Some Applications Of Unsaturated Soil Mechanics In Thailand: An Appropriate Technology Approach
W. Mairaing, A. Jotisankasa and S. Soralump
ABSTRACT: This paper is involved with some applications of unsaturated soil mechanics on several problems in Thailand, namely rainfallinduced landslide, dam engineering as well as other volume change problems. In particular, the concept of appropriate technology has been considered in applying unsaturated soil mechanics for these problems. Utilization of the in-house-built miniature tensiometer and relative humidity sensors with conventional standard apparatus has been proposed as an appropriate technology in the country for testing of unsaturated shear strength, volume change as well as other unsaturated hydraulic properties (Soil-Water Characteristic Curve and permeability function). Regarding rainfall-induced landslide, unsaturated soil mechanics has been used in correlating rainfall intensity with slope instability and developing a critical rainfall criteria which has been used in Geographic Information System (GIS) to create dynamic hazard map as well as providing a real-time early warning of landslide based on soil moisture and rain-fall. A case of leakage detection technique as well as volume change analysis for embankment dam are briefly explained. Finally, some aspects of unsaturated soil mechanics education in Thailand is discussed.
Calculation Of Heave Of Deep Pier Foundations
J.D. Nelson, K.C. Chao, D.D. Overton and R.W. Schaut
ABSTRACT: Design of pier and grade beam foundations in highly expansive soils is one of the most important and challenging aspects of geotechnical engineering. Existing design methods consider only uniform soil profiles, and piers with limited length to diameter ratios. These methods are restricted with regard to evaluation of more complex aspects of pier heave. A finite element method of analysis was developed to compute pier movement in expansive soils having variable soil profiles, complex wetting profiles, large length-to-diameter ratios, and complex pier configurations and materials. The model has been named APEX (for Analysis of Piers in EXpansive soils). This paper describes the method of analysis and demonstrates its validity using several case histories. The results of pier design using APEX are compared with those of both conventional rigid pier analyses and elastic pier analyses. A series of simplified design charts developed using APEX are presented to facilitate its use. The results show the versatility of the model with regard to variable soil profiles and wetting zones.
In-Situ And Laboratory Investigations Of Stress-Dependent Permeability Function And SDSWCC From An Unsaturated Soil Slope
C. W. W. Ng and A. K. Leung
ABSTRACT: Permeability function of an unsaturated soil, k(y), where y is suction, is a vital hydrogeological property that governs seepage in various geotechnical problems. Owing to considerably long test duration, direct measurement of k(y) is often avoided if at all possible. Instead, numerous semi-empirical predictive equations have been developed to determine k(y) indirectly. However, effects of drying-wetting history and net normal stress are not generally considered, casting doubts on the validity of some semi-empirical predictive equations. In this paper, stress-dependent k(y) and stress-dependent soil-water characteristic curve (SDSWCC) of a decomposed silty clay are investigated under both field and laboratory conditions. To measure effects of drying and wetting on k(y) directly, an in-situ one-dimensional (1D) permeability test was carried out using the instantaneous profile method on a saprolitic hillslope in Hong Kong. In the laboratory, a new 1D stress-controllable soil column was developed to determine stress-dependent k(y) and SDSWCC on block samples taken from the same hillslope. Effects of drying-wetting cycle(s) and net normal stress on measured stress-dependent k(y)s and SDSWCCs are explored and analysed. By comparing measured and predicted k(y)s, the predictability of some existing semi-empirical equations is evaluated.
Measurements Of Shrinkage Induced Pressure (Sip) In Unsaturated Expansive Clays
A.J. Puppala, T. Wejrungsikul, V. Puljan and T. Manosuthikij
ABSTRACT: Unsaturated expansive soils are located in many regions of the world. Expansive soils can swell more than 100% and shrink more than 50% of its original volume. When these soil movements are totaled, they often result in significant distress to low overburden structures such as pavements and residential buildings. Cracking occurs when the shrinkage or desiccation induced pressure inside the expansive soil matrix exceeds the tensile strength of the same soils. In general, practitioners use soil tests such as linear shrinkage strain and Atterberg limit tests to determine shrinkage strain potentials of soils. However, these tests do not provide shrinkage induced soil pressures generated within the soil. The main objective of this paper is to present a new technique to measure the shrinkage pressure inherently induced inside the matrix of clays. This test termed as Shrinkage Induced Pressure (SIP) is evaluated for providing repeatable and reliable measurements. SIP test results are compared with Indirect Tensile (IDT) strength test results to explain the shrinkage mechanisms in the soils.
KEYWORDS: expansive clay, cracking, curling, shrinkage, shrinkage induced pressure (SIP), indirect tensile (IDT) strength
Unsaturated Soil Mechanics For Slope Stabilization
H. Rahardjo, A. Satyanaga, E. C. Leong
ABSTRACT: Rainfall-induced slope failures commonly occur in the unsaturated zone above groundwater table in many steep residual soil slopes. During a rainy season, desiccated soils with higher permeabilities will increase rain infiltration into slopes causing an increase in pore-water pressures in the zone above the groundwater table. In addition, the groundwater table may rise to result in a further increase in pore-water pressures. As a result, the shear strength of the soil will decrease and factor of safety of the slope can decrease to below a critical value, triggering slope failure. Therefore, it is important to be able to protect unsaturated soil zone within a slope by controlling the
groundwater level and the flux boundary conditions across slope surface as a slope stabilization method. In this paper, the mechanisms for maintaining unsaturated zone in a slope using several slope stabilization methods are described using field examples involving site investigation, numerical analyses and instrumentation. The effectiveness of each slope stabilization method is assessed using principles of unsaturated soil mechanics.
The Development Of Unsaturated Soil Mechanics At Imperial College, London
J.R. Standing
ABSTRACT: Saturated soil mechanics is a complex subject because of the particulate form of the solid phase of soil, its interaction with the aqueous water phase and also because soil is a product of nature and so has potentially great variability. When the soil dries such that there is also an air phase it becomes unsaturated and its behaviour is far more complex because of the interface between the air and the water and the volumetric response of the air under changing conditions of pressure and temperature. Additionally the pressure in the water phase becomes negative (tensile) and measuring such pressures has until recently been fraught with problems. As many parts of the world are covered by unsaturated soils, understanding their response would significantly enhance engineering design and analysis. This paper describes the research work done at Imperial College over the past decades to advance our understanding of unsaturated soils. The work is considered under four main headings of theoretical formulations, laboratory experimentation, field studies and numerical analysis research.
Climate Change And The Role Of Unsaturated Soil Mechanics
D.G. Toll, J. Mendes, P.N. Hughes, S. Glendinning and D. Gallipoli
ABSTRACT: The Intergovernmental Panel on Climate Change (IPCC) provides convincing evidence of global warming as a result of increased greenhouse gas production. There has been a greater occurrence of extreme climate events in recent decades. We need to ensure that our buildings and infrastructure can cope with such events and possibly more extreme events in the future. A good grounding in unsaturated soil mechanics will be necessary to understand future changes involving the drying and desiccation of soils that will occur in dry seasons and the wetting and infiltration processes that prevail during wet seasons. To predict the impacts of climate change will require the use of robust numerical modelling of climate/soil interactions that can be used to model the effects of future climate regimes. To achieve this we need high quality field observations involving climate/soil interaction that can be used to validate the models. This paper reports on a study in the UK to acquire such data.
Some Mining Applications Of Unsaturated Soil Mechanics
D.J. Williams
ABSTRACT: Unsaturated soil mechanics continues to play poor relation to saturated soil mechanics, although an unsaturated soil at a given density is stronger, less compressible and less permeable (i.e. performs better) than the same soil in a saturated state. There are many examples of unsaturated conditions in the mining field, including the wetting-up and drain-down of initially dry surface waste rock dumps; the irrigation and drain-down of heap leach materials; the drain-down, desiccation and rewetting of mine tailings; the dewatering of mineral products such as coal; the shear strength and compressibility of stored mine wastes; and the performance of geo-covers placed on mine wastes on rehabilitation. This paper highlights the key unsaturated soil mechanics parameters, overviews the nature of mining and processing wastes, and some products, and discusses the issues involved. Some applications of unsaturated soil mechanics addressing the shear strength, compressibility and permeability of mine wastes, and mineral products, are presented, together with data to highlight them.
