Sayedeh zahra Hosseini Teshnizi

DefinitionMethod of study to investigate soils and rocks in the Earth’ssubsurface by means of long and narrow holes drilled througha variety of specialized methods.IntroductionSuccessful engineering works often benefit from a clear andbetter understanding of the nature of soil and rock belowground. In the absence of extensive trenching and excavationand to complement noninvasive geophysical explorationtechniques, borehole investigations can be carried out, includ-ing the analysis and characterization of the soil and rockrecovered. Su ch investigations allow the identification of thesoils or rocks present, as well as an understanding of theirphysical properties on the basis of field and laboratory tests.Borehole investigations allow practitioners to determinethe nature and location of the different soil/rock layers, collectsamples, carry out in sit u tests and permeability tests, and, ifnecessary, install piezometers and other subsurface monitor-ing tools. The location of the boreholes is chosen dependingon the objective of the project and characteristics of the tests,with due con sideration to the type of works planne d.Borehole SystemsBoreholes may be drilled by two primary systems: percussionor rotary techniques. The former relies on the use of a toolthat advances with successive hitting movements, driven by ahammer that is dropped, with its energy transmitted by meansof rods to a solid tool or hollow tube (sampler ) placed at thebottom of the borehole. This system, which has its advantagesin unconsolidated soils (silt, sand and gravel), usually takeslonger and is more expensive than rotary dril ling. The rotarytechnique (Fig. 1) is the most frequently used method forsubsurface exploration. A cutting tool is used to collect sam-ples using a helical auger or drill bit that moves forward bymeans of a bit crown that is usually widia or diamond tipped.In the case of auger drilling, alternative methodsare needed to obtain samp les, which is normally carriedout discontinuously. This technique is mainly used inuncemented soft to medium consistency soils or in rocks.In rotary core drilling, a rock cy linder referred to as “core”may be extracted as the drilling advances and are stored in apipe screwed to the crown, which is called a “core barrel.”This may be a simple tube or a rotating double tube in whichthe inner tube is mounted on bearings.

Permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. The term “filter fabric” is more expressive, but it has fallen into comparative disuse. Geotextiles are really fabric materials used in a “geo,” that is an earth-related, engineering context.

Successful engineering works often benefit from a clear and better understanding of the nature of soil and rock below ground. In the absence of extensive trenching and excavation and to complement noninvasive geophysical exploration techniques, borehole investigations can be carried out, including the analysis and characterization of the soil and rock recovered. Such investigations allow the identification of the soils or rocks present, as well as an understanding of their physical properties on the basis of field and laboratory tests. Borehole investigations allow practitioners to determine the nature and location of the different soil/rock layers, collect samples, carry out in situ tests and permeability tests, and, if necessary, install piezometers and other...