Settlement Trough Width 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.

Progressive development of soil arching and deformations in two and three-dimensional trapdoor tests

This study conducted Two- and three-dimensional (3D) trapdoor tests using a newly developed trapdoor test device, to investigate the evolution of soil arching and fill deformation with different relative fill densities and fill heights. The test results show that the trapdoor settlements normalized by trapdoor width required for the soil arching ratios to reach minimum and ultimate values increased with fill height. In tests with dense fill, both the minimum and ultimate soil arching ratios were smaller compared to tests with loose fill at the same fill height. Two symmetrical slip surfaces developed from the trapdoor edges, with their inclination angles depended on the dilatation angle of the sand. The proposed Gaussian distribution function with fitting parameters well matched the measured fill settlement profile. In the dense fill tests, the settlement trough width and volume loss induced by trapdoor settlement gradually decreased with fill elevation due to its strong shear dilation behavior. Conversely, the loose fill exhibited weaker shear dilation behavior, resulting in a larger settlement region. The settlement trough width and volume loss ratio, derived from the measured fill deformation, can be used to predict the fill deformation, including the surface settlement.

Assessing and predicting surrounding rock settlement troughs in the subsea tunnel: A case study of Haicang Tunnel

To ensure the safety of subsea tunnel construction, it is crucial to prevent extreme deformation of the surrounding rock. An assessment and prediction study on the surrounding rock deformation induced by the excavation of the subsea tunnel using the three-bench method was conducted, based on Haicang Subsea Tunnel in Xiamen, China. A series of numerical simulations and on-site monitoring were conducted to reveal the evolution of the displacement field of the surrounding rock. The influences of various factors on the settlement trough of the surrounding rock above the subsea tunnel were also investigated, including seawater, bench length, and bench spacing. The rapid ring closure of the primary support by adopting short benches is imperative to control the arch settlement and settlement trough width. The settlement resulting from the excavation of the upper and middle benches contributed to 90% of the total deformation, as revealed by both numerical simulation and in-situ monitoring. Subsequently, an empirical formula was proposed to predict the settlement trough curves of surrounding rock at different depths above the seabed tunnel.

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.

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.

Study on Ground Settlement Patterns and Prediction Methods in Super-Large-Diameter Shield Tunnels Constructed in Composite Strata

This study focuses on investigating the surface settlement characteristics induced by the construction of a super-large-diameter shield tunnel in composite strata. By utilizing a combination of field monitoring and numerical simulation analysis, the surface settlement patterns encountered during the construction process in horizontally distributed typical soil–rock composite strata were summarized based on the 16.03 m super-large-diameter shield tunnel project in the southerly extension of He’ping Avenue in Wuhan. In addition, the collected data were used to enhance the Peck empirical formula. The results of the study show the following: (1) Significant non-uniform settlement occurs along the tunneling direction when the shield machine passes through soil–rock composite strata. The range of non-uniform settlement is approximately 3.1 times the tunnel diameter (D) in soil sections and 1.9 times the tunnel diameter (D) in rock sections. (2) The impact of composite strata on the maximum settlement is greater than its effect on the settlement trough width, with a larger impact within the soil sections compared to the rock sections. (3) The Peck correction formula, which takes into account the distance between the monitoring cross-section and the composite interface, provides more accurate predictions than the original Peck empirical formula.

Analysis of Surface Settlement Induced by Shield Tunnelling: Grey Relational Analysis and Numerical Simulation Study on Critical Construction Parameters

Excessive surface settlement poses significant challenges to shield tunnelling construction, resulting in damage to adjacent buildings, infrastructure, and underground pipelines. This study focused on investigating the surface settlement induced by shield tunnelling during the construction of Qingdao Metro Line 6 between Haigang Road Station and Chaoyang Road Station. Firstly, the settlement data from the left line of the shield tunnel were evaluated by grey relational analysis. The relational coefficients were calculated to assess the correlation degrees of each influential parameter. Subsequently, the four critical influential parameters with the highest relational degrees were chosen to investigate their effects on surface settlement through numerical simulations under different scenarios. The results show that the four parameters with the highest relational degrees were thrust, grouting pressure, earth pressure, and strata elastic modulus. It should be noted that the strata elastic modulus significantly affects surface settlement, while the grouting pressure influences the settlement trough width in weak strata. Moreover, improper thrust magnitude can lead to an increase in surface settlement. Based on these findings, recommendations are proposed for the right-line tunnel construction and practical countermeasures for surface settlement during shield tunnelling construction are provided.

Predictions of ground surface settlement for shield tunnels in sandy cobble stratum based on stochastic medium theory and empirical formulas

This paper focuses on the prediction of ground surface settlement induced by shield tunnelling in sandy cobble stratum. Based on the stochastic medium theory, an analytical solution to predict the surface settlement is developed considering the difference between soil and tunnel volume loss. Then, the effects of tunnel geometries, influence angle and volume loss on the characteristics of surface settlement are discussed. Through back analysis, a total of 103 groups of field monitoring data of surface settlement induced by shield tunnelling in sandy cobble stratum are examined to investigate the statistical characteristics of the maximum settlement, settlement trough width and volume loss. An empirical prediction is presented based on the results of back analysis. Finally, the analytical solution and empirical expression are validated by the comparisons with the results of model tests and field monitoring. Results show that the soil at ground surface has an overall dilative response for most of the shield tunnelling in sandy cobble stratum. In addition, the developed analytical solution is applicable and reasonable for surface settlement prediction. Meanwhile, the proposed empirical formula also shows good performance in some cases, providing an approach or a reference for engineering designers to preliminarily evaluate the surface settlement.

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”.

Modification of Peck Formula to Predict Surface Settlement of Tunnel Construction in Water-Rich Sandy Cobble Strata and Its Program Implementation

There are few studies on the land subsidence induced by shield tunneling in the water-rich sandy gravel stratum, which is of high research value. Linear regression and measured data were employed in this study to investigate the land subsidence induced by shield tunneling when crossing the water-rich sandy gravel stratum from Mudan Dadao Station to Longmen Dadao station of Luoyang Metro Line 2. The maximum land subsidence correction coefficient, α, and the settlement trough width correction coefficient, β, were introduced to modify the peck formula to predict land subsidence induced by shield tunneling in Luoyang’s water-rich sandy gravel stratum. It was discovered that the original Peck formula needs to be modified because its prediction result was significantly larger than the actual value. When the value ranges of α and β in the modified Peck formula were 0.379~0.690 and 0.455~0.508, respectively, the modified Peck formula presented a minor error, in terms of the prediction curve, compared with the original formula, and the prediction result was more reliable. The best prediction result could be obtained when α = 0.535 and β = 0.482. In addition, Python could effectively improve the calculation efficiency of the Peck formula modification.

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

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

Modification of the Peck Formula for a Double-Track Shield Tunnel under Expressway Subgrade

In practice, asymmetric formation disturbance occurs due to the sequence of excavation though parallel double-track tunnel is a typical symmetrical engineering. Based on a shield tunneling project of a section of the Suzhou Rail Transit under the subgrade of the Shanghai–Nanjing Expressway, a finite element model was established to obtain a numerical solution that was validated by the measured data to guarantee reliability. According to the construction characteristics of the shield method, two correction coefficients—namely the soil loss rate correction coefficient α and the settlement trough width correction coefficient β—were introduced. A modified Peck formula suitable for the preceding tunnel and the subsequent tunnel was proposed. The applicability of the modified Peck formula was verified by another similar project. The results showed that the numerical solution can better reflect the actual settlement of the highway subgrade under shield tunneling. The results calculated by the classic Peck formula had a large error in comparison with the measured data. The modified empirical formula could more accurately predict the settlement of the expressway subgrade caused by the shield method when α1 = 0.38 and β1 = 2.08 for the preceding tunnel and α2 = 0.29 and β2 = 1.99 for the subsequent tunnel.

Theoretical Analysis on the Effectiveness of Pipe Roofs in Shallow Tunnels

When a pipe roof is used as a pre-support for the surrounding rock in a shallowly buried tunnel, accurate prediction of the support effectiveness of the pipe roof is important in order to ensure the rationality of the pipe roof structure design. Based on analysis of pipe roof pre-support effects, considering the construction time of pipe roof structures and the interaction mechanisms between the steel pipes of the pipe roof and the surrounding rock, we establish a calculation model of the surrounding rock pressure acting on each steel pipe of the pipe roof on the semi-circular pre-support boundary. Through comparison and analysis with the measured results, we demonstrate that the calculation model for surrounding rock pressure and the calculation model for stress and deformation of the pipe roof are reasonable. According to the deformation coordination conditions between the steel pipe of the pipe roof and the surrounding rock on the pre-support boundary and alongside the Peck formula, we establish a theoretical analysis method for pipe roof pre-support effectiveness based on the indexes of the ground loss rate, settlement trough width, and maximum ground surface settlement, thereby realizing a quantitative evaluation of pipe-roof pre-support effectiveness. At the same time, the effects of steel pipe diameter, circumferential spacing, and excavation footage length on the pre-support effectiveness of the pipe roof are analyzed. The conclusions can be used as a basis for the design and optimization of pipe roofs and as a guide for the application of pipe roofs.

Role of Shear Deformability on the Response of Tunnels and Pipelines to Single and Twin Tunneling

Tunneling can compromise the safety and serviceability of existing buried infrastructure because of settlements, crack openings, dislocations, and material strains. A continuum-based soil-structure interaction model, implementing an equivalent Timoshenko beam, is used to evaluate the excavation-induced settlements and longitudinal deformations of existing tunnels and pipelines. Both single and twin tunneling scenarios are examined. The shear flexibility of shield and sprayed concrete lining tunnels may be significant. This increases tunneling-induced settlements while it decreases tilt, curvature, and the associated bending moment, with implications for optimal monitoring installations. In this work, a new dimensionless shear factor is introduced, governing the relative importance of shear and bending deformations and accounting for the settlement trough width. This can be used to evaluate if a pure-bending, shear-dominated, or mixed deformation mode should be expected. Design charts to assess existing infrastructure affected by either single or twin tunnels are proposed.

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.

Laboratory Test of EPB Shield Tunneling in Mixed-Face Conditions

Field measurements and laboratory tests were carried out to study the mechanical behaviors of soil in response to earth pressure balance (EPB) shield tunneling in mixed-face conditions, i.e., layers of granite and sand. Specifically, an experimental investigation was carried out using a laboratory-scale model to replicate the EPB tunneling operations in such ground conditions. The effects of the ratio of rock/sand at the tunnel face (Tr/Ts) and the cover-to-diameter ratio (C/D) on the soil pressure in the chamber, ground displacement, and volume loss were examined. The results show that the soil's response to the mixed-face conditions differs significantly from that in the homogenous ground and highly depends on the ratio of rock/sand, especially for relatively shallow tunnels. As the ratio of rock/sand at the tunnel face increased, the pressure gradient in the chamber became more inconsistent. The translated cumulative curve does not always provide a good fit in the mixed-face conditions, particularly in cases when the rock/sand ratios are high. A smaller width of settlement trough has been observed for cases with a large rock/sand ratio compared to that in clay and cohesionless soil.

Analysis of Ground Movement during Large-Scale Pipe Roof Installation and Artificial Ground Freezing of Gongbei Tunnel

This paper analyzes the vertical ground movement during large-scale pipe roof installation and artificial ground freezing of Gongbei tunnel of the Hong Kong-Zhuhai-Macau bridge project. The transverse ground settlement during pipe roof installation is analyzed. The ground loss volume ratio and settlement trough width coefficient during pipe jacking are estimated based on the field measurement of ground settlement. The interaction of pipes during multiple jacking is investigated. The effect of frost heave control by pregrouting, limiting frozen soil thickness, and combination of the two methods is evaluated. The analysis shows that the ground settlement during pipe roof installation by jacking 37 pieces of 1620 mm steel pipes is relatively small with a maximum value of 2.2 cm. The reinforcement to ground provided by the fore-jacked pipes reduces the ground loss volume ratio and, consequently, the ground settlement during the follow-up pipe jacking. The artificial ground freezing generates a relatively large ground heave with a maximum value of 7.8 cm. Pregrouting plays a critical role in the frost heave control by reducing the heave by about 33%. Limiting the frozen soil thickness by heating pipes serves as an effective supplement to frost heave control by reducing the heave by about 9%. The combination of the two measures reduces the ground heave by about 42%. Findings from this paper provide valuable reference to the tunnel construction using pipe roof and artificial ground freezing as presupport.

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.

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.

Visualization and digitization of model tunnel deformation via transparent soil testing technique

With the increasing demand for transportation infrastructure, the construction of urban tunnel systems linking different areas is indispensable. The deformation and the failure process during a tunnel excavation are essential concerns for geotechnical engineers. However, few studies have systematically investigated the effect of the ground loss ratio on tunnel deformation and the inequality between the ground loss ratio and the volume of the settlement trough. An experimental study using the transparent soil testing technique is performed herein for better visualization and digitization purposes. The three dimensional vertical and horizontal deformation patterns of a single tunnel are investigated for both the surface and the stratum right below considering different ground loss ratios. The relationship among the empirical constant of the settlement trough width, buried depth, depth–diameter ratio, and ground loss ratio is presented.