Uneven Settlement Research Articles

Full-Scale Loading Test of Jet Grouting in the Artificial Island–Immersed Tunnel Transition Area of the Hong Kong–Zhuhai–Macau Sea Link

In the Hong Kong–Zhuhai–Macau Bridge mega project, several ground treatment methods were applied in the transition area between the artificial island and immersed tube tunnels to reduce the potential uneven foundation settlement underlying the tunnel, as the backfilled sand layer is more than 10 m around it. One of the foundation improvement methods involves the combination of preload and high-pressure jet grouting (HPJG) columns. Current field tests, such as core bowling, standard penetration test, and plate loading test, are not suitable for evaluating the strength of this reinforced foundation. This study presents a full-scale load test to examine the construction quality and effects of an HPJG-reinforced foundation. A novel method was designed based on the Boussinesq equation to simulate the additional stress distribution from the immersed tube tunnel. The tangent modulus method considering the impact of modulus nonlinearity was employed to calculate the nonlinear settlement of the treated foundation. Preferable settlement results were obtained using a set of pre-embedded high-precision hydrostatic leveling systems. Both the measured data and calculated settlement demonstrate the reasonableness of the present in situ test.

Adaptability Evaluation of Rotary Jet Grouting Pile Composite Foundation for Shallow Buried Collapsible Loess Tunnel

The deformation control effect of loess tunnel composite foundation plays an important role in optimization design and reinforcement effect evaluation. Systematically evaluate the adaptability of the composite foundation of jet grouting pile in shallow collapsible loess tunnel. Taking the shallow buried section of Fujiyao Tunnel with a buried depth of 20 m as an example, using MIDAS finite element numerical simulation software, the foundation deformation control during construction and settlement control after construction are systematically studied, the differential deformation control is analyzed, and the reinforcement effect of the tunnel bottom is evaluated. The results show that the uplift displacement can be controlled by changing the pile length and increasing the replacement ratio. The combination of long and short piles can significantly reduce the uneven settlement and plastic zone of the foundation. The uneven settlement of 9 mm can be used as the evaluation index of the composite foundation reinforcement effect in a shallow buried section of the loess tunnel.

Extended UH model and deformation prediction of high-speed railway subgrade

For the rapidity of trains in high-speed railway, it is crucial to guarantee the reliable and safe operation. Strict controls are needed to prevent excessive subgrade deformation. In order to perform more accurate subgrade deformation calculation, the constitutive model used in simulation should demonstrate the small-strain stiffness for uneven settlement calculation, and illustrate time-induced deformation for post-construction deformation. An E-UH model is established based on the original UH model. In the E-UH model, the elastic hysteresis relation is added to describe the initial high stiffness and nonlinear stiffness decay. In addition, the E-UH model also couples the equivalent formula between overconsolidated characteristics and time-induced deformation. Then the effectiveness of this new model is testified by element test prediction. By means of the second development interface of a finite element software, the E-UH model is developed as a subroutine and applied to numerical simulation of subgrade deformation. The simulation represents that the E-UH model is capable of performing deformation prediction during the subgrade construction and post-construction phases, and indicates that considering small-strain stiffness can make the uneven settlement more prominent. This research provides a practical and efficient constitutive model for numerical simulation of the high-speed railway subgrade deformation.

Stability analysis and numerical simulation of foundation in old goaf under building load

This study comprehensively analyzes the safety and stability of old goaf under construction engineering based on specific projects using a variety of research methods. The Beijing Mentougou mining area is used as the research background. The methods of field investigation, laboratory testing, engineering drilling, geophysical exploration, theoretical calculation, and numerical simulation are combined to quantitatively analyze the stability of the foundation and ground buildings in old goaf. The influence depth of the building load and height of the caving crack zone are calculated using the “three-zone theory” to judge if the goaf is at risk of activation. Further simulation is conducted using two types of finite element analysis software, which increases the reliability of the numerical analysis. The results demonstrate that uneven subsidence of approximately 100 mm occurs in the buildings and ground surface, and subsidence of approximately 50 mm occurs in the goaf roof. It is also proven that goaf affects the stability of the surrounding rock and building foundation. Finally, a goaf treatment scheme is proposed. The treatment effect is found to be remarkable through field tests and numerical simulations, ensuring the safety and stability of a building foundation. The combination of theoretical calculation and numerical simulation can effectively evaluate the safety and stability of the project under load, and has a strong promotion and application value. The research results meet the needs of engineering practice, and provide a great reference value for the rational utilization of the land above the old goaf in the Mentougou district of Beijing and similar mining cities, which has a good theoretical significance and application prospect.

Embankment deformation characteristics analysis of an expressway widening project near a pond

New and old subgrade stability is a crucial problem for widening projects in soft soil foundations because uncoordinated deformations can cause serious engineering accidents, even disasters. In order to ensure the stability of a widening expressway project near a pond in the Qinbei section, a series of on-site investigations, lab tests, and numerical analyses was performed. The settlement and displacement of on-site monitoring were carried out during the construction period to verify the analyzed results. It was found that the uneven settlement caused heavy settlement and displacement of the embankment; thus, net cracks and longitudinal cracks occurred in the expressway. The new embankment was also affected by the weak foundation; therefore, the foundation should be reinforced before the construction of the widening part. Considering the economy and effectiveness of the widening project, the replacement method was recommended for the weak foundation reinforcement based on the numerical analysis and on-site motoring results. Water pumping had a significant effect on the settlement of the embankment. Water pumping caused seepage in the foundation and increased the effective stress of the soil, making the foundation more consolidated. The pond slope should be reinforced before the construction of the embankment because it was not confined by the surrounding soil. Therefore, the slope soil could not provide sufficient passive soil pressure and easily slide.

Mechanical properties of film-bag sand cofferdam: theoretical analysis and numerical study

ABSTRACT To study the mechanical properties of the membrane bag sand cofferdam under the action of geotextile hoop during the construction, the theoretical derivation of the film-bag sand enhancement mechanism was carried out firstly. A finite element model of sand blowing cofferdam with measured material parameters was established based on the ANSYS platform, and then different pipes were used to calculate the bag height under self-weight and external load, and the variation law of self-weight and external load, as well as the sand blowing cofferdam under different concrete slab thickness was analyzed. The main conclusions include: (1) The relationship between the height of the membrane sandbag and the tensile force of the soil sandbag is proposed, the relationship between the shape of the sandbag and the external load is further deduced. (2) The axial tension of the type bag is proportional to the quadratic of the height of the type bag sand without considering the friction condition. (3) As the concrete slab thickness increases, the vertical settlement of the blown sand cofferdam gradually decreases under the action of the cast-in-place bracket, and the reduction of the uneven settlement in the cross-bridge direction is greater than that of the vertical settlement.

Selection of equipment for oil tank repair in northern conditions

Introduction. The oil industry is a key component of the economy of the Russian Federation. A large number of tanks are used to store oil, each of which needs timely repair. According to the results of some research, almost half of the accidents are caused by excess uneven settlement of the tank, which causes premature failure. To restore the serviceable and operable condition of the tanks, it is necessary to carry out repair work, the quality and efficiency of which depends on the repair equipment used. An urgent task is to justify the choice of equipment for the repair of tanks, in particular, steel tanks of a vertical type.Methods and materials. A review of the different types of tanks was carried out and showed that vertical steel tanks are the most widely used. One of the ways to eliminate the uneven settlement of the tank is to raise it with the help of jacks and form a new base with the elimination of the slope.Results. The repair process for a 10,000 m3 steel vertical tank was considered. The values of the mass of the tank were obtained when filling with liquid petroleum products at 1% of the maximum occupancy. The value of the load on one lifting device is obtained. The design of the device structure and the strength calculation in the Compass 3D program were completed.Сonclusions. The most efficient type of the lift from the existing ones was determined, and its design was modernized. The strength calculation showed that the hydraulic lift is efficient under the given conditions.

Optimal design of FBG flexible sensor for high-precision monitoring of three-dimensional deformation of power transmission line tower foundation

During the operation of the power transmission line tower foundation, uneven settlement and horizontal sliding were formed due to the damage of the local environment or external force. It is the most direct and effective way to realize the transformation from “passive response” to “active prevention and control” by real-time and long-term monitoring of the tower foundation and providing automatic early warning. In this paper, based on FBG (fiber Bragg grating) sensing technology, a FBG flexible sensor with temperature self-compensation characteristic was developed, which can be used for real-time monitoring of three-dimensional deformation field of tower foundation. Based on the strain information measured by the sensor, a coordinate transformation fitting algorithm was applied to reconstruct the deformation field of the tower foundation. To improve the displacement sensing precision of the flexible sensor, the influence of the length of the cemented layer and the groove radius on the strain transfer coefficient was analyzed, and the orthogonal curvature obtained by the sensing point was corrected by cubic spline interpolation. In the displacement sensing experiment, the mean absolute errors along the x-axis direction after interpolation correction were 1.84 mm (Type 1), 1.52 mm (Type 2) and 1.96 mm (Type 3), respectively; the mean absolute errors along the y-axis direction were 1.64 mm (Type 1), 2.34 mm (Type 2) and 1.21 mm (Type 3), respectively. After interpolation correction, the maximum absolute error percentages of the measuring points along the x-axis were 9.62% (Type 1), 9.01% (Type2) and 10.23% (Type 3); the maximum absolute error percentages along the y-axis were 10.44% (Type 1), 9.53% (Type2) and 9.43% (Type 3). Therefore, the designed FBG flexible sensor can be competent for the task of monitoring the three-dimensional deformation field of the tower foundation, which has important significance and application promotion value.

Analysis of the influence of uneven settlement on the existing shield tunnel lining

The transverse deformation of the tunnel under various loads is unavoidable with the long-term operation of the subway, and the problem of uneven settlement is gradually highlighted. A three-dimensional of tunnel lining model is established in ABAQUS to simulate the uneven settlement and transverse deformation on the safety performance, in which the deformation, internal force, and damage are further analyzed. Based on the simulation, safe settlement values for the shield tunnel with different level of existing transverse deformations (L) are suggested. Because the internal force and damage are not only related to the settlement value (∆) but also to the length of the tunnel where the settlement occurs, the ratio of the settlement value (∆) to the corresponding length (L) of the shield tunnel ∆/L which is called the uneven settlement coefficient is proposed as an index. The uneven settlement coefficient ∆/L is given for different transverse deformations to extend the applicability of the safe settlement values, which provides theoretical support for on-site monitoring and tunnel maintenance to some extent.

Influence of Shield Tunnel Oblique Penetration Construction on Existing Large‐Span Masonry Structures

When the shield tunnel obliquely penetrates the large‐span masonry building, the ground deformation caused by shield construction may cause the risk of deformation and cracking of the existing masonry structure held above. Based on a shield tunnel obliquely penetrating a large‐span masonry building in Zhengzhou, a three‐dimensional finite element model of building‐stratum‐shield tunnel interaction was established by MIDAS‐GTS, and the laws of settlement, deformation, and damage of the building were studied. Results show that when the first line (left line) of the tunnel is penetrated, the settlement groove along the horizontal direction of the building presents a “V” shape, while after the second line (right line) is penetrated, which changes from “V” shape to “W” shape, and the maximum settlement value of the building caused by the first line can account for about 2/3 of the total settlement value. The maximum tensile strain of both the building’s south and north walls occurs at the bottom of the wall within the range of the tunnel, which develops upward and gradually weakens. Influenced by the oblique crossing angle, the maximum positions of settlement and strain for the building’s front and rear walls are offset to some extent. With the masonry building’s stiffness increasing, the uneven settlement of buildings decreases linearly, and with the tunnel oblique crossing angle increasing, the uneven settlement increases exponentially, while with the tunnel buried depth increasing, the uneven settlement shows an exponential downward trend.

Post-Foundation Studies Using Integrated Geophysical and Geotechnical Methods at New Agbor Road, Uromi, Edo State, Nigeria

Globally, the incessant failure of buildings has drastically led to an increase in the loss of lives and properties, posing lots of concerns about the causes of these devastating effects. This research evaluates the immediate and remote causes of probable foundation failure on some buildings at Ohunyon Street, Uromi, Edo State, using integrated geophysical and geotechnical methods. By optimizing the measured field, calculating the apparent resistivity data, and interpreting the generated electrical resistivity tomography by using the SAS 1000 terrameter and RES2DINV software, a variation in soil resistivity and type was established. The geotechnical method required performing Atterberg limit-index studies on the gathered soil specimens in the region as well as geological laboratory grain size analyses. The pole-dipole results showed two weak zones and one moderately competent zone, whereas the dipole-dipole results revealed three primary layers: topsoil (sandy clay), clayey loam, and silty loam. The results also revealed regular clay permeation within the loam at depths ranging from 0.9 to 1.9 m, indicating yearly wetness, volumetric expansion, shrinkage, and uneven ground settlement. The geotechnical survey results provided useful information on both the textural soil test and the Casagrande soil analysis. All of the results were highly correlated, providing pertinent information regarding the factors responsible for the buildings’ failure and recommending that the foundations of these buildings be reinforced by piling to depths of 2 m (6.6 ft) below the ground surface in order to prevent future failures. This work has distinctly shown how integrated geophysical and geotechnical methodologies can potentially be used to evaluate subsoil competency.

Linear Dynamic Analysis and Design of Raft Foundation considering Long-Term Deflection and Uplift Check

The Mat or Raft Foundations are widely used these days because we cannot use isolated footings and combined footings everywhere. As the spacing of the column is not uniform in the actual structures it may result in large uneven settlements at the base of the high-rise buildings. In a Mat foundation load from the superstructure is distributed evenly on the soil and uneven deflection is eliminated. Mat or raft foundation can be used with drops or without drops and with beams or without beams. For structures built on low-bearing capacity soil raft foundations, it is a good alternative as it reduces the settlement by distributing loads from super-structure to very large. In this study, the analysis and design of Mat Foundation for a G+7 story building are done by considering long-term deflection and uplift pressure accounts. For this study, Etabs v19.1.0 and Safe v20.0.0 software is used. The analysis is done by performing Response Spectrum Analysis or Linear Dynamic Analysis. After the analysis, results are collected in terms of short-term deflection, Uplift Pressure, long-term deflection, and punching shear and compared with permissible limits specified by the code IS 1904 (Part-1):1986. Results show that all values like deflection, uplift pressure and punching shear are under the permissible limits.

Stress-strain state of base strip foundation strengthening with a structure combined with a blind area

The article discusses a modified strengthening construction of the strip foundation, combined with a blind area, which makes it possible to increase the efficiency of this strengthen method. The results of experimental studies to verify the operability of structural protection measures are presented, and also to obtain the basic regularities of the stress-strain state of the foundation construction of a frameless building operated on an unevenly deformable base. The results of numerical studies for two cases are presented: strip foundation without strengthening construction, and strip foundation with strengthening construction. As a result of numerical studies, the dependences of the average vertical movements of the footing of the strengthened and non- strengthened foundation on the load, as well as its full bearing capacity in both cases, were obtained. The most effective application of this strengthening construction is in conditions in which the maximum critical pressures can be reached on certain sections of the strip foundation. For example, with significant uneven settlements along the length of the strip foundation.

Isogeometric Analysis of Longitudinal Displacement of a Simplified Tunnel Model Based on Elastic Foundation Beam

Serious uneven settlement of the tunnel may directly cause safety problems. At this stage, the deformation of the tunnel is predicted and analyzed mainly by numerical simulation, while the commonly used finite element method (FEM) uses low-order continuous elements. Therefore, the accuracy of tunnel settlement prediction is not enough. In this paper, a method is proposed to study the vertical deformation of the tunnel by using the combination of isogeometric analysis (IGA) and Bézier extraction operator. Compared with the traditional IGA method, this method can be easily integrated into the existing FEM framework, and ensure the same accuracy. A numerical example of an elastic foundation beam subjected to uniformly distributed load and an engineering example of an equivalent elastic foundation beam of the tunnel are given. The results show that the solution of the IGA method is closer to the theoretical solution of the initial-parameter method than the FEM, and the accuracy and reliability of the proposed model are verified. Moreover, it not only provides some theoretical support for the longitudinal design of the tunnel, but also provides a new way for the application and popularization of IGA in tunnel engineering.

Forecast of differential settlement of structures using data of monitoring system

The article analyzes the results of observations of uneven settlement of various buildings, obtained in the course of long-term observations with the help of automated systems of deformation monitoring. The main purpose of the work is to evaluate the possibilities of predicting sedimentary processes using statistical forecasting models. Emphasis is placed on approach using time series analysis algorithms. The results of simulation using the integrated autoregressive moving average model are demonstrated. To build a forecast, data on the foundation settlement over a 5-year period were used. Predictive values obtained for 1-year and 2-year intervals are compared with the data of real observations. The comparison showed that at the chosen forecasting horizon, the deviation of the predicted settlement value from the actually observed one is comparable to the accuracy of sediment measurement by hydraulic leveling sensors. The study showed the promise of using this approach to predict the integrity of structures within the framework of an automated system of deformation monitoring.

Evaluating the efficiency of rail gauge maintenance in Siberia

The state of gauge geometry is the basis for safe and uninterrupted train operations under the mixed traffic conditions, as well as in the sections where trains with increased weight and length, including wagons with an increased axle load, are handled. When passing such trains, the state of gauge geometry deteriorates. This leads to increased labour costs for track maintenance, which is also caused by climatic features. Under such conditions, it is important to carry out effective gauge maintenance works. To analyse an impact of maintenance on gauge geometry, it is offered to determine the effect of uneven settlement of the under sleeper base in spring on the dynamics of each type of deviation. To evaluate the efficiency of preventive track alignment in the plan and profile, an analysis of graphical charts for the state of gauge geometry depending on track maintenance by gangs of track fitters and preventive track alignment by machine systems was carried out. It is also revealed that the efficiency of preventive alignment is significantly reduced under harsh climatic conditions, especially for the tonnage handled exceeding 600 million tonnes gross, and should therefore be carried out more frequently.

Analysis of Uneven Settlement and Deformation of the Existing Railway under the Condition of Mined-out Area after Mining

Analysis of Uneven Settlement and Deformation of the Existing Railway under the Condition of Mined-out Area after Mining

Mapping Tunneling-Induced Uneven Ground Subsidence Using Sentinel-1 SAR Interferometry: A Twin-Tunnel Case Study of Downtown Los Angeles, USA

Synthetic Aperture Radar (SAR) interferometry is a formidable technique to monitor surface deformation with a millimeter detection resolution. This study applies the Persistent Scatter-Interferometric Synthetic Aperture Radar (PSInSARTM) technique to measure ground subsidence related to a twin-tunnel excavation in downtown Los Angeles, USA. The PSInSARTM technique is suitable for urban settings because urban areas have strong reflectors. The twin tunnels in downtown Los Angeles were excavated beneath a densely urbanized area with variable overburden depths. In practice, tunneling-induced ground settlement is dominantly vertical. The vertical deformation rate in this study is derived by combining Line of Sight (LOS) deformation velocities obtained from SAR images from both ascending and descending satellite orbits. Local and uneven settlements up to approximately 12 mm/year along the tunnel alignment are observed within the allowable threshold. No severe damages to aboveground structures were reported. Furthermore, ground movements mapped one year before tunnel construction indicate that no concentrated ground settlements pre-existed. A Machine Learning (ML)-based permutation feature importance method is used for a parametric study to identify dominant factors associated with the twin-tunneling induced uneven ground subsidence. Six parameters are selected to conduct the parametric study, including overburden thickness, i.e., the thickness of artificial fill and alluvium soils above the tunnel springline, the distance between the two tunnel centerlines, the depth to the tunnel springline, building height, the distance to the tunnel, and groundwater level. Results of the parametric analysis indicate that overburden thickness, i.e., the thickness of artificial fill and alluvium soils above the tunnel springline, is the dominant contributing factor, followed by the distance between tunnel centerlines, depth to the tunnel springline, and building height. Two parameters, the distance to the tunnel, and the groundwater level, play lesser essential roles than others. In addition, the geological profile provides comprehension of unevenly distributed ground settlements, which are geologically sensitive and more concentrated in areas with thick artificial fill and alluvium soils, low tunnel depth, and high groundwater levels.

Experiments and Modeling of the Attenuation of the Dynamic Elastic Modulus of Saturated Red Clay under Cyclic Loading

Due to the long-term effect of cyclic traffic loads, the accumulated deformation of red clay subgrades is increasing, strength is decreasing, and problems such as uneven settlement are occurring. In order to improve the stability and durability of red clay subgrade, this paper analyzes the effects of cyclic stress ratios and compactness on the development of the dynamic elastic modulus of saturated red clay. This is achieved through dynamic triaxial tests on red clay in the Qingyuan County, Zhejiang Province, China. The results show that the saturated red clay has an attenuation threshold cyclic stress ratio under cyclic loading. The attenuation threshold cyclic stress ratio prediction models were constructed based on the confining pressure and compactness, respectively. By introducing the concept of a relative cyclic stress ratio, the prediction model of the dynamic elastic modulus of saturated red clay (as based on cyclic vibration times and close cyclic stress ratio) is constructed. The model realizes the prediction of the dynamic elastic modulus of red clay under arbitrary cyclic vibration times via the initial cyclic stress ratio, compactness, and other parameters. It provides a theoretical basis for rationally evaluating the dynamic stability of red clay subgrade under cyclic loading.

Asymmetric talik formation beneath the embankment of Qinghai-Tibet Highway triggered by the sunny-shady effect

Energy budget beneath the road embankment strongly impacts the permafrost thermal state and stability of the overlying infrastructure. However, magnitudes and rates of daily heat flux caused by the sunny-shady effect are poorly understood. Herein, we investigated the sunny-shady effect on heat flux characteristics of road embankments through long-term observations and numerical simulation. Simulated and observed soil temperatures at depth were in good agreement over the 2007–2012 period. Simulated results show that maximum differences in the annual heat budget were 19.8 MJ/m2, 61.3 MJ/m2, and 103.2 MJ/m2 for the cases with the mean annual near-surface ΔT of 1 °C, 3 °C, and 5 °C, respectively, in comparison to the reference case without the sunny and shady effect. These processes triggered the talik initiation and development on the sunny side and enlarged laterally and vertically. Talik area for the ΔT of 5 °C was more than 5 times larger than that of 1 °C. Finally, the sunny and shady effect can cause asymmetric road damage, such as uneven settlement and longitudinal cracking. The net finding is potentially helpful for better understanding differential embankment deformation, as well as for improving the design of the engineered mitigation measures.