The document describes a top-down construction method using an island cut method for retaining the soil around an excavated basement. Temporary soil berms are constructed using the island cut method to provide stability and passive resistance for the diaphragm walls during construction. Excavation occurs in stages, with each basement level being constructed before further excavation. Instrumentation monitors slope stability and settlement during construction, with contingency plans in place to implement remedial measures if trigger values are reached. Photographs document the various construction stages.

1. BASEMENT
RETENTION
SYSTEM

2. TOP DOWN CONSTRUCTION
WITH
ISLAND CUT METHOD

3. DESIGN
WALLAP - Retention System Design
WinStabl – Slope Stability Analysis
Plaxis – Finite Element Analysis

4. CONCEPT
PROVISION OF SOIL BERM
(ISLAND CUT METHOD)
CONCOURSE CONCOURSE
LRT CUT
-Excavation at the centre of the pit leaving soil
B1 B1
berm to provide adequate passive resistance
B2 B2
PROPOSED PROPOSED
TOP DOWN CONSTRUCTION
DIAPHRAGM DIAPHRAGM
WALL WALL
B3 B3
-once the inner core has been built to
concourse level, top down construction will be
carried out at periphery by not compromising
the passive resistance needed by the wall.
ISLAND CUT METHOD

5. CONSTRUCTION
SEQUENCE

6. DIAPHRAGM WALL AND BOREDPILE CONSTRUCTION
- From existing ground level
- Plunging columns placed at designated locations

7. FORMING SOIL BERMS TO INNERSIDE OF THE BASEMENT
- Slope stability is ensured
- Immediate guniting after slope formation to ensure proper slope
protection.

8. PROPOSED TEMPORARY SLOPES
(ISLAND CUT METHOD)

9. OG
L= 2
7.0m
RL .
2 3.0 m
m
1 6.9
RL.
RL. 25.0m
OGL=29.0m

10. Area 1

11. CONSTRUCTION OF OUTER COLUMNS AT THE INNERCORE
CONSTRUCTION OF CONCOURSE SLAB AT THE PERIPHERY
CONSTRUCTION OF INNERCORE
CONSTRUCTION OF SUPERSTRUCTURE ABOVE CONCOURSE
LEVEL TO LEVEL 3 AT BOTH LRT AND CUT SIDE
-Simultaneous construction to reduce waiting time

12. CONCOURSE LEVEL SLAB IS COMPLETELY CONSTRUCTED
ACROSS THE BASEMENT
- To ensure enough bracing for the wall
EXCAVATION TO BASEMENT 1 LEVEL

13. BASEMENT 1 SLAB CONSTRUCTION IS COMPLETED
- To ensure second level restraint to the wall
EXCAVATION TO BASEMENT 2 LEVEL

14. BASEMENT 2 SLAB CONSTRUCTION IS COMPLETED
- To ensure third level restraint to the wall
EXCAVATION TO BASEMENT 3 LEVEL

15. BASEMENT CONSTRUCTION IS COMPLETED

16. INSTRUMENTATION
• Inclinometer
• Settlement Markers / Stations
• Survey Markers
• Strain Gauges
Monitoring
• Real Time Monitoring
• Daily evaluation on the results
• ‘Life Made Miserable’

17. CONTINGENCY
MEASURES

18. IF TRIGGER VALUE IS REACHED :
FURTHER EXCAVATION IS STOPPED
INSTRUMENTATION READINGS TO BE EVALUATED
REMEDIAL MEASURES TO BE IMPLEMENTED IF
REQUIRED
- Slope reinstatement works using soil nails, rubble
pitching, etc
- Internal strutting works
- Temporary Ground Anchor
- Stress relief method
- Strutting against completed slab
- Strutting against completed basement 3 slab

19. CONSTRUCTION STAGE PHOTOGRAPHS

20. CONSTRUCTION STAGE PHOTOGRAPHS

21. CONSTRUCTION STAGE PHOTOGRAPHS

22. CONSTRUCTION STAGE PHOTOGRAPHS

23. CONSTRUCTION STAGE PHOTOGRAPHS

24. CONSTRUCTION STAGE PHOTOGRAPHS

25. CONSTRUCTION STAGE PHOTOGRAPHS

26. CONSTRUCTION STAGE PHOTOGRAPHS

27. CONSTRUCTION STAGE PHOTOGRAPHS

28. Finally………………….

29. After Loooooooong Hectic Period……………

30. Successful Completion