Soil Mechanics - Essay Example

CONTENTS Sl. No. Page No Introduction 2 2. Primary elements of best site investigation scheme 2 3. Various techniques that can be used for subsurface exploration 4 4. Conclusion 6 5. References 8 Soil Mechanics Introduction Soil mechanics can be considered as a method that applies the principles of engineering mechanics to soil to predict the mechanical nature of soil. This is significant to various divisions of engineering, such as civil engineering, geotechnical engineering and engineering geology. This can be used in the design of foundations, embankments, retaining walls, earthworks and underground openings (Wikipedia, 2007). Soil is said to be a collective of mineral particle, including organic components and it exist mainly in three phases (solid, liquid, and gaseous). There are six major properties to determine how the soil of a particular site will hold the stresses put over it by the weight of structures. They are internal friction, cohesion, compressibility, elasticity, permeability and capillarity. Internal friction is the resistance of a soil mass to sliding and cohesion means molecular attraction between soil particles. These two properties of the soil decide tendency of soils to shear or slide along planes. Compressibility is the ability of the soil to become denser by different means such as vibration and tampering and elasticity is said to be the ability of the soil to expand after being compressed. Permeability is the capability of the soil to manage the flow of water and capillarity is efficiency of the soil to draw water upward from a water source (Soil mechanics, 2007). This essay mainly gives brief idea about the primary elements of best site investigation scheme and techniques that can be used for subsurface exploration. Primary elements of best site investigation scheme The purpose of site investigation is to gather a correct information base since the site exploration is the basis for all successive choice and actions. This has to be correctly planned and implemented by expert personnel, which gives an information base regarding all potential risk and must make sure that there is no danger to personnel, general public and environment. The lacks of these information’s can cause improper remedial planning with possible disastrous result. The scope of site exploration provides an incorporated hazard and risk assessment that can control the risk at source thereby having a bearing on potential targets. There are no fixed rules as to the method used for an investigation; budgets, tender scopes, and the nature of the site will all speak the form of an analysis plan. Planning an investigation of a theoretical project structure including all elements from project requirement through to remediation is shown in fig.1. Even though individual projects have their own objectives, they will have a combination of elements of risk appraisal (yellow boxes), susceptibility evaluation (green boxes), risk appraisal (orange box) and risk management (pink boxes). Carrying out the study in stages is seen as an important way of discovering and refining site investigation priorities, making sure safe operational practices and reducing costs. Collection of baseline information from a desk study or first round field visit is necessary. The study using past data sets or from several site visits also allow for the rates of change in the glacial environment to be determined. Normally these rates give the hint of the importance for remediation. The design of improvement works may also need information diverse from that used for a risk appraisal, requiring further data collection. Therefore stages may include first round desk studies, survey visits and monitoring, and remote monitoring. The level to which these can be accomplished depends on the individual project specifications. There are various Investigation techniques exist for distinguishing the glaciological, geological, geotechnical and hydrological conditions of a site. When choosing site investigation techniques the following points are to be considered: The level of accuracy needed for the particular stage, the type of evaluation or testing required, whether samples required, recording and storage of data, reporting of data (format, timing) and quality assurance method. Data management holds the entire range of activities involved in the handling of data. These activities include Data Policy, Data Acquisition, Data Ownership, Documentation and Metadata compilation. Quality Assurance (QA) is a significant means of inspection and ensuring the legality of the events and data used for risk appraisal purposes. Health and Safety directive relates to substances on site or to the physical atmosphere. Regulatory and political aspects of site investigation works may be subject to prior authorization by the regulatory authorities (geologyuk.com, 2003). Various techniques that can be used for subsurface exploration Various techniques are used for subsurface exploration for the purpose of site development. The simplest way used by both ancient and modern engineers to determine the subsurface condition is to dig a test pit and look into it to obtain view of subsurface soil condition. These test pits are often used by geotechnical engineers, particularly to map the level of surface abnormal conditions such as buried organic soils, debris, waste, or shallow rock features. The drawbacks of this method include a partial depth of examination and the lack of ability to determine soil properties such as strength, compressibility, and permeability. Another method used is the soil borings by a drilling rig; provide the engineer a greater depth of examination and a hollow or solid stem auger used to determine the types of soil under the ground surface. But, this method also does not provide the strength properties vital to geotechnical engineers. One of the most widely used methods is the Standard Penetration Test (SPT) boring, used in combination with rotary “mud” drilling to get disturbed samples of soil from the required depths. This test gives several engineering soil properties such as relative density, dry unit weight, modulus of elasticity and friction angle etc. Cone Penetrometer Test (CPT) overcome the disturbance issue common to the SPT and this device, extensively used in Europe and US, can efficiently used to decide the soil types in the underground profile and also estimate their engineering properties. The above exploration methods provide a very limited knowledge of the underground conditions even though number of test locations is used. Different geophysical methods came up to help overcome this major problem. Out of these testing systems Ground Penetrating Radar (GPR) (fig. 2) is possibly the most popular geophysical exploration system used. GPR uses high frequency, pulsed electromagnetic waves to get subsurface data. EM wave is propagated into the ground and is reflected back to the surface from objects which are contrast to electrical properties. GPR is commonly used for sinkhole study, void discovery, roads and runways pavement appraisal, and utility location. Electrical Resistivity (ER) analyses also used extensively to assess certain properties of the subsurface soils. The resistivity of different soils varies on the moisture content and the concentration of dissolved ions. The resistivity can be used to estimate the soil types below the ground. Another modern progress in this area is the Multi-Channel Analysis of Surface Waves (MASW), which read the frequency distribution of the surface waves created by the earth vibration impact. These devices can be mounted on a movable platform and moved along a survey line to obtain a great deal of data in a short period of time. These are the few geophysical devices used by the engineers to know underground conditions (Mongeau, et al, 2005). Conclusion The primary elements of site investigation and techniques used for the surface exploration have been explained briefly in the above paragraphs. The assessment on environmental impact has to be an ongoing activity to help the project managers to avoid threat to the project from an environmental risk. This will help to avoid unwanted delay in project sanction and prevent redesign. The major advantages of well planned and implemented subsurface exploration and testing process are the better dependability on engineering principles and less doubt of subsurface conditions, which can lessen setbacks during construction. Fig. 1: Example project structure for glacial risk assessment and management. Source: http://www.geologyuk.com/mountain_hazards_group/pdf/Chapter_5.pdf Fig.2 Ground Penetrating Radar survey Source: http://www.ardaman.com/downloads/Subsurface%20Exploration.pdf References geologyuk.com, (2003). Site Investigation And Data Management, Retrieved March 29, 2007, from http://www.geologyuk.com/mountain_hazards_group/pdf/Chapter_5.pdf Mongeau, M.L., Ardaman, P.E. and Associates (2005). Exposing the Underground: A Primer on Subsurface Exploration Techniques, Florida Engineering Society, March 2005, pp. 21-22. Retrieved March 29, 2007, from http://www.ardaman.com/downloads/Subsurface%20Exploration.pdf Soil mechanics (2007). In Encyclopædia Britannica. Retrieved March 29, 2007, from Encyclopedia Britannica Online: http://www.britannica.com/eb/article-9068533 Wikipedia, (2007) Soil mechanics, 22 March 2007, Wikimedia Foundation, Inc., Retrived on 28 March 2007 from http://en.wikipedia.org/wiki/Soil_mechanics Read More