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Zhao X.,Southwest Jiaotong University | Zhao X.,Key Laboratory of High speed Railway Engineering | Zhao X.,Purdue University | Salgado R.,Purdue University | Prezzi M.,Purdue University
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2015

The use of combined anchoring systems for slope stability enhancement is becoming more frequent. In combined anchoring systems, active anchors (e.g. prestressed tiebacks) and passive anchors (e.g. soil nails) are used simultaneously to stabilise a slope. Although stability analysis of slopes with either active or passive anchors used separately is routine in engineering practice, experience with slopes in which these two types of anchoring systems are used in combination is considerably more limited. For example, there are questions concerning the load sharing between active and passive anchors. In this study, centrifuge tests are designed to investigate the contribution of passive anchors to the overall stability of a slope by monitoring the deformation and stress distributions in anchored slope models. Centrifuge model tests are carried out on six model slopes at the same acceleration of 100 g with different types of reinforcement: active anchors for four models and a combined anchoring system for two models. The experimental results show that the passive anchors in the combined anchoring system make an important contribution to the overall stability of the slopes. The tests are then used to verify a slope stability program that can consider both types of anchors acting together. © ICE Publishing: All rights reserved Source

Cui K.,Southwest Jiaotong University | Cui K.,Key Laboratory of High speed Railway Engineering | Lic W.,Southwest Jiaotong University
Materials Research | Year: 2016

In this paper, the mechanical, dry shrinkage and frost resistance performance of cement stabilized graded stone with framework and dense structure were investigated. A higher cement content owns a correspondingly better mechanical performance. With the different moisture content, the dry shrinkage and frost resistance performance of cement stabilized graded stone showed a similar improving and deteriorating trend. The specimens (sample 0, 1, 2, 3), with different moisture content (4%, 5%, 6%, 7%) in a 6% cement content, were measured and analyzed. A sample contained low moisture content has a relatively loose and dry mixtures, which owns a insufficient cement hydration reaction and low strength, finally leads to a weaker dry shrinkage resistance performance. Moreover, the high moisture content sample has a damp and flabby reaction procedure, which has a larger amount of moisture evaporation and further deteriorated dry shrinkage. The moisture content significantly influence the pore parameters of prepared samples, whose trend followed those of dry shrinkage and frost resistance performance. The pore size distribution of these composites shifted toward smaller pore size scope with a proper moisture content. In addition, scanning electron micrographs (SEM) showed that the denser microstructure of prepared cement stabilized graded stones. Source

Zhan Y.,Southwest Jiaotong University | Zhan Y.,Key Laboratory of High speed Railway Engineering | Zhao R.,Southwest Jiaotong University | Ma Z.J.,University of Tennessee at Knoxville | And 3 more authors.
Engineering Structures | Year: 2016

Concrete-filled steel tube (CFST) member is widely used for building, bridge and foundation structures because of its excellent performance. When a CFST member is subjected to axial loads, the filling concrete is confined by the steel tube, resulting in a tri-axial state of compression that improves its strength, stiffness and ductility. However, the cracking of concrete in tension zone would decrease this enhancement when the CFST member is subjected to flexure, especially when it is used as a major flexural member with large-scale section in bridges. To overcome this weakness, the prestressed CFST concept is investigated in this paper. Eight prestressed CFST beams with large-scale section (300 × 450 mm) were tested under bending. Two concrete strengths (C50 and C60) and two different degrees of prestressing (0.26 and 0.40) were studied in the experimental program. The full vibration and grouting method was introduced to gain a good performance of specimens. The perfobond rib shear connector was adopted to achieve the composite action. The flexural behaviors were verified by comparing with predictions from a proposed model considering the confinement effects. A simplified method is proposed to determine the ultimate moment capacity based on the plastic stress block hypothesis. Both experimental and analytical results show that the prestressed strands could significantly enhance the confinement effect of the core concrete under bending, which, in turn, improves the prestressed CFST beam performance in strength, stiffness and ductility. © 2016. Source

Zhai W.,Southwest Jiaotong University | Wei K.,Key Laboratory of High speed Railway Engineering | Wei K.,Southwest Jiaotong University | Song X.,Southwest Jiaotong University | Shao M.,Southwest Jiaotong University
Soil Dynamics and Earthquake Engineering | Year: 2015

A field measurement of ground vibration was performed on the Beijing-Shanghai high-speed railway in China. In this paper, the experimental results of vertical ground vibration accelerations induced by very high speed trains running over a non-ballasted track on embankment with speeds from 300 to 410. km/h are reported and analyzed in detail for the first time. Characteristics of ground vibration accelerations in both time and frequency domains are analyzed based on the test data. It is shown that the periodic exciting action of high-speed train bogies can be identified in time histories of vertical accelerations of the ground within the range of 50. m from the track centerline. The first dominant sensitive frequency of the ground vibration acceleration results from the wheelbase of the bogie, and the center distance of two neighboring cars plays an important role in the significant frequencies of the ground vibration acceleration. Variations of time-response peak value and frequency-weighted vertical acceleration level of ground vibration in relation with train speed as well as the distance from the track centerline are also investigated. Results show that the time-domain peak value of ground vibration acceleration exhibits an approximately linear upward tendency with the increase of train speed. With the increasing distance from the track centerline, the frequency-weighted vertical acceleration level of the ground vibration attenuates more slowly than the time-domain peak value of the ground vibration acceleration does. Severe impact of high-speed railway ground vibration on human body comfort on the ground occurs at the speed of 380-400. km/h. The results given in the paper are also valuable for validating the numerical prediction of train induced ground vibrations. © 2015. Source

Zhan Y.,Southwest Jiaotong University | Zhan Y.,Key Laboratory of High speed Railway Engineering | Ma Z.J.,University of Tennessee at Knoxville | Ma Z.J.,Southwest Jiaotong University | And 3 more authors.
Journal of Bridge Engineering | Year: 2016

In this study, push-out tests were conducted to evaluate the interface behavior between steel and concrete connected by bonding. Twelve sets of specimens with different adhesive thicknesses, modulus of elasticity, and interface roughness were investigated. Failure modes, ultimate loads, and load-slip relationships are reported and analyzed in the paper. The experimental results show that factors such as modulus of elasticity of adhesive materials, adhesive thickness, and interface roughness affect the interface behavior. An analytical model is proposed to predict the ultimate load value and the load-slip relationship. The comparison between test results and analytical predictions shows good agreement. © 2016 American Society of Civil Engineers. Source

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