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Date:16 April 1998
Author: Etienne Mendez, Geo Technologies, Ltd., Trinidad & Tobago
Subject: Caribbean School Project - Siparia
Project Site: Trinidad, West Indies
Description of Problem: A site was developed by cutting a slope
and constructing a large school on the flat space created. The soils consisted largely of a highly permeable single
sized sand. While the upslope of the site (cut) was retained with a wall 6.0m high, the downslope of the site was
constructed to a grade determined by the angle of response of the soils. Slope failure occurred in 1993, approximately
one year after completion, and threatened the building foundations. Top of Slip was ~2.0m from the building line.
The Client took remedial measures in the form of Temporary 4" Steel Pipe Piles @ 10'0" crs, more or less,
supporting steel plate and further braced with 4" Steel Pipe. Evidence of subsequent movement prompted the
Client to seek a permanent position.
Proposed Solution / Selected Solution: The Client accepted a solution
which was proposed by Geo Technologies Ltd., calling for the driving of Manta Ray MR-3 and MR-4 Anchors, through
the existing temporary retaining structure to support a new retaining wall built on the outside of the steel sheet
pile wall. Holes were first cut in the steel sheet to a diameter of 150mm to enable the driving of the Anchors.
A total of 210 Anchors were so installed to maximum depths of 12.0m from
the face of the existing structures, through the relatively loose fills, into a firm competent strata. Anchors
were locked to design loads before attaching to the INTERBLOC Units. Length of wall is 40.0m, with a maximum height
of 6.0m.
The Anchors were connected via the Anchor Rods and spreader bars, to HDPE geogrids, which were further connected
to INTERBLOC Segmented Retaining Wall Units, with the void between the temporary steel sheet pile wall and the
new filled with importance compacted fill. A 10-oz geotextile filter fabric was placed between the fill and the
INTERBLOC Units, so as to prevent any loss of fines as a result of subterranean water flows. The INTERBLOC Units
were established on a strip leveling pad of lightly reinforced concrete which doubled as a drainage channel for
subsoil flows.
Anchors: 120 MR-3 Anchor Assemblies; 90 MR-4 Anchor Assemblies, SAR
58 Anchor Rods, Reducer Nuts, All Thread Rods. Spreader bars for connecting the anchor rods to the Geogrid comprised
2" x 1/4" steel flat with integral carbon steel sleeve on center to receive anchor rod for pulling geogrid
taut.
Installation Equipment:
- HB90 Anchor Driver
- HB90-14 Anchor Driving Hammer
- GPU 18-8 Power Unit
- SGC-14 Drive Steel with 8' Drive Steel Extensions
Conclusion / Results: The works were completed in four (4) months,
with the minimum disturbance to the school operations and even to the adjacent properties, as the sound pressure
levels of the GPU18 were quite acceptable to neighbors.
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