Question 1
(a) State three causes of collapse of the sides of a trench while the excavation
works are in progress.
(b) Sketch a cross section through a trench excavation in a moderately firm
soil and label three parts.
(c) Sketch a cross section through a deep strip foundation.
Observation
However, some of them were not able to:
- state the three causes of collapse of the sides of trench;
- sketch a cross-section through a deep strip foundation instead they sketch
wide strip.
The expected response to question 1 is as given below:
(a)
(i) general shear failure of the embarkment created by the trench side;
(ii) effect of freezing and thawing on soil particles in embarkment created by
the trench;
(iii) failure due to heavy loads being placed near the edge of the trench;
(iv) variation in soil strata;
(v) instability of earth materials in a made up ground which may be hidden
just behind the sides;
(vi) collapse due to flooding of the trench;
(vii) failure of timbering system used to support sides of the trench excavation;
(viii) rainfall causing land slide.
(b)
or