Determination of swelling potential of a fissured expansive clay in a large cell

Faseel S. Khan, Shahid Azam

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Expansive Soils

ABSTRACT: This study presents preliminary results of swelling potential for a local unsaturated expansive soil in a large cell. The sample exhibited an initial swelling of 6% after one day of inundation and a primary swelling of 46% after 210 days (seven months). The top surface consisted of alternate crests and troughs of up to 15 mm with respect to the average soil height. The sample is expected to enter into the secondary swelling range in the coming months. A comparison with a conventional test indicated the absence of differential swelling in the later test. RÉSUMÉ Cette étude présente les résultats préliminaires du potentiel de gonflement d'un sol local gonflant non saturé. L'échantillon présente un gonflement initial de 6 % après un jour d'inondation et un gonflement primaire de 46 % après 210 jours (sept mois). La surface supérieure est composée de crêtes et de creux alternés avec une hauteur maximale de 15 mm par rapport à la hauteur moyenne du sol. L'échantillon devrait entrer dans la phase de gonflement secondaire dans les prochains mois. Une comparaison avec un test classique a indiqué l'absence de gonflement différentiel dans ce dernier essai 1 INTRODUCTION Expansive soils are mostly found in the arid to semi-arid regions around the globe. Such soils affect construction sites throughout the globe, though covering only a small percent (1% to 2%) of the total land area. According to Puppala and Cerato (2009), the problems associated with expansive soils cost about thirteen billion dollars of annual damage to infrastructure in the United States. These soils are widely found in the Canadian prairies such as in the provincial capitals (Regina, Winnipeg and Edmonton) as well as several rural municipalities in the region. The damages are generally seen in the form of wavy roadways, inclined cracking in slab-on-grade basements and masonry walls, and fatigue and breakage in underground storage tanks and buried pipelines. This is because these soils are characterized by large volume changes associated with swelling and shrinkage. Swelling potential is the measure of the increase in volume of an unsaturated soil due to the adsorption of water. The swelling potential is measured in accordance with ASTM Standard Test Methods for One-Dimensional Swell or Collapse of Soils (D4546-14) in a 60 mm diameter ring. This test gives reasonable estimates for intact samples. However, the top surface of expansive clays is cracked due to seasonal weather variations. Morris et al. (1992) reported that crack depths from 0.5 to 6.0 m are observed in the natural soils of Australia and Canada. The fissures consume part of the swelling movement by expanding laterally and cause the soil to swell in a differential manner. Therefore, the conventional oedometer test cannot capture the lateral movement due to its small dimensions. Azam and Wilson (2006) have used a large mould (300 mm diameter) to capture swelling of a natural undisturbed fissured soil and confirmed that large-scale samples effectively captured the soil behaviour due to fissuring thereby representing actual field conditions. The purpose of this study was to determine the swelling potential of a fissured expansive clay in a large cell. A large 600 mm diameter plexiglass cell was fabricated at the University of Regina and filled with soil to represent the desiccated field condition. Water was added on top of the soil and the soil movement was recorded with time. The swelling potential from the large cell was compared with an identical 60 mm diameter sample in a conventional oedometer test. 2 MATERIALS AND METHODS Clay samples were collected from near the town of Avonlea which is located 50 km south of Regina. A representative soil sample was retrieved from the surface using a shovel and a bucket. The sample was collected from the east side of Avonlea creek using sealed plastic bags, placed in 20 L buckets and transported to the Geotechnical Testing Laboratory at the University of Regina. The sample was stored at 20oC. The index properties were determined for preliminary soil assessment according to standard ASTM test methods as follows: (a) specific gravity (Gs) by the Standard Test Method for Specific Gravity of Soil Solids by Water Pycnometer (D854-10); (b) grain size analysis using the Standard Test Method for Particle-Size Analysis of Soils (D422-63(07)); (c) liquid limit (wL), plastic limit (wp) and plasticity index (Ip) by the Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils (D4318-10); (d) soil classification by the Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System) (D2487-11); (e) natural water content (w) by the Standard Test Method for Laboratory Determination of Water (Moisture) Content of soil and Rock by Mass (D2216-10) and (f) Standard Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens (D7263-09).

RÉSUMÉ: mination of swelling potential of a fissured

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Faseel S. Khan; Shahid Azam (2014) Determination of swelling potential of a fissured expansive clay in a large cell in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper142,author = Faseel S. Khan; Shahid Azam,title = Determination of swelling potential of a fissured expansive clay in a large cell,year = 2014}