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Chou Y.,Lanzhou University of Technology | Chou Y.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | Sheng Y.,CAS Lanzhou Institute of Geology and Geophysics | Chen J.,CAS Lanzhou Institute of Geology and Geophysics | And 2 more authors.
Cold Regions Science and Technology | Year: 2015

In permafrost regions, embankment stability has been destroyed with longitudinal cracks primarily caused by transverse asymmetric settlement. And shady-sunny slope effect is a principal factor which might result in embankment asymmetric settlement. Based on field data of some typical sections along the Chai-Mu Railway (simply called CMR) with obvious shady-sunny slopes, which is located on the Qinghai-Tibet Plateau, the ground temperature characteristics and settlement deformation properties of the embankment have been analyzed. This paper has studied how the different engineering measures, including rubble ventilation embankment, thermal pipe revetment embankment, rubble and thermal pipe revetment joint embankment, did influence the shady-sunny slope effect. The results show that: (1) Both thermal pipe revetment embankment and rubble ventilation embankment have perfect effect on cooling the roadbed in permafrost regions. However, for thermal pipe revetment embankment, the sunny-shady phenomenon and asymmetric settlement of embankment have been avoided if thermal pipe has been strengthened in sunny side. For rubble ventilation embankment, the sunny-shady effect has been hardly eliminated even though the rubble has been strengthened in sunny side. Although some composite embankments, such as the rubble and thermal pipe revetment joint embankment, have been successfully applied in the Qinghai-Tibet Railway, it is difficult to completely eliminate the sunny-shady slope problem along the CMR because of the complicated engineering geological conditions and the bad permafrost environments. (2) Along the CMR, in all common embankments - the observed results show that the settlement deformation is within 30. cm that is within the settlement standards of the National II Class Railway. Even the settlement deformation of thermal pipe subgrade and rubble ventilation embankment was able to meet the National I Class Railway standards - 20. cm. (3) On the basis of the above, some corresponding countermeasures and advice are proposed. First, rational use of the synthetic application of engineering measures must be taken. For example, let the structural mechanics measures and temperature controlled measures unify altogether to prevent longitudinal cracks. Second, the specific work conditions and details such as engineering geological condition, permafrost environments as well as other local factors including the slope orientation have to be taken into account in order to put forward rational engineering measures and accurate design parameters. Finally, it is essential to protect and to comprehensively evaluate the permafrost environment, which is the ultimate basis of permafrost engineering. © 2014 Elsevier B.V.


Chou Y.,Lanzhou University of Technology | Chou Y.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | He B.,Lanzhou University of Technology | He B.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | And 3 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2014

The structural characteristics is a basic attribute of soil, which has a strong influence on engineering properties of soil. The effect of structural characteristics on the mechanical properties of frozen loess has been investigated. Based on triaxial compression tests of remolded frozen loess and artificial structured frozen loess with different content of cement, this paper studied how the confining pressure, initial water content, temperature and the cement amount had influenced the frozen loess' strength behavior. The experimental results showed that in the same experiments, there were some differences of the stress-strain relationship between the unsaturated and saturated frozen loess. The temperature and confining pressure were the main important factors that influenced the shearing strengths of frozen soil. The lower the temperature is, the higher the failure strength is. The shearing strengths of unsaturated frozen loess are increasing with confining pressure, but that of saturated frozen loess has little relationship with confining pressure. The initial water content is another main factor affecting the frozen loess strength. As the increase of water content, the frozen loess strength is also increasing, but there is a peak point. After it the frozen loess strength would decrease gradually with the water content increasing, and the strength of saturated frozen loess reached the lowest. With regard to the unsaturated frozen loess, the yield strength and failure strength are both increasing with the content of cement. For the saturated frozen loess, the yield strength is increasing with the content of cement, too. However, the failure strength has little relationship with the cement content. The mentioned factors have obvious influence on the structural characteristics of frozen loess, but the cement content and water content are the dominating factors. The mechanical properties and structural characteristics of frozen loess depend on not only the single factor, such as confining pressure, initial water content, temperature and the cement amount etc., but also on possible interaction of the various factors. At last, the comprehensively structural coefficient M which correlates closely with parameters of shear strength was presented. By regression analysis, the exponential function relationship between M and c, as well as M and tan, were obtained, respectively. Moreover, the exponential functions were validated feasible. © 2014 ejge.


Yaling C.,Lanzhou University of Technology | Yaling C.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | Yaling C.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Binbin H.,Lanzhou University of Technology | And 2 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2014

In order to explore how the freezing-thawing action influences on the structural strength of loess, the direct shear tests of remolded loess and artificially structural loess were performed, respectively. The influence of freezing and thawing action on shear strength and related indexes of soil samples with different water contents and different cement contents has been analyzed. The result shows that freezing and thawing action makes the soil cohesion can become bigger, but there is no prominent change of internal friction angle. Both the water content and cement content have influence on the shear strength of the soil samples before and after freeze-thaw circle. When the water content remains constant, the internal friction angle of soil samples has changed a little with the cement content increasing before and after freeze-thaw circle, but the cohesion has been larger. When the cement content keeps constant, the cohesion has increased first and then decreased with the water content increasing, but the internal friction angle has changed a little. Under the same condition, the structural strength of soil after freeze-thaw is higher than that before freeze-thaw. The structural strength of soil has increased with the cement content increasing before and after freeze-thaw. Dry density is a very important index for evaluating soil strength. Even under the same soil compaction energy, there are some differences in initial dry density of the soils due to different water contents. So, the experimental results may present more complex features. © 2014 ejge.


Chou Y.,Lanzhou University of Technology | Chou Y.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | Chou Y.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Xingqiang C.,Lanzhou University of Technology | And 3 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2013

The structural characteristics are the basic attributes, which have a strong influence on engineering properties of soil. The effect of structural characteristics on the mechanical properties of frozen loess has been investigated. Based on triaxial compression tests of remolded frozen loess and artificial structured frozen loess with different content of cement,this paper studied how the confining pressure, initial water content, temperature and the cement amount influenced the frozen loess' strength behavior. The test results showed that in the same experiments, there were some differences of the stress-strain relationship between the unsaturated and saturated frozen loess. The temperature and confining pressure were the main important factors that influenced the shearing strengths of frozen soil. The shearing strengths of unsaturated frozen loess are increasing with confining pressure, but that of saturated frozen loess has little relationship with confining pressure. The initial water content is another main factor affecting the frozen loess strength. As the increase of water content, the frozen loess strength is also increasing,but there is a peak point. After it the frozen loess strength would decrease gradually with the water content increasing, and the strength of saturated frozen loess reached the lowest. With regard to the unsaturated frozen loess, the yield strength and failure strength are both increasing with the content of cement. For the saturated frozen loess, the yield strength is increasing with the content of cement, too. However, the failure strength has little relationship with the cement content. The mentioned factors have obvious influence on the structural characteristics of frozen loess, however the cement content and water content are the dominating factors. The mechanical properties and structural characteristics of frozen loess depend on not only the single factor, such as confining pressure, initial water content, temperature and the cement amount etc., but also on the possible interaction between the mentioned factors. At last, the comprehensive coefficient M which correlates closely with parameters of shear strength was presented. By regression analysis, the exponential function relationship between M and c as well as M and tanf was obtained respectively. Moreover, the exponential functions were validated feasible. © 2013, EJGE.


Chou Y.,Lanzhou University of Technology | Chou Y.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | Chou Y.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Li B.,Lanzhou University of Technology | And 3 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2015

Repeated freeze-thaw circle can make the loess' structure loose and make it weak, which is one of the main causes for the increase of collapse deformation of loess foundation. The collapsibility experiments have been performed on undisturbed loess, remolded loess and artificially structured loess with different amount of cement. The effect of freeze-thaw action (including different freeze-thaw circles), remolded process, water content and cement content on the collapsibility coefficient was analyzed. Some conclusions are deduced. (1) According to the definition of "collapsibility coefficient" and experimental curves, the effect of freeze-thaw action on collapsibility coefficient was obviously displayed. Discrimination of the undisturbed loess, remolded loess and artificially structured loess in collapsibility property is compared and explained. Whether for undisturbed loess, remolded loess or artificially structured loess, freeze-thaw circle makes the collapsibility coefficient become bigger under different water contents and different cement contents. (3) The initial freeze-thaw action has heavy effect on collapsible property. And the collapsibility coefficient increment has generally increased with the number of freeze-thaw cycles. However, when the number of freeze-thaw cycles is more than 15 times, the collapsibility coefficient remains substantially unchanged. The initial dry density is a very important index for evaluating the collapsibility coefficient of loess. When the water content of soil samples is about 16% (near the optimum water content), the initial dry density has reached the extremum value, so the collapsibility coefficient increment reaches a peak under the same number of freeze-thaw cycles. © 2015 ejge.


Wang D.-Q.,Lanzhou University of Technology | Zhu Y.-P.,Lanzhou University of Technology | Zhu Y.-P.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education
Gongcheng Lixue/Engineering Mechanics | Year: 2014

There is no effective method to analyze and calculate the stability of supporting structure with prestressed anchors, especially when the influences by prestress are taken into account. Valid quantitative analysis methods are rarely given in documents published. From plenty of literatures on qualitative analysis, the prestress exerted on the anchor plays a positive role in improving the stability of slope. The soil stress state is transformed by the additional stress caused by the prestress, thus the stability of slope can be enhanced. The prestress is treated as a concentrate force and discomposed into horizontal force and vertical force, so as to estimate the additional stress in the soil and analyze the stability of slope. By this method, the reinforcement of the prestress is embodied, and the stability analysis of supporting structure with prestressed anchors will be more precise and reliable. Moreover, analytical calculation shows that the method can be simplified to consider the horizontal force and ignore the vertical force when the anchor inclinations are among the common range.


Wang D.-Q.,Lanzhou University of Technology | Zhu Y.-P.,Lanzhou University of Technology | Zhu Y.-P.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2012

There are no effective ways to calculate the stability of prestressed anchor support considering the effect of prestress. Usually, the anchor is treated as a soil nail, and the safety factor is calculated by the same method of calculating soil nailing provided in standards. A simplified method is provided for calculating the safety factor of prestressed anchor support by treating the prestress as a concentrated force. Its feasibility is verified by finite element software.


Yaling C.,Lanzhou University of Technology | Yaling C.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | Gongqi Y.,Lanzhou University of Technology | Gongqi Y.,Northwest Center for Disaster Mitigation in Civil Engineering of Ministry of Education | And 2 more authors.
Electronic Journal of Geotechnical Engineering | Year: 2015

Based on field data, distribution characteristics and influential factors of embankment longitudinal cracks in permafrost regions were summarized. Moreover, according to the thermo-mechanical elastic-plastic element method, a 2D coupled thermal-mechanical model was set up to simulate how the sunny-shady slope has effected on the embankment longitudinal cracks in warm permafrost regions. The corresponding conclusion had a good agreement with the field results. (1)The high embankments with obvious shady-sunny slope effect are more likely to develop longitudinal cracks at the beginning of roadbed service. When the height of embankment was less or equal to 2.0m, the probabilities to develop longitudinal cracks were very small in all conditions. (2) The "0 displacement line" is originally presented. The development of longitudinal cracks is due to strength failure of permafrost. Once the permafrost under sunny slope thaws into soft soil layer, there will be tensile stress in the embankment. When the most tensile stress in the embankment takes place, the longitudinal cracks depends on whether there appears "0 displacement line" or not on the embankment bottom. Where the "0 displacement line" is, where the longitudinal crack happens. (3) The uneven settlement between the sunny side and the shady side results in that the whole embankment slants to the sunny side. And the soil deformation of sunny slope is influenced by the thaw bowl (soft layer) under it, so the settlement of the sunny side is more than that of the shady one. The longitudinal crack was caused by both horizontal and vertical displacement. As a result, the longitudinal crack goes through the embankment in a slantwise direction. © 2015 ejge.

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