May_1966 — Page 64

PLAN

SCA L

150

100

200 FT

PRINCESS #

MARGARET

ROAD

PERTH ST

ARGYLE ST.

WATERLOO RD

D

ARGYLE

ST

WATERLOO

ROAD

Preliminary Design

Preliminary design work was com- menced late in 1963 with a scheme to provide a two-lane 24 ft. wide flyover from Princess Margaret Road to Waterloo Road passing over the complex and the junction with Perth Street, with a total length of ap- proximately 1,300 ft. including two ramps.

Early in 1964, however, it was decided to construct а three-lane/ carriageway to provide a two-lane one-lane tidal flow, which the traffic surveys indicated would be required when in full operation. Owing to the very restricted road width available in Princess Margaret Road it was

necessary to lengthen the flyover to 1,681 ft. in order to provide for the 33 ft. wide carriageway.

Site Investigations

It was known that a number of large pipes and sewers lay along the alignment of the proposed flyover, as well as a multitude of small drains, cables and ducts. To obtain accurate information on their alignment and levels it was decided to have trial holes excavated at each pier position prior to percussion borings.

Disturbed soil samples were taken and standard penetration tests were carried out at about 10 ft. intervals or at "change of soil". The samples

indicated that decomposed granite underlay sand and fine clay at depths varying from 10 ft. to 40 ft. below ground level, with the water table about 12 ft. below ground level.

Design

The basic outline shape of the piers was governed by the restrictions imposed by the limited road width available.

The main design considerations made were as follows:——

(a) A minimum clear headroom of 16 ft. 6 in. below the fly-

over.

(b) Single centre support

CAST-IN-SITU R C BEAM

PRESSTRESSED BEAM OR UNIVERSAL STEEL BEAM

RC.C CANTILEVER BEAM 4 ́DIA DRAIN PIPE INSPECTION EYE

58

IN

• CONDUIT AT CIC

DETAILS OF PIER PROFILES

CARRIAGEWA

FULL SUPERELEVATION ON CURVES

R.C.C. ROAD SLAB (CAST - IN – SITU)

L.C.C❘ PIER

3 CA

+

4

& FT

# CC PILE CAP

2020 VANES

X

I

(APPROX.)

L-o

WAT

!

(c)

Design speed 30 m.p.h.

(d)

Max. gradient 1:15.

ft.

(f)

(e) Minimum horizontal radii 238

Minimum vertical curve 200 ft. length. (g) Loading

loading

M.O.T. H.A.

The horizontal alignment was practically predetermined in that the flyover had to be carried above the existing roadways, while the vertical profile was controlled by the clear- ances required at the main complex, Perth Street, and by the road width restrictions at the southern end of the project.

A scheme was prepared with 35 ft. spans, except at the three major crossings where 60 ft. spans were proposed. Using these spans, normal reinforced concrete I-beams were proposed for the short spans with prestressed I-beams for the 60 ft. spans. The design calculations show- ed that the construction depths for both forms of construction were al most identical so that a smooth soffit profile was achieved.

A second scheme was also pre- pared using 55 ft. equal spans with prestressed I-beams on all spans, but utilising the cast-in-situ road slab to act as a composite structure.

After considerable detailed exa- mination of both schemes had been

Far East Architect & Builder May, 1966