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Geotechnical Investigations

Major Activities performed

Diamond core drilling

In rock drilling, Diamond core drilling is done to obtain an accurate core sample. Drilling through overburden (soil and sub soil) is done with a casing bit made of tungsten carbide inserts. When rock is encountered a casing pipe is placed in the hole to prevent the collapse of loose material. Core drilling is then done through the rock with the use of a diamond bit. When required, standard penetration test is done in the soil to ascertain the bearing capacity. Undisturbed samples of soil are also obtained for laboratory testing.

Deep exploratory drilling is mostly done with wire line system by which the core is recovered in a few minutes by retrieving the inner tube through the drill string using a cable. The drill rods are retained until the diamond bit is replaced.


Grouting is a process of injecting cement slurry to the foundation of structures for the purpose of sealing seepage, cracks and fissure or filling of voids. Its purpose is to render the mass impervious to percolation, improve strength and elastic properties, reduce settlement under existing loads and increase shearing resistance for stability against lateral movement.

In dams its function is so control seepage and leaks and reduce the hydrostatic uplift pressure on the base of the structure. In earthen dams it is used to form a cut off curtain beneath the impervious sections of the dam, to fill cracks and to dry up springs in the foundation area.

Grouting is done in the foundation of buildings to increase the bearing capacity and to reduce vibration caused by heavy machinery. In tunnels grouting is done ahead of excavation to prevent seepage of water into the tunnel excavation to consolidate rock surrounding the bore and to fill voids between the tunnel lining and rock. In excavations, grouting is done to form a cut off or coffer dam to help excavation.

Drilling Tube wells

There are two basic methods of drilling tube wells; cable tool (percussion) and rotary. Machinery for using both methods is in use in the Department. These drill rigs are generally of a larger capacity than the core drills and are cither truck or trailer mounted and incorporates a mast of 20ft. pulls, draw works including a bull reel and a sand reel, a cat head, a heavy duty mud pump and a hydraulic pump together with the prime mover. The capacity of these drills is in the range of 500 ft. with 8” diameter.

Rotary drilling

Rotary drilling is done applying continuous pressure with rotary action in cutting the rock with a tri-cone bit. The formations encountered in water well drilling are such that a fish tail or roller cone bit can be used economically. For effective penetration, removal of cuttings from the bottom of the hole and for cooling and lubricating the bit, pressure circulation of liquids or the application of air pressure is necessary. Fluids used for circulation is drilling mud - Bentonite clay mixed with water. The mud is fed in to the string through a swivel fixed on top of the kelly.    As drilling progresses through the soil, the mud seals up the walls of the drill hole and prevents the collapsing of the hole.

Cable Tool or percussion Drilling

This method employs the principle of freely falling of a chisel bit to deliver rhythmic blows against the bottom of the hole. The bit breaks the rock in to small fragments and in the case of unconsolidated formations loosens the material. In either case the reciprocating action of the bit breaks up the fragments and mixes the particles with water introduced in to any hole by means of a hailer. The slurry is removed by a sand pump or bailer inserted in to the hole with  the aid of the sand reel. In hard formations the bit has to be sharpened frequently resulting in very low progress. This form of drilling is noisy and inefficient. The only advantage lies in the fact that the rig is rugged. It is now regarded as an outmoded type of drill, when compared to rotary drills.

At present, the Engineering Geology Division is one of the pioneering organizations that directly provide consultancy service not only to leading governmental institutions but also to nongovernmental organizations across the Island.

Last Updated on Thursday, 25 April 2013 02:39  

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