Which of the following statements is/are true regarding Wash Boring? i. Wash boring is mainly used for advancing a hole in the ground. Once the hole has been drilled, a sampler is inserted to obtain soil samples for testing in a laboratory. ii. The method is suitable for taking good quality undisturbed samples above ground water
- AOnly (i)Correct
- BOnly (ii)
- CBoth (i) and (ii)
- DNeither (i) nor (ii)
Solution
Concept
Applicability and procedure of wash boring
Formula
NONE
Step-by-step solution
1. Wash boring is a fast, efficient method for advancing a borehole using a chopping bit and water jetting. 2. Once the desired depth is reached, the wash bit is replaced by a sampler to retrieve soil samples. 3. Wash boring disturbs soil heavily and is unsuitable for obtaining high-quality undisturbed samples. Answer: A
Explanation
Wash boring is an exploratory drilling technique primarily used to advance a hole in the ground by jetting water through a chopping bit. Because the high-velocity water jetting and drilling action severely disturb the soil, it cannot yield high-quality undisturbed soil samples. Therefore, statement i is correct while statement ii is false, making option A the right choice.
Why the other options are wrong
B) Wash boring causes heavy soil disturbance and is unsuitable for obtaining good quality undisturbed samples. C) Statement (ii) is false because soil samples obtained from wash boring are severely disturbed. D) Statement (i) is true as wash boring effectively advances boreholes prior to sampling.
Shortcut
Wash boring is used for advancing holes, but it severely disturbs soil and cannot yield undisturbed samples.
Common mistake
Selecting option C by assuming wash boring yields undisturbed samples, whereas the water jetting severely disturbs soil structure.
Correct answer: A) Only (i)