Consider the following statements regarding anticline and syncline : 1. The presence of a syncline creates problem of seepage in a dam foundation. 2. There will be more bending of the anticlines in the upper strata and more joints due to tension stresses compared to lower strata. 3. A tunnel passing through a syncline will experience more lateral pressure in the middle part away from the portals. Which of the above statements are correct ?
- A1 and 2 only
- B1 and 3 only
- C2 and 3 onlyCorrect
- D1, 2 and 3
Solution
Concept
Engineering significance of folds
Step-by-step solution
1. In an anticline the upper strata are stretched (tension), giving more joints and bending, while the lower strata are compressed (statement 2 correct). 2. A tunnel through a syncline meets higher rock pressure in the middle, away from the portals, because of the greater overburden and the convergence of beds (statement 3 correct). 3. Seepage problems on dam foundations are normally linked with anticlinal structures, where beds dip away from the axis; a syncline is generally favourable (statement 1 is not accepted).
Explanation
Folding creates tension in the upper part of an anticline and compression in a syncline. Tunnels in synclines experience high lateral pressures in the central part, and dams on synclines are generally safer against leakage than those on anticlines.
Why the other options are wrong
Statement 1 is dropped because a syncline is generally favourable for a dam foundation, so options (a), (b) and (d) are not accepted.
Shortcut
Anticline = tension on top; syncline = high pressure at the centre of a tunnel.
Common mistake
Assuming synclines cause leakage.
Correct answer: C) 2 and 3 only