Landslide failures detection and mapping using Synthetic Aperture Radar: Past, present and future

Influence of lixiviation by irrigation water on residual shear strength of weathered red mudstone in Northwest China: Implication for its role in landslides' reactivation

The behavior of reactivated and first-failure landslides after large displacements is controlled by the available shear resistance in a shear zone and/or along slip surfaces, such as a soil-bedrock interface. Among the factors influencing the resistance parameter, the dependence on the shear rate can trigger catastrophic evolution (rate-weakening) or exert a slow-down feedback (rate-strengthening) upon stress perturbation. We present ring-shear test results, performed under various normal stresses and shear rates, on clayey soils from a landslide shear zone, on its parent lithology and other lithologies, and on clay-rock interface samples. We find that, depending on the materials in contact, the normal stress and the stress history, the shear-rate-dependent behaviors differ. We discuss possible models and underlying mechanisms for the time-dependent behavior of landslides in clay soils.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2017GL076214

Shear-Rate-Dependent Behavior of Clayey Bimaterial Interfaces at Landslide Stress Levels

Analysis of the causes of large-scale loess landslides in Baoji, China

In the present study, we investigate the influence of shearing rate on the residual strength parameters, ϕ
 r, in landslide soils using ring-shear tests at two shearing rates (0.01 and 0.5 mm/min) under selected effective normal stresses. The landslide soil samples used for this study cover a wide range of soil types and properties. Relationships between the ϕ
 r and soil properties, such as liquid limit, plasticity index, and the clay fraction show that the ϕ
 r decreases with increasing soil LL, I
 p and CF. The differences in the ϕ
 r at two shearing rates, ϕ
 r (0.5) − ϕ
 r (0.01), under different effective normal stresses are either negative or positive values of which the maximum magnitude is generally about 1.0°. The relationships between the ϕ
 r (0.5) − ϕ
 r (0.01) and the soil properties (LL, I
 p, and CF) are not exhibited in a regular pattern. On the other hand, the ϕ
 r (0.5) and ϕ
 r (0.01) determined at each effective normal stress suggest that the tendency for increased negative effect of the ϕ
 r with decreasing effective normal stress is more noticeable in the slow shearing rate range. The absolute value of ϕ
 r (0.5) − ϕ
 r (0.01) at lower effective normal stress is found to be greater than 1.0°, with the maximum of about 4.0°. The negative shearing rate effect on ϕ
 r at low effective normal stress is affected by the undulating shear behavior due to poor or no slickenside development.

Shearing rate effect on residual strength of landslide soils in the slow rate range

We use a ring-shear apparatus to examine the relationship between the residual strength and mineralogical properties of landslide soils and find a significant relation between the residual strength parameter, φr, and the total content of layer silicate minerals prone to preferred orientation within the bulk soil. In this context, the total content of smectite, vermiculite, chlorite, and mica in the sub-425-μm soil fraction is a suitable mineralogical parameter for estimating the magnitude of φr. Plotting φr as a function of total mineral content forms a chair-shaped curve, based on which we classify landslide soils into three groups. In the first group of soils, sliding appears to be controlled by minerals such as quartz, feldspar, calcite, dolomite, and layer silicate minerals other than smectite, vermiculite, chlorite, and mica and their φr is almost constant at ∼32°. In the second group of soils, the controlling mineralogical factor for sliding quickly shifts from nonpreferred-orientation minerals to preferred-orientation minerals and φr decreases from 30° to 10°. In the third group of soils, sliding is well controlled by preferred-orientation layer silicate minerals and φr gradually decreases from 10° to 5°. The results show that the relationship can be used for predicting φr of a wide range of landslide soils that differ in geology, soil type, mineralogical properties, and shear strength.

Platy layer silicate minerals for controlling residual strength in landslide soils of different origins and geology

Based on a laboratory study of drained direct shear tests of remoulded, pre-cut and polished specimens and drained ring shear tests of uncut and remoulded specimens of slip surface materials of five landslide soils, significant correlations of the mobilized shear strength parameters, cohesion (c, c
 r) and internal friction angle (Φ, Φr), are proposed. The investigated soils consisted of the slip surface material belonging to tuffaceous clay, mudstone, loess and siltstone. Most of the previous studies on residual shear strength measured by reversal direct shear and ring shear devices have obtained significantly different results using the two devices, even when pre-cut and polished specimens were used in the direct shear device. In this study, the residual shear strength values of remoulded specimens measured by a ring shear device are shown to significantly correlate with the drained large displacement shear strength values of remoulded specimens, which were measured using pre-cut and polished specimens in a direct shear device. The correlation between the cohesion measured in the two shear devices is expressed by the linear relationship, $$ {c_{\text{r}}} = 0.{7394}c - {6}.{6857} $$
 , while the correlation between the friction angle measured in the two devices is expressed by the linear relationship, $$ {\Phi_{\text{r}}} = {1}.0{852}\Phi - {6}.0{247} $$
 . The proposed linear correlations for effective cohesion (c′) and effective friction angle (Φ′) have yielded significant coefficients of determination within an effective normal stress range of 30–150 kN/m2.

Correlation of large displacement drained shear strength of landslide soils measured by direct shear and ring shear devices

Effects of overconsolidation ratios on the shear strength of remoulded slip surface soils in ring shear

The tank cascade system (TCS) has been used for over 2000 years for water management in Sri Lanka. Since surface water is limited in the dry zone of Sri Lanka, agricultural production, especially of upland crops, relies on groundwater for irrigation. We sampled 29 wells in the Ulagalla cascade, a prominent TCS near Anuradhapura city in the dry zone of Sri Lanka, in Yala (dry) and Maha (wet) seasons, the two main cropping seasons in Sri Lanka. We evaluated the suitability of groundwater for irrigation using the analytic hierarchy process and geographical information system. Water quality did not vary notably between seasons. However, it deteriorated with the onset of high intensity heavy rain, especially during the Maha season. A water quality zoning map indicated that groundwater in 4% and 96% of the study area is suitable and moderately suitable for irrigation, respectively. Irrigation water quality in tank cascade landscapes and similar environments can be assessed using this methodology and our results.

Sho Kimura

Papers

Shearing rate effect on residual strength of landslide soils in the slow rate range

Platy layer silicate minerals for controlling residual strength in landslide soils of different origins and geology

Correlation of large displacement drained shear strength of landslide soils measured by direct shear and ring shear devices

Effects of overconsolidation ratios on the shear strength of remoulded slip surface soils in ring shear

Classification of Groundwater Suitability for Irrigation in the Ulagalla Tank Cascade Landscape by GIS and the Analytic Hierarchy Process