Embankment Height Research Articles

LES Study on the Embankment Height Effect on the Aerodynamic Characteristics of a Generic High-Speed Train

LES Study on the Embankment Height Effect on the Aerodynamic Characteristics of a Generic High-Speed Train

Field Measurements and Numerical Simulation of Snowdrift on Railway Subgrade

Abstract Snowdrift is a major natural hazard, endangering basic installation and human life in cold regions. Drifting snow can cause snow grains to accumulate on the road, blocking transportation, reducing visibility, and even leading to fatal traffic accidents. Field measurements and numerical simulations of roadbed snow characteristics were carried out along the railway in snowy weather to study the effect of snowdrift on railway subgrade. The influence of a typical roadbed structure is considered, and the basic model of a typical subgrade structure under the action of snowdrift is proposed. Snow particles that accumulate on the embankment present a U-shaped distribution along the inflow direction. Within the increase of embankment height, wind velocity on the roadbed surface is accelerated, and snow cover is reduced, thus mitigating the snow drift disaster of the embankment. Snow covers at embankment heights of 1 and 2 m are considerably greater than those at 3 and 5 m, and identical with those at roadbed heights of 3 and 5 m. Along the inflow direction, the snow cover on the cutting presents an M-shaped distribution. As cutting depth is reduced, wind velocity inside the cutting is decelerated, and snow cover is increased, which aggravates the snow drift disaster of the cutting. The snow depths of roadbed parts at 1-, 2-, and 3-m depths of the cutting are nearly the same, and that at a 5-m depth of the cutting is relatively small but still larger than that on the embankment. Numerically simulating the snow-driving wind via computational fluid dynamics, which can consider the motion characteristics of snow particles and their influence on flow field, is feasible. Simulation results agree with the measured results. Thus, this research provides a path for the further prediction of snow cover pattern.

Membrane Effect of Geogrid Reinforcement for Low Highway Piled Embankment under Moving Vehicle Loads

In this paper, the membrane effect of geogrid reinforcement was investigated based on numerical simulation to understand the serviceability and deformation of highway piled embankments under moving vehicle loads. The membrane effect of geogrid reinforcement in low embankments (i.e., the ratio of embankment height to pile spacing is less than 1.5) was clearly emphasized. It has been found that the maximum settlement of geogrid occurs in the central area between the piles, and the maximum tension was concentrated at the corner of the pile cap. Due to the attenuation of the soil arching effect under moving dynamic loads and the punching mechanism, the settlement and tension of the geogrid increased considerably by approximately 35% and 23% compared to those under static loads. A parametric study was also achieved, and the results presented that the geogrid reinforcement tension increased by increasing the pile spacing, embankment height and geogrid stiffness, vehicle wheel load and vehicle velocity. It was also found that the reinforcement tension was most sensitive to the pile spacing among all the parameters considered in this paper, whose magnitude increased by approximately 104% as the pile spacing increased from 2.0 m to 2.5 m under dynamic loads.

THE EFFECT OF SOIL STABILIZATION AND REINFORCEMENT ON THE STABILITY OF EMBANKMENT ON SOFT SOIL

The construction of toll roads in South Sumatra faces two problems. First, most of the road sections are built on soft soil deposits, so the soil must be improved to speed up consolidation process and to improve bearing capacity. Second, the embankment required to reach the design elevation of the toll road is quite high so that reinforcement is needed to improve slope stability. This paper contains the results of a study on the effect of soil improvement using PVD and vacuum pressure, installation of geotextile layers and pile at the toe of embankment slopes, on the stability of the embankment. The analysis were carried out using data obtained from the construction of the Kayu Agung – Palembang toll road Section 1A, including geometry data, soil stratification, and configuration of PVD installation and soil reinforcement. Slope stability analysis was carried out using the Morgenstern & Price method which is integrated in SLOPE/W program. The results of the analysis show that the safe embankment height for the original soil condition is 3.5 m while the required height of embankment was 6 m. Analysis made for the 6 m high embankment using soil properties after ground improvement with PVD and vacuum pressure shows the FoS is still below 1.5. The presence of geotextile layers and pile improved the performance of the embankment and increased the FoS to 2.410. The slope is still in a safe condition with FoS of 1.762 after the construction of toll road and traffic load which induces a combined load of 35 kPa.

A rheological model for georeinforced embankments based on piled foundations

Concrete columns are commonly used methods to improve the performances of embankments on soft soil strata. To further reduce settlements and stresses on the soft foundation soil, geosynthetic reinforcements are often installed at the base of embankments. Existing design methods for these “geostructures” commonly does not take into consideration both the effect of the embankment construction process and the stiffness of the system components (embankment, soft soil, column and geosynthetics) as design parameters. As a consequence, these approaches do not allow the estimation of the settlements at the top of the embankment. In this paper a new rheological model capable of assessing both tensile forces in the geosynthetic and settlements at the embankment top induced by the construction process is presented. In this model, the variables defining the system performance (tensile forces in geosynthetics, stresses acting on piles and settlements) are explicitly related to the embankment height, interpreted as a generalized loading variable. The model has been validated on the results of 3D numerical analyses.

Influence of Biaxial Geogrid at the Ballast Interface for Granular Earth Railway Embankment

The development of reinforcements for soil has made an impact in most of the civil engineering sectors especially transportation. The use of geogrids is frequent in roadways but they are also finding use in railways. The major impact that geogrids could have is providing desired stiffness to a section by reducing material and serving as a proper reinforcement material. In the current study, an attempt has been made to redesign the railway embankment economically with the help of geogrids. Biaxial geogrid is used to substitute the blanket layer (thickness up to 100 cm) in the railway embankment by fulfilling the strain modulus requirement of the embankment, calculated using a plate bearing test as per DIN 18134. The experiment is performed on the embankment replicated in a metallic test chamber with granular soil as subgrade and geogrid is placed beneath the ballast. The experimental study is validated by a 3-D numerical model using Midas GTS NX software. The experimental analysis shows an improvement of 31.47% in the second modulus of the earth embankment. For the implementation of this study, a design section of Indian railways is adopted. With the help of geogrid, a reduction of 50% is observed in the embankment height, thereby reducing the overall costs.

Internal stability analysis of column-supported embankments: Deterministic and probabilistic approaches

Geosynthetic-reinforced and column-supported (GRCS) embankment is a practical and cost-effective technique for reinforcing soft soils. Internal stability of the column-supported embankment, which is engaged in shearing and bending failure modes, is one of the key issues that geotechnical engineers encounter in the design. To deal with this problem, numerical models are currently used. In this study, a simplified model has been developed for predicting the potential of internal instability in GRCS embankments. The validity of the deterministic model was verified by comparing the predicted safety factors with experimental and numerical observations. The findings show that the proposed model has the potential to accurately evaluate the internal stability of GRCS embankments. Moreover, probabilistic approaches were also used to undertake the reliability and sensitivity studies of column-supported embankments. The bending moment failure mode has a larger impact on the stability of the GRCS embankment than the shear failure mode. It is also found that the safety factor of shearing and bending failure modes is strongly influenced by the undrained soft soil shear strength. Furthermore, the reliability study demonstrates that the embankment height and the number of column rows are important factors in determining the efficiency of GRCS embankments in resisting internal instability.

Stability Analysis of Pile-Supported Embankments over Soft Clay Considering Soil Failure between Piles Based on Upper Bound Theorem

Most analytical methods used to analyze the stability of pile-supported embankments are based on shear and bending failure of piles. However, the centrifuge test and practical engineering show that rigid pile-supported embankments have a failure mode of soil sliding around piles. Therefore, the stability analysis method of the pile-supported embankment under the failure mode of the soil sliding around piles based on the upper bound theorem is given in this study. First, the failure mechanism is assumed to be a rigid body and slide along two logarithmic spiral surfaces in the embankment and soft soil. The rate of external work and internal energy dissipation of the failure mechanism are further obtained, wherein the internal energy dissipation rate of piles is obtained based on the limit state of soil sliding around piles. Secondly, according to the equation formed by the upper bound theorem, the optimization model of the safety factor function when the potential slip surface is passing through different pile rows is obtained. Then, the algorithm of solving the model is given and the overall safety factor of the pile-supported embankment is obtained. Compared with other methods, the advantage of this method is that it considers the influence of embankment soil property and the width perpendicular to the two-dimensional plane on the pile load and the influence of the soil internal friction angle on the slip surface. Finally, it can be concluded from parametric analysis that: with the increase of the horizontal distance from piles to the slope toe, the reinforcement effect of piles first increases and then decreases; with the decrease of the embankment height and the increase of the soft soil cohesion and internal friction angle, the overall safety factor of the embankment increases.

Finite-Element Analysis on the Tensile Membrane Effect in Geogrid Reinforced Piled Embankment under Dynamic Loading

This study presented a numerical investigation of the tensile membrane effect in the geogrid reinforced piled embankment under dynamic loading. It has been found that the maximum sag of the geogrid was attained at the center of two adjacent piles, while localization of tensile force was observed at the corners of the pile caps. Under the dynamic loading, the sag and the strain of the geogrid increased when compared with the static loading, an increase of around 45.9% and 24% was, respectively, yielded for the sag and the strain of the geogrid. This increase of tension in the geogrid may mainly result from the degradation of the soil arching effect under dynamic loading. A parameter study was performed, and it showed that the tensile force in the geogrid increases with the rise of the embankment height, the clear pile spacing, and the tensile stiffness of the geogrid. However, the increase of the friction angle of the embankment fill led to a decrease in the tension in the geogrid, which may benefit from the improvement of the soil arching developed in the embankment fill. It was found that the tensile behavior of the geogrid was the most sensitive to the pile spacing. When pile spacing increased from 2.0 m to 3.0 m, the tensile force in the geogrid increased by about 248%.

Safety Factors Investigation Based on FEM and LEM Approach in Toll Road Embankment Slope

The Pejagan-Pemalang toll road which is a Section II project was designed at different embankment heights on soft soil subgrade. The process involved investigating the slope stability of these embankments through the determination of the safety factor. This can be achieved using different methods such as the limit equilibrium method (LEM) and the finite element method (FEM) which are considered the standard approaches. However, the presentation of different numerous results for the safety factors (SF) in landslide calculations usually makes it difficult for the engineer to understand some uncertain conditions. Therefore, this study aims to determine the safety factors using LEM and FEM approaches at different conditions. The soil subgrade used was in SPT and three models of the properties were obtained. Moreover, a Geo-Studio program with Slope-W analysis was applied using the Morgenstern-Price for the LEM and PLAXIS for the FEM. The height was varied at 2 to 8m with the slope H: V at 1:1, 1:1.5, and 1:2. The simulation was conducted at three different levels of groundwater. The results showed that the height, embankment geometry, and groundwater levels were affected in the SF analysis using the two methods. It was also discovered in all categories that higher embankments had smaller SF while the higher angle of slope produced a higher SF. Furthermore, the properties of the soft soil were observed to have influenced the SF result as indicated by the narrow difference in the correlation between the embankment height and SF. The results of the LEM and FEM were also compared and the observations were explained. The findings of this study are expected to serve as a guide for engineers, especially those in road toll projects, to determine the optimum model needed to predict slope failure in embankments for toll roads.

Numerical Simulation and Forecasting Model of Snow Drift Hazard in Yanchong Expressway with Embankment Form

To reasonably predict the snow drift hazard of expressway embankment in alpine mountainous area, in this paper, the computational fluid dynamics (CFD) numerical simulation method is used to analyze the distribution law of flow field of snow drift, the regression orthogonal design method is used to establish the prediction model of snow drift hazard in the expressway with the embankment form. Results show that different factors have different effects on snow drift hazard, the influence of embankment slope is the largest, followed by the coupling term of embankment slope and wind speed, the wind speed, the coupling term of embankment height and embankment slope, the coupling term of the mountain relative height and embankment slope, and the embankment height, while the influence of the distance between embankment and mountain-embankment slope coupling is the smallest. Numerical simulation and field observation have confirmed that the combined action of the terrain and embankment of Yanchong expressway Chicheng branch line leads to great changes in wind speed, resulting in uneven distribution of snow. A large amount of snow can be accumulated at the foot of the leeward slope of the mountain and the windward slope of the embankment, and there is less snow on the embankment pavement. By comparing the snow drift prediction model and CFD numerical simulation results, the error of the prediction model established in this paper is only 8.67%, which has high applicability. The research of this paper can provide a theoretical reference for the prediction and prevention of snow drift hazard on expressway embankment in alpine mountainous area.

The performance and bearing capacity of bottom ashes filled embankment

The municipal solid waste incineration bottom ash (IBA) as the fill material in the geotechnical applications is a wise solution where IBA will save the bulk of earth material and can bring huge economic benefits, particularly for the embankments. In this study a series of experimental model tests of embankments filled with IBA and sand were conducted and considered two different slope ratios to investigate the performance of IBA as the fill material. During the testing, the vertical stress distribution, horizontal deformation, and vertical settlement inside of the embankment were monitored. Test results demonstrated that the IBA embankment compared with the sand embankment when slope ratios of 1:1.5 and 1:1.75, enhanced the bearing capacity by 25% and 20%, respectively, and under the same vertical pressure reduced the vertical settlement by 47% and 39.6%. When the embankment shear failure occurred, the lateral deformation inside the IBA embankment was reduced by 27.36% and 23.66%, respectively, compared with the sand embankment, under the conditions of slope ratio of 1:1.5 and 1:1.75, and the lateral deformation distribution along the height of embankment was more homogeneous. These results indicated that the use of IBA as fill material for embankments can be an economical and effective method to save the earth material.

Field investigation of steel pipe pile under lateral loading in extensively soft soil

The construction of railway and highway embankments has a significant influence on the behavior of existing pile foundations, especially in the situation of high embankments and extensively soft soils, which are commonly encountered in coastal areas. A high embankment might produce large lateral movement and bending moment to the existing adjacent piles, which would cause the failure of the pile if the surcharge loading is not properly considered. A field test was designed and performed to investigate the effect of lateral surcharge loading on the existing adjacent pile in extensively soft soils. A 4 m high embankment was constructed in five lifts and was close to the existing adjacent steel pipe pile with a length of 35 m. The deformation of the pile and the soft soils, the excess pore water pressure, and lateral earth pressures were measured during the surcharge loading test. The test results showed that the lateral displacement of the steel pipe pile at the ground surface exceeded 229.9 mm and could not maintain constant due to the surcharge loading. The lateral displacement decreased along with the pile depth and was relatively small when the pile depth exceeded 10 m. Large lateral displacements were observed in the soft soils at different locations. The surcharge loading zone showed obvious downward displacements, while the soft soils close to the loading zone showed upward displacements. The excess pore water pressure changed regularly with the construction of the embankment, and its maximum value reached 53.6 kPa. The lateral earth pressures that acted on the pile continuously increased with the increase in the embankment height, which caused large deformation of the pile.

Train-induced vibration and subsidence prediction of the permafrost subgrade along the Qinghai-Tibet Railway

Railway track design and maintenance researchers have been pursuing reliable methods for predicting the long-term performance of the Qinghai-Tibet railway (QTR) subgrade. Based on theoretical analysis, numerical simulation, field monitoring and laboratory tests, this paper studied the train-induced vibration response characteristics of the Beiluhe subgrade of the QTR to evaluate the impact of railway vibration loads on the ice-rich permafrost layer. The results show that increasing the embankment height can significantly reduce the additional dynamic stress of the ice-rich permafrost layer. Moreover, increasing the mean annual ground temperature (MAGT) and decreasing the embankment height will aggravate permafrost table vibration-induced subsidence. This study also analysed the relationships between the train-induced permafrost table vibration subsidence and the MAGT, the ice-rich permafrost layer thickness and the embankment height and predicted the permafrost table vibration subsidence in the DK1136 test section under different global warming conditions. The analyses and prediction demonstrate that the appropriate embankment height of the DK1136 section is 3–3.5 m, and the application of engineering measures for actively cooling the permafrost foundations is the best choice for reducing vibration-induced subsidence, thawing settlement and compression deformation.

Field Test on Deformation Characteristics of Pile-Supported Reinforced Embankment in Soft Soil Foundation

In this work, the settlement deformation of the soft-soil subgrade and the deformation law of the geogrid were studied based on field tests carried out on the pile-supported reinforced embankment of the Rongwu Expressway in the Xiong’an New Area. The settlement and deformation law of the reinforcement area and the underlying layer of the pile-supported reinforced embankment, the settlement law of the transverse and longitudinal sections of the subgrade, and the deformation law of the bidirectional geogrid were analyzed. The results show that reducing the pile spacing and embankment height can effectively reduce the foundation settlement. The change in the pile spacing mainly affected the settlement in the reinforcement area, while the embankment height mainly affected the substratum settlement; the differential settlement in the subgrade cross-section was mainly caused by the settlement in the reinforcement area. The settlement at the center of the subgrade was obviously higher than that at the shoulder. In terms of the geogrid deformation law of the subgrade cross-section, the geogrid deformation at the center line of the subgrade was the largest. With the increase in the distance from the center line, the geogrid deformation gradually decreased. In terms of the deformation law of the biaxial geogrid, the tensile deformation of the geogrid in the center of two piles was greater than that in the center of four piles. The transverse tensile deformation of the geogrid was greater than the longitudinal tensile deformation. The tensile stress of the reinforced materials was calculated according to four specifications, and the applicability of various methods was evaluated.

Practical seismic fragility estimation of Japanese railway embankments using three seismic intensity measures

This study proposes a practical fragility estimation equation for Japanese standard models of railway embankments using the peak ground acceleration, peak ground velocity, and Arias intensity. The analytical models were implemented as unreinforced and geosynthetic-reinforced embankment models. A sensitivity analysis of the seismic fragility estimation of the embankment models was conducted on various embankment heights, average values of friction angles in the backfill soil, and tensile strengths of the primary reinforcement. Consequently, a unique formula for the fragility function in the presence of different seismic intensities was successfully presented. The parameters of the fragility function were successfully estimated using commonly used design parameters, such as the embankment height, average value of the friction angle of the backfill soil, and average value of the tensile strength. Additionally, another sensitivity analysis using different seismic databases was conducted to explore the effect of the seismic database on the fragility curve estimation of railway embankments. As a result, using different seismic databases, different fragility curves were obtained. These results highlight the importance of checking the sensitivity of the seismic database when developing the fragility curve.

Research progress on train operation safety in Xinjiang railway under wind environment

Abstract Railway lines in the Xinjiang wind area face severe wind disasters year-round, which seriously affects the safety and economy of the railway in China. Therefore, the wind characteristics and statistics of wind-induced accidents along the Xinjiang railway lines are presented and the basic research route for evaluating the train running safety under crosswinds and effective measures to improve the windproof performances of trains are proposed, which are meaningful to deal with wind-induced train accidents. Based on this research route, a series of numerical simulations are conducted to evaluate train safety and the corresponding measures are provided. The results show the following. The running safety of the train under crosswinds mainly depends on the aerodynamic loads acting on the train. The relationships between the safe speed limit and train type, the load weight, the embankment height, the road cutting depth, the railway line curve parameters, the yaw angle and other factors are obtained. The critical wind-vehicle speed relationship, as well as the engineering speed limit value under different running conditions, are determined. Large values of the aerodynamic and dynamic indices mainly appear in special locations, such as near earth-embankment-type windbreak walls, shallow cuttings and the transition sections between various types of windbreak walls. Measures such as increasing the height of the earth-embankment-type windbreak walls, adding wind barriers with reasonable heights in shallow cuttings and optimizing the design of different types of transition sections are proposed to significantly improve the safe speed limits of trains under crosswinds.

Structural reliability analysis of in-service API X65 natural gas pipeline using statistical data

The failure probability of the pipeline in the structural reliability assessment was evaluated by the relationship between the resistance of the pipe material to an external load or stress. The stress acting on the natural gas pipeline is affected by the circumferential stress and the longitudinal stress generated by the internal pressure, the thermal stress caused by the temperature difference during installation and operation, the bending stress caused by the buried depth, the embankment height, and vehicle load. The failure probabilities of the API X65 pipes were evaluated by the Von-Mises stress criterion as the maximum allowable stress criterion under the combined stresses. First-order reliability method as approximate analytical methods was used to perform the failure probability analysis on the natural gas pipelines. The failure probabilities of the pipelines were evaluated with buried depth in a range of 1.5–30 m and wheel load in the range of 2.5–20 ton. The failure probabilities were evaluated under the conditions that internal pressure of 7 MPa, temperature difference of −45 °C, soil density of 18.9 kN/m3.

Dynamics of Embankment Slope Stability under Combination of Operating Water Levels and Drawdown Conditions

This study investigated the potential influence of operating water levels and loading conditions on the slope stability of an embankment dam. Four different operating reservoir levels (normal, reduced, embankment height, and overflow) were considered in the study. Numerical modeling was used to investigate the problem in the case of the Chardara dam within the Syrdarya catchment in Kazakhstan. Based on the drawdown rates and operating conditions, minimum factor of safety values ranging from 0.56 (total failure) to 2.5 were retrieved. Furthermore, a very high correlation was observed between drawdown days, the minimum factor of safety values, the maximum factor of safety values, and pore-water pressures, with correlation coefficients ranging from 0.561 to 0.997 (strong to very strong correlation). On the other hand, the highest negative correlation of 0.997 was observed between the minimum factor of safety values and pore-water pressures. Additionally, based on the results from the analysis of variance, three reservoir operating levels (normal, embankment height, and overflow) resulted in p-values less than 0.05, indicating that the variations in the factor of safety values from the drawdown rates were statistically significant. The findings of this study demonstrated that, not only may the drawdown rate be detrimental to the embankments, but that different operating levels can also affect slope stability in different ways.

EVALUASI KELONGSORAN DAN ALTERNATIF PERKUATAN MENGGUNAKAN GEOTEKSTIL DENGAN PROGRAM GEOSLOPE (STUDI KASUS: KELONGSORAN TOL CIPALI KM 122 JALUR B)

Reinforcement of a slope is a step that is often taken in increasing the Safety Factor (SF) of an embankment or excavation. In the road toll Cikopo - Palimanan the road which discount a lot of excavation and heap case the resulted in the magnitude of the possibility landslide. This studies to evaluate about handling of a landslide STA on the road toll Cikopo - Palimanan namely at KM 122 + 600 Line B here reinforcement sed is Geotextile. The analysis is used in calculating the Safety Factor (SF) manually or using a program Geoslope using methods Bishop where the field of landslide divided into several segments to be calculated force that worked in the segments from the analysis manually without the influence of the earthquake number of safeties is 1.6 and by using the program the result is 1.5. For analysis is with the influence of the earthquake (kh) of 0,2 obtained the numbers of safety 1.05 using manual analysis and 0.9 using the program. From these results, the slope without reinforcement with the influence of the earthquake must be strengthened because SF 1.10. Reinforcement using geotextiles is divided into 2 because the embankment height is > 6 meters, namely the lower zone and the upper zone, with the distance between the geotextile and the length of the geotextile being the lower zone of 0.30 m and 30 m, while for the upper zone the distance between the geotextile and the length of the geotextile is 0. 60 m and 18.5 m. From the results of the geotextile use as reinforcement have Safety Factor score at 1.49 which increased by 40% from the condition without reinforcement Keywords: Geotextile, Landslide, Reinforcement, Safety Factor.