Settlement Trough Research Articles

Effects of Different Construction Sequences on Ground Surface Settlement and Displacement of Single Long Pile due to Twin Paralleled Shield Tunneling

Shield tunneling activities inevitably pass through pile foundations at close distance in densely urban areas. Various studies have investigated the interaction between newly constructed tunnels and existing pile foundations. However, the influence of different construction sequences of twin paralleled shield tunneling on single long pile is seldom considered. A case was found in the project of Changsha Metro Line 5, where the twin paralleled tunnels were constructed near the Wanjiali Viaduct piles. A three-dimensional finite element model was established to analyze the pier settlement, ground surface settlement trough, and the vertical and horizontal displacement of pile under different construction sequences in layered soil. The results show that the adjacent pile and surrounding environment are affected substantially with the change of construction sequence of twin paralleled tunnels. The construction sequence of condition (b), in which the tunnel closer to the pile foundation is first constructed and then the tunnel farther away from the pile foundation is second constructed, can reduce the settlement of pier by 13.1%, the maximum surface settlement by 7.0%, the maximum vertical displacement of pile foundation by 7.9%, and the maximum horizontal displacement by 6.9%. The present findings can provide reference for similar projects.

Influence of water pressure on deep subsea tunnel buried within sandy seabed

For a subsea tunnel, the changeable high water pressure is of great significance in the soil-water-tunnel interaction. In this study, a series of parametric studies were conducted to investigate the effect of high water pressures on the seabed settlement and the earth pressures as well as the axial forces and bending moment of a tunnel lining during excavation. The simulation results disclose that the seabed settlement along the transversal tunnel direction increased linearly with the rising water level and the ranges of settlement troughs can be up to around 5 D (D, tunnel diameter) in width. Similarly, the settlement along the longitudinal tunnel direction featuring a semi-trough shape also shows a linear increase with the rising water level, and the maximum influence zone could reach a length of 3 D in front of the excavation face. With the increase of water pressure during tunneling, the total earth pressures along the perimeter of a circular tunnel lining increased significantly and their distributions were prone to be more uniform around the tunnel perimeter. As a result, the deep sea tunnel lining has a typical feature of large axial force and relatively smaller bending moment.

Dynamic prediction model for surface settlement of horizontal salt rock energy storage

In order to theoretically calculate the surface settlement of horizontal salt rock energy storage, the conformal mapping method in the complex variable function was adopted, and the superposition principle and viscoelastic correspondence principle were considered to derive a theoretical displacement formula. This formula can be used to calculate the radial displacement of the surrounding rock on the cross section of horizontal elliptical cylindrical salt rock storage at any time, and then the volume shrinkage of the storage can be obtained. Based on the assumption that the volume shrinkage during the long-term operation of the horizontal salt rock storage is proportional to the volume of the surface settlement trough, a compound power function was proposed to describe the surface settlement curve, and then a dynamic prediction model for the surface settlement of the horizontal salt rock storage was established. The numerical simulation results of surface settlement during the long-term operation of horizontal elliptical cylindrical salt rock storage were used to verify the rationality of the surface settlement model. The comparison shows that when the operation time is 0, the error between the settlement of the center point calculated from theoretical model and that from numerical simulation is 241.61%, and then the error gradually decreases with increasing time. When the operation time exceeded 3 years, the settlement at the center point and the surface settlement curves calculated from the theoretical model are all in good agreement with numerical simulation results, and the maximum error, occurs at the center point of surface, is only 8.11% when the operation time is 15 years.

The Influence of Construction Scheme of Asymmetric Three-Cabin Utility Tunnelling on the Surface Settlement Behaviour

The asymmetric three-cabin structure is one of the favourite choices in urban utility tunnel engineering, as it can provide a higher space utilization and clearer classification for pipelines. However, few work has been done on utility tunnel in such special cross-section during undercutting construction until now. Besides, as the loose soil layers such as sand and silt are often encountered during the utility tunnelling, its influence on surface settlement become one of the main concerns. This study focuses on the influence of the construction scheme on the surface settlement details for an asymmetric three-cabin utility tunnel. A 3D finite element method (FEM) model was established including both the stratum and a utility tunnel based on the Beijing Daxing International Airport (BDIA) Expressway Urban Utility Tunnel project. With this model, the behaviour of the surface settlement with the undercutting construction of the utility tunnel was investigated, and the causes and values of surface settlement in five construction stages were analyzed. By changing the construction spacing and sequence of mid and side cabins, the surface settlement and structural deformation were compared. The numerical results demonstrated a strong correlation between the cross-section shape and surface settlement characteristics. And the symmetry line of the surface settlement trough was offset by 1 m to the side with the larger cross-section. The second (excavation of upper bench in mid-cabin) and fourth (excavation of upper bench in side-cabin) stages caused the largest surface settlement, which were 41.9% and 18.07% of the total settlement, respectively. In addition, after optimizing the field tunnelling scheme, the surface settlement was reduced by 31.9% using the side-tunnel first construction sequence. The proposed numerical model is able to predict the settlement characteristics in each construction stage, which is important and provides a basis for further studies on the surface settlement mechanism and optimal design of the asymmetric three-cabin utility tunnelling scheme.

Subsurface settlements of shield tunneling predicted by 2D and 3D constitutive models considering non-coaxiality and soil anisotropy: a case study

Appropriate constitutive models and reliable excavation and support sequences are believed to be the major concern in using finite element (FE) analysis to simulate shield tunnel excavation. This paper presents systematic two-dimensional (2D) and three-dimensional (3D) FE analyses employing a number of constitutive models accounting for initial soil anisotropy and non-coaxial plasticity, as evidenced within site investigations from the Tsinghuayuan Tunnel of the Jing-Zhang high-speed railway in China. The aim is to assess the effects of both the initial soil anisotropy and non-coaxiality on longitudinal and transverse tunneling-induced surface settlements. It is shown that the excavation procedures combined with the degree of cross-anisotropy are key towards the accurate prediction of maximum vertical displacements from tunneling, matching field data. Knowledge of the initial soil strength anisotropy can further improve the shape prediction of the transverse tunneling-induced surface settlement troughs. When considering n = 0.6 and β = 0° in simulations, the transverse surface settlement trough obtained is almost coincident with monitored field data. Initial stiffness anisotropy used in the prediction of shield tunnel-induced surface settlements in sandy pebble soils does improve realism of results significantly. The maximum longitudinal settlement predicted by considering cross-anisotropy is larger than that predicted by its isotropic counterpart.

Research on Surface Subsidence of Long-Span Underground Tunnel

In the process of urban rail transit construction, underground excavation method is often used in subway station construction. Based on a large number of measured data of Qingdao Metro Line 3, this paper analyzes and studies the ground subsidence law of long-span shallow buried excavation station. The research results show that vertical surface settlement will be caused by the excavation of both sides of the guide hole, but the settlement is relatively small, basically within −10 mm. Large surface settlement will occur during the middle or middle guide hole excavation, with a large settlement up to −30 mm. Through data fitting, it is found that the regression analysis using cubic polynomial of one degree can get better fitting effect. The horizontal surface variation rules of underground excavation stations are affected by the tunnel depth, geological conditions, management level of monitoring units, monitoring layout and monitoring accuracy, and so on. The differences in horizontal surface deformation and settlement between stations are large. Wannianquan Road Station basically conforms to the deformation law of ground settlement trough in Peck, and Junfeng Road Station directly above belongs to the whole subsidence type. This study has accumulated a large number of surface settlement monitoring data, which can provide a certain reference for the subsequent design of similar lines.

Study on Surface Settlement Law of Shield Construction in Mudstone Stratum

In order to explore the influence of groundwater on the surface settlement law of shield construction under mudstone with different weathering degrees, this paper studies the influence of buried depth on surface settlement under different weathered mudstone, and the influence law of groundwater in stratum and different depths of water level on settlement of shield construction using a three-dimensional(3D) numerical model establish by finite element software based on the engineering background of Chengdu Metro Line 18. The results show that: (1) With the increase of buried depth, the range of lateral settlement trough on the surface gradually increases, but the maximum settlement gradually decreases. By analyzing the buried depth and the maximum surface settlement, it is found that the buried depth ratio has a logarithmic relationship with the corresponding maximum surface settlement. (2) The construction settlement increases obviously when there is groundwater in the stratum compared with when there is no groundwater. (3) The depth of water level above the vault and the maximum settlement caused by shield construction basically conform to the linear law. For every 1m increase in the depth of water level above the vault, the maximum settlement value can increase by about 0.43 mm. Compared with the field monitoring data, the calculation results are basically consistent, which shows the reliability of the calculation. This paper aims to provide experience for similar projects.

Deformation and Numerical Simulation Analysis of Deep Foundation Pit Excavation of Nanjing Yangtze River Floodplain Metro Station

Based on the foundation pit excavation construction of a subway station under the soft soil layer of the Nanjing Yangtze River floodplain, Numerical simulation of foundation pit construction process is carried out to study the deformation law of surrounding soil and surrounding structure during foundation pit construction. The research shows that the established finite element numerical model can better predict the structural and stratum deformation caused by the excavation of the foundation pit; the lateral displacement of the ground wall and the ground settlement behind the wall based on different constitutive models are different, but the overall trend is the same. The lateral displacement of the diaphragm wall presents a “bulging” pattern. The surface settlement around the pit shows a settlement trough at a certain distance from the connecting wall. The horizontal displacement of the diaphragm wall increases with the increase of the excavation depth of the foundation pit, and the maximum horizontal displacement occurs above the excavation surface. The conclusions obtained have certain guiding significance for subsequent construction and parameter optimization.

Surface Deformation Law of Cixian Section of the South-to-North Water Transfer Project

The disturbance of ground deformation caused by pipe jacking construction has become one of the important factors affecting the safety of the surrounding buildings and environmental changes. The construction of the sewage pipe network, which is in the Cixian section of the South-to-North Water Diversion Middle Route, is taking as an example. Theoretical prediction and field tests are conducted to research the ground settlement deformation caused by the disturbance of pipe jacking construction. Research indicates that the surface settlement near Hexie Avenue in Ci County meets the engineering safety requirements when the volume loss rate of the local layer is controlled within 6.9%. And the maximum surface settlement within the construction range of the Ci County section of the South-to-North Water Diversion Project was within 2.5-4 mm, which did not break the safety threshold. Suggested values for the formation loss rate and settlement trough width coefficient index are proposed for similar working conditions, which are 3.31% and 0.525 respectively. Relevant research results provide a reference for the study of ground deformation prediction under similar working conditions.

Short and Long-term Behaviours of Bored Tunnels in Port-Said Clay

This study investigates the behaviour of bored tunnels in the Port-Said very soft to firm clay deposit in El-Tina Plain, north-eastern Egypt. Recent studies provided full characterization of the physical, mechanical and time-dependent properties of Port-Said Clay. This characterization enabled simulating its constitutive behaviour using the stress-dependent Modified Cam Clay model. The finite difference method is utilized to simulate the interaction between the tunnel and Port-Said Clay. The results are presented in terms of the pore water pressure regime, shear strain level, ground surface settlement and tunnel lining bending moment. The results show significant effect of the face and grouting pressures on the tunnel’s short and long-term behaviours. The term “reference hydrostatic pressure” is introduced to evaluate short-term face stability as a more practical and easy-to-quantify parameter compared to the conventional stability number. New empirical equations are developed to describe the long-term surface settlement trough (maximum settlement and trough width) in terms of the grouting pressure and tunnel diameter for tunnels in similar soft clay deposits.

A Theoretical Calculation Method of Ground Settlement Based on a Groundwater Seepage and Drainage Model in Tunnel Engineering

Seepage is ubiquitous during tunneling in areas with high groundwater tables. The ground settlement trough on a single tunnel is well described by Peck’s formula, but it cannot reflect the settlement caused by seepage. In this paper, assuming that the groundwater inside and outside the tunnel is a one-dimensional steady-state seepage condition, the groundwater seepage and drainage model of the tunnel was established. Based on the model and the principle of groundwater dynamics, the seepage flow calculation formula was derived, and the dewatering funnel curve equation of the groundwater level surface of a tunnel aquifer was obtained. A case study of a tunnel project in Gansu Province was carried out, and the influence of seepage on the effective stress of the stratum around the tunnel and the calculation of ground settlement caused by seepage were analyzed. The results show that seepage makes the effective stress of the upper soil layer of the tunnel increase, which leads to an increase in ground deformation; when the groundwater level of the tunnel is greatly lowered, the seepage has a significant influence on the vertical deformation of the stratum.

Experimental investigation on greenfield surface settlement in cohesionless medium due to staged tunneling

Understanding the ground response during tunneling is essential to evaluate the safety of existing infrastructures. Soil–tunnel interactions are a complex phenomenon and depend on the various parameters of soil and tunnel. Physical modeling plays an essential role in understanding the influence of different parameters on the surface settlement due to tunneling. Physical modeling in controlled conditions allows us to investigate and distinctly identify the effect of soil parameters and tunnel on the ground response. This paper presents a novel experimental procedure to simulate the ground loss phenomenon due to tunneling. The developed scaled-down model can simulate the different percentage of volume loss for progressive tunnel construction under 1 g. The ground response has been studied for various volume loss percentages (1–10%) and different soil cover-to-diameter ratio of a tunnel in cohesionless medium. Ground response in terms of the maximum surface settlement, width of transverse surface settlement trough, transverse, and longitudinal influence zone of surface settlement have been measured and reported. Results from the present study match reasonably well with the other reported studies. The reasonability of the results demonstrates the applicability of the current approach to study the ground response due to the tunnel's staged construction.

Assessment of surface settlement induced by tunnel excavations for the Esenler–Başakşehir (Istanbul, Turkey) Subway Line

In most modern cities, public transportation demands are being addressed by constructing subways. The construction of tunnels, especially in weak and shallow subsurface strata, may cause significant damage to infrastructure and superstructures, however. In this study, surface deformations at four different locations along the Esenler–Basaksehir subway line, which is situated on the European side of Istanbul, were examined, with the aim of determining an appropriate method for the reliable estimation of settlement caused by shallow subsurface excavations in locations at high risk of damage. In this context, data from monitoring and numerical analysis were assessed together. Where horizontal, closely spaced twin tunnels were excavated consecutively at the same elevation, it was found that the excavation of the first tunnel disturbed the geological strata to the extent that the second tunnel encountered problems with those strata. Accordingly, it was observed that the maximum surface settlement caused by the first tunnel increased following excavation of the second tunnel, even though it had the same excavation geometry, and the settlement trough slid asymmetrically over the second tunnel.

Optimization of Construction Parameters and Deformation Characteristics of Large-Section Loess Tunnel: A Case Study from Xi’an Metro

Loess geological tunnels are characterized by weak geological structure and poor self-stability of surrounding rock, so effectively controlling the excavation face distances of different caverns is of great significance for guiding the safe construction of large-section tunnels. Based on the excavation of large-section loess tunnel from Xi’an Metro Line 4, the optimal excavation face distance is determined based on Midas numerical model. Then, the surface settlement and horizontal deformation are analyzed based on monitoring data, and, finally, the rationality of excavation face distance is verified. The results show that the influence of excavation face distance on surface settlement, vault settlement, and horizontal deformation is consistent. The surface settlement mainly occurs in the range of −20∼20 m from the tunnel centerline and the settlement trough formed has asymmetric characteristics. The vault settlement and horizontal deformation undergo first a rapid settlement and then a slow settlement. The connection between initial support and middle partition is mainly tensile stress and the middle and bottom parts of the supporting structure are mainly compressive stress. Numerical results suggest that the optimal excavation faces distance of L1, L2, and L3 which can be 4, 9, and 9 m, respectively. Construction monitoring data show that the double-sides heading method has a significant effect on surface settlement, vault settlement, and horizontal deformation. The surface settlement occurs within the range of −17∼6 m from the tunnel centerline. The maximum vault settlement and horizontal deformation are 73.00% and 65.50% of the maximum allowable. It can be seen that the actual excavation parameters optimized by Midas numerical model have high reliability.

The role of TBM asymmetric tail-grouting on surface settlement in coarse-grained soils of urban area: Field tests and FEA modelling

This paper examines the role of TBM tail-grouting on surface settlement of coarse-grained soils in urban area. The influence of tail grouting on the ground surface settlement is firstly demonstrated through a challenging shield-driven tunnel project in Beijing City, China. FEA modelling incorporating the excavation sequence and tail grouting details is then set up to support the field observations, based on which the influences of different TBM tail-grouting parameters on ground settlement are investigated, especially the asymmetric tail-grouting in which one of the two grouting openings at the upper part of the shield tail is malfunctioned. It is shown that the grouting volume variation is inconsistent with the development of the grouting pressure, and the ground deformation in coarse-grained soils is directly related to the tail-grouting pressure rather than the grouting volume ratio. Asymmetric tail-grouting will result in notable offset of the maximum surface settlement point in settlement trough from tunnel centerline which correlates exponentially with the parameter ξ defined to represent the asymmetry ratio of the grouting pressure.

Ground Deformation Characteristics Induced by Mechanized Shield Twin Tunnelling along Curved Alignments

This paper investigates the ground deformation characteristics induced by mechanized shield twin tunnelling along curved alignments by adopting the nonlinear three-dimensional (3D) finite element method (FEM). The performance of the adopted FEM is demonstrated to be satisfactory by comparing the numerical analysis results with the field monitoring data in a typical case history and with the predicted results generated by a modified version of the Peck’s empirical Gaussian formula. It has been found that the tunnelling-induced transverse ground surface settlement troughs and the distributions of the subsurface horizontal and vertical ground displacements are mostly similar in both form and magnitude for the considered various radii of curvature of tunnel alignment including 50 m, 100 m, 150 m, 200 m, 250 m, 300 m, 400 m, and infinity (i.e., straight-line tunnel). Considering the variational characteristics of the ground deformations with the magnitude of the radius of curvature, the radius of curvature of 100 m can be regarded as a critical tunnel alignment radius of curvature controlling the transformation of the curved tunnelling-induced ground deformational behaviors. For the benefit of geotechnical engineers interested in curved tunnelling with a small radius of curvature, a discussion of the technologies for reducing the overexcavation and improving the accuracy of tunnel lining segment installation is also presented.

Study on influence characteristics of shield tunnel depth and spacing on settlement in clay strata

The surrounding ground disturbance and surface settlement induced by shield construction are the key problems of tunnelling control and necessary to be studied. Taking the shield tunnel project of Beijing Subway Line 14 as the research background, this paper studies the influence of tunnel spacing and depth on surface settlement distribution by numerical simulation method, and analyzes the relationship between the two factors and maximum settlement. The results indicate that the increase of tunnel depth or tunnel spacing leads to the decrease of the maximum settlement and the settlement reduction rate increases. With the increase of tunnel depth, the settlement trough presents approximately symmetrical distribution, and the symmetry axis is inclined to the first tunnel. With the increase of tunnel spacing, the superposition effect of twin tunnel excavation decreases, and the settlement trough transits from U-shaped to W-shaped with the maximum settlement decreasing relatively from single peak to double peaks. Also, the tunnel depth or spacing is highly correlated with the maximum settlement in a certain range, and the tunnel depth has a stronger linear correlation than the tunnel spacing. The research results provide certain theoretical guidance and references for the prediction of ground deformation and settlement control of shield construction.

Study on construction risk and control technology of subway tunnel in soft soil stratum

Taking the shield crossing Huangma road of Beijing new airport line as the engineering background, main construction risks of large section shield crossing Huangma road in soft soil layer were analyzed. Taking the support pressure of excavation face as the research object, the influence of shield excavation on the surrounding soil and surface deformation of the working face were studied, and the corresponding reinforcement measures were proposed. According to the field monitoring data after reinforcement, the settlement trough of 8.8m shield was predicted based on peck formula. The results show that the width coefficient of settlement slot of 8.8 m shield machine varies from 0.41 to 0.46, with an average value of 0.42.

Empirical evidence for estimation of subsurface settlement caused by tunneling in sand

Tunneling is vital for augmenting urban infrastructure systems in big cities. However, the ground movement or settlement induced by tunneling can cause significant damage to the surrounding buildings, bridges, roadways, pipelines, and so on. Several theoretical and empirical methods have been proposed to estimate the settlement trough at the ground surface caused by tunneling. Subsurface settlement caused by tunneling in clay has been investigated extensively to evaluate the safety of pipelines and foundations above tunnels based on the assumption of a constant volume of the settlement trough along the depth. However, subsurface settlement induced by tunneling in sand has not been understood well due to the change of volume of settlement trough along the depth. Even though an empirical method was developed by the author based on lab-scale model test results, it has not been validated using observational data from case histories. In this study, three case histories from the literature were used to verify the effectiveness of the aforementioned empirical method for estimating the subsurface settlement caused by tunneling in sand. The comparison of the calculated results and measurements from the case histories demonstrates that the empirical method is effective to predict the subsurface settlement caused by tunneling in sand.

An Anisotropic Model for the Numerical Analysis of Tunneling-Induced Settlements in the Paris Area

In many cases, numerical simulations cannot accurately predict the settlements induced by the construction of shallow tunnels: the settlements troughs obtained numerically tend to be wider than the observed ones. This can lead to underestimating the differential settlements and thus the potential damages to buildings above ground. This article proposes an elastoplastic model aiming to improve the results of finite element simulations and more precisely the width of the settlement trough. The key feature is the introduction of transverse isotropy in the elastic part of the model. The model makes it possible to clearly identify the influence of each parameter on the mechanical behavior. In particular, one of the parameters controls the shape of the settlement trough. The model was implemented in the finite element code CESAR-LCPC and used to model the settlements observed during the construction of a tramway line in the outskirts of Paris. The results show the effectiveness of the proposed approach.