Subgrade Deformation Research Articles

Moisture influence on structural responses of pavement on expansive soils

Expansive soils are prone to heave and shrinkage due to changes in their natural moisture content. It would be helpful to predict distresses in pavement induced by heave/shrinkage because of long-term moisture variations in the subgrade considering specific environmental conditions. The virtual load method (VLM) has recently been developed to identify virtually distributed load that produces an equivalent deflection of the pavement caused by heave/shrinkage of expansive subgrade soils. In this research, a pavement section of interstate highway 220 (I-220) in Northern Louisiana is considered to implement the VLM and analyze structural behavior due to natural migration of water in unsaturated soil layers. Heave/shrinkage of the soils is computed from the predicted moisture content changes in subgrade using software VADOSE/W. In applying the Winkler’s model in the inverse theory to identify expansive soil-induced stresses in the pavement, a new iteration algorithm is proposed to consider the pavement-soil interaction. Special attention is drawn to the location of absolute maximum shear forces and bending moments in the pavement and their influences on the subgrade deformation. The effects of pavement stiffness and swelling pressure of the subgrade expansive soils are presented to understand the behavior of pavement on expansive soils.

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.

Study on Deformation Characteristics of Low-Highway Subgrade under Traffic Load

Highway subgrade bears millions of traffic loads over the years, and its strength, stiffness, and long-term stability gradually decline. In this paper, dynamic triaxial tests were carried out to study the time evolution and spatial distribution of strain and pore pressure of highway-subgrade soil under the action of traffic load. The influence of traffic load on subgrade deformation was analyzed. Furthermore, a numerical-calculation model of the subgrade was established. The deformation characteristics of subgrade under driving load were analyzed. The main conclusions can be drawn as follows: (1) With the increase in loading times, the cumulative strain and pore pressure can be roughly divided into three stages: rapid-growth stage, slow-growth stage, and equilibrium stage. (2) The influence of traffic load on the cumulative strain and pore-water pressure of subgrade soil decreases rapidly with the increase in depth. (3) The amplitude of traffic load has a tremendous influence on the strain and pore pressure of subgrade soil, especially for shallow subgrade. (4) As the distance from the subgrade surface increases, the maximum deformation appears at the edge of the subgrade.

Soil State Testing Using Heavy Vehicle Vibrations

Changes in the elastic characteristics of the railway subgrade have been determined using nonstop long-term (more than 50 days) train passage seismic observations. We examined the records of the broadband sensitive seismometer TC-120s in the low-frequency band (below 0.1 Hz) to obtain the subgrade response to various train passages and its relaxation after unloading. Analytical models of subgrade deformation by the train are proposed. When comparing models in the experiment, we showed that a lowpass filter (below 0.1 Hz) provides waveforms with parameters determined by the deformation properties of the soil. We carried out statistical processing of 1600 train seismic records and determined parameters characterizing the subgrade reaction to the vibration effects created by trains in the ultra-low-frequency range. Therefore, we can use these parameters to monitor after daily averaging and weekly smoothing. When observing the spring thawing of the soil, we considered the sensitivity of seismic monitoring using heavy vehicle vibrations, particularly changes in the soil state properties under a rise in ambient temperature. The presented observations can be used for seismic monitoring technology at an early stage of hazardous processes in the subgrade.

Effects of Principal Stress Rotations and Excess Pore-Water Pressure Changes on Soft Subgrade Deformation of Airfield Mat Structures under Pseudodynamic Loading

AbstractThe Airfield Mat 2 (AM2) matting system typically is employed as an expedient surface for airfields. It usually is emplaced over soft existing subgrades due to logistical, material, and equ...

Analysis of Deformation Characteristics of Filled Subgrade Treated by Micro-Pile

Deformation control of fill subgrade is a difficult point in the field of highway engineering. This article relies on the treatment project of micro-piles for subgrade deformation of K555 + 070～K557 + 710 section of Qingdao-Yinchuan Expressway. Settlement and stress monitoring was carried out at the toe of the roadbed, the shoulder, and the center of the roadbed. We use Midas/GTS modeling trial calculation. A new method to check the simulation results of the deviation rate is proposed. A calculation model of the stress and deformation of the subgrade in the whole life cycle is established. The results of comparative analysis, monitoring, and simulation are as follows. ① The compression and consolidation of the fill account for most of the settlement and deformation of the roadbed in the whole life cycle. ② Subgrade center settlement is the sensitive part of subgrade deformation. ③ After piles are added, the deformation extremes at the toe of the slope, the shoulder, and the center of the roadbed are all reduced by more than 96%. The research results can provide theoretical guidance for the analysis of the stress and deformation characteristics of the subgrade before and after the micro-pile treatment.

Retaining Technology for Deep Foundation Pit Excavation Adjacent to High-Speed Railways Based on Deformation Control

Considering the deep foundation pit of a car dumper room close to the Beijing–Baotou railway, the countermeasures of the foundation pit design are analyzed according to the surrounding environment and stratum conditions. Through Midas GTS software as well as field measured results, the construction effect on the adjacent railway subgrade is discussed. Therefore, the deformation characteristics of the foundation pit as well as the retaining structure, including the railway subgrade, caused by the excavation process, are revealed. The results show that the five-sided water-stop structure formed by cement piles around and at the bottom of the pit avoids the consolidation settlement of the adjacent railway subgrade caused by deep dewatering and also reduces the lateral displacement (i.e., in a horizontal direction) and the heave of the pit bottom. As a result, the lateral displacement near the railway side is larger than that of the retaining structure on the other side due to the subgrade on the pit side. The cross-lot bracing across the foundation pit will transfer the bias pressure of the subgrade to the retaining structure far away from the railway, while the transfer effect of the knee bracing is not obvious. The deformation of the railway subgrade and its evolution rate caused by the removal of internal bracing is significantly greater than the subgrade deformation and the change rate of deformation caused by excavation. The research results provide useful guidance for the deep foundation pit design.

Numerical Analysis of Additional Stresses in Railway Track Elements Due to Subgrade Settlement Using FEM Simulation

The prediction of additional stresses in ballasted track due to subgrade deformation is the main objective of the present paper. In this context, a 2D finite element model of ballasted railway track was built using the ANSYS Workbench program. Based on this model, an investigation of stresses and deformation values of track elements was conducted in three cases with different contact types. It was found that the case introducing the status of a new track, which has frictional contacts between sleepers and ballast with bonded contacts between other elements, has lower stresses in most of the track elements. Moreover, this case was applied for studying the effect of the settlement on track elements. It was found that stresses increased with increasing the settlement value. The average percentages of increased stresses are 4.18%, 5.85%, and 7.21% in railhead, tie plate, and sleeper, respectively, due to a 1 mm increase in the settlement. Finally, a second-degree polynomial equation was derived to predict the additional stresses in each element due to track settlement. It is expected that this study would help to decrease the maintenance costs and extend the service life of the track elements by predicting the additional stresses in them.

Analysis on Control Indicators for Settlement and Deformation of the Rock-Filled Subgrade in Mountainous Area

Analysis on Control Indicators for Settlement and Deformation of the Rock-Filled Subgrade in Mountainous Area

Monitoring Analysis and Numerical Simulation of the Land Subsidence in Linear Engineering Areas

Non-uniform land subsidence can cause subgrade deformation and threaten the safety of linear projects such as high-speed railways. The Lunan high-speed railway is taken as the research background. Combined with the hydrogeological and engineering geological conditions, the regional land subsidence is analyzed by the combined method of the differential interferometric synthetic aperture radar (D-InSAR) and small baseline subset interferometric synthetic aperture radar (SBAS-InSAR), which is verified by using precise leveling and GPS monitoring data. The accurate land subsidence analysis of large-scale linear engineering is realized. The distribution situation and change laws of land subsidence in linear engineering areas are revealed. Then, a three-dimensional coupled numerical model of land subsidence along a large-scale linear project is established by using the finite difference method. The spatial distribution characteristics of land subsidence in the linear engineering area are quantitatively analyzed and predicted. The main factors affecting land subsidence and the degree of land subsidence are discussed while keeping the pumping rate constant. The results show that: 1) The combined method of D-InSAR and SBAS-InSAR has high accuracy in the land subsidence monitoring of linear engineering. 2) There are five non-uniform settlement funnels along the Lunan high-speed railway. The groundwater over-extraction and coal mining are the main reasons for the land subsidence. 3) Realizing water source conversion and reduce groundwater exploitation are the main factors in linear engineering areas as soon as possible.

Testing and Evaluation on Dynamic Response of a New Modified Soil Subgrade under Freeze-Thaw Cycles

Abstract Dynamic response analysis is an effective method of evaluating the strength, deformation, and stability of subgrade under repeated vehicle traffic loads. It is usually premised on the results of a field test, which not only requires a lot of manpower and money but also can be easily affected by extraneous factors. In this study, a laboratory test was conducted in order to examine the dynamic response of a new type subgrade: silty clay (SC) modified by fly ash and crumb rubber (RFS). A novel tester was adopted in order to simulate and impulse traffic loads with different vehicle speeds/weights on subgrade materials. In addition, the dynamic stress and acceleration responses of RFS and SC were analyzed under varying speeds and axle loads under 0–5 freeze-thaw (F-T) cycles. Thereafter, scanning electron microscope tests were conducted to bring about clarity regarding the effect on the internal structural changes of two test soils in order to elaborate on the reasons for these dynamic response changes. According to the findings of these tests, the dynamic stability of SC is better than the RFS before F-T cycles. However, the RFS provides better resistance to F-T dynamic stability as the F-T cycle goes on. In particular, the RFS is more suitable for subgrade filling in seasonally frozen regions. Against this backdrop, the current article proposes a convenient method to evaluate the dynamic response of subgrade in laboratory, besides providing a reference for the dynamic characteristics of RFS.

Long-term uplift of high-speed railway subgrade caused by swelling effect of red-bed mudstone: case study in Southwest China

A high-speed railway must support fast-moving vehicles and have strict low-deformation requirements. However, many high-speed railways encounter the problem of abnormal subgrade deformation caused by expansive rocks. In this study, the Neijiangbei station of the Chengdu-Chongqing high-speed railway in Southwest China, where the subgrade has undergone continuous and stable uplift during the construction and operation periods, was considered as an example. The Jurassic red-bed mudstone widely distributed in this area is a typical expansive rock, and its swelling effect is the main cause behind the uplift of the subgrade. Results of water-absorption tests, disintegration tests, and expansion tests indicate that the red-bed mudstone is characterized by easy disintegration, slow water absorption, and long-term swelling. A decoupling analysis method for the seepage and swelling of red-bed mudstone was proposed to simulate the water infiltration through the fissures and the temporal and spatial changes in the swelling. Using monitoring data, an inversion analysis of the high-speed railway subgrade uplift was conducted, and the subgrade deformation was predicted. The results suggest that the main changed area of the moisture-content field in the rock formation was a small area near the fissure layer. The moisture content of the mudstone increased rapidly in the first few years of infiltration and increased slowly over subsequent decades. Correspondingly, the subgrade uplift increased rapidly in the first few years after excavation owing to the swelling of the mudstone; thereafter, the growth rate decreased, but the subgrade uplift maintained long-term continuous growth for several decades.

Influence of the deep pit construction on a settlements of surrounding buildings

Various methods exist for calculating the subgrade settlements of foundations built on soil subgrade without defects and damages. The physical and mechanical characteristics of such soil subgrade are usually determined using the results of engineering and geological surveys and other methods that characterize their in-situ conditions before construction. It is usually assumed that these characteristics are constant throughout their life cycle regardless whether they get later disturbed by buildings and/or structures. In fact, the mechanical characteristics of the soils of the subgrade vary and are subject of continuous changes due to various factors. Therefore, the use of existing calculation methods often lead to inadequate estimates of settlements of subgrade and foundations of buildings and structures. Assessment of vertical deformations of soil subgrade in the zone of influence of deep pits usually falls in this category. The method for calculating the settlement of bases and foundations of buildings was developed taking into account the formation and development of defects and damages in the soil structure in the zone of influence of a deep pit. It is based on a method of layer-by-layer summation, taking into account the spatial stress state of the soil mass and changes in the mechanical state of the soil due to surcharge conditions.

A deep learning forecasting method for frost heave deformation of high-speed railway subgrade

Deformation of high-speed railway subgrades, due to low temperatures, is a common phenomenon in cold regions. In winter, the uneven frost heave of subgrade soil would cause hazards to train safety. It is therefore necessary to estimate and predict the subgrade properties. Since the variation of frost heave is non-stationary over time, traditional time series analyses have difficulties where complex physical parameters are not available. In this study, we introduce two models based on deep learning technology to predict frost heave deformation of railway subgrade. These include the artificial neural network (ANN) and long-short term memory (LSTM) network, where we used data of four sections to build the ANN and LSTM. The experimental results of the LSTM model provided lower MAE and RMSE with different datasets. The prediction of three deep deformations for the K1959 + 580 and K1962 + 618 section with slight fluctuation in the data and the performance of the ANN with MAE is 0.0090‐–0.0660 and 0.0069‐–0.0201 of the LSTM models. In the K2005 + 948 and K2029 + 829 section, ANN and LSTM estimated the frost heave deformation with MAE of 0.0061‐–0.0681 and 0.0054‐–0.0309 for a more intense fluctuation on the deformation. Our findings suggest that the network topology of the LSTM model with 12 hidden neurons performs best with fewer parameters, with an average RMSE of 0.0210 mm and MAE of 0.0138 for all the training samples, indicating that the deep learning model has high precision in this scenario.

Evolution characteristics of crack and energy of low-grade highway under impact load

ABSTRACT To analyse the feasibility of the low-grade highway as a launch site in military applications and improve the pavement crushing technology in civilian applications, this study investigates the evolution characteristics of a low-grade highway under impact load, including deflection, crack, and energy, via the continuum–discontinuum element method (CDEM). To this end, this paper proposes an energy statistics algorithm, and the correctness is verified. Then, a quarter three-dimensional numerical model of an asphalt concrete highway is established, and the effectiveness of CDEM in simulating the deflection of the highway under impact load is validated. Finally, an existing asphalt concrete highway structure is selected to study the evolution characteristics via numerical simulation. The results demonstrate the consistency between the variations of deflection at the load centre and the impact load. The deflection is primarily caused by the compressive deformation of subgrade. Crack planes mainly occur when the impact load increases rapidly. The variation of various constituent energies is different but closely related to the change in impact load.

Permanent deformation modelling of large-size unbound pavement materials tested in a heavy vehicle simulator under different moisture conditions

ABSTRACT Climate changes alter the environmental conditions which pavement design is based on, invalidating empirical design methods. Transition to mechanistic design requires the ability to model the behaviour of pavement materials under relevant environmental conditions. An accelerated pavement test (APT) is designed to test two instrumented pavement structures under moisture conditions which are altered by raising the groundwater table (GWT). Open-graded and well-graded subbase materials are used to investigate the effect of gradation on moisture dependency. Pavement response behaviour is modelled using a non-linear elastic (NLE) approach. Accumulation of permanent deformation under different moisture conditions is calculated by two models and compared to measured surface rutting. Moisture transport through the structures differs due to the subbase gradation. Increased GWT accelerates the accumulation of permanent deformations in both structures, identified by both models. One model provides a significantly better fit to the subgrade deformations and the width of the rutting profile.

Deformation behaviour and influence mechanism of thaw consolidation of embankments on the Qinghai-Tibet Railway in permafrost regions

With the thermal disturbance caused by engineering construction and global warming, thaw consolidation has become a primary source of subgrade deformation in permafrost regions. Based on the large-strain consolidation theory described by the updated Lagrangian, we study the thermal stability and the thaw consolidation in an ordinary subgrade at the warm and ice-rich permafrost (WIRP) site of the Beiluhe Qinghai-Tibet Railway (QTR) by establishing a thermo-mechanical coupled model. The research results are as follows: The initial mean annual ground temperature (MAGT) of the site influences the permafrost degradation on the Qinghai-Tibet Plateau due to construction and climate warming, exacerbating the thaw consolidation and creep of the ice-rich permafrost. The settlement rate and subgrade settlement increase with increasing embankment height, ice-rich permafrost layer thickness, and initial MAGT. Railway maintenance methods, such as ballast filling and track lifting, increase the subgrade weight, thus increasing the WIRP subgrade settlement. Furthermore, we predict the thaw consolidation of the DK1136 section of the QTR for the next 50 years. The prediction formulas of the cumulative settlements of the subgrade top and permafrost are established, and various suggestions for maintaining the railway subgrade of the WIRP site are proposed.

Опыт реологических расчетов одного из оползневых участков земляного полотна на Дальневосточной железной дороге

The safety of railway transport is affected by the quality of the superstructure, which is closely connected with the condition of the roadbed. In areas with a high precipitation and complex terrain landslides and local flow, causing deformation of the subgrade are possible. From here relevant is the prediction of the rheological state of landslide-prone sections of the railway with the change in humidity of the base soil subgrade. In the article on the basis of the theoretical developments of the authors an example of the rheological calculation of one of the landslide sites of the Far Eastern Russian railway is considered. There is a fairly good convergence of settlement data with the results of independent observations of resistance and deformities of the earth canvas, which allows us to recommend the developed developments for practical application. There is a fairly good convergence of calculated data with the data of independent observations of the stability and deformations of subgrade, which allows us to recommend the obtained developments for practical applications.

Comparison of numerical modeling results from laboratory and field obtained unsaturated flow parameters

Moisture and suction variation beneath pavement contribute significantly to the volumetric deformation of expansive subgrade in response to climatic loading. In order to quantify the damage due to climatic loading, estimation of moisture, and suction variation in pavement subgrade is of paramount importance. The objective of the current study is to investigate the moisture and suction variation in response to precipitation events with the aid of numerical modeling in the unsaturated pavement subgrade. In unsaturated soils where the voids are filled with both water and air, the SWCC describes the volume of the voids that remain filled with water as the soil drains pore water. The SWCC has been identified as the vital soil information required to analyze seepage, stability, and volume change problems involved in unsaturated soils. However, the selection of unsaturated flow parameters is typically laboratory-based which represents specific conditions rather than a dynamic scenario of the field. In this study, an attempt was undertaken to conduct numerical modeling using field generated unsaturated flow parameters along with five other predictive models. Results indicated the distinct variation of moisture and suction distribution in subgrade from the same rainfall event while using laboratory versus field generated SWCC unsaturated flow parameters. In addition, predicted model yielded output was also varying with the field generated parameters’ output. Instead of using laboratory-generated static parameters, it was found that field generated dynamic unsaturated flow parameters were able to capture better suction variation at the pavement subgrade.

Foundation Adaptability and Subgrade Deformation Analysis of High-Speed Railway above the Mined-Out Areas

Foundation Adaptability and Subgrade Deformation Analysis of High-Speed Railway above the Mined-Out Areas