in the creek and restored the slope to l:10. After this, the stability of the
landfill, in terms of safety against sliding, will increase about 705,
according to idealized slope stability analysis.
2. A pile supported bridge was built to convey traffic around the most
critical area, and a pile supported seawall was constructed at the perimeter
of the landfill. Following this addition, the stability of the landfill will
increase about 120% by avoiding traffic loads.
3. The weight on the upland was reduced by removing the heavyweight fill
from the area and replacement with lightweight slag fill. After this change,
the stability of the landfill increased about 110%.
The soil stability analysis was made at the most critical section. It was
estimated that after the remedial work, up to 3 ft of settlement is expected
to occur in the fill during 30 years. Therefore, the parking areas and
roadway on grade were designed to accommodate the expected settlement by using
flexible unit block pavers. It will permit differential settlement, provide
effective surface drainage, and will be aesthetic in appearance. Surface
drainage was accomplished by a grid of dry well catch basins. The remedial
work provided an adequate factor of safety against dangerous lateral movement
of the fill. This has been verified by monitoring of movements previously
Other features of this project included application of a precisely
controlled construction sequence and monitoring system to minimize disturbance
of the landfill and to observe fill movements during construction. The
sequences of construction specified and implemented were:
Install 15 tell-tale tripods in Dorsey Creek to monitor and
avoid a mud wave during stone berm filling.
Place stone berm at the toe and on the slope of the embankment
Drive H piles for seawall and bridge support according to a
Construct pile caps, seawall and bridge.
Replace heavyweight fill on the upland area with lightweight
Place flexible pavers and dry wells for drainage on the parking
Fig. 2 shows a section of the landfill with remedial work.
The monitoring system has included taking continuous readings on the
tripods in the creek, observation points on the library building, settlement
platforms on the fill, and slope indicators in the fill. The grades of stone
berm placed underwater were checked by sounding periodically during and after
the stone filling.