FOCUS AREAS
Unsaturated soils contain both air and fluid phases in their pores and occur throughout the world. They can be either naturally occurring soils, such as those found in arid and tropical zones, or artificially created soils such as those that are formed by compaction. One of their major features is their volume and strength change behaviour upon wetting and drying.
Even without a major change in the volume the reduction of matric suction due to infiltration of water causes significant reductions in shear strength which is the main mechanism for the rain induced landslides. Many natural slopes and cut steep cut slopes in the country are safe during the dry season due to prevailing high matric suctions but subjected to failure during the periods of high intensity short duration rainfalls and/or low intensity prolonged rainfalls. Modelling this process and identifying the changes to the matric suction and pore pressure regime in slopes and associated reduction of shear strength is of utmost importance.
Thus, it is necessary to establish; Soil Water Characteristic Curves (SWCC), Permeability functions, Variation of Shear strength with matric suction of natural soils forming sloping grounds in the country. Various testing techniques such as; direct shear tests with suction measurements, flow of water through an unsaturated soil with continuous suction measurements during drying or wetting, achieving equilibrium at a matric suction in pressure plate apparatus are being used currently in this context. Research is also conducted to establish SWCC using particle size distribution. Comparison of numerical and experimental results on effect of infiltration in a model soil fill in laboratory is also in progress.
PUBLICATIONS
- Vasanthan N, Kulathilaka SAS (2020), Properties of an Unsaturated Residual Soil behind a Failed Slope in Sri Lanka, Geotechnical Journal, Journal of the South East Asian Geotechnical Society.
- Rajeevkaran P, Kulathilaka SAS (2019), Pullout Resistance of Soil Nails in Unsaturated Residual Soils, 16th Asian Regional Conference of International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE), Taiwan.
- Ranjan Kumara WEP, Kulathilaka SAS (2019), Study of pullout resistance of soil nails in tropical residual soils, Geotechnical Journal, Journal of the Sri Lankan Geotechnical Society.
- Kankanamge L, Kulathilaka SAS, Karunarathna SWBS, Karunawardena WA, Bandara KN (2019), Rainfall Induced Shallow Landslides in Sri Lanka: Development of Rainfall Thresholds Using the Fundamentals of Unsaturated Soil Mechanics. 10th Annual National Building Research Organization (NBRO) Symposium, Equitable Resilience, Sri Lanka, pp. 173- 184.
- Dilanthi HPW, Kulathilaka SAS, Vasanthan N (2018), Shear strength and Permeability Characteristics of some Sri Lankan Residual soils, UNSAT2018, Hong Kong.
- Kankanamge L, Jotisankasa A, Hunsachainan N, Kulathilaka SAS (2018), Unsaturated Shear Strength of a Sri Lankan Residual Soil from a Landslide-Prone Slope and its Relationship with Soil–Water Retention Curve, International Journal of Geosynthetics and Ground Engineering, 4(3), p.20.
- Vasanthan N, Kulathilaka, SAS (2016), Establishment of Shear Strength Characteristics of Some Unsaturated Sri Lankan Residual Soils Paper published at the 7th Annual National Building Research Organization (NBRO) Symposium, Innovations for Resilient Environment, Sri Lanka.
- Karunasena GKGM, Kulathilaka SAS (2016), Determination of Permeability Characteristics and SWCC of an Unsaturated Residual Soils in Sri Lanka, Civil Engineering Research Symposium (CERS), University of Moratuwa.
- Vasanthan N, Idirimanna IAND, Kulathilaka SAS (2015), Establishment of Fundamental Characteristics of Unsaturated Sri Lankan Residual Soils, 6th Annual National Building Research Organization (NBRO) Symposium, Innovations for Resilient Environment, Sri Lanka.