Surface Settlement Trough Research Articles

Numerical Modeling of Soil and Structure Behavior for Tunneling in Different Types of Soil

This note studies the correlation between surface and tunnel volume loss in various types of dry soil via finite element method. The effect of small strain stiffness, the buoyancy effect of soil, and tunnel overburden depth are considered in the 2D tunneling model. The results show that both surface volume loss ratio and settlement trough width parameter in the empirical solution can be expressed as a linear equation of tunnel volume loss ratio for 1D overburden shallow tunnels. Furthermore, the surface volume loss ratio can be presented as a non-linear polynomial equation of overburden depth and tunnel volume loss ratio in a 3D space, and this equation holds in different types of soil. The ranges of required fitting parameters and upper and lower bounding surfaces are suggested for various types of soil. Knowledge of this correlation between surface and tunnel volume loss is valuable, as it can be employed in practice for preliminary tunnel design in the absence of tunneling induced maximum ground settlement.

Measurement and analysis of surface settlement caused by construction of quasi-rectangular shield tunnel in rich water-sand stratum.

The study is based on a section of the Zhengzhou Metro Line 8 quasi-rectangular shield tunnel. Field excavation trials were conducted to analyze the surface settlement patterns caused by the construction of a large-section quasi-rectangular shield tunnel in the rich water sand layer in Zhengzhou. Based on the characteristics of the rich water sand layer, ground settlement control measures were proposed. The research findings show that the surface settlement caused by the construction of the large-section quasi-rectangular shield tunnel in the rich water sand layer exhibits a temporal curve pattern of slow settlement (Stage I: pre-arrival of the shield), rapid settlement (Stage II: shield passage, Stage III: shield tail exiting 14.4 ~ 18m), and stable settlement (Stage IV: late settlement). In Stage I, controlling the excavation rate to maintain balance between the cutter face pressure and soil pressure is effective. In Stage II, injecting lubricating mud between the shell and the sand layer to reduce soil friction and shear slip is recommended. In Stage III, increasing the synchronous grouting volume at the shield tail and adjusting grouting pressure, as well as timely filling the shield tail construction gap, are effective methods to reduce surface settlement. The Peck formula was used to fit the transverse settlement trough on the surface, with a linear correlation coefficient R²=0.983, validating the use of the Peck formula to predict surface settlement troughs for quasi-rectangular shield tunneling in the rich water sand layer. These research findings can provide data support and reference for similar projects.

Soil Displacement of Slurry Shield Tunnelling in Sandy Pebble Soil Based on Field Monitoring and Numerical Simulation

Due to its inherent advantages, shield tunnelling has become the primary construction method for urban tunnels, such as high-speed railway and metro tunnels. However, there are numerous technical challenges to shield tunnelling in complex geological conditions. Under the disturbance induced by shield tunnelling, sandy pebble soil is highly susceptible to ground loss and disturbance, which may subsequently lead to the risk of surface collapse. In this paper, large-diameter slurry shield tunnelling in sandy pebble soil is the engineering background. A combination of field monitoring and numerical simulation is employed to analyze tunnelling parameters, surface settlement, and deep soil horizontal displacement. The patterns of ground disturbance induced by shield tunnelling in sandy pebble soil are explored. The findings reveal that slurry pressure, shield thrust, and cutterhead torque exhibit a strong correlation during shield tunnelling. In silty clay sections, surface settlement values fluctuate significantly, while in sandy pebble soil, the settlement remains relatively stable. The longitudinal horizontal displacement of deep soil is significantly greater than the transverse horizontal displacement. In order to improve the surface settlement troughs obtained by numerical simulation, a cross-anisotropic constitutive model is used to account for the anisotropy of the soil. A sensitivity analysis of the cross-anisotropy parameter α was performed, revealing that as α increases, the maximum vertical displacement of the ground surface gradually decreases, but the rate of decrease slows down and tends to level off. Conversely, as the cross-anisotropy parameter α decreases, the width of the settlement trough narrows, improving the settlement trough profile.

Three-dimensional numerical analysis of twin tunnelling in two-layered soil strata

Tunnelling induces stress change and displacement in the ground. The excavation of a new tunnel in stratified soil can trigger different patterns of stress redistribution, which may adversely influence nearby tunnels. Research on multi-tunnel interaction has mainly been performed on the assumption of a uniform ground. The effects of different soil stratifications on tunnelling interaction remain poorly understood. In this paper, three-dimensional numerical parametric studies verified by previous centrifuge tests were carried out to analyse the twin tunnelling effects in two-layered soil. An advanced hypoplastic constitutive model that can capture stress-, path-, and strain-dependency of soil behaviour is adopted. Numerical cases investigated include perpendicular twin tunnelling in two sand layers with different relative densities and the location of the interface between the two sand layers. It is revealed that larger settlements and a wider surface settlement trough occur when tunnelling in two-layered soil strata than in a uniform ground. This is because of the wider and larger soil arch induced in two-layered soil strata. The structural response including tunnel deformation, induced bending moment, and induced hoop stress of the existing tunnel can be greater when tunnelling in layered soil strata than in a uniform ground owing to larger stress relief. Moreover, the combination of bending moment and hoop stress can exceed the M−N failure envelope of the structure in layered soil. A conventional simplified assumption of a uniform ground can underestimate of the influence of new tunnel excavation on existing tunnels, resulting in unsafe designs.

Ground settlement and tunnel response due to twin-curved shield tunnelling in soft ground with small clear distance

Twin curved tunnels are often encountered in shield tunnelling, where significant complexities in densely exploited underground space are observed. In this study, the ground settlement and tunnel deformation due to twin-curved shield tunnelling in soft ground were investigated using numerical simulation and field monitoring. Different curvature radii of twin curved tunnels and subsequent effects of tunnel construction were considered to reveal the tunnelling effect on ground surface settlement and tunnel deformation. The results show that the settlement trough yields one offset towards inside of curved shield tunnelling. The location of settlement trough and maximum settlement were affected by curvature radius but except for the shape and width of settlement trough. Adjacent parallel twin-curved shield tunnelling could increase the offset of existing settlement trough and maximum settlement. Then, an empirical prediction of surface settlement trough due to twin-curved shield tunnelling with same tunnel diameters in soft clay was proposed, which was applicable to curvature radius less than 800 m. Finally, a minimum radius of 600 m of curvature tunnel was proposed in terms of allowable convergence deformation of tunnel. The result could provide guidance on safety evaluation for twin curved shield tunnelling construction.

Ground settlement prediction for open caisson shafts in sand using a neural network constrained by empiricism

Accurate prediction of soil settlements induced by open caisson construction in sand is essential for safe and reliable delivery of critical underground urban infrastructure. This paper presents a novel prescriptive design approach using a neural network (NN) constrained by empirical relationships, referred to as an ’empiricism-constrained neural network’. The proposed approach is benchmarked using a traditional closed-form empirical expression. Both methods are calibrated using experimental data from reduced-scale laboratory testing for the prediction of surface and subsurface settlement trough shape and magnitude. The outcomes demonstrate that while both methods accurately capture the primary effect of caisson depth on surface and subsurface soil settlements, the NN approach exhibits superior prediction accuracy. These methods are developed in a form amenable for routine design use in industry and have the potential for broader applicability in other design scenarios, such as building damage assessment and risk-assessment exercises.

Elastic analytical method with machine learning for predicting the stratum displacement field induced by shallow tunneling

Support vector regression (SVR) with sparrow search algorithm (SSA) is developed as the machine learning (ML) model to predict maximum surface settlement smax caused by tunneling. A novel method for calibrating boundary conditions of analytical solution is proposed, where the maximum surface settlement derived by the analytical method is equal to smax predicted by SSA-SVR method. The elastic analytical solution for stratum displacement of a shallow tunnel is presented by the complex variable method, when the calibrated nonuniform displacement function is applied as the tunnel displacement boundary condition. The proposed analytical solution-machine learning (AM) method can predict the stratum displacement field prior to the tunnel excavation. Seventy-three tunnel engineering cases are employed to verify the rationality of the proposed SSA-SVR method in predicting smax. The value of R2 in the training and test process is 0.894 and 0.877, respectively. Taking Heathrow Express Trial Tunnel as an example, the potential of the proposed AM method in predicting stratum displacement is presented where the influence of cohesion strength, internal friction angle, Young's elastic modulus of stratum, tunnel radius and depth are considered. The proposed AM method can well predict the stratum surface settlement trough curve, vertical and horizontal displacement at different positions.

Collapse behavior and mechanical response of the cobble stratum during the shield driving

The cobble stratum is prone to collapse during the shield driving. It is important to understand the collapse behavior of cobble stratum for construction safety of the tunnel. Taking Tsinghuayuan Tunnel in Beijing as the background, a test of shield tunnelling in the cobble stratum is performed using the model shield with the diameter of 280 mm. A total of 5 collapse pits occur on the ground surface during the test process. The settlements at the surface and subsurface are measured to analyze the collapse process of the cobble stratum, as well as the earth pressure in the region above the tunnel crown. The quadratic partial derivative of the settlement and earth pressure are used to judge the collapse moment of the soil. The test results show that the collapse of the cobble stratum develops with a uniform speed from the bottom to up with the shield advancing, and that the collapse region extends to the surface after the cutter head passes through the center of the collapse pit 0.5D ∼ 1.0D. Meanwhile, the final earth pressure is much smaller than its initial value only in the region above the tunnel crown, indicating the collapse region concentrating in the position directly above the crown in the cross-section. In addition, the shape of surface settlement trough changes significantly with the collapse development. Development curves of two characterization physical quantities of the surface settlement trough, i.e., the maximum settlement and width coefficient, are respectively close to the “S” shape and the inverse “S” shape.

Analysis of surface settlements induced by tunnel excavation with EPB-TBM

Purpose. To investigate the efficiency of various approaches to predict surface settlements due to tunnel excavation. Methodology. To appreciate the surface displacements, our study is focalized on the case of a real tunnel in a layered ground (Algiers’s Metro), where a tunnel boring machine was driven for the first time in this country. Firstly, the surface settlement trough was calculated with empirical, analytical, and numerical (FEM) methods. Secondly, a set of numerical analyses was carried out to inspect the evolution of surface settlement as the TBM progresses. Finally, a parametric study was performed to examine the construction step most productive for surface settlement. Findings. FEM is a useful tool for predicting surface displacements due to tunnelling, especially when assigning an adequate and sophisticated behaviour model. Originality. A reference numerical model which represents well the construction procedures of the Algiers tunnel has been established. Practical value. This study illustrates that the results obtained by FEM with the use of Hardening Soil as a constitutive model to represent the soil are almost identical to those measured during the tunnel excavation. On the other hand, the empirical formulas available in the literature are not always efficient to predict surface movements.

Soil disturbance induced by EPB shield tunnelling in multilayered ground with soft sand lying on hard rock: A model test and DEM study

A large scale model test and numerical simulation using three dimensional discrete element method (3D DEM) were carried out in parallel to study the soil disturbance induced by earth pressure balanced (EPB) shield tunnelling in multilayered ground with soft sand lying on hard rock. The model test used a miniature EPB shield machine which could fully reproduce the real tunnel construction of excavation and support. The DEM model simulating the model test was developed to capture the microscopic mechanisms of ground deformation. The surface and subsurface settlement were closely recorded in model test and compared with those of homogeneous ground to clarify the influence of underlying rock on the movement of overlying sand. The volume ratio of rock to sand in excavated muck was closely recorded in DEM simulation to quantitatively analyse the over excavation of soft sand. Results show that both the surface and subsurface settlement trough in multilayered ground are narrower than those in homogeneous ground, while the subsurface settlement in multilayered ground is larger than that in homogeneous ground. The width parameter of settlement trough decreases nonlinearly along the gravitational direction. The over excavation of overlying soft sand is influenced by the ratio of hard rock to tunnel cross section and the rotating speed of shield cutterhead.

Numerical simulation of ground surface settlement of underpass building in tunnel boring machine double-line tunnels

Ground surface settlement under subway tunnel construction is one of the main sources of urban ground surface settlement, which may threaten the safety of existing buildings. Therefore, it is necessary to study the influence of subway tunnel construction on the safety and stability of surface subsidence. In the current study, the ground settlement originating from the operation of a tunnel-boring machine (TBM) while excavating a double-line tunnel that underpasses existing buildings is studied. To this end, numerical simulations were carried out and experimental data were analyzed. The boring parameters for the underpass interval section were derived by simulating the construction process and analyzing the TBM parameters in a real project. Then, the influence of thrust force, grouting pressure, and frictional force was considered on the surface settlement. For spatial locations between the existing buildings and the tunnel in the underpass area, the width of the ground surface settlement caused by different excavation sequences of the TBM two-line tunnel was analyzed. The obtained results demonstrate that the performed calculations are consistent with the monitoring data. It is found that the width and depth of the ground surface settlement trough are affected by the distance between the existing buildings and the TBM construction tunnel. However, the settlement location is independent of the excavated sequence but depends on the location of the TBM tunnel and the existing building.

Laboratory experiments and discrete element modeling on the surface failure induced by EPB tunneling: The effects of cutterhead open ratio and relative tunneling depth

This paper presents laboratory tests and high-fidelity numerical simulations to examine the ground failure induced by Earth Pressure Balance (EPB) Shield Tunneling in granular soils. Specifically, we designed and conducted laboratory tests using a reduced-scale EPB Shield Tunnel machine, and built corresponding three-dimensional (3D) discrete-element method (DEM) models to simulate the dynamic excavation process and to gain further understandings of the mechanisms of the ground movement. The study is particularly focused on the combined influences of the cutterhead open ratio and the relative tunnel depth on the ground motions and stress perturbations during the EPB tunneling, which remain understudied in existing studies. The results show that the open ratio of the cutterhead has significant effects on the ground failure in granular soils, especially in cases of relatively shallow tunnels. The larger the open ratio of the cutterhead, the wider the surface and subsurface settlement trough and the greater the soil pressure in the chamber. The pressure distribution in the soil chamber with a larger cutterhead open ratio is significantly more non-linear than that of the case with a smaller cutterhead open ratio. For a given cover-to-diameter ratio (C/D) of the tunnel, the width parameter (k) is generally constant regardless of the depth for the case with a large cutterhead open ratio, especially in the relatively shallow tunnels, while it increases non-linearly with the depth for the case with a small cutterhead open ratio, especially in relatively deep tunnels. Furthermore, soil arching mechanisms are analyzed qualitatively with respect to different cutterhead open ratios and C/Ds. The study demonstrates quantitatively the response of ground surface to the cutterhead open ratios and C/Ds as well as the associated ground failure mechanisms through a combination of laboratory experiments and 3D DEM simulations, providing further insights into the ground behaviors during the dynamic EPB tunneling process.

Centrifuge modelling of tunnelling below existing twin tunnels with different types of support

Tunnel excavation below existing tunnels produces ultimate and serviceability problems to the existing tunnels. The behaviours of induced stresses on the existing tunnels haven't yet been fully recognized. In this study, a centrifuge model test was adopted to investigate the effects of new tunnelling on two existing overlying tunnels. One existing tunnel model simulated a prototype composite lining tunnel and the other simulated a prototype segmental lining tunnel. The volume loss produced by new tunnel excavation was modelled by an in-flight actuator system. The surface settlements, the existing tunnels settlements, the soil pressures on existing tunnels, the bending movements of existing tunnels, and the joint behaviours of existing tunnels were monitored. The volume of surface settlement trough was much smaller than the soil volume moving into the tunnel, due to the heave of the tunnel bottom and the dilation of sand during shearing. The maximum settlement of the segmental lining model was larger than that of the composite lining model as the equivalent bending stiffness of the composite lining model was larger than that of the former. Due to new tunnel excavation, the soil pressures on different positions of the existing tunnel behaved differently, and the bending movements of the existing tunnels decreased. Moreover, the joint deformation of existing tunnel caused by new tunnel excavation could be classified into three types: (1) translation, (2) rotation, and (3) combination of both.

Construction analysis of Guiyang Metro passing across Guiyang Railway Station in karst zone

The Huo-Sha Tunnel of the Guiyang Metro Line 1 in China runs from the Guiyang Railway Station to the Shachong road station, and it passes close to the railway station platform. The minimum distance between the crown and pile foundation is only 2.19 m, and the settlements of existing buildings are strictly controlled, such as pile foundations. Existing comprehensive measures, such as super pipe shed support, surrounding rock reinforcement, inverted arch grouting, and lining strengthening, are stringently adopted to prevent the influence of construction on the operation of station buildings and in-service railways, high-speed railways, and other buildings. In this study, the changing laws related to existing building subsidence, subgrade settlement, station longitudinal displacement variation, and the development trends of lining safety, stability, eccentricity, compression types, and internal force of the lining are analyzed. The following results are presented. The Huo-Sha Tunnel was gradually excavated. The roadbed settlement of the Guiyang Railway Station platform gradually increased, but it did not exceed the existing railway deformation control standards for the subsurface excavation section. The longitudinal distribution of the existing railway settlement is approximately a normal curve after the construction of the secondary lining. The outcome is consistent with the law of the surface settlement trough proposed by Peck, and the range is −50 to 50 m. The stress of the lining is primarily concentrated at the arch waist and crown, the compression types include large and small eccentricities, and the axial force value gradually increases symmetrically from the crown to the arch footing, while the maximum axial force appears at the arch footing, and all control indicators meet the corresponding control standards. The subgrade settlement of the skew section adheres to the deformation control standards of the existing railway of subsurface excavation sections after the stabilization of the secondary lining deformation.

Study on the Restraint Effect of Isolation Pile on Surface Settlement Trough Induced by Shield Tunnelling

Isolation piles are widely used to control the influence of shield tunnelling on adjacent buildings as an effective protective measure. However, the restraint effect of isolation pile on surface settlement trough is rarely explored from the internal mechanism. Firstly, the restraint mechanism of isolation piles is investigated from the pile-soil-tunnel interaction mechanism. Secondly, based on the Melan solution and the Loganathan formula, the analytical solution of surface settlement trough under the influence of adjacent isolation piles is derived. Thirdly, in order to satisfy the engineering analysis scale and reflect the friction characteristics between isolation pile and soil particles simultaneously, the FDM-DEM coupling technique is introduced to establish a numerical model including discrete medium and continuum medium. Finally, the applicability and reliability of the analytical solution and the FDM-DEM coupling numerical solution are verified by comparing field measured data. The results indicate that the surface settlement trough under the influence of isolation piles will have an asymmetric distribution. Surface settlement tends to develop more to the opposite side of the tunnel when isolation piles are pre-installed on one side. The findings of the study have substantial theoretical significance and engineering reference value.

The Influence of Non-synchronous Excavation of Twin Curved Shield Tunnels

The theoretical model of twin curved shield tunnels and refined numerical model considering the characteristics of wedge-shaped segment ring joints were established in this paper. Two construction schemes of taking the inner side or outer side of the twin curved tunnels as the first tunnel were conducted for comparison. Then two main characteristics of curved tunnel construction (over-excavation and yaw excavation loadings) were taken as variables to explore their response to the approaching construction caused by unsynchronized driving of twin curved shield tunnels. The ground surface settlement troughs obtained by the analytical solution and numerical simulation are in good agreement with the monitoring result. On the condition that the curved tunnel at the inner side is taken as the first tunnel, the excavation will intensify the ground settlement and the internal forces of its segment. In the case that the overcutting gap is not of large volume, it is advisable to first excavate the curved tunnel at the outer side, and then construct the curved tunnel at the inner side. The influence of soil loss on the ground disturbance is greater than that of construction loadings. The excessive overcutting gap not only easily induces a sharp increase in the ground vertical displacement, but also may lead to the movement of soil at the inner and middle sides towards the inner side of the curved tunnels, and causes the soil at the outer side to move towards the outer side of the curved tunnels. Remarkably, excessive overcutting gap may lead to large horizontal displacements of the ground surface.

Theoretical analysis of the barrier effect of embedded isolation piles on tunneling-induced vertical ground displacements

This paper proposes an elastic solution for evaluating tunneling-induced vertical ground displacements due to the restraint of embedded isolation piles. Based on the modified Loganathan-Poulos (L&P) formula and the general form of the Melan/Mindlin solution, the restrained tunneling-induced vertical ground displacements can be calculated according to the displacement compatibility condition at the pile-soil interface. The solution can consider the relative vertical slip between the pile shaft and the surrounding soil and the embedding of the pile tip into the supported soil. The method is verified through comparisons with existing analytical solutions, boundary element program and field-measured data. Parametric analysis indicates that the parameters associated with the isolation pile (the distance of the tunnel axis from the pile axis, the pile length and the relative pile axis stiffness) and the soil (Poisson's ratio, the friction angle and the ground volume loss) have important influences on the ground surface settlement troughs and the barrier efficiency. The results also show that the pile skin-soil shear stiffness, which characterizes the relative slip between the pile shaft and the surrounding soil, determines the barrier efficiency. When the pile-soil interface is completely bonded, the contact state of the pile tip with the supported soil also has a nonnegligible impact on the barrier efficiency.

Analytical Study on Surface Settlement Troughs Induced by the Sequential Excavation of Adjacent and Parallel Tunnels in Layered Soils

In this paper, the settlement troughs induced by the excavation of adjacent and parallel tunnels in layered soils were studied. Firstly, a trough width parameter calculation method in layered soils was established based on the propagation model of the plastic zone and unloading disturbance zone. Secondly, the mechanism of the superposition disturbance between parallel tunnels is analyzed, and a method for calculating additional settlement trough is proposed. Finally, the applicability of the proposed model was demonstrated with two case studies of the parallel tunnels. The following conclusions were obtained: the difference of soil properties in layered soils had a significant influence on the width parameter of surface settlement trough; a Gaussian curve can describe the additional settlement caused by superimposed disturbance; and finally, the relationship between the ground loss induced by superposition disturbance and the ground loss induced by the preceding tunnel was approximately linear. The model presented in this paper is highly effective and convenient for use in practice and extends the calculation method of surface settlement trough based on the Gaussian curve.

Surface settlement in saturated loess stratum during shield construction: Numerical modeling and sensitivity analysis

During shield construction of Xi'an metro, saturated loess stratum with loose soil structure and poor engineering properties is often encountered, which is prone to cause excessive surface settlement (SS) and risk to the safety of upper infrastructures. Six factors that affect SS during shield construction and post-construction stages in Xi’an metro were focused, including shield tail grouting pressure ratio δ, eccentric over-excavation ratio α, groundwater decline, shield earth chamber pressure λ, shield tail grout filling ratio ξ, and leakage position of lining. According to Peck's formula, two characteristic parameters of SS were defined, i.e., maximum surface settlement (MSS) and settlement trough width (STW). Based on the Biot's theory, the computation of fluid–solid coupling during shield construction in saturated loess stratum was realized. Local sensitivity analysis indicates that SS of saturated loess stratum is more sensitive to shield tail grout filling ratio, eccentric over-excavation ratio, groundwater decline and grouting pressure ratio. In order to reduce the SS and its influence range, the following standards should be satisfied, i.e., ξ > 60%, α ≤ 0.5%, 1.0 ≤ δ ≤ 1.1 and 0.9 ≤ λ < 1.6. Moreover, in the post-construction stage, the closer the leakage position to the bottom of the tunnel, the greater the induced MSS and the wider the STW, and waterproofing measures for the lining near the bottom plate should be taken to ensure that the relative permeability coefficient of the lining β ≤ 0.001. The groundwater level should also be maintained in the overlying stratum.

Numerical analysis on surface settlement in parallel rectangular pipe jacking construction

In recent years, rectangular pipe jacking technology has been gradually applied in urban underground engineering. Based on a parallel rectangular pipe jacking project, a three-dimensional finite element model is established for numerical analysis, and the surface settlement caused by rectangular pipe jacking construction is studied. The research shows that the pipe jacking construction has the most obvious impact on the soil above the pipe jacking axis, and when the clear distance between parallel rectangular pipe is 1D (D indicates the pipe inner width), the main influence range of pipe jacking construction on soil mass is about 1D along the longitudinal direction of pipe jacking. With the increase of parallel rectangular pipe distance, the surface settlement trough becomes wider and the maximum surface settlement decreases. The main influence range of parallel rectangular pipe jacking construction at the outside of the pipe jacking is about 1D~1.37D along the lateral direction. When the pipe distance is greater than 2D, the interaction between parallel pipe jacking is weak, and the influence range at the outside of pipe jacking is almost the same as that of single pipe jacking construction. The research results can provide a reference for the design and construction of similar pipe jacking projects.