Hydro-Mechanical Properties of an Unsaturated Frictional Material
Hydro-Mechanical Properties of an Unsaturated Frictional Material
Hydro-Mechanical Properties of an Unsaturated Frictional Material
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2 CHAPTER 1. INTRODUCTION<br />
Figure 1.1: Global Humidity Index (from UNEP/GRID <strong>an</strong>d UEA/CRU)<br />
- Collapsing soil<br />
- Shrinkage <strong>an</strong>d swelling soil<br />
- Compaction <strong>of</strong> soil<br />
Depending on the type <strong>of</strong> soil, for inst<strong>an</strong>ce clay, silt or s<strong>an</strong>d, the above given phenomena<br />
have to be taken into account, when designing constructions such as dams, emb<strong>an</strong>kments,<br />
foundations or slopes.<br />
1.2 Scope <strong>an</strong>d Objectives<br />
The scope <strong>of</strong> the present work is the investigation <strong>of</strong> <strong>an</strong> unsaturated gr<strong>an</strong>ular material <strong>an</strong>d<br />
its hydro-mech<strong>an</strong>cial behavior. Furthermore, the phenomena (e.g. collapse, hysteresis) that<br />
belong to it, which is import<strong>an</strong>t for reliable prediction <strong>of</strong> settlements <strong>of</strong> buildings, failure mech-<br />
<strong>an</strong>isms as base failure <strong>of</strong> strip footing or square footing, slope stability as well as the flow<br />
<strong>of</strong> fluid through dams in geotechnical engineering practice. Low suction values, for inst<strong>an</strong>ce<br />
are able to maintain the stability <strong>of</strong> slopes or to improve the stiffness <strong>of</strong> a soil. Therefore<br />
experimental <strong>an</strong>d theoretical <strong>an</strong>alysis were conducted on Hostun s<strong>an</strong>d. The contribution <strong>of</strong><br />
capillary stresses (i.e. matric suction), which is the main force affecting the hydro-mech<strong>an</strong>cial<br />
behavior <strong>of</strong> <strong>an</strong> unsaturated gr<strong>an</strong>ular material, is usually ignored in conventional <strong>an</strong>alysis <strong>of</strong><br />
civil engineering constructions, for inst<strong>an</strong>ce when predicting the bearing capacity <strong>of</strong> shal-<br />
low foundations or settlements <strong>an</strong>d deformations <strong>of</strong> buildings. Based on these concepts <strong>an</strong>d<br />
models, constructions <strong>an</strong>d buildings are designed <strong>an</strong>d dimensioned.<br />
To predict reliable unsaturated soil properties deep underst<strong>an</strong>ding <strong>of</strong> its coupled hydro-<br />
mech<strong>an</strong>cial behavior is required. Compared to clayey soils the s<strong>an</strong>d is not undergoing shrink-<br />
age <strong>an</strong>d swelling. Experiments for prediction <strong>of</strong> the hydro-mech<strong>an</strong>cial unsaturated soil be-<br />
havior are commonly focused on cohesive soils as silts <strong>an</strong>d/or clays. The complete hydro-<br />
mech<strong>an</strong>cial behavior <strong>of</strong> s<strong>an</strong>d has been poorly investigated to date. This behavior is quite<br />
different compared to silty or clayey soils. There is limited laboratory data available in liter-
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