A Comprehensive Method for the Risk Assessment of Ground Fissures:Case Study of the Eastern Weihe Basin

Ground fissures are influenced by the coupling of geological factors and human activi-ties.They threaten the safety of infrastructure and restrict town planning in many areas in China.One of the area most severely affected by ground fissures is the Weihe Basin in North China,which has the most extensive distribution of ground fissures and all the elements that control their occurrence,pro-viding an ideal study area for the study of ground fissures.In this study,we took the eastern Weihe Ba-sin as the study area and determined the distribution and hazard characteristics of ground fissures via field investigation.Based on the analytic hierarchy process,we propose a multi-level,comprehensive method for evaluating the hazards of ground fissures.This method considers the geological back-ground,development status,and triggering factors of ground fissures,including all nine currently known assessment indices of ground fissures.We used judgment matrices to rank the constructed ground fissure assessment index system at the single and total levels and quantified the nine assessment indices of ground fissures according to the field survey data.Finally,we plotted the ground fissure risk zoning map and evaluated the ground fissure risk at the study area.Our findings indicated that the proposed method could facilitate ground fissure hazard assessment and prediction and provide support for hazard prevention and urban/rural planning.

Identification of landslide spatial distribution and susceptibility assessment in relation to topography in the Xi＇an Region, Shaanxi Province, China

Landslides are among the most serious of geohazards in the Xi＇an Region, Shaanxi, China, and are responsible for extensive human and property loss. In order to understand the distribution of landslides and assess their associated hazards in this region, we used a combination of frequency analysis, logistic analysis, and Geographic Information System （GIS） analysis, with consideration of the spatial distribution of landslides. Using the GIS approach, the five key factors of surface topography, including slope gradient, topographic wetness index （TWI）, height difference, profile curvature and slope aspect, were considered. First, the distribution and frequency of landslides were considered in relation to all of the five factors in each of three sub-regions susceptible to landslides （Qin Mountain, Li Mountain, and Loess Tableland）. Secondly, each factor＇s influence was deter- mined by a logistic regression method, and the relative importance of each of these independent variables was evaluated. Finally, a landslide susceptibility map was generated using GIS tools. Locations that had recorded landslides were used to validate the results of the landslide susceptibility map and the accuracy obtained was above 84%. The validation proved that there is sufficient agreement between the susceptibility map and existing records of landslide occurrences. The logistic regression model produced acceptable results （the areas under the Receiver Operating Characteristics （ROC） curve were 0.865, 0.841, and 0.924 in the Qin Mountain, Li Mountain and Loess Tableland）. We are confident that the results of this study can be useful in preliminary planning for land use, particularly for construction work in high-risk areas.

Initiation Mechanism of Loess Mudflows by Flume Experiments

The structure of loess is loose,and the shear strength of loess drops sharply after contact with water.Therefore,loess mudflows have become a common geological disaster on the Chinese Loess Plateau.In order to study the initiation mode and mechanism of loess mudflows,in this study,seven sets of flume experiments were designed by controlling the slope angle and rainfall intensity.The results show that(1)when the slope angle is between 10°and 20°,there are two initiation mechanisms of loess mudflows:mudflow(large scale)and retrogressive toe sliding,and mudflow(small-scale)and retrogressive toe sliding.(2)The main method by which water infiltrates into the soil accumulation is mainly vertical infiltration,which is not affected by the slope angle and the seepage direction of the accumulation soil.(3)The liquefaction of loess is the root cause of loess mudflows.Water infiltrates into the area with an uneven density and a large amount of water accumulates in this area.Thus,the water content of the loess increases and the pore water pressure increases quickly and cannot dissipate in time,so the loess liquefies and the liquefacted area continues to spread and become larger.Thus,loess mudflows(large scale)occur.The increase in pore water pressure was captured in the seven sets of experiments.However,the order of the rising positions in the accumulation were different.This requires us to carry out tracking of the particle displacement inside the soil and the spatial changes in the internal structure of the soil in future research.