SUMMARY OF DECOMPOSED GRANITE FILLING TEST RESULTS
For Contracts of: Chatham Road Flyover; Canal Road Flyover; Canal Road Flyover Extension &
Associated works; Lai Chi Kok Bridge & Lai Chi Kok Interchange.
Trench backfilling was complicated by existing services on the same align- ment but strict control of placing and compaction, with hand ramming where power ramming was impossible, en- sured that settlement did not occur when the road was re-opened to traf- fic. Also at Chatham Road a length of pipe-drain was installed by tunnelling below the main junction and this successfully prevented what otherwise would have been a very considerable Fig. 3 obstruction to traffic flow.
Filling
All filling to embankments and ramps was compacted to a density of at least 90% of the maximum density obtained in the B.S. Standard Compac tion Test (Fig. 3). This was achieved without difficulty by carefully con- trolling moisture content and layer thickness. The normal range of opti- mum moisture content was 10% 16%, but the top limit was 20% when a more clayey material was used, and for the latter case a layer thickness of less than 1 ft. before compaction was required.
Compaction equipment was either 8 12 ton smooth wheel or rubber- tyred rollers. Boulders were removed as material was placed, but small-size hard material was retained provided it was well distributed throughout the fill.
Often when filling on reclaimed ground, initial rolling prior to placing fill revealed soft or spongey areas. In such circumstances excavation was ordered for the removal of the unsuit- able material; in those cases when the depth of unsuitable material preclud- ed its complete removal, a rock blank et was laid to form a base for new filling. Movements of retaining walls were recorded as fill was placed and thereafter, and top copings were not constructed until such movement was minimal. Roadworks on fill likewise were delayed for some time after com- pletion of filling to allow a period for settlement of the underlying ground.
In some instances marker plates and follow-down rods were installed during filling; subsequently levels of marks on the rods were recorded as a means of determining settlement at various loca- tions. This allowed an earlier com- mencement on roadworks, since ap- proval to start was given immediately there was no risk of damage to com- pleted work.
Care was taken to overfill and com- pact at the outer faces of embank-
LAI CHI KOK INTERCHANGE
CHATHAM ROAD |CANAL ROAD
FLYOVER
FLYOVER
CANAL ROAD FLYOVER EXTEN.
LAI CHI KOK
BRIDGE
Ave. Field M/C
Ave. Field Density
Ave. Opt. M/C
Ave. Max. Dry
14.7
14.2
15.2
13.9
12.2
106.1
103.0
104.3
105.2
103.9
16.7
15.3
15.5
15.6
14.4
Density
Ave. B.S. Ratio.
114.2
112.8
94.6
92.5
114.8
94.2
113.5
93.3
112.1
93.6
ments for subsequent trimming to the required profile. This avoided possible underfilling which is difficult to correct, since any material added to a face, no matter how well compacted and benched into the original, would be likely to scour away during heavy rain.
Piling
Piles of 18 in. x 18 in. cross-section were used, prestressed when exposed to marine conditions but ordinary re- inforced concrete elsewhere. Lengths ranged from 25 ft. to 95 ft.
Various methods of handling piles have been adopted by the contractors. The prestressed section allowed simp- ler handling methods without the risk of cracking provided reasonable care was taken. The longer reinforced con- crete piles required special lifting ar- rangements which were troublesome at locations such as the Canal Road fly- over where the working site was re- stricted by adjacent buildings and roads.
More than 2,000 piles were driven with relatively infrequent head damage, using hammers weighing 6-8 tons. Pile heads were provided with an
LOAD (tons)
fa
L
additional mesh of light steel around the main reinforcement within the 2- inch concrete cover thinckness and particular care was taken to ensure that each main bar was sawn square and located at exactly the same dis- tance from the driving face of the pile. Rope mats were provided between the pile head and driving helmet.
When a penetration of more than half the pile length was achieved, fur- ther driving was continuous until reaching the final set, unless below- ground obstructions or plant break- down made this impossible.
The maximumn specified pile test load was 200 tons, and for this the contractors used final 10-blow sets of 11⁄2 to 2 in. with an 8-ton hammer on 3 ft. drop or to 14 in. with a 6-ton hammer and the same drop, the lesser dimension applying when driving was completed with a steel dolly between the pile and the hammer. All contrac- tors chose to determine pile lengths by probing although given the option of driving individual test piles.
Using standard probing equipment, an 'n' value of about 150 was adopted as the criterion for pile length. Con- siderable build-up of skin friction oc-
LOAD TEST RESULTS FOR 18" x 18" PILES
Normal test compared with failure due to driving obstruction
T 2
Fig. 4
Spical result of
food tast
(normal pila)
2nd text to 50tons in 2 lood increments
3rd test to 100 tons in Epton increments
Paikune during initial test when frictional resistance overcome
Normal Sat: 8 ton hommec
jo blows pac
MOVEMENT
Far East BUILDER, January 1971
39