Discussion. R.A.F. Tengah Airfield Reconstruction With Particular Reference to Earthworks.

Abstract

(Tropical Section, Road Research Laboratory) wrote that the Authors' description of large scale earth-moving operations in the wet tropical climate of Singapore provided much useful data on the standards of workmanship which could be attained under these adverse conditions. The extent of the adverse weather conditions could be seen in Fig. 7(a) which showed that rainfall was commonly of the order of 10 in. per month and occasionally this amount fell during a single week. That the standard of compaction in the embankments was high might be judged from Table 1 which showed that the maximum settlement recorded after 18 months was 0.86 in. for a 16-ft high fill overlying a particularly troublesome area of soft and wet soil. The figures shown were very similar to those obtained in Southern England2 and Kenya3 on closely controlled embankment construction.63. Work in East Africa on the compaction of soils on road construction schemes4 had shown that the most important single factor determining the level of compaction which could be achieved by normal techniques was the moisture content of the soil at the time of compaction. With moisture contents at or slightly in excess of the optimum moisture content in the B.S. Compaction Tests densities equal to the maximum dry density value in that test were readily attained; with moisture contents dry of the optimum moisture content in the B.S. Compaction Test, field densities averaged 93% of the laboratory maximum dry density values. In wet tropical climates the provision of moisture would not be a problem and the use of construction techniques which minimized the soaking of loose uncompacted layers by rainfall as outlined in &$30-31 ensured that the pavement builder exploited the climatic advantages of his environment to the full. 64.In 5 21 the Authors commented on the difficulties of achieving a target dry density of 112 Ib/cu. ft which was based on the values achieved in a trial embankment. In the writer's experience such a state of affairs was common and variations of the magnitude indicated in Fig. 4 and 8 10 were often found within quite localized areas of a visually uniform soiL4 It was therefore important that, when using dry density as a measure of compaction in the field, the values found were compared with a laboratory compaction test carried out on exactly the same soil. This could most easily be achieved by performing the laboratory compaction test on soil dug from the holes during the measuring of the dry density in the field.