Soil classification systems worldwide capture great physical insight and enable geotechnical engineers to anticipate the properties and behavior of soils by grouping them into similar respo...

https://ascelibrary.org/doi/pdf/10.1061/%28ASCE%29GT.1943-5606.0001705

Revised Soil Classification System for Coarse-Fine Mixtures

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

Strength recovery from residual state in reactivated landslides

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

Samples were collected form the O'dokoro landslide in Niigata prefecture for the mineralogical analysis. The O'dokoro landslide occurs in the sheared belts, located 5 km west from the Itoigawa-Shizuoka Tectonic Line and is positioned in the serpentinite melange. Lamellar serpentinite sample from the bedrock serpentinite bodies contained less than 20% of clay in the particle-size distribution, and the clay fraction consisted of antigorite with a small amount of talc. No other minerals were detected and no mineralogical difference with the particle-size fraction was noticed. In contrast, the clayey material (the fault clay) sampled from the fault-fractured seams which is expected to have a mineralogical similarity to the slip surface, showed the clay content of 50%. The clay fraction was dominated by vermiculite and chlorite accompanied by smectite, talc and amphiboles. Antigorite was not identified, and progress of vermiculization of chlorite was indicated. Chlorite in the fault clay was regarded as Mg- or MgFe-chlorite and was possibly formed by serpentinization of mafic minerals. Vermiculite was probably transformed from chlorite by faulting. Argillation and the increase in the swellability of minerals were proposed to make favorable the slip-surface formation in the O'dokoro landslide in the sheared belts.

Clay mineralogical approach to the slip-surface formation in the o'dokoro landslide, niigata, central japan

In order to increase the accuracy of stability analysis of the first time slide in the bedrock, it is important to clearly perceive the characteristics of geological structure, the residual strength acting on the slickenside surface of discontinuities, and the peak strength of the fractured mudstone in the slip surface zone.Concerning the landslide of the Neogene mudstone discussed in the present report, it was found that the slip surface has been formed by being strongly controlled by the strikes of bedding and fault planes, cutting through the fractured mudstone. The residual and peak strength parameters obtained from the ring shear test and the triaxial compression test were as follows: cr=7kPa and φr=16° for the slickenside surfaces; cf′=75kPa and φf′=36° for the specimens of mudstones having opening cracks; cf′=95kPa and φf=42° for the mudstones having internal cracks and microcracks. For the stability analysis a new method was introduced to assess the parameters of average shear strength along the slip surface, and applying the strength parameters mentioned above, c′=11kPa and φ′=17.5° were obtained.

Control of Geological Structure and Parameters of Average Shear Strength along the Slip Surface in a Landslide in the Neogene Mudstone in Okinawa

本研究では, 物理的・鉱物学的性質を異にする地すべり土についてリングせん断試験を行い, せん断挙動に及ぼす鉱物組成の影響を分析し, 応力～変位曲線の類別化を試みた。シルト・砂分が多く, 粘土含有量が20%より少ない試料でもピークから残留への明瞭な強度逓減が認められた。強度逓減量は, 配向性鉱物総量との関係において凸型変化を示した。地すべり土の応力～変位曲線は, 含有される鉱物総量に基づいて4タイプに類別できた。

The influence of mineral composition on the ring shear behavior of landslide soils

せん断試験により得られた強度定数を活用して, 黄土高原二道岔地すべりの不安定化のメカニズムについて議論した。移動層は馬蘭黄土からなり, 馬蘭黄土と頁岩基盤の境界付近がすべり面となっている。まず, すべり面採取土についてリングせん断試験を行って完全軟化強度および残留強度特性を明らかにし, 地すべりを再滑動させる地下水位を安定解析により算定した。次に, 地すべりの初生には, 平均すべり面強度を低下させる低い残留強度の関わりが不可欠であることを明らかにした。

Shear strength characteristics and destabilization of the Erdaocha landslide, loess plateau, China

沖縄本島中南部から南西琉球弧の宮古島にかけて分布する新第三紀島尻層群の灰色泥岩は脆性度の高い海成の過圧密粘土で, 小断層面, 節理面等があり, すべり面を形成しやすい地盤である。隆起量の大きい島尻層群露出域では, 小断層のような構造的弱面を素因とする初生型すべりが発生する。琉球層群が帽岩となっている地形では崩積土型すべりが起こる。島尻層泥岩の初生すべりには以下の特徴がある。(1) 地質構造的弱面がすべり面に転化する。(2) 弱面では, 残留強度かあるいはその付近まで強度が低下している。(3) すべり面の一部にはピーク強度を発揮する破砕泥岩が介在し, 構造的な弱面と共にブロック全体の滑動に抗している。(4) すべり発生の直接的な引金は, 主にせん断応力増加を伴う人為的な地形改変と, 間隙水圧を上昇させる破砕ゾーンへの雨水浸入である。

Keizo Sasaki

Papers

Clay mineralogical approach to the slip-surface formation in the o'dokoro landslide, niigata, central japan

Control of Geological Structure and Parameters of Average Shear Strength along the Slip Surface in a Landslide in the Neogene Mudstone in Okinawa

The influence of mineral composition on the ring shear behavior of landslide soils

Shear strength characteristics and destabilization of the Erdaocha landslide, loess plateau, China

Landslides in Neogene Shimajiri Mudstone in Okinawa