Jianbing Peng

Probability prediction model for landslide occurrences in Xi’an, Shaanxi Province, China

Landslides are increasing since the 1980s in Xi’an, Shaanxi Province, China. This is due to the increase of the frequency and intensity of precipitation caused by complex geological structures, the presence of steep landforms, seasonal heavy rainfall, and the intensifcation of human activities. In this study, we propose a landslide prediction model based on the analysis of intraday rainfall (IR) and antecedent effective rainfall (AER). Primarily, the number of days and degressive index of the antecedent effective rainfall which affected landslide occurrences in the areas around Qin Mountains, Li Mountains and Loess Tableland was established. Secondly, the antecedent effective rainfall and intraday rainfall were calculated from weather data which were used to construct critical thresholds for the 10%, 50% and 90% probabilities for future landslide occurrences in Qin Mountain, Li Mountain and Loess Tableland. Finally, the regions corresponding to different warning levels were identified based on the relationship between precipitation and the threshold, that is; “A” region is safe, “B” region is on watch alert, “C” region is on warning alert and “D” region is on severe warning alert. Using this model, a warning program is proposed which can predict rainfall-induced landslides by means of real-time rain gauge data and real-time geo-hazard alert and disaster response programs. Sixteen rain gauges were installed in the Xi’an region by keeping in accordance with the regional geology and landslide risks. Based on the data from gauges, this model accurately achieves the objectives of conducting real-time monitoring as well as providing early warnings of landslides in the Xi’an region.

A study of a flowslide with significant entrainment in loess areas in China

Flowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and/or casualties. The Dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment. To analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis, a field investigation was conducted. Specimens were sampled on site to carry out laboratory tests, including a triaxial test, sieve analysis, and chemical component analysis. The parameters were used in the runout study employing an energy-based runout model. An analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess. Finally, the entrainment model was incorporated into the runout model to simulate the post-failure process of this case. Energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation. The simulation results were compared with the measurements, including runout distance, total volume, erosion depth, deposition height at different sections, and velocities at specific locations. The results indicate that the energy-based runout model, together with the entrainment model, can capture the kinematic characteristics of the Dagou flowslide. Therefore, it is feasible to use this model to predict the runout characteristics of flowslides in similar areas. Copyright (c) 2017 John Wiley & Sons, Ltd.

An experimental study of the mechanical characteristics of fractured loess in western China

Microstructural changes in the loess deposits due to the presence of joint planes is one of the primary causes of the geohazards (ground fissures, ground subsidence, landslides, collapses, and soil and water losses) that occur in the loess regions of western China. By means of uniaxial tensile tests and triaxial shear tests conducted under different confining pressures, we tested fractured loess Q2 samples with five fracture plane inclination angles (0°, 30°, 45°, 60°, and 90°) taken from Sanyuan County, Shaanxi Province in western China, where geohazards are prevalent. Analysis of the tensile stress–strain and shear stress–strain relationships of the fractured loess specimens revealed the characteristics of the fractures that induce instability in this area. These results provide important baseline data for future research on the mechanism of geohazards in the loess regions of western China.

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 determined 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.

A Scale Model Test on Dynamic Soil-Tunnel Interactions

Soil-structure interactions are important for the safety of the underground structures under earthquake loads. In this paper, model tests were conducted on 1/60 scaled model of the prototype Xi’an metro tunnel. The seismic response data including the acceleration, the displacement and the dynamic soil pressure between the tunnel and soil were measured by testing the scaled model on a shaking table. From the test result, it is concluded that 1) the effects of tunnel and soil interactions are important for the bulk dynamic responses; 2) the soil pressure and the acceleration changed with the seismic inputs. The soil pressure at the top of the tunnel increased while the pressure at the bottom decreased; 3) the acceleration of the tunnel is greater than the adjacent soils.

Stabilization of Loess Using Nano-SiO2

Improving the performance of loess is of significant importance for lowering its collapsibility and water sensitivity to construction requirements and for geohazard mitigation. The present paper studies the changes in mechanical, structural, and mineralogical properties of nano-SiO2-treated loess with different contents and curing days. The mechanical behavior was examined by unconfined compressive strength (UCS) of untreated and treated loess. To better understand the mechanisms of stabilization, particle size distributions, scanning electron microscope (SEM) images, and X-ray diffraction (XRD) analyses were carried out. The results show that the UCS increase with increasing contents and curing days due to nano-SiO2 addition produced coarser particles, denser packing, and smaller pores in treated loess. The changes in the properties can be attributed to the formation of aggregation and agglomeration, with greater particle sizes and more interparticle contact. In addition, the results from mineralogical component analysis further confirm that physical structure modification controls the changes in mechanical and fabric properties, rather than chemical component alteration. Even small nano-SiO2 additions can also provide great improvement when curing days are enough for the treated loess. These findings reveal that nano-SiO2 has the potential to serve as a cost-effective stabilized additive that treats the universal loess.

Erratum for ‘Rapid loess flow slides in Heifangtai terrace, Gansu, China’ Quarterly Journal of Engineering Geology and Hydrogeology, 50, 106–110

Jianbing Peng1, Fanyu Zhang2* & Gonghui Wang3 1 Department of Geological Engineering, Chang’an University, Xian, Shaanxi Province, 710054, China 2 MOE Key Laboratory of Mechanics on Disaster and Environment in Western China, Department of Geological Engineering, Lanzhou University, Lanzhou, Gansu Province, 730000, China 3 Research Center on Landslides, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto, 611-0011, Japan J.P., 0000-0003-4689-7717; F.Z., 0000-0002-9102-3704 *Correspondence: zhangfy@lzu.edu.cn

Prototype Model Tests of Soil and Tunnel Interactions under Earthquake Forces

This paper presents test results of a prototype model of soil and metro tunnel interaction on a 1/40 scale in laboratory. The horseshoe-shaped metro tunnel model was mounted on a shaking table to induce earthquake forces for simulating the seismic activities in the Xi’an metro system. The effects of fault lines (in the form of ground fissures) on the soil-tunnel interaction were also investigated. The seismic response data including the acceleration, displacement and dynamic soil pressure between the tunnel and soil, were measured to test the scale model. The test results conclude that 1) the tunnel-soil interaction had significant influence on the bulk dynamic response of the system; 2) the soil pressure and the acceleration changed with the seismic inputs. The soil pressure at the top of the tunnel increased while the pressure at the bottom decreased; 3) the acceleration of the tunnel was greater than that of the adjacent soil; 4) the soil settlements within the vicinity of the fissure were larger as compared to the settlements further away from the fissure.