boring methods in soil exploration
The following types of boring methods are generally utilized in the construction site.
- Auger boring
- Auger and shell boring
- Wash boring
- Percussion boring
- Rotary boring
- Auger boring
Augers are suitable for cohesive and other soft soils over water table. They are either be conducted manually or mechanically. Hand augers are applied up to a depth upto 6 m. Mechanically operated augers are recommended for larger depths and they are also ideal for gravelly soils. Augers are categorized as (a) spiral auger and (b) post-hole auger. Samples retrieved from the soil created by the augers are critically mistreated and are suitable for verifying identity only. Auger boring is somewhat acceptable for explorations at shallow depths and for exploratory borrow pits.
Also read : GRADING OF AGGREGATES FOR CONCRETE
Auger and shell boring
Cylindrical augers and shells containing cutting edge or teeth at Iower end suitable for the formation of deep borings. Manually operated rigs are utilized for depths up to 25 m and automated rigs up to 50 m. Augers are appropriate for soft to stiff clays, shells for very inflexible and hard clays, and shells or sand pumps for sandy soils. Small boulders, thin soft strata or rock or cemented gravel are crushed with chisel bits affixed to drill rods. The hole normally needs a casing.
Wash boring is a rapid and uncomplicated process for developing holes in different types of soils. Boulders and rock can't be infiltrated by this method. Under this method, initially a casing is provided through which a hollow drilled rod containing a sharp chisel or chopping bit at the lower end is entered. Water is entered forcibly under pressure through the drill rod that is optionally elevated and dropped, and also rotated. The consequential chopping and jetting action of the bit and water decomposes the soil. The cuttings are pushed forcibly up to the ground surface in the form of soil-water slurry via the annular space among the drill rod and the casing. The change in soil layer could be presumed from the rate of development and colour of wash water. The samples retrieved from the wash water are almost useless for ascertaining the perfect geo-technical properties of soil./p>
Under this method, soil and rock productions are crushed with frequent blows of heavy chiesel or bit suspended by a cable or drill rod. Water is entered to the hole at the time of boring, unless already existing and the slurry of pulverised material is bailed out at gaps. The method is ideal for developing a hole in different types of solis, boulders and rock.
Rotary boring is a very rapid method of developing hole in both rocks and soils. A drill bit is attached to the lower end of the drill rods, is revolved with a appropriate chuck, and is always retained in firm contact with the bottom of the hole. A drilling mud, generally a water solution of bentonite, with or without other admixtures, is incessantly pushed down forcibly to the hollow dril rods. The mud directing upwards gets the cuttings to the surface. This method is also defined as mud rotary drilling and the hole generally needs no casing.
Rotary core barrels, arranged with commercial diamond-studded bits or a steel bit with shots, are also effective for rotary drilling and at the same time acquiring the rock cores or samples. The method is also knowb as core boring or core drilling. Water 15 circulated down drill rods at the time of boring.
Record of borings
In all exploration work, crucial step should be keeping a perfect and precise record of borings. Soil/rock samples are accumulated at different depths, throughout boring. These samples are examined in the laboratory for recognition and classification.
The samples are properly conserved and organized serially based on the depth at which they are found.