Tunnels In Clay Research Articles

Eco-Friendly Shield Muck-Incorporated Grouting Materials: Mix Optimization and Property Evaluation for Silty Clay Tunnel Construction

As shield tunnels increase, managing shield muck strains construction and the environment. To mitigate this problem, shield muck replaced bentonite in silty clay to improve synchronous grouting slurry. Initially, the physical attributes and microstructural composition of shield muck were obtained, alongside an analysis of the effects of the muck content, particle size, and general influencing factors on the slurry properties through standardized tests and regression models. Subsequently, leveraging three-dimensional response surface methodology, admixture interactions and multiple factor impacts on the slurry were explored. Finally, utilizing the SQP optimization technique, an optimal slurry blend ratio tailored for actual project needs was derived for improved muck slurry. The findings reveal with the decreasing bleeding rates as the muck content rises, the particle size diminishes. An inverse relationship exists between the muck content and slurry fluidity. At soil–binder ratios below 0.6, a decrease in the soil–binder ratio intensifies the influence of the water–binder ratio on the slurry density, bleeding rate, and setting time. The fly flash–cement ratio inversely correlates with the slurry bleeding rate, while the ratio greater than 0.6 is positively correlated. For muck particle sizes under 0.2 mm, the fly flash–cement ratio inversely impacts the density, while over 0.2 mm, it correlates positively. The optimal proportion for silty clay stratum synchronous grouting slurry, substituting muck for bentonite, includes a water–binder ratio of 0.559, binder–sand ratio of 0.684, fly flash–cement ratio of 2.080, soil–binder ratio of 0.253, particle size under 0.075 mm, and water-reducing admixture of 0.06.

Experimental and Numerical Study on the Treatment Effect of Horizontal Lateral Grouting on the Deformation of Shield Tunnels in Clay

Experimental and Numerical Study on the Treatment Effect of Horizontal Lateral Grouting on the Deformation of Shield Tunnels in Clay

Twin-tunnelling: Case studies in clay

New developments in the theory and practice of tunnel construction are essential for the industry to progress but it is the relationship between these two areas that is equally as important. Tunnelling practice has greatly benefited from laboratory research; specifically, centrifuge modelling linked with field measurements. The wide body of work on the construction of single tunnels has led to the identification of parameters and techniques that are widely accepted for predicting and assessing the magnitude and extent of tunnelling ground movements. However, the usage of twin tunnels in urban areas for transportation purposes have increased and better understanding on the associated ground displacements are required. This paper firstly provides background to ground displacements due to single tunnel, twin tunnel constructions and common prediction methods used in practice. Then, it introduces recent technological advancements in centrifuge modelling, applied to the complex geotechnical events of twin-tunnelling, that has led to further insight. The tunnelling induced ground displacements obtained from twenty four case studies in clay around the world and eighteen centrifuge tests are presented for further analyses. From that, a comparison between the recent theories of proximity-dependent tunnelling-induced ground movements with case histories has been carried out to establish their validity and limitations. Published field measurements have been reanalysed taking into account newly discovered relationships between the tunnels’ proximity and the magnitude and extent of ground movements, reflected via volume loss and the settlement trough width, respectively. The applicability to field measurements of the additional volume loss prediction method (derived from consideration of the experiment work) for tunnelling in clay is assessed.

Predicting Tunnel-Induced Settlement in Cohesionless soils in Greenfield Condition

Rapid population growth and increasing congestion worldwide are placing greater demands on existing infrastructure. A solution to this problem is the use of tunnels to construct underground transportation systems. However, tunnelling induces settlement troughs that may result in severe or possibly irreparable damage to nearby infrastructure. For this reason, the effects of tunnelling must be well understood and predicted in the tunnel design stage, to prevent structural damage due to design oversights. Although tunnelling in clay has been extensively studied by previous researchers, the literature lacks reliable settlement estimation techniques for tunnels embedded in granular soil media. In this study, an extensive parametric analysis is conducted to examine the effects of the tunnel diameter, embedment depth, soil density, and shield conicity (tail void gap) on tunnel-induced settlement. Based on the results of the parametric analysis, the authors propose an effective, user-friendly solution that utilizes artificial intelligence software to predict tunnel-induced surface subsidence. The reliability and accuracy of the proposed solution are demonstrated by comparisons with 12 different sets of measured field data.

A unified method of predicting soil deformations induced by various shaped-section tunnelling in clays

A unified method of predicting soil deformations induced by general and special-section tunneling in clays is proposed. Assuming that the tunneling-induced ground loss can be divided into infinite ground loss elements, and the soil deformation induced by the overall ground loss is equal to the sum of deformation due to each unit ground loss, the soil deformation due to unit ground loss is first derived based on elasticity theory solution. The soil deformation induced by random shaped-section tunneling is then obtained by integrating along the overall ground loss distribution, and the expressions are presented in the Cartesian and polar coordinate forms, respectively. By means of several cases of single circular tunneling, the reliability of the unified method is well verified through comparing with the measured data, and the performance of this method is quantitatively evaluated against the error analysis of the predictions. Taking the double-O-tube (DOT) shield tunnel for example, the unified method is further applied to predict soil deformation induced by special-section tunneling. The results show that the shape of the surface settlement curve caused by DOT shield tunneling also presents an inverted Gaussian curve. With the increase of the soil depth, the settlement of soil above the DOT shield tunnel increases slightly first and then decreases, and the settlement trough width keeps decreasing, resulting in the change of the shape of the settlement curve from “V” to “W”.

The stability evaluation of clay tunnels via the non-linear deterioration of physical and mechanical properties of surrounding rocks

Simple, fast, and reliable methods for the stability evaluation of tunnels can facilitate the construction and development of tunneling projects. The problems related to tunnel stability at this stage can be well analyzed via theoretical analysis method, model test method, or numerical analysis method. On the other hand, those methods are hard to be effectively analyzed these projects with higher importance, shorter decision and design period, and more urgent construction period. This paper proposed research works on the stability evaluation of clay tunnels. Firstly, a state function with the variables of stress and strain state is presented to predict the stress and strain states of surrounding rocks caused by tunnel excavation, which characterize the physical-mechanical state of surrounding rocks (also called stability state). Secondly, the non-linear deterioration of the physical and mechanical properties of surrounding rocks will be simulated, and the expressions and calculation methods of the tunnel stability reserve factor will be yielded. Finally, the results of the proposed method were compared with the strength reduction method and the limit equilibrium method with a clay tunnel example. The comparison between the three feature points of the arch crown, sidewall, and arch bottom showed that the stability reserve factor of the clay tunnel was smaller than those of the strength reduction method and the limit equilibrium method. The values of limit displacement obtained by the proposed method were closer to the field monitoring data than that of the strength reduction method. Therefore, this study could be better applied to the stability evaluation of clay tunnels.

Plasticity solutions for ground deformation prediction of shallow tunnels in undrained clay

Elastic-plastic contraction solutions of a cavity within an infinite soil mass are widely used to estimate ground response curves of deep tunnels. The pressure-convergence response of soil around shallow tunnels, however, tends to vary with tunnel embedment ratio. To account for the embedment ratio effect, this paper presents a general solution procedure for undrained contraction analysis of a thick-wall cylinder or spherical shell of isotropically hardening soils, by which a set of analytical and semi-analytical large strain solutions for several Cam-Clay soil models is derived. Results obtained with the new solutions show that the cavity contraction response highly depends on the soil stress history (overconsolidation ratio) and the radial thickness of the surrounding soil. A limit ratio of the outer to the inner radii exists, beyond which the thickness ratio effect becomes negligible. The limit ratio for a spherical shell is smaller than that for a hollow cylinder, and it decreases with the overconsolidation ratio of soil. Based on the analogy between cavity contraction and tunnel convergence, theoretical methods for predicting ground response curves of shallow plane-strain tunnels in clays are proposed and validated by comparing with relevant experimental and numerical simulation results. The solutions can also provide valuable benchmark methods for verifying various numerical programmes.

Pile group response induced by adjacent shield tunnelling in clay: Scale model test and numerical simulation

The shield tunnelling adjacent pile group was a common phenomenon in urban metro construction, and additional internal force and displacement field of pile group was disadvantageous to existing superstructure. In this paper, a micro shield machine was invented to simulate the shield tunnelling process, and a series of physical scale model tests and 3-D nonlinear FE models were employed to investigate the pile group (2 × 2) response with different minimum distance between pile group and the tunnel central line (Hm) in clay. The results indicated that large additional bending moment and axial force was induced by shield tunnelling, the maximum bending moment was near the tunnel center line, and the amplitude of maximum bending moment in the lateral section (My) was three to five times of that in the longitudinal section (Mx). The maximum lateral displacement emerged at the tunnel central line, and the vertical displacement distributed uniformly along pile length. The negative shaft resistance between pile group and surrounding soil obviously reduced the axial bearing capacity. The shielding effect of the front pile on the rear pile greatly reduced its internal force and displacement, but it gradually weakened with increase of Hm. The internal force and displacement of pile group decreased quickly with increased of Hm. The research results in this paper can provide a reference for the design and construction of shield tunnels near pile group.

Design equation for stability of a circular tunnel in anisotropic and heterogeneous clay

The safety assessment of tunnel stability is critical to tunnel construction and requires accurate analysis to obtain a reliable prediction. Strength anisotropy is an important aspect of clay behavior, but it is mostly neglected in practical stability analyses. In this study, the effects of undrained strength anisotropy and strength nonhomogeneity on the stability of unlined circular tunnels in clays are investigated. The static approach of lower-bound (LB) analysis using finite-element and second-order cone programming is employed to examine the aforementioned effects. The anisotropic shear strength of clay is modeled by employing an elliptical yield function under plane strain conditions. A complete set of dimensionless parameters covering the cover depth ratios of tunnels, normalized overburden pressure ratios, normalized strength gradient ratios of clays, and anisotropic strength ratios, are systematically investigated. The new LB solutions indicate that the stability load factor of the problem has a nonlinear relationship with the cover depth ratio and the anisotropic strength ratio, and there exists a linear relationship with the normalized overburden pressure and the normalized strength gradient. Their influence on the predicted failure mechanism is parametrically evaluated. A statistically approximate stability equation of unlined circular tunnels in anisotropic and non-homogeneous clay is proposed for the first time, which contains four new stability factors, namely, constant undrained strength, linearly increasing strength gradient, undrained strength anisotropy, and soil unit weight, and it can serve as a fast and accurate tool for predicting the undrained stability of this problem in practice.

Analysis of the Soil Loss and Settlement of Silty Clay with Different Subclassifications

There is an ever-growing demand for the construction of silty clay stratum tunnels; therefore, effectively controlling the surface settlement caused by tunnel construction has become an important task. Since the physical indexes of silty clay greatly influence strength and deformation, based on the physical and mechanical indexes of 3192 groups in three areas, quantitative and determinative indexes for the subclassification of silty clay are proposed using K-means clustering and the tracking records of the actual project. Then, the soil loss and settlement of different subclassifications of silty clay are studied through the standard Gauss error function. Empirical formulas for calculating the width of the settlement trough and the soil loss rate are proposed. The dispersion of the settlement parameters with different subclassifications indicates that the soil properties of the silty clay strata vary greatly with subclassification, and the influence range of the surrounding soil disturbance caused by excavation also varies. In addition, the change in the soil loss rate with the propulsion of the tunnel face in the same monitoring section is discussed. For subgrade V, the increasing soil loss rate reaches a maximum when the tunnel face reaches the monitoring sections. For subgrades VI1 and VI2, this rate changes mainly during the timeframe spanning from 5 days before excavation to 5 days after excavation. A numerical simulation was also carried out to validate the applicability of the Peck formula for silty clay tunnels. The numerical prediction and field measured data show that when the cover-to-diameter ratio is between 1 and 3, it is reasonable to use the Peck formula to analyze the surface settlement of a silty clay tunnel. This paper can provide guidance based on experience for the subclassification of the soil surrounding rock and for the prediction of the ground surface settlement.

Numerical analysis for the role of soil properties to the load transfer in clay foundation due to the traffic load of the metro tunnel

Abstract Soil properties play important role to the metro tunnel settlement induced by traffic load of metro operation. Numerical studies on this topic are still rare due to the lack of accurate dynamic constitutive models of clay. In this study, a new critical state based bounding surface plasticity model for natural structured clays is first developed. It is able to consider the initial and induced anisotropy of natural clay and the structure disturbance to the initial size of yield surface and to the initial adhesive stress by cyclic loading at low-stress levels. The applicability of the present model is evaluated through comparisons between the predicted and the measured results of numerous stress-path tests on Shanghai clay and Vallericca stiff clay. The model is then implemented as a user-defined model in a finite difference code. A typical tunnel in clay is simulated using the implemented model coupled with Biot’s consolidation, for which the stress distribution pattern in subsoils around tunnels due to train movement is investigated. The role of the dynamic constitutive model has been highlighted by comparing the simulation results of a static constitutive model and a dynamic constitutive model. The influences of the soil properties such as the anisotropy, structure ratio, and adhesive mean stress have been found significant to the load tranfer.

Movements of ground and existing structures induced by slurry pressure-balance tunnel boring machine (SPB TBM) tunnelling in clay

This paper presents a comprehensive study of field measurement of ground movements and displacements of adjacent existing structures induced by large diameter slurry pressure-balance tunnel boring machine (SPB TBM) tunnelling in clay. The evolution of displacements at six transverse monitoring sections against the distance of TBM cutterhead from corresponding instrumentations is characterized and interpreted in conjunction with recorded TBM tunnelling parameters. Measured results highlight that adjacent existing structures move almost synchronously along with ground except the magnitude, and stiffer structures can greatly resist deformation than pure soil does. The cast-in-place piles constructed between current tunnel and elevated bridge can effectively block the propagation of tunnelling-induced deformation. Results also show that the compensation effect of tail grouting on ground displacements is limited to the local areas which are close to the grouting position, and this effect attenuates as the distance from grouting position increased. The final “inwards” or “outwards” trend of surrounding soil relative to the tunnel relies on the injected grouting volume. The observation indicates that TBM tunnelling parameters at a transverse section can not only influence ground settlements there but also influence ground settlements ahead and behind this section along longitudinal direction to varying degrees. This longitudinal effect can be considered by introducing the impact coefficients of face pressure and tail grouting. The measured data of surface settlements along tunnel longitudinal axis and predicted ones using Loganathan-Poulos formula with and without considering this longitudinal effect are compared. The compared results indicate the longitudinal effect should be taken into account for the accuracy of prediction. The paper can provide valuable references for settlement prediction due to TBM tunnelling in clayey soil.

Face stability analysis of a shallow horseshoe-shaped shield tunnel in clay with a linearly increasing shear strength with depth

The face stability of a horseshoe-shaped shield tunnel in undrained clays with a linearly increasing strength is numerically and analytically investigated in this paper. Based on the kinematic approach of limit analysis, a continuous velocity field for a horseshoe-shaped shield tunnel is proposed to evaluate the limit support pressure of both the collapse and blow-out of the tunnel face. Moreover, the analytical results are compared with those obtained from the numerical simulation and other existing literatures. The results show that the horseshoe-shaped shield tunnel can improve the face stability compared to the circular shield tunnel. Finally, an improved velocity field is proposed, which provides a more realistic failure pattern and a better upper bound solution of the limit support pressure for the horseshoe-shaped shield tunnel.

Determination of Deformation Mechanism and Countermeasures in Silty Clay Tunnel

AbstractDeformation control and stability analysis are very important for tunnel construction. Large deformations of the constructed primary support accompanied by lining cracking and spalling occu...

Interaction between an underground parking and twin tunnels – Case of the Shiraz subway line

Three-dimensional numerical analyses were developed to study the interaction between twin tunnels and underground parking in an urban area. The mechanized tunneling procedure and segmental lining were accurately simulated using a finite difference code and a nonlinear perfectly plastic constitutive model (CYsoil). In this paper, the interaction between tunneling in clay and an underground parking was performed using two scenarios: construction of the underground parking above the existing tunnels and excavating the twin tunnels under the existing parking. The soil/structure interaction is investigated in terms of soil movements, structural forces induced in the tunnel lining and displacements of the parking structure. On the base of the numerical results, the construction sequence of underground structures, which are located nearby to each other, have a considerable effect on the soil and structures behavior.

Undrained Stability of Unlined Square Tunnels in Clays with Linearly Increasing Anisotropic Shear Strength

In general, the undrained strength anisotropy of clays is found in nature. Its effect on a stability problem during undrained loading should be considered in order to get a more accurate and realistic safety assessment. In this paper, the undrained stability of unlined square tunnels in anisotropic and non-homogeneous clays is investigated by the lower bound finite element limit analysis using second-order cone programming. The anisotropic undrained strength of clays is modelled by using an elliptical strength envelope under plane strain conditions. The stability analyses of the problem are performed by the comprehensive investigations of the effects of the cover-depth ratio, the normalized overburden pressure, the normalized strength gradient, and the anisotropic strength ratio on the stability load factor and associated failure mechanisms. The computed lower bound solutions are validated with the existing results of square tunnels in isotropic clays. The new approximate equations of the stability load factor and factor of safety for square tunnels in anisotropic and non-homogeneous clays are first time presented by using a nonlinear regression, hence providing a reliable, accurate and convenient tool for stability analyses of the problem in practice. The numerical results reveal that the strength anisotropy has a significant impact on the stability load factor, especially when anisotropic clays have much difference in undrained strengths between compression and extension.

Upper-bound solutions for the face stability of a non-circular NATM tunnel in clays with a linearly increasing undrained shear strength with depth

The face stability of the NATM tunnels (the New Austrian Tunneling Method) in undrained clays with a linearly increasing strength is numerically and analytically investigated by defining two types of the safety factors F in this paper. Based on the kinematic approach of the limit analysis, a continuous velocity field for an open-face tunnel is proposed. Moreover, the calculated solutions are compared with the results obtained from the numerical simulation and other existing literatures to validate its effectivity and superiority. The stability charts for different influence factors are also provided. Finally, an improved velocity field is presented, which provides a closer result to the real situation of the face collapse.

Quantitative Evaluation of Ground Movements Caused by Grouting during Shield Tunnelling in Clay

Grouting has been deemed as one of the most effective measures for mitigation of ground movements during tunnel construction in soft soil. Notwithstanding that, a reliable measure to quantitatively evaluate the grouting‐induced ground movements during shield tunnelling in soft soil has not yet been developed. This paper presents a simple method capable of quantitatively estimating the ground movements associated with grouting for tunnel‐boring operations where the grouting parameters and soil properties are taken into consideration. The grouting process is simplified as the expansion of a cylindrical cavity with a uniform radial stress applied at soil‐grout interface in a half plane, and the analytical solution proposed by Verruijt is introduced for determining the ground movements by the expansion of the cylindrical cavity. The proposed method is verified with a case history undertaken in London Clay. The results obtained suggest that this procedure would be helpful in managing the grouting parameters adopted in upcoming soft ground tunnelling project and mitigating the environmental impacts on nearby properties.

Stability of Circular Tunnels in Clay with an Overlay of Sand

Stability of Circular Tunnels in Clay with an Overlay of Sand

Numerical Evaluation of Settlement trough Width Parameter

Construction of tunnel results in ground movements with a settlement trough which is well described by a Gaussian distribution curve. For near surface settlements, it was established that the trough width i is an approximately linear function of the tunnel depth zo in relation to a trough width parameter K and broadly independent of tunnel construction method and tunnel diameter (except for very shallow tunnels where the cover to diameter ratio is less than one). The choice of an appropriate value of K may require some judgement, since it depends on whether the ground is primarily cohesive or frictional. Published literatures recommended that for practical purposes K could be taken as 0.5 for tunnels in clays and 0.25 for tunnels in sands and gravels. This paper discusses the evaluation of trough width parameter which has not been studied much for typical soil types encountered in the Klang Valley of Malaysia (e.g. Kenny Hill formation weathered materials, granitic soil, alluvium, etc.) of which are commonly in cohesive-frictional nature. The main objective of study is to investigate, using numerical method, the arbitrary relationship of the trough width parameter for different soil types in terms of its effective shear strength parameters and stiffness parameter. A parametric study was carried out to identify parameter(s) which have a significant influence on the settlement trough width and simple equation is presented subsequently for estimating appropriate K values for empirical calculation. This study has excluded two-layered system of different geology where, for example, a tunnel in Kenny Hill formation is overlain by significant thickness of alluvium deposits. Preliminary findings based on numerical analysis showed some promising results. Effort to continually build up the field database to further refine the deduced relationship for the surface settlement trough width parameter is in progress over the course of construction for Klang Valley MRT tunnels.