Soil Investigation And Drilling ( Types,Drill Bits )

The first oil wells were drilled in China in the

4th century or earlier. They had depths of up

to 243 meters and were drilled using bits

attached to bamboo poles.

By the 10th century, extensive bamboo

pipelines connected oil wells with salt

springs. Until the advent of internal

combustion engines in the late 19th century,

the primary method for drilling rock involved

muscle power be it human or animal. Rods

were turned by hand, using clamps attached

to the rod. The rope and drop method

invented in China.

Four drilling methods are widely used, each depending on

the type of information required and/or the rock types being drilled.

1- AIR ROTARY DRILLING

2- AIR PERCUSSION DRILLING

3- MUD ROTARY DRILLING

4- DIAMOND CORE DRILLING

This is a quick and

economical method of

producing a sample.

Compressed air is forced

down the drill pipe and, as it

returns to the surface, it

carries with it rock chips

made by the rotating bit.

This method is used in soft

rock materials to about 25m

deep.

This method is used for

penetrating hard rock types

to a depth of around 300m.

Rather than a rotating bit, a

hammer bit is forced

through the rock by

compressed air. As in air-

rotary drilling, rock chips are

brought to the surface by

the returning air.

This method is used for

drilling through soft rocks,

sand and clay layers

especially in the search for

coal, oil or gas. A special mix

of clay and water is forced

down the drill hole turning a

rotary bit, with rock chips

returning in the "mud" slurry.

This method is used for holes

up to 3km .

This method involves a pipe

encrusted in industrial

diamonds being used to drill

through rock layers, with a

"core" of rock being left in

the centre of the pipe. This

core is recovered and gives

information not only about

the rock types, but also

about the relationships

between the rock layers in

detail.

There are a variety of drill mechanisms which can be used

to sink a borehole into the ground. Each has its advantages

and disadvantages. Some of them are given below :

DRILL BITS

Drill bits come in a huge variety of shapes and sizes. Standard

drill bits are generally designed for wood, metal, or masonry.

Some of them are given below :

Brad point bits are also known as dowel or W-

point bits. Brad point bits are designed to cut clean, straight

holes in all types of wood.

Auger bits are used to make large, deep, accurate

holes in dry timber.

Paddle bits are also called wood spade bits. These

bits have a pointed tip that starts the hole. The spade-shaped

blade follows to drill a large.

Metal bits are also known as high-speed steel

(HSS) or twist bits. They are usually black in color and can be

used for wood and plastic. Most metal bits come with

cylindrical shanks, but some feature quarter inch hex shanks.

Reduced shank HSS bits allow one to drill a hole that is larger than the drill’s chuck would normally allow.

Rivet bits are specifically designed for drilling

holes for rivets. They often have flutes on both ends. Rivet bits

are made to drill shallow holes through thin metal.

Masonry drill bits are designed to drill into a

variety of masonry surfaces. These bits often have tips that are

made of extra-hardened material.

Rotary bits have carbide tips for added strength and

durability. They can be used to drill into stone, brick, concrete,

and cement .

Percussion bits are designed for use with drills with

hammering functions. Using the hammer function allows one to

penetrate masonry more easily.

Diamond bits are used for hard-surfaced

masonry. They can also be used on porcelain.

Multi - purpose bits can be used in both rotary

and hammer drill modes. They can be used to drill through

nearly anything, including plastic, wood, ceramic tiles, masonry, and metal.

Glass and tile bits have tungsten-carbide

tips that are spear shaped. These can penetrate a tile

or a piece of glass before enlarging the hole to the diameter of the tip’s base.

Specifically related to the subsoil

beneath the site under investigation can could be

a part of or separate from the site investigation.

A well designed site investigation can often

lead to project cost savings in the long term by

allowing contractors foresee potential problems.

1- Determine the suitability of the site foe the

proposed project.

2- Determine an adequate and economic

foundation design.

3- Determine the difficulties which may arise

during the construction process and period.

4- Determine the occurrence and/or cause of all

changes in subsoil condition,

Methods chosen will depend on several

factors :

1- Size of contract.

2- Type of proposed foundation.

3- Type of sample required.

4- Type of subsoil's which may be encountered.

Generally the following soil investigation

techniques are employed for the majority of projects :