Question

Given below are two statements:
Statement (I): The porosity of a soil cannot exceed 100 per cent.
Statement (II): The degree of saturation cannot be zero per cent.

In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Think of oven-dried soil to test whether degree of saturation can really be zero.

Answer 1

The Correct Option is C

Step 1: Recall the definition of porosity. Porosity \(n = \dfrac{V_v}{V_t}\times 100\), where \(V_v\) is the volume of voids and \(V_t\) is the total volume of the soil sample.
Step 2: Since the voids are physically part of the total volume, \(V_v\) can never be greater than \(V_t\). In the extreme case of a soil that is entirely voids with no solid grains at all, \(V_v\) would equal \(V_t\), giving \(n = 100\%\). So porosity has an upper limit of 100 percent and can never cross it. Statement (I) holds.
Step 3: Now look at degree of saturation, \(S = \dfrac{V_w}{V_v}\times 100\), where \(V_w\) is the volume of water present in the voids.
Step 4: Consider a soil sample that has been fully oven dried, so no water at all remains in the void spaces. Here \(V_w = 0\), which makes \(S = 0\%\). This is a perfectly normal, achievable soil condition, so degree of saturation can indeed become zero. Statement (II), which claims it cannot be zero, is therefore false.
Step 5: Statement (I) is true, Statement (II) is false.