Micro-mechanism of the interaction between sand and geogrid transverse ribs
- Authors: Zhou, J. , Chen, Jianfeng , Xue, Jianfeng , Wang, J. Q.
- Date: 2012
- Type: Text , Journal article
- Relation: Geosynthetics International Vol. 19, no. 6 (2012), p. 426-438
- Full Text: false
- Reviewed:
- Description: To study the interaction between sand particles and geogrids, pullout tests were performed on one type of geogrid in Pingtan medium sand. The sand motion around the ribs was captured by high-resolution digital camera and CCD camera. The images were analysed with the aid of digital photography measurement and micro-image analysis. Microscopic particle motion and displacement fields around the transverse ribs were then obtained to verify the macro behaviour of the sand–rib interaction. It was found that the thickness of shear band increases with the normal stress applied, and the shear zone is asymmetrical to the soil–rib interface. A near wedge shape shear zone was observed by analysing the shear strain around the ribs, which indicated that a punching shear failure mechanism may be applicable to the tested geogrid in medium-dense sand. Comparison of various models for bearing capacity of geogrids shows that the size and shape of bearing members should be considered in the calculation of bearing resistance of geogrids.
Experimental measurement and numerical computation of geogrid tension in centrifuge modeling
- Authors: Chen, Jianfeng , Yu, Songbo , Xue, Jianfeng , Shi, Zhenming
- Date: 2011
- Type: Text , Journal article
- Relation: KSCE Journal of Civil Engineering Vol. 15, no. 8 (2011), p. 1343-1348
- Full Text: false
- Reviewed:
- Description: Tension measurement of geogrid is essential in reinforcement mechanisms studies. Geogrid is a nonlinear flexible material with large apertures, it is difficult to measure the tensions mobilized in geogrid, especially in scaled-down geogrid in centrifuge modeling. In this study, strain gauges were glued onto the surface of model geogrid with epoxy resin and were calibrated through multi-stage and continuous tensile tests. Generalized Kelvin model was used to fit the constitutive curves from the tensile tests. The model is capable to describe time-dependent and nonlinear behavior of the composite material of epoxy resin and model geogrid. Based on generalized Kelvin model, tensions in the model geogrid were measured in a centrifugal modeling of a reinforced embankment on soft clay. A finite element model was developed to simulate the centrifuge modeling and a comparison was carried out between the computed and measured tensions. The numerical results basically captured the measured reinforcements, indicating that the method of reinforcement measurement proposed in this study is appropriate and reasonable.
Failure mechanism of geosynthetic-encased stone columns in soft soils under embankment
- Authors: Chen, Jianfeng , Li, Liang-Yong , Xue, Jianfeng , Feng, Shou-Zhong
- Date: 2015
- Type: Text , Journal article
- Relation: Geotextiles and Geomembranes Vol. 43, no. 5 (2015), p. 424-431
- Full Text: false
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- Description: The reaction of geosynthetic-encased stone columns (GECs) in soft soils under embankment loading was modeled with an indoor physical model test and numerical models using three dimensional and two dimensional finite element methods. The experimental and three dimensional numerical modeling results showed that the failure of the GECs is caused by the bending of the columns rather than shear. Three dimensional finite element analysis showed that the distribution of unbalanced lateral loading acting on the columns is symmetric about a 'hinge point' above the plastic hinge, rather than triangle or uniform distribution. An equivalent shear resistance model of the GECs is proposed based on the distribution of the unbalanced lateral loadings on the wall. The stability of the embankment was analyzed in two dimensional finite element method by transforming the columns into equivalent soil walls using equivalent bending resistance and equivalent shear resistance methods. It was found that results from equivalent bending resistance method is closer to the estimations from the three dimensional analysis, which agrees with the bending failure mechanism of the GECs. It is suggested that one more row of such columns may be required to provide higher lateral resistance in the soils in front of the toe to improve the stability of the embankment. © 2015 Elsevier Ltd.
Performance of a geogrid reinforced soil wall on PVD drained multilayer soft soils
- Authors: Chen, Jianfeng , Tolooiyan, Ali , Xue, Jianfeng , Shi, Zhenming
- Date: 2016
- Type: Text , Journal article
- Relation: Geotextiles and Geomembranes Vol. 44, no. 3 (2016), p. 219-229
- Full Text: false
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- Description: A geogrid reinforced soil wall was built on Prefabricated Vertical Drain (PVD) improved multilayer soft soils at the end of a road embankment in Shanghai, China. One day after the last loading stage, an arc shaped settlement was observed on the embankment surface with little observable cracks on the side slopes, and sudden increase of pore water pressure was observed in the piezometers installed in the PVD improved zone. A three dimensional finite element analysis was carried out to compare the performance of the wall with PVDs functional and dysfunctional. The comparison supported the assumption that the PVDs may have failed during construction due to bending or kinking of PVDs caused by the large settlement and lateral movement in the ground. The analysis showed that the movement of the wall toe is very sensitive to its location in the cross direction. Therefore attention should be paid while using toe movement as an indication of wall stability. It shows that the failure had mainly taken place in between the shoulders of the embankment rather than the whole wall. For a full slide to develop, pull out or tensile failure may occur in the reinforcements on the side slopes. Large stresses can be generated in the geogrids in the cross embankment direction due to the uneven settlement observed in the ground. Considering this, biaxial geogrid should be considered if the stress is too high and the inclusion of wrap around geogrids on the side slopes may help to increase the integrity and stability of the wall. © 2015 Elsevier Ltd.
Distribution and zoning of reinforcement loads for reinforced soil slopes
- Authors: Zhang, Wan , Xu, Qiang , Chen, Jianfeng , Xue, Jianfeng
- Date: 2017
- Type: Text , Journal article
- Relation: Jiaotong Yunshu Gongcheng Xuebao/Journal of Traffic and Transportation Engineering Vol. 17, no. 6 (2017), p. 28-35
- Full Text: false
- Reviewed:
- Description: Based on the result of centrifuge model test, the finite element models of reinforced soil slopes with different slope heights and angles were established. The maximum reinforcement loads in the slopes were calculated by using the strength reduction method when the safety factor was 1.30. The influence of slope height and angle on reinforcement load distribution along the height was analyzed by normalizing reinforcement load and slope height. Furthermore, the distribution and zoning of reinforcement loads were discussed by combining with the measured reinforcement loads of field reinforced soil slopes. Analysis result shows that the computed location and shape of slope sliding surface and the safety factor at slope failure are in agreement with the centrifuge model experiment results. The distribution of reinforcement load is little influenced by slope height, whereas greatly influenced by slope angle. With the increase of slope angle, the location of maximum reinforcement load transfers from the mid height to the bottom of slope. According to the total distribution of reinforcement loads, the sums of maximum loads in reinforcement layers within the top ⅓ and the bottom ⅔ of slope account for ¼ and ¾ of total reinforcement tensile force, respectively. The upper part of slope requires less reinforcement loads. If using one zone method that assumes a uniform reinforcement load distribution along slope height to distribute total reinforcement tensile force, the lower degree of safety of slope will decrease. The total reinforcement tensile force of reinforced soil slopes can be distributed into zones according to slope angle. When the slope angle is no more than 1.0:1, the total reinforcement tensile force can be distributed into three zones with equal height. The reinforcement tensile force within the top, middle and bottom zones account for ⅓, ½ and ⅙ of total reinforcement tensile force, respectively. When the slope angle is in the range from 1.0:1 to 2.0:1, its upper ⅓ of height is regarded as top zone, and the bottom ⅔ of height is regarded as bottom zone. The reinforcement tensile force within the top and bottom zones account for ⅕ and ⅘ of total reinforcement tensile force, respectively. When the slope angle is no less than 2.0:1, it can be also divided equally into three zones. The reinforcement tensile forces within the top, middle and bottom zones account for ⅙, ⅓ and ½ of total reinforcement tensile force, respectively. More measured data can be collected to enrich the database of reinforcement loads, so that the zoning method of reinforcement tensile force according to slope angle for reinforced soil slopes can be further completed and validated. © 2017, Editorial Department of Journal of Traffic and Transportation Engineering. All right reserved.
Mechanical responses of Boeing 747 running on runways
- Authors: Wang, Xing-tao , Chen, Jianfeng , Ye, Guan-bao , Yang, Dong , Xue, Jianfeng
- Date: 2016
- Type: Text , Journal article
- Relation: Jiaotong Yunshu Gongcheng Xuebao/Journal of Traffic and Transportation Engineering Vol. 16, no. 2 (2016), p. 1-9
- Full Text: false
- Reviewed:
- Description: Based on the large amounts of measured strains and deflections of runway pavement at Denver International Airport, the main characteristics of deflections and strains at different positions of pavement were analyzed when Boeing 747 was running on runway, and the load transfer capacities of different joints, the residual deformations and strain rates of pavement at the typical positions were researched. Analysis result shows that the edge and middle of slab have 2 strain peaks respectively, which corresponds with the number of aircraft's main gear axles. The transverse strain (perpendicular to the running direction of aircraft) only has one type, while the longitudinal strain (parallel to the running direction of aircraft) shows 2 times' transformation between tension and compression. The peak-strain recovery between gear axles at the bottom of longitudinal joint edge is significant, its peak strain and peak-strain recovery are 1.2 times and 2.5 times as much as the values at the top of longitudinal joint edge respectively, which means more prone to cracking and fatigue damage. When the aircraft is running, the maximum strain rates occur at the joint, and the maximum tensile and compressive strain rates are 9.1×10-4 s-1and 7.6×10-4 s-1 respectively, and belong to quasi-static strain rate, so their impact on the deformation of concrete slab are ignored. The deflection curves at the slab's middle have 1 peak, but there are 2 peaks at the slab's corner and transverse joint edge. The relative residual deformation at corner of slab is largest, the deformation at the middle of slab is least, the relative residual deformation rate at the corner of slab is 2.60-4.59 times as large as the value at the middle of slab, and compared with other locations, the corner more easily occurs void with base. The load-transferred coefficient of hinged joint is about 1, the load-transferred coefficient of dummy joint is lower compared with hinged joint, the load-transferred characteristic of dummy joint has directionality, but the load-transferred characteristic of hinged joint is non-directional. © 2016, Editorial Department of Journal of Traffic and Transportation Engineering. All right reserved.