Stratum Settlement Research Articles

Modeling test study on influence mechanism of large-span double-arch tunnels in proximity to existing tracks

This paper aims to study the influence mechanism of the large-span double-arch tunnels in proximity to existing tracks using 1 g model test. A novel non-contact device able to measure settlements automatically is developed to improve the test accuracy. During the test, the strata settlement, surrounding rock stress and track deformation induced by tunnel excavation are measured simultaneously. The results show that: (1) The excavation of the double-arch tunnel induces an asymmetric “W”-shaped horizontal surface settlement. The horizontal surface settlement near the centerline of the first excavation side is the largest. (2) The U-shaped groove structure exhibits an “M”-shaped deformation, while its structure produces bulges near the maximum horizontal surface settlement. (3) After excavation, the longitudinal surface settlement gradually decreases along the excavation direction, which causes the tilting or bottom voids of the U-shaped groove structure. The U-shaped groove structure may experience torsional shear damage under the load imposed by the train.

GFNS: An OpenGL-based tool for shield tunneling simulation in 3D complex stratum

Shield tunneling under complex geological conditions may lead to uneven surface settlement, thereby posing risks of damaging adjacent structures. This paper introduces the Geological Model for Numerical Simulation (GFNS) software, which employs OpenGL to implement a 3D geological model. The software incorporates an advanced geological stratum meshing algorithm based on conditional statements, facilitating the swift construction of numerical models for shield tunneling in intricate geological formations. In this study, a numerical model for shield tunneling in complex geological conditions was developed using GFNS. The research investigated potential risk levels to adjacent structures due to shield tunneling through alternating soft and hard geological strata along the tunnel's longitudinal axis. Moreover, the influence of shield excavation position and construction parameters on surface settlement was analyzed. Finally, a comparison was conducted with the traditional parallel geological modeling approach. The results revealed that simulating shield tunneling while considering complex geological conditions demonstrates a stronger correlation with the laws of stratum settlement. Thus, GFNS offers an auxiliary modeling method for simulating shield tunneling under complex geological conditions.

A Study of User Satisfaction with and Acceptance of a Hydrology and Stratum Subsidence Monitoring System

A Study of User Satisfaction with and Acceptance of a Hydrology and Stratum Subsidence Monitoring System

Numerical Simulation of Ground Subsidence Factors Resulting from Unpressurized Pipeline Rupture Below the Water Table

The rupture of an unpressurized pipeline below the water table can lead to the leakage of groundwater along with soil particles into the pipeline. This not only causes blockages in the pipeline but, more critically, can result in ground subsidence. Understanding the factors influencing this phenomenon is a subject of great interest. To delve into this matter, this study employs the DEM-CFD methodology to synergistically encompass particle dynamics and interactions within the flow domain. It introduces an innovative framework for simulating water and soil erosion subsequent to the rupture of subaqueous unpressurized pipelines. This pioneering approach introduces a novel modeling and simulation paradigm catering to the analysis of intricate phenomena of this nature. Upon validating the flow field, our investigation specifically focused on three key factors: particle friction coefficient, groundwater level, and particle size distribution. We conducted a thorough examination of the process and mechanism of water and soil loss at the pipeline leakage point and the subsequent development of stratum subsidence. Our results indicate that particles with a friction coefficient of 0.6 had a reduced maximum displacement by 8.9%, compared to particles with a friction coefficient of 0.3. Similarly, a groundwater depth of 2 m resulted in a 29.6% decrease in maximum displacement compared to a 4 m depth, with a corresponding 160.9% increase in maximum force chain strength. Discontinuous particle gradation, in contrast to continuous gradation, yielded a notable 40.3% reduction in maximum displacement and a substantial 495.1% increase in maximum force chain strength. This underscores the noteworthy influence of particle friction coefficient, groundwater table elevation, and soil particle diameter on the stability of the overlying soil strata in the vicinity of a compromised unpressurized conduit.

Study on Stratified Settlement and Weak Reflectivity Fiber Grating Monitoring of Shield Tunnel Crossing Composite Strata

This paper proposes a set of field test technology system for layered settlement of composite strata based on weak reflectivity fiber Bragg grating sensing technology based on the shield project of “Keyuan Station ~ Shenzhen University Station” section of Shenzhen Metro Line 13, and through the comparison and verification of three-dimensional numerical simulation and field monitoring, the law and distribution characteristics of disturbance settlement of ground surface and overlying strata during shield tunneling are systematically analyzed, and the vertical and horizontal zoning (layer) system for the spatial and temporal evolution of layered settlement of composite strata during shield tunneling is constructed. On this basis, the targeted settlement control technical measures and recommendations are proposed. The findings show that the weak reflectivity fiber grating sensing technology can better perceive the evolution law and distribution characteristics of vertical and horizontal settlement of composite strata caused by shield tunneling, which is in good agreement with the numerical simulation results, and has the advantages of automation and high precision, it can be used as a supplement and alternative method for traditional measurement methods. The stratum deformation is small and layered settlement is not obvious in shield approaching stage (−5D~0), after shield crossing and shield tail falling (0~3D), the stratum is the longitudinal main deformation zone of shield tunneling disturbance, and the influence range of the whole tunneling disturbance is about (−1D~3D). Meanwhile, according to the influence degree of shield tunneling disturbance, the overlying strata of the tunnel can be divided into main disturbance layer and secondary disturbance layer, and the main disturbance layer is located in the range of 0.5D above the tunnel. In addition, based on the different stages of shield tunneling and the vertical and horizontal zoning (layers) of existing structures such as buildings (structures), the settlement control measures and suggestions are proposed. The research results demonstrate the feasibility of weak reflectivity fiber grating for distributed and continuous strata monitoring. It has important guiding value for improving the understanding of settlement law produced from shield construction in composite strata and analyzing and predicting potential risks resulting from shield construction. It also provides reference value for future subway design and construction.

Numerical analysis of the geomechanical responses during natural gas hydrate production by multilateral wells

Multilateral wells are acknowledged as a promising well type to achieve the commercial development of natural gas hydrate. Previous studies have validated the efficacy of multilateral wells for hydrate mining without considering the geomechanical responses. However, effective stress increases during hydrate extraction by depressurization, and the reservoir skeleton degrades with hydrate dissociation, which might induce stress concentration, stratum subsidence, seafloor inclination, and other hazards. Understanding the geomechanical responses is thus crucial for the design of hydrate exploitation utilizing multilateral wells. As a continuation of our previous study, a coupled thermal-hydrologic-mechanical model was constructed to investigate the geomechanical responses during hydrate production by multilateral wells. Results reveal that multilateral wells can upgrade geomechanical risks and gas production capacity for hydrate exploitation. Stress concentration and stratum sinks are prevalent around the multilateral well. Increasing production pressure may alleviate stratum subsidence but has a noticeable impact on gas production. Since stratum inclination generated by hydrate mining with multilateral wells is minimal, geological catastrophes are most improbable. For utilizing multilateral wells in hydrate extraction, it is recommended to pay more attention to wellbore and wellhead safety.

Hydrate Dissociation Evaluation and Stratum Subsidence Response Induced by Depressurization in Hydrate-Bearing Permafrost

Hydrate Dissociation Evaluation and Stratum Subsidence Response Induced by Depressurization in Hydrate-Bearing Permafrost

A New Calculation Method for Tunneling-Caused Stratum Settlement

To improve the prediction accuracy for the stratum settlement induced by tunnels and obtain a theoretical method for determining the influence radius of settlement, a new empirical formula for the surface settlement curve is proposed in this study, and the slice method is introduced into the calculation of the influence radius of settlement. It is assumed that the disturbance boundary of the tunnel is a circular arc surface, the disturbed soil is divided into multiple slices, and the sliding force and resistance on the circular arc are obtained through a stress analysis of the slices. An arc with the same values of the sliding force and resistance can be determined as the actual disturbance boundary of the overlying strata as formed by the subsurface tunneling. On this basis, the influence radius of settlement and maximum settlement at different depths can be determined, and the settlement curve can be depicted by substituting the influence radius and maximum settlement into the expression of the settlement curve. The rationality of the proposed method is verified based on four sets of measured data. The surface settlement curves and the settlements at different depths on the center line of the tunnel obtained by the new method are generally consistent with the measured data.

Buckling behavior of buried pipe crossing stratum subsidence area

Stratum subsidence is one of the important factors threatening the pipe safety. Buckling phenomenon occurs on the pipe crossing subsidence area that may cause leakage accidents. The pipe soil coupling numerical model was established in this paper, buckling behavior of buried pipe crossing stratum area was investigated. The effects of subsidence displacement, radius-thickness ratio, internal pressure, buried depth and stratum on buried pipe’s mechanical behavior were discussed. The results show that buckling appears on the pipe when subsidence displacement is large. With the increasing of subsidence displacement, diameter-thickness ratio and buried depth of pipe, the buckling phenomenon becomes more serious. When the internal pressure of pipe increases, the buckling mode changes from concave fold to convex wrinkle gradually, and it is more serious with the increasing of internal pressure. The pipe in rock stratum is more dangerous than that in clay stratum and sand stratum. Those results can be used for the evaluation and maintenance of gas or hydrogen pipes.

Mechanical response of inclined TBM tunnel due to drainage settlement of deep sandstone aquifer

Drainage of deep aquifers can cause stratum settlement, which has significant effects on the architectural structures within them. Especially for inclined TBM tunnels, the settlement may lead to the longitudinal differential deformation and damage of segments. However, most previous studies on the effects of aquifer drainage settlement on deep structures have focused on the vertical shaft in coal mines, and little attention has been paid to inclined TBM tunnels in deep sandstone aquifers. Through the physical model test and numerical simulation, in this study, the mechanical characteristics and deformation behavior of an inclined TBM tunnel in the deep water-bearing sandstone and impermeable mudstone before and after the aquifer drainage were investigated. The distribution and variation of stresses, internal forces, and deformation on tunnel segments before and after drainage were systematically analyzed along the tunnel longitudinal and circumferential directions. Results show that the whole tunnel is always under compression and mainly subjected to the coupling effect of bending moment and axial compression in the longitudinal direction. After drainage, the longitudinal and circumferential stresses as well as circumferential axial force increase remarkably at the tunnel sidewall but decrease at the tunnel crown and invert. While for the circumferential bending moment, by contrast, it increases at the three positions. In addition, the tunnel experiences a noticeable bending at the junction of the two strata after drainage due to the synchronous settlement with the sandstone, resulting in severe stress concentrations and the formation of the longitudinal shear band at the stratigraphic junction.

Comparison study of Excavation Stability using Different Tunnel Excavation Methods

For the safety and efficiency of tunnel construction, optimal schemes for tunnel excavation with different surrounding rock grades should be proposed to provide references for engineering construction. Through 3D numerical simulation, the mechanical properties of the surrounding rock during tunnel construction were studied by 3D numerical simulation. For different surrounding rock grades, three different excavation methods were simulated. A comparative analysis of ground settlement, surrounding rock displacement, and maximum principal stress caused by different construction methods was also performed. The results show that different construction methods have a small impact on the displacement of surrounding rock. When the surrounding rock is of grade I, the maximum vertical displacement of the excavation surface is less than 2 mm. Bench cut method can be used for excavation with fast construction speed. When the surrounding rock is of grade IV, the stratum settlement and excavation surface displacement are large. The Center diagram method can ensure the construction progress and minimize the vertical displacement of surrounding rock. When the surrounding rock is of grade V, the displacement caused by tunnel excavation further increases. The double-side drift method can be adopted to minimize the stratum settlement and surrounding rock displacement.

EXPERIMENTAL INVESTIGATION ON METHOD OF STRATUM SETTLE￣MENT COORDINATION TO PREVENT AND CONTROL COALMINE SHAFT FAILURE

In recent years,many experts and scholars have carried out theoretical and experimental research on the mechanism of additional stress in shaft lining and the corresponding eliminating methods. On the basis of these researches,this paper proposes the strata settlement coordination method,analyzes the mechanism of the proposed method,carries out an experimental study on the change of additional stress in shaft lining in the soil layer,as well as analyzes the effectiveness of the proposed method while it is used in eliminating the additional stress. By setting different isolation coordination conditions,the proposed method acquires the stress variation of shaft lining and the settlement deformation of soil surface in the strata settlement process. In the experiment,there are sudden increases in the vertical strain of the shaft lining. The first group without isolation coordination body,the sudden increase values are obviously higher than the latter three groups. In addition,the settlement of the ground surface in the process of strata subsidence can be decreased using the method of stratum settlement deformation. The proposed method can decrease the sudden increase values and the steady values of shaft lining vertical strain effectively. In the meantime,the horizontal strain of cylinder can keep steady. Therefore,the proposed method can be developed to be a potentially effective approach for prevent and control lining failure of coal mine shaft.

Stratum Settlement during Depressurization of Horizontal Wells in Gas Hydrate Reservoirs

Stratum Settlement during Depressurization of Horizontal Wells in Gas Hydrate Reservoirs

Analysis of Stratum Subsidence Induced by Depressurization at an Offshore Hydrate-Bearing Sediment

Gas production from an offshore hydrate-bearing sediment (HBS) by depressurization will reduce the strength of cementation and increase the effective stress of hydrate reservoirs, which can result ...

Study on temporal and spatial distribution law of thaw settlement displacement by horizontal freezing method

After freezing construction, the damage caused by thawing settlement mainly comes from the displacement and settlement of strata, which leads to uneven settlement of underground pipelines and surface buildings in the project area. In this paper, based on the three-dimensional finite element analysis, the settlement displacement field of artificial frozen soil in a subway connecting passage is analyzed, and the parameters such as elastic modulus, density and specific heat change with temperature are considered in the model. The change of mechanical parameters in the soil layer is given by the temperature field, which makes the mechanical parameters of each point in the soil layer different. In addition, the temperature field of the soil layer changes with time, and finally makes the mechanical parameters change point by point, so as to ensure that the simulated melting and settlement calculation process is more in line with the actual working conditions. The calculation results of settlement displacement show that the settlement displacement field of soil layer changes nonlinearly with time and space. The research results of this paper provide reference for the position and time node of the control measures of thawing settlement.

Evaluation and formation model of Cambrian high-quality source rocks in the southeast margin of North China Plate

In response to the question of whether effective Cambrian source rocks are developed in the North China Plate, field investigations on the southern margin of North China have been carried out. High-quality marine argillaceous source rocks of continuous thickness of 35 m in the Lower Cambrian were discovered in the south-eastern margin of North China Plate. Phosphorus nodules are common in the source rocks. The TOC is 1.19%∼29.70%, with the average of 7.31%. The organic matter comes from low-level biological algae. Because the carbon isotope of kerogen is relatively more negative, it is judged to be mainly benthic algae. The converted vitrinite reflectance (Ro) from measured bitumen reflectance is 2.24%∼3.45%, which is an over-mature source rock. The Lower Cambrian source rocks in the southern margin of North China occurred under the background of rising sea levels. After the glaciers on the southern margin of the North China Plate melted, the Qinling rift trough developed and the stratum subsidence caused rapid transgression of seawater from southeast to northwest. At this time, algae multiply in large numbers, and after death they accumulate with phosphorus-containing materials to form phosphorus-containing organic matter. Benthic algae mainly live in deep-water shelf not affected by waves and tides. Therefore, the development of source rocks is mainly in the deep water shelf.

Progressive Deformation Failure Characteristics of Highway Tunnel Working Face in Sand Pebble Stratum

The sand pebble stratum is typically unstable with discrete particles. The most important constituent elements are sand and pebbles. The surrounding rock of tunnels in the sand and pebble stratum has prominent engineering problems, such as being loose, easy to collapse, and unstable when exposed to water. Therefore, it is critical to ensure the safety of tunnel construction in this stratum. This paper studies the failure modes of surrounding rock on sand and pebble tunnel working face of different excavation footage, and the formation of subsidence law starting from the micro-mechanical and motion characteristics of particulate matter. This study is based on the Bai Heqiao tunnel of the Wudu expressway in Gansu Province. The results show that the instability failure of the surrounding rock mainly occurs in the upper part and sliding area in front of the tunnel working face. The sliding area is a curved body after the failure of the tunnel working face. The deformation and failure of the surrounding rock in the lower half of the tunnel working face are relatively small, and are gradually transferred from the vault to the surface, resulting in the subsidence of the surface and collapse. The deformation degree of the surrounding rock in the region closer to the tunnel vault is more obvious. After the formation is stabilized, the maximum subsidence deformation occurs above the tunnel vault. The final settlement amount of the stratum is also different with different footage. The smaller the excavation footage, the smaller the stratum settlement amount. Therefore, the appropriate excavation footage is selected as the principal safety control index during the excavation with the short-step method. The research results provide the necessary reference for the fine design and construction of tunnel engineering in the sand pebble stratum.

Analysis of Stratum Settlement Laws Caused by the Construction of Shallow-Buried Expressway Tunnels with Large Span and Small Spacing

Many tunnels with large spans and small spacing have been constructed due to the rapid development and construction of China’s expressways. The stratum settlement caused by the construction of these tunnels in shallow sections is large and difficult to control, and ensuring stratum stability is a key issue in the construction of expressway tunnels. According to the research differences in the prediction of stratum settlement under the tunnel construction at present, based on stochastic medium theory, in this study, the prediction formula for stratum settlement in the construction of double-line tunnels was revised and optimized by monitoring the construction of expressway tunnels with large spans and small spacing in shallow sections. The accuracy of the revised formula was verified by comparing it with on-site monitoring data. A numerical calculation method was also used to select effective deformation control measures. Results showed that the revised prediction formula of stratum settlement could roughly predict the position and shape of the settlement tank and reflect the uneven settlement caused by the mutual influence of double-line excavation. The accuracy of stratum settlement prediction was high. Moreover, reasonable grouting could effectively reduce stratum settlement. A reasonable grouting plan should be selected during construction in accordance with the actual situation to avoid material wastage and increased costs caused by excess grouting.

Mechanical behavior analysis of buried pipeline under stratum settlement caused by underground mining

The stratum settlement caused by underground mining is one of the main geological disasters that threaten and damage buried pipelines. Therefore, the mechanical behavior of buried pipe under stratum settlement is investigated in this paper. Effects of pipeline parameters, mining area parameters and inclination directions of mining area on mechanical behavior of the buried pipeline are discussed. The results show that the maximum Von Mises stress and the maximum vertical displacement of pipeline are located in the middle of the pipeline during the mining process. As the excavation length increases, the Von Mises stress, the circumferential strain and vertical displacement increase. However, there is only stress concentration in the pipeline, and does not appear yield deformation. The vertical displacement of the pipeline is much greater than the horizontal displacement. The maximum stratum displacement appears on the upper surface of the mining area and it is stratum settlement. In addition, as the diameter-thickness ratio, buried depth, surrounding soil thickness of the pipeline and the height and the width of mining area increase, the maximum Von Mises stress, the circumferential strain and maximum vertical displacement of the pipeline increase, but they decrease with the increase of the buried depth of mining area. Whether the mining area is horizontal inclination or longitudinal inclination, the maximum Von Mises stress and maximum vertical displacement of pipeline are located in the middle of the pipeline. The maximum Von Mises stress, the circumferential strain and vertical displacement of pipeline decrease with the increase of the inclination angle. However, for the mining area of longitudinal inclination, the pipeline would produce horizontal displacement, the horizontal displacement of the pipeline increases with the increase of longitudinal inclination angle, and the position of the maximum strain of the pipe appears to shift. For the mining area of horizontal inclination, with the increase of horizontal inclination angle, the right side of vertical displacement curves approximately overlap, but the left side separates from each other.

Numerical Simulation Study of Stratum Subsidence Induced by Sand Leakage in Tunnel Lining Based on Particle Flow Software

To obtain the dynamic development process of the stratum subsidence of sandy soil layer induced by the cracks of the tunnel lining, and the formation and dynamic change of soil arch during the process of subsidence, a sily-type sand gushing model was established by the particle flow software (PFC2D). The parameters of sandy soil particles were calibrated by biaxial compression test. Furthermore, the flow pattern of sand in the process of stratum subsidence caused by sand leakage induced by cracks in the tunnel lining, the change of the inter-particle force chain during the formation of the soil arch were simulated. It was shown that when the stratum subsidence induced by the cracks of the tunnel lining occurred, the development process of sand collapse was a dynamic process accompanied by the formation and destruction of soil arches. And the ratio of crack width of lining to particle diameter and the internal friction angle between the sand were important factors of sand collapse disaster in the process of stratum subsidence. The necessary conditions for sand collapse were that the ratio of crack width of lining to particle diameter reached 5.1 and the friction coefficient reached 0.6. With the increase of the width of the sand leakage crack, a stable contact force arch was more and more difficult to be formed.