Proposal of a Method to Easily Understand Rainfall Infiltration in Railway Embankments

Slope failures due to heavy or prolonged rain have been occurring frequently in Japan in recent years.In railway embankments,even small-scale surface collapse can result in track deformation.Currently,train operation during rainy periods is regulated according to empirical rules based on rainfall and disaster history.However,the validity of operation regulations is lacking because the rainfall infiltration circumstances inside the slope are unknown.We have been attempting to understand rainfall infiltration in railway embankments by applying a method of predicting surface collapse from observations of volumetric water content in the soil.We used previous field monitoring and model experiments to propose a method for easily understanding the state of rainfall infiltration in the surface layer of an embankment using the relative history of volumetric water content at different depths.In this study,we applied this simple determination method to railway embankments with different topography and geological environments to demonstrate the versatility of the method.

Investigating the performance of passageway corridor for ground reinforced embankments against rockfall

Rockfall disasters can result in damages to various structures such as highways and buildings.Ground reinforced embankments(GRE) are one of the barrier types used to prevent rockfall. GRE absorb the impact energy of the hitting rock blocks by the movement of fine soil particles triggered by the penetration of the rock in the soil. In this process,stresses in the wall are distributed in both the transverse and longitudinal directions. GREs on the valley slopes can be hundreds of meters long, so such structures cause difficulty in transition to valley slope behind the embankments. Especially, access to areas such as agricultural, pasture or forest lands behind the GRE becomes a challenge. The current paper presents the design of passageways in GRE using the finite element method to provide safe corridors at several different parts within the hundreds of meters long structures. A total of 4 different passageway designs for GRE were developed. Each finite element model was subjected to rockfall with different kinetic energies of 500, 1000 and 3000kJ. The obtained results showed that 44% increase in structure volume increased the impact capacity from 500 kJ to 3000kJ.Furthermore, the critical displacement caused by rockfall impact with an energy of 3000 kJ was reduced by 31%. It was determined that the support applied with the reinforced concrete wall did not reach the desired energy absorption value due to its rigid structure, and even collapsed at 3000 kJ.

Performance analyses of two-phase closed thermosyphons for road embankments in the high-latitude permafrost regions

Two-phase closed thermosyphons(TPCTs)are widely used in infrastructure constructions in permafrost regions.Due to different climatic conditions,the effectiveness of TPCT will also be different,especially in the extremely cold region of the Da Xing'anling Mountains.In this study,a series of three-dimensional finite element TPCT embankment models were established based on the ZhanglingMohe highway TPCT test section in Da Xing'anling Mountains,and the thermal characteristics and the cooling effect of the TPCTs were analyzed.The results indicated that the TPCTs installed in the northeastern high-latitude regions is effective in cooling and stabilizing the embankment.The working cycle of the TPCTs is nearly 7 months,and the cooling range of the TPCTs can reach 3 m in this region.However,due to the extremely low temperature,the TPCT generates a large radial gradient in the permafrost layer.Meanwhile,by changing the climate conditions,the same type of TPCT embankment located in the Da Xing'anling Mountains,the Xiao Xing'anling Mountains,and the Qinghai-Tibet Plateau permafrost regions were simulated.Based on the comparison of the climate differences between the Qinghai-Tibet Plateau and Northeast China,the differences in the effectiveness of TPCTs were studied.Finally,the limitations of using existing TPCTs in high-latitude permafrost regions of China were discussed and the potential improvements of the TPCT in cold regions were presented.

Finite Element Modeling of Geotextile Reinforced Embankments on Soft Clay

The use of geotextiles as a reinforcement material for improving the factor of safety against slope failure in embankments built on soft clay is becoming a common practice. This work is intended to help understand the effect of the geotextile reinforcement has on such embankments and to provide a design aid for civil engineers that enables them to quickly estimate the factor of safety against slope failure. Seventy four different cases were modelled and analyzed using a finite element software, GeoStudio 2018 R2. The results showed that the optimum improvement was achieved when using a single layer of geotextile reinforcement placed at the base of the embankment, by which the factor of safety increased by up to 40%. Adding a second layer, a third layer and a fourth layer, increases the safety factor by 2.5%, 1% and 0.5% respectively. Different charts for different heights of embankments were presented to aid in finding the most suitable slope angle and number of reinforcement layers required to achieve a certain safety factor.

Reliability assessment for serviceability limit states of stiffened deep cement mixing column-supported embankments

The reliability and deterministic analyses of wood-cored stiffened deep cement mixing and deep cement mixing column-supported embankments(referred to as WSCSE and DCSE,respectively)considering serviceability limit state requirements are presented in this paper.Random field theory was used to simulate the spatial variability of soil
cement mixing(SCM)material in which the adaptive Kriging Monte Carlo simulation was adopted to estimate the failure probability of a column
supported embankment(CSE)system.A new method for stochastically generating random values of unconfined compressive strength(qu)and the ratio(Ru)between the undrained elastic modulus and qu of SCM material based on statistical correlation data is proposed.Reliability performance of CSEs concerning changes in the mean(μ),coefficient of variation(CoV),and vertical spatial correlation length(θv)of qu and Ru are presented and discussed.The obtained results indicate that WSCSE can provide a significantly higher reliability level and can tolerate more SCM material spatial variability than DCSE.Some performance of DCSE and WSCSE,which can be considered satisfactory in a deterministic framework,cannot guarantee an acceptable reliability level from a probabilistic viewpoint.This highlights the importance and necessity of employing reliability analyses for the design of CSEs.Moreover,consideration of only μ and CoV of qu seems to be sufficient for reliability analysis of WSCSE while for DCSE,uncertainties regarding the Ru(i.e.both μ and CoV)and θv of qu cannot be ignored.

Application of Anti-seepage Technology in the Construction of Hydraulic Engineering Projects

With the development of China's economy,the implementation scale and scope of hydraulic engineering projects are increasing,and the application of anti-seepage technology has an important influence on the construction quality of hydraulic engineering.In this paper,the significance and problems of the application of anti-seepage technology in the construction of hydraulic engineering projects were mainly analyzed,and specific application strategies were proposed.

Numerical analysis of geosynthetic-reinforced embankment performance under moving loads

The performance of geosynthetic-reinforced embankments under traffic moving loads is always a hotspot in the geotechnical engineering field.A three-dimensional(3D)model of a geosynthetic-reinforced embankment without drainage consolidation was established using the finite element software ABAQUS.In this model,the traffic loads were simulated by two moving loads of rectangular pattern,and their amplitude,range,and moving speed were realized by a Fortran subroutine.The embankment fill was simulated by an equivalent linear viscoelastic model,which can reflect its viscoelasticity.The geogrid was simulated by the truss element,and the geocell was simulated by the membrane element.Infinite elements were utilized to weaken the boundary effect caused by the model geometry at the boundaries.Validation of the established numerical model was conducted by comparing the predicted deformations in the cross-section of the geosynthetic-reinforced embankment with those from the existing literature.On this basis,the dynamic stress and strain distribution in the pavement structure layer of the geosynthetic-reinforced embankment under a moving load was also analyzed.Finally,a parametric study was conducted to examine the influences of the different types of reinforcement,overload,and the moving load velocity on the geosynthetic-reinforced embankment.

Wind-sand flow simulation and radius optimization of highway embankment under different vertical curve radius

It is of great practical value to explore the correlation between the vertical curve radius of desert highway and the increase of sand accumulation in local lines,and to select the appropriate vertical curve radius for reducing the risk of sand accumulation.In this study,three-dimensional models of desert highway embankments with different vertical curve radii were constructed,and Fluent software was used to simulate the wind-sand flow field and sand accumulation distribution of vertical curve embankments.The results show that:(1)Along the direction of the road,the concave and the convex vertical curve embankments have the effect of collecting and diverging the wind-sand flow,respectively.When the radius of the concave vertical curve is 3000 m,5000 m,8000 m,10000 m and 20000 m,the wind velocity in the middle of the vertical curve is 31.76%,22.58%,10.78%,10.53%and 10.44%,higher than that at both ends.When the radius of the convex vertical curve is 6500 m,8000 m,10000 m,20000 m and 30000 m,the wind velocity at both ends of the vertical curve is 14.06%,9.99%,6.14%,3.22%and 2.41%,higher than that in the middle.The diversion effect also decreases with the increase of the radius.(2)The conductivity of the concave and convex vertical curve embankments with different radii is greater than 1,which is the sediment transport roadbed.The conductivity increases with the increase of radius and gradually tends to be stable.When the radius of the concave and convex vertical curves reaches 8000 m and 20000 m respectively,the phenomenon of sand accumulation is no longer serious.Under the same radius condition,the concave vertical curve embankment is more prone to sand accumulation than the convex one.(3)Considering the strength of the collection and diversion of the vertical curve embankment with different radii,and the sand accumulation of the vertical curve embankment in the desert section of Wuma Expressway,the radius of the concave vertical curve is not less than 8000 m,and the radius of the convex vertical curve is not less than 20000 m,which can effectively reduce the sand accumulation of the vertical curve embankment.In the desert highway area,the research results of this paper can provide reference for the design of vertical curve to ensure the safe operation of desert highway.

Prediction of high-embankment settlement combining joint denoising technique and enhanced GWO-v-SVR method

Reliable long-term settlement prediction of a high embankment relates to mountain infrastructure safety.This study developed a novel hybrid model(NHM)that combines a joint denoising technique with an enhanced gray wolf optimizer(EGWO)-n-support vector regression(n-SVR)method.High-embankment field measurements were preprocessed using the joint denoising technique,which in-cludes complete ensemble empirical mode decomposition,singular value decomposition,and wavelet packet transform.Furthermore,high-embankment settlements were predicted using the EGWO-n-SVR method.In this method,the standard gray wolf optimizer(GWO)was improved to obtain the EGWO to better tune the n-SVR model hyperparameters.The proposed NHM was then tested in two case studies.Finally,the influences of the data division ratio and kernel function on the EGWO-n-SVR forecasting performance and prediction efficiency were investigated.The results indicate that the NHM suppresses noise and restores details in high-embankment field measurements.Simultaneously,the NHM out-performs other alternative prediction methods in prediction accuracy and robustness.This demonstrates that the proposed NHM is effective in predicting high-embankment settlements with noisy field mea-surements.Moreover,the appropriate data division ratio and kernel function for EGWO-n-SVR are 7:3 and radial basis function,respectively.

Behavior of soil lateral deformation under embankments

Based on analysis of additional horizontal stress in the soil underembankment load, the behavior of the lateral deformation of the soil along the depth is studied. Theresult shows that the distribution of lateral deformation along the depth is arch-shaped, whichcorresponds nicely with the observed data. According to this, a new prediction model is establishedto forecast the lateral deformation. The shapes of the model curve with three parameters in themodel a, b and c are presented. The three parameters can easily be determined by three measured data(s_0, 0), (s_1, h_0)and (s_2, 2h_0). This model is applied to study two cases. The comparisonsillustrate that the displacement predicted by the model corresponds nicely with the measured data.

Behaviors of pile-supported embankments in highway engineering

Based on the variational approach for pile groups embedded in soil modeled using a load-transfer curve method, a practical method was conducted to estimate the settlement of symmetric pile group supported embankments. The working mechanism of composite foundations improved by rigid or semi-rigid columns is analyzed by this method. Under equivalent strain conditions, the pile-soil stress ratio approaches the pile-soil modulus ratio up to a limited value of pile stiffness （Rm〈10）; in the subsequent stages of high pile stiffness （Rm〉10）, a further increase in the pile-soil modulus ratio cannot lead to a significant increase of stress transferred to the columns in composite foundations. The major influencing factor of the stress concentration from soil to pile in a high pile-soil modulus ratio is the padding stiffness. For the composite foundation improved by cement mixing columns, the effective column length is about 15 to 20 m and it is a more economical and effective design when the column length is less than 15 m.

Comparison between responses of reinforced and unreinforced embankments due to road widening

The objective of this work is to compare the responses of geosynthetically-reinforced embankment and unreinforced embankment due to road widening by using the centrifuge model tests and a two-dimensional(2D) finite element(FE) model. The measured and calculated responses of the embankment and foundation exposed to road widening include the settlement,horizontal displacement,pore water pressure,and shear stresses. It is found that the road widening changed the transverse slope of the original pavement surface resulting from the nonuniform settlements. The maximum horizontal movement is found to be located at the shoulder of the original embankment. Although the difference is small,it is clearly seen that the geosynthetic reinforcement reduces the nonuniform settlements and horizontal movements due to road widening. Thus the reinforcement reduces the potential of pavement cracking and increases the stability of the embankment on soft ground in road widening.

Research on EPS application to very wide highway embankments in permafrost regions

In order to maintain the thermal stability of very wide highway embankments in permafrost regions, the thermal isolation material EPS is often utilized. To examine the effects of this insulation on the China National Highway （G214）, two-dimensional finite element analysis of temperature fields was conducted for varying widths of highway embankments with and without EPS insulation. The numerical results show that in permafrost regions the effect of thermal aggregation on asphalt pavement is more obvious when highway embankments are wider, and, specifically for the G214 highway, the insu- lation should be more than 25 cm thick for 24-m-wide embankments. However, considering other factors such as the struc tural rationality of the embankments and high engineering costs, it might not be feasible to install EPS insulation in 24-m-wide embankments of the G214 highway when the height of the embankments is less than 3.65 m.

Analysis of the stability and seismic behavior of the geosynthetic-reinforced embankments under earthquake

The stability and seismic behavior of geosynthetic-reinforced embankments during the earthquake is not well known.In this paper,the damage types of embankments were summarized,and the seismic stability of reinforced embankment were analyzed through an earthquake damage investigation in the Wenchuan earthquake region.Then,large-scale shaking table model tests were performed on the geosynthetic-reinforced embankment.The results show that the damage level of the reinforced embankment was almost less than that of the unreinforced embankment.The peak seismic earth pressure was nonlinear along the height of the embankment,the largest peak seismic earth pressure was roughly in the middle of the embankment slope.The peak ground accelerations(PGA)amplification factor first showed an increasing pattern and then a decreasing pattern with the increase of elevation,but there was a final increasing trend along the height of the reinforced embankment.The results can help to establish the proper design of the reinforcement embankments under earthquake conditions.

Lateral displacement of silty clay under cement-fly ash-gravel pile-supported embankments: Analytical consideration and field evidence

Based on back analysis of lateral displacements measured in situ by using the analytical solution, a useful method for estimating stress concentration ratio of geosynthetic-reinforced and pile-supported(GRPS) embankments was proposed. In order to validate the proposed method, a full-scale high-speed railway embankment(HSRE) with four instrumented subsections over medium compressibility silty clay was constructed in three stages. The soil profile, construction procedure and monitoring of settlements and lateral displacements of the four test sections were described. The field deformation analysis results show that 1) the combined reinforcement of CFG piles and geosynthetic layer perform well in terms of reducing lateral displacements; 2) the development of lateral displacements lags behind the increase of fill load, which can be attributed to the vertical load transfer mechanism of the pile foundation; and 3) pile length has a dominant effect on the stress distribution proportion between piles and surrounding soils. The comparison between predicted and experimental results suggests that the proposed analytical solution and the back analysis-based method are capable of reasonably estimating the lateral deformation and the stress concentration ratio, respectively, if the appropriate soil elastic modulus is chosen.

Simplified analytical solution for stress concentration ratio of piled embankments incorporating pile–soil interaction

Piled embankments have been extensively used for high-speed rail over soft soils because of their effectiveness in minimizing differential settlement and shortening the construction period.Stress concentration ratio,defined as the ratio of vertical stress carried by pile heads(or pile caps if applicable)to that by adjacent soils,is a fundamental parameter in the design of piled embankments.In view of the complicated load transfer mechanism in the framework of embankment system,this paper presents a simplified analytical solution for the stress concentration ratio of rigid pile-supported embankments.In the derivation,the effects of cushion stiffness,pile–soil interaction,and pile penetration behavior are considered and examined.A modified linearly elastic-perfectly plastic model was used to analyze the mechanical response of a rigid pile–soil system.The analytical model was verified against field data and the results of numerical simulations from the literature.According to the proposed method,the skin friction distribution,pile–soil relative displacement,location of neural point,and differential settlement between the pile head(or cap)and adjacent soils can be determined.This work serves as a fast algorithm for initial and reasonable approximation of stress concentration ratio on the design aspects of piled embankments.

Strengthening long-term embankments maintained on permafrost soils

An analysis of the reasons for the displacements of long-term embankments maintained on permafrost soils indicates that they mainly occur due to plastic deformations in the layer of seasonal freezing and thawing;therefore,the reconstruction of permafrost is not effective in this case.It is proposed to strengthen these embankments with the help of using jet technology for cementation of the top layer of the roadbed.This approach is considered through the example of the deforming embankment on 6,278 km of the Turinskaya-Karymskaya section of the Trans-Siberian Railway.

Delta River Swampy Areas Earth Fill Embankments Primary Consolidation Management Issues

It is well known that soft silty clayey and even peaty soils especially existing in Great River Deltas Swampy Areas,under important Earth Fill Embankment Construction experience huge and hardly bearable primary consolidations settlements along with the minor but not negligible consequent secondary consolidation effects.In order to properly manage these particular huge settlements environments,it is very important to follow up the settlements monitoring data,by a macroscopic soil volume interpretation along with some amendments namely some mathematical added variabilities of the classic Terzaghi Primary Consolidation Equation,which are examined in a companion paper recently published in this Journal.In this paper some indications are given about how to face the macroscopic soil volume primary consolidation settlements,and especially it is suggested how to interpret the misleading laboratory consolidation test values of the coefficient of consolidation.Moreover,some design alternative solutions are examined to grasp both the potential technical and economic benefits along with their consequent disadvantages.Finally,this paper underlined the primary role of the supervision engineer to get a good estimate in the settlements forecasting and his related ability to understand the meaning of anomalous monitoring data and to timely make and match the primary consolidation settlements forecasting calculation adjustments.

Vibration diagnostics of weak base embankments

In this paper the theoretical background was analyzed for vibration diagnostics method and experience in its application for weak base embankments. General schemes of survey and recommendations on hardware systems and further prospective development are outlined.

Analysis of the effects of rising temperature for embankments under seismic loads in cold regions

The effect of temperature rising for frozen soil because of dynamic load was investigated by indoor tests.Roadway and railway embankments are always loaded by dynamic loads such as earthquakes and vehicles.Because the Qinghai-Tibetan Plateau is a re-gion where earthquakes occur frequently,it is essential to consider the temperature-rising effect of earthquakes or vehicles on railway and road embankment.In this paper and according to the theories of heat transfer and dynamic equilibrium equations,as-suming frozen soil as thermal elastic-viscoplastic material,taking the combination of thermal and mechanical stresses into account,we present the numerical formulae of this dynamic problem,and the computer program of the two-dimensional finite element is written.Using the program,the dynamic response analyses for embankments loaded by earthquake are worked out.Analysis in-dicated that the temperature-rising effect result from earthquakes for embankment in nonuniform distribution in some small areas,the maximum rising temperature is 0.16 ?C for consideration in this paper.