Download Cyclic behavior of diatomaceous soils

Influence of diatom microfossils on soil compressibility
Díaz-Rodríguez, J.A. and González-Rodríguez, R.
Department of Civil Engineering, National University of Mexico, MEXICO
Email: [email protected]
ABSTRACT
There are several sites in the world where diatom microfossils has been detected in the soil deposits
(e.g., Mexico City, Mexico and Osaka Bay, Japan). These soil deposits are characterized to have
singular physical and mechanical properties that do not follow the well established empirical
equations relating index properties with strength and deformation parameters. However, the
specialized literature on the topic is very scarce.
Diatoms are unicellular algae, grow in water rich in dissolved silica, consuming the dissolved silica,
diatoms secrete outer shells of silica to form a frustule, that comprising two valves, one overlapping
the other like the lid of a box. Diatoms live in almost all kinds of aquatic and semi-aquatic
environments that are exposed to light. Diatomite or diatomaceous earth is a porous and lightweight
sedimentary rock resulting from accumulation and compaction of diatom remains over a geological
time scale.
Some natural soils with diatom microfossils that have been studied in detail include the Mexico
City soil (Díaz-Rodríguez, et al. 1998; Díaz-Rodríguez 2003) and Japan marine clays (Shiwakoti, et
al 2002; Tanaka and Locat, 1999). For the first case, it is considered that the diatom microfossils
content range between 55% and 65% (based on dry weight).
To evaluate the influence of diatom microfossils on the soil compressibility, this paper presents the
experimental results of a series of odometer tests using an artificially prepared mixtures of diatom
microfossils and kaolin (D+K). The experimental program followed in this investigation consisted
in the elaboration of five mixtures: diatomite (D) was mixed with kaolin (K) in proportions of 0%
diatomite (100K), 20% diatomite (20D+80K), 40% diatomite (40D+60K), 60% diatomite
(60D+40K) and 100% diatomite (100D). All the mixtures were performed based on weight
proportions.
CONCLUSIONS
The observations and discussions of this study reveal the impact of diatom microfossils on the onedimensional consolidation testing of the soil mixtures of diatomite and kaolin. Some conclusions
are the following:
1. The consolidation curves show different characteristics depending on the diatomite content.
2. The compression of the mixtures first decreases (i.e., 40D-60K mixture). As the diatomite
content continues to increase, the compression begins to increase (i.e., 60D-40K mixture).
3. The consolidation mechanism of diatomaceous soils is complex, however, an attempt was
made to explain the influence of diatoms microfossils on the soil compressibility.