Ground Settlement Trough Research Articles

Study on instability mechanism of tunnel face in clay-gravel strata under confined water conditions based on DEM-CFD coupling method

A coupled discrete element methods (DEM)-computational fluid dynamics (CFD) method was adopted to study the tunnel face instability mechanism in clay-gravel composite strata with confined water. This method was verified by the results of the transparent soil model tests previously conducted by the authors. On this basis, The DEM microscopic change trends and the variation in the composite strata and soil stresses were systematically analyzed. The results show that under confined water conditions, the failure zone of the lower gravel strata is wider, with a decrease of about 30° with the horizontal direction. The width of the ground settlement trough has widened by about 43.8%, while the maximum surface subsidence has reduced by about 46.2%. Further, the effect of confined water on the vertical stress of the soil is significant; nevertheless, it has almost no effect on the average horizontal stress. Moreover, the horizontal displacement of the lower gravel stratum is larger than the upper clay stratum, while this rule is not observed under no confined water conditions. To avoid tunnel face instability in clay-gravel composite strata, the horizontal displacement and the variation of vertical stress in front of the tunnel face should be carefully monitored during shield tunnel construction.

Numerical Modelling of Tunnel-Ground Interaction with Building Existence

Tunnel is complex and risky construction. When excavation of tunnel take place, the original ground equilibrium will affected thus lead to the stress redistribution and ground movement. Tunnel construction in the urban city is in concerned as tunnel will passes under a lot of existing building. Therefore, in this study, a series of simulation of tunnel construction with and without external building was conducted. Numerical model by means ABAQUS Software was conducted based on tunnel-soil-load model was developed. From the result, it can be concluded that soil stress redistributed when excavation of soil occurs especially near to the tunnel periphery. The ground settlement trough depicts a significant maximum settlement for the model with high external load and producing flat u-shape in the middle of settlement trough pattern.

Study on the restraint control of an isolation pile on an existing high-speed railway during the close passing of a shield machine

The impact of shield construction on the close lateral passing of high-speed railways can threaten the safety of operating high-speed railways. To study the deformation characteristics of the shield structure after the application of isolation piles from the ground surface and the deformation characteristics of the bridge piers of an overpassing high-speed railway, we analyze the mechanism of isolation pile restraint control and establish a three-dimensional numerical model of a shield structure to study the situation of a high-speed railway with a metro interval under passing a high-speed railway passenger line project. Combined with the measured data and numerical simulation data of the same construction stage, we study the impact of shield structure lateral passing on high-speed railway piers and surrounding ground surface in terms of the disturbance changes and the effect of isolation, as well as the effect of the lateral passing of the shield tunnel on the surface of the bridge piers and the surrounding area and the control effect of the isolation piles on the deformation. The results show that the isolation pile can block the development of the soil layer rupture surface and the stress path. The isolation pile has a good control effect on the vertical displacement of the bridge pier. The vertical displacement of the bridge pier decreases from 0.6 mm to 1.1 mm after the single- and double-track tunneling, and the displacement changes along the depth direction from non-uniform to relatively uniform. The vertical displacement of the ground surface includes both uplift and settlement, which occur at the same time. When the shield tunneling advances, the form of the ground settlement trough is changed from a “V” shape formed by the right single-track tunneling to a “W” shape after the double-track tunneling. The isolation pile can effectively control the influence range of tunnel excavation; its lateral displacement form changes regularly, and the lateral uplift is always in a “double-C outward expansion” shape. The initial excavation greatly disturbs the initial stress field, so it is necessary to pay attention to the control and management of measures to destroy the initial stress field.

Tunnel depth effect to pile in Tunnel's influence zone

The increased population in urban areas resulted in high demand for public facilities; hence, tunnels became popular, especially in developed countries. However, tunnel activity may alter the original ground equilibrium, leading to a ground stress release. These may result in an adverse pile response and potential hazard to a nearby building structure. Previous research focuses on the tunnel-pile interaction but solely investigates in homogeneous soil formation. Therefore, this paper presents the tunnel-pile-ground interaction with various tunnel depths in multiple soil formations. A three-dimensional model was developed by using the finite element method of ABAQUS based on Circle Line Stage 3 (C852) projects in Singapore. The models were carried out in two stages: first, by investigating the tunnel-induced ground movements (free-field condition) and second, with the presence of a pile. The tunnel model depth varied at respective ratios of C/D of 1, 2, 3, and 4. The results show, with a low tunnel depth ratio, a high maximum ground settlement is obtained. The longitudinal settlement trough presents a smooth surface settlement curve for free-field conditions, but a chimney-like transition at the pile periphery for conditions with the pile. The ground settlement trough for tunnelling near to adjacent pile leads to a skewed maximum settlement towards the pile. A higher C/D ratio produced higher lateral stress induced on the pile but the opposite for a lower C/D ratio. Pile was significantly affected and shown by extensive lateral stress for the pile body that lies parallel to the tunnel depth.

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.

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 study of surface failure induced by tunnel construction in sand

An experimental study was conducted to determine the effects of tunnel construction on ground movements in sand. In this regard, a small-scale three-dimensional model test was developed, and several laboratory model tests were carried out under single gravity in a sand sample with three different relative densities of 30, 50, and 75% and a cover-to-diameter ratio of 3. To simulate the volume loss induced by the tunnel boring machine, the casing method was utilized. In the model tests, an elastic aluminium liner was used as a tunnel supporting system and a pipe casing was utilized to model a tunnel shield. By pulling out the tunnel shield progressively and replacing it with tunnel liner, the soil was allowed to move toward the tunnel and the surface settlements were measured by using linear variable differential transformers. The results show that increasing the value of the relative density of sand reduces the ground movements induced by tunneling. The settlement trough width increased almost linearly with increment of the overburden. Also, the results reveal that in dense sand the ground settlement trough is slightly less than the volume loss. For loose sand, the volume of settlement trough is nearly twice the volume loss. In shallow tunneling and loose sand produces remarkable movement on the ground surface.

The influence and calculation method of ground settlement induced by tunnel construction in sand

ABSTRACT In order to study the influence of tunnel construction on ground settlement in sand, the distribution and variation characteristics of ground settlement during tunnel construction were explored through model tests. The results showed that during tunnel construction in sand, the variations of surface settlement and ground settlement at different ground depths were basically the same at the same monitoring section. The distribution and variation characteristics of the ground settlements along the width and length directions of the tunnel were basically the same. The ground loss increased in power function from the surface to the underground. The maximum ground settlement and the width coefficient of the settlement trough were strongly positively correlated with the ground loss. Based on the experimental study and statistical analyses, the relation between ground loss and ground surface loss at different burial depths was established. The calculation of an equation of ground loss at different depths was put forward, and the calculation of an equation of the width coefficient of ground settlement trough was modified, both of which enable the calculation for ground settlement in an arbitrary position above the tunnel during tunneling.

Research on tunnel ground settlement characteristics by shield method and pipe-jacking method based on numerical simulation

Based on a shield tunnel, the ground settlement by shield method and pipe-jacking method in straight tunnel and curve tunnel was studied. The ground settlement curves by the two methods were analyzed by numerical simulation. Compared with straight tunnel, the ground settlement trough in curve tunnel is shifted to the bending direction by about 0.5D. The overall ground settlement difference between shield and pipe-jacking method is relatively small in straight tunnel, and the settlement in curve tunnel by pipe-jacking method is more than that by shield method. With the excavation of the tunnel, the ground settlement trend in curve tunnel is more obvious than that in straight tunnel. And the settlement difference is relatively large in the middle of the tunnel for both straight tunnel and curve tunnel.

Surface subsidence characteristics of fully overlapping tunnels constructed using tunnel boring machine in a clay stratum

This study investigates the characteristics of vertical soil deformation induced by fully overlapping tunnels constructed using a tunnel boring machine (TBM). The Peck formula is improved to consider the variation in the tunnel axis depth and stratum loss ratio. Comparing the settlements both monitored and simulated on the fully overlapping tunnels of the Tianjin Metro, it is shown that our improved Peck formula is suitable to predict the surface settlement of fully overlapping tunnels. The present comprehensive research shows that during the construction of fully overlapping tunnels, the ultimate maximum settlement value is more affected by the construction of an upper-line tunnel than by the construction of a lower-line tunnel. The width of the ground settlement trough in fully overlapping tunnels construction is only affected by the lower-line tunnel, but the final settlement value is not simply the sum of the settlements of the two tunnels. The overlapping effect between the upper and lower lines reduces the stratum loss and the maximum settlement caused by excavation of the upper-line tunnel.

Deformation behaviors of existing tunnels caused by shield tunneling undercrossing with oblique angle

The impact of twin shields tunneling undercrossing with an oblique angle on the existing tunnels is complicated and still lacks of understanding. This paper investigated the deformation behaviors of the existing tunnels with new twin tunnels construction undercrossing obliquely based on numerical simulation on a case history in Changsha, China. The accuracy of numerical analysis was verified in comparison with the field measurement. The variation of the ground settlement trough and the earth pressure acting on the existing tunnel during the shield tunneling was analyzed. Then, the transversal deformation, internal forces and torsion behavior of the existing tunnels induced by the new tunnels excavation were obtained. Additionally, a parametric study was conducted to investigate the impact of the intersection angle between the new and existing tunnels on the deformation behaviors of the existing tunnel. The results show that due to oblique intersection, the transversal deformation and internal forces of the existing tunnel show obvious asymmetrical characteristic, and an unrecoverable local torsional deformation of the existing tunnel on both side of new tunnel can be observed after shield tunneling. The parametrical analysis indicates that the intersection angle significantly influences on the maximum settlement of the existing tunnel bottom, which is up to 27.53% larger in parallel case than that in perpendicular case, and decreases rapidly as the interaction angle varies from 30° to 60°. Nevertheless, the maximum settlement of the existing tunnel crown is unaffected by the intersection angle.

Prediction of Ground Settlement Due to Excavation of a Quasi-Rectangular Shield Tunnel Based on Stochastic Medium Theory

In this study, a method for calculating the ground loss-induced ground settlement during quasi-rectangular shield (QRS) tunnelling was investigated. Based on stochastic medium theory, an equation for calculating QRS tunnelling-induced transverse ground settlement was derived. A tunnelling face convergence mode coefficient, α, was introduced to make the derived equation applicable to various tunnelling face convergence modes. A modified equation for calculating the longitudinal variation in the ground loss ratio (e) was proposed to calculate e for any arbitrary cross-section in the tunnelling direction. On this basis, the proposed equation was longitudinally expanded, and an equation for calculating the three-dimensional (3D) ground settlement was obtained. A simplified model for additional grouting pressure was established, and the influence of additional grouting pressure on surface deformation was analysed. In addition, the proposed method was used to calculate the QRS tunnelling-induced ground settlement, and the results were compared with actual measurements. It is found that the predicted ground settlement obtained using the proposed method matches the actual measurements relatively well and reflects the 3D variations in the ground settlement. As α increases, the maximum ground settlement increases and the width of the ground settlement trough decreases, whereas the positions of the inflection points of the settlement curve remain unchanged. The horizontal distance between the inflection points is approximately twice the width of the tunnel.

Deformation characteristics and safety assessment of a high-speed railway induced by undercutting metro tunnel excavation

Stratum deformation (settlement) is a challenging issue in tunnel engineering, especially when construction of metro tunnels has to undercut high-speed railway. For this purpose, we used the FLAC3D software to analyze the stratum settlement characteristics of high-speed railway at different crossing angles intersected by metro tunnel, in terms of ground settlement trough, stratum slip line and irregularity of ballastless tracks. According to the evolution of the stratum settlement at different angle regions, an optimized angle is proposed for the actual project design. In order to reduce the influence of stratum settlement on the safety of high-speed railway, an approach of safety assessment is proposed for the shield engineering undercutting high-speed railway, as per Chinese specifications using numerical results and on-site conditions. A case study is conducted for the shield tunnel section crossing the Wuhan – Guangzhou High-speed Railway between the Guangzhou North Railway Station and the Huacheng Road Station, which represents the first metro tunnel project passing below a high-speed railway in China. A series of measures is taken to ensure the safe excavation of the shield tunnel and the operation of the high-speed railway. The results can provide a technical support for performing a safety evaluation between high-speed railways and metro tunnels.

Deriving Spatio-Temporal Development of Ground Subsidence Due to Subway Construction and Operation in Delta Regions with PS-InSAR Data: A Case Study in Guangzhou, China

Subways have been an important method for relieving traffic pressures in urban areas, but ground subsidence, during construction and operation, can be a serious problem as it may affect the safety of its operation and that of the surrounding buildings. Thus, conducting long-term ground deformation monitoring and modeling for subway networks are essential. Compared with traditional geodetic methods, the Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) technique offers wider coverage and denser measurements along subway lines. In this study, we mapped the surface deformation of the Guangzhou subway network with Advanced Synthetic Aperture Radar (ASAR) and Phased Array Type L-band Synthetic Aperture Radar (PALSAR) data using the Interferometric Point Target Analysis (IPTA) technique. The results indicate that newly excavated tunnels have regional subsidence with an average rate of more than 8 mm/year, as found on Lines Two, Three, Six, and GuangFo (GF). Furthermore, we determined the spatio-temporal subsidence behavior of subways with PALSAR in delta areas using Peck’s formula and the logistic time model. We estimated the tunneling-related parameters in soft soil areas, which had not been previously explored. We examined a section of line GF, as an example, to estimate the ground settlement trough development. The results showed the maximum settlement increased from −5.2 mm to −23.6 mm and its ground loss ratio ranged from 1.5–8.7% between 13 July 2008 and 19 January 2011. In addition, we found that the tunnels in line GF will become stable after a period of about 2300 days in peak subsidence areas. The results show that the proposed approach can help explain the dynamic ground subsidence along a metro line. This study can provide references for urban subway projects in delta areas, and for the risk assessment of nearby buildings and underground pipelines along metro lines.

Non-linear description of ground settlement over twin tunnels in soil

Tunneling inevitably leads to ground settlement. The ground settlement trough over a single tunnel is well described by the generally accepted Peck’s formula. A new model of settlement trough is proposed by extending Peck’s formula to the case of horizontally aligned twin tunnels, which is a widely used tunnel configuration in urban metro projects. The feasibility of the new model is demonstrated through exploration of a large amount of ground settlement data accumulated from a metro tunnel project in China. Two numerical methods are implemented in the data exploration process to solve the problem of non-linear curve-fitting and estimation of model parameters. The Levenberg–Marquardt method is shown to be more suitable than the Nelder–Mead method. Based on the new model of settlement trough, a new method for calculating ground loss over twin tunnels is also proposed. The concluded empirical value of the ratio of ground loss is considered to provide an excellent reference for similar urban railway projects in the future.

Three Dimensional Numerical Analysis of Ground Settlement Induced by Shield Tunneling

The fine numerical simulation is used to study the ground settlement of complex stratum owing to shield construction by ANSYS program. It is shown that the closer the distance between soil layer and the axis of tunnel is, the smaller the disturbance of construction is, the obvious the ground surface settlement is. The value of the maximum settlement at the center of the surface is 7.4mm. The maximum settlement of vault is 14mm. The ground subsidence in cross section distribution is shaped of normal distribution. The closer the distance between soil layer and ground surface is, the smaller the vertical displacement is, the bigger the width of settlement trough of soil layers is. The width of settlement trough is 25m. The volume loss rate of shield tunnel is about 0.32%. The width coefficient of ground settlement trough is 0.56. The tendency of ground settlement decrease to become gentle with the advance of shield construction. The ground settlement keeps constant after tunnel face advancing to 30m.

Impact of Double-O-Tube Shield Tunnel Construction on Grillage Beams Foundation Frame Building

Considering the interaction of building-soil-tunnel, the grillage beams foundation frame building vertical crossed by Double-O-Tube (DOT) shield tunnel was simulated by 3D MIDAS/ GTS software, and the impact of construction on the building was analyzed. The results show that: the ground settlement trough caused by DOT shield tunnel can be fitted by peck formula; during the passage of the shield tunneling through the building, the settlement of the building increased and settlement trough was wilder; the settlement was stable and had a little rebound when shield machine already passed the building; with the increase of driving distance, the first principal stress P1 increased and then was stable; with the increase of L, the shape of foundation settlement curve changed, and the maximum differential settlement between columns increased but was small.

Prediction of Ground Settlements Associated with Shield Tunnelling

There is much uncertainty to estimate the ground settlement associated with shield tunnelling due to the complicatedly interacted conditions between tunnelling methods and soil characteristics. Accordingly, if the shape of the ground settlement could be quantitatively predicted, it would be very effective for the assessment of its influence on the existing structures. It is presented that the shape of the ground settlement trough can be expressed as the product of the normal distribution function and the error function by introducing the mathematical model. The field observations were also carried out at the four sites of the shield tunnel construction in the Metropolitan areas. Besides, the model test was done, in which the settlements of sand layers were measured by the X-ray techniques. The following conclusions are obtained. The lateral and longitudinal profiles of the ground settlement trough are well fitted with the normal distribution curve and the error function curve, respectively. The parameter which represents the width of settlement is roughly proportional to depth of tunnel and its proportional constant depends upon soil characteristics. In clay the ratio of lost ground is positively correlated with OFS (Simple Overload Factor) defined by construction conditions and soil characteristics. Consequently the maximum settlement can be calculated by using these relationships.