main plant adopted a layered excavation method of "central groove pre-splitting and reserved protective layer". The excavation height of each layer was determined based on the location of key structures such as the rock wall crane beam. The excavation height of layer II was 9.0m, and the excavation height of each layer from layer III to VII was 8.6m.

[0041] When excavating the high sidewalls of the main plant to the location of the busbar tunnel, the central trench was excavated using a crawler hydraulic drilling rig for vertical drilling and stepped blasting. Pre-splitting blasting holes were installed at the interface with the protective layers on both sides, with a spacing of 80cm between the holes. The blasting cycle advance in the central trench was 6.0–10.0m, exceeding the protective layers on both sides by at least 30m. A 3.5m thick protective layer was reserved on the upstream and downstream sidewalls, using a two-arm drilling rig for horizontal drilling. Smooth blasting was used along the design structural edges, with a single blast length of no more than 10m for the protective layer, and the excavation working faces of the protective layers on both sides were staggered by no less than 30m.

[0042] Regarding blasting vibration control, according to the Sadovsky formula The maximum permissible charge for a single blast is calculated. The equivalent site coefficient K and the equivalent attenuation index α, including the effect of pre-cracks, are calibrated through field small-charge blasting tests. The vibration isolation effect of the pre-cracks is used as one of the input conditions for optimizing blasting parameters, and the maximum permissible charge for a single blast is calculated accordingly.

[0043] As excavation progresses through each layer, the on-site monitoring system acquires real-time vibration attenuation data after crossing the pre-cracks, continuously correcting and iteratively optimizing the calibration parameters. Specifically, the process of continuous correction and iterative optimization of the calibration parameters in this implementation is as follows:

[0044] Before the completion of circumferential pre-splitting blasting and the commencement of layered excavation of the high sidewalls of the main tunnel, a blasting vibration monitoring system is deployed within the supported sections of the intersecting tunnels. Specifically, a monitoring section is set up at the arch crown and the middle of both sidewalls at the intersection of the busbar tunnel and the main powerhouse, with 3-5 measuring points arranged at each monitoring section. The monitoring instrument used is a TC-4850 blasting vibration meter equipped with a three-component velocity sensor. The sensor is fixed to a hard, flat rock surface after being mixed with gypsum powder and water, ensuring a firm bond with the bedrock and its ability to move with the rock mass. Before fixing the sensor, the loose soil at the measuring point is cleaned and the surface is leveled, then covered with gypsum powder mixed with water to ensure a firm bond between the sensor and the measuring point surface. The sensor installation direction is perpendicular to the excavation outline of the high sidewalls of the main tunnel, with the angular error controlled within 3°.

[0045] After the circumferential pre-splitting blasting is completed and before the first round of blasting excavation of the high sidewall of the main tunnel, a small-charge blasting test is conducted to calibrate the initial parameters. Test boreholes are arranged in the area to be excavated in the high sidewall of the main tunnel, and single-hole blasting is carried out using different single-hole charges. During each blast, the peak particle vibration velocity at the measuring points of the supported section of the intersecting tunnel is recorded using the deployed monitoring system, and the distance R from the blast source is also recorded. According to the Sadovsky formula... The least squares method was used to perform regression analysis on the measured data, and the equivalent site coefficient, including the influence of pre-cracked vibration isolation, was obtained by inversion. and equivalent decay index After the initial calibration is completed, and This serves as the input parameter for the first round of blasting in the construction area.

[0046] During the layered excavation of the high sidewalls of the main tunnel, real-time data acquisition was conducted using the pre-deployed monitoring system for each round of blasting. Before blasting, the operational status of the monitoring instruments was checked to ensure that the sensors were securely fixed, the data cables were reliably connected, and the recorder parameters were correctly set. After the blast was triggered, the monitoring instruments automatically completed the acquisition, amplification, and analog-to-digital conversion of the vibration signals, recording the peak value of the three-dimensional vibration velocity, the dominant frequency, and the duration of vibration at each measuring point. After each round of blasting, on-site technicians connected the recorder to a portable computer via a data cable to read the complete vibration data for that round of blasting.

[0047] After data acquisition for each round of blasting was completed, the vibration waveforms were processed using specialized analysis software. The acquired vibration waveform data was first filtered to remove high-frequency noise interference. Then, a Fourier series was used to fit the vibration waveform data; the fitting function expression is as follows:

[0048] ;

[0049] Where t is time. , , Here, ω represents the Fourier fitting coefficients, and ω is the fundamental frequency. The peak values ​​of particle vibration velocities at each measuring point are obtained through fitting.

[0050] Substituting the actual parameters of this round of blasting (maximum single-explosive charge Q, blast source distance R) and the measured peak vibration velocity V into the Sadovsky formula, a regression analysis was performed using the least squares method. Specifically, the formula... Taking the logarithm of both sides, we get ,make Then the above formula can be written as Using the measured data from this round and previous rounds of blasting, according to Calculate the equivalent decay index ,in , The sample mean is then calculated. The values ​​of K′ and α′ are continuously updated through the continuous accumulation of monitoring data.

[0051] After obtaining the corrected equivalent site coefficient and equivalent decay index Then, it is substituted into the Sadovsky formula, combined with the safe vibration velocity threshold. Calculate the maximum permissible single-explosive charge for the next round of blasting based on the actual distance R from the blast source. On-site technicians adjusted the charge parameters for the next round of blasting based on the calculation results to ensure that the particle vibration velocity met the design requirements.

[0052] As the excavation of each layer of the high sidewall of the main tunnel progresses, the effective vibration isolation area of ​​the pre-cracks is gradually exposed, and the vibration isolation effect of the pre-cracks changes accordingly. After each round of blasting, the above data acquisition, analysis, and parameter correction steps are repeated to continuously adjust the calibration parameters. Through multiple iterations, the equivalent site coefficient K′ and the equivalent attenuation index α′ gradually converge to the true values ​​that reflect the current geological conditions and the actual vibration isolation effect of the pre-cracks, thereby ensuring that the maximum single-explosive charge of each round of blasting can maximize blasting efficiency while ensuring safety.

[0053] If monitoring data after a round of blasting shows that the peak vibration velocity at the measuring points of the supported section of the cross chamber exceeds the safety threshold, or if the vibration waveform shows obvious abnormalities (such as waveform superposition and enhancement, sudden changes in the dominant frequency, etc.), subsequent blasting operations should be immediately suspended. On-site technicians should work with the supervising engineer to analyze the monitoring data, identify the cause (such as partial non-connection of pre-cracks, sudden changes in geological conditions, etc.), and, if necessary, supplement the pre-cracks or adjust the blasting plan. Construction can only resume after safety has been confirmed.

[0054] After the excavation of the protective layer of the main plant's sidewalls is completed, the busbar tunnels will be fully connected to the main plant. The muck removal operations at the intersection of the four busbar tunnels will be carried out sequentially, and muck removal must not be organized simultaneously in the same area. Immediately after connection, the intersection section will be reinforced with additional system anchor bolts, wire mesh, and shotcrete.

[0055] Deformation monitoring sections were set up at the intersection to monitor surrounding rock convergence and blasting vibration. The monitoring frequency was dynamically adjusted according to the deformation rate: twice a day when the deformation rate was ≥5 mm / d; once a day when the deformation rate was 1–5 mm / d; once every two days when the deformation rate was 0.5–1 mm / d; once every two–3 days when the deformation rate was 0.2–0.5 mm / d; and once a week when the deformation rate was <0.2 mm / d. The monitoring data were statistically analyzed every 15–30 days to evaluate the support effect and the stability of the surrounding rock, and the support plan was dynamically adjusted as necessary.

[0056] The dynamic adjustment process is as follows: In the deformation monitoring sections set in the intersection section, each section is arranged with a total of 5 measuring points at the arch crown and the two side walls. The monitoring items include surrounding rock convergence deformation and arch crown settlement. Each round of monitoring data is recorded by on-site technicians and preliminarily sorted every ten days; every 15 to 30 days, the engineering and technical department of the project department conducts systematic statistical analysis on the monitoring data, which specifically includes drawing the deformation-time process line to intuitively judge the deformation trend of the surrounding rock, calculating the daily deformation rate and comparing it with the allowable value of the specification, judging whether the surrounding rock tends to be stable through deformation acceleration analysis, and using exponential function or logarithmic function for regression analysis to predict the final deformation and compare it with the design reserved value; according to the statistical analysis results, the surrounding rock stability state is divided into three levels: stable state (the deformation rate is continuously less than 0.2mm / d, and the cumulative deformation does not exceed 70% of the design reserved value), basically stable state (the deformation rate is between 0.2 and 0.5mm / d, the cumulative deformation exceeds 70% but does not exceed 90%), and unstable state (the deformation rate is greater than 0.5mm / d with no obvious slowing trend, or the cumulative deformation exceeds 90%), and graded disposal is implemented accordingly: maintain the original support scheme for the stable state, intensify monitoring to 2 times a week and strengthen on-site patrol for the basically stable state, immediately report for the unstable state and take reinforcement measures such as adding systematic anchor bolts, supplementary shotcreting, adding steel arches or prestressed anchor cables, and initiate the design change procedure if the deformation still does not converge after the reinforcement support; after each statistical analysis is completed, a phased monitoring report is compiled, which is reviewed by the project technical person in charge and then copied to the supervision and design units, and all monitoring data are filed uniformly, so as to realize the whole-process control of surrounding rock deformation and the dynamic optimization and adjustment of the support scheme, and ensure the long-term stability and construction safety of the intersection section under the conditions of high ground stress and strong blasting disturbance.

[0057] Embodiment 2

[0058] This embodiment takes the construction of the intersection part of the main cavern with a rock crane beam and multiple parallel busbar tunnels in the underground powerhouse of a pumped storage power station as an example, and focuses on illustrating the protection measures for the special sensitive structure of the rock crane beam and the staggered-distance construction method for multiple parallel intersecting caverns.

[0059] The main and auxiliary powerhouses are provided with rock crane beams, which are located in the second excavation layer of the main powerhouse. 4 busbar tunnels are arranged in parallel between the main powerhouse and the main transformer cavern with a spacing of 25m, and the staggered distance between the working faces of each busbar tunnel along the longitudinal direction of the main powerhouse is not less than 30m.

[0060] The busbar tunnel near the lower part of the rock wall crane beam is excavated first using the method of this invention. The pre-splitting depth of the circumferential pre-splitting blasting holes is not less than 6m, and the pre-splitting cracks are ensured to be continuous and penetrate beyond the anchoring ends of the rock wall crane beam anchor rods (the anchor rod length is usually 6m), ensuring that the integrity of the rock mass on which the crane beam anchoring system depends is not damaged by subsequent blasting vibrations. Before the concrete of the rock wall crane beam reaches the design strength, excavation of adjacent tunnels within a 30m range is suspended. The 30m distance standard is consistent with the 30m advance protective layer for trenching and the 30m staggered construction of intersecting tunnels in layered excavation, ensuring that vibration attenuation is within the safe threshold.

[0061] The specific construction sequence for the four busbar tunnels is as follows: First, construct busbar tunnel #1, excavating 2.0m into the main plant building before completing the interlocking support and circumferential pre-splitting blasting. After busbar tunnel #1 is completed, construction of busbar tunnel #3 (staggered from #1 by 35m) begins, and simultaneously, the sidewalls of the main plant building in the area containing busbar tunnel #1 can begin layered excavation. After busbar tunnel #3 is completed, construction of busbar tunnel #2 (staggered from #3 by 35m) begins; and so on, with busbar tunnel #4 being constructed last. The staggered distance between each intersecting tunnel is no less than 30m. Construction of the next tunnel can only proceed after the excavation and support of adjacent staggered tunnel sections are completed, effectively avoiding the vibration superposition effect when blasting operations are carried out simultaneously in multiple intersecting tunnels.

[0062] The remaining construction steps are the same as in Example 1, and will not be repeated here.

[0063] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns, characterized in that, Includes the following steps: Before the main tunnel's high sidewall is excavated to the design elevation of the cross tunnel, the cross tunnel is excavated first and the lock support is completed. At the junction of the cross chamber and the main chamber, a circumferential pre-splitting blasting hole is set along the outline of the high side wall of the main chamber. After the circumferential pre-splitting blasting hole is detonated, a continuous pre-splitting crack is formed. The high sidewall of the main tunnel is excavated in layers. During the layered excavation process, the pre-cracks serve as an active vibration isolation barrier to block the propagation path of the blasting vibration waves generated by the blasting excavation of the high sidewall of the main tunnel towards the supported section of the cross tunnel. After the intersecting chamber is connected to the main chamber, the intersection section is reinforced with support.

2. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 1, characterized in that, The circumferential pre-splitting blasting holes are evenly arranged along the outline of the intersection of the cross chamber and the main chamber. The hole spacing of the pre-splitting holes is 70-90cm, the hole depth is 2.5-6.0m, and the pre-splitting holes adopt a non-coupled interval charging structure with a linear charge density of 200-400g / m.

3. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 1, characterized in that, When the cross tunnel is excavated first, it enters the main tunnel at a predetermined distance. The cross tunnel adopts a short advance, weak blasting, and multi-cycle excavation method. After excavation, the system anchor bolts and shotcrete support are completed in time. After the cross tunnel is excavated to the design cross section, the tunnel section within 1.5 times the tunnel diameter at the tunnel entrance is reinforced with support to complete the lock-in construction.

4. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 1, characterized in that, When there are multiple intersecting caverns arranged in parallel, the working faces of each intersecting cavern shall be staggered by a distance of not less than 30m along the longitudinal direction of the main cavern. Construction of the next cavern can only proceed after the excavation and support of the adjacent staggered cavern sections have been completed.

5. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 1, characterized in that, The layered excavation of the high sidewall of the main tunnel adopts a combination of central trenching and pre-splitting with reserved protective layers. The central trenching advances the protective layers on both sides by at least 30m, and the excavation working surfaces of the protective layers on both sides are staggered by no less than 30m. The protective layers are excavated after the central trenching.

6. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 1, characterized in that, When the high sidewall of the main chamber is excavated to the location of the intersecting chamber, according to the Sadovsky formula... The maximum single-explosive charge is calculated, where V is the particle vibration velocity, Q is the maximum single-explosive charge, R is the blast source distance, and K and α are the site coefficient and attenuation index calibrated through field blasting tests. The vibration isolation effect of the pre-crack is used as one of the input conditions for optimizing blasting parameters.

7. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 6, characterized in that, After the cross chamber is connected to the main chamber, a deformation monitoring section is set at the intersection to monitor the surrounding rock convergence and blasting vibration. The monitoring data is statistically analyzed regularly to evaluate the support effect and the stability of the surrounding rock. The monitoring frequency is dynamically adjusted according to the deformation rate.

8. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 7, characterized in that, The interlocking support includes setting multiple rows of interlocking anchors or pipe roofs in the area outside the excavation line of the cross-shaped tunnel entrance. The spacing between the interlocking anchors or pipe roofs is 0.3 to 1.0 m, the length of the anchor is 0.5 to 1 times the tunnel diameter, the top anchor is tilted upwards by 5 to 15 degrees, and the side anchors are tilted outwards by 5 to 15 degrees. When the set number of rows is reached, the tunnel face is covered with wire mesh and shotcrete to form an integral connection.

9. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to claim 1, characterized in that, When the main cavern is equipped with a rock wall crane beam, the cross caverns near the lower part of the rock wall crane beam are excavated first through the above steps. The pre-splitting depth of the circumferential pre-splitting blasting hole is not less than 6m and the pre-splitting crack is continuously connected. Before the concrete of the rock wall crane beam reaches the design strength, the excavation of the adjacent caverns within 30m of it is suspended.

10. The method for circumferential pre-splitting and vibration-damping excavation of intersecting caverns according to any one of claims 1 to 9, characterized in that, The cross chamber is any one or more of the following: busbar tunnel, traffic cable tunnel, main transformer traffic tunnel, or tail gate traffic tunnel; the main chamber is the underground powerhouse main and auxiliary powerhouse tunnel or the main transformer tunnel.

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