Subgrade Settlement Research Articles

Analysis on dynamic behavior of 400 km/h high-speed train system under differential settlement of subgrade

Whether the existing ballastless track subgrade settlement control standard of 350 km/h is applicable to the high-speed train of 400 km/h remains to be further research. This paper established a complete rigid flexible coupling dynamic model of vehicle-track-subgrade space based on the finite element method and multi-body dynamics theory. Combined with the fixed interface modal synthesis method and wheel/rail contact theory, the joint simulation of ABAQUS and UM is realized. The dynamic response of 400 km/h high-speed train under the condition of subgrade differential settlement is analyzed and compared with the current 350 km/h high-speed train. The results show that under the same subgrade differential settlement condition, when the train speed increases from 350 km/h to 400 km/h, the wheel rail interaction increases significantly, but does not exceed the specification limit. The amplitude of derailment coefficient is far lower than the maximum specification limit, while the amplitude of wheel load reduction rate exceeds the quasi-static limit in the specification. The impact of the increase of train speed on the lateral stability of the vehicle is greater than that on the vertical stability of the vehicle. At 400 km/h, each stability index of the train does not exceed the maximum specification limit, and sufficient safety margin is reserved. The increase of train speed has a great impact on the vertical acceleration of rail, and has little impact on the vertical acceleration of track plate and baseplate. In summary, the current subgrade settlement control standard of 350 km/h high-speed railway is also applicable to 400 km/h high-speed trains, and there is room for further speed increase.

Inversion and identification of vertical track irregularities considering the differential subgrade settlement based on fully convolutional encoder-decoder network

Differential subgrade settlement plays a key role in the formation of track geometry and significantly affects the running performance of a moving vehicle. This work therefore contributes to the on-line inversion of the track irregularities and the differential subgrade settlement hidden in the track irregularities is further excavated. To achieve the above goal, a vertically vehicle-track-subgrade coupled dynamics model with high accuracy and efficiency is first established by introducing the Green’s function method. The track irregularities are then generated by a probabilistic model and the rail deflections caused by the settlement are also accounted for. The vertical accelerations of the vehicle excited by track irregularities and various vehicle speeds are subsequently derived. On this basis, a 1-D fully convolutional encoder-decoder network is constructed to predict the track irregularities by treating the acceleration data as the network inputs. A total of seven scenarios involving different input variables are investigated and the results show that when the wheelset, bogie and car body accelerations are simultaneously considered in network training, the prediction performance achieves the optimum. Meanwhile, the network robustness with respect to various vehicle speeds and degradation levels of track irregularities is also demonstrated. Finally, a time–frequency unification method is employed to identify the settlement locations and wavelengths from the predicted track irregularities. Two cases are conducted to further illustrate the effectiveness of the presented settlement identification method.

Deformation Analysis of the Cable Reinforcement System of Large Section Box Culvert Roof Entry and Downward Penetration

For the underpass railway large-section box culvert jacking and pipe jacking project, the key to ensuring the normal operation of the existing railway is to maintain the smoothness and stability of the track, railway settlement monitoring and line reinforcement, and box culvert and pipe culvert attitude control are the keys to solving this problem. Taking the Beijing-Harbin high-speed railway project under a city road in Beijing as an example, the law of railway track settlement during the implementation of box culvert jacking was analyzed according to real-time monitoring data. The monitoring results show that accelerating the pouring of the bedding and grouting and strengthening the railway subgrade on both sides of the foundation pit can effectively control the settlement of the railway subgrade and reduce the impact of subsequent construction on the railway, and the line renovation and secondary grouting reinforcement can effectively improve the smoothness of the railway. Combined with the comparative analysis of numerical simulation results, the necessity of line refurbishment and rail fastening combination reinforcement in actual construction is verified.

Application of Spot Quality Evaluation in Subgrade Settlement Monitoring and Measurement System

Application of Spot Quality Evaluation in Subgrade Settlement Monitoring and Measurement System

Study on Railway Subgrade Settlement induced by an Ultra-Large-Diameter Shield Tunnel Crossing under Railway Subgrade

This paper presents a study on the influence of the construction of an ultralarge-diameter shield tunnel undercrossing the existing high-speed railway using the empirical method, numerical analysis method, and geotechnical centrifuge model experiment based on the Wuhan Lianghu Highway Tunnel project. The comparison of the results obtained from the three methods shows first, that the results obtained from the centrifuge model experiment and numerical simulation match well with the results obtained from the empirical method for the worst-case scenario and the most likely scenario, which are consistent with the unfavorable geological and construction conditions modeled in the centrifuge test and the possible geological and construction conditions modeled in numerical simulation. Second, both the results obtained from the numerical method and the centrifuge model experiment show that the asymmetry of the settlement of railway subgrade was induced by a shield tunnel, while the asymmetry of railway subgrade settlement curve is gradually weakening with tunneling. Third, the maximum settlement of the railway subgrade could vary between 20 mm (in the most likely scenario) and 65 mm (in the worst scenario). Both the results from the centrifuge test and the numerical simulation show that the allowed value of maximum differential settlement along the railway subgrade (5 mm/10 m) would be exceeded when the tunnel excavation passes the first track at 10 m. It indicates that some mitigation measures should be taken for controlling the influence of the construction of a shield tunnel, especially when the shield tunnel machine is about underneath the pass railway subgrade. It is suggested that the shield machine should underpass the railway subgrade during the skylight period of railway operation.

Dynamic evaluation of vehicle-slab track system under differential subgrade settlement in China's high-speed railway

Differential settlement is inevitable in soil subgrade which has a direct impact on the service performance of ballastless track systems and the running quality of high-speed trains. In order to estimate the effect of differential subgrade settlement on the dynamic performance of the vehicle–slab track system, a detailed theoretical model considering nonlinear subgrade support and track weight is established. The filtering effect of the layered composite track structure on the subgrade settlement is taken into account. Related dynamic performance indexes are evaluated in terms of running safety and ride comfort of high-speed trains as well as the dynamic performance of the infrastructure, to obtain a control threshold of the differential subgrade settlement for the slab track system of China's high-speed railway. The results show that the uncoordinated deformation between the slab track and the subgrade has significant influence on the dynamic characteristics of the system. Compared with the running safety, the ride comfort of the vehicle and the dynamic performance of the track structure are more susceptible to the differential subgrade settlement. The relative short-wave differential settlement below 20 m has significant impact on the track and subgrade vibration, especially the dynamic rail displacement. The differential settlement with a wavelength above 20 m is more detrimental to the car body acceleration, namely the ride comfort. In particular, a sensitive wavelength of the differential subgrade settlement at 10–20 m poses a high jumping derailment risk to the running safety. Accordingly, the dynamics-based control thresholds of differential subgrade settlement are put forward for different settlement wavelengths.

Variation of water bodies along highways in the Qinghai–Tibet Plateau over the past 20 years: A case study of G109 and G219

Abstract The water bodies existing along highways in the high altitude areas of the Qinghai–Tibet Plateau (QTP) will aggravate subgrade settlement and road damage, and affect the long-term stability of road networks. Based on remote sensing and geographic information system (GIS) techniques, this study analyzed the changes in the number and area of water bodies along the G109 and G219 highways in the QTP in the past 20 years. The results showed that between 2000 and 2019, the number of water bodies along the two highways increased by 24 and 19%, respectively, and their area increased by 26 and 19%, respectively. The area and the number of water bodies >1 km2 in the permafrost area and those <1 km2 in the seasonal permafrost area both changed significantly. The change in the number of water bodies in the permafrost area was positively correlated with annual average temperature, while that in the seasonal permafrost area was significantly positively correlated with annual precipitation. This study provided basic data that could be used in studies on the interrelationship between engineering and water bodies within the context of climate change and will contribute to revealing the mechanisms through which engineering projects affect frozen soils.

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.

Accumulative Plastic Deformation of the Improved Completely Weathered Granite Subgrade in High-Speed Railway

The improvement and reuse of completely weathered granite (CWG) with poor engineering properties for backfilling embankments can help protect the environment and bring great economic benefits. The embankment of high-speed railways demands an extremely low additional subgrade settlement under long-term dynamic loads. To analyze the applicability of the improved CWG used for subgrade filling, a series of laboratory dynamic triaxial and field cyclic loading tests were carried out. On the basis of the test results, a calculation model of accumulative plastic strain considering the dynamic stress ratio and the cement content was established. Using the proposed model and the numerically calculated dynamic stress, the accumulative plastic deformation of an embankment filled with improved CWG under various driving conditions was calculated and discussed. The variation of accumulative plastic deformation of the improved CWG with loading cycles could be described by a power function. The dynamic stress level had a significant influence on the accumulative plastic strain, and the strain in the bottom layer of the subgrade bed was greatly attenuated. Accordingly, most of the accumulative plastic deformation attenuation occurred within the depth range of the subgrade bed. The final total accumulative plastic deformations of the embankment were less than 2 mm (5 mm for the limit value) after 4 million times of high-speed train loadings, proving that the improved CWG can be used for subgrade filling. The influence of the axle load on accumulative plastic deformation was more significant than that of the train speed. The proposed calculation model of the accumulative plastic strain could provide valuable reference for similar railway engineering.

Numerical Analysis of the Influence of Foundation Replacement Materials on the Hydrothermal Variation and Deformation Process of Highway Subgrades in Permafrost Regions

Affected by global warming, permafrost thawing in Northeast China promotes issues including highway subgrade instability and settlement. The traditional design concept based on protecting permafrost is unsuitable for regional highway construction. Based on the design concept of allowing permafrost thawing and the thermodynamic characteristics of a block–stone layer structure, a new subgrade structure using a large block–stone layer to replace the permafrost layer in a foundation is proposed and has successfully been practiced in the Walagan–Xilinji section of the Beijing–Mohe Highway to reduce subgrade settlement. To compare and study the improvement in the new structure on the subgrade stability, a coupling model of liquid water, vapor, heat and deformation is proposed to simulate the hydrothermal variation and deformation mechanism of different structures within 20 years of highway completion. The results show that the proposed block–stone structure can effectively reduce the permafrost degradation rate and liquid water content in the active layer to improve subgrade deformation. During the freezing period, when the water in the active layer under the subgrade slope and natural ground surface refreezes, two types of freezing forms, scattered ice crystals and continuous ice lenses, will form, which have different retardation coefficients for hydrothermal migration. These forms are discussed separately, and the subgrade deformation is corrected. From 2019 to 2039, the maximum cumulative settlement and the maximum transverse deformation of the replacement block–stone, breccia and gravel subgrades are –0.211 cm and +0.111 cm, –23.467 cm and –1.209 cm, and –33.793 cm and –2.207 cm, respectively. The replacement block–stone subgrade structure can not only reduce the cumulative settlement and frost heave but also reduce the transverse deformation and longitudinal cracks to effectively improve subgrade stability. However, both the vertical deformation and transverse deformation of the other two subgrades are too large, and the embankment fill layer will undergo transverse deformation in the opposite direction, which will cause sliding failure to the subgrades. Therefore, these two subgrade structures cannot be used in permafrost regions. The research results provide a reference for solving the settlement and deformation problems of subgrades in degraded permafrost regions and contribute to the development and application of complex numerical models related to water, heat and deformation in cold regions.

Laboratory Experiments and Numerical Simulation Study of Composite-Material-Modified Loess Improving High-Speed Railway Subgrade.

Construction of high-speed railway subgrade on loess soils in the Loess Plateau is risky because such soil is susceptible to differential settlements. Various soil-improvement methods have been used to enhance the mechanical properties of loess. Lime-ash soil and cement-lime soil are the most commonly used methods in the improvement of loess subgrade, while few studies have been found on loess subgrade improvement by using composite material consisting of traditional materials and new materials. A series of direct shear tests and unconfined compressive tests were conducted on the loess specimen with the addition of three kinds of composite materials: traditional material cement, new material polypropylene fiber and SCA-2 soil curing agent. The numerical simulation was conducted on loess subgrade in an actual engineering practice. The experimental results show that cement, polypropylene fiber and SCA-2 soil curing agent can effectively improve the shear strength and compressive strength of loess, and the influence degree is cement > fiber > curing agent. Additionally, based on the relative strength characteristics of the improved loess, an optimal improvement scheme for the composite-material-modified loess was obtained: 16% cement content + 0.5% fiber content + 4% curing agent content. The numerical simulation results revealed that the compressive strength index of the improved loess has a significant impact on the subgrade settlement, and the optimal improvement scheme obtained from comprehensive analysis can effectively improve the settlement of high-speed railway subgrade under vibration load.

Study on the In Situ Test of the Treatment Effect for the Riverbank Soft Soil Subgrade in the Hetao Area

The Inner Mongolia Hetao area has a widely distributed riverbank fluvial soft soil with high groundwater levels and ground surface water. This situation may incur some potential engineering problems for the Linhe-Baigeda section of the Beijing-Xinjiang Expressway, such as subgrade settlement control and waterproofing. In situ experiments were conducted on the site using five subgrade base treatment schemes for subgrade construction. The long-term monitoring of various technical indicators like settlement, earth pressure, pore water pressure, and reinforcement material deformation was carried out. Study results show that the cumulative settlement generated when the double-layer geogrid reinforces the subgrade base is 6.9 cm, which is the smallest among the five subgrade base reinforcement methods, and the cumulative settlement of the subgrade base reinforced with a single-layer geocell is the largest, which is 15.4 mm. The size and distribution of subgrade earth pressure change significantly during farmland irrigation. When the single-layer geocell reinforces the base, the subgrade stress is smaller than that of the other four, and the average earth pressure is 8 kPa. The membrane-pulling effect of reinforcement material significantly disperses the upper load of subgrade backfill soil, and the subgrade settlement control with different base treatment schemes meets the technical requirements.

Subgrade and Pavement Design Strategies for Different Road Settlement Sections

The quality of road engineering construction largely determines the road operation safety and driving comfort. However, in road engineering construction, the settlement of subgrade and pavement has always been an insurmountable problem. Therefore, in road construction practice, targeted treatment should be carried out for the sections prone to settlement, and subgrade and pavement design strategies for these settlement sections should be carried out, so as to reduce the risk of settlement and ensure the improvement of road engineering quality and safety.

Reinforcement Effect Investigation of Geogrids in the Junction between New and Existing Subgrades in Highway Widening

Abstract To investigate the reinforcement effect of geogrids with different laying schemes in subgrade widening, one tested road was selected in northern China, and the subgrade deformation and the geogrid strains were analyzed by field testing, the centrifuge model test, and numerical calculation. It was revealed that the geogrid strain of the construction period was mainly derived from the roller’s compaction. The addition of the geogrid is helpful to prevent shear sliding of the new subgrade. In the centrifugal model test and numerical calculation, the geogrid reinforcement was proved to be effective in reducing the settlement of the new subgrade, but little effect to the existing one. Strain of the lower geogrid layer was generally larger, and the connection line of maximum strain points in each layer is close to the shear-sliding location of the new subgrade. The reinforcement effect of different geogrid layers changed noticeably, and the bottom one played a major role in withstanding the tensile stress.

Assessment of the Landfill Barrier System through Numerical Analysis: Rehabilitation and Expansion of Belgrade Landfill Case Study

There are still many unmanaged landfills around the world that pose significant potential environmental problems. One of the largest unmanaged landfills in Europe, which has been used for more than 40 years to deposit waste from Serbia’s capital, Belgrade, is the Vinča landfill. A revitalization and extension of this landfill was proposed that would allow its sustainable operation in the future. The revitalization project considered building a capping layer on the surface of the current landfill, which will close it and which will serve as a liner on the bottom of the new landfill. The use of a composite system including a HDPE geomembrane is considered in the project. New landfill settlements were predicted using the FEM method utilizing a Hardening-soil constitutive model for subgrade. Both immediate settlements of subgrade caused by waste deposition and primary consolidation settlement were calculated. The results show that a substantial increase in the settlement of the geomembrane subgrade can be expected during the primary consolidation period, due to the high rate of filling compared to the permeability of the subgrade. The total settlement of the new landfill in its crown is expected to be between 2.73 and 4.52 m. The axial force in the geomembrane will not exceed the tensile strength of the membrane at any time during or after the new landfill operation.

Study of Problems Related to Laying Ballastless Track in the Turnout of Ballasted Track at High-Speed Railway Stations

Due to the complex dynamic interactions of the vehicle-track system in the turnout of high-speed railway stations on a ballasted track, the geometric position of the line changes rapidly. In order to improve the stability of the line, the ballasted track in the turnout area of the stations can be replaced by a ballastless track. Based on the engineering background of laying ballastless track in the turnout area of Zhonglan’s high-speed railway station, this paper studies the subgrade reinforcement scheme, subgrade settlement prediction, and ballasted-ballastless track transition section setting. The result shows that, in order to meet the requirements of laying ballastless track in the turnout area, a reinforcement scheme of subgrade impact rolling, surcharge preloading, and closed water isolation on the subgrade surface is proposed. Based on the commonness and individuality of the grey Verhulst, hyperbola, and Deng Yinger prediction model, this paper optimizes the combination of the three models. The sum of squares of the minimum errors of the combined model is used as the objective function to solve the optimal weighting coefficient, and in this way the combined prediction model is constructed. Through the prediction comparison, we found that the accuracy of the three-model combination prediction model is better than any single- or two-model combination, and its adaptability and reliability are stronger and more reliable. This dynamic analysis model of vehicle tracks was established to carry out the dynamic response analysis under the conditions of fastener stiffness grading transition and ballast glue grading curing ballast bed transition. The results show that the dynamic response indexes under the two transition modes meet the requirements for the smooth running of trains. Due to the convenience of fastener stiffness transition construction and easier replacement, this measure is recommended.

Construction analysis of Guiyang Metro passing across Guiyang Railway Station in karst zone

The Huo-Sha Tunnel of the Guiyang Metro Line 1 in China runs from the Guiyang Railway Station to the Shachong road station, and it passes close to the railway station platform. The minimum distance between the crown and pile foundation is only 2.19 m, and the settlements of existing buildings are strictly controlled, such as pile foundations. Existing comprehensive measures, such as super pipe shed support, surrounding rock reinforcement, inverted arch grouting, and lining strengthening, are stringently adopted to prevent the influence of construction on the operation of station buildings and in-service railways, high-speed railways, and other buildings. In this study, the changing laws related to existing building subsidence, subgrade settlement, station longitudinal displacement variation, and the development trends of lining safety, stability, eccentricity, compression types, and internal force of the lining are analyzed. The following results are presented. The Huo-Sha Tunnel was gradually excavated. The roadbed settlement of the Guiyang Railway Station platform gradually increased, but it did not exceed the existing railway deformation control standards for the subsurface excavation section. The longitudinal distribution of the existing railway settlement is approximately a normal curve after the construction of the secondary lining. The outcome is consistent with the law of the surface settlement trough proposed by Peck, and the range is −50 to 50 m. The stress of the lining is primarily concentrated at the arch waist and crown, the compression types include large and small eccentricities, and the axial force value gradually increases symmetrically from the crown to the arch footing, while the maximum axial force appears at the arch footing, and all control indicators meet the corresponding control standards. The subgrade settlement of the skew section adheres to the deformation control standards of the existing railway of subsurface excavation sections after the stabilization of the secondary lining deformation.

Numerical Analysis of the Influence of Block-Stone Embankment Filling Height on the Water, Temperature, and Deformation Distributions of Subgrade in Permafrost Regions

The hydrologic and thermal states of foundation soils have an important influence on subgrade stability in degrading permafrost regions. However, thawing settlement remains a problem in the permafrost regions of Northeast China, because there are few relevant research results in this area, and the foundation deformation mechanism caused by the hydrologic and thermal changes of foundation soils is not clear. Therefore, a subgrade structure with large block stones as embankment filler was proposed to improve the foundation thawing settlement, and it has been successfully implemented in the road project (Yiershi–Chaiqiao section of 308 Provincial Highway) in Inner Mongolia Autonomous Region. To study the action mechanism of this structure on the subgrade deformation, a numerical model of the hydro–thermal–mechanical interaction process in unsaturated frozen soil was established, and the calculation of the water content, temperature, and deformation conditions of the subgrade within 20 years of the highway were carried out. The results show that the embankment block-stone layer can reduce the total heat of the deep foundation, and reduce the migration of unfrozen water from the deep foundation to the active layer. It can also increase the hydrologic and thermal convective flux inside and outside the block-stone layer, thus raising the permafrost table and reducing the subgrade deformation. The block-stone layer thickness has an important influence on the subgrade stability. By comparing the hydrologic, thermal change, and deformation of the block-stone structures with different thicknesses (5.0 m, 4.0 m, 3.5 m, 3.0 m, and 2.0 m), we found that when the thickness of the block-stone layer is 4.0 m, the subgrade stability is the best. In this case, the maximum uneven settlement and the maximum transverse deformation difference of the top surface of the subgrade are +0.521 cm and +0.462 cm, respectively. The subgrade stability is less optimal when the block-stone layer thickness is greater or less than 4.0 m. Thus, there exists an optimal embankment filling height related to the hydrologic and thermal conditions of the foundation soils. This study helps to elucidate the effect of unfrozen water content change on subgrade deformation during permafrost degradation and provides an important reference for solving the problem of thawing settlement of subgrade in permafrost regions.

Numerical model for the settlement of loess subgrade in operation period reinforced by rotary jet grouting pile

The problems of subgrade settlement failure and uneven settlement are quite prominent due to hydraulic migration. The loess in the natural state has the characteristics of high strength and low compressibility. Composite foundation method is to set a certain proportion of reinforcement (pile) in the natural foundation, so that the pile and soil jointly bear the load, and has the effect of compaction method and displacement method. Based on the actual case of a highway disease in Shanxi Province, this paper studies the influence of treatment measures of rotary jet grouting pile penetrating or not penetrating the loess soil on the uneven settlement of highway subgrade in loess region by means of field investigation, analysis and numerical calculation. The results found that the lateral friction resistance of rotary-jet grouting pile penetrates through the loess is small. When the rotarjet pile is long and the underlying soft layer is relatively thick (4.5 m), the settlement of the foundation also quickly enters the stable state. When the underlying loess is deep, the settlement of the foundation increases with time.

Performance Evaluation of Tunnel-Slag-Improved High Liquid Limit Soil in Subgrade: A Case Study

The application of tunnel-slag-improved high liquid limit soil as filling materials in subgrade is a green environmental technology. This study explored the influence of tunnel slag mixing on the physical and mechanical properties of improved soils, based on the engineering background of Liyu highway, Guangxi Province, China. Firstly, the optimal moisture content, maximum dry density, shear strength parameters, California bearing ratio (CBR) and resilience modulus of plain and tunnel-slag-improved high liquid limit soils were experimentally determined. Results showed that the direct utilization of untreated soil was unacceptable in subgrade practice. A significant enhancement of integrity of high liquid limit soils could be obtained by tunnel slag mixing, and the value of 15% was determined as the optimal tunnel slag content in soils, leading to improved soil performance meeting the specification requirements. Then, numerical simulation on the stability of subgrade slope of tunnel-slag-improved soils at the content of 15% was conducted. It also reported the long-term subgrade settlements. The feasibility of utilization of tunnel slag in improving properties of high liquid limit soils was further validated. Finally, a good application of tunnel-slag-improved high liquid limit soil as subgrade filling materials in Liyu highway was achieved. The findings in this study could provide useful guidance for similar engineering.