4
Fig. 7. 18-ton smooth steel drum roller on fill material in Fig. 8. Vibrating roller on lime-stabilized working course paved area
filling on side long slopes. After disking, the uncompacted fill was very vulnerable to rain, and a grader and the 18 ton steel drum roller were kept in attendance to smooth the surface and allow the water to run off.
Owing to the weather there was generally a lapse of several days be- tween the compaction of each layer and this proved sufficient to prevent excessive pore water pressure de- veloping.
Type 3 soil proved to be too diffi- cult to use as fill below pavements as the optimum moisture content of be- low 20% could not be reached, largely on account of frequent rain. This material was therefore used as fill in turfed areas where the specification only required a density similar to that of the undisturbed soil, which was ap- proximately 85% B.S. heavy compac- tion. It was spread in 18 in. layers. levelled out with D8 bulldozers and after a period of time settled down to a dry density generally above that of the undisturbed soil.
Even after several weeks of dry weather the natural moisture content in the cuts was in the region of 30%. It was noted that in dry weather the most effective method of lowering the moisture content of the soil was by ripping the cuts to a depth of about 18 in. on the day prior to cutting. This method seemed more efficient
than disking the fill but was ΠΟΓΕ susceptible to rain.
As the dry density of undisturbed material in the pavement cuts was some 8% lower than the dry density of the compacted fill, it was decided
to
remove 2 ft. of soil below the working course and replace it with compacted fill.
The volume of cut and fill on the site was approximately 5,000,000 cu. yd. each, but losses of volume, mainly due to compaction, brought the total up to 6.5 million cu. yd of fill, mea- sured as excavated volume. By the end of July 1964 the progress on earthworks on account of the weather was two months behind schedule, and with the wetter months still ahead it would have been difficult to catch up.
However, there was a large deposit of alluvial sand adjacent to and to the east of the centre of the airport and in August it was decided to use this as a borrow area to complete the re- mainder of the fill under pavements. About 600,000 cu, yd, of this sand was brought on to the site. The properties of the sand are shown in Table I. The Type A sand was used as fill and compaction of it presented no problems as the natural moisture con- tent was about 11%, which was near to the optimum. It was found that it could be placed in 18 in. lifts and that dry densities of 98% B.S. heavy com-
paction could be attained after ten passes of the 18 ton steel drum roller.
In areas to be paved, the density of each 6 in. layer of Type 1 fill was checked at points on a 100 ft. x 100 ft. grid. If the samples failed to reach the specified density, the area was rolled and tested again until a dry density of 95% B.S. heavy compac tion was achieved. In a few cases in the lower layers of fill dry densities of 93% B.S. heavy compaction were ac- cepted, but in the top 2 ft. of fill all dry densities were above 95% B.S. heavy compaction.
No moisture control was actually imposed on the contractor during compaction because of the uncertain weather conditions. The moisture content after the specified compaction had been achieved was found to be close to the field optimum. A few in situ CBR tests were taken on the layers of compacted fill as a check on the expected CBRS on the formation.
When the fill reached formation level in pavement areas it was fine graded to correct level with a toler- ance of maximum ± 0.04 ft. In situ CBR tests were taken on each 100 ft. x 100 ft. square. The formation was proof rolled with the 80 ton roller and generally there was по noticeable movement or rutting under the roller on Type 1 soil fills, but there was some surface pushing on Type A sand
N
Fig. 9. Laying binder or base course
Far East Architect & Builder May, 1967
Fig. 10. Batching plant used for production of all bituminous materials for pavements
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