Excavation Process Research Articles

A particle-scale insight into the face stability of shallow EPB shield tunnels in dry cobble-rich soil

The aim of this paper is to provide a particle-scale insight into the face stability of shallow (C/D = 1.0; C = tunnel buried depth and D = tunnel diameter) earth pressure balanced (EPB) shield tunnels in cobble-rich soil, considering both the dynamic excavation process and particle size gradation. The work was performed by three dimensional discrete element method (DEM). Results show that particle size greatly influences the movement of cobble particles. The coarse particles serve as the skeleton of the ground and provide the stability. The erosion of fine particles has little influence on tunnel face stability, while the erosion of middle particles weakens tunnel face stability. The limit support pressure pf increases with increasing cutterhead rotating speed, and the normalized limit support pressure pf/γD (γ = soil unit weight, D = tunnel diameter) obtained in this paper is larger than existing researches. The abrupt increase of middle particles in the muck composition can be recognized as the forewarning information against face failure.

Deformation Law of Tunnels Using Double-Sidewall Guide Pit Method under Different Excavation Sequences

The double-sidewall guide pit method finds extensive application in the construction of large cross-section tunnels in soft rock strata due to its minimal disruption to the surrounding rock, thereby enhancing tunnel stability. To investigate the loading and deformation patterns of the surrounding rock and tunnel support using the double-sidewall guide pit method, this study compares the impacts of various construction sequences on surface settlement, surrounding rock stress, and lining stress using indoor model tests. The experimental results show that after excavating the upper guide hole on one side, the excavation of the lower guide hole on the same side is carried out. The upper and lower support structures form a closed loop, and the structure can better constrain the surrounding rock and control the deformation of the surrounding rock, whereas the lower structure can share the stresses suffered by the upper structure. Therefore, compared with the upper and lower excavation methods, the surface settlement caused by the left and right excavation methods is smaller, the disturbance to the surrounding rock is smaller, and the supporting structure is more evenly and stably stressed in the excavation process.

Analysis of the response subsidence and grouting treatment in the goaf of multi-layer inclined coal seam

Based on existing researches, field drillings and numerical simulations are carried out in this paper to analyze the problems of subsidence control in the goaf of multi-layer inclined coal seam. Midas/GTS NX is used to build a three-dimensional calculation model of the goaf. A new method of using borehole data to check simulation parameters is proposed. The whole process of goaf excavation, construction of roadbed (pile foundation) and grouting treatment is analyzed. Analysis theory of different subgrade construction schemes and grouting treatment process on goaf is established. Response characteristics of displacement and equivalent stress and strain of goaf in multilayer inclined coal seam are obtained. A new method for analyzing the characteristics of the stress and deformation of the rock strata before and after grouting in the goaf under the conditions of different foundation schemes on the surface is provided in this research.

A Stability Analysis of an Abandoned Gypsum Mine Based on Numerical Simulation Using the Itasca Model for Advanced Strain Softening Constitutive Model

An abandoned gypsum mine has been discovered beneath the route of a highway construction in Hunan province, south China. Due to the highway construction and operations safety, there is an urgent need for a comprehensive stability analysis of the abandoned mining area. The 3D laser scanning detection technique has been adopted, and over 400 drillholes were strategically placed near the highway to capture the spatial information of the abandoned gypsum mine. The ore body has an average mining thickness of about 3 m, and the depth of the mining roof ranges from 40 to 60 m, with an average span of 16 m. Based on the research achievements in the engineering geological investigation, rock mass quality assessment, and geometry information, a simplified numerical model has been established for stability analysis. The numerical model employed the IMASS rock mass constitutive model to conduct a stability analysis of the abandoned gypsum mine during the excavation process and in the medium to long term. The IMASS constitutive model can effectively reflect the entire process of rock mass from microscopic damage to macroscopic instability, and the numerical simulation of current and long-term stages provides a much greater understanding of the mining room stability and the effect of various geo-mechanical parameters not considered in traditional empirical methods. The abandoned gypsum mine stability is guaranteed in the mining and current stages. However, the numerical results showed that a 0.4 m spalling thickness of the sidewalls can cause an overall instability and failure of the abandoned mine, and reinforcement measures must be taken for long-term safety. The stability of the abandoned gypsum mine with filling solutions was also evaluated numerically.

Monitoring the Geometry of Powered Roof Supports—Determination of Measurement Accuracy

This paper presents a system for measuring the geometry of powered roof support sections (Shield Support Monitoring System, SSMS). The problem of measuring the geometry of powered roof support sections for the purpose of predicting geological hazards during the rock excavation process is presented. Information on the construction and implementation of the SSMS and research at the Budryk Mine is included. The research aimed to evaluate both the precision and accuracy of the measurement apparatus created, as well as to examine how operating conditions affect the system’s usability. An analysis of inclinometer measurement errors in the prototype system was conducted during in situ tests, demonstrating minimal scattering and high sensor accuracy according to the provided data.

Development of a Displacement Prediction System for Deep Excavation Using AI Technology

This manuscript delineates an innovative artificial intelligence-based methodology for forecasting the displacement of retaining walls due to extensive deep excavation processes. In our selection of 17 training cases, we strategically chose a wall configuration that was not influenced by the corner effects. This careful selection was conducted with the intention of ensuring that each deep excavation instance included in our study was supported symmetrically, thereby streamlining the analysis in the ensuing phases. Our proposed multilayer functional-link network demonstrates superior performance over the traditional backpropagation neural network (BPNN), excelling in the precise prediction of displacements at predetermined observation points, peak wall displacements, and their respective locations. Notably, the predictive accuracy of our advanced model surpassed that of the conventional BPNN and RIDO assessment tools by a substantial 5%. The network process model formulated through this research offers a valuable reference for future implementations in diverse geographical settings. Furthermore, by utilizing local datasets for the training, testing, and validation phases, our system ensures the effective and accurate execution of displacement predictions.

Viscos-elastic-plastic solution for deep buried tunnels considering tunnel face effect and sequential installation of double linings

Tunnels excavated in soft rock under high in situ stress are usually accompanied by large time-dependent deformation, slow convergence, and long periods of increased support load due to the strong rheological properties of the surrounding rock. This paper presents a time-dependent solution for deeply buried supported circular tunnels excavated in viscoelastic-plastic strain-softening rock masses, in which both the whole process of longitudinal excavation and the sequential installation of two elastic linings are considered. In the solution, the surrounding rock obeys a Burger-creep viscous elastic–plastic strain-softening model and two stages, referring to the “tunnel face influence stage” and the “creep stage”, are divided to derive the explicit expressions of the time-dependent tunnel convergences and support loads, in which the former stage accounts for the effect of stress release based on the elastic–plastic analysis, and the latter concentrates on the long-term response induced by the viscous behavior of the ground. To account for the different rock qualities, tunnel face advance rates, and lining tunnel support locations, the elastic–plastic strain-softening solution in the former stage is divided into three cases and the viscos-elastic–plastic solution in the creep stage includes two sub-solutions depending on the evolutions of stress paths being considered or not. For validation purposes, the provided analytical solutions are compared with the numerical results by finite-difference simulations and previous solutions. Following that, parametric studies are conducted to compare the stresses, deformations, and support loads under different stages and solutions. Finally, to further verify the applicability of the solutions in practical tunnels, the convergences, support loads and lining stresses of a typical tunnel cross-section in the Saint Martin La Porte access adit are successfully predicted. Overall, the proposed solutions in this study provide a profitable idea for deriving various viscoelastic-plastic or elasto-viscoplastic explicit solutions that can simultaneously account for both the rock rheology and tunnel face effect.

A statistical bonded particle model study on the effects of rock heterogeneity and cement strength on dynamic rock fracture

Numerical modelling and simulation can be used to gain insight about rock excavation processes such as rock drilling. Since rock materials are heterogeneous by nature due to varying mechanical and geometrical properties of constituent minerals, laboratory observations exhibit a certain degree of unpredictability, e.g. with regard to measured strength and crack propagation. In this work, a recently published heterogeneous bonded particle model is further developed and used to investigate dynamic rock fracture in a Brazilian disc test. The rock heterogeneities are introduced in two steps—a geometrical heterogeneity due to statistically distributed grain sizes and shapes, and a mechanical heterogeneity by distributing mechanical properties using three Weibull distributions. The first distribution is used for assigning average bond properties of the grains, the second one for the intragranular bond properties and the third one for the bond properties of the intergranular cementing. The model is calibrated for Kuru black diorite using previously published experimental data from high-deformation rate tests of Brazilian discs in a split-Hopkinson pressure bar device, where high-speed imaging was used to detect initiations of cracks and their growth. A parametric study is conducted on the Weibull heterogeneity index of the average bond properties and the grain cement strength and evaluated in terms of crack initiation and propagation, indirect tensile stress, strain and strain rate. The results show that this modelling approach is able to reproduce key phenomena of the dynamic rock fracture, such as stochastic crack initiation and propagation, as well as the magnitude and variations of measured quantities. Furthermore, the cement strength is found to be a key parameter for crack propagation path and time, overloading magnitudes and indirect tensile strain rate.

Supporting behavior evolution of ultra-deep circular diaphragm walls during excavation: Monitoring and assessment methods comparison

Ultra-deep circular excavations present unique challenges in geotechnical engineering due to their complex behavior and the scarcity of relevant case studies. This paper presents a comprehensive study on the excavation behavior of the deepest circular excavation (77.3 m) ever built in China through field monitoring and computational methods. The excavation process leads to the transformation of the underground diaphragm walls into an elliptical cylinder shape, elongated in one direction and shortened in the perpendicular direction. The outer annular reinforcement primarily experiences compressive stresses, while the inner annular reinforcements undergo tensile stresses, attributed to the spatial deformation of the cylinder structure. The findings emphasize the significance of considering 3D deformation and accurate characterization of internal forces to ensure the structural integrity and stability of such complex geotechnical systems. Three computational methods, including the 2D load-structure method, the 3D load-structure method, and the stratum structure method, were employed to analyze the deformation and internal forces. Comparison between measured data and calculated results reveals differences and highlights the effectiveness of the 3D load-structure and stratum structure methods in capturing the observed behavior. The study contributes to the understanding of circular excavation for designs in geotechnical engineering.

Analysis of unstable block by discrete element method during blasting excavation of fractured rock mass in underground mine

During the excavation process in fractured rock masses in underground mines, blasting excavation can cause dangerous block collapses on surrounding rock. The applicable blasting method can effectively reduce the damage of surrounding rock caused by blasting disturbance. In order to investigate the impact of blasting disturbances of dangerous blocks in fractured rock mass drift, this study focuses on the instability characteristics of dangerous blocks during the excavation process in a mine located in Jilin Province. Based on detailed detection of discontinuities characteristics in the study area, the damage effects of shaped charge hydraulic blasting and conventional blasting on surrounding rock structure are analyzed and compared by using equivalent static method. The 3DEC discrete element software was used to analyze the instability characteristics of surrounding rock dangerous blocks under these two different blasting methods. The results indicate that using shaped charge hydraulic blasting can effectively reduce the impact of blasting disturbances on the excavated rock mass and minimize dangerous block collapses during drift excavation.

Excavation of a tunnel with conventional method in urbanized context – A case study from Line 15 South of Grand Paris Express

AbstractAs part of the Grand Paris Express project, the work package of Metro Line 15 South Lot T2C is situated near Villiers Sur Marne in the south‐eastern outskirts of Paris. It consists in two mechanized tunnels, principal as well as maintenance and storage site lines, respectively 4.7 and 2.2 km long, connected by a shaft approximately 180 m long (O807), 92 m of which is characterized by a traditional tunnel. This article presents the study carried out for the detailed design of the conventional tunnel which is excavated in the Calcaire de Champigny formation, a succession of layers with typical characteristics of a heavily fractured rock mass alternates with marly others, sometimes showing dissolution phenomena due to the presence of gypsum. Due to the urbanized context and the workface planning, a particular construction stage was also foreseen: the lower part of the section has been excavated by tunnel boring machine when the upper was finalized. The discussion is completed with the results of the monitoring activity, designed to check the correct behavior during and after the excavation process.

Numerical analysis for supporting and deformation of complex foundation pit groups in unstable areas of karst strata

Due to the extensive karst development zone in karst areas, the stability of the underground soil layer is poor. The support of foundation pits in this area will be affected by complex environmental factors, and if not handled properly, it will cause significant safety hazards and economic losses. In this paper, the three-dimensional finite element model of the complex foundation pit and adjacent foundation pit group was established with the help of Midas GTS NX numerical software, and numerical simulation was carried out for the whole foundation pit excavation and construction process, and the deformation results of the adjacent foundation pit support structure of the complex foundation pit group and the soil outside the foundation pit were obtained. The results show that the underground wall of the complex foundation pit shifted to the north under the action of buttresses, with a similar “cantilever” displacement pattern on the south side of the underground wall in the center, a “push-back displacement” on the north side of the underground wall in the center, and a “ventral” displacement pattern at the corners of the grounded wall and on the east and west sides. Combined with the field measurement data, the support piles in the internal support system have a “cantilever” displacement pattern under the condition of massive soil unloading in the vicinity of the foundation pit, while the supporting piles show a “parabolic” displacement pattern under the action of the corner internal support. The deformation characteristics of the foundation pit in the presence of adjacent pits are significantly different from the results based on empirical laws. The results of the above study will provide useful technical guidance for the safety of excavation support for foundation pit groups in complex environments and the reasonable control of the surrounding environment.

Computer information technology-based green excavation of tunnels in complex strata and technical decision of deformation control

Abstract Currently, information processing of tunnel engineering has mainly adopted conventional mathematical statistics-based methods. Moreover, some nonlinear processing methods are implemented to derive more insights, even though the degree of research is not deep enough. In the research, the rock mechanics test is carried out by drilling a method and taking samples in situ according to the construction technology of tunnels in complex geological conditions and implementing computer information-based methods. Also, rock mechanics tests are carried out in the excavation test area of the flat tunnel. Based on the tests using physical properties, such as deformation, tensile, uniaxial compression, triaxial compression, and longitudinal wave velocity, the physical and mechanical characteristics of the surrounding rock in the tunnel area are comprehensively evaluated, and the stability of the tunnel rock mass is assessed to devise convenient conditions for the subsequent research of the complex geological tunnels based on green excavation. The particle density of sandy mudstone, the bulk density, the porosity, and the natural water content are represented by 2.67 ± 0.61 g/cm3, 2.56 ± 1.42 g/cm3, 7.45%, and 2.86%, respectively, in terms of physical characteristics. These indicate that the sandy mudstone structure is relatively loose, with relatively large pores, micro-fractures, and a high degree of natural water content. The representative deformation test curve of the rock block shows that the ratio of deformation modulus to the compressive strength of the rock block is 650 on average, and Poisson’s ratio ranges from 0.21 to 0.38. These show that sandy mudstone has deformation properties after compression. The tensile strength of sandy mudstone, the shear strength, and c are represented by 1.25 ± 0.23 MPa, f = 1.32, and = 2.35 MPa, respectively. The stated test results can provide a scientific basis for selecting engineering design and its construction parameters in similar areas. In addition, the measurement results show that the surrounding rock will gradually increase, and the tunnel space will gradually become shorter with the increase of buried depth when the gravity stress field occurs. The linear elastic displacement of soft rock is smaller than that of elastic–plastic analysis, and the deeper the tunnel is buried, the larger the displacement difference would be. Therefore, establishing a stable and orderly monitoring and detection system could fully understand the intrinsic law between surrounding rock stress release and surrounding rock pressure and obtain accurate monitoring and measured data to evaluate the grading management standard of a tunnel at the ultimate displacement. In a word, this research provides a feasible idea to study the decision process of green excavation and deformation control technology of tunnels in complex strata.

Deformation rule of bored pile & steel support for deep foundation pit in sandy pebble geology

Regarding the whole excavation process of the support system of the Southwest Jiaotong University Station of Chengdu Metro Line 6 (the deep foundation pit bored pile + steel support and support system) as the engineering background, this paper studies the deformation rule of the deep foundation pit bored pile + steel support of the sandy pebble foundation. The deformation rule of this support system, the settlement rule of the ground surface outside the pit, and the rule of the uplift of the loose at the bottom of the pit are studied. A key analysis of the positive corner of the foundation pit is conducted, and the rationality of the optimization of the support scheme is evaluated. This paper provides effective guidance for the subsequent deep foundation pit construction and provides a reference for deep foundation pit construction.

True Triaxial Test and Research into Bolting Support Compensation Stresses for Coal Roadways at Different Depths

During the excavation and support construction process used in coal mine roadways, the stress path is the unloading of in situ stress and the compensation of support stress. The 150 mm × 150 mm × 150 mm coal mass samples were obtained in situ underground and prepared, the true triaxial loading–unloading–confining pressure restoring test method was used, and the mechanical response and deformation failure evolution characteristics of the coal seam during the excavation and support process of the shallow, medium depth, and deep coal roadways in the coal mine were simulated and studied. Based on the distribution law of the bolt and cable support stress field, the support compensation stress required for the stability of the surrounding rock after the excavation of the coal roadway with different burial depths was determined, and the corresponding roadways’ surrounding rock control technologies were proposed. This study’s results indicate that the compensation stress required for support in shallow coal roadways (with a burial depth of about 200 m) was much less than 0.1 MPa. A single rock bolt support can keep the surrounding rock of the roadway stable; the compensation stress required for support in the medium buried coal roadway (with a depth of about 600 m) is around 0.1 MPa, and the combined support of rock bolts and cables can meet the support requirements. Deep coal roadways under high stress (with a depth of about 1000 m) require support to provide compensation stress. Even if the compensation stress reaches 0.2 MPa, the surrounding rock of the roadway will experience varying degrees of creep. In this study, it was necessary to increase the support density and surface area of rock bolts and cables, the pre-tension forces of rock bolts and cables were improved, and in synergy with grouting modification, destressing and other technologies could control the large deformation of the surrounding rock of the roadway in 1000 m deep coal mines. This study’s results provide a theoretical basis for the selection of control technologies for use in coal roadways at different depths.

Evolution of mechanical parameters of Shuangjiangkou granite under different loading cycles and stress paths

Surrounding rocks at different locations are generally subjected to different stress paths during the process of deep hard rock excavation. In this study, to reveal the mechanical parameters of deep surrounding rock under different stress paths, a new cyclic loading and unloading test method for controlled true triaxial loading and unloading and principal stress direction interchange was proposed, and the evolution of mechanical parameters of Shuangjiangkou granite under different stress paths was studied, including the deformation modulus, elastic deformation increment ratios, fracture degree, cohesion and internal friction angle. Additionally, stress path coefficient was defined to characterize different stress paths, and the functional relationships among the stress path coefficient, rock fracture degree difference coefficient, cohesion and internal friction angle were obtained. The results show that during the true triaxial cyclic loading and unloading process, the deformation modulus and cohesion gradually decrease, while the internal friction angle gradually increases with increasing equivalent crack strain. The stress path coefficient is exponentially related to the rock fracture degree difference coefficient. As the stress path coefficient increases, the degrees of cohesion weakening and internal friction angle strengthening decrease linearly. During cyclic loading and unloading under true triaxial principal stress direction interchange, the direction of crack development changes, and the deformation modulus increases, while the cohesion and internal friction angle decrease slightly, indicating that the principal stress direction interchange has a strengthening effect on the surrounding rocks. Finally, the influences of the principal stress interchange direction on the stabilities of deep engineering excavation projects are discussed.

Evolution of Subkilometer-scale Impact Craters on the Lunar Maria as Constrained from Mini-RF Data and Topographic Degradation Model

Physical properties (e.g., ejecta size and distribution) of impact craters are crucial and essential to understanding the ejecta excavation and deposition process, estimating rock breakdown rate, and revealing their evolution characteristics. However, whether these physical properties are scale-dependent and how they evolve in different radial regions needs further studies. In this study, we first investigated the physical properties and evolution of sub-kilometer (D ≤ 800 m) craters on lunar maria based on the radar circular polarization ratio (CPR). In addition, we estimated the periods over which rocks and blocky ejecta are exposed and buried in the shallow subsurface layer (termed as exposure time) in different radial regions and assessed the retention time and degradation states for potential radar anomalous craters. We found that in the central region of craters, the largest median CPR occurs after an 80 Myr delay following crater formation. In the rim region, there is no obvious CPR peak in the first 100 Ma, whereas in the upper wall region, an evident CPR peak occurs beyond 100 Ma and could last over one billion years. In addition, the probable exposure time of rocks and blocky ejecta is estimated to be ∼2.0 Gyr (central region), ∼2.7 Gyr (upper wall region), ∼2.1 Gyr (rim region), and ∼0.6 Gyr (continuous ejecta blanket region). We also propose that the retention time of radar anomalous craters depends on the crater size, whereas their degraded states are independent of crater size.

Analyzing the Stability of Rock Surrounding Deep Cross-Tunnels Using a Dynamic Velocity Field

With the increasing number of deep rock engineering projects, many different types of tunnels have emerged, such as cross-tunnels. These tunnels intersect with each other in rock, which causes potential safety hazards. We must analyze the stability of the surrounding rock, to ensure worker safety. This article presents a method for dynamically assessing the stability of the surrounding rock in deep-buried cross-tunnels. The method consists of two main analysis steps: (1) P-wave velocity field inversion; and (2) Stability analysis of the surrounding rock. The P-wave velocity field inversion involves inverting the S-wave velocity field by Rayleigh wave and inverting the P-wave velocity field by adjoint state traveltime tomography. Then, a method of stability analysis is proposed which is used to update the mechanical properties of the rock (based on the continuously updated wave velocity field). The elastic modulus of the surrounding rock is approximated throughout the excavation process. CASRock V1.0 (Cellular Automation Software for engineering Rockmass fracturing processes) is used to assess rock damage via the equivalent plastic shear strain and local energy release rate. The new method is used to analyze the stability of a new tunnel excavated in Jinping (in China). The results reveal the severity and spatial distribution of the damage caused. The yield depth is concentrated near the sidewalls, while the top and bottom of the tunnel exhibit a smaller depth. The yield depths present a particular pattern of change (high–low–high–low) with increasing distance from tunnel #2. Finally, this research enriches our understanding of excavating deep cross-tunnels and makes an important contribution to improving worker safety in deep cross-tunnels.

Roof Stability of Underground Limestone Mining with Stratified Joints during Excavation Process

Roof Stability of Underground Limestone Mining with Stratified Joints during Excavation Process

Simulation of bench stepping and optimization of bolt parameters based on multiple geological information fusion

In the stability analysis and design of rock support for tunnels, the establishment of a refined numerical model relies on reliable and accurate geometrical information of structural planes. To better analyze and optimize the tunnel construction method and support mode, it is crucial to establish a refined numerical model for the tunnel. Based on the developed geotechnical intelligent analysis and multi-interpretation system, the feature extraction and interpretation of the rock mass structural surface are achieved. Meanwhile, coupled with multiple geological information, the comprehensive analysis and judgment of rock mass structural surface information are achieved through continuous dynamic tracking. According to this method, based on grade IV fractured rock data collected from the construction site of Dapuling tunnel, the safe distance of step in bench excavation method has been optimized based on the numerical modelling, and the corresponding bolt support design. The optimized tunnel excavation process is more stable and safer, providing a scientific basis for predicting, identifying, controlling, and preventing rockfall disasters during the excavation process of tunnels and underground caverns in fractured rock masses.