622
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
place decreases, and the attenuation of the surface manifestation
of differential settlement increases. For the case illustrated in
Figure 4, the differential settlement at the base of the cap
decreases from 122 mm to 43 mm as the cap thickness increases
from 12 m to 24 m. The corresponding maximum differential
settlement at the surface (over a 9-m horizontal distance)
decreases from 56 mm to 8 mm.
Figure 4. Sample Results from FLAC Analysis
The results of the surficial manifestation analyses, presented
as plots of surficial total and differential settlements versus
thickness of fill cap (for a range of assumed values of cavities
filled by migration of fines and collapse, p), are plotted in
Figure 5. This chart was used to select a suitable thickness of
removal and replacement based on the differential and total
settlement tolerance of the proposed structures.
5 CONCLUSIONS
The seismic and hydrocollapse settlement potential of
uncontrolled inert debris fills containing significant oversize
clasts could not be evaluated by conventional means.
Laboratory testing of representative material was not feasible
because of particle size limitations. BPTs and seismic shear
wave velocity surveys were ineffective in differentiating well
compacted fills from uncontrolled fills. An alternative approach
consisted of the following steps:
Based on the results of large scale in-situ density
and grain size distribution tests, an upper bound estimate of
cavity volume was made (approximately 6.6% of total
debris fill volume).
Figure 5. Surface Man station of Settlements
percent of total fill thickness with an average of
ake ground motions similar to
tabase of
observed settlements under moderate seismic events.
AM
ce II
Cha
Geo
tration tests, Reliance
Pyk
tional shaking.
J .Geotech. Engrg. Div.,
ASCE, 101(4),
Silv
loading.
J. Soil Mech. and Found. Div.,
ASCE, 97(9), 1171-
Stew
eotechnical
and Geoenvironmental Engineering,
127(11) 905-919
ife
A settlement model based on partial filling of cavities by
fines migration and collapse of nested structure was
developed. Parametric analyses of various degrees of
cavities filling were performed to account for heterogeneity
of the debris fill and to obtain a range of likely settlements.
Estimated settlements due to seismic shaking ranged from
0.4 to 1.1
0.85%.
The predicted settlements from this model were compared
to published case histories of seismic settlement of
unsaturated fills under earthqu
the design ground motions.
The proposed remedy for rendering the site suitable for
building development was partial removal of the uncontrolled
debris fill and replacement as a properly compacted fill cap.
Based on numerical modeling, charts were developed relating
thickness of fill cap to estimated surficial differential settlement.
To meet local building code requirement of maximum 25 mm
differential settlement over a 9-m length, 22 m of removal and
replacement will be necessary. The depth of removal and
replacement may be reduced, provided the differential
settlement tolerance of the structure is increased by structural
improvements such as stiffened foundation systems including
mat foundations, post tensioned slabs and grade beams. The
reliability of predictions by this approach may be increased by
physical modeling of debris fill settlement under the effects of
seismic shaking and saturation, and developing a da
9 m
(a) 12 m Compacted Soil Cap
75 m
90 m
120 m
105 m
Max. ρ
diff
= 55 mm
Max. ρ
diff
= 120 mm
Max. ρ
diff
= 8 mm
Max. ρ
diff
= 43 mm
Max. ρ
diff
= 105 mm
Max. ρ
diff
= 33 mm
(b) 18 m Compacted Soil Cap
(c) 24 m Compacted Soil Cap
ρ
diff
- Diffential settlement over horizontal distance of 9 m
- Original grid
- Deformed grid (distortion magnified by a factor of 20)
6 REFERENCES
EC Geomatrix, Inc., 2008.
Closure geotechnical report, Relian
landfill improvements,
Vulcan Materials Company, Irwindale.
rles J.A. 2008. The engineering behavior of fill materials: the use,
misuse and disuse of case histories.
Géotechnique
58 (7), 541-570.
matrix, 2007.
Documentation of Becker pene
landfill improvement, Azusa and Irwindale.
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multidirec
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art J.P., Bray J.D., McMahon D.J,. Smith P.M., and Kropp A.L.
2001. Seismic performance of hillside fills.
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