Identification of modes of slope instability

Different types of slope failure are associated with different geological structures and it is important that the slope designer be able to recognize potential stability problems during the early stages of a project. Some of the structural patterns that should be identified when examining pole plots are outlined on the following pages.

Stereographic Analysis of Structural Geology

Stereographic projection
Stereographic projection comes in very handy for representing points lying on a three-dimensional surface in two dimensions for improved analysis. Stereographic presentations remove one dimension from consideration so that lines or points alone may stand for planes and points for lines. One important limitation of stereographic projections is that they consider only angular relationships between lines and planes; they do not stand for the position or size of the feature.

Structural Geology & Data Interpretation

The structural geology is a very important factor that significantly influences the stability of rock slopes. It refers to naturally occurring breaks in the rock, like bedding planes, joints, and faults, generally termed as discontinuities. The properties related to discontinuity in relation to stability are orientation, persistence, roughness, and infilling. The importance of discontinuities lies in the fact that they represent planes of weakness in the much stronger, intact rock; therefore, failure tends to occur preferentially along these surfaces. The discontinuities themselves may directly influence stability—these are the slopes shown in Figure 1. In Figure 1(a) the face is formed by the bedding planes, which are continuous over the full height of the cut; this condition is termed a plane.  Alternatively, slope failure may occur on two discontinuities that intersect behind the face, as illustrated in Figure 1(b)—this condition is termed a wedge failure.

Soil Mechanics & its Importance

Introduction

Soil Mechanics, the branch of Geology and Geotechnology foretells the performance characteristics of soils with the techniques of civil engineering of dynamics, fluid mechanics, and other technologies. In general, it deals with the study of composition, strength, consolidation, and application of hydraulic principles to face problems related to sediments and other deposits. Soil mechanics is one of the major sciences for resolving problems related to geology and geophysical engineering. Soil mechanics studies are also very important for civil engineers based on the findings of which engineering structures are constructed. The type of construction, type of equipment to be used, and type of foundation with the support material in relation to construction works are a lot affected by the soil mechanics studies. Basically, we study modes of soil formation, physical and chemical properties of soils, dynamic loading of soils, permeability, consolidation, etc. In the subsequent sections of this article, we will go into detail about major aspects of studies in soil mechanics.

Soil and its basic characteristics

Formation of Soil
Soil is a combination of minerals and organic constituents in solid, gaseous, and aqueous forms. It truly possesses layers of particles that differ in physical, mineralogical, and chemical properties from the original materials because of the actions of the atmosphere, hydrosphere, and other causes. Soil particles are the products of broken rocks changed by the impacts of the chemical and environmental effects that include weather and erosion. Soil particles fill loosely creating a formation of soil filled with pore spaces. The modes of soil formation are important to study since they help in determining properties of some soils. Knowing the type of soil one has to deal with can easily tell about its cohesiveness, adhesiveness, acidity, and other related factors. We cannot draw any concrete inferences merely by doing soil studies, but we surely can narrow our research parameters by studying the basic characteristics of soil, such as color, texture, and nature of soil.

Hydrogeology

The occurrence, distribution, storage, and flow of groundwater beneath the surface are the subjects of hydrogeology. Groundwater, often known as subsurface water, is any water that is found below the surface of the Earth. Groundwater requires very little treatment to be used, in contrast to surface water. One element of the hydrologic cycle in nature is groundwater. Groundwater seeps through natural cavities and intergranular pores in rocks, known as primary openings, as well as discontinuities like fractures, joints, and solution cavities, known as secondary openings. While secondary openings can be found in most igneous and metamorphic rocks as well as in certain sedimentary rocks, primary openings are typically found in sedimentary rocks.

Weathering of rocks and formation of soil

The exposed rocks of the earth's surface are subject to continuous decay, disintegration and degradation by certain physical, chemical and biological agents. This phenomenon is called rock crumbling. The physical/mechanical weathering of rocks is due to temperature fluctuations due to cycles of water freezing and thawing opening the rock mass in ancient humid climates and thermal effects in hot arid (arid) regions. Rainwater causes chemical weathering of rocks due to the chemical action of dissolved atmospheric gases (carbon dioxide, hydrogen, nitrogen, etc.). Organisms (nesting animals such as earthworms, ants and rodents) and plants also cause rock to break down through their physical activity. People also break rocks in different ways.