西南交通大学学报

Field Test of Ground Vibration Induced by High-Speed Train on Elevated Bridge

LI Xiaozhen, ZHANG Zhijun, RAN Wenmin, CHEN Guiyuan, ZHANG Xun

2016, 29(5): 815-823. doi: 10.3969/j.issn.0258-2724.2016.05.001

[Abstract](655)

Abstract:
To study the ground vibration induced by high-speed trains across bridges, a field test was carried out in vicinity of a simply supported box-girder with a span of 32 m on Tianjin-Qinhuangdao railway line. Ground vibrations in the longitudinal, lateral and vertical directions were measured with train speeds in the range 250-385 km/h. The test data were analyzed in both time and frequency domains. The results show that cyclical peaks of acceleration can be clearly distinguished in the near field, and the excitation frequencies of wheelbase and the adjacent bogie space of the front and rear cars make the main contributions. The dominant frequency of ground vibration in the three directions is 25-80 Hz, and the vertical ground vibration attenuates mainly in the dominant frequency band; however, the longitudinal and lateral ground vibrations obviously attenuate in 1-80 Hz. For all test train speeds and all test points, the vertical ground vibrations are stronger than the longitudinal and lateral ground vibrations, and the maximum difference of vibration acceleration levels (VALs) between the longitudinal and lateral ground vibrations is about 2 dB. A phenomenon of amplification for the longitudinal and lateral ground vibrations is observed at the distance of about 30 m. Overall VAL of the near field increases about 6 dB when the train speeds increases from 250 to 320 km/h. However, the differences of overall VALs at all locations are less than 2 dB while speeds in the range of 330-385 km/h.

Analytic Identification of Bridge Nonlinear Motion-Induced Aerodynamic Parameter

XIONG Long, LIAO Haili, WANG Qi, MA Cunming

2016, 29(5): 824-831. doi: 10.3969/j.issn.0258-2724.2016.05.002

[Abstract](578)

Abstract:
As nonlinearity component of motion-induced force plays a key role in wind-induced vibration of bridge, it is very important to reasonably determine the nonlinear aerodynamic parameters. According to the detached-forced vibration wind tunnel tests, an analytic identification method for nonlinear aerodynamic parameters, which combines the eigensystem realization algorithm and nonlinear least square, was proposed with consideration of the analytical expression of nonlinear self-excited force. Numerical simulation results of ideal flat plate show that the identification results are in good agreement with the theoretical values in the noise-free case, and the maximum identification error is only 3.7% when there is additional 20% Gaussian noise. It means that the proposed analytic method has strong anti-noise ability. In addition, the numerical simulation results of nonlinear aerodynamic force show that the analytic method can accurately estimate the order of nonlinear motion-induced aerodynamic force, and with additional 20% Gaussian noise, the maximum identification error of the phase and amplitude of each harmonic is only 3.2%. Finally, wind tunnel tests were carried out to verify the feasibility and effectiveness of proposed method.

Optimizing Flared Hood of Tunnel Based on Aeroacoustics

YAN Yaguang, YANG Qingshan, LUO Jianjun

2016, 29(5): 832-839. doi: 10.3969/j.issn.0258-2724.2016.05.003

[Abstract](574)

Abstract:
In order to alleviate the sonic boom caused by aerodynamic effect in a tunnel, design parameters of the tunnel entrance with a flared hood were optimized. By solving the FW-H equation with Green's function, the pressure and pressure gradient of the initial compression wavefront in the tunnel were obtained. Then, the cross-sectional area function, the entrance cross-section area and the length of the flared hood were optimized according to the characteristics of the flared hood. The optimization results show that the peak pressure gradient decreases with an increase in the length of the tunnel hood. Considering economic factors, the optimal length of the flared hood is 10 times the tunnel diameter. With the optimized cross sectional area function and entrance area of the tunnel hood, the curves of pressure present a linear growth, and the peak pressure gradient is reduced by 63.9%. Consequently, the abrupt change of pressure at the tunnel entrance is avoided, and the phenomenon of the micro pressure wave such as sonic boom can be relieved effectively.

Experimental Investigation of Deformation and Geogrid-Soil Interface Behavior of Triaxial Geogrid

CAO Wenzhao, ZHENG Junjie, ZHOU Yanjun, WU Wenbiao, JIANG Jinguo

2016, 29(5): 840-846. doi: 10.3969/j.issn.0258-2724.2016.05.004

[Abstract](556)

Abstract:
In order to investigate the behavior of geogrid-soil interface of traxial geogrid, a series of laboratory pullout tests focusing on triaxial geogrid were conducted considering the effect of two kinds of pullout directions, referred to as TX_0 case and TX_90 case, respectively. The geogrid displacements were measured at four sections along the geogrid specimens. Based on the measurements, the relation between pullout force and pullout displacement and the deformation of each geogrid segment were studied. Furthermore, the dilatancy/shrinkage behavior, the relation between the average friction and relative displacement, and the effect of pullout directions on the interface strength were also analyzed. The experimental results demonstrate that the degree of compaction has a great influence on the pullout force and shear dilatancy/shrinkage behavior of the geogrid-soil interface. As the normal stress increases, the shear shrinkage increases while the shear dilatancy decreases. The shear displacements corresponding to the maximum shear dilatancy/shrinkage also increase with the increase of normal stress. The interface friction develops in a progressive mode and an elasto-plastic softening characteristic is observed of the interface behavior. The geogrid-soil interface strength of the TX_0 case is higher than that of the TX_90 case when the normal stress is higher than 20 kPa.

Experimental Study on Axially Loaded Circle-Section Concrete Columns Confined by CFRP under Long-Term Load

PAN Yi, WU Xiaofei, WAN Li, YUAN Shuang

2016, 29(5): 847-854. doi: 10.3969/j.issn.0258-2724.2016.05.005

[Abstract](597)

Abstract:
In order to analyze the effect of creep in concrete and CFRP(Carbon Fiber Reinforced Plastic)on the axial compressive behavior of CFPP confined concrete column under the sustained load, a total of twelve circular columns specimens were tested under three types of the long-term axial load modes. The failure characteristics of specimens were observed and the influence of sustained load on the deformation, the peaks of the strain and the stress of CFPP confined concrete columns were studied under different load modes and ratio of sustained load. The experimental results show that all of the CFRP confined columns lose carrying capacity due to the rupture of CFRP in loop direction, and the position of rupture generally locates at the mid-height of concrete column. The axial strain of CFRP confined concrete is smaller than that of unconfined specimens, and the deformation increases with the load magnitude. Under different sustained load types, the long-term axial preload have different effects on peak stress and peak strain of CFRP confined concrete. In general, the peaks of the stress and strain of concrete decrease along with the increment of the ratio of sustained load. When the ratio of sustained load is relatively high, peak stress and strain will decrease about 13% and 6% , respectively.

Experimental Study on Influence of Particle-Size Distribution on Permeability Coefficient of Sand

YANG Bing, LIU Yifei, WAN Fentao, YANG Tao, FENG Jun, ZHAO Xingquan, ZHENG Dongsheng

2016, 29(5): 855-861. doi: 10.3969/j.issn.0258-2724.2016.05.006

[Abstract](729)

Abstract:
In order to investigate the influence of particle-size distribution on permeability of sand, the influence of uniformity coefficient, gradation coefficient, mean diameter, and void ratio on permeability coefficient was studied by constant head test. The significance of the influencing factors was then analyzed using orthogonal experimental design, and the relationships between the factors and the permeability coefficient were discussed by control variable method. The experimental results show that the permeability coefficient increases with the increase of gradation coefficient, and decreases with the uniformity coefficient. When the uniformity coefficient increases up to a certain value, the permeability coefficient tends to be stable (e.g.Cu=11 in this study). There is a nearly linear, positive correlation between permeability coefficient and mean diameter. With the increase of the mean diameter, the increasing amplitude of permeability coefficient can be up to two orders of magnitude.

Mechanical Properties of Tou Mortise-tenon Joints of the Traditional Timber Buildings in the South Yangtze River Regions

CHUN Qing, PAN Jianwu, DONG Yunhong

2016, 29(5): 862-869. doi: 10.3969/j.issn.0258-2724.2016.05.007

[Abstract](639)

Abstract:
In order to study the structural performance and its influencing factors of the Tou mortise-tenon joints which are widely used in the traditional timber buildings in the South Yangtze River Regions, the failure modes, hysteretic curves, skeleton curves, rotation rigidities of the mortise-tenon joints under low-cycle reversed load were analyzed by the scaled model tests. With the consideration of the nonlinear contact influence of the mortise-tenon joint and the nonlinear stress-strain behavior of the timber material, the mechanical properties of the Tou mortise-tenon joints were analyzed by ANSYS software, and the theoretical results were compared with the experimental ones. The comparison results show that the hysteretic curves of the Tou mortise-tenon joints appear to be Z shaped and have the obvious pinch effects. During the tests, these mortise-tenon joints orderly experience the elastic stage, the yield stage and the failure stage. The failure mode of these joints are the fracture of tenon, and the ultimate rotation angles range from 0.11 to 0.14 rad. The theoretical results agree well with the experimental ones. Finally, the relationship of in-plane rotational rigidity (vertical) KV, out-of-plane rotational rigidity (horizontal) KH and tortional rigidity KR of the Tou mortise-tenon joint was obtained, i.e., KV: KH: KR is about 2.5∶1∶1.

Numerical Analysis of Aerodynamic Noise of Motor Car Bogie for High-Speed Trains

ZHANG Yadong, ZHANG Jiye, ZHANG Liang, LI Tian

2016, 29(5): 870-877. doi: 10.3969/j.issn.0258-2724.2016.05.008

[Abstract](574)

Abstract:
In order to study the aerodynamic noise characteristics of motor car bogie in high-speed trains, an aerodynamic model of motor car bogie was established, a preliminary study on the aerodynamic noise source of the motor car bogie was made using the steady-state RNG k- turbulence model and the broadband noise source model, and the far-field aerodynamic noise was analyzed by combined use of the transient-state large eddy simulation (LES) and Lighthill' s acoustic analogue theory. The results show that the wheel set, bogie frame, traction motor-1, bolster, vertical shock absorber, anti-rolling torsion bar and other protruding parts on the windward side are the aerodynamic noise source of the bogie. Among them, bogie frame has the largest contribution to the total far-field aerodynamic noise of the bogie, the wheel set and anti-rolling torsion bar have the secondary contribution, and the vertical shock absorber and bolster have the third contribution amount. Compared to the above components, the traction motor-1, traction motor-2, air spring and lateral shock absorber have less contribution to the total noise. In addition, the far-field noise of the motor car bogie is a broadband noise, characterized by attenuation, amplitude and aerodynamic noise directivity. The main energy of the noise in the low frequency band is concentrated at the centre frequencies 25 and 50 Hz, and the power spectral density distribution does not change with the train speed.

Detection Method of Low-Frequency Oscillation in Traction Power Supply System Based on Single-Phase dq Transformation and Improved PRONY Algorithm

WANG Hui, WU Mingli, LI Wenfeng, WANG Guanhong, LI Ying, TAO Xiangyu

2016, 29(5): 878-885. doi: 10.3969/j.issn.0258-2724.2016.05.009

[Abstract](571)

Abstract:
Electrical low-frequency oscillation in traction power supply systems causes vehicle traction system shutdown, which results in severe service delay. The mathematical descriptions of the oscillated voltage and current were presented based on the analysis of a large amount of measured data. The line voltage oscillation mechanism was also explained in a brief way through a simple electrical model representing the traction power supply system and locomotives. Considering the features of the single-phase power supply, the d-axis component of the line voltage was obtained by a single-phase dq transformation, and chosen as the characteristic signal and the detection object. Then, a detection method was designed based on the improved PRONY algorithm to identify the dominant pattern of low-frequency oscillation. The detection method was verified by the measured data from actual low-frequency oscillation cases. The results show that the designed detection method can identify the low-frequency oscillation with the frequency lower than 30Hz, magnitude over 0.01(p.u.), and calculate the dominant oscillation pattern and send out an alarm signal.

Modelling and Analysis of Combined Co-phase Traction Power Supply System Based on Vx Connection Traction Transformer

CHEN Minwu, LUO Jie, XIE Shaofeng, XIA Yankun, JIANG Wenbing

2016, 29(5): 886-893. doi: 10.3969/j.issn.0258-2724.2016.05.010

[Abstract](632)

Abstract:
As the key technology of new generation traction power supply system,the design of co-phase traction power supply system should match different connection traction transformers to optimize the comprehensive compensation strategy of power quality and reduce the capacity and cost of power flow controller (PFC) . A new scheme of combined co-phase traction power supply system was developed for high-speed and heavy-haul railways, which adopts auto-transformer (AT)traction mode and Vx connection transformer. First, based on the relationship of the connection angles of different ports, the model for the electrical parameter transformation between three-phase power grid and single-phase traction load was built. Second, according to the principle of comprehensive compensation of three-phase unbalanced voltage and reactive power, the operation current calculation formula for each port was deduced with the limited power quality as a constraint. Further, the dynamic compensation control scheme of PFC was presented. Compared with the current compensation schemes, it can ensure the compensation targets with the decrease of 10%-58% in the compensation capacity. Finally, the compensation model and control strategy are verified by the simulation on the operating characteristics of the proposed system under different loads verified .

Method of Parameter Coordination Optimization for Grid-Connected Photovoltaic System

LI Qi, YANG Hanqing, HAN Ying, CHEN Weirong

2016, 29(5): 894-901. doi: 10.3969/j.issn.0258-2724.2016.05.011

[Abstract](525)

Abstract:
The parameter design of grid-connected photovoltaic (PV) system is significant for its stable operation. In this work, a method of parameter coordination optimization was proposed for grid-connected PV system, by establishing the small-signal mathematical model of PV system, including PV cell, inverter, transformer and gird. By analyzing eigenvalues (root locus plot) in stable conditions, the boundary values of system parameters are available. Then the objective function for coordination optimization was built involving small-signal stability, damping ratio and stability margin. And the backtracking search algorithm (BSA) was adopted to optimize the system parameters. The simulation test is carried out to compare the dynamic system responses before and after parameter optimization. Simulation test results show that when system suffers small disturbances, the optimized grid-connected PV system can reach a new stable point within 0.1 s, and its dynamic response is improved 50% than that of the original system.

Fair Secure Two-Party Computation Protocol Based on Game Theory

WANG Jie

2016, 29(5): 902-909. doi: 10.3969/j.issn.0258-2724.2016.05.012

[Abstract](531)

Abstract:
Since complete fairness cannot be achieved in traditional two-party computation, a rational two-party computation protocol, based on game theory, was proposed, which regards player as rational. At first, the game model of secure two-party computation was put forward in the extensive game framework. Secondly, according to the description of game model, the ideal function FRPCP of rational secure two-party computation and rational two-party computation protocol RPCP were presented. Finally, the security, fairness and Nash Equilibrium of protocol was analyzed. The analysis results show that the protocol RPCP can realize ideal function FRPCP safely in the hybrid model; meanwhile, under the Bilinear Diffie-Hellman (BDH) assumption, the best strategy of the rational players is to choose cooperation; and when the game achieves Nash Equilibrium, all players can obtain the right results fairly.

Improved Artificial Bee Colony Algorithm for Disassembly Line Balancing Problem

ZHANG Zeqiang, HU Yang, CHEN Chong

2016, 29(5): 910-917. doi: 10.3969/j.issn.0258-2724.2016.05.013

[Abstract](586)

Abstract:
The disassembly line balancing problem (DLBP) has been mathematically proved to be NP-complete. The search processes of traditional algorithms for DLBP are so random that they tend to get local optimum due to DLBP' s exponential time complexity for large scale cases. To overcome the shortcomings of traditional algorithms, an improved artificial bee colony (ABC) algorithm was proposed based on a multi-objective optimization model for the DLBP, where the main objectives to achieve are to minimize the number of workstations, equilibrate workload, and remove hazardous and high-demand components as early as possible. This algorithm includes four phases. In the initial solution generation phase, the hazardous index and demand measure are used to improve the convergence property of the algorithm. In the employed bee phase, a variable step length search strategy is introduced to take a further search for better solutions and speed up the elimination of inferior solutions. In the onlooker bee phase, a hybrid search strategy that combines the traditional search with the disturbance search is adopted. In the scout bee phase, a search strategy based on estimation of distribution is constructed. The proposed algorithm was applied to solve 70 test cases to verify its validity. As a result, optimal solutions were obtained for 65 cases and the optimization rate is 92.86%. In addition, the algorithm was applied to solve a 10-task case and a 52-task case. The results show that the demand measures to obtain the optimal solution for the 10-task case are 9 730, which is 360 less that by ant colony optimization; meanwhile, better solutions for the balance rate, number of workstations and cost are obtained for the 52-task case. Compared to the traditional ABC algorithm, the improved algorithm has a significantly superior performance in solving large-scale DLBPs.

A Novel Time-Approaching Search Algorithm for Energy-Saving Optimization of Urban Rail Train

LIU Wei, WANG Dong, LI Qunzhan, CUI Mengyu

2016, 29(5): 918-924. doi: 10.3969/j.issn.0258-2724.2016.05.014

[Abstract](567)

Abstract:
To ensure energy-saving and punctual operation of urban railway, a time-approaching search method was proposed. The energy-saving control model of urban railway that satisfies timing running was established . A set of optimal conditions for energy-saving control was derived according to the Pontryagin maximum principle. The energy consumption of a train under different energy-saving operations was calculated . On this basis, we presented an optimization method of dividing the train operation period into sections. The change point of train operation is determined using time-approaching search method to meet the requirements of energy-saving and timing. A section from Tieli Road to Youyi Road of Shanghai Metro Line 3 is taken as an example. Compared with measurement results in the practical loading process, the energy comsuption is reduced by 12.5% using time-approaching search algorithm.

Dynamic Sorting Method for Road Network Primary Intersections Based on PageRank Algorithm

GUO Haifeng, ZHANG Changshi, MU Yuanjie, ZHENG Yayu, GONG Wei

2016, 29(5): 925-930. doi: 10.3969/j.issn.0258-2724.2016.05.015

[Abstract](518)

Abstract:
In order to classify intersections of a city under saturated traffic operating conditions, sort-by-importance measures for intersections should be provided. Considering the static connections and dynamic influences of traffic volume between intersections, a key busyness index that can reflect the busy degree of each intersection in the road network is proposed on the basis of a modified PageRank algorithm. This busyness index is then used for sorting important intersections in the road network and analyzing their situations. Results show that the intersections that are sorted in the front are very busy and important. By taking into consideration of the whole intersections in a road network, the busyness index can make up the disadvantage of the saturation index that can only evaluate the situation of single intersections, and therefore is capable of reflecting accurately the mutual influences of the connection relations among intersections under saturated conditions. Compared with the sorted results by saturation index, the ranking orders by business index of 40% intersections change within 3 positions, 30% drop by 7 positions, and 30% rise by 8 positions. The obtained findings can be used to classify intersections of a city under saturated traffic conditions to timely find the key intersections.

Consistent Vehicle Routing Problem Considering Traffic Congestion and Workload Balance

LIU Hengyu, RU Yihong

2016, 29(5): 931-937. doi: 10.3969/j.issn.0258-2724.2016.05.016

[Abstract](551)

Abstract:
In order to investigate the effects of transportation congestion and workload balance on the delivery routing of express delivery companies which wish to provide consistent services, a consistent vehicle routing problem considering traffic congestion and workload balance was proposed and a mixed integer programming model for this problem was constructed. In view of the model' s NP-hard property, a two-phase template-based simulated annealing method (TSA) was applied to solve this problem. The TSA attains an initial route plan by constructing template routes first, and then optimizes them using the simulated annealing method to decrease the total travel time. To verify the validity of the proposed model and algorithm, numerical experiments were conducted using three benchmark data sets. Results show that the model and TSA can solve this problem effectively. The traffic congestion will significantly increase the total travel time by an average of 18.38% and increase the difference between the earliest and latest arrival time at the same customer within any two days by an average of 12.92%. Besides, when the average difference of the delivery men's shipment quantity decreases by 35.82%, the total travel time and the difference between the earliest and latest arrival time at the same customer are only increased by 2.29% and 1.68%, respectively.

Optimization of Train Diagram Structure for High-Speed Railway

ZHANG Xiaobing, NI Shaoquan, PAN Jinshan

2016, 29(5): 938-943. doi: 10.3969/j.issn.0258-2724.2016.05.017

[Abstract](701)

Abstract:
To improve the carrying capacity of high-speed railway, the structure of the train diagram was optimized by drawing compact train diagram and designing reasonable operation scheduling for trains. The optimization problem of the train diagram structure was transformed into a traveling salesman problem (TSP). Taking the total cost of the all routes as a goal, a 0-1 integer programming model was proposed, and then solved using the genetic algorithm. Finally, the model was verified through a real case study using the data of Beijing-Shanghai high-speed railway in 2015, and the optimized train diagram was compared with the original scheme. Computation results show that the total operation time of 39 trains was reduced from the 628 min in the original scheme to the 495 min in the optimized schedule, a reduction by about 21.2%. Therefore, the optimal alternative can meet better the demand for intensive dispatching during the peak period or in sudden burst condition of passenger flow.

Influence of Notch Stress Concentration on Fatigue Properties of 5083-H111 Aluminum Alloy in Very High Cycle Regime

YAN Guiling, WANG Hong, KANG Guozheng, DONG Xuancheng

2016, 29(5): 944-950. doi: 10.3969/j.issn.0258-2724.2016.05.018

[Abstract](532)

Abstract:
In order to correctly evaluate the reduction and sensitivity of fatigue strength to a notch of 5083-H111 aluminum alloy specimen in very high cycle regime, very high cycle fatigue tests were carried out by ultrasonic fatigue technique at a frequency of 20 kHz, using symmetric tension-compression loading within 105-1010 cycles for hourglass-type smooth specimens and two types of notched specimens. The scanning electron microscope (SEM) was used for analysis of the fracture morphology. The experimental results show that the S-N curves exhibited an extreme platform type for the smooth specimens and a continuous decline type for the notched specimens. The fatigue performances of the 5083-H111 aluminum alloy decreased significantly because of the notch stress concentration. Most of the cracks initiated in the surface, but the fish-eye morphology was not found. The macro fatigue striation was concave for the specimen with a theoretical stress concentration factor of 1.94, and the fatigue crack sources were distributed around the fracture surface in specimens with a theoretical stress concentration factor of 2.90. The influence of notch stress concentration on fatigue properties was dependent upon the mechanism of crack initiation. Since only one kind of surface crack initiation mechanism exists in 5083-H111 aluminum alloy, the fatigue notch coefficient and notch sensitivity coefficient increase with increasing number of cycles within the range of 109.

New Landscape Indexes to Quantify Spatial Patterns of Urban Roofs

HUANG Rui, SHEN Zhongwei

2016, 29(5): 951-957. doi: 10.3969/j.issn.0258-2724.2016.05.019

[Abstract](510)

Abstract:
A prerequisite to establish the interrelation between the urban landscape pattern and ecological process is to make a quantitative description of roof landscape patterns. Taking roof area and isolation factor into account, three measuring indexes are constructed by the theory of island biography. Of them, the minimum height (MIH) measures the contact or segregation between the building roof plaque and the ground; the accessibility index (ACI) reflects the possibility for living creatures to reach the roof from the ground, stay and even inhabit here; and the resistance index (RI) measures the difficulty of biological and other ecological factors in flowing and inhabiting on the ground and within the roof area. Empirical studies and correlation analysis results show that the three index values are within the defined range; there is a strong negative correlation between MI and ACI; MIH and RI, as well as ACI and RI, are relatively independent. The use of landscape indices in scientific planning of ecological networks can effectively increase landscape connectivity.

Collapse Mechanism and Stability Evaluation of Shattered Slope under Wind Loading

HUANG Runqiu, PEI Xiangjun, LUO Jing

2016, 29(5): 958-970. doi: 10.3969/j.issn.0258-2724.2016.05.020

[Abstract](533)

Abstract:
To reveal collapse mechanisms of shattered slope under wind loading, the slope stability assessment system was built. Based on the field survey of shattered slopes and valley wind measurement, the large-scale wind tunnel tests in various conditions were conducted by using Shidaguan collapse as an example. The results indicate that Shidaguan collapse is a typical case of shattered slope collapsing in a sudden burst under wind loading. This mode of collapse are hardly controlled by structural plane because of the unique slope structure. Meanwhile, since the distribution of river valley wind is affected by the topographical elements, it becomes complicated and varied. Thus the sudden collapse mode undergoes fast breakdown-crumbling-collapse as a whole, quite distinct from slope failure mechanisms under general gravity force. The loosing and cracking of the rock masses is fundamental to the collapse, while the gradual weathering is the main factor. Besides, the strong river-valley winds aggravate the collapse. Furthermore, the wind speed leading to rock masse instability is in inverse proportion to wind incident angle, as well as the height-width ratio of mass, and the width of the trailing edge crack.

Disaster Characteristics and Destructive Mechanism of Typical Loess Landslide Cases Triggered by Human Engineering Activities

PENG Jianbing, WU Di, DUAN Zhao, TANG Dongqi, CHENG Yuxiang, CHE Wenyue, HUANG Weiliang, WANG Qiyao, ZHUANG Jianqi

2016, 29(5): 971-980. doi: 10.3969/j.issn.0258-2724.2016.05.021

[Abstract](724)

Abstract:
In order to reveal the mechanism of loess landslide hazards induced by human engineering activities, typical loess landslide cases were studied using field investigations, physical model tests, and stress path tests. Analyses were made for the formation of shear zones triggered by heap loading, the evolution patterns of loess landslides triggered by unloading, and the development process of loess landslides induced by irrigation. The results show that in loess landslides triggered by heap loading and unloading, vertical joints and cracks easily evolve into a fracture belt. Under the action of shear stresses, shear creep zones expand from the toe to the internal of a slope gradually and develop into shear zones that penetrate the slope, which leads to the overall deformation and failure of slopes. Physical model tests reveal that the loess landslides triggered by heap loading have a typical feature of two sliding zones in shallow and deep layers. The loess landslides triggered by irrigation mainly develop in the loess tableland edge. The long-term irrigation will uplift the groundwater and cause the formation of a saturated zone in the slope body. The creep shear failure then occurs to the slope under the gravity load, resulting in the start of a landslide. In addition, the large-scale fast loading process will cause the liquefaction of the shallow loess in the front section of the slope body, and eventually triggers long-range loess mud flow landslides.

Disasters Caused by Deep-Seated Catastrophic Landslides and Prediction of Their Potential Sites

CHIGIRA Masahiro

2016, 29(5): 981-986,944. doi: 10.3969/j.issn.0258-2724.2016.05.022

[Abstract](499)

Abstract:
In order to understand the mechanism of deep-seated catastrophic landslides and make prediction of their potential sites, some typical deep-seated catastrophic landslides occurred in Asia were analyzed comparatively. From the aspects of two landslide-inducing factors, earthquake and rainfall, the characteristics of landslides prepared by chemical weathering processes and gravitational deformation were analyzed. Rainfall plays a significant role in the occurrence of deep-seated catastrophic landslides. The results show that for the earthquake-induced catastrophic landslides, the potential site can be predicted by considering the chemical weathering of different kinds of rocks, mechanical preparation and antecedent rainfall; for the rain-induced catastrophic landslides, the topographic features of gravity slope deformation and the geological structures can be used for prediction.

Mechanical Effect of Pre-consolidation Pressure of Structural Behavior Soil

WANG Qing, KONG Yuanyuan, ZHANG Xudong, RUAN Yunkai, CHEN Ye

2016, 29(5): 987-994. doi: 10.3969/j.issn.0258-2724.2016.05.023

[Abstract](593)

Abstract:
Special soil such as loess, saline soil, red soil, Xiashu loess, soft soil, or solidified dredger fill, has high pre-consolidation pressure (Pc) and high over-consolidation ratio (OCR), and with the increase of soil depth, the Pc value decreases obviously. To investigate these uncommon facts, soil structure force, structural strength and other issues in structural soils were analyzed. From experimental data, the factors affecting pre-consolidation pressure (Pc) were discussed, including the soil cementation type, soil genesis characteristics, original rock structure and environment. Soil structural strength was determined according to the compression curves of undisturbed and remolded soil, and the formation mechanism of structure force was explored. The results show that those factors affect the soil structure strength, which changes pre-consolidation pressure. It is found that the pre-consolidation pressure includes two parts, the traditional pre-consolidation pressure and soil structural strength; the structure force is the solidified bond strength between particles. Finally, the definitions of structural strength and structural soil were presented.

Study on Formation Mechanism of Diffuse Failure Landslide

XU Qiang, PENG Dalei, LI Weile, DONG Xiujun

2016, 29(5): 995-1004. doi: 10.3969/j.issn.0258-2724.2016.05.024

[Abstract](518)

Abstract:
An investigation was made into several landslide cases in recent years to summarize common characteristics of the landslides composed of saturated loose granular materials. These landslides typically exhibited complete collapse accompanied by unique phenomena such as abrupt failure, static liquefaction, and high-speed and long-runout motion. Their failure mechanism was extremely similar to the diffuse failure as discovered in the field of soil mechanics, and hence can be viewed as a new type of landslide failure mode. In addition, the primary failure mechanism of the diffuse landslide was discussed through physical simulation experiment. The results indicate that diffuse landslides generally occur to saturated loose granular materials with evident strain-softening characteristics, such as silt, sand, and gravel soil. As the stress in the soil reaches the critical state, any external micro-disturbance may trigger an abrupt failure of the slope. The abrupt failure is typically accompanied by an excess pore water pressure and a phenomenon of static liquefaction. After loss of stability, the soil generally undergoes a rapid flow-like mass movement, which may result in catastrophic geological disasters and should be highly valued.

Experimental Study on Effect of Soil Salinity on Electro-Osmosis in Montmorillonite Clay

SHI Zhenming, ZHOU Yuanyuan, PENG Ming, ZHUANG Yanfeng

2016, 29(5): 1005-1013. doi: 10.3969/j.issn.0258-2724.2016.05.025

[Abstract](468)

Abstract:
In order to investigate the permeability of montmorillonite clay with different salt content under an electric field, a laboratory device was designed to capture the drainage, current intensity, voltage, and water content during electro-osmotic drainage tests at four different salinities in montmorillonite. The results show that the permeability increased significantly during electro-osmotic drainage in the electric field. Under 40 V voltage the drainage rate in electro-osmosis was as large as 1 000 times that in normal drainage tests. The electric permeability coefficient increased first and then decreased with an increase in the salt content because of the effect of montmorillonite molecular structure and electrolyte concentration. When the salt content was near 0.5%, the drainage reached a maximum. With the salt content increasing, the effective potential of the soil decreased but the current and the potential drop between cathode and anode increased, reflecting that the energy consumption at the interface increased with the increase of salinity. In addition, a short-circuit connection between the cathode and anode electrodes resulted in a charge redistribution in the process of electro-osmosis. After the electro-osmosis, the potential distribution was found not uniform: the potential of the middle region was the lowest, and the direction of current was different in the soil.

Regional Warning of Debris Flow Hazards after Wenchuan Earthquake in Longmenshan Region

ZHANG Yongshuang, YAO Xin, GUO Changbao, LI Lingjing, YANG Zhihua, DU Guoliang

2016, 29(5): 1014-1023. doi: 10.3969/j.issn.0258-2724.2016.05.026

[Abstract](593)

Abstract:
Massive loose deposits caused by the Wenchuan earthquake on May 12, 2008 have resulted in significant decrease of rainfall threshold of post-earthquake triggering debris flow in comparison with pre-earthquake level. Based on the post-earthquake debris flow characteristics analysis in the Longmenshan region, the regional rainfall threshold of triggering debris flow and its regional differences were discussed. The 72-hour rainfall distribution characteristics of post-earthquake triggering debris flows are as follows: 75-100 mm in YingxiuWenchuan area, 100-160 mm in MaoxianBeichuan area, 160-200 mm in around above regions and PingwuQingchuan area, and 200 mm or more in YanmenChaba area and YuliPingwu area. Based on comprehensive analysis of seismogeology, topographic and geomorphic conditions, extreme rainfall and regional characteristics of post-earthquake debris flows, the regional rainfall threshold of triggering debris flow, as well as the warning index system, for earthquake-stroked region was established. The weighted information model was adopted to complete debris flow susceptibility assessment in the earthquake-stroked Longmenshan region. Then, taking the annual maximum 72-hour rainfall as a main trigger factor, the debris flow hazard assessment and regional warning study in 5 years after the Wenchuan earthquake were conducted. The results show that the regional debris flow hazard is dynamic, and the areas with high debris flow hazard change with the spatial distribution of rainfall and loose deposits.

Variation of Horizontal Arch Height of Granite Residual Soil Slope in Vertical Direction

LI Dengfeng, HU Xiewen, ZHAO Xiaoyan, YUE Zongyu

2016, 29(5): 1024-1032. doi: 10.3969/j.issn.0258-2724.2016.05.027

[Abstract](466)

Abstract:
Soil arch height of slope anti-slide pile determines the stress distribution of the pile and pile measures. The paper study the variation of soil arch height along the length of the pile, which could provide a theoretical basis for the precise design of slope anti-slide pile and measures between the pile and the pile. Firstly, the numerical simulation technology is adopted to explore the variation law of soil arch height along the direction of pile depth. Combined with theoretical analysis, the mechanical model of soil arch between piles was established. A method for calculating the height of soil arch between piles with embedded depth was proposed. The results show that the soil arch height varies significantly at different depths from the pile top. In the range of 4.5 m above sliding surface and under the pile top, the soil arch appears, while below the sliding surface, the effect of soil arch could be neglected.

Experimental Study on Dynamic Shear Modulus and Damping Ratio for Unsaturated Mixed Soil

CUI Kai, LIN Weikang

2016, 29(5): 1033-1040. doi: 10.3969/j.issn.0258-2724.2016.05.028

[Abstract](487)

Abstract:
Talus mixed soil, widely distributed throughout the Western Sichuan mountainous area, is often unsaturated in nature. Dynamic shear modulus and damping ratio are essential parameters of the dynamic properties in the analysis of seismic response. In order to study the influential factors on these two parameters, dynamic triaxial apparatus was used to obtain the dynamic backbone curve and hysteresis curve of mixed soil under cyclic loading with small strain, as well as fitted Gd/Gmax- and - curves. The functions of two curves varying with the water content and the fine particle content were analyzed. The research results show that the saturation and fine particle content have significant effects on the dynamic shear modulus and damping ratio, and mineral constituents also play a role in the changes of these two parameters. Based on the comparative analysis, the recommended values of dynamic shear modulus ratio and damping ratio suitable were provided for talus mixed soil in saturation and non-saturation states.

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2016 Vol. 29, No. 5