that traffic delays were kept to a mini- mum. Details of temporary traffic signs were agreed before-hand with the contractor, the lettering size and colouring being in accordance with Traffic Engineering Office standards. Each contract presented different problems; at Chatham Road flyover it was traffic intensity, at Canal Road flyover the restricted and very congest- ed site area and at Lai Chi Kok inter- change the number of intersecting roads and the steady build-up of through traffic.
Utilities
The positions of existing utilities were shown on a drawing issued to contractors at tender stage. The accu- racy of this drawing, however, depend- ed entirely on the correctness of in- formation supplied by public utility companies and Government authori- ties, thus for each contract it was necessary to arrange trial pits to locate utilities accurately prior to the com- mencement of major excavation or foundation work.
Liaison meetings between the con- tractor and those responsible for ser- vices were arranged in order to agree revised routings and a programme for any alterations. Initially these were attended by representatives of all uti- lity companies and Government of fices, but this was found to be less effective than smaller more frequent meetings dealing separately with each utility and co-ordinated by the resi- dent engineer's staff. In this way, many of the problems involved with utilities were avoided but some delays nevertheless occurred and at such times the resident staff on site took an
200
"
100
active part in eliminating difficulties in order to achieve improvement in pro- gress.
To eliminate possible settlement of new road construction where back filling had been done by the utility companies' contractors, the resident engineer's staff kept a watching brief and arranged testing as necessary to confirm that the backfilling was ade- quately compacted.
Base construction
Ground level roads were construct ed with a flexible base except in small areas where the proper compaction of such a base was impracticable.
After grading and compaction of the formation to a density of at least 95% of that obtained by the B. S. Standard Compaction Test, a 6 in. thick sub-base layer comprising mixer- run graded crushed rock sized from 11⁄21⁄2 in. to fines was laid and compacted by roller. Strict supervision eliminated segregation during laying, and compac tion by an 8-10 ton smooth wheel roll- er was sufficient to achieve dry densi- ties ranging from 135 to 140 lb. per cu. ft. (Fig. 6).
During rolling, it was necessary to scarify the surface lightly by sweeping between each pass, thereby exposing to the roller wheels the larger-size aggregate which otherwise was covered by a layer of fines which absorbed some of the compactive effort. When properly laid and compacted, the sub- base remained in good condition throughout adverse weather providing that wheeled traffic was not allowed to run on the surface until any surplus moisture had dispersed. Run-off oc- curred naturally since cross-fall was
+
provided and the sub-base was design- ed to act as a drainage blanket with a filter drain along the lower edge.
Base construction comprised two 4 in. layers of graded crushed rock of similar grading to the sub-base layer, each layer being compacted. For com- pacting roadstone around manholes, road gullies and the like, hand ram- ming or the use of a small vibratory roller was necessary.
Roadstone compaction can be speeded up by using a vibratory plate compactor, which should weigh about 2 tons. An initial pass with a smooth wheel roller prevents the plate digging into the roadstone on its first pass.
Expansion joints and bridge deck railings
:
The expansion joints at Lai Chi Kok Bridge and Chatham Road flyover were similar. They comprised mild steel plates bedded in bituminous com- pound to bridge 11⁄2 in. gaps and set into recesses formed along the edge of both capping beams and deck slabs, asphalt surfacing being laid continu- ously across each joint. The joints were waterproofed either by water- bars built into the concrete structure or by neoprene membranes stuck with special adhesive to the concrete each side of the joints.
For the later Lai Chi Kok inter- change and Canal Road flyover pro- jects, epoxy mortar nosings with a polysulphide liquid polymer joint sealer, as now recommended by the Ministry of Transport in the United Kingdom were used. The epoxy mor- tar comprised 3/16 in. black chips selected for wearing quality, combined with quartz sand into which a small
B. 5. SIEVE APERTURES OR NUMBERS
100_150_100. 12
3624
1⁄44 % %
مو
مع
To
60
100
06
* PASSING
* १
Grading of selected avarty
Sand
combined Grading
土
% by weight chips
56.1%
bank 41.0%
| Camast=−2.3 %
∙Grading of selected
chips
Average density after Compaction 13866)je3. (dry density)
+
EPOXY MORTAR : AGGREGATE GRADING Note: 1. Epoxy/Aggregate ratio 1:9 gave sufficient apoxy for mixing
and priming" all surfaces before mortar "was placed. 2. Tasting 6′′ cubes :
20 blows Compaction 1 Parsity 192 : 3 day Strength BT001/ 35
+
+
+
"
940/2
Fig. 6. ROADSTONE
TYPICAL GRADING CURVE
Fig. 7.
Far East BUILDER, February 1971
37
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