EVERY PRECAUTION SHOULD BE TAKEN TO ENSURE GOOD DRAINAGE SYSTEM FOR DECIDING UPON THE ANGLE OF REPOSE, REQUIRED FOR DESIGN CONSIDERATION EFFECTING RAINS UPON THE SOIL.

DRAINAGE OF RETAINING WALLS AND WEEP HOLES :-- To prevent water pressure behind the wall, drainage should be provided by the use of large material against the back of the wall and by weep holes. Walls retaining soils through which water freely passes, such as clean gravel and sand, should have a drain of loosely packed rubble running along the back footings, from which good sized weep holes from 1.8 to 3m apart, should lead through the base 

. With more alternative soils , a drain at least 250 to 300 mm wide should run nearly the whole way up the back of the wall. The mouths of the weep holes should always be carefully protected by loose packing. In some cases extra weep holes at higher level may be advisable, which may be 50 to 75 mm square, or 75 mm pipes may be used at about 2 m intervals (in staggered positions) vertically and horizontally, the lowest being 30 cm from the ground level. Weep holes should be given a fall of 1 in 8 from the back of the masonry to the face. Weep holes should be provided in all abutments and wing walls.Failure of retaining walls is generally due to unequal settlement of the foundations, excess of toe pressure, and lack of drainage. Most of the failures are in clayey soils which exert much heavier pressure when saturated as clay swells through absorption of water. Therefore, when deciding upon the angle of repose for the design purpose, due consideration must be given to the effect of rains upon the soil which make the angle of repose flatter. The tendency of the backing to slip is very much increased, when the material is saturated with water, therefore, every precaution should be taken to ensure good drainage:-- Er Fateh chand Guleria, Director, RTI welfare Association registered number HPCD 3552 Bilaspur Himachal Pradesh, phone number 9459334377