Factors Contributing to Landslide Susceptibility of the Kope Formation, Cincinnati, Ohio

ABSTRACT The objective of this study was to evaluate the factors that contribute to the high frequency of landslides in the Kope Formation and the overlying colluvial soil present in the Cincinnati area, southwestern Ohio. The Kope Formation consists of approximately 80 percent shale inter-bedded with 20 percent limestone. The colluvium that forms from the weathering of the shale bedrock consists of a low-plasticity clay. Based on field observations, LiDAR data, and information gathered from city and county agencies, we created a landslide inventory map for the Cincinnati area, identifying 842 landslides. From the inventory map, we selected 10 landslides that included seven rotational and three translational slides for detailed investigations. Representative samples were collected from the landslide sites for determining natural water content, Atterberg limits, grain size distribution, shear strength parameters, and slake durability index. For the translational landslides, strength parameters were determined along the contact between the bedrock and the overlying colluvium. The results of the study indicate that multiple factors contribute to landslide susceptibility of the Kope Formation and the overlying colluvium, including low shear strength of the colluvial soil, development of porewater pressure within the slope, human activity such as loading the top or cutting the toe of a slope, low to very low durability of the bedrock that allows rapid disintegration of the bedrock and accumulation of colluvial soil, undercutting of the slope toe by stream water, and steepness of the slopes.

Suction effects on the tensile strength and unconfined compression of unsaturated soils

The soil-water characteristic curve is an important relation of unsaturated soils, that expresses the variation of the amount of water retained in the soil as a function of its suction. In these soils, drying or wetting can have a great influence on their resistance parameters. This work presents and discusses the effects of increased suction on the tensile strength and unconfined compression of unsaturated soils. Suction was evaluated using the filter paper and the dew point technique, while the resistance parameters were obtained through the “Brazilian Test” and uniaxial compression. Three different soils from Rio de Janeiro were studied: two young residual soils, in which the influence of the soil structure was also verified through tests on undisturbed and reconstituted samples, and a colluvial soil. The results allowed to conclude that the increase of suction, in a first moment, generates an increase in the resistance parameters of these soils. With the continuation of the drying process, the mechanical behaviour of the soils varied, being able to maintain the resistance or showing a drop related to high suction values.

Growth and Nutrient Acclimation of Evergreen Oak Seedlings Infected with Boletus reticulatus in Infertile Colluvial Soil in Warm Temperate Monsoon Asia: Evaluation of Early Growth

Soil erosion after harvesting of forest plantations can create infertile colluvial soil, therefore, seedlings used for site reforestation should be equipped against nutrient-poor edaphic conditions. The oak genus is a suitable candidate for such reforestation efforts. Oak is an ectomycorrhizal (ECM) tree genus known to grow under infertile environments. In this study, the initial stage of tree growth in three species of oak seedlings inoculated with a spore suspension of ECM fungus was monitored to evaluate the acceleration of seedling growth and nutrient uptake. I selected Quercus acuta Thunb., Quercus glauca Thunb., and Quercus salicina Blume, as these are common, evergreen, broad-leaved woody species commonly found in Southwestern Japan. The seedlings were inoculated with Boletus reticulatus and planted in infertile colluvial soils collected from a site that had undergone soil erosion. I also compared the ecophysiological characteristics of the potted seedlings planted in colluvial soil and normal forest soil. After six months of cultivation, Q. glauca with the ECM showed the highest growth rate in the fertile forest soil and had leaves with a higher nutrient content. In contrast, root dry mass increased slightly in Q. acuta and Q. salicina planted in colluvial soil. In all species, the seedling’s ECM colonization rate in colluvial soil was lower than that in forest soil, yet the increase in nutrient uptake in the former was not obvious. The contents of K and Ca in the roots of Q. acuta and Q. salicina increased with B. reticulatus infection. I concluded that the inoculation with a B. reticulatus spore suspension effectively accelerated the growths in all three Quercus species. Q. glauca favored a fertile environment, and Q. acuta and Q. salicina suitably acclimated to both soil types. Thus, these species were selected as potential future candidates for reforestation in such eroded sites.

Relación entre la permeabilidad teórica y experimental en suelos del entorno de Oviedo (Asturias, NW de España) Relationship between theoretical and experimental permeability in soils around Oviedo (Asturias, NW of Spain)

Resumen: Se ha estudiado la permeabilidad al agua de tres suelos del entorno de Oviedo (N de España) y su relación con algunas de sus propiedades índice. En campo, se realizó una caracterización y clasificación geotécnica, distinguiéndose un aluvión (Nora), coluvión (Ules) y eluvión (Piedramuelle). En laboratorio, se ha medido varias propiedades índice para clasificar los suelos según el Sistema Unificado de Clasificación de Suelos (SUCS). Se han determinado los coeficientes de permeabilidad teóricos y experimental (permeámetro de carga constante), realizándose una comparación entre ellos y su relación con algunas propiedades índice.Palabras clave: Suelos, permeabilidad, SUCS, límites de Atterberg.Abstract: The permeability to water of three soils in the surroundings of Oviedo (N of Spain) and its relationship with some of their index properties has been studied. The characterization and geotechnical classification made in the field allow us to distinguish three soil types: an alluvial soil (Nora), a colluvial soil (Ules) and an eluvial soil (Piedramuelle). The index properties for classifying soils according to the Unified System of Soil Classification (USCS) have been measured in the laboratory. The theoretical and experimental permeability coefficients have been determined, using a steady flow permeameter for the experimental one. The comparison between these coefficients and their relationship with the soil index properties have been studied.Keywords: Soils, permeability, USCS, Atterberg limits.

APPLICATION OF PFC 3D FOR SLOPE MOVEMENT ON COLLUVIAL SOIL

In the mountainous area of the tropics, soil creep often occurs on residual soil and colluvial deposit. The rate of this phenomenon varies from very slow to extremely slow and is difficult to detect without equipment as well as model. Within PFC3D (Particle Flow Code in three dimensions) granular materials such as soils are simulated by balls. And the PFC3D model was applied for colluvial soil creep. Although existing of some limitations, this application determined direction of creeping as well as zone of creeping of culluvial soil.