Determining the Shear Resistance in Landslides with Respect to Shear Displacement and Shearing Time in Drainage-Controlled Ring Shear Tests

Shear stress is an important parameter in estimating the slope stability and flow dynamics in mass movements. The ring shear test can often be employed to determine the residual shear stress because of its suitability for large deformations for assumed in situ stress and drainage conditions. Determination of the residual shear stress of weathered landslide materials composed of coarse-grained sediments was examined with respect to the shear displacement and drainage condition. Based on the experimental results, the shear stress of landslide materials has typical maximum and minimum values (i.e., peak and residual shear stress). The measured shear stress generally increases with an increase in shear speed regardless of drainage condition. In general, the residual shear stress can be measured when a relatively long shearing time is applied. The residual shear stress, which is known as the minimum shear resistance at the initiation of landslide occurrence along the pre-existing slip surface of the landslide body, is also measurable even though limited shear displacement (0.1–100 mm) and shear speed (0.1–100 mm/s) are applied. The minimum range of residual shear stress of weathered soils obtained from the ring shear tests is roughly half of the value obtained from the direct shear tests. The residual shear stress can be used to estimate the reactivation of slope movement

Submarine Landslides: Science, Technology and Challenges

8 pages, 11 figures.Peer reviewe

Numerical Analysis of Shear and Particle Crushing Characteristics in Ring Shear System Using the PFC2D

The shear and particle crushing characteristics of the failure plane (or shear surface) in catastrophic mass movements are examined with a ring shear apparatus, which is generally employed owing to its suitability for large deformations. Based on results of previous experiments on waste materials from abandoned mine deposits, we employed a simple numerical model based on ring shear testing using the particle flow code (PFC2D). We examined drainage, normal stress, and shear velocity dependent shear characteristics of landslide materials. For shear velocities of 0.1 and 100 mm/s and normal stress (NS) of 25 kPa, the numerical results are in good agreement with those obtained from experimental results. The difference between the experimental and numerical results of the residual shear stress was approximately 0.4 kPa for NS equal to 25 kPa and 0.9 kPa for NS equal to 100 kPa for both drained and undrained condition. In addition, we examined particle crushing effect during shearing using the frictional work concept in PFC. We calculated the work done by friction at both peak and residual shear stresses, and then used the results as crushing criteria in the numerical analysis. The frictional work at peak and the residual shear stresses was ranged from 303 kPa·s to 2579 kPa·s for given drainage and normal stress conditions. These results showed that clump particles were partially crushed at peak shear stress, and further particle crushing with respect to the production of finer in shearing was recorded at residual shear stress at the shearing plane

Mechanical Properties of Concrete with Bamboo Chips

Mechanical properties of concrete with bamboo chips as a potential source of aggregates have been investigated in this study.The measurement of this investigation includes slump loss, compressive strength, strain at peak compressive stress, modulus of elasticity, compressive toughness ratio, and splitting tensile strength. A 0.5-cm-thick bamboo chip was cut to a 1 cm (width) × 1 cm (height) piece and then dried, wetted, and coated to minimize water absorption.The coarse aggregates in the concrete specimen were replaced with 10%, 20%, and 30% (by volume) of each bamboo chip. The testing results showed that the compressive strength and splitting tensile strength of concrete with bamboo chips decrease with increasing bamboo chip content (BCC). It is considered that the decrease of strengths is due to the weak bond between the mortar and the bamboo chip

Rheological characteristics of marine sediments from the Ulleung Basin, East Sea to estimate the mobility of submarine landslides

Special issue Geological implications for submarine geohazards, Ulleung Basin, East Sea.-- 17 pages, 12 figures, 1 tableIn estimating the geohazards posed by submarine landslides, the rheological properties of marine sediments are of significant importance for their postfailure dynamics. We report an experimental study of the rheological behavior of marine sediments taken from the Ulleung Basin, East Sea and their influence on numerical simulations of debris flow runout. Marine sediments exhibit a typical yield stress behavior, such as that of low-activity clays. For the materials examined, different yield stresses are observed depending on the shearing methods. Steady-state and oscillatory shear tests were conducted for different volumetric concentrations of sediment. According to the test results, the Bingham yield stresses under controlled shear stress and shear rate range from approximately 100 Pa to 1500 Pa, but the yield stresses under oscillatory shear loads range from approximately 25 Pa to 3500 Pa for a given sediment concentration. In the latter cases, the value obtained in the elastic region is approximately doubled. Experiments under steady-state and oscillatory shear loads can be helpful in determining the yield points in the elastic and viscous regions and in explaining changes in the structure of the soil sample due to shear. We apply the range of measured yield strength values to numerical simulations of debris flow runout using a Herschel-Bulkley model and find that only the lowest values of yield strength, despite the low sediment concentrations, could account for the observed runout and thickness distribution. We infer that significant wetting must occur during debris flow motion to attain the observed runoutThis research was supported by the KIGAM research project (21-3412-1; 21-9851). Special thanks for the research project entitled “Study on submarine active faults and evaluation of the possibility of submarine earthquakes in the southern part of the East Sea, Korea”. Many thanks for CSIC research funding. This work acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)Peer reviewe

Four-Year Monitoring Study of Shallow Landslide Hazards Based on Hydrological Measurements in a Weathered Granite Soil Slope in South Korea

To build a comprehensive understanding of long-term hydro-mechanical processes that lead to shallow landslide hazards, this study explicitly monitored the volumetric water content (VWC) and rainfall amount for a weathered granite soil slope over a four year period. From the 12 operational landslide monitoring stations installed across South Korea, the Songnisan station was selected as the study site. VWC sensors were placed in the subsurface with a grid-like arrangement at depths of 0.5 and 1.0 m. Shallow landslide hazards were evaluated by applying an infinite slope stability model that adopted a previously proposed unified effective stress concept. By analyzing the variations in the monitored VWC values, the derived matric suctions and suction stresses, and the calculated factor of safety values, we were able to obtain numerous valuable insights. In particular, the seasonal effects of drainage and evapotranspiration on the slope moisture conditions and slope stability were addressed. Preliminary test results indicated that continuous rainfall successfully represented the derived matric suction conditions at a depth of 1.0 m in the lower slope, although this was not the case for the upper and middle slopes. The significance of a future study on cumulative field monitoring data from various sites in different geological conditions is highlighted