Settlement Prediction Research Articles

Application of the Richards Model in Settlement Prediction of Loess-Filled Foundations

The Richards equation has high plasticity and compatibility. Compared with other curve equations, it has higher applicability and accuracy in describing S-shaped curves. It can describe the changes in the initial growth stage, rapid growth stage, and stable growth stage of organisms well and reflect the slow-fast-slow change characteristics of growth. In this paper, the Richards model is introduced into the settlement deformation prediction of loess-filled foundation. Taking a high-loess fill site in northern Shaanxi Province as an example, continuous settlement deformation monitoring is carried out for the filling during the project operation period, and the settlement characteristics of a loess-filled foundation are studied using the monitoring results. It is considered that the settlement deformation curve of a loess-filled foundation has similar characteristics; that is, its deformation increases slowly in the early stage, rapidly in the middle stage, and is basically stable at a fixed value in the later stage. Its cumulative deformation time history curve is a smooth S-shaped curve, and the cumulative settlement increases with time and tends to converge. Analysis shows that the time history curves of cumulative settlement, the settlement deformation rate, and the acceleration of loess foundation filling are highly consistent with the Richards model. Compared with the modified exponential model and hyperbolic model, the predicted results are closer to the measured results; that is, the Richards growth model can be used to predict the settlement deformation of a fill foundation.

Research Findings on the Application of the Arch Structure Model in Coal Mining, a Review

Studying the movement law and failure mechanism of overburden is important to underground safety production, aquifer protection, surface subsidence and ecological protection. A commonly used model, the arch structure model, for studying overburden movement is systematically reviewed in this paper. First, the arch structure in the mining field is divided into an unconsolidated layer arch, beam arch (hinged arch), and overburden arch according to arching medium. On this basis, the research progress and existing problems of these three arch structure models are discussed according to the research means, including theoretical modeling, numerical simulation, similar simulation, and field measurements. The application of the arch structure model focuses on the prediction and prevention of mining pressure and surface subsidence, and there are relatively few means to actively regulate overburden arch. Thus, three control methods of the arch structure in underground coal mining are proposed: the preset arch structure method before coal mining, process control arch methods during coal mining, and end reinforcement control arch methods after coal mining. Finally, the main research focus on the arch structure model in the future is discussed.

A Novel Analytical Model of Mining Subsidence Considering Time Effect Based on the Probability Integral Theory

Surface subsidence caused by underground coal mining has received wide attention due to its impact on the ecological environment. To obtain first-hand data on mining subsidence, we arranged line measurement stations in the mining area of the Weiqiang coalfield and implemented surface movement observation at its first mining working face and obtained the dynamic subsidence curve. The subsidence curves reflected the initial, active and declining stages of subsidence at each measurement point at a basic level, and were consistent with the general rule of surface subsidence. To accurately analyze the surface movement caused by coal mining, based on the probability integral method and considering the actual advancement progress of the working face, a new three-dimensional dynamic prediction model, namely the strip unit mining model, was proposed. The core assumption of this model was that the longwall mining is regarded as the result of superposition of many units of mining. Considering the influence of different mining times and periods after mining, the subsidence time function of two-time factors was introduced into the strip unit mining model, and the final formulation of the dynamic subsidence prediction of the three-dimensional surface is derived by considering the time factor. Based on the analysis of the measured data of the Weiqiang coalfield, the prediction parameters of surface movement were obtained, and the surface movement and deformation are predicted via the probability integral method. Finally, the measured surface subsidence was compared with the theoretically-predicted one. The good match showed that the parameters of the probability integral method, determined according to the measured data, meet the requirements of geological conditions and mining settings in the mining area, and the predicted subsidence curves agreed well with the field measurements, demonstrating the effectiveness of the newly-developed strip unit mining model.

A closed form shape function describing 3D settlement field around a deep excavation in sand

Soil movements produced around deep excavations are one of the main issues to be addressed during design and construction of underground structures in urban environment. Several methods to predict ground movements are currently available. Semi-empirical methods correlate displacements and simple geometrical features of the excavation; these methods predict separately transversal and longitudinal settlement troughs or at least provide a conservative envelope of them and they are mainly based on empirical data of excavations in clay. Numerical methods based on the solutions of FEM or DFM models usually provide prediction of the green field subsidence. In this paper existing 2D semi-empirical methods are first shortly reviewed. Some of these methods are then modified and combined into a new 3D analytical description of the subsidence trough around a deep excavation. The proposed two variable subsidence function depends on several parameters: four independent parameters defining the overall shape and the maximum settlement acting as a scale parameter. Settlement fields reproduced by a 3D FEM nonlinear parametric study of deep excavations inspired by real case studies are thus presented and discussed. The newly proposed 3D analytical description is applied to fit the FEM results and some fundamental relationships among geometrical features of the excavation pit and the 3D shape function parameters are identified. These relationships are validated via the application to three case studies of deep excavations in sand where the subsidence was controlled by the deformation of the retaining structures finding a satisfactory and encouraging agreement.

Predictive Models to Evaluate the Interaction Effect of Soil-Tunnel Interaction Parameters on Surface and Subsurface Settlement

Nowadays, the need for subway tunnels has increased considerably with urbanization and population growth in order to facilitate movements. In urban areas, subway tunnels are excavated in shallow depths under densely populated areas and soft ground. Its associated hazards include poor ground conditions and surface settlement induced by tunneling. Various sophisticated variables influence the settlement of the ground surface caused by tunneling. The shield machine's operational parameters are critical due to the complexity of shield-soil interactions, tunnel geometry, and local geological parameters. Since all elements appear to have some effect on tunneling-induced settlement, none stand out as particularly significant; it might be challenging to identify the most important ones. This paper presents a new model of an artificial neural network (ANN) based on the partial dependency approach (PDA) to optimize the lack of explainability of ANN models and evaluate the sensitivity of the model response to tunneling parameters for the prediction of ground surface and subsurface settlement. For this purpose, 239 and 104 points for monitoring surface and subsurface settlement, respectively, were obtained from line Y, the west bond of Crossrail tunnels in London. The parameters of the ground surface, the trough, and the tunnel boring machine (TBM) were used to categorize the 12 potential input parameters that could impact the maximum settlement induced by tunneling. An ANN model and a standard statistical model of multiple linear regression (MLR) were also used to show the capabilities of the ANN model based on PDA in displaying the parameter's interaction impact. Performance indicators such as the correlation coefficient (R2), root mean square error (RMSE), and t-test were generated to measure the prediction performance of the described models. According to the results, geotechnical engineers in general practice should attend closely to index properties to reduce the geotechnical risks related to tunneling-induced ground settlement. The results revealed that the interaction of two parameters that have different effects on the target parameter could change the overall impact of the entire model. Remarkably, the interaction between tunneling parameters was observed more precisely in the subsurface zone than in the surface zone. The comparison results also indicated that the proposed PDA-ANN model is more reliable than the ANN and MLR models in presenting the parameter interaction impact. It can be further applied to establish multivariate models that consider multiple parameters in a single model, better capturing the correlation among different parameters, leading to more realistic demand and reliable ground settlement assessments. This study will benefit underground excavation projects; the experts could make recommendations on the criteria for settlement control and controlling the tunneling parameters based on predicted results. Doi: 10.28991/CEJ-2022-08-11-05 Full Text: PDF

Creep and breakage behavior of broken rock in the caved zone of abundant mines under triaxial compression condition

It is essential to deeply understand the deformation behavior of overburden above the goaf after mining for the ecological restoration of abandoned mines and the reuse of underground space. Due to the large voids and complex structures, the broken rock in the caved zone is sensitive to time effects, and the deformation behavior is the most complicated. Therefore, a self-made broken rock specimen was made which can freely deform in the lateral direction and withstand confining pressure. A series of rheological tests were performed on these specimens under various confining pressures, axial pressures, and gradations. The research results show that the creep behavior of broken rock undergoes decelerated creep or stable creep stages, depending on its level of axial pressure, and there is no accelerated creep stage. Compared with the confining pressure, the axial pressure plays the main role in the creep deformation of the specimen. Moreover, the broken rock gradation of the triaxial creep experiment affects the relative breakage index Br. When the proportion of rock blocks of the original gradation increases with the particle size of each group, the relative breakage index Br is the largest; on the contrary, it is the smallest. The relative breakage index Br is positively correlated with the confining pressure. In addition, a fractional-order creep model for broken rock in the caved zone of the goaf was proposed, and its fitting results are better than those of the classical Burgers model. Based on the proposed fractional-order creep model, a long-term subsidence prediction model of the caved zone after mining is also proposed, which can provide a theoretical basis for the long-term stability analysis of the abandoned mine.

Analytical Study on the Ground Settlement Induced by Pipe-roof Tunnelling Considering the Interaction between Socketed Pipes

Pipe-roof Pre-construction Method (PPM) is a pre-reinforcement method widely adopted in shallow large section tunnelling in the urban area. As one of the key indexes needed to be controlled, ground surface settlement and axis deviations induced by pipe-roof tunnelling attract increasing attention, but the interaction between socketed pipes (ISP), including shielding and constraint effects, has been lack of consideration in practice. By incorporating deformation coefficient and deviation coefficients, this paper proposed a new analytical method to account for the effect of ISP on the ground movement. Then, a numerical model to consider ISP and sequential jacking process was established and a series of simulations were carried out for a large pipe-roof tunnelling project. By comparing with the analytical results, the deviation coefficients were determined for the proposed model and the effect of ISP on the surface settlement was further revealed. Finally, the rationality and effectiveness of the proposed method were confirmed by contrasts with traditional methods and numerical calculations. The results show that an approximately 37% error rate could be reduced by the new method. This research is helpful for a better understanding of the effect of ISP, and therefore benefits the effective prediction and control of the surface settlement induced by pipe-roof tunnelling.

Variational encoder geostatistical analysis (VEGAS) with an application to large scale riverine bathymetry

Estimation of riverbed profiles, also known as bathymetry, plays a vital role in many applications, such as safe and efficient inland navigation, prediction of bank erosion, land subsidence, and flood risk management. The high cost and complex logistics of direct bathymetry surveys, i.e, depth imaging, have encouraged the use of indirect measurements such as surface flow velocities. However, estimating high-resolution bathymetry from indirect measurements is an inverse problem that can be computationally challenging. Here, we propose a reduced-order model (ROM) based approach that utilizes a variational autoencoder (VAE), a type of deep neural network with a narrow layer in the middle, to compress bathymetry and flow velocity information and accelerate bathymetry inverse problems from flow velocity measurements. In our application, the shallow-water equations (SWE) with appropriate boundary conditions (BCs), e.g., the discharge and/or the free surface elevation, constitute the forward problem, to predict flow velocity. Then, ROMs of the SWEs are constructed on a nonlinear manifold of low dimensionality through a variational encoder and the bathymetry inversion problem is derived on the low-dimensional latent space in a Hierarchical Bayesian setting. The reformulation allows variational inference with a small number (e.g., O(100) of ROM runs and efficient uncertainty quantification. We have tested our inversion approach on a one-mile reach of the Savannah River, GA, USA. Once the neural network is trained (offline stage), the proposed technique can perform the inversion operation orders of magnitude faster than traditional inversion methods that are commonly based on linear projections, such as principal component analysis (PCA), or the principal component geostatistical approach (PCGA). Furthermore, tests show that the algorithm can estimate the bathymetry with good accuracy even with sparse flow velocity measurements.

Enhanced safety prediction of vault settlement in urban tunnels using the pair-copula and Bayesian network

To analyze and study the key control factors of the risk of vault deformation in tunnels excavated at small clear distances, a risk assessment method based on a pair-copula Bayesian network (PCBN) model is proposed. Based on an analysis of the factors affecting the settlement of the vault of an excavated tunnel, an index system for the risk assessment of the vault settlement is established. A PCBN model based on a pair-copula function and BN can effectively deal with the complex risk system and the correlation problems within the risk system. Using the constructed PCBN model, a risk analysis of the dome settlement caused by the excavation in the Donghu Tuanshan tunnel in Wuhan is carried out, and the risk status of the dome settlement of the tunnel is determined to be basically safe. It can be determined from this research that a pair-copula correlation concept combined with a BN retains the strength of both concepts, and a safety risk analysis method for the settlement of tunnel vaults based on the PCBN model is proposed to perform real-time and effective safety risk assessment and provide decision support for the shield construction stage. Through a correlation analysis of the risk indicators of the risk system, it is determined that the risk indicators that have the most significant impact on the deformation of the vault are the state of the groundwater, the complexity of the construction environment, the soil quality of the tunnel arch bottom, and the soil quality of the tunnel vault. These risk indicators are used as key risk indicators for decision-making. Based on this method, decision-making suggestions for reducing the risk of vault deformation are proposed. Good results are achieved in project implementation, and safety management of the vault deformation of a small clear excavated tunnel is provided.

Prediction of track settlement at high-speed railway transitions between embankment and bridge in the proximity of a turnout

It is well known that transition zones are subject to high differential settlement rates mainly due to the rapid change in track system stiffness as well as materials used. This problem is even more notable in high-speed lines where the dynamic effects are critical. In this paper, a methodology that combines large FE track models and vehicle-track MBS software with relatively low computational costs is proposed to calculate the long-term track behaviour in transition areas. The substructure dynamic characteristics are captured using an equivalent Lump Parameter (LP) model whose parameters are tuned against the FE track model to correctly reproduce the frequency response of the full track. The dynamic behaviour of the whole system is predicted using the in-house vertical vehicle-track software RailDyn. A settlement algorithm accounting for the development of hanging sleepers is then used in iterative simulations. A typical European high-speed transition zone between embankment and bridge is considered as a case study and various scenarios are analysed, including when a switch is located in proximity. Results show that the cement-bound reinforced and layered design considered creates a smooth increase of stiffness through the transition. On the other hand, localised differential settlement is predicted at the position of change in track stiffness, leading to an increase of stress in the ballast layer and a decrease in the layers beneath. The long-term soil behaviour at the switch panel is found to be completely dissociated from the behaviour at the transition when located at or more than 25 m from the bridge, as is the current practice.

Developing Predictive Models of Collapse Settlement and Coefficient of Stress Release of Sandy-Gravel Soil via Evolutionary Polynomial Regression

The collapse settlement of granular soil, which brings about considerable deformations, is an important issue in geotechnical engineering. Several factors are involved in this phenomenon, which makes it difficult to predict. The present study aimed to develop a model to predict the collapse settlement and coefficient of stress release of sandy gravel soil through evolutionary polynomial regression (EPR). To achieve this, a dataset containing 180 records obtained from a large-scale direct shear test was used. In this study, five models were developed with the secant hyperbolic, tangent hyperbolic, natural logarithm, exponential, and sinusoidal inner functions. Using sand content (SC), normal stress (σn), shear stress level (SL), and relative density (Dr) values, the models can predict the collapse settlement (∆H) and coefficient of stress release (CSR). The results indicated that the models developed with the exponential functions were the best models. With these models, the values of R2 for training, testing, and all data in the prediction of collapse settlement were 0.9759, 0.9759, and 0.9757, respectively, and the values of R2 in predicting the coefficient of stress release were 0.9833, 0.9820, and 0.9833, respectively. The sensitivity analysis also revealed that the sand content (SC) and relative density (Dr) parameters had the highest and lowest degrees of importance in predicting collapse settlement. In contrast, the Dr and SC parameters showed the highest and lowest degrees of importance in predicting the coefficient of stress release. Finally, the conducted parametric study showed that the developed models were in line with the results of previous studies.

Formula of Passive Earth Pressure and Prediction of Tunneling-Induced Settlement in Anisotropic Ground Based on a Simple Method

Formula of Passive Earth Pressure and Prediction of Tunneling-Induced Settlement in Anisotropic Ground Based on a Simple Method

Prediction of Post-Construction Settlement of Road Embankment on Soft Soil Deposits

Organic soils are often considered problematic soils around the world due to several reasons. Excessive settlement is one of the main concerns when constructing infrastructure on soft grounds with organic soil deposits. Ground improvement is mainly carried out on the sub surfaces that lack the strength and stability to bear the structure to be constructed and undergo large settlement during operation. Different soft-ground treatment methods must be applied based on the soil properties to reduce the expected settlements during construction and operation periods. In this context, it is essential to know the behaviour of the subsurface after the ground improvement process. This study mainly investigates the accuracy of the settlement prediction methods during the post-construction stage of the Colombo-Katunayake Expressway Project in Sri Lanka. Settlement prediction was done for the Defect Liability Period using the hyperbolic method, the Mesri method and the Ladd method. A comparison of the predicted settlement with the measured field settlement was done to assess the accuracy of the settlement prediction methods. The comparison showed that the hyperbolic method was more accurate and convenient for predicting the settlement of the embankment. KEYWORDS: Soft ground treatment methods; Preloading; consolidation settlement; Asaoka method; hyperbolic method

Partially-drained deformation properties of anisotropically overconsolidated clay by triaxial tests with cyclic confining pressure

The subgrade clay in situ may be anisotropically overconsolidated, the traffic-induced dynamic stress field on the subgrade clay can be simulated more accurately by the simultaneous application of cyclic axial stress and cyclic confining pressure by the VCP test, and the partially drained condition represents a more appropriate field scenario for the cyclic response of subgrade clays under long-term traffic loading. To mimic the coupling of the above factors, this study performed a large number of cyclic triaxial tests on a overconsolidated clay in partially drained condition. The ratio of the radial consolidation stress to vertical consolidation stress (K), cyclic stress ratio (CSR) and the ratio of cyclic deviatoric stress amplitude to cyclic mean principal stress amplitude (ηampl) are proposed, and their effects on the partially-drained permanent and resilient deformation behaviors of saturated clay are investigated. Test results show that the increase of consolidation-induced anisotropy (i.e., the decrease of K) leads to a remarkable increase of permanent axial strain, while it induces a first slight growth and then a decrease of permanent volumetric strain. Based on the shakedown theory, the allowable cyclic stress ratio separating the shakedown ranges of metastable and stable is determined, and it is unrelated to either K or ηampl. The effects of ηampl on the permanent axial strain are related to the shakedown range, and a uniform linear relationship is established between the permanent volumetric strain and cyclic mean principal stress amplitude. The anisotropically overconsolidated clay produces stiffness hardening in partially drained condition, in which the increase of both CSR and ηampl promote the hardening. It is suggested the prediction and control of subgrade clay settlement in engineering practice should consider all the factors involved in this study.

Prediction and Control Method of Long-Term Vehicle-Induced Settlement of High-Speed Railway Tunnel in Diatomite Stratum

Prediction and Control Method of Long-Term Vehicle-Induced Settlement of High-Speed Railway Tunnel in Diatomite Stratum

A practical approach for modeling twin-tunnel excavation in Ho chi minh city

The prediction of ground settlement under tunnel excavation is still challenge. Almost engineer uses Mohr-Coulomb model in practice due to the conventional geotechnical investigation data. This paper describes the study of tunnel lining behaviors and ground surface settlement under tunneling process with a typical case study of twin tunnels excavation in Ho Chi Minh city, Vietnam. The advanced material model namely Hardening Soil model is used to investigate the proposing twin-tunnel with numerical approach. The internal forces of tunnel lining and ground settlement, which achieved from Hardening Soil model and the available results from Mohr-Coulomb model, are then made comparison between two models which yields some important differences for analysis. Since the experimental works for qualifying stiffness parameters in Hardening Soil model are missed in the Metro Line 1 project in Ho Chi Minh city, an empirical formula is proposed in the paper as a guide for estimating the required data in modelling process

Time series monitoring and prediction of coal mining subsidence based on multitemporal InSAR technology and GSM-HW model

The surface subsidence caused by coal mining will cause serious environmental problems, and an effective monitoring and prediction system is indispensable. Aiming at this phenomenon, a mining subsidence monitoring and dynamic prediction model combining time series stacking differential interferometric synthetic aperture radar (TSS-DInSAR) technology, small baseline subset InSAR technology (SBAS-InSAR), and golden section method-Holt–Winters (GSM-HW) model was proposed. First, based on the nine scene images of Sentinel-1A satellite in the study area, the time series subsidence of 811 work-face in Guobei coal mine from April 5 to July 10, 2021, was obtained using TSS-DInSAR and SBAS-InSAR monitoring technologies, respectively. Then, the original training samples of the GSM-HW model were generated by combining the cumulative surface subsidence results monitored by TSS-DInSAR and SBAS-InSAR, and the monitoring and prediction of surface subsidence were realized using this model. The experimental results show that the application of TSS-DInSAR and SBAS-InSAR monitoring technology to the impact of surface mining in mining areas has certain reliability, and the GSM-HW prediction model can make up for the deficiency of a single HW model in parameter optimization. The maximum fitting accuracy and prediction accuracy of the model for the 10 monitoring pilot sites are 96.9% and 98.4%, respectively, which can provide a reference for the design of surface monitoring and prediction system in the mining area.

Numerical Study on Stratigraphic and Structural Deformation Patterns Considering Surface Load with Pile-Beam-Arch Method Construction

Due to soil disturbance during the construction of metro stations, the initial stress of the stratum is modified, leading to ground settlement within a particular range, fracturing the surrounding buildings and even causing significant ground deformation and building collapse. This paper employed the Pile-Beam-Arch method to assemble the Daguanying Station of Beijing Metro Line 7 as the engineering background. The numerical calculation method was used to study the regulations of ground settlement and structural deformation throughout the construction stage. Meanwhile, the effect of surface loading was taken into account and surface settlement control strategies were suggested. Finally, the Stochastic medium theory was used to predict surface settlement. It was evident from the study’s findings that the pilot tunnels excavation and the arches installation accounted for 67% and 23.1% of the total surface settlement, respectively, and produced the most surface settlement. Surface settlement can be significantly reduced by utilizing grouting reinforcement technology and the pilot tunnels excavation approach of “upper first, then lower and side first, then middle”. The structure was much less stressed during the pre-construction stage, with the maximum principal stress ranging from 1 to 5 MPa; after construction was finalized, the maximum principal stress reached 14.203 MPa, concentrating mostly in the middle column part, which was the consequence of the combined action of the upper load and the lower soil uplift. Additionally, there was a linear relationship between the surface load and ground settlement. The bottom slab and the middle column were situated where the structure’s most unfavorable components were concentrated. The conclusions of the surface settlement prediction demonstrated that there were discrepancies between the theoretical calculation and the simulated; thus, the prediction results were more conservative. The study results can serve as a reference for construction sites.

Evaluation of Asaoka and Hyperbolic Methods for Settlement Prediction of Vacuum Preloading Combined with Prefabricated Vertical Drains in Soft Ground Treatment

This study evaluated the use of the Asaoka and hyperbolic methods to estimate the ultimate settlement of soft ground treated by vacuum preloading combined with prefabricated vertical drains. For this aim, a large-scale physical laboratory model was constructed. The model was a reinforced-tempered glass box containing a soil mass with dimensions of 2.0 × 1.0 × 1.2 m (length × width × depth). Physical models of this scale for the same purpose are rare in the literature. The soil was taken from a typical coastal region in Dinh Vu Hai Phong, Vietnam. The surface settlement near and between the two drains was measured right after the vacuum preloading started. Important properties of the soil were tested to evaluate the effectiveness of the treatment method. The measured settlement was used in the Asaoka and hyperbolic methods to predict the potential ultimate settlement. The results showed the superiority of the vacuum consolidation approach in improving fundamental engineering properties of soft soil. Furthermore, the ultimate settlement predicted by both methods showed a good agreement with the measured value, proving that the Asaoka and hyperbolic methods are suitable for the estimation of the ultimate settlement of soft soil treated with vacuum consolidation.

Normality Test for Influence Function of Mining Surface Subsidence Based on Network Observation Station

Coal is the primary energy source in China, while underground mining is the mainstream way of coal mining. By triggering surface movement and deformation, underground mining can cause damage to arable land, buildings, roads, and so on, which is detrimental to the ecological environment in the mining area. In order to assess the severity of damage caused by this to the ground buildings and ecological environment in the mining area, it is necessary to predict mining-induced surface subsidence before the mining activities are carried out. Currently, the most used prediction method is the Probability Integral Method. It is based on probabilistic theory to mathematically demonstrate that the surface downwelling caused by underground extraction conforms to normal distribution. However, there is a lack of validation with measured subsidence basin data. Since the 1960s, China has been paying increased attention to the study of mining subsidence. However, there are still few network stations built across China to monitor subsidence basin. Herein, SPSS software is applied to re-analyze these valuable historical data. By analyzing the observation results and comparing them with the calculation results as obtained by using the probability integral method, it can be found out that the surface subsidence in the center of the subsidence basin conforms to normal distribution, not the subsidence at the edge of the subsidence basin. Therefore, it is inevitable for errors to occur at the edge of the subsidence basin when the normal distribution function is used as the mining influence function to calculate the surface subsidence. This conclusion is expected to provide practical reference for the prediction of surface subsidence in coal mines, and this experience can be extended to the mining of other solid minerals.