Qingdao Metro Line Research Articles

A novel Bi-LSTM method fusing current and historical data for tunnelling parameters of shield tunnel

Reasonable shield tunnelling parameters play a crucial role in controlling ground stability and enhancing tunnelling efficiency. Predicting shield tunnelling parameters before excavation is of paramount importance. A novel deep learning method is introduced, integrating bidirectional long short-term memory (Bi-LSTM) layers, and fully connected (FC) layers to fuse current and historical data for shield tunnelling parameters prediction. Historical data captures the impact of excavated sections on the current predicted ring, while current data considers present conditions. A feature fusion method eliminates dimensional differences between historical and current data. The resulting tensor, encompassing both data types, is fed into the FC layer to generate predictions. The effectiveness of the method is demonstrated by predicting shield cutter head torque for Qingdao Metro Line 4 in China, outperforming traditional Bi-LSTM, MLP and RF methods significantly. Ablation studies further analyze the impact of different component modules and structural parameters on model performance. Overall, this innovative approach offers accurate shield tunnelling parameters prediction, enhancing ground stability and tunnelling efficiency.

Tensile Deformability of Shotcrete in Tunnel Primary Support: A Case Study

Shotcrete strain in the primary support of a tunnel will produce non-loading strain at an early age due to the influence of its own temperature change, hardening shrinkage, spraying force, and other factors, which means that current strain-monitoring results fail to reflect the real strain, and the strain value after stabilization is high. In addition, tensile strain may be evident in the final result, even exceeding the tensile warning value, but, in actuality, the on-site lining is very stable, with no cracks or damage. Therefore, it is necessary to understand the strain characteristics of shotcrete in the primary support of a tunnel. Based on the long-span tunnel project at Shishan Road Station on the Qingdao Metro Line 6, in situ and indoor pull tests of concrete strain were designed while only considering temperature change, hardening shrinkage, and spraying force. This study shows the following: (1) The strain in shotcrete is greatly affected by temperature changes, hardening shrinkage, and shotcrete force in the first three days, reaching its peak value in the second to third days, while tending to be stable at about the seventh day. (2) The real strain of the shotcrete was tested, and the warning value was adjusted from 90 με to 120 με. (3) The strain value at the third day was taken as the initial value, and the previous monitoring results were revised. The revised results align with the trends shown during real tests performed on-site, providing guidance for tunnel engineering support monitoring.

Intelligent Identification of Surrounding Rock Grades Based on a Self-Developed Rock Drilling Test System

The classification of surrounding rock is crucial for formulating safe tunnel construction plans and support measures. However, the complex geological environment of tunnels presents a challenge in obtaining accurate drilling parameters for rock mass classification. This paper presents the development of a rock drilling testing system, which includes a propulsion speed acquisition system, oil pressure acquisition system, air pressure acquisition system, and an automatic data acquisition system. This system enables real-time, high-precision automatic collection and storage of parameters such as propulsion speed, with data collected twice per second for each parameter. Leveraging the Qingdao Metro Line 6 as a case study, we conducted rock mass drilling and constructed a rock mass classification database. By employing kernel density estimation and Pearson correlation analysis, we quantified the correlation between rock mass classification and the drilling parameters. The results indicated that relying on a single drilling parameter is insufficient for accurately determining rock mass classification. Both impact pressure and rotational pressure showed the strongest correlation with rock mass classification, each with a correlation coefficient below −0.8 (indicating a strong negative correlation). Outlier values of drilling parameters were excluded using the interval method. Based on the remaining data, we established an intelligent rock mass classification model using the random forest algorithm. This model demonstrated good accuracy and generalization performance, with an average accuracy exceeding 0.9. The proposed rock drilling testing system, combined with the intelligent rock mass classification model, forms an integrated system for the intelligent identification of rock mass grades. This system has significant implications for the intelligent and safe construction of drill-and-blast tunnels.

Experimental Study on Stability Analysis of Shallow-Buried Metro Station Hard Rock Excavation under Blasting Vibration Effect

Abstract By considering a certain metro station of Qingdao Metro Line 4 as the research object, a three-dimensional geotechnical testing model has been developed to analyze the stress and deformation characteristics of the surrounding rocks under blasting vibration effect. The simulation of the surrounding rock blasting process is achieved through an electric spark source. We conducted simulation tests on the excavation stability of shallow-buried hard rock metro stations with and without considering blasting damage effects, respectively. The stress, displacement, and primary support stress changing laws of the surrounding rock under different overburden thicknesses using the arch cover method and the primary support arch cover method have been revealed. Finally, we analyzed the applicability of the primary support arch cover method in terms of vault settlement, clearance convergence, and floor heave. Results show that the surrounding rock of the arch has roughly gone through three deformation stages, namely a slow deformation stage, rapid deformation stage, and stable deformation stage. Whether it is blasting excavation or non-blasting excavation, the settlement of the arch is within a safe and controllable range. Because of the refinement of the excavation process by the primary support arch cover method, the stress release is relatively stable throughout the entire excavation process, but the significant impact of blasting vibration on the surrounding rock cannot be ignored. The excavating of the left and right guide holes is the key process for the displacement and stress variation. The deformation and stress generated by the arch cover method have a small difference compared to the deformation and stress generated by the primary support arch cover method, indicating that the latter excavation method can be used under current engineering geological conditions. No large-area collapse and instability occurred in the experimental process, which provides a theoretical basis for similar projects.

Research on Optimization Design of Tunnel Blasting Scheme Adjacent to Buildings

The section of Jialingjiang Road Station to Xiangjiang Road Station along Qingdao Metro Line 13 is located in Qingdao, China. All of them show obvious characteristics, being soft on the top and hard on the bottom, and the interval tunnel is faced with the problem of existing adjacent buildings. In order to ensure the smooth progress of construction, as well as minimize the damage to the buildings, a new mechanical excavation combined with a blasting construction scheme for the adjacent buildings is proposed. In this scheme, the step method is used for excavation. The upper step is in the weak stratum, and the mechanical method is therefore used for excavation; the lower step is in the hard stratum, and the drilling-and-blasting method is thus used for excavation. Using FLAC3D 5.0 finite difference software and the method based on blasting an equivalent load, the vibration velocity at adjacent buildings caused by the combined mechanical excavation and blasting scheme, as well as the traditional full-section blasting scheme, is compared and analyzed. Further, the construction parameters of the combined mechanical excavation and blasting scheme are compared and selected based on building settlement, the plastic zone of surrounding rocks, building vibration velocity and other factors. The results show that under the mechanical excavation blasting scheme, the peak particle velocity of each monitoring point decreases significantly compared with that under the full-section blasting scheme, with a maximum reduction of 61.1%, which is within the allowable range of the project, demonstrating the rationality of the new scheme. Finally, the mechanical excavation advance in the upper step is determined as 0.5 m. The optimized parameter construction effect is monitored and evaluated, the problems encountered in the project are successfully solved using the combined mechanical excavation and blasting scheme, and the expected construction period is shortened by 3 months, which shows the rationality of the blasting construction scheme proposed and its parameters, as well as the validity of the calculation results. The research results can be used as a reference for the construction scheme design of similar projects.

Sandy aquifer collapse mechanism and accident treatment of the Qingdao metro tunnel

The tunnel collapse occurred during the construction of the Qingdao Metro Line Ⅰ, resulting in a pit measuring approximately 10 m in diameter and 7 m in depth on the ground surface. The collapse inflicted substantial economic losses, casualties, and subsequent disruptions to ongoing construction activities. To clarify the causes of this collapse and investigate the underlying factors, a comprehensive approach combining field surveys and numerical simulations was undertaken. The results show that the collapse was primarily attributed to inadequate support when facing the challenging geological conditions, poor surrounding rocks (Grade VI) and a high volume of groundwater. The combination of abundant water and sand seeped into the tunnel, culminating in a catastrophic ground collapse. Notably, the arch roof experienced extensive deformation and damage due to the significant seepage pressure, which was exacerbated by the absence of timely support. Then, ground grouting was promptly conducted to repair the affected area and reinforce the tunnel structure. Subsequent monitoring of surface deformations following the resumption of tunneling operations indicated the effectiveness of the disaster treatment approach. These achievements constitute a reliable theoretical foundation for similar projects, particularly in terms of environmental protection and ensuring safe construction practices.

Analysis of Surface Settlement Induced by Shield Tunnelling: Grey Relational Analysis and Numerical Simulation Study on Critical Construction Parameters

Excessive surface settlement poses significant challenges to shield tunnelling construction, resulting in damage to adjacent buildings, infrastructure, and underground pipelines. This study focused on investigating the surface settlement induced by shield tunnelling during the construction of Qingdao Metro Line 6 between Haigang Road Station and Chaoyang Road Station. Firstly, the settlement data from the left line of the shield tunnel were evaluated by grey relational analysis. The relational coefficients were calculated to assess the correlation degrees of each influential parameter. Subsequently, the four critical influential parameters with the highest relational degrees were chosen to investigate their effects on surface settlement through numerical simulations under different scenarios. The results show that the four parameters with the highest relational degrees were thrust, grouting pressure, earth pressure, and strata elastic modulus. It should be noted that the strata elastic modulus significantly affects surface settlement, while the grouting pressure influences the settlement trough width in weak strata. Moreover, improper thrust magnitude can lead to an increase in surface settlement. Based on these findings, recommendations are proposed for the right-line tunnel construction and practical countermeasures for surface settlement during shield tunnelling construction are provided.

Construction mechanics behavior of double-layer primary support arch cover method

The double-layer primary support arch cover method, as a recently flourishing innovative construction technique, is steadily gaining prominence in subterranean engineering projects across various regions in China. Its widespread adoption is particularly notable in the construction of tunnels within soft upper and hard lower geological strata. This article, grounded in practical field observations, conducts a comparative analysis between the primary support arch cover method and the double-layer primary support arch cover method in terms of deformation control. The results underscore the deformation control advantages offered by the double-layer primary support arch cover method.To delve deeper into the construction mechanics of the double-layer primary support arch cover method within soft upper and hard lower geological strata, this study employs indoor model experiments and numerical simulations. It scrutinizes deformation patterns, including surface subsidence, arch crown settlement, and structural stress, during the tunnel excavation process employing the double-layer primary support arch cover method. Additionally, drawing insights from its practical application in the construction of Qingdao Metro Line 2′s Xiaogang Station, this research explores the applicability and construction mechanics of this method.The study reveals that the double-layer primary support arch cover method efficiently harnesses the load-bearing capacity of the underlying hard rock formations, effectively controlling deformations in the surrounding rock within the arch section. This article also highlights the critical importance of the removal of temporary vertical supports to construction safety and elucidates the mechanical behavior transition and operative mechanisms of the second-layer arch during the construction process.

Analysis of Arch Forming Factors of Shallow Buried Hard Rock Tunnel under Overlying Load

To investigate the arching effect of shallow buried hard rock tunnels under overlying load, the engineering scenario of a subway station on Qingdao Metro Line 6 is utilized. A large-scale tunnel loading model test is conducted, in conjunction with finite element numerical simulations, to analyze the impact of various overburden ratios on strata arching. The results show that: when the tunnel excavation span is certain, with an increase in the overlying rock mass, the stress diffusion process of the surrounding rock can be better accomplished to form the arch effect. This means that the thickness of the overburden of the tunnel determines whether or not the surrounding rock appears to have a stratified arch effect. When the tunnel overlying rock thickness is certain, the span of the tunnel determines the shape of the formation into an arch, that is, the curvature of the arch. The joint surface is an important factor in tunnel stability. When the overlying load increases to a certain value, the rock mass at the joint plane slips relatively, leading to the displacement phenomenon of the surrounding rock, which then affects the formation and shape of the formation arch.

Comparative Study of the Rock-breaking Mechanism of a Disc Cutter and Wedge Tooth Cutter by Discrete Element Modelling

The operation of a shield tunnel boring machine (TBM) in a high-strength hard rock stratum results in significant cutter damage, adversely affecting the thrust and torque of the cutter head. Therefore, it is very important to carry out the research on the stress characteristics and optimize the cutter parameters of cutters break high-strength hard rock. In this paper, the rock-breaking performance of cutters in an andesite stratum in the tunnel of Qingdao Metro Line No. 8 was investigated using the discrete element method and theoretical analysis. The rock-breaking processes of a disc cutter and wedge tooth cutter were simulated by software particle flow code PFC3D, and the rock-breaking degree, stress of the cutter, and rock-breaking specific energy were analyzed. The rock damage caused by the cutter in a specific section was divided into three stages: the advanced influence, crushing, and stabilizing stages. The rock-breaking degree and the tangential and normal forces of the wedge tooth cutter are larger than that of the disc cutter under the same conditions. The disc cutter (wedge tooth cutter) has the highest rock-breaking efficiency at a cutter spacing of 100 mm (110 mm) and a penetration depth of 8 mm (10 mm), and the rock-breaking specific energy is 11.48 MJ/m3 (12.05 MJ/m3). Therefore, two types of cutters with different penetration depths or cutter spacing should be considered. The number of teeth of wedge tooth cutters can be increased in hard strata to improve the rock-breaking efficiency of the shield. The research results provide a reference for shield cutterhead selection and cutter layout in similar projects.

Long-term performance of a subway source heat pump system with two types of front-end heat exchangers

The rapid development of subways and resulting deterioration of the thermal environment in tunnels have led to thermal pollution of underground spaces, which is a problem that cannot be ignored. The subway source heat pump system (SSHPS) with a tunnel-lining capillary heat exchanger (CHE) is an effective technology for solving this problem. Existing researches mainly focused on the short-term performance of the SSHPS. Few studies have analyzed the long-term performance of the system under complex periodic boundary conditions. In this study, a simulation model of an SSHPS, which conforms to an actual demonstration project located in Lingshanwei Subway Station of Qingdao Metro Line 13, was built by coupling a flat CHE for the open-cut section and a circular CHE for the concealed excavation section of a subway tunnel. Field test results of the SSHPS performance were compared with those of the simulation. The maximum relative error is 13.96%, which shows that the simulation model has high accuracy and can satisfy the requirements of practical engineering applications. Based on the verified model, the system performance under complex periodic boundary conditions was simulated for 10 consecutive years. The results indicate that the average heat flux of the flat and circular CHEs has little variation during the continuous operation of the system for 10 years, and the variations during the cooling and heating seasons are less than 1.24 W/m2 and 0.36 W/m2, respectively. The annual air temperature increments in the tunnel with flat and circular CHEs are approximately 0.226 °C and 0.324 °C, respectively. The average coefficients of performance of the heat pump unit in the cooling and heating seasons are 4.43 and 5.11, respectively, indicating that the heat pump unit operates efficiently throughout the year. The main reason for the long-term high performance of SSHPS is the annual thermal balance of the subway tunnel. The thermal balance of the subway tunnel during long-term operation should be considered when designing an SSHPS system. This study can provide a reference for optimizing the design and operation of the SSHPS.

Stability Analysis of Tunnel Surrounding Rock When TBM Passes through Fracture Zones with Different Deterioration Levels and Dip Angles

In fracture zones, tunneling with a double-shield Tunnel Boring Machine (TBM) presents significant challenges, including deformation overrun of the surrounding rock, TBM jamming, and excavation face collapse. To assure the tunnel construction safety and efficiency, it is necessary and crucial to conduct a stability analysis of the tunnel surrounding rock when a TBM passes through the fracture zones. The tunnels from Jiadingshan Road Station to Anshan Road Station in Qingdao Metro Line 8 are constructed by double-shield TBMs. It inevitably passes through fracture zones with different deterioration levels and dip angles. In this study, based on this construction section, numerical models of fracture zones with different deterioration levels and dip angles were developed to analyze the displacements of tunnel vaults, inverts, and haunches. In addition, the maximum shear stresses of the surrounding rock were analyzed. Finally, the displacement and shear stress variation patterns of the surrounding rock with different deterioration levels and dip angles were obtained. The findings reveal the stability behavior of tunnels under various fracture zones. They can serve as a valuable reference and theoretical foundation for future tunnel construction projects utilizing double-shield TBMs in areas with fracture zones.

Case Study and Risk Assessment of Water Inrush Disaster in Qingdao Metro Line 4

Water inrush is one of the most frequent and catastrophic hazards in tunnel engineering, and poses serious threats to the safety of engineering and personnel. This paper presents a case study of a water inrush and ground collapse in the Qingdao Metro Line 4, which caused a cave-in with the diameter and depth of about 30 m and 6 m, respectively. Based on the field data and numerical modelling, the causes of the disaster were analyzed. A numerical model was used to analyze the changes of surface settlement, vault settlement and water pressure during the tunnel excavation. The results of the study indicate that the cause of this disaster was the failure of the tunnel vault surrounding rock caused by the weakening of the tunnel surrounding rock and water pressure, which in turn triggered the water inrush in the tunnel and caused a large volume of surface collapse. As the tunnel was excavated from the slightly weathered area to the strongly weathered area, the vault settlement increased, and the influence zone expanded towards the surface due to the continuous decrease in the strength of the surrounding rock. In particular, a negative pore water pressure zone was formed in a certain area around the tunnel during the water inrush. The negative pressure zone caused the surrounding groundwater to converge here, leading to an increase in the amount of water inflow, which also increased the scope and scale of the impact of this disaster. A risk assessment method for water inrush in tunnels is proposed. According to the geological and engineering characteristics of Qingdao area, the evaluation index system of tunnel water inrush risk was established. An RBF neural network was improved by gray correlation analysis and a PAM clustering algorithm to establish the tunnel water inrush risk assessment model. Comparing the evaluation data with the actual data, the prediction data of a traditional RBF neural network and a BP neural network, the accuracy and reliability of the model were verified. This study has value in reducing the occurrence of water inrush in a composite formation tunnel.

Construction applicability of mechanical methods for connecting aisle in the bohai mudstone stratum with high water pressure

China’s traditional connecting aisle construction technology is mainly to combine soil reinforcement with mining excavation. The technology is relatively mature, but it has shortcomings such as long construction period and long-term construction settlement. In order to overcome the above shortcomings, mechanical methods for connecting aisle technology has become increasingly mature after years of research and development, and has been successfully applied in many areas. For the cross-sea tunnel project, this technology was first tried and applied in the interval tunnel of Qingdao Metro Line 8. It is challenging to construct the connecting aisle by mechanical method in Bohai mudstone stratum with high water pressure, which has the construction difficulties such as high excavation requirements, high requirements for post-support function and limited space of main tunnel. In this study, a cutter, propulsion system, and back supporting system were designed to handle the key and difficult points and risks of the aforementioned construction. Furthermore, targeted construction schemes were adopted for sleeve sealing, sleeve removal, and improvement of sleeve sealing. The applicability of the improved mechanical construction method to the geological conditions of the Qingdao area was verified through a numerical simulation. The research results can provide a reference for the mechanical construction of connecting aisle under similar formation conditions.

Analysis and Intelligent Prediction for Displacement of Stratum and Tunnel Lining by Shield Tunnel Excavation in Complex Geological Conditions: A Case Study

This paper presents the analysis and intelligent prediction for the displacement of stratum and tunnel lining of Qingdao Metro Line 4 by earth pressure balance (EPB) shield tunnel excavation in complex strata. When the tunnel is excavated in different stratum sections, the tunneling parameters of shield machine are systematically analyzed and compared, and the vertical displacement of the tunnel crown and the horizontal convergence deformation on both sides are investigated. When the tunnel body passes through the soft soil stratum and rock stratum, the curves of the vertical displacement of the stratum surface with time are respectively discussed. A machine learning method for predicting stratum surface deformation induced by shield tunnel excavation in complex strata is developed, where extreme learning machine (ELM), particle swarm optimization (PSO) algorithm and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> -fold cross-validation method are comprehensively considered. 65 data samples are collected from the field monitoring data of Qingdao Metro Line 4 and each data sample includes seven input values and one output value. The developed PSO-ELM has good prediction performance for stratum surface vertical displacement due to shield tunnel excavation. The case study in this work can provide a practical reference for similar tunneling projects.

Collaborative optimization of train timetable and speed trajectory considering stochastic photovoltaic power: A two-step approach

Faced with the integrated system composed of the train power system, the photovoltaic (PV) power system, and the energy storage system (ESS), this research studies the energy-efficient operation and energy management strategy from the perspective of both train optimal control and timetable optimization, aiming at achieving a long-term energy consumption reduction. A two-step approach for collaboratively optimizing the train timetable, speed trajectory, and energy management strategy considering the stochastic characteristics of PV power generation is proposed to solve this large-scale complex problem. Before the two-step approach, a mixed-integer linear programming (MILP) model is established to optimize the energy consumption of the inter-station operation. On this basis, explicit energy consumption expressions for all inter-stations of the entire line are obtained by the proposed data fitting method. The historical PV power data is clustered to generate scenarios with different probabilities to characterize the stochastic PV power. The first step of this two-step approach is to minimize the total energy consumption expectations of all inter-stations determined by the obtained explicit energy consumption expressions to optimize the timetable while ensuring the total time and time window constraints are met. The second step is to minimize the weighted sum of energy consumption under all possible scenarios to obtain the optimal speed trajectory and energy management strategy based on the optimized timetable obtained in the first step. The validity of the model is verified by case studies using the real data of Qingdao Metro Line 11 under both scenarios with and without PV power. This study provides a novel method for energy-efficient operation and energy management of the integrated system and demonstrates the prospect of the proposed two-step stochastic optimization in reducing the net grid-supplied energy for the long-term operation of urban rail transportation systems.

Risk Assessment Study on Mechanical Connecting Aisle Construction in the Bohai Mudstone Stratum with High Water Pressure

With the in-depth advancement of underground transportation in China, the connecting aisle is used as a link between different underground spaces to provide sufficient security and connection. The basic structural units of underground and aboveground spaces play an extremely important role. The use of the mechanical connecting aisle construction of over mucky strata is difficult, and it is easy to have an impact on the main tunnel. To ensure the safety of connecting aisle construction, studies should be performed on the construction technology, equipment, scheme, and related risk analysis of mechanical connecting aisle construction. In this study the work breakdown structure-risk breakdown structure combined with the expert investigation method is used to comprehensively identify the construction process, construct the risk index system of mechanical connecting aisle construction, determine the initial risk value, and comprehensively use the fuzzy-analytic hierarchical process to establish a fuzzy complementary judgment matrix, obtain the risk-weighted correction value, and quantitatively evaluate the risk source level of the mechanical connecting aisle construction. Based on the assessment method, the risk assessment of the mechanical connecting aisle construction project in Daqing section of Qingdao Metro Line 8 was performed, 113 potential risk sources were identified, and the comprehensive assessment obtained 7 major risk sources such as “improperly designed construction organization,” “instability of excavation surface,” and “easy leakage of lower river crossing” that were greater than the total risk average of 2.053. Corresponding risk response measures were proposed, which provided a reference for the risk assessment of similar projects in the construction of similar projects on mechanical connecting aisle construction in the Bohai mudstone stratum with high water pressure.

Investigation on Vibration Influence Law of Double-Shield TBM Tunnel Construction

Double-shield TBM is more efficient than shield tunnel construction in hard rock strata. It is widely used in subway tunnel construction, such as in Qingdao and Chongqing in China. However, construction vibration problems caused by double-shield TBM critically affect human comfort in surface buildings. In order to study the vibration influence law of double-shield TBM, the on-site monitoring plan of double-shield TBM is developed, relying on a tunnel section of Qingdao Metro Line 4. Then, the vibration monitoring results are analyzed, and the time domain and frequency domain characteristics of vibration acceleration are obtained. Subsequently, taking vibration peak acceleration as the research object, the transverse and longitudinal vibration laws of double-shield TBM construction are studied. Finally, according to the standard of human comfort in buildings, the vibration influence ranges of double-shield TBM construction are obtained. The research results can provide a reference for the vibration effect of double-shield TBM passing through houses, highways and bridges. Moreover, it can also provide a basis for the disputes that double-shield TBM tunnel construction affects the lives of inhabitants.

Primary support optimization of large-span and shallow buried hard rock tunnels based on the active support concept

Considering the large-span underground excavation subway station of Qingdao Metro Line 6 of China for analysis, it is necessary to optimize the traditional support system by investigating relevant codes and other tunnel projects. Based on the active support concept, a high prestressed rock bolt support system is proposed, and the optimization direction is defined to apply a high prestress force to rock bolts, increasing the appropriate spacing between supporting arches and strengthening support at key parts such as the large arch foot area, sidewalls and junctions. Numerical calculations and field monitoring are performed to analyze and evaluate the new support system. Numerical simulation results show that the new support system can effectively improve the stress state of the surrounding rock; the tensile stress area markedly decreases in size or disappears; and the plastic area also decreases in size. Field monitoring results show that the settlement of the arch crown is concentrated at 2–5 mm and the deformation rates are less than 0.5 mm/day. The supporting arches, shotcrete and rock bolts are all less than the yield strength and a high safety reserve. These results verify the safety and rationality of the proposed support system, which can be used as a reference for similar projects.

Quantitative Design Method for Grouting in Sand Layers: Practice in Qingdao Metro Line 2

Grouting is an effective method to reduce permeability and improve the mechanical performance of sand layers, preventing a disastrous inrush of sand and water. A scientific grouting design scheme is the premise for satisfying grouting reinforcement requirements. Due to a lack of theoretical basis for current grouting designs, grouting projects are conducted empirically and blindly. This paper presents a quantitative design method for grouting in sand layers. Based on this method, a quantitative design is realized for judgment of the grouting mode, determination of grouting range and calculation of grouting reinforcement effect. Moreover, for the fracture–compaction grouting mode, a theoretical model is proposed to calculate the grouting process, considering the coupling effect of grout flow and sand layer deformation. Meanwhile, a calculation method for reinforcement is put forward, which can connect macroscopic performance of the grouted body and individual performance of grout veins, compacted sand and undisturbed sand. In order to verify the efficiency of the grouting design method, it has been used in a sand grouting project in Qingdao Metro Line 2. In this project, judgment of the grouting mode, selection of grouting type and determination of grouting parameters have been completed based on the design method. Several inspection approaches have been performed to evaluate the effectiveness of the grouting design, showing that engineering stability was guaranteed after the grouting operation.