Tunneling Parameters Research Articles

Face support pressure impact on the surface deformation during TBM tunneling

There is currently an intense infrastructure development in large cities. One of the most significant projects are the structures for transport purposes, which include the subway. Underground structures construction in conditions of dense urban area is associated with the solution of complex geotechnical problems, such as ensuring the safety of surface buildings and structures located in the work impact zone and work safety during tunneling. Determination of the required tunneling parameters in the design process must take into account the difficulties of geological conditions and possible inaccuracies in defining these conditions.

A framework for assessing tunnel drainage-induced impact on terrestrial vegetation

The tunnel projects elevate the transport of large cities, but they also bring negative impacts on the terrestrial vegetation, particularly in mountainous rural areas. Aside from the immediate effects during construction, the tunnel drainage can have long-term effects on the terrestrial vegetation by depleting shallow groundwater resources adjacent to the tunnel. Previous research proposed a number of analytical and numerical methods for determining allowable tunnel drainage rates in order to keep terrestrial vegetation from wilting. These methods, however, only provide local estimates of drainage-induced drawdown and an approximate steady-state groundwater budget based on tunnel design parameters, ignoring soil water dynamics that have a direct influence on vegetation roots. As a result, we propose a comprehensive integral vulnerability assessment framework (IVAF) for assessing tunnel drainage's long-term regional impact on terrestrial vegetation. This framework couples a stochastic groundwater model, including tunnel parameters, with a topsoil model that includes soil–plant-atmosphere continuum (SPAC) components and creates regional vegetation vulnerability maps based on the vulnerability concept. It aims to provide a tool for tunneling experts by revealing the long-term tunnel drainage-induced changes between regional groundwater and soil water. The vulnerability assessment was applied to an example tunnel project in a moderately mountainous region. Vulnerability maps reveal the most likely influenced zones by tunnel drainage. The vulnerability index has been summarized via rooting depth segmentation, demonstrating the drawdown effect on topsoil. The assessment results show that IVAF is capable of establishing detailed groundwater and land cover connectivity on topsoil levels in poorly-sampled areas, as well as identifying potential vulnerability caused by tunnel drainage-induced drawdown.

In silico анализ особенностей пространственной организации молекул целлюлаз из различных продуцентов

The spatial structure of the enzyme largely determines the mechanism of its functioning. In particular, changes in the number, structure, and localization of internal cavities, tunnels, and pores in an enzyme molecule can change its thermal stability, the mechanism of substrate diffusion to the active site, and the features of interaction with the microenvironment. The composition, localization, and structure of internal cavities, tunnels, and pores in Thermotoga maritima cellulases associated with various ligands and having amino acid substitutions have been studied. The parameters of pores, tunnels, and cavities were calculated using the Mole software. An assumption was put forward about the effect of these modifications on the change in the structure of the enzymes presented in the work. The data analyzed in this work are of significant value for understanding the processes of conformational rearrangements in the molecules of cellulases from Thermotoga maritima when they are bound to various ligands and in the presence of point mutations, which can be useful in designing industrial catalysts based on these proteins and studying their physiological role within the producer organism.

Predictive Models to Evaluate the Interaction Effect of Soil-Tunnel Interaction Parameters on Surface and Subsurface Settlement

Nowadays, the need for subway tunnels has increased considerably with urbanization and population growth in order to facilitate movements. In urban areas, subway tunnels are excavated in shallow depths under densely populated areas and soft ground. Its associated hazards include poor ground conditions and surface settlement induced by tunneling. Various sophisticated variables influence the settlement of the ground surface caused by tunneling. The shield machine's operational parameters are critical due to the complexity of shield-soil interactions, tunnel geometry, and local geological parameters. Since all elements appear to have some effect on tunneling-induced settlement, none stand out as particularly significant; it might be challenging to identify the most important ones. This paper presents a new model of an artificial neural network (ANN) based on the partial dependency approach (PDA) to optimize the lack of explainability of ANN models and evaluate the sensitivity of the model response to tunneling parameters for the prediction of ground surface and subsurface settlement. For this purpose, 239 and 104 points for monitoring surface and subsurface settlement, respectively, were obtained from line Y, the west bond of Crossrail tunnels in London. The parameters of the ground surface, the trough, and the tunnel boring machine (TBM) were used to categorize the 12 potential input parameters that could impact the maximum settlement induced by tunneling. An ANN model and a standard statistical model of multiple linear regression (MLR) were also used to show the capabilities of the ANN model based on PDA in displaying the parameter's interaction impact. Performance indicators such as the correlation coefficient (R2), root mean square error (RMSE), and t-test were generated to measure the prediction performance of the described models. According to the results, geotechnical engineers in general practice should attend closely to index properties to reduce the geotechnical risks related to tunneling-induced ground settlement. The results revealed that the interaction of two parameters that have different effects on the target parameter could change the overall impact of the entire model. Remarkably, the interaction between tunneling parameters was observed more precisely in the subsurface zone than in the surface zone. The comparison results also indicated that the proposed PDA-ANN model is more reliable than the ANN and MLR models in presenting the parameter interaction impact. It can be further applied to establish multivariate models that consider multiple parameters in a single model, better capturing the correlation among different parameters, leading to more realistic demand and reliable ground settlement assessments. This study will benefit underground excavation projects; the experts could make recommendations on the criteria for settlement control and controlling the tunneling parameters based on predicted results. Doi: 10.28991/CEJ-2022-08-11-05 Full Text: PDF

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

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

Caloric effects in an open Fermi–Hubbard optical dimer due to onsite and heat bath-induced two-particle interactions

The immersion of the Fermi–Hubbard optical dimer in a mean field Fermi gas, acting as a heat bath, modifies the behavior of the statistical mechanical properties of the particles trapped in it. This is done by varying the two-particle interactions induced by the heat bath and the onsite two-particle interaction U. It is shown that in the presence of the heat bath-induced interaction, the partition function Z drops to a minimum finite value in the repulsive regime of U at the normalized temperature region kBT≲t/2, where t is the tunneling parameter. In this temperature region, the convergence points of the respective isolines of the entropy S and the heat capacity CV move towards each other. Such shift in their features finetune S and CV relative to their behavior in the absence of two-particle interactions with the bath.

Superposition control of extreme water levels in surge tanks of pumped storage power station with two turbines under combined operating conditions

This paper investigates the superposition control of extreme water levels (EWLs) in surge tanks of pumped storage power station (PSPS) with two turbines under combined operating conditions (COCs). Firstly, for PSPS with upstream and downstream surge tanks (UDST) and two turbines, the model and ten COCs are presented. The superposition control strategy of EWLs in UDST is designed. Secondly, the most favourable superposition time and the most unfavourable superposition time under COCs, i.e. superposition control moments, are determined. The concepts of initial gradient and superposition gradient are proposed to reveal the control mechanisms. Finally, the influences of tunnel parameters on superposition control moments are analyzed. The results show that tangential points for water level - flow velocity curves of initial operating condition and superposition operating condition are not the superposition control moments. For ten COCs, the most favourable superposition time is the moment of minimum superposition gradient, and the most unfavourable superposition time is contrary. With the increase of sectional area and decrease of length for tunnel, the superposition control moments decrease. Because the initial gradient and superposition gradient are mainly affected by tunnel parameters, the hydraulic coupling oscillations of UDST have no effect on superposition control moments.

Study on disc cutter chipping of TBM based on field data and particle flow code simulation

Using tunnel boring machines to excavate high-strength intact rock masses is becoming more common. Due to the interactions between disc cutters and rocks, abnormal wear of disc cutters, especially cutter chipping, has become a common phenomenon. Existing research has mainly focused on normal wear of disc cutters without addressing abnormal wear cases. This study used the disc cutter consumption data of a tunnel project in China to investigate the abovementioned problem based on field research. According to the failure patterns and fracture surface characteristics, the cutter chipping patterns were mainly categorized into four types: granule chipping, patch chipping, primary collapse, and secondary collapse. To further simulate the evolution of disc cutter chipping, based on the linear plastic bond model, a new contact model called the modified plastic bond (MPB) model was proposed to solve the metal simulation problem in Particle Flow Code software. To this end, a set of uniaxial tensile and compressive tests were initially conducted to verify the applicability of the MPB model. Then, a series of three-dimensional rock-cutting simulation tests were conducted to reflect the evolutionary processes involved in each type of cutter chipping. The cutter chipping mechanism and morphological characteristics were classified and summarized in detail. The results revealed that the cutting speed and penetration growth led to a rising trend in the probability and intensity of the cutter chipping. The presence of initial defects also induced an adverse effect on the service life of the cutter. The results indicated suitable working conditions for the cutter and suggested ways to control tunneling parameters and avoid frequent cutter chipping cases.

Research on Strata Deformation Induced by EPB Tunneling in Round Gravel Stratum and Its Control Technology

Recently, many studies have been conducted on the stratum deformation induced by earth pressure balance (EPB) shield tunneling in soft soil and sand. Movement laws vary largely among different strata. However, at present, relevant research mainly focuses on soft soil and sand, whereas little attention has been paid to the movement law of round gravel stratum with higher instability. In this study, a field monitoring test was carried out on the EPB shield machine when it passes through the round gravel stratum. Based on the analysis of monitoring results under different chamber earth pressures, thrust force, the torque of the cutter, grouting pressure, and grouting volume, the relationships between shield tunneling parameters and their influence on the disturbance of the surrounding soil mass were investigated. It was found that the surface deformation shape of the monitoring section of the south and north lines conforms to the Gaussian curve. The vertical deformation of the stratum at the tunnel axis is the largest. The maximum value is observed when the cutter head reaches the monitoring section. The horizontal deformation reaches a maximum value at the stage of the shield tail pass section. The strata deformation is not only related to the strata properties but also has a strong positive correlation with the shield tunneling parameters. The chamber earth pressure is the main factor affecting the stratum deformation before the arrival of the cutter head, and the grouting volume is the main factor affecting the strata deformation during the stage of the shield tail pass section.

Prediction of Tunnelling Parameters for Underwater Shield Tunnels, Based on the GA-BPNN Method

Reasonable tunnelling parameters for underwater shield tunnels play an important role in maintaining driving efficiency and safety. In this paper, a neural network method was developed to predict tunnelling parameters. Soil properties and geometric parameters were taken as inputs for the neural network, which output the tunnelling parameters, such as advancing thrust, rotation, penetration, torque of the cutter head, and support pressure. In order to improve the stability of the neural network, a genetic algorithm (GA) with a global searching ability was used to optimize the initial weight of the neural network (GA-BPNN). The accuracy of the algorithm, based on GA-BPNN, was studied through an underwater shield tunnel project. The results showed that the integration of GA into the neural network significantly improves the prediction ability for shield tunnelling parameters, especially for adjustable parameters. Later, the developed GA-BPNN model was further utilized to predict and set the range of shield tunnelling parameters in fine sand stratum of high risk. Through a comparative analysis of tunnelling parameters, the reasons leading to ground instability have been found out, and the effectiveness of ground pre-reinforcement has been verified.

Calculation Method for Investigating the Behavior of Ground Surface Settlement of Underpass Buildings in TBM Double-Line Tunnels

This study aims to investigate the behavior of ground surface settlement in TBM double-line tunnels constructed under existing buildings and to devise a calculative representation for that behavior. Numerical simulation and field monitoring methods were used to examine the Zhongcong Tunnel in Chongqing Metro Line 9. The ground surface settlement was analyzed using an orthogonal test of 3D numerical simulation methods. The results showed that ground surface settlement was influenced by TBM tunneling parameters and the location of the existing building in the following manner. The existing building reduced the settlement trough width. Surface settlement was increased by frictional and palm surface thrust forces but reduced by grouting pressure. The settlement trough width of the first excavation iz correlated with that of the last excavation iy. To accommodate the influence of existing buildings, the tilt factor of the settlement trough TR was introduced to improve the formula for calculating the ground surface settlement of TBM double-line tunnels. The improved formula was validated by comparing the calculated results with actual measurements.

Multi-objective optimisation of tunnel parameters in a liquefied sand lens under seismic loads

If underground structures built close to the surface lie within a liquefied sand lens, they will be significantly damaged in the case of a seismic event. To achieve an optimal design in terms of depth, diameter and tunnel lining thickness, it is important to consider factors such as ground subsidence, bending moment and axial forces exerted on the tunnel lining. This study intended to perform multi-objective optimisation of relevant tunnel parameters within a liquefied sand lens location under seismic loads. The Flac3D software was used to model the saturated sand lens and determine changes in pore water pressure and effective tension after lens liquefaction. An artificial neural network was used to find optimal values in the genetic algorithm. All optimal design points were obtained per the target function with a revised non-dominated sorting genetic algorithm II algorithm. The results pertaining to depth, diameter and tunnel lining thickness were in opposition to one another, as reducing ground subsidence resulted in increased bending moment and axial force exerted on the tunnel lining. According to the results, it is possible for the designer of the tunnel to use Pareto charts in order to determine the optimal values regarding tunnel depth, diameter and lining thickness within the liquefied sand lens.

Method for predicting the stress state of the lining of underground structures of quasi-rectangular and arched forms

A method for predicting the stress-strain state of the lining of underground structures, the shape of the cross-section of which is different from the circular outline, is considered. The main task of the study is to develop a methodology for assessing the influence of the parameters of the cross-section shape of underground structures on the stress state of the lining. To solve this problem, a method for calculating the stress state of the lining for arched tunnels with a reverse arch and quasi-rectangular forms is substantiated and developed. The methodology was tested, which showed that the accuracy of the prediction of the stress state of the lining is sufficient to perform practical calculations. An algorithm for multivariate analysis of the influence of the cross-sectional shape of underground structures of arched and quasi-rectangular shapes on the stress state of the lining is proposed. Parametric calculations were performed using the developed algorithm and regularities of the formation of the stress state of the lining of underground structures for various engineering and geological conditions, as well as the initial stress state field, were obtained. A quantitative assessment of the influence of geometric parameters of tunnels on their stress-strain state was performed.

Scale Effect of the Model Extent on Seepage Analysis of Circular Tunnels under Drained Conditions

Numerical simulations have been widely used to predict groundwater inflow into tunnels during excavations. An appropriate geometric size of a numerical model is crucial for reducing the simulation time and ensuring the accuracy of numerical results. However, to the best of our knowledge, no information concerning the scale effect of the model extent on the seepage characteristics of tunnels under drained conditions has been published. This study evaluates how the model extent affects the tunnel inflow, drawdown, and water pressure via the Signorini type variational inequality formulation. A series of two-dimensional finite element models are conducted with various combinations of tunnel parameters, including tunnel radius, initial groundwater level, lining thickness, and relative permeability. Subsequently, a comprehensive function to yield the optimum model extent within an allowable error is proposed. Interestingly, the optimum model extent for both tunnel inflow and water pressure decreases with an increase in the relative permeability, whereas that of the drawdown exhibits the opposite pattern. A model extent of no less than 200 times the tunnel radius is recommended to acquire accurate model results and is verified with existing analytical methods. This study therefore not only highlights the drainage effect of the tunnel but also provides universal suggestions for engineering practice.

Surface Settlement during Tunneling: Field Observation Analysis

We address the effect of three groups of factors on supplementary ground surface displacements during tunnel construction. The first group of factors includes the engineering and geological properties of the massif in which the tunneling is conducted; the second group includes the structural features of the designed tunnels and surrounding buildings, and the third group includes the engineering parameters of the tunneling process. The research takes advantage of the geotechnical monitoring data obtained during the construction of underground facilities and the engineering parameters of shield tunneling during construction of single- and double-track Moscow underground lines by using EPB (earth pressure balance)–TBM (tunnel boring machines) in different soils. The dependence of additional displacements, occurring above the designed tunnel, on the TBM pressure, is addressed in detail. The presence of a close interdependence is evidenced by a correlation coefficient equal to 0.77. No dependence of the settlement on the diameter or depth of the designed tunnel, the distance from the tunnel axis to the monitored object, the loading that comes from a building in the affected area, or the boring rate was identified. The consideration of this parameter can be used to predict the soil displacement around the tunnel at construction facilities having similar geological profiles and boring parameters.

Analysis and Application of Surrounding Rock Mechanical Parameters of Jointed Rock Tunnel Based on Digital Photography

Analysis and Application of Surrounding Rock Mechanical Parameters of Jointed Rock Tunnel Based on Digital Photography

Numerical Simulation Research on Optimization of Large Deformation Control Parameters in Layered Slate Tunnel

In order to explore the deformation characteristics of layered slate tunnels under different dip angles of rock formations, a numerical simulation research method for optimization of large deformation control parameters of layered slate tunnels is proposed. The plane deviation, plane deformation, and DP parameters of the structure are obtained through the calculation mode. When studying the effect of overlapping rock masses on the stability of thick tunnels, the incidence angle of the rock structure is assumed to be zero. The estimated thicknesses of the dolomite limestone surrounding the tunnel are 0.3 m, 0.4 m, 0.5 m, 0.6 m, 0.7 m, 0.8 m, and 0.9 m, respectively. Select the vertical displacement to be analyzed as the result of the calculation. In order to study the influence of the structural slope on the tunnel stability, the thickness of the rock layer was 0.6 m, and the structural slopes of 5°, 15°, 30°, 45°, 60°, 75°, and 85° were used for simulation calculations. During on-site construction, focus on monitoring the tunnel section deformation before the secondary lining construction. Every 10-20 m, when the surrounding rock changes, the observation section of the enclosure convergence and vault settlement is arranged, and the peripheral displacement rate and the vault settlement rate are calculated according to the observed deformation. The results show that the vertical displacement of the top of the tunnel is generally in a “V” shape, that is, the maximum settlement in the tunnel; when the layer thickness is 0.3 m, the maximum vertical displacement of the rock layer is 7.2 mm, and the total settlement in the lining support tunnel is 8.23 mm. When the layer thickness is 0.9 m, the vertical displacement of the rock layer is 5.14 mm, and the total settlement in the lining support tunnel is 5.22 mm2; when the layer thickness was changed from 0.9 m to 0.3 m, the maximum vertical displacement of the rock layer increased by 140%, and the settlement at the vault increased by 158%. At this time, the focus of tunnel support is on both sides of the lining structure and the vault with large vertical settlement. The phenomenon that the section of YK51+032 first decreases and then increases due to the sudden appearance of mud in the surrounding YK51+040, resulting in increased short-term deformation. Only the ZK49+356 section at the entrance of the left line has a large deformation due to the thin overlying stratum, and other sections are relatively consistent, indicating the reliability of the calculation results.

Numerical Simulation on Dynamic Response of Existing Tunnel to Moving-Axle Loads under the Influence of Oblique Shield Crossing the Intersection Area

A 3D dynamic finite element model is developed to study the response of the existing tunnels’ concrete structure under the influence of different train speeds and undercrossing with fixed shield excavation. The intersection area of Metro Line 3 in Guangzhou and the intercity railway between Foshan and Dongguan is used as the case study. A programming idea simulating oblique moving-axle loads in the numerical model by using function expressions to constrain activity area is proposed. The Hilber–Hughes–Taylor time-integration scheme is used to calculate the dynamic response parameters of the double-channel rectangular cross section tunnels. Considering fixed excavation steps in the process of shield crossing, acceleration and deformation of the existing tunnels were analyzed under the moving-axle loads of trains at different speeds. From the perspective of the vibration and deformation of existing tunnels, shield excavation and moving speed have their own emphasis on the dynamic influence of the existing tunnel. In addition, the calculation results of the numerical simulation are in good agreement with the data obtained from some field tests, which further verifies the reliability of the calculation method of the numerical model. The results of this research can guide the arrangements for reinforcement measures for existing tunnels in the later stage.

Experimental Study on Shield Tunneling Control in Full Section Water-Rich Sand Layer of Collapsible Loess

Taking China’s first application of domestic shield tunneling in a water-rich sand layer for crossing a high-speed railway as research background, the influence of changes in the shield tunneling parameters on ground settlement is analyzed based on field tests, and a construction control method suitable for shield tunneling under a risk source in a water-rich sand layer is proposed. The test results show that the use of 10% sodium bentonite as the soil modifier for soil pressure balance shield tunneling into the water-rich sand layer has advantages, while adding 50% loess into the bentonite slurry in the gravel sand layer can greatly improve the impermeability of the soil; the settlement of soil can be effectively reduced by using the special segment with grouting holes for deep grouting and applying the adaptive transformation of the shield cutter. Based on the statistical analysis results, a reasonable range for the cutter head torque, cutter head speed, chamber pressure, bentonite injection volume, and advanced speed in the water-rich sand layer can provide a construction control basis for similar projects and provide data support for the compilation of relevant specifications.

Study on launch tunnelling parameters of a shield tunnel buried in pebble soil with existing pipelines base on discrete continuous coupling numerical method

A computational scheme coupling the particle flow code in three dimensions and fast Lagrangian analysis of continua in three dimensions techniques is implemented to evaluate the coupling effects of different discrete and continuous coupling computing modes under a gravity stress field. Based on the optimal coupling mode that can consider the computational efficiency and coupling effect, a three-dimensional discrete-continuous coupling numerical model is established to realize the dynamic excavation of a shield tunnel. The effects of launch excavation chamber filling rates and shield tunnelling control parameters on the ground surface and pipeline settlement in the initial stage are examined. With the increase in the initial chamber filling rate, the convergence rate of the surface and pipeline settlements increases, and the total settlement significantly decreases. Moreover, although the disturbance range of shield tunnelling to the strata decreases, the thrust and torque of the shield machine increase. As the cutter head speed varies, the settlement of the surface and pipeline and thrust of the shield machine do not significantly change. However, the torque of the shield machine significantly increases with the increase in the cutter head rotation. The tunnelling speed, ground disturbance range, and shield torque are weakly correlated; however, as the tunnelling speed increases, the thrust of the shield machine increases and the stratum displacement tends to be uplifted. With the increase in the screw conveyor rotation speed, the settlement of the surface and pipeline increases, and the thrust of the shield machine decreases. The torque of the shield machine, range of ground disturbance, and screw conveyor rotation speed are only weakly correlated. The thrust and torque calculated using the coupling numerical model are close to the measured values, which demonstrates the reliability of the coupling numerical model.