Excavation Scheme Research Articles

Vibration reduction effect of retaining pile structure under the action of damping hole—A case study

In the context of mitigating the impact of blasting-induced seismic waves on excavation processes and reducing the vibrational load on retaining pile structures, this study examines the influence of predetermined damping hole parameters on the damping effect. It also evaluates the protective efficacy of damping holes on retaining pile structures. Leveraging the foundation pit project at the Julong Avenue Station of Wuhan Metro Line 7 as a reference, on-site blasting construction was monitored to obtain vibration velocities at the top of the retaining pile structure. A numerical calculation model for blasting in the foundation pit was established using LS-DYNA software, and its reliability was verified through the integration of on-site monitoring data at the top of the retaining pile. Multiple damping hole excavation schemes were devised, and their effects on the damping effectiveness were analyzed with respect to various parameters. Safety criteria for the stability of the retaining pile structure were proposed based on the ultimate tensile stress criterion, ultimate shear stress criterion, and Mohr’s criterion. Under the optimized scheme, the dynamic response characteristics of the retaining pile structure were analyzed, and the practical application effects on-site were observed. The research findings indicate that the depth, spacing, and number of damping holes have a significant impact on the damping effect. The safety criterion for the vibrational velocity of the retaining pile structure during blasting is determined to be 26.10 cm/s. Under the optimized scheme, the vibrational velocities at various monitoring points on the retaining pile structure all fall within the safe range, with a maximum reduction rate of 30.9%.

Excavation response and reinforcement practice of large underground caverns within high-stress hard rock masses: The case of Shuangjiangkou hydropower Station, China

The construction of large-scale underground caverns poses numerous challenges due to their massive scale and high complexity. Among them, stability has always been a major concern during the construction process of large underground caverns within high-stress hard rock masses. It is not only influenced by the geological background of the project but also by the engineering activities during construction. This study takes the construction of the Shuangjiangkou (SJK) hydropower station as a case study and combines field investigations to summarize engineering issues and solutions under high geostress in three aspects. Firstly, it focuses on estimating and modifying the in-situ stress field of the underground caverns in the deep-cut valley area using limited geostress testing data and the observed failure phenomena in the pilot tunnel. Secondly, it discusses the typical failure phenomena of caverns under high geostress, including global stress-induced failures and local vein-controlled failures, as well as the corresponding failure mechanisms and treatment measures. Finally, it addresses the special failure phenomena occurring in the protective layer of the rock-anchored beam and optimizes the excavation scheme based on the observed failure patterns. The research results and solutions provided in this study, based on the case of the SJK hydropower station, are expected to serve as a reference for subsequent construction of large underground caverns within high-stress hard rock masses.

GBDT-based multivariate structural stress data analysis for predicting the sinking speed of an open caisson foundation

ABSTRACT Open caisson foundations are often used in large-span bridge construction because of their advantageous, and an open caisson foundation gradually sinks to a predetermined position via earth excavation. Excessive sinking speed may result in various construction risks (e.g. inclination and structural damage of the open caisson). To prevent these risks, it is important to analyse the sinking situation of the foundation and predict the sinking speed during the sinking process. A sinking speed prediction model is proposed based on the gradient boosting decision tree (GBDT) algorithm, and the model can extract the data features of the structural stress monitoring data to predict the sinking speed of open caissons. Taking the supersized open caisson foundation in the Changtai Yangtze River Bridge Project as a case study, the proposed model was validated by using the monitoring data of this foundation. The validation results of this project indicate that the proposed model has high prediction accuracy, short time consumption, a good prediction effect and high practicability. Based on the model’s prediction, an earth excavation scheme can be flexibly adjusted to prevent the potential construction risks of open caissons caused by excessive sinking speed.

Influence of external insert angle on structural deformation of long pipe shed with shallow hole

The long pipe shed advanced support has the characteristics of large construction difficulty, wide support range, and easy deviation. The difference in construction dip angle will produce a different plastic zone of surrounding rock and supporting effects, and the rationality of advanced support design plays an important role in the safety of tunnel opening excavation. Based on the Tianshan Tunnel project, this paper aims at the problems of the loose pebble layer structure, poor cohesion, strong permeability, shallow excavation is not easy to form a confined arch, and easy to causes surrounding rock deformation and failure. Combined with the new method theory, the finite difference software FLAC3D was used to simulate seven excavation schemes of the shallow tunnel entrances. The mechanism and effect of advance support and the influence of construction angle on support effect are analyzed, and the simulation values are compared with the measured data. The results show that using long pipe shed advanced support can effectively reduce the disturbance of excavation to lose pebble rock mass and reduce the convergence value of surrounding rock. The plastic zone of surrounding rock produced by different angles can be divided into three parts. The structural stability difference of the C1 zone is small, and that of the C3 zone is large. The bending moment, shear force, and shape variables of the pipe shed decrease with the increase of the dip angle, while the axial force increases with the increase of the dip angle. According to the similarity between the simulated curve and the measured curve, the best supporting effect can be achieved when the dip angle of the pre-supporting pipe shed is set in the range of 0° ~ 3°.

Rescue technology of the jamming accident for the double-shield TBM in complex geological conditions: A case study

More than 80 TBM jamming accidents had been recorded in the Water Diversion Project from the Hongyan River to the Shitou River in Shan’xi Province, China, resulting in substantial losses. This paper aims to investigate the rescue technology for the jamming accidents of the double-shield TBM in the project through a five-year geotechnical in-situ investigation. Firstly, the engineering background, the geological and hydrological conditions, the construction method, the possible jamming hazards, and the support system is introduced in detail. Then, the jamming accidents of the double-shield TBM are classified into the five kinds in total, namely, the shield jamming accident, the cutter head jamming accident, the jamming accident in the fault fracture zone, the jamming accident in the large-deformation section, and the jamming accident at water-rich and severely weathered broken rock section. And corresponding causes of accidents is analyzed at the same time. Afterward, the rescue technology adopted for the typical jamming accidents is explored, including the small pilot tunnel scheme, the advanced grouting scheme, the advanced large pipe shed scheme, the circular excavation scheme, and the auxiliary tunnel scheme. Finally, the prevent approaches for the jamming accident of the TBM are proposed, hoping to guide the same projects.

Influence of Anisotropic Stress Conditions on Tunnel Deformation and Sequential Excavation Performance in Rock Mass

Abstract This study looks at how anisotropic stress conditions affect the mechanical response of circular tunnels in rock mass using a finite element plane strain model. The deformation response and evolution of the yield zone are evaluated using a non-linear Hoek-Brown failure criterion. The results show that predictions made under the widely employed assumption of isotropic stress conditions significantly underestimate the deformations for in-situ stress ratios greater than 1.0 and overestimate the values for in-situ stress ratios less than 1 under full-face excavation. The pattern of the yield zone changes noticeably as the in-situ stress ratio changes. With stress anisotropy, the yield zone becomes asymmetric. When the in-situ stress ratio is less than 1.0, the yield zone concentrates on the sidewalls and transitions to the crown when the in-situ stress ratio assumes values greater than 1.0. Also, the effect of anisotropic stress conditions on the performance of two commonly used excavation support schemes is studied. The results emphasize the importance of consideration of the in-situ stress ratio for prediction of tunnel deformation and selection of sequential excavation schemes.

Numerical back analysis method of three-dimensional in situ stress fields considering complex surface topography and variable collinearity

Numerical back analysis based on incomplete in situ stress measurements is widely used to estimate the three-dimensional (3D) in situ stress fields of large deep underground caverns. However, the variable collinearity caused by complex geological environments has rarely been considered. This paper proposes a numerical back analysis method for 3D in situ stress fields based on stepwise regression (BSSR). In BSSR, the collinearity between independent variables is associated with the surface topography, and insignificant variables caused by variable collinearity are eliminated through stepwise regression. BSSR was applied to the underground powerhouse of a hydropower station for validation, and the results showed that it can reliably estimate the 3D in situ stress field despite the complex geological environments. Multidimensional mathematical models of in situ stress fields were established with the improved predictive ability and clear physical meaning, which can quantify the contributions of six geological actions and three stress sources. The findings of this study can help with understanding the formation mechanism of in situ stress fields for large, deep underground caverns in complex geological environments and provide a useful reference for optimizing excavation schemes and support designs.

Stability analysis of tunnel under coal seam goaf: Numerical and physical modeling

The goaf formed by coal seam mining would dramatically reduce the strength and stiffness of the ground in and around the goaf, which is not conducive to tunnel excavation near the mined-out area. By establishing the Finite differential method and Discrete element method coupling numerical analysis method and conducting similar model test, the influence of dip angle, thickness and distance of coal seam goaf on the stability of unsupported tunnel excavation is studied. The results show that when the tunnel under the goaf is excavated, the circumferential stress increment increases first and then decreases along the radial direction of the tunnel, the radial stress increment gradually decreases to zero along the radial direction of the tunnel, the displacement is approximately distributed in a trough shape, and the maximum displacement is at the top of the tunnel. The area of the stress loosening zone (SLZ) is negatively correlated with the dip angle and the distance of the goaf, and positively correlated with the thickness. The SLZ near the goaf is larger, and the peak value of the asymmetry is about 1.35. When the thickness of the mined-out area is 1.8–2.1 m, the SLZ and displacement around the tunnel increase sharply and then become stable. When the dip angle of the mined-out area is greater than 30° or the distance exceeds 1.3 times tunnel diameter (D), the asymmetry converges. The research results of this paper are of great importance to the design and construction of tunnel support and the formulation of excavation schemes.

Influence of the Large-Span Pile-Beam-Arch Construction Method on the Surface Deformation of a Metro Station in the Silty Clay–Pebble Composite Stratum

The Pile-beam-arch (PBA) method is a new and effective construction method for the urban metro station. It is the key to ensuring the safe construction of the station to clarify the influence of PBA method construction on surface deformation under unfavorable geological and large span conditions. Based on a station of Beijing subway, this paper studies the surface deformation law of the large-span PBA method in different construction stages under silty clay-pebble composite stratum by means of FLAC 3D numerical analysis and field monitoring of level. Then the influence of the excavation scheme of the pilot tunnel and the construction scheme of the secondary lining of the arch on the surface deformation is simulated and analyzed. The results show that, through numerical simulation, the ratio of pilot tunnel excavation: pile-beam construction: vault initial support construction: vault secondary lining construction is about 5:1.1:3.3:0.6. The settlement deformation mainly occurs in the excavation stage of the pilot tunnel. Through the comparative analysis of the field monitoring results and the numerical simulation results, it can be seen that the two results are highly consistent, which verifies the accuracy of the numerical simulation results. The pilot tunnel excavation scheme of excavating the middle first and then excavating both sides, first through the upper layer and then through the lower layer, and the scheme of one-time construction of the secondary lining of the arch are better. The research results promote the further maturity and perfection of large-span PBA method construction under unfavorable geology and provide reference for similar projects.

Displacement Analyses of Main Structure of Parallel Pit Excavation and Analysis of Countermeasures

To solve the impact on the pre-existing main structure due to the need for early traffic restoration of urban roads within the cross-hub and the difficulty of co-ordinating a construction plan among groups of pits, a construction method combining TD and BU was proposed. By establishing a three-dimensional finite difference method (FDM) of parallel pit excavation considering the small strain constitutive model of the strata, the influence of four different excavation schemes on the pre-existing main structs is studied. The results of the study show that: (1) the asynchronous excavation of the pit on both sides of the cover excavation area causes additional deformation of the steel pipe structs; sequential excavation produces the greatest additional deformation of the steel tube columns, followed by staggered excavation and the least simultaneous excavation; (2) the middle 1 slab enhances the overall stiffness of the main structure in the cover excavation area, reducing the additional deformation caused by the unsynchronized excavation of the pit, with the maximum horizontal deformation of 5.8 mm, a reduction of 61%; (3) the greater the depth of excavation and the closer the distance from the pit, the more obvious the deformation of the steel pipe column; and (4) the function relationship between δhm/H and the relative stiffness coefficient Rd was obtained by fitting, and the maximum controlled mis-step spacing of the foundation excavation on both sides was 4.3 m when the middle 1 floor slab was cast.

Stability Analysis of Surrounding Rock of an Underground Cavern Group and Excavation Scheme Optimization: Based on an Optimized DDARF Method

The surrounding rock stability of an underground cavern group is an important issue in the process of cavern excavation, which has the characteristics of large displacement, discontinuity and uneven deformation, so the calculation and analysis are very complicated. The optimized discontinuous deformation analysis for rock failure method was adopted to analyze the stability of the surrounding rock of a real underground engineering cavern group under different excavation schemes. The cracking process of surrounding rock under different excavation schemes, the depth of crack expansion and the vertical displacement of the arch and bottom floor were obtained, and the following conclusions are drawn: (a) After the completion of the excavation, the stability problems mainly appeared in the surrounding rocks of the arch, left wall, right wall and bottom floor of the main powerhouse, in the surrounding rocks of the arch, left wall and bottom floor of the main transformer chamber and in the surrounding rocks of the arch, right wall and bottom floor of the tailrace surge tank. (b) Fault f2 has an influence on the stability of the surrounding rock of the tailrace surge tank, while fault f1 has no influence on the stability of the cave group. (c) The scheme of simultaneous excavation of three caverns shows the advantages in the crack propagation depth of surrounding rock and vertical displacements of caverns.

Influence analysis and relationship evolution between construction parameters and ground settlements induced by shield tunneling under soil-rock mixed-face conditions

This study investigates the influences of the key shield parameters on tunneling-induced ground settlements considering the dynamic excavation process. The advanced machine learning method in conjunction with principal component analysis is applied to evaluate the nonlinear relationships between ground settlements and the multi-parameters in the soil-rock composite ground. Considering the interaction among multi-factor, the nonlinear relationships of excavation characteristic parameters are developed by the correlation analysis to quantify shield machine performance in the mixed ground. Predictions on ground settlements in the soil-rock mixed-face are conducted in good agreement with the in-site measured data from the Nanjing Metro Line No. S7 tunnel. The implementation effects of the Light-GBM based model are evaluated by RMSE and R2. Subsequently, the influence weights of the most important influencing factors are ranked to control the parameters, which will be beneficial to optimize the excavation scheme during the dynamic construction process. Finally, the empirical formulas are proposed according to the high-correlation parameters as well as the measured datasets by the nonlinear multiple regression process, which can provide guidance for shield tunnel operation in the soil-rock composite ground.

The Influence of Pile-Beam-Arch Construction on the Stratum and Station Support Structure

The PBA construction method is suitable for urban subway construction in situations with dense traffic and many surrounding buildings and can effectively reduce surface disturbance and control surface subsidence. Based on field-measured data, this study creates numerical finite element models of 3D stratum-structure, studies the influence of each process conversion on the subsidence of the ground surface and the force of the station supporting structure during the construction of the PBA station, and clarifies the optimal construction parameters. The research results show that the consistency between the field monitoring data and the simulation data is more than 80%, which verifies the correctness of the model. It is concluded that the formation of the pile-beam-arch is the main part of the supporting structure and that digging the pilot tunnel and the formation of the beam arch are the control factors of surface settlement. Based on this, the best sequence of pilot tunnel excavation and arch buckle of the two-story two-span station is obtained, and the optimal pilot tunnel excavation scheme of first the middle and then the side, first the upper and then the lower, and the best arch buckle scheme of the synchronous arch buckle on both sides is determined. The results of the research can serve as a guideline when selection the construction parameters for similar PBA stations.

Curve forming prediction of coal mine roadway based on RBF interpolation.

Underground roadway excavation is a complex process, especially roadway curved excavation. In addition, the rationality of the design of coal mine roadway excavation scheme directly affects the speed of roadway excavation. The more reasonable the scheme design, the more conducive to rapid excavation. In order to avoid the influence of invalid construction on the efficiency of roadway excavation, this paper studies the forming of roadway bend. Based on the analysis of the tunneling process of the roadway curve, the mathematical model of the roadway curve is established. Taking the turning radius of the roadway curve as the evaluation index, the influence of various factors on the roadway curve excavation is analyzed. The research shows that the radius of the roadway curve increases with the increase of the feed rate, the working space position of the roadheader and the required width of the roadway, and decreases with the increase of the working space angle. Then, combined with the advantages of KNN algorithm, an interpolation model for calculating the radius of the curve is established based on RBF algorithm, and the radius of the tunnel curve is reconstructed and predicted. It provides a basis for the rational design of the construction process of the roadway bend and a reliable numerical algorithm for the design of the radius of the roadway bend. It also provides a theoretical basis for improving the efficiency of high roadway excavation in coal mines.

Mechanical Behavior and Excavation Optimization of a Small Clear-Distance Tunnel in an Urban Super Large and Complex Underground Interchange Hub

Close excavation section spacing, the mutual influence and interpenetration of various processes, and the multiple disturbances of the middle rock pillar in a small clear-distance tunnel pose great difficulty to construction. This study adopted the small clear-distance tunnel of Xiamen Haicang Evacuate Channel as the research object. The tunnel belonged to a small clear-distance tunnel in an urban super large and complex underground interchange hub where complex adjacent small clear-distance tunnels were adopted. ABAQUS was used to analyze the influence of different excavation schemes, lithological grades, and footage lengths for tunnel stability. The deformation and stress characteristics of the tunnel’s surrounding rock and lining structure in different excavation schemes (full section method, bench method, center diaphragm (CD) method, and double wall heading method), lithological grades (III, IV and V), and footage lengths (3 m, 4 m and 5 m) were introduced. The results showed that the double wall heading method could effectively control the horizontal displacement of the hance, and the overall stress state of the lining in the CD and double wall heading methods were reasonable. The vertical displacement of the surface and vault was positively correlated with the elastic modulus of the rock mass. When no temporary support was present in the grade V rock mass, the area from the hance to the arch foot was prone to large deformation. Reducing the footage was beneficial to controlling the deformation of the vault and hance. This study can provide a reference for the on-site construction of small clear-distance tunnels.

Decision criteria and intelligent decision method for tunnel excavation scheme selection considering carbon emissions

The tunnel construction process is accompanied by high resource consumption and non-negligible greenhouse gas emissions. Reducing the carbon emissions from this process is an issue that should be considered in the decision-making stage. For tunnel construction using the drill-and-blast process, selecting a reasonable excavation scheme is a feasible method for reducing carbon emissions. This paper proposes an evaluation index system that takes into account the stability of the tunnel construction process and the reasonable assessment of carbon emission levels. For various scenarios with different focus on stability requirements, theoretical deductions are used to filter out the key indicators that should be used as assessment items. For the determination of carbon emission assessment indicators, this study is guided by the life cycle theory, and in the determined calculation boundary, the reference of previous projects and expert opinions are selected as the item source to fill the unfavorable situation in which the carbon emissions of different excavation schemes cannot be accurately calculated because of the lack of bills of quantities in the engineering decision stage. This paper also proposes an intelligent decision method based on a support vector machine to better complete the task of calculating and ranking the utility of excavation schemes to adapt the proposed multi-factor parallel evaluation system. Finally, the proposed decision indicator system and decision method were applied to the selection of the excavation scheme in an engineering case, and reasonable and realistic scoring results were obtained.

Optimal Design and Application of Earthwork Excavation Scheme for Deep Foundation Pit: Taking the New Construction of the Entrance and Exit of the Underground Passage in the Central area of the Pudong Senlan Block as an Example

<p>In the process of building construction, the optimization of the construction scheme has always played a great role in saving construction costs, reducing construction risks and speeding up the construction progress. This paper studies the optimization of the implementation plan of the deep foundation pit earthwork excavation stagein the actual case, and analyzes the results of the optimization of the plan, so that the optimized new plan can accelerate the construction period and save money while ensuring the project quality and construction safety. The construction cost has played a significant role.</p>

Research on the excavation stability evaluation method of Chaqishan ancient landslide in China

It is well known that the deformation and failure during the slope excavation often depends on the excavation height and slope rate. Based on the theory of loading and unloading response ratio, the present study established an evaluation model of the excavation dynamic load-increasing displacement response ratio and created the instability criterion. During the excavation, the stability law of the Chaqishan ancient landslide was analyzed using the Midas GTS NX finite element software, and four slope excavation schemes were redesigned. The results show that, the variation law of the excavation dynamic load-increasing displacement response ratio was consistent with the evolution law of stability coefficient, and there was an obvious negative correlation between them. Therefore, the stability variation law in the slope excavation could be evaluated using the evaluation model of excavation dynamic load-increasing displacement response ratio.

Research on stability of steep bank slope and reserved thin-walled rock cofferdam during excavation of intake foundation pit

The intake of water diversion project is generally located on the bank slope above the large reservoir or deep water area of a river. Due to the influence of water level change and hydraulic action, the rock mass of bank slope is seriously weathered and broken, leading that the rock mass has low strength and is easy to collapse or landslide. In this paper, the water intake engineering of the long-distance diversion project in central Shanxi Province is selected as the research object. The multi-point displacement meter is used to monitor the slope deformation after anchorage and concrete retaining wall support. Based on the FLAC3D V6.0 software, the numerical simulation of the excavation process of the steep reinforced river bank slope is carried out, and the long-term deformation of the slope is predicted. The excavation scheme of retaining outer thin-walled rock wall as water cofferdam is proposed. The excavation process of foundation pit, which is supported with concrete-filled steel tubular pile reinforcing cofferdam and concrete supporting beam, is simulated. It is found that the upper part of the steep slope supported by anchor cable and concrete retaining wall is stable, and the large deformation and plastic failure of the water-retaining thin rock wall are mainly affected by the disturbance of foundation pit excavation. The concrete-filled steel tubular pile support avoids the collapse of the reserved thin-walled cofferdam, and the horizontal beam in the foundation pit improves the stress state of the external wall of the foundation pit. The research results of this paper reveal the evolution mechanism of rock mass deformation and failure during excavation of foundation pit on steep bank slope, and provide guidance for excavation and support of foundation pit for similar bank slope.

Stability prediction and optimal angle of high slope in open-pit mine based on two-dimension limit equilibrium method and three-dimension numerical simulation

The optimization design of the open pit slope can ensure safety in production at the same time bring considerable economic benefits, so it is necessary to evaluate the stability of the initial excavation scheme of the high slope in an open-pit mine and optimize the initial slope angle according to the evaluation results. In this paper, an exhaustive study of Anyi open-pit mine in mouding County Yunnan province China has been made, and the following results have been achieved: (1)Confirmed the geological factors which affected the slope stability of open-pit mine; (2)Quantified the stability of the open-pit mine slope; (3) Under the premise of safety, the angle of the open pit high slope has been optimized on the base of the calculations of the open-pit mine high slope stability so as to ensure the maximum economic benefit. In this paper, the study area was divided into six zones. Firstly, qualitative analysis of slope stability was made by analogy method of engineering geology and stereographic projection method according to the orebody location, the properties of rock and soil in slope, the height of slope, and so on. The analysis shows that the preliminary design of slope angle is so large to ensure safety. Secondly, the stability of different slopes of a high slope is the quantitative analysis of different zones in high slope was made by two-dimensional limit equilibrium method and the finite difference method. In this paper, the mechanical parameters of rock are obtained by a laboratory test, and the stability of the high slope is quantitatively analyzed by two-dimensional limit equilibrium and three-dimensional numerical simulation.