Dynamic collaborative support method for micro-perturbation grouting of deep foundation pit underpass in water-rich sand layer

Abstract

The present application relates to the field of construction engineering technology, and provides a kind of water-rich sand layer deep foundation pit underpass micro-perturbation grouting dynamic collaborative support method, comprising: micro-perturbation grouting construction, grouting is carried out outside the contour line of foundation pit slope and underpass, to form grouting reinforcement curtain;Stratified excavation is carried out under the protection of the grouting reinforcement curtain;Early strength shotcrete support, after excavation, early strength concrete is sprayed to the excavation face using wet spraying process, to form a support shell, to timely close the water-rich sand layer excavation face, resist groundwater pressure;Dynamic monitoring and adjustment, real-time monitoring is carried out during construction, and construction parameters are adjusted according to monitoring data;Wherein, the grouting operation surface is ahead of the excavation operation surface, to provide a pre-reinforced safe operation surface for excavation;The spray support operation surface follows the excavation operation surface, to timely close the water-rich sand layer excavation face.The present application can effectively block seepage and prevent piping, to realize high efficiency and high safety of water-rich sand layer construction.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and in particular to a dynamic collaborative support method for micro-disturbance grouting of a deep foundation pit underpass in a water-rich sand layer. Background Technology

[0002] With the acceleration of urbanization, the number of municipal underground road projects is increasing. These projects are mostly located in the core urban areas, surrounded by dense buildings and complex underground pipelines, and involve deep excavation pits and high requirements for the connection between underpasses and box culvert structures. Traditional deep foundation pit support techniques mainly include sheet pile support and soil nailing wall support. While these traditional techniques have certain applicability under normal geological conditions, they have significant limitations in special geological environments such as water-rich sand layers.

[0003] Constructing deep foundation pit tunnels in water-rich sand layers presents multiple technical challenges: (1) Difficulty in controlling formation disturbance Water-rich sandy layers are characterized by high permeability and poor self-stability. The upper layer is often located at the interface between silty soil and medium-coarse sand strata, with significant differences in soil properties. The lower layer is mostly medium-coarse and fine sand. Traditional high-pressure grouting reinforcement techniques easily lead to ground heave and crack expansion, causing deformation of surrounding buildings and excessive settlement of underground pipelines. Especially at the junction of underpasses and existing box culvert structures, excessive ground disturbance will directly affect structural safety and functionality.

[0004] (2) Insufficient support timeliness Traditional shotcrete has a long initial setting time and slow early strength development, making it unable to form effective support in a timely manner after excavation of water-rich sand layers. After the excavation face of water-rich sand layers is exposed, geological hazards such as quicksand and piping are prone to occur under water pressure, requiring the support structure to have load-bearing capacity within a short period of time. Conventional shotcrete cannot meet the urgent need for rapid closure and reduced exposure, and the excessively long support cycle leads to the accumulation of construction risks.

[0005] (3) Poor process coordination In traditional construction methods, grouting reinforcement, layered excavation, and shotcrete support are relatively independent processes, lacking an effective time-series coordination mechanism. Inappropriate spacing between grouting and excavation, and excessive lag of shotcrete support behind the excavation face, lead to a disconnect between the reinforcement, excavation, and support processes, making it impossible to establish a continuous and stable construction control system in high-risk strata such as water-rich sand layers. The information fragmentation between processes also prevents timely feedback of monitoring data to guide adjustments to construction parameters.

[0006] (4) Failure of interlayer water control The sandy layer contains abundant groundwater, and seepage channels easily form at the strata interface, making it difficult for the outer water-stop curtain of the retaining structure to completely seal off the groundwater. Traditional single horizontal or vertical grouting is insufficient to construct an effective three-dimensional water-stopping system, resulting in an extremely high risk of leakage and a high likelihood of foundation pit collapse or damage to the surrounding environment.

[0007] To address the aforementioned technical challenges, traditional solutions suffer from the following main drawbacks: (1) Lack of grouting technology suitable for water-rich sand layers Traditional grouting techniques often use conventional pressure parameters without considering the special needs of water-rich sand layers. Improper selection of grouting pressure leads to uncontrollable ground disturbance, severe grout loss, and an inability to form a continuous and effective reinforcement curtain. Furthermore, it makes it difficult to achieve the stringent target of controlling the settlement of surrounding pipelines to within 3mm.

[0008] (2) Lack of early-strength and impermeable shotcrete technology Traditional shotcrete formulations are not adapted for water-rich sand layers, resulting in slow early strength development and insufficient crack and seepage resistance. Under high water pressure in water-rich sand layers, the support shell is prone to shrinkage cracks, leading to groundwater infiltration and support failure, making it unable to withstand excavation loads and effectively stop water in a timely manner.

[0009] (3) Lack of a dynamic and coordinated closed-loop control system Traditional construction methods lack an integrated collaborative control mechanism for grouting, excavation, and support, and there is a lack of reasonable timing coordination and real-time monitoring feedback between each process. Key parameters such as grouting advance distance and support lag distance are determined based on experience, without the ability to dynamically adjust based on monitoring data, making it difficult to cope with sudden risks in the construction of water-rich sand layers.

[0010] (4) Lack of spatial three-dimensional reinforcement design Traditional grouting reinforcement often employs a single grouting method. In environments where water-rich sand layers are difficult to control interlayer water, a single reinforcement method is insufficient to block seepage channels and provides inadequate water-stopping stability. Summary of the Invention

[0011] The purpose of this invention is to solve at least one technical problem in the background art and to provide a dynamic collaborative support method for micro-disturbance grouting of deep foundation pits underpasses in water-rich sand layers.

[0012] To achieve the above objectives, this invention provides a method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits and tunnels in water-rich sand layers, characterized by comprising: S1. Micro-disturbance grouting construction: Grouting is carried out outside the outline of the foundation pit slope and the underpass to form a grouting reinforcement curtain. S2. Excavation is carried out in layers and sections under the protection of the grouting and reinforcement curtain; S3. Early-strength shotcrete support: After excavation, early-strength concrete is sprayed onto the excavation face using a wet spraying process to form a support shell, which can promptly seal the excavation face of the water-rich sand layer and resist groundwater pressure. S4. Dynamic monitoring and adjustment: Real-time monitoring is conducted during construction, and construction parameters are adjusted based on the monitoring data; Between step S1 and step S2, the grouting working face is ahead of the excavation working face, providing a pre-reinforced safe working face for excavation; between step S2 and step S3, the shotcrete working face closely follows the excavation working face, promptly sealing the excavation face of the water-rich sand layer.

[0013] According to one aspect of the present invention, the grouting adopts a low-pressure slow injection and layered segmented process.

[0014] According to one aspect of the invention, the grout is a cement-water glass two-component grout.

[0015] According to one aspect of the present invention, grouting reinforcement includes a dual reinforcement method of horizontal grouting and vertical grouting. Horizontal grouting involves drilling a hole horizontally on the excavation surface of the foundation pit and then injecting a cement-water glass grout. Vertical grouting involves drilling a hole vertically at a predetermined distance outside the outline of the underpass and then injecting a cement-water glass grout.

[0016] According to one aspect of the invention, the horizontal grouting and the vertical grouting form a spatially intersecting, continuous, grid-like waterstop curtain outside the outline of the underpass channel.

[0017] According to one aspect of the present invention, the initial setting time of the cement-water glass slurry after mixing is controlled at 10 to 15 minutes.

[0018] According to one aspect of the invention, the early-strength concrete contains an early-strength agent and polypropylene fibers.

[0019] According to one aspect of the present invention, the mix proportion of the early-strength concrete is cement:sand:crushed stone = 1:2:2.5, and the dosage of early-strength agent is 8% to 10%.

[0020] According to one aspect of the present invention, the real-time monitoring includes monitoring the settlement around the foundation pit, and when the settlement value exceeds a preset value or the displacement rate reaches a preset value, the excavation is immediately stopped and reinforcement measures are taken.

[0021] According to one aspect of the invention, the reinforcement measures include: increasing grouting pressure, thickening shotcrete, reducing excavation speed, or increasing grouting hole density.

[0022] According to the present invention, a dynamic synergistic support method for micro-disturbance grouting in deep foundation pits with water-rich sand layers is proposed. A low-pressure, slow-injection, layered and segmented process is used to inject cement-water glass dual-liquid grout, forming a closed water-stop curtain through horizontal and vertical cross-grouting. Under the protection of this curtain, excavation is carried out in layers and segments. Immediately afterwards, early-strength concrete mixed with an early-strength agent and polypropylene fiber is sprayed to achieve rapid sealing and load-bearing. Settlement and displacement are monitored in real time throughout the process; if limits are exceeded (e.g., settlement ≥ 3mm), excavation is immediately stopped and reinforcement is initiated. The key synergy is that grouting precedes excavation, and support follows immediately, forming a seamless connection between reinforcement, excavation, and support. This invention can ensure that ground settlement is controlled within the threshold range, shorten the support cycle by more than 60%, effectively block seepage, prevent quicksand piping, and achieve micro-disturbance, high efficiency, and high safety in the construction of deep foundation pits in water-rich sand layers. Attached Figure Description

[0023] Figure 1 The flowchart illustrates a method for dynamic collaborative support of micro-disturbance grouting for deep foundation pits in water-rich sand layers according to an embodiment of the present invention. Detailed Implementation

[0024] The invention will now be discussed with reference to exemplary embodiments. It should be understood that the described embodiments are merely intended to enable those skilled in the art to better understand and thus implement the invention, and are not intended to imply any limitation on the scope of the invention.

[0025] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment".

[0026] Figure 1 This is a schematic flowchart illustrating a dynamic collaborative support method for micro-disturbance grouting in deep foundation pits underpasses in water-rich sand layers, according to an embodiment of the present invention. Figure 1 As shown in this embodiment, the method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits under passages in water-rich sandy layers includes: S1. Micro-disturbance grouting construction: Grouting is carried out in the horizontal direction of the foundation pit and vertically outside the outline of the underpass to form a grouting reinforcement curtain. S2. Excavation is carried out in layers and sections, under the protection of a grouting-reinforced curtain; S3. Early-strength shotcrete support: After excavation, early-strength concrete is sprayed onto the excavation face using a wet spraying process to form a support shell, which can promptly seal the excavation face of the water-rich sand layer and resist groundwater pressure. S4. Dynamic monitoring and adjustment: Real-time monitoring is conducted during construction, and construction parameters are adjusted based on the monitoring data; Between steps S1 and S2, the grouting working face is ahead of the excavation working face, providing a pre-reinforced safe working face for excavation; between steps S2 and S3, the shotcrete working face closely follows the excavation working face, promptly sealing the excavation face of the water-rich sand layer.

[0027] In this embodiment, in step S1, micro-disturbance grouting is performed outside the outline of the foundation pit slope and the underpass (grouting is performed horizontally in the foundation pit and vertically outside the outline of the underpass) to form a grouting reinforcement curtain. Micro-disturbance grouting is a construction method that injects grout at lower pressure and slower speed, allowing the grout to primarily penetrate and fill the pores of the strata rather than split the strata. This avoids the ground heave or crack expansion that may be caused by traditional high-pressure grouting, minimizing the disturbance to the surrounding soil caused by the grouting construction itself. Choosing the grouting location outside the outline of the foundation pit slope and the underpass means that the grouting is precisely targeted at reinforcing the outer boundary of the area to be excavated, forming a continuous reinforcement curtain outside the outline of the passage. On the one hand, the grouting curtain fills the pores of the water-rich sand layer with grout and cements the loose sand particles, transforming the originally poorly self-stabilizing strata into a reinforced zone with a certain strength and integrity, providing pre-support for subsequent excavation; on the other hand, the continuous and dense grouting curtain can effectively block the interlayer seepage channels formed by the strata interface in the water-rich sand layer, preventing groundwater from flowing into the foundation pit and reducing the risk of piping and quicksand disasters from the source.

[0028] Furthermore, in step S2, the excavation is carried out under the protection of a grouting-reinforced curtain and in a layered and segmented manner. The protection of the grouting-reinforced curtain has two meanings: first, spatially, the excavation operation is always located within the grouted-reinforced area, rather than directly excavating in the original strata; therefore, the soil around the excavation face already possesses high strength and impermeability. Second, temporally, excavation only begins after the grouting reinforcement is completed and an effective curtain is formed, ensuring that the excavation operation always has a pre-reinforced barrier as a support. In this embodiment, the layered and segmented approach further limits the excavation method, controlling the excavation height of each layer and the excavation length of each segment, prohibiting large-area or deep excavation at once. The technical advantages of this approach are twofold: Firstly, because the excavation face is encased in a grouting curtain, the risk of collapse or sand inrush during excavation is significantly reduced, thus improving construction safety. Secondly, controlling the excavation height of each layer and the length of each section effectively controls the rate and extent of ground unloading, avoiding stress concentration and severe ground displacement caused by excessive excavation at one time, thereby significantly reducing surface settlement and deformation of surrounding pipelines. At the same time, the regular and flat excavation face also provides a good adhesion base for subsequent shotcrete.

[0029] Furthermore, in step S3, after excavation, early-strength concrete is sprayed onto the excavation face using a wet spraying process to form a support shell. The purpose is to promptly seal the excavation face of the water-rich sand layer and resist groundwater pressure. In water-rich sand layers, once the excavation face is exposed, groundwater, under pressure, will carry fine soil particles from the sand layer towards the excavation face. If not sealed promptly, this can easily evolve into quicksand or even piping. Therefore, timely sealing means minimizing the time interval between excavation and support. Spraying is typically performed immediately after each layer and section of excavation is completed, preventing prolonged exposure of the excavation face. Early-strength concrete ensures that the concrete sprayed onto the excavation face can harden and gain strength in a very short time, thus rapidly sealing the excavation face. The resulting support shell is a continuous, dense concrete shell directly attached to the surface of the excavation face. The technical effects of this shell are reflected in three aspects: First, it physically seals the excavation face, preventing sand particles from seeping out under water pressure and cutting off the path of quicksand. Second, after the shell hardens, it can immediately withstand the soil and water pressure of the excavation face, preventing excessive deformation of the surrounding rock. Third, the shell and the grouting reinforcement curtain formed in step S1 cooperate spatially. The grouting curtain is mainly responsible for the water stoppage and reinforcement of the outer strata, while the shotcrete shell is mainly responsible for the immediate sealing and bearing of the excavation face. Together, they form a double seepage prevention and bearing system of outer curtain and inner shell. Even if there are minor defects in the outer grouting curtain, the inner shell can act as a second line of defense to prevent groundwater from entering the foundation pit.

[0030] Furthermore, in step S4, real-time monitoring is conducted during construction, and construction parameters are adjusted based on the monitoring data. This means that throughout the entire construction cycle, data such as stratum deformation and support structure status are continuously or frequently collected by deploying monitoring instruments. This data serves two purposes: firstly, it is used to determine the safety of the current construction status in real time. If abnormal trends are detected in indicators such as settlement, displacement, or seepage, timely warnings can be issued and countermeasures taken before reaching dangerous thresholds. Secondly, the monitoring data serves as feedback information to dynamically optimize subsequent construction parameters. For example, based on the actual settlement after excavation of a certain section, the excavation speed or grouting pressure of the next section can be appropriately adjusted. This forms a closed-loop control mechanism of monitoring, analysis, adjustment, and re-monitoring, enabling the construction plan to adapt in real time to the complex and variable geological conditions of the water-rich sand layer, avoiding the blindness and lag that may result from experience-based construction.

[0031] In this embodiment, "grouting face preceding excavation face" means that the grouting operation is always located ahead of the excavation face in the direction of excavation. In other words, at any construction section, grouting reinforcement is completed in advance, and then the excavation operation proceeds to that section. This sequential constraint of reinforcement before excavation ensures that the excavator always operates in a pre-reinforced, safe stratum, rather than risking excavation in the original water-rich sand layer. Secondly, "shotcrete support face immediately following excavation face" means that after each layer and section of excavation is completed, shotcrete support operation immediately follows, minimizing the distance between the support face and the excavation face. This means that once the excavation face is formed, it is covered by the concrete shell with almost no time interval. These two sequential relationships together construct a collaborative control mode of grouting preceding excavation and support immediately following excavation, the technical effect of which is to achieve seamless connection of the three processes of reinforcement, excavation, and support in space and time. In essence, pre-grouting provides a pre-reinforced safety zone for excavation, enabling excavation operations to proceed under low-risk conditions. After excavation, support is immediately installed, instantly sealing and bearing the newly exposed excavation face, eliminating the dangerous exposure period of prolonged unsupported excavation common in traditional construction. Furthermore, there are no waiting or gaps caused by disjointed procedures between grouting and excavation, or between excavation and support. This close collaboration fundamentally solves two core challenges in deep foundation pit construction in water-rich sandy layers—large-scale ground disturbance and high seepage risk—because pre-reinforcement controls the source of ground deformation and promptly seals and prevents seepage channels. Simultaneously, the compact and uninterrupted process significantly improves overall construction efficiency, overcoming the contradiction in traditional methods where safety comes at the cost of slowness, or speed comes at the cost of risk.

[0032] Furthermore, according to one embodiment of the present invention, the grouting adopts a low-pressure slow injection and layered segmented process.

[0033] In this embodiment, low pressure refers to the grouting pressure being precisely adapted to the formation characteristics: controlled at 0.3–0.5 MPa in soft soil and 0.6–0.8 MPa in sandy layers. This pressure range ensures effective penetration and filling of formation pores with grout while avoiding formation uplift or fracture propagation caused by high-pressure grouting. Slow grouting refers to gradually increasing the pressure to the design pressure during the grouting process and maintaining it stably for 3–5 minutes, allowing the grout to slowly fill the sandy layer pores through penetration and diffusion, rather than forcibly fracturing the formation. Simultaneously, the layered and segmented process is further refined as follows: grouting is carried out in segments of 1.0 m along the length of the grouting hole, with an interval of no less than 24 hours between adjacent grouting holes to prevent grout leakage. The grouting volume per hole is dynamically calculated based on the formation porosity and the volume of the solidified material multiplied by a coefficient of 1.2, ensuring that the grouting volume accurately matches the actual needs of the formation. 24 hours after grouting is completed, the continuity of the reinforced curtain is checked using ground-penetrating radar, or the compressive strength of the reinforced body is checked by core drilling (required ≥1.5MPa). Any areas that fail to meet the requirements are then re-grouted. The technical effects of the above-mentioned parameterized control include: low-pressure, slow grouting ensures uniform penetration of the grout into the water-rich sand layer, preventing grout loss or formation fracturing, minimizing disturbance to surrounding buildings and underground pipelines, with measured settlement of surrounding pipelines controlled within 3mm; segmented grouting combined with inter-hole interval construction effectively prevents grout leakage, ensuring each grouting section forms an independent curtain with a thickness ≥1.2m and reliable continuity; dynamic calculation of grouting volume and post-grouting testing ensure the compressive strength of the reinforced body and the integrity of the curtain, increasing formation cohesion by 50%–80% and internal friction angle by 20%–30%, fundamentally blocking inter-layer seepage channels in the water-rich sand layer and preventing geological disasters such as piping and quicksand. In summary, the low-pressure slow injection and layered segmented process, through precise control of pressure, segment length, grouting volume, and testing parameters, achieves micro-disturbance, high uniformity, and high reliability in the grouting reinforcement of water-rich sand layers, providing a stable pre-reinforced safe working surface for subsequent excavation.

[0034] Furthermore, according to one embodiment of the present invention, the grouting slurry is a cement-water glass two-component slurry.

[0035] In this embodiment, the grouting slurry uses a cement-water glass two-component slurry with a volume ratio of 1:0.8 to 1:1.2. After mixing, this two-component slurry rapidly gels through the chemical reaction between cement and water glass, with an initial setting time controllable within 10-15 minutes. This characteristic has significant technical benefits for water-rich sand layers: these layers have high permeability and porosity. If ordinary cement-based single-component slurry is used, the slurry is easily lost under the dynamic action of groundwater, making it difficult to effectively accumulate in the designated area. The cement-water glass two-component slurry, however, has a short gel time and quickly loses its fluidity after mixing, effectively resisting dilution and scouring by groundwater, preventing slurry loss in water-rich strata, and ensuring effective filling around the grouting holes. The initial setting time of 10-15 minutes satisfies the construction window required for grouting pumping and permeation diffusion, while preventing pipe blockage or grouting interruption due to excessively rapid gelation, thus ensuring the continuity and controllability of the grouting operation. The cement-water glass two-component grout, after gelation, forms a stone-like structure with high early strength and good impermeability. It can rapidly cement loose sand particles in water-rich sand layers, transforming poorly self-stabilizing strata into a continuous and dense reinforced curtain, effectively blocking interlayer seepage channels and preventing geological disasters such as piping and quicksand. Compared to ordinary cement grout, the two-component grout has a lower shrinkage rate and a tighter bond with the sand layer interface, reducing micro-cracks between the grout and the strata after solidification and improving the long-term stability of the water-stop curtain. In summary, by adapting the volume ratio and initial setting time of the cement-water glass two-component grout to the water-rich sand layer, it achieves controllable injection, rapid gelation, effective filling, and reliable water stoppage, making it a key material guarantee for micro-disturbance grouting reinforcement technology.

[0036] Furthermore, according to one embodiment of the present invention, grouting reinforcement includes a dual reinforcement method of horizontal grouting and vertical grouting. Horizontal grouting involves drilling a hole horizontally on the excavation surface of the foundation pit and then injecting a cement-water glass grout. Vertical grouting involves drilling a hole vertically at a predetermined distance outside the outline of the underpass and then injecting a cement-water glass grout.

[0037] In this embodiment, horizontal grouting and vertical grouting form a continuous spatial grid-like waterstop curtain with vertical intersections outside the outline of the underpass.

[0038] In this embodiment, grouting reinforcement employs a dual reinforcement method of horizontal and vertical grouting. Horizontal grouting involves drilling holes horizontally along the excavation face (i.e., the pit sidewall) with a diameter of Φ50–Φ80 mm, a drilling depth exceeding the excavation face by 2.0 m, a hole spacing of 1.0–1.2 m, and a hole inclination ≤1%. After drilling, a cement-water glass dual-liquid grout is injected. Vertical grouting involves drilling holes vertically along the tunnel outline at a location 1.5–2 m outside the tunnel outline, and similarly injecting a cement-water glass dual-liquid grout. These two grouting methods form a vertically intersecting continuous water-stopping curtain in space, with the following technical effects: Horizontal grouting primarily reinforces the excavated soil surrounding the sidewalls of the foundation pit, forming a horizontal reinforcement layer. This layer extends horizontally along the pit sidewalls, effectively blocking the seepage path of lateral groundwater into the pit while simultaneously increasing the shear strength of the sidewall soil, preventing collapse or excessive deformation of the sidewalls during excavation. The drilling depth for horizontal grouting exceeds the excavation face by 2.0m, ensuring that the reinforcement covers the entire excavation depth and avoiding reinforcement blind spots.

[0039] Vertical grouting is injected vertically downwards at a distance of 1.5–2m from the outer edge of the underpass outline, forming a vertical water-stop curtain. This distance (1.5–2m) ensures the curtain adheres closely to the underpass structure, avoiding excessive reinforcement and waste, while also providing sufficient space to prevent disturbance to the underpass outline during drilling. The main function of the vertical grouting curtain is to cut off the vertical seepage channels formed by groundwater along stratum interfaces (such as the interface between silty soil and medium-coarse sand), preventing the sudden surge of confined water at the bottom.

[0040] The horizontal grouting layer and the vertical grouting curtain intersect vertically in space, overlapping at their junction outside the outline of the underpass (due to grout flow and seepage), together forming a closed, spatially grid-like continuous waterproofing and reinforcement ring. This three-dimensional intersecting structure overcomes the limitations of a single grouting method (horizontal or vertical only): single horizontal grouting cannot block vertical seepage at the bottom, and single vertical grouting is difficult to control lateral horizontal seepage. The double grouting, through its cross-coverage, achieves comprehensive, all-around waterproofing and reinforcement of the water-rich sand layer.

[0041] Furthermore, according to one embodiment of the present invention, the early-strength concrete contains an early-strength agent and polypropylene fibers.

[0042] In this embodiment, the mix proportion of the early-strength concrete is cement:sand:crushed stone = 1:2:2.5. 8%–10% of a composite early-strength agent and an appropriate amount of polypropylene fiber are incorporated into the early-strength concrete. The early-strength agent accelerates the cement hydration reaction, shortening the initial setting time of the concrete to within 15 minutes and controlling the final setting time to within 30 minutes. It can withstand excavation loads within 2 hours after spraying, thus meeting the urgent need for rapid closure and reduced exposure of the excavation face in water-rich sand layers, effectively preventing sand from seeping out of the excavation face under water pressure. The polypropylene fiber is randomly distributed in the concrete to form a three-dimensional network reinforcement structure. On the one hand, it inhibits the generation of early plastic shrinkage cracks and reduces microcracks formed by water evaporation and chemical shrinkage; on the other hand, it improves the fracture toughness and impermeability of the concrete, extends the seepage path, and prevents groundwater from seeping in along cracks and causing support failure. The combination of early strength agent and polypropylene fiber achieves a synergistic effect of rapid load-bearing and crack resistance and seepage prevention, enabling the shotcrete shell to quickly play a supporting role in the high water pressure environment of water-rich sand layer, and to maintain structural integrity and water-stopping stability for a long time.

[0043] Furthermore, according to one embodiment of the present invention, real-time monitoring includes monitoring the settlement around the foundation pit. When the settlement value exceeds a preset value or the displacement rate reaches a preset value, excavation is immediately stopped and reinforcement measures are taken.

[0044] In this embodiment, the reinforcement measures include: increasing the grouting pressure, thickening the shotcrete, reducing the excavation speed, or increasing the density of grouting holes.

[0045] In this embodiment, real-time monitoring is one of the core components of the dynamic collaborative control system, focusing on monitoring settlement around the foundation pit. The aforementioned preset values ​​are specifically: settlement ≥ 3mm, or displacement rate ≥ 2mm / d. These two preset values ​​are determined based on the deformation sensitivity of the water-rich sand layer and the protection requirements of the surrounding environment (dense buildings and underground pipelines), and have clear physical significance: a settlement of 3mm is a critical threshold for controlling the safe operation of surrounding pipelines, while a displacement rate of 2mm / d reflects whether the stratum deformation has entered an accelerated phase, serving as a sensitive indicator for early warning.

[0046] When the monitoring data reaches or exceeds the preset value, excavation is immediately stopped and reinforcement measures are taken. In this embodiment, data is collected in real time at a high frequency (e.g., settlement monitoring once every 2 hours) to ensure that any minor deformation exceeding the standard can be detected in time, preventing deformation from accumulating to an uncontrollable level. Compared with post-construction inspection or low-frequency sampling in traditional construction, real-time monitoring can capture instantaneous anomalies in stratum deformation, winning valuable time for emergency response. Immediately stopping excavation is the first line of defense in risk control. Excavation is the main source of stratum unloading; stopping excavation can immediately block the driving force of deformation development, preventing accelerated settlement or chain reactions such as quicksand and piping caused by continued excavation. Reinforcement measures include: increasing grouting pressure (e.g., increasing by 0.1-0.2 MPa), thickening shotcrete (e.g., increasing by 20-30 mm), reducing excavation speed (e.g., ≤3 m / d), or increasing the density of grouting holes (e.g., reducing the spacing to 0.8 m). These measures target different causes of settlement exceeding limits: if settlement is caused by insufficient grouting, then grouting density is increased or pressure is raised; if it is caused by insufficient support stiffness, then shotcrete thickness is increased; if it is caused by excessive excavation speed, then the speed is reduced. The selection of measures can be dynamically decided based on the characteristics of monitoring data (settlement rate, distribution range, etc.). Through a closed-loop mechanism of monitoring, early warning, stopping, reinforcement, and re-monitoring, construction parameters are always kept under control. Even in complex and variable water-rich sand layers, settlement can be strictly controlled within 3mm, avoiding major safety accidents such as foundation pit collapse or pipeline damage caused by excessive deformation.

[0047] According to the above-described scheme of the present invention, this invention proposes a dynamic synergistic support method for micro-disturbance grouting in deep foundation pits with water-rich sand layers. A low-pressure, slow-injection, layered and segmented process is used to inject cement-water glass dual-liquid grout, forming a closed water-stop curtain through horizontal and vertical cross-grouting. Under the protection of this curtain, excavation is carried out in layers and segments; subsequently, early-strength concrete mixed with an early-strength agent and polypropylene fiber is sprayed to achieve rapid sealing and load-bearing. Settlement and displacement are monitored in real time throughout the process; if limits are exceeded (e.g., settlement ≥ 3mm), excavation is immediately stopped and reinforcement is initiated. The key synergy is that grouting precedes excavation, and support follows excavation, forming a seamless connection between reinforcement, excavation, and support. This invention can ensure that ground settlement is controlled within the threshold range, shorten the support cycle by more than 60%, effectively block seepage, prevent quicksand piping, and achieve micro-disturbance, high efficiency, and high safety in the construction of deep foundation pits in water-rich sand layers.

[0048] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this application.

[0049] It should be understood that the sequence number of each step in the invention and its embodiments does not absolutely imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

Claims

1. A method for dynamic coordinated support of micro-disturbance grouting for underpasses in deep foundation pits in water-rich sandy layers, characterized in that... include: S1. Micro-disturbance grouting construction: Grouting is carried out outside the outline of the foundation pit slope and the underpass to form a grouting reinforcement curtain. S2. Excavation is carried out in layers and sections under the protection of the grouting and reinforcement curtain; S3. Early-strength shotcrete support: After excavation, early-strength concrete is sprayed onto the excavation face using a wet spraying process to form a support shell, which can promptly seal the excavation face of the water-rich sand layer and resist groundwater pressure. S4. Dynamic monitoring and adjustment: Real-time monitoring is conducted during construction, and construction parameters are adjusted based on the monitoring data; Between step S1 and step S2, the grouting working face is ahead of the excavation working face, providing a pre-reinforced safe working face for excavation; between step S2 and step S3, the shotcrete working face closely follows the excavation working face, promptly sealing the excavation face of the water-rich sand layer.

2. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 1, characterized in that, The grouting process employs low-pressure, slow-injection, and layered / segmented techniques.

3. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 1, characterized in that, The grouting slurry is a cement-water glass two-component grout.

4. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 1, characterized in that, Grouting reinforcement includes both horizontal and vertical grouting methods. Horizontal grouting involves drilling horizontal holes at the excavation surface of the foundation pit and then injecting cement-water glass grout. Vertical grouting involves drilling vertical holes at a predetermined distance outside the outline of the underpass and then injecting cement-water glass grout.

5. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 4, characterized in that, The horizontal grouting and the vertical grouting form a continuous, spatially intersecting grid-like water-stop curtain outside the outline of the underpass.

6. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 3, is characterized in that, The initial setting time of the cement-water glass slurry mixture is controlled at 10-15 minutes.

7. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 1, characterized in that, The early-strength concrete contains an early-strength agent and polypropylene fibers.

8. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 7, is characterized in that, The mix proportion of the early-strength concrete is cement:sand:crushed stone = 1:2:2.5, and the dosage of early-strength agent is 8% to 10%.

9. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 1, characterized in that, The real-time monitoring includes monitoring the settlement around the foundation pit. When the settlement value exceeds the preset value or the displacement rate reaches the preset value, the excavation is stopped immediately and reinforcement measures are taken.

10. The method for dynamic coordinated support of micro-disturbance grouting for deep foundation pits underpasses in water-rich sand layers according to claim 9, characterized in that, The reinforcement measures include: increasing grouting pressure, thickening shotcrete, reducing excavation speed, or increasing the density of grouting holes.

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