Critical dynamic stress and shakedown limit criterion of coarse-grained subgrade soil

2020 ◽  
Vol 23 ◽  
pp. 100354
Author(s):  
Bin Zhai ◽  
Wuming Leng ◽  
Fang Xu ◽  
Sheng Zhang ◽  
Xinyu Ye ◽  
...  
Keyword(s):  
Dynamic Stress ◽  
Coarse Grained ◽  
Subgrade Soil ◽  
Critical Dynamic ◽  
Shakedown Limit

scholarly journals New Structure for Strengthening Soil Embankments

2018 ◽  
Vol 2018 ◽  
pp. 1-16
Author(s):  
Fang Xu ◽  
Wuming Leng ◽  
Rusong Nie ◽  
Qishu Zhang ◽  
Qi Yang
Keyword(s):  
Shear Modulus ◽  
Large Scale ◽  
Dynamic Stress ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Triaxial Tests ◽  
Additional Stress ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
Critical Dynamic

A new prestressed reinforcement device (PRD) consisting of two lateral pressure plates (LPPs) and a reinforcement bar is developed to strengthen soil embankments by improving the soil confining pressure and providing lateral constraint on embankment slopes. The reinforcement effects of PRDs were demonstrated by investigating the beneficial effects of increasing confining pressure on the soil behavior via the performance of a series of large-scale static and cyclic triaxial tests on a coarse-grained embankment soil. The results show that PRDs can effectively improve the soil shear strength, bearing capacity, ability to resist elastic and plastic deformation, critical dynamic stress, and dynamic shear modulus, and empirical methods were also developed to determine the critical dynamic stress and initial dynamic shear modulus of the embankment soil. Moreover, 3D finite element analyses (FEAs) with an LPP width of 1.2 m were performed to analyze the additional stress field in a prestressed heavy-haul railway embankment. The FEAs showed that the additional stress at a given external distance from the border of an LPP first increased to a maximum value and then gradually decreased with increasing depth; the additional stress was transferred to the zones where the subgrade tends to have higher stresses with peak stress diffusion angles of 34° (slope direction) and 27° (longitudinal direction); and a continuous effective reinforcement zone with a minimum additional stress coefficient of approximately 0.2 was likely to form at the diffusion surface of the train loads, provided that the net spacing of the LPPs was 0.7 m. The reinforcement zone above the diffusion surface of the train loads can act as a protective layer for the zones that tend to have higher stresses. Finally, the advantages and application prospects of PRDs are discussed in detail. The newly developed PRDs may provide a cost-effective alternative for strengthening soil embankments.

scholarly journals Devising a procedure for assessing the subgrade compaction degree based on the propagation rate of elastic waves

2021 ◽  
Vol 1 (5 (109)) ◽  
pp. 6-15
Author(s):  
Vitalii Kovalchuk ◽  
Ivan Kravets ◽  
Olga Nabochenko ◽  
Arthur Onyshchenko ◽  
Olexander Fedorenko ◽  
...  
Keyword(s):  
Elastic Waves ◽  
Propagation Rate ◽  
Coarse Sand ◽  
Technical Condition ◽  
The Body ◽  
Coarse Grained ◽  
Subgrade Soils ◽  
Subgrade Soil ◽  
Study Results ◽  
Characteristic Features

This paper reports the analysis of the methods for estimating the technical condition of the subgrade underneath a constructed railroad track or road during its operation. The study results have proven that the issue related to monitoring and controlling high-quality compaction of a heterogeneous subgrade remains relevant and requires the construction of reliable experimental methods for assessing the subgrade degree of compaction. A procedure for determining the compaction of subgrade in the laboratory has been devised, based on inertial microcomputer technologies, which makes it possible to assess the degree of compaction of subgrade soils depending on the propagation rate of an impact's elastic waves. An experimental study has been performed into the propagation rate of elastic waves across a homogeneous subgrade made of coarse-grained sand and a heterogeneous subgrade made of coarse sand with a layer of clay in the middle of the prism. The study results established that the propagation rate of an elastic wave in a heterogeneous subgrade accepts a lower value than the rate of wave propagation in a homogeneous subgrade. Through the dynamic interpretation, by using a discriminant statistical analysis, the characteristic features have been defined in the distribution of accelerations in the body of the homogeneous and heterogeneous subgrade, depending on the degree of compaction, which would make it possible to monitor the state of the subgrade during operation. As the degree of the subgrade soil compaction affects the technical condition of roads

scholarly journals Critical Dynamic Stress and Accumulative Deformation Evolution of Embankment Silty Clay Subjected to Cyclic Freeze-Thaw

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Lina Wang ◽  
Zhiyu Weng ◽  
Tianliang Wang ◽  
Qiang Liu ◽  
Guoyu Li ◽  
...  
Keyword(s):  
Plastic Strain ◽  
Dynamic Stress ◽  
Permanent Deformation ◽  
Triaxial Tests ◽  
Silty Clay ◽  
Cold Regions ◽  
Freeze Thaw ◽  
Critical Dynamic ◽  
Permanent Settlement ◽  
Embankment Stability

In cold regions, the permanent settlement of embankment is mainly caused by the repeated freeze-thaw process and long-term repeated train loads. Meanwhile, the critical dynamic stress (σdcr) is an important parameter index for determining embankment stability. Therefore, the accumulative permanent deformation evolution and critical dynamic stress of embankment soil subjected to cyclic freeze-thaw were studied using dynamic triaxial tests. Firstly, a numerical model for calculating critical dynamic stress considering the repeated freeze-thaw process was proposed, which shows that the critical dynamic stress of embankment soil rapidly decreases in the first two repeated freeze-thaw cycles, whereas it tends to be stable after the subsequent freeze-thaw process. Next, based on the normalization of the critical dynamic stress, an explicit model for predicting accumulative plastic strain (εp) of embankment soil was established. The above model considers freeze-thaw times, repeated dynamic stress amplitude (σd), and loading times, in which all material parameters of Qinghai-Tibet silty clay were presented. Thus, the critical dynamic stress and accumulative plastic strain models established in this paper can be applied to judge the embankment stability and predict the embankment settlement induced by train loads in cold regions.

Accumulated permanent strain and critical dynamic stress of frozen silty clay under cyclic loading

2018 ◽  
Vol 153 ◽  
pp. 130-143 ◽  
Author(s):  
Jiahui Wang ◽  
Xianzhang Ling ◽  
Qionglin Li ◽  
Feng Zhang ◽  
Yan Li
Keyword(s):  
Cyclic Loading ◽  
Dynamic Stress ◽  
Silty Clay ◽  
Permanent Strain ◽  
Critical Dynamic

scholarly journals Experimental study on permanent deformation characteristics of coarse-grained soil under repeated dynamic loading

2021 ◽  
Author(s):  
Huihao Mei ◽  
Sajjad Satvati ◽  
Wuming Leng
Keyword(s):  
Stress State ◽  
Strain Rate ◽  
Dynamic Stress ◽  
Stress Amplitude ◽  
Permanent Deformation ◽  
Confining Pressure ◽  
Coarse Grained ◽  
Deformation Characteristics ◽  
Permanent Strain ◽  
Coarse Grained Soil

AbstractPractical assessment of subgrade settlement induced by train operation requires developing suitable models capable of describing permanent deformation characteristics of subgrade filling under repeated dynamic loading. In this paper, repeated load triaxial tests were performed on coarse-grained soil (CGS), and the axial permanent strain of CGS under different confining pressures and dynamic stress amplitudes was analysed. Permanent deformation behaviors of CGS were categorized based on the variation trend of permanent strain rate with accumulated permanent strain and the shakedown theory. A prediction model of permanent deformation considering stress state and number of load cycles was established, and the ranges of parameters for different types of dynamic behaviors were also divided. The results indicated that the variational trend of permanent strain rate with accumulated permanent strain can be used as a basis for classifying dynamic behaviors of CGS. The stress state (confining pressure and dynamic stress amplitude) has significant effects on the permanent strain rate. The accumulative characteristics of permanent deformation of CGS with the number of load cycles can be described by a power function, and the model parameters can reflect the influence of confining pressure and dynamic stress amplitude. The study’s results could help deepen understanding of the permanent deformation characteristics of CGS.

scholarly journals Evaluation of Critical Dynamic Stress and Accumulative Plastic Strain of an Unbound Granular Material Based on Cyclic Triaxial Tests

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5722
Author(s):  
Qishu Zhang ◽  
Wuming Leng ◽  
Bin Zhai ◽  
Fang Xu ◽  
Junli Dong ◽  
...  
Keyword(s):  
Plastic Strain ◽  
Dynamic Stability ◽  
Large Scale ◽  
Dynamic Stress ◽  
Triaxial Tests ◽  
Cyclic Triaxial ◽  
Cyclic Triaxial Tests ◽  
Cycle Number ◽  
Critical Dynamic ◽  
Grey Relational

Critical dynamic stress (σcri) and accumulative plastic strain (εp) are primary indicators regarding the dynamic stability of unbound granular materials (UGMs). This study aims to seek an effective method to evaluate the dynamic stability of UGMs used in railway subgrades. First, the dynamic characteristics of an UGM used in railway subgrade bed construction were investigated by performing a series of large-scale cyclic triaxial tests, with the results showing that εp versus cycle number (N) curves can be categorized into stable, failure, and critical patterns. Grey relational analyses were then established, where the analyzed results demonstrated that the εp–N curve pattern and final accumulative plastic strain (εs) of the stable curves are strongly correlated with the moisture content (w), confining pressure (σ3), and dynamic deviator stress (σd). The analyzed grey relational grades distributed in a narrow range of 0.72 to 0.81, indicating that w, σ3, and σd have similar degrees of importance on determining the εp–N curve patterns and the values of εs of the UGM. Finally, a data processing method using a back-propagation (BP) neural network is introduced to analyze the test data, and an empirical approach is developed to evaluate the σcri (considering the effects of σ3 and w) and εs (considering the effects of σ3, w, and σd) of the UGM. The analyzed results illustrated that the developed method can effectively reflect the linear/non-linear relationships of σcri and εs with respect to σ3 and/or σd. The σcri approximately increases linearly with increasing σ3, and a simple empirical formula is proposed for the σcri. In addition, εs and its variation rate increase non-linearly with increasing σd but decrease non-linearly as σ3 increases.

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