Subgrade Slope Research Articles

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.

Numerical Investigation of the Anti-infiltration and Anti-Erosion Performance of Composite Layers Mixed With Polyacrylamide and Basalt Fibre for the Protection of Silt Subgrade Slopes

In view of the failure characteristics of rainfall erosion and imbricate layered sliding of silt subgrade slopes, this paper proposes a slope surface protection technology that is a composite protection layer that combines basalt fibre for reinforcing soil and polyacrylamide for solidifying soil. The anti-infiltration and anti-erosion performances of these proposed composite layers were systematically investigated through the finite element and discrete element numerical simulation methods. Based on the optimum proportions of polyacrylamide and basalt fibre found in a series of mechanical experiments, Geo-studio software was used to simulate numerical tests of rainfall infiltration of the silt subgrade slope, and the variation laws of volumetric water content and pore water pressure at the characteristic points and the selected sections of the slope were discussed. In addition, the PFC2D particle flow program was used to develop numerical tests on the slope erosion process of the composite layers and to analyze the degree of soil erosion during the process. The influences of layer thickness on infiltration and erosion were considered. In conclusion, the results indicate that the composite layers can effectively improve the anti-infiltration and anti-erosion performances of the silt subgrade slope. This highlights that the thickness of composite layers mixed with basalt fibre can satisfy the design parameter requirements for anti-erosion performance.

Theoretical analysis and optimization of frame protection to control shallow slope stability and soil erosion

The frame protection is widely used for highways or railways to prevent the subgrade slope from shallow instability. However, the frame structure's design is empirical, and the theoretical analysis of the soil-structure interaction is scarce at present. By analyzing the critical stability conditions of soil particles of the shallow slope under rainfall infiltration, the paper discusses the shielding effect of the frame structure against erosion, together with the stabilization impact and the bearing behavior of frame protection. Under the unfavorable seepage condition, the equation of anti-erosion safety factor and the shallow stability analysis method, as well as the strength examination method of the frame structure, are established. On this basis, an mathematical optimization model is established, which takes the geometric parameters as decision variables, and anti-erosion stability, shallow stability, and safety of frame structure as constraints, and the minimum masonry quantity and shortest construction axis under unit protection area as objective functions. Finally, a case study involving numerical investigation and validation is implemented based on the mathematical optimization model, and the recommended optimal geometric parameters of the frame structure are given, considering the requirement of structural safety and cost-efficiency. The theoretical method and optimization model proposed in this paper can guide the frame structure's design in practical engineering.

Study on the Influence of Sponge Road Bioretention Facility on the Stability of Subgrade Slope

With the large-scale application of sponge city facilities, the bioretention facility in urban roads will be one of the key factors affecting the safety of construction facilities in areas with abundant rainfall. In this study, by establishing a three-dimensional finite element model for numerical analysis and combining it with geotechnical tests, the effects of bioretention facility on water pressure distribution, seepage path, and slope stability under rainwater seepage conditions are proposed. In addition, this study puts forward the relationship between the parameters of the bioretention facility and the stability of the slope in combination with the effect of runoff pollution control, which provides direction and basis for the planning, design, and construction of sponge cities in road construction.

A longitudinal analysis of collapsibility with predictions over the southeastern Loess Plateau in China

Loess presents very unique collapsible behaviour due to its special under-compactness, weak cementation and porousness. Many environmental issues and geological hazards including subgrade subsidences, slope collapses or failures, building cracking and so on are directly caused by the collapsible deformation of loess. Such collapsible behaviour may also severe accidents due to sinkholes, underground caves or loess gullies. Moreover, with the increasing demand of construction and development in the loess areas, an in-depth research towards effective evaluation of loess collapsibility is urged. Currently no studies have made attempts to explore a rather complete and representative area of Loess Plateau. This paper thus provides a novel approach on spatial modelling over Jin-Shan Loess Plateau as an extension to experimental studies. The in-lab experiment results have shown that shown that the porosity ratio and collapsibility follow a Gaussian distribution and a Gamma distribution respectively for both sampling areas: Yan’an and Lv Liang. This establishes the prior intuition towards spatial modelling which provides insights of potential influential factors on loess collapsibility and further sets a potential direction of the loess studies by considering an extra dimension of spatial correlation. Such modelling allows robust predictions taken into account of longitudinal information as well as structural parameters and basic physical properties. Water contents, dry densities, pressure levels and elevations of samples are determined to be statistically significant factors which affect the loess collapsibility. All regions in Lv Liang area are at risk of high collapsibility with average around 0.03, out of which roughly a third of them are predicted to be at high risk. Clear spatial patterns of higher expected collapsibility in the southwest comparing to the northeast are shown adjusting for influential covariates. On reference guidelines for potential policy makings, county-level regions with the highest expected loess collapsibility are also identified.

HHT-Based Seismic Damage Analysis of a Subgrade Slope Reinforced by a Gravity Retaining Wall

HHT-Based Seismic Damage Analysis of a Subgrade Slope Reinforced by a Gravity Retaining Wall

Influence of snow cover on temperature field of frozen ground

Research on the effect of snow on the temperature field of frozen ground is of great significance to the laying of underground oil pipelines, design of roads, and control of frost damage in cold regions. The heat transport laws of frozen ground with phase changes under periodic temperature boundary conditions were analyzed based on data monitoring in this paper. Based on the boundary conditions determined by the monitoring data, the numerical calculations of frozen ground and subgrade with/without snow cover were carried out, and the effects of snow cover on the temperature fields of frozen ground and subgrade in cold regions were explored. Monitoring results demonstrate that the temperature at different sections of frozen ground with phase change presents a sine-like function under the periodic temperature boundary condition. According to monitoring data, when the thickness of the natural surface snow cover is about 25 cm, the daily average minimum temperature of soil at 0.1 m from the surface will rise by about 10 °C compared to that without snow cover during a year (in a cycle); nevertheless, when combined with numerical calculation, the permafrost table increases by about 2.87 m, and the permafrost base decreases by more than 5.59 m. Under the boundary conditions set in this paper, the permafrost under the subgrade disappears in a greater area due to the construction of the subgrade in the snow-covered area. In addition, the elliptical thawing soil area produced by the lower part of the slope of a snow-covered subgrade will adversely affect its stability.

Numerical analysis of an expansive subgrade slope subjected to rainfall infiltration

Numerical analysis of an expansive subgrade slope subjected to rainfall infiltration

Experimental study on site filling of sandy soil for railway subgrade

Applying cohesive soil to wrap fine sand on a subgrade slope is a new type of filling technology in railway subgrade construction. The choices of specific compaction methods and quality evaluation indicators are critical for achieving high compaction quality. In this paper, a series of field rolling tests with different compaction machines was carried out in the experimental section of China Menghua railway. Then, the compaction quality was gauged considering different indexes such as relative density (Dr), degree of compaction (K), coefficient of subgrade reaction (K30) and dynamic modulus of deformation (Evd). It is shown that adopting clayey soil (namely, wrapping soil) to cover a sandy roadbed slope can keep the internal humidity of the subgrade stable. For compaction of the fine sand used in this study, it was better to select a bulldozer to squeeze along the longitudinal and horizontal directions alternately six times, and the lift thickness was set at 35 cm. The results show a linear relationship between Evd and K30 for the sand. The application of Evd as a substitute for K30 in the compaction evaluation of sand subgrade can lead to significant efficiency.

Numerical stability analysis of superhigh-fill subgrade underlying acute inclined mined-out area with underground coal fire

According to the borehole drilling detection results of a superhigh-fill highway subgrade that crossed an open-pit coal mined-out area with an underground coal fire (UCF) in Urumqi, China, a numerical model of the subgrade and substrata was established. The variations of the stability characteristics of the highway pavement and the subgrade slope with respect to the substrata properties under the effects of coal-seam combustion were analyzed via thermal-stress coupled calculations using the finite-difference software FLAC3D. When the coal body underlying the subgrade underwent burnout and the combustion cavity formed, the bearing capacity of the strata decreased significantly. Under the effect of the heavy self-weight of the high-fill subgrade body and other external loads, such as the vehicle load on the pavement, collapse was likely, followed by the formation of a large sink basin on the surface of the subgrade. The displacement of the highway suffering from UCF increased gradually. The displacement development was divided into two stages: the swelling stage due to rock-mass expansion and the collapse stage due to the burnout of the coal body. The concrete geocell had a good reinforcement effect on the subgrade in which the settlement of the basin occurred under the effects of the UCF. When part of the geocell was deformed under external loads, the loads were transferred to the neighboring concrete geocell located in the stable region. Thus, the concrete geocell in the stable region constrained the geocell in the unstable region from deforming. Furthermore, a parametric analysis with varying combustion conditions indicated that a higher heat-release intensity, wider combustion region, and shallower combustion depth lead to greater stability hazards for the overlying subgrade.

Performance Test and Stability Analysis of Jute Ecological Bag on Subgrade Slope

Ecological bags have been gradually adopted for ecological protection on the subgrade slope because of their good soil fixation effect, strong water retention performance, fast construction and other advantages. Ecological bags made of natural jute have obvious attributes in environmental protection and economic efficiency. In this study, the tensile and the tearing strength of the common-used jute cloth have been tested. The result shows that the strength meet the requirements of the standards. Compared with current frequently-used ecological bag made of non-woven cloth, the jute ecological bag has large apertures, which is suitable for the growth of dicotyledon plants. Moreover, its high friction coefficient with the soil is beneficial to the structure stability on the slope. On the other hand, a stability evaluation method has been established for the jute ecological bags on the subgrade slope under natural and heavy rainfall conditions. Then the steel wire mesh fixed by the anchor rods is used to enhance the stability of the jute ecological bags, which constitute the ecological protection system for the subgrade slope. Also, the stability of the protection system is analyzed and calculated.

Multifactor Analysis of Calibration and Service Quality of the Soil Moisture Sensor Applied in Subgrade Engineering

The soil is an important natural resource, and its moisture status plays a key role in the strength and stability of the soil structure. In civil industries including the agriculture engineering and the forestry engineering, moisture sensors are widely used to test and monitor the engineering properties and long‐term service performance of soil. The influence of multiple factors on the quality and the accuracy of the soil moisture sensor should be taken into account. Both laboratory and field tests were performed by the time‐domain reflectometry (TDR) method. The soil dielectric constant and magnetic permeability under different moisture contents, different temperatures, and different dry densities were comprehensively evaluated. At the same time, the sensitive factors in the service performance of the TDR sensor have been revealed by the real state of tested soil samples. Based on the testing principle of TDR, a calibration calculation model has been developed to evaluate accurately the moisture content of the subgrade slope. The results show that both the moisture content and the dry density had a significant influence on the dielectric constant and the magnetic permeability of soil. The developed calculation model has a good fitting effect and stability. Through the model, the influence of moisture content and temperature on the soil dielectric constant has been analyzed, and the fitting goodness is above 90%. After half a year of settlement, the soil was gradually drained and consolidated, and the moisture content of the subgrade section gradually decreased. It verified that the monitoring method determined by the laboratory calibration test was effective and accurate.

Experimental study on the shear stiffness and damping ratio of the coarse-grained soil against geogrid interface

Geosynthetic-reinforced soil structures are mostly used to retain subgrade slope of highway and railway. For the design and performance analyses of geosynthetic-reinforced soil structures under repeated loading, such as those induced by compaction, traffic and earthquakes, the understanding of cyclic soil–geosynthetic interface behaviour is of great interest. Nevertheless, experimental data concerning this type of behaviour are very scarce. A laboratory study was carried out and is described in this paper. This paper presents the behaviour of an interface between a coarse-grained soil and a geogrid under cyclic loading conditions. A large-scale direct shear test device able to perform displacement-controlled cyclic tests was used. The results obtained are presented and discussed, especially the effects of the displacement amplitude and normal stress on the shear stiffness and damping ratio are investigated. The dynamic response parameters of the soil-geosynthetic interface are greatly affected by the number of cycles, and the variations in the two parameters with the number of cycles are related to the normal stress and the shear displacement amplitude. when at large displacements, the damping ratio decreases first and then stabilizes with the number of cycles. However, at small displacement, the shear stiffness and damping ratio are all decrease somewhat at the initial stage of cyclic shearing. As the experimental materials used in this study are relatively single, and further experimental research should be carried out in the future. The shear parameters of interface in this study can provide reference for the design of reinforced soil structure.

Study on the Evaluation Method of Subgrade Slope Green Protection Effect in Dry-Hot Valley of Sichuan-Tibet Railway

In view of the harsh environment in the dry-hot valley of Sichuan-Tibet railway and the important role of the green protection of the subgrade slope in railway construction and ecological restoration, this paper evaluates the effect of the green protection of the subgrade slope in dry-hot valleys of the Sichuan-Tibet railway. First, an evaluation index system for the green protection effect of railway subgrade slopes is established in terms of the soil matrix quality, vegetation community quality, and protection performance of the slopes. Second, game theory is adopted to combine the improved-group-analytic-hierarchy-process method and the vector-angle-cosine method and thus determine the weight of each evaluation index. Moreover, the membership-cloud-gravity-center method is used to evaluate the green protection level of the railway subgrade slope, and an evaluation cloud map is drawn with the help of MATLAB software to further analyze the evaluation. Finally, a section subgrade slope of the DHV area of the Sichuan-Tibet railway is selected as the evaluation object, and the green protection effect is evaluated to verify the applicability and effectiveness of the model. The study provides a theoretical basis for the protection of subgrade slopes and ecological restoration in the DHV area.

WIND-TUNNEL EXPERIMENT ON SAND DEPOSITION MECHANISM AND OPTIMAL MEASURES OF WIND-BREAK WALL ALONG RAILWAY IN STRONG WIND AREA

The Lan-Xin Railway II from Lanzhou to Xinjiang is the first high-speed railway which passes through the strong wind zones in the world, and it passes through the famous Yan Dun, Hundred Miles, Thirty Miles and Dabancheng wind zones. The total length of the railway is more than 462.4 kilometers, accounting for 65.1${\%}$ of the total length of railway in Xinjiang. Strong winds can do great harm to the operation, maintenance and transportation of railways. In order to resist the damage of strong wind to train, a large number of wind-break walls were built along the Lan-Xin Railway II. The wind-break wall reduces the strong wind damage, but brings a new disaster caused by sand sedimentation. To solve the problem of this engineering practice, this paper puts forward the idea of setting up the second retaining wall at different positions on the leeward side of existing wind-break wall to reduce sand particles sedimentation. The wind tunnel experiment was employed to simulate the wind-sand flow environment. Three typical configurations are considered: 1) single wind-break wall; 2) two walls and the second one locates at the top of the leeward slope of subgrade; 3) two walls and the second one locates at the foot of the leeward slope of subgrade. The decrease rates of the horizontal velocity, number density, horizontal transport flux and deposition rate of sand particles at the height of 0.1 m after the second wall are respectively 8${\%}$$\sim $12${\%}$, 51${\%}$$\sim $69${\%}$, 20${\%}$$\sim $73${\%}$ and 26${\%}$$\sim $38${\%}$, by comparing to the case without the second wall. It is found that the second retaining wall at the foot of the leeward slope of subgrade is optimal. The research result of this paper is helpful to optimize the preventing sand sedimentation measures of existing railway lines and towns in the strong wind zone.

Embankment Displacement PLAXIS Simulation and Microstructural Behavior of Treated-Coal Gangue

The purpose of this study is to investigate the displacement of coal gangue filling material in road construction and microstructural behavior of treated coal gangue by considering the environmental factors of aqueous solutions with different acidity. The displacement analysis of the coal gangue embankment model has been done by means of the finite element method PLAXIS. Furthermore, using the scanning electron microscope, the energy dispersive system, and the Raman spectrometer to analyze the microscopic mechanism in the view of microstructure, elements, the integrity of carbon structure and the stability of chemical bonds of coal gangue. The results show that the larger displacement of the treated coal gangue subgrade is within 4.0 m below the top of the subgrade, and the maximum displacement value is about 7 mm, which is less than the displacement of untreated coal gangue sample. While the treated A-CG and T-CG grain size, surface area and internal friction angle increase, the unstable carbon structure is destroyed, so its shear strength, compression performance, and consolidation effect are improved. S-CG particles are coated with Na-Si-Al gel, which enhances the density, viscosity and shear strength, thus ensuring the stability of the coal gangue subgrade. The treated coal gangue subgrade slope foot displacement, boundary shear stress and safety factor are all meet the specification requirements.

Analysis and Influence of Salt Content on Stability of Saline Soil Subgrade Slope

In order to determine the stability of the subgrade of the saline soil subgrade under different salt contents in the cold region. Two soil samples were selected to determine the salt content and mechanical parameters, and then the Slide software was used to analyze the stability of subgrade slope. The results show that the less the salt content, the greater the shear strength of the soil and the higher the stability of the subgrade slope.

Stability Analysis of Slope of Saline Soil Subgrade in Gravel Block Based on SLIDE

The saline soil roadbed in the cold region is affected by salt crystallization and migration, and the soil strength parameters change significantly. In order to determine the influence of salt migration on the stability of the roadbed under the conditions of laying gravel barriers of different thickness in the saline soil roadbed in cold regions. First, determine the type and physical parameters of saline soil in cold regions. Secondly, for the saline soil roadbed with different thickness of gravel partition in the base of the road, the slope software is used to analyze the stability of the subgrade slope, and the stability of the gravel partition is obtained. The effect of slope stability. The results show that when the gravel partition layer is set at the base of the road, the overall stability of the subgrade slope decreases with the increase of the thickness of the partition. When the thickness of the partition is more than 20cm, the dangerous sliding surface is transferred to the surface of the slope partition. The thickness of the partition layer increases, and the dangerous sliding surface remains stable, which provides reference data for the design of the saline soil roadbed in the cold region.

Experimental research on the dynamic response characteristics of the transition subgrade induced by heavy-haul train passage

The dynamic response of the subgrade under moving train loads provides information on subgrade settlement prediction, condition evaluation, and so forth. This paper presents the field dynamics tests on the transition subgrade in the Shuo-Huang heavy-haul railway in China. The variation characteristics of the peak dynamic displacements along the track and subgrade slope were analyzed, and the random distribution characteristics of the peak dynamic displacements at the subgrade shoulder were studied. The response characteristics of the subgrade during the train passage were investigated, and the attenuation regularities of vibration along the subgrade slope were identified. The results indicated that the action of the train moving loads on the subgrade has obvious periodicity, and two bogies in the adjacent wagons should be considered as one loading unit. The peak dynamic displacements at the subgrade shoulder obey normal distribution under the repeated loading of the loading unit. The subgrade bed is dramatically influenced by the dynamic loadings of the trains, and the moving train loads have little influence on the part below the subgrade bed. The results of the research provide the basis for the evaluation of instantaneous and long-term dynamic stability of the subgrade and offer guidance for simulating train moving loads in the model test and numerical analysis to study the dynamic response of the subgrade.

Stability of the Railway Subgrade under Condition of Its Elements Damage and Severe Environment

Investigation of damages of the subgrade slope in combination with its overwetting and rolling stock loading, which significantly affects safety traffic of the railway transport, has been carried out. The complex method of slope stability estimation of the subgrade is developed, which includes calculation of loads and vibration action of rolling stock on the main site of the subgrade, as well as the dynamic model of vibrations propagation in the body of the subgrade embankment and the model of plastic deformations accumulation. Dynamic and nonlinear plastic models are based on a finite-element model of the cross section of the subgrade. The plastic model takes into account the characteristics of soil strength of the subgrade, depending on the area of the vibration load impact. The developed method allows to carry out the estimation of external and internal factors impact on occurrence of subgrade destruction, which is of practical value for safety state estimation of the railway transport.