Determination of volumetric changes in cracked expansive clays
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TECHNICAL PAPER
Determination of volumetric changes in cracked expansive clays Qihang Huang1 · Shahid Azam1 Received: 25 April 2020 / Accepted: 17 August 2020 © Springer Nature Switzerland AG 2020
Abstract The main objective of this research was to determine volumetric changes in cracked expansive clays. The presence of soil discontinuities was captured by using appropriate soil property functions, namely: a bimodal water retention curve and a sigmoidal swell–shrink curve. Field measurements were used in empirical equations to predict volume changes, and the results were validated using published data (laboratory testing, numerical modeling, or site monitoring). The results indicated that the average swell potential and swell pressure of the expansive Regina clay are 18 ± 2% and 155 ± 15 kPa, respectively. Likewise, heave was found to be 20–30 mm at surface and gradually diminished at 1.75 m depth. The predicted results closely matched the ranges and trends as validated using published data of laboratory testing, numerical modeling, or site monitoring. It is concluded that for natural and compacted expansive soils, the bimodal water retention curve differentiates between flow through the cracks and through the soil matrix. Likewise, the proposed sigmoidal equation accurately describes the swell–shrink curve with most of the deformations between the shrinkage limit and the crack limit. Keywords Expansive clay · Soil cracks · Volumetric changes · Water retention curve · Swell–shrink curve
Introduction Expansive clays are widely distributed in arid and semiarid regions of the globe [1]. According to Chen [12], these soils originate from weathering of igneous rocks (such as in India and South Africa) and sedimentary rocks (such as in North America and the Middle East). Such high plasticity soils cause acute volume change issues particularly for lightly loaded facilities [26]. In Regina (Saskatchewan, Canada), extensive damages to surface (houses and roads) and underground (pipeline and sewers) infrastructure have been routinely reported [22, 38]. This is attributed to the presence of specific minerals (belonging to the smectite and illite groups) possessing high water adsorption and retention capacity due to their large surface areas and net negative charges [33]. The predicted annual loss related to expansive clay issues totals $30 billion in the USA and China [30]. A comparable cost should be expected for hazards due to
* Shahid Azam [email protected] 1
Environmental Systems Engineering, Faculty of Engineering and Applied Science, University of Regina, 3737 Wascana Parkway, Regina, SK S4S 0A2, Canada
similar soils in the Canadian Prairies owing to the extreme climatic conditions prevalent in the region. Heave and settlement are governed by in situ stresses, that is, normal stress and soil suction [17]. The normal stress mostly remains unchanged under a structure and is low for near-surface facilities. In contrast, soil suction varies considerably at shallow depths because of exposure to seasonal varia
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