Geotechnical Engineering – An analysis

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Geotechnical engineering

Geotechnical engineering deals with the behavior of earth materials. Geotechnical engineering uses principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials; determine the relevant physical/mechanical and chemical properties of these materials; evaluate stability of natural slopes and man-made soil deposits; assess risks posed by site conditions; design earthworks and structure foundations; and monitor site conditions, earthwork and foundation construction.

A typical geotechnical engineering project begins with a review of project needs to define the required material properties. Then follows a site investigation of soil, rock, fault distribution and bedrock properties on and below an area of interest to determine their engineering properties including how they will interact with, on or in a proposed construction. Site investigations are needed to gain an understanding of the area in or on which the engineering will take place. Investigations can include the assessment of the risk to humans, property and the environment from natural hazards such as earthquakes, landslides, sinkholes, soil liquefaction, debris flows and rockfalls.

Soil and rock mechanics for Geotechnical engineering

In geotechnical engineering, soils are considered a three-phase material composed of rock or mineral particles, water, and air. The voids of a soil, the spaces in between mineral particles, contain the water and air.

The engineering properties of soils are affected by four main factors: the predominant size of the mineral particles, the type of mineral particles, the grain size distribution, and the relative quantities of mineral, water and air present in the soil matrix. Fine particles (fines) are defined as particles less than 0.075 mm in diameter.

Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and water) and particles (usually clay, silt, sand, and gravel) but soil may also contain organic solids and other matter. Along with rock mechanics, soil mechanics provides the theoretical basis for analysis in geotechnical engineering, a subdiscipline of civil engineering, and engineering geology, a subdiscipline of geology. Soil mechanics is used to analyze the deformations of and flow of fluids within natural and man-made structures that are supported on or made of soil, or structures that are buried in soils.

Rock mechanics is a theoretical and applied science of the mechanical behavior of rock and rock masses; it is that branch of mechanics concerned with the response of rock and rock masses to the force fields of their physical environment. Rock mechanics is concerned with the application of the principles of engineering mechanics to the design of structures built in or of rock. The structure could include-but not limited to- a drill hole, a mining shaft, a tunnel, a reservoir dam, a repository component, or a building. Rock mechanics is used in many engineering disciplines, but primarily used in Mining, Civil, Geotechnical, Transportation, and Petroleum Engineering.

Investigation for Geotechnical engineering

Geotechnical investigation is a procedure that determines the stratigraphy (study of rocks) and relevant physical properties of the soil underlying the site. This is done to ensure that this substructure, which is eventually going to hold up homes, is safe and enduring. Geotechnical investigations have acquired substantial importance in preventing human and material damage due to the earthquakes, foundation cracks, and other catastrophes.

  • Geotechnical investigations can be as simple as conducting only a visual assessment of the site or as detailed as a computer-aided study of the soil using laboratory tests.
  • The purposes of a Geotechnical Investigation are to investigate the soil and geologic conditions of a property and to provide recommendations and design criteria for construction.
  • The scope of a Geotechnical Investigation includes review of the available literature; conducting on-site exploration, mapping/logging and sampling; and laboratory testing of samples obtained in the field.
  • The collected data is analyzed and geotechnical criteria for foundations, retaining walls, site grading and site drainage are developed.
  • This criterion chiefly consists of the load bearing capacities and anticipated lateral forces from the onsite soil and rock.
  • The culmination of the investigation is a report summarizing the field and lab findings; conclusions regarding the geotechnical impacts of the site; and recommendations for the most technically suitable construction. Geotechnical investigations have become an essential component of every construction to ensure the safety of human beings and materials.
  • Geotechnical investigations are executed by highly experienced geotechnical engineers and geologists to acquire information regarding the physical characteristics of soil and rocks.
  • The purpose of geotechnical investigations is to design earthworks, pilings and foundations for structures, and to execute earthwork repairs necessitated due to changes in the subsurface environment.
  • A geotechnical examination includes surface and subsurface exploration, soil sampling, and laboratory analysis.
  • Geotechnical investigations are also known as foundation analysis, soil analysis, soil testing, soil mechanics, and subsurface investigation. The samples are examined prior to the development of the location.

For any civil engineering project, however big or small, it is of primary importance that a proper field survey and a very precise geotechnical investigation be conducted. Geotechnical investigation is an integral part of the construction process which is done to obtain information about the physical characteristics of soil/rock around a site. It is a below-ground investigation wherein the soil strata is sampled and tested to establish its characteristics, which will influence the construction project.

These investigations form the basis for planning, designing, and constructing the structures. The serviceability and performance of the structure depend on the accuracy and adequacy of these investigations. How accurate the information in the geotechnical report is strongly influences the design, construction, project cost, and safety.

Unfortunately, many people underestimate the importance of proper geotechnical investigation during the conceptual phase of a project. One of the greatest causes of foundation failure is insufficient knowledge of ground conditions.

There have been some instances where attempting to save on such site investigations have led to disastrous results. Because structures that are designed on assumed or inadequate data can lead to long term complications. It may also result in loss of life and property, endanger residents, damage adjoining structures, and essentially be rendered non-functional for intended purpose.

Thus soil investigations provide the engineer with knowledge of the subsurface conditions at the site of an engineering project. It allows the engineer to work out safe and economical design of a project and inform the construction engineer about the material and conditions he will encounter in the field.

Foundation consideration for Geotechnical engineering

In engineering, a foundation is the element of a structure which connects it to the ground, and transfers loads from the structure to the ground. Foundations are generally considered either shallow or deep. Foundation engineering is the application of soil mechanics and rock mechanics in the design of foundation elements of structures.

The design and the construction of a well-performing foundation must possess some basic requirements that must not be ignored. They are:

  • The design and the construction of the foundation is done such that it can sustain as well as transmit the dead and the imposed loads to the soil. This transfer has to be carried out without resulting in any form of settlement that can result in any form of stability issues for the structure.
  • Differential settlements can be avoided by having a rigid base for the foundation. These issues are more pronounced in areas where the superimposed loads are not uniform in nature.
  • Based on the soil and area it is recommended to have a deeper foundation so that it can guard any form of damage or distress. These are mainly caused due to the problem of shrinkage and swelling because of temperature changes.
  • The location of the foundation chosen must be an area that is not affected or influenced by future works or factors.

Foundations provide the structure’s stability from the ground

  • To distribute the weight of the structure over a large area so as to avoid overloading of the soil beneath.
  • To anchor the structures against the changing natural forces like Earthquakes, floods, frost-heave, tornado or wind.
  • To load the sub-stratum evenly and thus prevent unequal settlement.
  • To provide a level surface for building operations.
  • To take the structure deep into the ground and thus increase its stability, preventing overloading.
  • Specially designed foundation helps in avoiding the lateral movements of the supporting material.

Retaining wall support system for Geotechnical engineering

A retaining wall is a structure that holds back earth. Retaining walls stabilize soil and rock from downslope movement or erosion and provide support for vertical or near-vertical grade changes. Cofferdams and bulkheads, structures to hold back water, are sometimes also considered retaining walls. The primary geotechnical concern in design and installation of retaining walls is that the weight of the retained material creates lateral earth pressure behind the wall, which can cause the wall to deform or fail. The lateral earth pressure depends on the height of the wall, the density of the soil, the strength of the soil, and the amount of allowable movement of the wall. This pressure is smallest at the top and increases toward the bottom in a manner similar to hydraulic pressure, and tends to push the wall away from the backfill. Groundwater behind the wall that is not dissipated by a drainage system causes an additional horizontal hydraulic pressure on the wall.

The types of retaining walls are;

  • Gravity wall
  • Piling wall
  • Cantilever wall
  • Anchored wall
  • Earthworks

Earthworks are engineering works created through the processing of parts of the earth’s surface involving quantities of soil or unformed rock.

Excavation may be classified by type of material

  • Topsoil excavation
  • Earth excavation
  • Rock excavation
  • Muck excavation – this usually contains excess water and unsuitable soil
  • Unclassified excavation – this is any combination of material types

Excavation may be classified by the purpose;

  • Stripping
  • Roadway excavation
  • Drainage or structure excavation
  • Bridge excavation
  • Channel excavation
  • Footing excavation
  • Borrow excavation
  • Dredge excavation
  • Underground excavation

Geosynthetics for Geotechnical engineering

Geosynthetics are a type of plastic polymer products used in geotechnical engineering that improve engineering performance while reducing costs. This includes geotextiles, geogrids, geomembranes, geocells, and geocomposites. The synthetic nature of the products makes them suitable for use in the ground where high levels of durability are required; their main functions include drainage, filtration, reinforcement, separation, and containment. Geosynthetics are available in a wide range of forms and materials, each to suit a slightly different end-use, although they are frequently used together. These products have a wide range of applications and are currently used in many civil and geotechnical engineering applications including roads, airfields, railroads, embankments, piled embankments, retaining structures, reservoirs, canals, dams, landfills, bank protection and coastal engineering.

Observation method for Geotechnical engineering

In geotechnical engineering, during the construction of earth structures (dams and tunnels, for example) the observational method is a continuous, managed and integrated process of design, construction control, monitoring and review enabling appropriate, previously-defined modifications to be incorporated during (or after) construction. All these aspects must be demonstrably robust. The objective is to achieve greater overall economy, without compromising safety