6 DIFFERENT METHODS OF BORING USED FOR SOIL EXPLORATION

Where direct methods fail, boring methods are used for more in-depth exploration. These provide both disturbed and undisturbed samples depending on the method of boring. When selecting a boring method for a particular job, the following should be considered:

  • The material to be faced and the relative efficiency of various boring methods in such materials
  • Available facility and accuracy with which changes in soil and groundwater conditions can be determined
  • Possible material error for sampling

There are different types of boring methods:

  1. displacement boring
  2. wash boring
  3. auger boring
  4. rotary drilling
  5. percussion drilling
  6. continuous sampling

1. displacement boring

It is a combined method of sampling and boring operation. The closed bottom sampler, slit cup or piston type is inserted into the ground to the desired depth. The sampler is then separated from the soil beneath it by rotating the piston and finally the piston is released or withdrawn. The sampler is then pushed down again and the sample is taken. After the sampler is withdrawn and the sample is removed from the sampler, the sampler is placed in the closed position and used again for another depth.

Properties

  • Simple and economical method without excessive caving. Therefore not suitable for loose sand.
  • Major changes in soil character can be traced through penetration resistance.
  • These are 25mm to 75mm holes.
  • This requires fairly continuous sampling in hard and dense soil, either to avoid damage to the sample or to avoid an objectionably heavy construction pit.

2. wash boring

This is a popular method due to the limited equipment used. Its advantage is the cheap and easy-to-use portable handling and drilling equipment. Here an open hole is first made on the ground so that soil sampling or rock drilling operation can be done at the bottom of the hole. The hole is advanced by cutting and rotating the action of the light bit. Water forced under pressure through rods driven inside the hole and harvested by jets of water.

In India “Dheki” operation is used, i.e., a pipe of diameter 5 cm is placed vertically and filled with water using a horizontal lever arrangement and by the process of application of suction and pressure, the clay solution Comes out of the tube and goes down the pipe. , This can be done to a depth of 8m-10m (excluding the depth of the hole already made).

Seeing the change in the color of the soil, there is a change in the character of the soil, it can be recognized by any experienced person. It gives completely poor sampling and is not suitable for very soft soils, fine to medium grain cohesive soils and cemented soils.

wash boring
wash boring

3. auger boring

Augers
Augers

This method is fast and economical, using simple, lightweight, flexible and inexpensive equipment for even the smallest of holes. It is very suitable for soft to hard adhesive soils and can also be used to determine ground water level. This degrades the removed soil but is better than wash boring, percussion or rotary drilling.

This method of boring is not suitable for very hard or compacted soils, very soft soils, then the hole may flow. This method is also not suitable for completely saturated non-contact soils.

4. rotary drilling

The rotary drilling method of boring is useful in case of highly resistant levels. It deals with locating rock strata and accessing quality rocks from cracks, crevices and joints. It can also be easily used in sands and silts. Here, the bore hole is deeply advanced by rotary percussion method which is similar to wash boring technique. A heavy string of drill rod is used for the throttle. Broken rock or mud fragments are removed by circulating water or drilling mud pumped through a drill rod and bit up through a bore hole, from where it is placed in a settling tank for recirculation. is collected in. If the depth is less and the soil is stable, water alone can be used. However, drilling fluids are useful because they serve to stabilize the bore hole.


Drilling mud is a solution of bentonite in water. Drilling fluid causes a stabilizing effect on the bore hole, partly due to the higher specific gravity than water and partly due to the formation of clay cakes at the edges of the hole. Since the stabilization effect is provided by these drilling fluids, no casing is required if drilling fluids are used.

This method is suitable for boring holes of 10 cm in diameter, or more preferably 15 to 20 cm in most rocks. It is not beneficial for pores less than 10 cm in diameter. The depth of different levels can be ascertained by inspection of the cuttings.

rotary drilling system
rotary drilling system

5. percussion drilling

percussion drilling
percussion drilling

In case of hard soil or soft rock, auger boring or wash boring cannot be employed. For such leveling, percussion drilling is usually adopted. Here the advancement of the hole is done alternately by lifting and dropping a heavy drilling bit which is attached to the bottom end of the drilling bit which is attached to the cable.

Adding sand to the soil increases the cutting action of the drilling bit. Whereas, when faced with rough soils, the soil may need to be mixed to increase the carrying capacity of the solution.

After the carrying capacity of the soil is reached, the churn is removed and the slurry is removed using balers and sand pumps. Changes in soil character are identified by the composition of the outgoing solution.

The stroke of the bit varies according to the ground condition. Generally, it occurs at a rate of 35-60 drops/min at 45-100 cm depth.

It is economical for holes not less than 10 cm in diameter. It can be used in most soils and rocks and can drill any material.


One of the main disadvantages of this process is that the material under the hole is disturbed by the heavy blows of the chisel and therefore it is not possible to obtain good quality undisturbed samples. It cannot detect even thin layers.

6. continuous sampling

The sampling operation advances the borehole and boring is accomplished by continuously sampling. Casing is used to prevent caving in the soil. It provides more reliable and detailed information on soil conditions than other methods. Hence it is widely used in search of elaborate and specialized foundations for important structures.

This is a slower method and more expensive than intermittent sampling. When modern rotary drilling rigs or power driven augers are not available, continuous sampling can be used to advance large diameter borings into hard and hard strata of clay and mixed soils.

In the Boston District, the Corps of Engineers has made rapid progress and reduced costs by the use of continuous sampling in advancing 3-inch diameter borings through compact gravel glacials, which are difficult to penetrate by any boring method.

Author

Dr. Dipankar Choudhary (IIT Bombay)

Source (NPTEL)


Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.