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Zhang Y.,Beijing Jiaotong University | Yang S.,Beijing Jiaotong University | Luo X.,Beijing Institute of Surveying and Mapping | Fang J.,Transportation Institute | And 2 more authors.
Revista Tecnica de la Facultad de Ingenieria Universidad del Zulia | Year: 2016

The BDS (BeiDou Navigation Satellite System) has been widely used in business, military and individual affairs, nevertheless, this single system is still deficient in poor positional accuracy. The paper targets at this problem, putting forward an integrated positioning algorithm of BDS/GPS/GLONASS on the basis of isobar random model. First of all, we combine the three systems to conduct observation, which makes the visible stars increase greatly and we can gain more accurate positioning information. Then we apply isobar random model to locate the position to further improve the positioning accuracy. When only considering the satellite clock error and receiver clock error, we conduct instance simulation on the integrated positioning algorithm. The result shows that in comparison with the single Compass Navigation Satellite System, this integrated algorithm has higher positioning accuracy.


Wang P.-C.,Beijing Jiaotong University | Liu J.-K.,Beijing Jiaotong University | Li X.,Beijing Jiaotong University | Li X.,Qinghai Research and Observation Base | Fang J.-H.,Qinghai Research and Observation Base
Tiedao Xuebao/Journal of the China Railway Society | Year: 2014

With the discrete element method(DEM), biaxial compressions test conditions for crushed rock aggregate were established in the Fish language and the Clump logic commands in PFC2D were incorporated into the computer language to simulate the crushed rock aggregate of irregular shapes. Compared with large-scale laboratory triaxial tests, the parameters of the numerical model were calibrated and validated. The stress-deformation and shearing strength of the crushed stone aggregate of three typical particle sizes were analyzed. The research results demonstrate as follws: The confining pressure influences the stress-strain characteristics of aggregate significantly; for aggregate of different particle sizes, along with adding of the confining pressure, the peak deviatoric stress increases while the stress ratio decreases; within the specified range of confining pressure initial compression and subsequent dilation are observed with the aggregate, the higher the confining pressure, the larger the compression and the smaller the dilation; the shear strength envelope of the aggregate is nonlinear, under the same confining pressure, the shear strength increases with increasing of particle sizes; the apparent friction angle decreases with adding of the confining pressure, under the same confining pressure, the larger the particle size of the aggregate, the larger the apparent friction angle.


Li X.,Beijing Jiaotong University | Li X.,Qinghai Research and Observation Base | Wang P.-C.,Beijing Jiaotong University | Ao G.-D.,Beijing Jiaotong University | Fang J.-H.,Qinghai Research and Observation Base
Tiedao Xuebao/Journal of the China Railway Society | Year: 2014

Discontinuous deformation analysis (DDA) is considered to be an efficient way to study deformation behavior of ballast, in which polygon particles can be easily captured. In this paper, a new method was proposed to generate polygon particles and was successfully implied in DDA simulation of spontaneous stacking and uniaxial compression process of ballast. The results demonstrate as follows: The spontaneous repose angle of ballast is affected by the angle of friction of particle surfaces, interlocking effect of particles and the angle of friction between particles and ballast slabs; the DDA method is a useful method for the investigation of deformation behavior of ballast; three stages can be identified in compaction of ballast as the elastic, plastic and elastic hardening stages, the hardening stress controls the plastic strain and has a function similar to the pre-consolidated stress.


Wang D.,Beijing Jiaotong University | Liu J.,Beijing Jiaotong University | Li X.,Beijing Jiaotong University | Li X.,Qinghai Research and Observation Base
Procedia Engineering | Year: 2016

Salt expansion is one of the major problems of subgrade involving saline soils. Salt expansion is induced by the crystallization of salt when the soil water content or temperature decreases. A case of salt expansion in subgrade composed by saline soil is introduced. It is located in G314 Road, which is one of the national highways in China, from Urumqi to Khunjerab. There is 3.40 ∼5.91% salt within 1.0 depth in the ground surface of the G314 (K587 + 035), which belongs to strong sulphate salty soil. The maximum salt expansion is up to 20 cm in G314 Road, which has a serious impact on the road. Salt expansion is majorly controlled by the salt crystallization and the transmission of water and salt. Based on the solute transport theory in porous media, the water flow theory and thermal conduction theory, the govern differential equations of coupled salt crystallization, salt transmission and water flow are established in this paper. The coupled water and salt transfer problem of saline soil is solved by a software named as COMSOL with the use of a secondary development module. To verify the method for simulating the coupled water and salt transmission process, the water and salt transfer process in a 1D soil column is simulated and the results are compared with the theoretical solution. The results show that coupled model of water and salt established in this paper can accurately predict salt migration and crystallization of saline soil. © 2016 The Authors. Published by Elsevier B.V.


Bai Q.-B.,Beijing Jiaotong University | Li X.,Beijing Jiaotong University | Li X.,Qinghai Research and Observation Base | Tian Y.-H.,Beijing Jiaotong University | Fang J.-H.,Qinghai Research and Observation Base
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

Frost heaving and thaw collapsing are the main defects of subgrade in permafrost areas and are highly related to the coupled heat-moisture migration. Based on the water flow theory of unsaturated soil and the heat transfer theory of soil, the differential equations for coupled water and heat transfer are established. The coupled water and heat transfer problem of frozen soil is solved using the secondary development of COMSOL Multi-physics. To verify the method for simulating the heat-moisture coupled process, the freezing and thawing processes of soil columns are simulated, and the results are compared with the measured data from laboratory tests. Finally, a case study is carried out for the subgrade in Maduo county, Qinghai Province, and the characteristics of the coupled heat-moisture migration in permafrost subgrade are analyzed. ©, 2015, Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering. All right reserved.

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