Clays and Clay Minerals Fields of interest for clays Various definitions Acients: Earths in the earth-air-fire-water system Definition of clay depends on discipline: Geologist grain size <2mm Engineer: property of plasticity Ceramicist: hardening on firing The clay cycle Formation of clay and clay minerals restricted to upper crust No chemical definition, but: Most clays are high in aluminum General: Minerals which normally dominate the fine (<2mm) fraction of rocks and soils. of clay minerals Basic building block of silica minerals is the SiO -4 4 silica tetrahedron Linked together at apical oxygen to form sheets Tetrahedral sheet does not exist by itself In clay minerals the tetrahedral sheet is always combined with a octahedral sheet A cation (Al +3, Mg +2, Fe +2 etc. but not Ca +2, Na +1, K +1 ) is surrounded by 6 neighbors (oxygens or hydroxyls) Minerals composed of octahedral sheets. Brucit Mg 3 (OH) 6 Gibbsite Al 2 (OH) 6 1
Formula of the tetrahedral sheet: Si 4 O 10-4 negative charge: only exists in combination with cations and and additional oxygens Formula of the octahedral sheet: Brucite: Mg 3 (OH) 6 all octahedrals occupied trioctahedral Gibbsite: Al 2 (OH) 6 2/3 of octahedrals occupied dioctahedral 1 tetrahedral sheet and 1 octahedral sheet linked together The unshared oxygen becomes part of the octahedral sheet Simplest clay mineral: Kaolinite Kaolinite Serpentine-Kaolin Group = 1:1 group no layer charge hydrogen bonds Serpentines Mg trioctaedric (generally not clay m.) Kaolins Al dioctaedric 2 tetrahedral sheets and 1 octahedral sheet linked together to form a sandwich structure 2:1 layer minerals Variation of Large interlayer cations Mica, Illite 2
Bentonite (ca. 90% montmorillonite) weathering product of volcanic glass Mixed-layer clay minerals Definition: Two or more layer types (i.e. mica, smectite, chlorite, etc.) are intermixed in vertical stacking sequence within a single crystal. Bonding is strong within the layers but week between the layers Different types of layers have nearly identical configuration of tetrahedral oxygens bounding the outer surfaces Mixed-layer clay are widespread in nature 2:1 layer minerals Illite-Smectite Mixed-layer clay minerals Criteria for characterization: Types of layer involved (e.g. illite, smectite, chlorite) Amount of each layer type (%) Stacking arrangement, or vertical sequence, of the component layers (e.g. regular, random) Example: randomly mixed-layered smectite/illite with 10% illite layers Identification of clay minerals Identification using Sample preparation: Cation saturation: with single, known cation prior to any treatment (K +, Mg 2+ ), excess salt removed 1. Air dry specimen 2. Ethylene glycol or glycerol saturation 3. Heating to 350 C or 550 C 4. Dimethylsulfoxide intercalation (not routinely used) Kaolinite: 7-Å peak dissapears upon heating / is shiftet after DMSO treatment 3
Illite: Smectite: 10-Å peak not affected by treatment Shifting of 001-peak affected by: type of interlayer cation single/double layer of H 2 O-molecules ethylene glycol solvation (swelling) heating (no H 2 O-layer) How does clay feel? Chlorite: 14-Å peak not affected by treatment How does clay feel? 4
Sisi Nubi project Sisi Nubi project Construction of new platforms Foundation and anchoring In situ tests Clay = soil from a engineering point of view Special testing methods for in situ testing of fine grained soils SPT: Standard penetration test hammering of a sampler tube into the ground under defined conditions and counting the strokes : elaborate testing method with a cone shaped probe; measurement of cone resistance, sleeve friction and pore water pressure Dilatometer / Flat Plate Dilatometer for measurement of the deformation and elastic properties of the soil Packer testing for in-situ determination of hydraulic conductivity Cone Penetration Test Probe Cone Penetration Test Cone Penetration Test Umbilical cable with data lines and hydraulic line 5
Results Continuous profile Clay = soil from a engineering point of view Various tests to determine the geotechnical of soils Direct shear test shear strength Triaxial shear test shear strength of drained or undrained sample Attenberg limits plasticity of clay, shrinkage Oedometer test consolidation and swelling Water content Hydraulic conductivity Sampling Extrusion of sample Sample preparation Shear test Mark of penetrometer test 6
Off-shore drilling specialities Off-shore drilling specialities Moon pool Rooster box Development project More likely problems for Swiss geologists (from Keusen, 2000) More likely problems for Swiss geologists More likely problems for Swiss geologists (from Keusen, 2000) What type of soil? - cohesive/non-cohesive Pore water pressure? -low/high.. 7