Excavation Sequence Research Articles

Three-Dimensional Modeling and Analysis of Ground Settlement Due to Twin Tunneling Using GIS

Ground settlement occurs because of the surrounding ground behavior during tunnel excavation. A high chance of its occurrence could cause the collapse of buildings; therefore, the accurate prediction and assessment of ground settlement are necessary when structures are concentrated in urban regions. This study leverages Geographic Information Systems (GIS) and 3D modeling to evaluate the effects of tunnel excavation on the ground settlement and damage of buildings along the Mandeok–Centum underground highway in Busan. It integrates the field topography with building data to simulate and visualize construction-induced interactions. Numerical analysis is used to assess the effects of the terrain elevation, building presence, excavation sequences, and lag distance between the twin tunnels on the settlement. The results indicate that high terrain elevation, dense building layouts, and shorter distances between tunnels increase settlement. Furthermore, this study deduces that bidirectional excavation causes a rapid increase in settlement compared with parallel excavation, which is evident from the variations in the inflection points during the excavation process. Finally, this study estimates the damage to buildings and ground settlements and visualizes risk maps using GIS, emphasizing the practicality of 3D modeling based on GIS.

Оптимизация технологических способов отработки калийных запасов при камерной системе разработки

The diverse demand for inorganic fertilizers has predetermined the intensification of potash mining, which is a raw material for their production. In this regard, it has become necessary to create risk management technologies for underground mining of potash deposits considering the spatial planning of mining operations while increasing the technological productivity of underground combine machines. The purpose of the study is to develop a technology to increase the technological productivity of mining set equipment to a level as close as possible to a combine at a minimum volume of preparatory work coupled with stopping operations. The subject of the study is the procedure for mining a designated mine field of potassium-magnesium deposit. Methods. The study applies a formal logistics approach based on an analysis of known facts and existing problems at a mining enterprise, the regulatory and technical documentation used and current scientific trends in this field. Based on the results of the analysis, conclusions and justifications were made. Then, a solution to the problem is proposed. Results. The study presents a modernized and improved potash mining method considering spatiotemporal changes. When planning the development of individual sections of a deposit, geological services carry out underground additional exploration to supplement geological knowledge of the area in question. Such work includes geological exploration, drilling wells from the face and perimeter of the mined-out void to select core for mechanical and chemical (furrow and core) testing, geophysical studies, etc. Discussion. The set purpose is achieved by preparing and developing the field with diagonal rooms. Prior to stopping operations, additional exploration drifts are carried out along the upper edge of the mined seam by paired faces along the entire length of the selected block. These mined out voids allow obtaining additional geological information about the section of the mine field being mined. Conclusion. A scheme for mining a selected field with a described sequence of stopping and cutting is proposed. The proposed scheme allows: to increase the technological productivity of mining set equipment to a level as close as possible to a heading-and-winning machine; to minimize the volume of preparatory work coupled with stopping operations. Resume. The proposed scheme for mining a selected section of a mine field with the described sequence of excavation allows us to increase the technological productivity of the mining complex to a level that is as close as possible to the technical productivity of a mining and shearer while simultaneously minimizing the volume of preparatory work, combining these works with the work of mining. Suggestions for practical applications and directions for future research. The research results can be useful in potash deposit mining by chevron cutting method considering spatial planning, safe mining operations and replenishment of geological information about the field.

Study on the Influence of Adjacent Double Deep Foundation Pit Excavation Sequence on Existing Tunnel Deformation Based on HSS Constitutive Model

With the increase in the number of buildings along the subway, the impact of building construction on the adjacent subway tunnels has gradually come to the forefront and become an important problem to be solved in the engineering field. In particular, the excavation and unloading process of deep foundation pits will trigger an additional deformation of the subway structure, which may pose a serious threat to the safety and stability of subway tunnels. This article is based on a foundation pit project in the sub-center of Beijing, focusing on the form of a connected double foundation pit. Using the HSS constitutive model for soil materials, this study simulates the deformation response of adjacent existing subway tunnels under three excavation sequences: sequential excavation, simultaneous excavation, and the comprehensive excavation of the connected double foundation pits. The study shows that, from the point of view of the total displacement of the whole construction process, the impact of a synchronized excavation of double pits on the existing tunnel line is relatively large in the process, and the impact of sequential excavation is relatively small in the construction cycle. The result of the similarity of the excavation sequence is the similarity of the impact trend. The volume of excavated earth determines the value of displacement change for each excavation scenario in each working condition and is also responsible for the convergence of changes. The trend of total tunnel displacement is more consistent with that of vertical displacement, which is dominated by vertical displacement, with horizontal displacement having a relatively small influence. The maximum value of the total tunnel displacement occurs at the side of the tunnel near the excavation area, and the direction is inclined to the excavation area. The application of supporting structures, especially the center plate and the bottom plate, can suppress the vertical deformation of the tunnel bulge.

A double tunnels model test study on mechanical properties of surrounding rock during tunnels excavation and creep stages

The tunnel engineering has become increasingly common with the needs of urban development. However, excavation sequence has a significant effect on the stability of the tunnel perimeter rock, which can lead to more unpredictable perimeter rock hazards and more difficulty in maintaining perimeter rock stability. In this study, to investigate the effect of different excavation sequences on tunnel deformation and creep, biaxial compression experiments were conducted on muddy siltstone specimens by using the acoustic emission (AE) and digital image correlation (DIC) techniques. The results indicated that, as the distance from the tunnel portal increases, the amount of stress and strain change decreases, with the largest values of stress changes occurring in the tunnel vault and middle area of twin tunnels. The specimen undergoes two stages in the creep process: deceleration creep and steady-state creep. The steady-state creep rate of the measurement points depends on the degree of excavation disturbance impact it experiences. The AE events during excavation can be divided into two phases: the quiet period when the specimen is not excavated and the active period when the specimen is excavated, and the cumulative counting curve shows a “stepwise” increase with the number of excavations. There is a sudden drop in the b-value during excavation and a decrease in the b-value during the deceleration creep phase. The results of this study can reflect the creep patterns of the surrounding rock under different excavation sequences, which can help to choose a more suitable excavation plan in terms of rock creep stability.

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.

Deformation analysis and protection measures of existing metro tunnels effected by river channel excavation in soft soils

The excavation of river channel in soft soils has an inevitable influence on adjacent metro tunnels. This paper investigates the effect of river channel excavation on the underlying metro tunnels and corresponding protective measures based on an engineering project in Fuzhou city, China. A three-dimensional finite element model is developed to calculate the vertical and horizontal displacements and diametrical distortion of tunnels under different excavation sequences and soil reinforcement measures. Real-time monitoring of the vertical and horizontal displacements and diametrical distortion of tunnels is carried out and analyzed in detail. The results show that the vertical displacements and diametrical distortion of tunnels are primarily caused by the excavation of the river directly above the tunnels, while the horizontal displacements are induced by the excavation of the river next to the tunnels. A combination of cement slurry with a portal form and concrete with a plate form is recommended to reinforce the bottom soil of rivers and protect the operational tunnels. The accuracy of the calculation model and the effectiveness of the protection measure are confirmed by using on-site measurements. The findings can provide useful reference for the safety assessment and protection measures of similar projects.

Surface settlement law of double-hole pipe-jacking tunnel undercrossing expressway

With the rapid urbanization process in China, there has been a significant development of urban underground spaces. The pipe-jacking method has gained popularity in various projects due to its advantages such as short construction period, adaptability to different soil conditions, and minimal excavation disturbance. This study focuses on a tunnel project involving double-hole rectangular pipe-jacking under an expressway. Utilizing FLAC software, a three-dimensional numerical model was created to analyze the impact of double-hole pipe-jacking construction on surface settlement and deformation of the expressway. The simulation results were validated by comparing them with field monitoring data. The study also investigated the impact of different construction parameters, such as excavation sequence and the angle of underpassing the expressway, on surface settlement. Additionally, the surface settlement curve at the slope bottom of the expressway exhibits asymmetric distribution and an offset center in the settlement trough. It is recommended to carry out the construction of double-hole pipe-jacking in the sequence of "big first and then small". Furthermore, when the included angle between the expressway and the jacking axis is 90°, the impact on surface settlement is minimized. This research provides valuable insights for the construction of double-hole pipe-jacking underpass structures in tunnel engineering.

Study on the Influence of Excavation of Superlarge and Ultra-Deep Foundation Pits on the Pile Foundation of Existing Viaducts

The rapid development of urban above- and underground transportation has brought an increasing number of deep foundation pit projects that close to existing urban viaducts. Excavation of the deep foundation pit projects leads to soil movement around the pile foundation, which adversely affects the adjacent existing pile foundation and seriously threatens the operation safety of the adjacent existing viaduct. In this paper, the three-dimensional numerical model of foundation pit excavation, viaduct, and pile foundation was established by using the MIDAS GTS against the background of the basement foundation pit project in the new Guangzhou Baiyun Station comprehensive transportation hub building, production, and life complex, where the interaction between foundation pit excavation and viaduct pile foundation was simulated. The influence of various excavation-related factors and different parameters of the pile foundation on lateral displacements of the pile body adjacent to the existing pile foundation was analyzed. The variables controlled in the numerical model included the different excavation depths of the foundation pit, the distance between the excavation surface and the adjacent pile foundation, the spatial effect of different excavation sequences, the diameter of the pile that adjacent to the existing pile foundation, and the elastic modulus of the bored occlusal pile support structure. The results indicated that the lateral displacement of the pile body of the bridge pile foundation was significantly affected by the excavation of the deep foundation pit. The excavation depth exerted the greatest influence on the lateral displacement of the pile foundation, followed by the distance between the pile foundation and the excavation surface, the excavation sequence of the foundation pit, and the elastic modulus and the diameter of the bored occlusive pile support structure. Among them, the pile foundation located at the corner of the foundation pit was negligibly affected by these influencing factors. The findings in this study can provide valuable experiences for similar projects.

Numerical Study of Dig Sequence Effects during Large-Scale Excavation

The appropriate excavation sequence can improve the overall stability of a foundation pit. In this study, eight schemes were created using FLAC3D to examine the impact of the excavation sequence on a foundation pit by analyzing a deep foundation pit in Nanjing, which had an irregular large rectangle shape. The results show that different excavation sequence schemes and different phases of the foundation pit can change the displacement values and the horizontal displacement type. The min–max normalization method was used to score the schemes in terms of six parameters and confirm the best excavation sequence scheme. In addition, the irregular shape of the foundation pit also leads to local differences in the stability of a foundation pit; the wide end is only slightly longer than the narrow end, but its displacement is significantly higher than that of the narrow end, so attention should be paid to reinforcing the weak parts when carrying out the support. This study can inform the selection of the excavation sequence for actual construction processes.

Study on the effect of excavation sequence of three-hole shield tunnel on surface settlement and segment deformation

In order to study the influence of excavation sequence of three-hole parallel shield tunnel on surface settlement and segment convergence, an improved “three-stage analysis method” was proposed to calculate the surface settlement of three-hole parallel shield tunnel. Based on Peck's existing theory, this method deduced the ground settlement formula under the three-hole parallel condition, and can calculate the ground settlement more accurately. Based on the engineering background of a shield tunnel section in Jiangsu Province, a three-dimensional model of a three-hole parallel shield tunnel was established by using Flac3d software, and the three-hole parallel shield tunnel was simulated under four working conditions: right–center–left, right–left–center, right–left–right and right–center (reverse)–left. This paper analyzed the influence of tunnel excavation sequence on surface settlement, soil displacement and deformation of tunnel segments. The construction sequence was optimized based on the above influencing factors. It was found that Case 4, S-type sequential excavation, produced the least ground settlement. The surface settlement value caused by S-type excavation sequence was only 11.41 mm, and the convergence value of the segments generated by S-type excavation sequence was relatively small. Considering the economic factors such as construction efficiency and benefit, the S-shaped excavation sequence was better. The new calculation method of tunnel surface settlement and the optimal sequence of tunnel construction proposed in this paper can provide reference for actual construction.

Research and optimization of tunnel construction scheme for super-large span high-speed railway tunnel in poor tuff strata

Abstract The rapid traffic developments create demands for shallow four-line high-speed railway tunnels in weak soils, while construction technologies of such tunnels have yet to be reported. In this article, the construction schemes for a shallow four-line high-speed railway tunnel with a span of 26.3 m in weak tuff strata are investigated by numerical analysis and in-situ tests. First, 20 construction schemes of the shallow super-large span high-speed railway tunnel are proposed and simulated by the Finite Difference Method, including eight schemes for grade V rocks and 12 schemes for grades IV and III rocks. The mechanical response of grade V rock mass is simulated by the Bolt–Kelvin Mohr–Coulomb rheological model. The influence of construction method, rock grade, area, quantity, and excavation sequence of pilot tunnels on the rock deformation and the internal force of the primary support are comparatively explored. For further analysis, an 8 month field test was conducted to study the optimized effect of the construction scheme. Finally, a suggested construction method selection chart for super-large span tunnels in weak rocks (spans between 17 and 34 m) has been proposed. The research conclusion could provide a reference for building the super-large span tunnel in complex conditions.

Back-analysis of sprayed concrete lined (SCL) tunnel junctions at Liverpool Street Crossrail station

Sprayed concrete linings (SCL) offer a versatile method of tunnel construction, particularly in regard to forming junctions since the lining acts as a shell structure which can redistribute the stresses around the opening efficiently. This process is easy to understand conceptually but it is much more difficult to illustrate in calculations. Conventional calculation methods make a number of far-reaching simplifications such as the assumption of linear elastic behaviour in the lining. This often leads to overly conservative designs and a residual concern over the loads in the lining. This study compares detailed measurements of strains recorded by distributed fibre optic sensors at a pair of junctions on the Crossrail project in London with a sophisticated numerical model of these tunnels. Having demonstrated that the results of the numerical model are broadly consistent with this unique set of field data, a variety of influences on the model have been examined. This includes the excavation sequence, the constitutive model for the lining and adjacent structures. The results indicate significant scope for the improvement of SCL junction design. Future papers will present the more results from other parts of this study along with their implications for the design of tunnel junctions.

Tunnelling with Full-Face Shielded Machines: A 3D Numerical Analysis of an Earth Pressure Balance (EPB) Excavation Sequence Using the Finite Element Method (FEM)

Urban tunnelling can be highly challenging, especially in areas where limited ground settlements and environmental disturbance is required. Mechanised tunnelling is usually preferred in such ground environments, specifically Slurry or EPBM (Earth Pressure Balance Machine), depending on the ground properties. Being able to predict the anticipated tunnel behaviour at the preliminary stages of the project can be very beneficial in optimising not only the design, but also control the construction activities and completion times. In practice, the short-term excavation response and support performance focus primarily on design, since most site characterisation inputs are focused on material properties gained from short-term testing. Although the analysis of tunnelling is a three-dimensional (3D) problem, conventional approaches and design methods employed during the design and construction of underground openings are often based on the ground’s static response in two dimensions (2D). In this paper, an initial 2D model is generated in PLAXIS2D and RS2 (Rocscience) to test advanced constitutive models and compare transverse settlement profiles; subsequently, a complete 3D FEM numerical model in RS3 (Rocscience) was used to simulate an Earth Pressure Balance (EPB) excavation sequence. The 3D numerical model simulates the relevant EPB components such as face pressure, TBM shield, backfilling of the tail void (time-dependent hardening of the grout) and gradual segmental lining erections in the longitudinal direction. The presented numerical approach can be used by tunnel designers and engineers to predict the soil response in EPBM tunnelling.

Three-dimensional laser scanning and numerical investigation on the influence of freeze-thaw and hang-wall mining on the instability of an open-pit slope

The instability of the open-pit slope and associated disasters of complex orebodies such as hanging-wall mining are the key problems to be solved urgently in the development of western resources. In this work, taking the hanging-wall mining in the open-pit mine of Hejing iron mine, for example, the disaster mechanism influenced by the coupling freeze-thaw and hanging-wall mining is systematically studied by 3D laser scanning and numerical simulation. Firstly, the rock mass structure information such as dip, dip angle, spacing, and equivalent trace length characteristics was obtained using 3D intelligent recognition technology. Then, numerical simulation is employed to reveal the influence of freeze-thaw and excavation sequences on the overall stability of the open-pit slope. The stress, displacement, plasticity zone, and maximum shear strain patterns are revealed in detail. The results show that the excavation engineering will lead to frequent increase and unloading of the internal stress of the rock mass, and the gradual increase of the goaf area will cause great damage to the rock mass. The slope failure mode is strongly impacted by freeze-thaw weathering and orebody excavation.

Pipe Curtain Deformation and Surface Subsidence Caused via Excavation of Transverse Pilot Tunnel under Pipe Curtain Support

Relying on the Shenyang Metro Line 4 Shifu Road station, the impact of the construction parameters of the transverse pilot tunnel on the surface subsidence and the pipe curtain deformation was first studied through numerical simulation, followed by the analysis of the impact of the excavation of the transverse pilot tunnel on the deformation characteristics of the pipe curtain through on-site monitoring. The results show the following: the excavation of the middle pilot tunnel is the key stage of the construction. The excavation sequence of H2 and H4 and H6 → H1 and H3 → H5 and H7 caused the least surface subsidence. Increasing the grouting width and improving the strength of the initial support can control the pipe curtain deformation very well, and it is reasonable to choose 1.5 m as the grouting width.

EXCASS system and Rock Mass Rating (RMR) classification for determining excavation method and tunnel support at Pelosika Dam Spillway Tunnel

Pelosika dam spillway tunnel was designed to drainage flood discharge and prevent overtopping. In recent investigations, the rock mass classification has not been done specifically in the spillway tunnel. This research aims to obtain technical geological data and information to define excavation methods and tunnel support. For more comprehensive research, engineering geological investigations were carried out regarding the Geological Strength Index (GSI), selecting excavation methods using EXCASS system and Rock Mass Rating (RMR) for tunnel support. The geological mapping showed that the study site was composed of 2 lithological units: quartz muscovite phyllite and pebblely sand deposits. The GSI value in the tunnel is between 14-25, indicating poor and very poor quality. Adopting the EXCASS system, the optimum method of excavation (EPIopt) in the Pelosika dam spillway tunnel are ripper easy and digger. While RMR values of 9 – 25 are classified as poor quality. Consequently, the appropriate method for the excavation sequence is using the top heading and bench and multiple drifts. And the recommended support system is a systematic rock bolt with wire mesh and shotcrete in the crown and walls with medium to light steel rib.

Research on Construction Sequences and Construction Methods of the Small Clear-Distance, Double-Arch Tunnel under an Asymmetrical Load

A small clear-distance, double-arch tunnel under an asymmetrical load combines the characteristics of small clear-distance, tunnels and double-arch tunnels, and the influence of an asymmetrical terrain must be considered. Its construction stability is a problem worth studying. This paper used the Wengcun tunnel as the engineering background. Midas/GTS finite element analysis software was used to study the effects of eight excavation sequences and two excavation methods on tunnel stability. The results showed that the deformation and force of the tunnel were asymmetric under the asymmetrical terrain. Both middle partition walls were deformed towards the shallowly buried side, and the shallowly buried side was deformed to a greater extent. Excavating shallow side tunnels first can effectively mitigate the impact of asymmetric terrain. The arch settlement of the Center Diaphragm Excavation Method is 1.33 cm, which is smaller than the three-step excavation method of 1.48 cm; however, this difference is not significant. The Three-bench Excavation Method was more efficient. Based on the conclusion of a numerical simulation, the construction site adopted the construction sequence of excavating the shallowly buried side tunnel first and adjusted the excavation method to the Three-bench Excavation Method.

A multi-stage Bayesian modelling for building the chronocultural sequence of the Late Mesolithic at Cueva de la Cocina (Valencia, Eastern Iberia)

This paper presents a refined Mesolithic chronocultural sequence as a result of matching data provided by the set of archaeological research conducted at Cueva de la Cocina (Valencia, Spain) in the 20th and 21st centuries and the new radiocarbon dates record. Because available data are of different quality, we apply a methodological framework based on Bayesian modelling approaches. To do this, we systematically order each one of the archaeological registers and then combine the information in a unitary general chronology. Our novel approach introduces Bayesian modelling from a double analytical procedure: using Bayesian chronological models applied to the stratigraphic sequence of Pericot's excavation in Cocina cave we build a general phase model using data from multiple years of archaeological fieldwork. One the most reliable layers have been defined, we use this information to define the rest of the sequence through a Predictive Bayesian approach. This approach sheds light on evolutionary questions from a macroscale regarding the socioecological dynamics of the last hunter-gatherers and their role for explaining the subsequent agricultural spread.

Substantiation of the optimal mining sequence of an ore deposit under conditions of high stress and low rock mass strength

Introduction. When choosing the mining sequences of an ore deposit, technological and organizational factors are mostly taken into account. However, when using systems with caving which involve considerable mined-out spaces, the geomechanical factor, which determines stability of mine workings, plays a determining role. The research objective is to reveal the dependence between the stability of the development and face-entry headings within the mined-out space influence zone and the excavation sequence of the isolated ore block under conditions of high stress and low ore and rock mass strength. Methods of research. Numerical modeling of the enclosing ore and rock mass secondary stressstrain state formation was carried out by the finite element method in the Rocscience RS3 program together with the original FEM software package. Modeling was performed for two variants of block excavation – from the center to the flanks and from one flank to the other along the strike. For the analysis, we proposed a coefficient representing the product of compressive stress concentration zones length by their existence duration. Results. Based on the analysis of the maximum stress concentration areas distribution in the marginal rock mass, as well as the time of their influence, the optimal sequence of actual mining was substantiated according to the factor of influence on bottom workings stress-strain state – from flank to flank along the strike. Conclusions. The obtained result confirms the model representations about the mechanism of rock mass stressed redistribution in the process of lens-shaped deposit excavation. The representations suggest that during mined-out space development along the strike, compressive stresses concentrate at its ends. However, the intensity of end sections expansion in the flank to flank variant is two times as high as in the center to flank variant. The duration of the stress concentration zones impact on the bottom workings is therefore less, which is indicated by the proposed coefficient.

Analysis of Loose Surrounding Rock Deformation and Slope Stability at Shallow Double-Track Tunnel Portal: A Case Study

A low-clearance tunnel portal in the shallow-buried, joint-developed, broken, and loose surrounding rock slope deposit may cause safety issues during construction. In this study, the Guanyin Mountain Tunnel of the Chong-Ai expressway was taken as a case study, and the characteristics of the loose and broken surrounding rocks, their low clearance, and shallow buried bias were comprehensively studied. The three-dimensional numerical model of the Guanyin Mountain tunnel portal section was constructed by the Rhino, AutoCAD, and FLAC 3D software, and the whole construction process of the tunnel portal was simulated. Under the conditions of loose and broken surrounding rocks, the surrounding rock deformation, surface settlement, and slope stability at the portal of the shallow buried tunnel with a small clear distance during the construction of the center diaphragm (CD) method and circular reserved core soil method were studied. The following conclusions are drawn. During the simulated excavation of the tunnel, the maximum surface settlement is 10.74 mm, which meets the requirement of the specification. When the left tunnel is excavated, the surrounding rock deformation of the right arch shoulder should be carefully considered. The maximum deformation value can reach 14.314 mm. After excavation, the deformation rate of the right tunnel is large, and initial support should be installed in time. Since the stratum rock at the portal of the tunnel is strongly weathered, the uplift value of the arch bottom is large and gradually decreases along the axial direction. The tunnel arch bottom and arch foot are plastic areas prone to tensile damage. Therefore, it is imperative to strengthen the inverted arch support of the tunnel in the strongly weathered rock stratum. The excavation sequence of the tunnel portal section adopts the method of excavating the left tunnel first and then excavating the right tunnel, which is more conducive to ensuring the slope stability.