Physical and geotechnical properties
Emma Niemeläinen1, Markku Juvankoski1, Teemu Karlsson2, Päivi Kauppila2, Tommi Kaartinen1, Jutta Laine-Ylijoki1, Elina Merta1, Ulla-Maija Mroueh1, Jarno Mäkinen1, Henna Punkkinen1 & Margareta Wahlström1, 1VTT Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, FINLAND; 2Geological Survey of Finland, P.O. BOX 1237, FI-70211 Kuopio, FINLAND
Information on physical and geotechnical properties of disposed waste, top/under cover layer and structure layer materials is a necessity. The geotechnical investigations aim at determining the properties which will form the basis for designing a safe waste storage area and waste disposal techniques. The extent and content of the measurements are determined by the choice of waste disposal technique and the safety requirements relating to storage (dam safety, risk of major accident, Government Decree 717/2009, Annexes 2 and 3). (Kauppila et al. 2013)
The geotechnical measurements of waste rock typically focus on the estimation of rock size and possibly of the specific weight to plan the slope of the edges of the waste rock pile, to take into account the risk of collapse and to estimate the consolidation of the ground under the pile (load-bearing capacity/estimate of the stability of the base). The measurement of the geotechnical properties of sludge wastes, such as tailings, is required to plan the safety and stability of the waste storage area, in which the key considerations are the choice of dam materials and dimensioning of the dams and evaluation of the maximum height of the waste storage pile. For tailings and watery sludges those geotechnical properties are determined that are used in planning of the dimensions of the waste storage area, the management of safety risks and planning of the after-care (Government Decree 717/2009 Annex 3). These include for example (Kauppila et al. 2013):
- distribution of grain size, specific surface area and shape of grains
- density/specific weight
- water content, water retention capacity and capillary conductivity
- pore water pressure (in raised sections of dams made from tailings)
- shear resistance (stability) and
- compaction and/or compressibility properties (for additional information see Rantamäki et al. 1979, see also CDN/TC292/WG1 2011)
The performance of disposed waste and the functionality of the top cover cannot be assessed solely based on material properties, as the technical performance (e.g. compaction mode) influences the final properties of the waste or the material in a layer. Technical characteristics of a layer (e.g. water permeability) are also highly influenced by external conditions (e.g. weather). Furthermore, ageing of materials has an effect on chemical and physical properties (e.g. carbonisation, pozzolanic reactions). In evaluation of waste materials containing biodegradable organic matter, also the degradation of materials in top covers and its influence on geotechnical properties needs to be taken into account. The main concern here relates to long-term stability.
Sampling for geotechnical properties may set special requirements on both the sampling approach and sampling equipment (e.g. need for undisturbed samples), which may in some cases drive a decision to determine them indirectly by a different test method or by field testing instead.
The most essential physical and geotechnical characterization methods for waste material are presented in this chapter. The main properties of waste materials recommended to be determined are bulk density, grain size distribution and water content. In unclear cases the classification of soil may be necessary. The main geotechnical properties to be tested are water permeability and compactability. The need for determination of the shear strength and friction depends on the disposal scenario and the selected closure technique: for example if the waste material is deposited in a pond, the determination of all these properties may not be needed. (Wahlström et al. 2009, Technical Committee 2012)
It is to be noted that the selection of properties to be determined varies case-by-case. When selecting the characterization and suitable determination methods one should always keep in mind the whole deposit structure, retaining/water management systems used and the waste materials itself. For example, in the case where geomembrane layer is used in the cover structure, the permeability of the disposed waste and the cover material is not necessarily required to be tested. Secondly, determination of bearing capacity is not needed for waste materials that will not carry loads. So selecting the characterization methods should be always based on the whole structure, retaining/purification systems used and the waste materials itself.
Suitable methods for determining the geotechnical properties above of the waste material are presented in Table 1 (Wahlström et al. 2009, Technical Committee CEN/TC 292 2012). Most of these methods have been published in CEN-ISO and/or SFS-EN standard series. These are applicable to wastes from extractive industries for each type (i.e. tailings, waste rock, overburden and topsoil). Furthermore, there is also some useful ASTM or other methods available, but generally the European methods, if existing, are primarily recommended.
Table 1 The recommended test methods for the evaluation of geotechnical properties of waste materials (Wahlström et al. 2009, Technical Committee CEN/TC 292 2012).
|Classification of soil
|SFS-EN ISO 14688-1||Geotechnical investigation and testing – Identification and classification of soil – Identification and description|
|SFS-EN ISO 14688-2||Geotechnical investigation and testing – Identification and classification of soil – Principles for a classification|
|Soil density, bulk density
|Geotechnical investigation and testing – Laboratory testing of soil – Determination of density of fine-grained soil|
|Tests for mechanical and physical properties of aggregates – Determination of particle density – Pycnometer method|
|SFS-EN 1097-3||Tests for mechanical and physical properties of aggregates – Determination of loose bulk density and voids|
|SFS-EN 1097-6||Tests for mechanical and physical properties of aggregates – Determination of loose bulk density and voids Tests for mechanical and physical properties of aggregates – Determination of particle density and water absorption|
|SFS-EN 1097-7||Tests for mechanical and physical properties of aggregates – Determination of the particle density of filler – Pycnometer method||Recommended for soils d < 0,063 mm|
|ASTM D1556||Standard test method for density and unit weight of soil in place by sand-cone method||Recommended for maximum density|
|Grain size distribution
|CEN-ISO/TS 17892-4/AC||Geotechnical investigation and testing – Laboratory testing of soils – Partical size distribution|
|ISO 3310-1:2000||Test sieves – Technical requirements and testing – Test sieves of metal wire cloth|
|SFS-EN 933-2||Determination of particle size distribution. Tests sieves, normal size of apertures|
|Water content||CEN-ISO/TS 17892-1||Geotechnical investigation and testing – Laboratory testing of soil – Determination of water content|
|SFS-EN 1097-5||Tests for mechanical and physical properties of aggregates – Determination of the water content by drying in a ventilated oven|
|SFS-EN 12880||Characterization of sludges – Determination of dry residue and water content||For sludges|
|Water permeability||CEN-ISO/TS 17892-11||Geotechnical investigation and testing – Laboratory testing of soil – Determination of permeability by constant and falling head|
|Compactability||SFS-EN 13286-2/AC||Unbound and hydraulically bound mixtures – Test methods for the determination of the laboratory reference density and water content – Proctor compaction||Recommended (up to 25 % >63 mm)|
|Shear strength, friction angle and bearing capacity (optional)
|CEN-ISO/TS 17892-5||Geotechnical investigation and testing – Laboratory testing of soil. Incrementing loading oedometer test||Oedometer|
|CEN-ISO/TS 17892-7||Geotechnical investigation and testing – Laboratory testing of soil. Unconfined compression test on fine-grained soils||Unconfined compressive strength|
|CEN-ISO/TS 17892-8||Geotechnical investigation and testing – Laboratory testing of soil. Unconsolidated undrained triaxial test||Triaxial test of unconsolidated undrained conditions|
|CEN-ISO/TS 17892-9||Geotechnical investigation and testing – Laboratory testing of soil – Consolidated triaxial compression test on water saturated soils||Triaxial test, consolidated undrained or drained conditions|
|CEN-ISO/TS 17892-10||Geotechnical investigation and testing – Laboratory testing of soil – Direct shear tests||Direct shear test|
In some cases additional information is required on the following properties (Wahlström et al. 2009, Technical Committee CEN/TC 292 2012):
- Plasticity (Method example: CEN-ISO/TS 17892-12, CEN-ISO/TS 17892-6)
- Shrinkage (Method example: ASTM D 427-39)
- Erosion sensitivity
- Liquefaction (Method example: In situ coring)
- Pore water pressure
- Porosity (Method example: SS 27117)
- Gas permeability
An extensive list of geotechnical properties and recommended determination methods is available in “Overall guidance document for characterization of wastes from extractive industry” (Technical Committee 2012) and in the Reference Document on Best Available Techniques for the Management of Tailings and Waste-Rock in Mining Activities (European Comission 2009).
European Commission 2009. Reference Document on Best Available Techniques for Management of Tailings and Waste-Rock in Mining Activities. January 2009.
Kauppila, P., Räisänen, M. L. & Myllyoja, S. 2011. Best Environmental Practices in Metal Ore Mining. Finnish Environment 29 en/2011.
Rantamäki, M., Jääskeläinen, R. & Tammirinne, M. 1979. Geotekniikka. Otatieto 464. Oy Yliopistokustannus/Otatieto, Helsinki, 307 p.
Technical Committee 2012. Technical Committee CEN/TC 292 2012. Characterization of waste – Overall guidance document for characterization of wastes from extractive industries. CEN/TR 16376:2012.
Wahlström, M., Laine-Ylijoki, J. & Vahanne, P. 2009. Materials for construction of top cover in landfills – Experience in the Nordic countries. TemaNord 2009:549.