LABORATORY III. Swelling behaviour, hydraulic conductivity

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1 LABORATORY III. Swelling behaviour, hydraulic conductivity

2 Requirements / tested properties (geotechnics) Granulometry Particle size distribution (curve) Density (Bulk, Dry, Specific) Water content, Degree of saturation Consistency limits (Atterberg limits) Swelling abilities Swelling pressure, Swell index Permeability Thermophysical properties Strength properties

4 Smectite Structure Tetrahedral layer Octahedral layer Tetrahedral layer Interlayer (Gallery) exchangeable cations neutral molecules (H2O) d 001 Tetrahedral layer O OH Si, Al Al, Fe, Mg Li < Na < K < Ca < Mg < NH 4 Dietrich Koch, S&B, ABM Projectmeeting, Äspö,

5 Different forms of water in the interlayer space of Montmorillonite Flake surface + - M M M Flake surface Bonded Water Free Porewater Dietrich Koch, S&B, ABM Projectmeeting, Äspö,

6 Swelling pressure components Steric water The swelling pressure is due to interlamellar hydration of expandable minerals and to osmosis related to interparticle forces. The firstmentioned depends on the type of adsorbed interlamellar cation, which determines the maximum number of hydrates and hence the maximum c-dimension of the stacks of lamellae. Number and thickness of interlamellar hydrate layers in Å for montmorillonite clay SKB TR-01-07, 15

7 Water Content w sat [%] Swelling Pressure σ sw [MPa] Swelling pressure components Thus, as shown by Table, the maximum interlamellar aperture is about 10Å for fully hydrated Na montmorillonite and about 6Å for Ca montmorillonite. These values correspond to a bulk density at saturation of around kg/m 3 for Na montmorillonite clay assuming perfectly parallel and uniformly spaced stacks of lamellae and about kg/m 3 for Ca montmorillonite, assuming that the stacks contain 3 5 lamellae in Na clay and about 10 lamellae in Ca clay. 100 Ca-Mg bentonite in mixture 5 80 w sat 4 60 water content at full saturation σ sw Dry Density ρ d [g/cm 3 ] SKB TR-01-07, 15

8 Water Content w sat [%] Swelling Pressure σ sw [MPa] Swelling pressure components This means that interlamellar hydration does not contribute to the bulk swelling pressure at lower densities. Higher densities mean that such hydration is hindered, which is manifested by a swelling pressure that may be many tens of MPa when there is only one interlamellar hydrate layer, i.e. if the bulk density exceeds about 2100kg/m 3 at saturation w sat 4 60 water content at full saturation σ sw Dry Density ρ d [g/cm 3 ] SKB TR-01-07, 15

9 Swelling pressure components Osmotic pressure Swelling pressure investigations unanimously demonstrate that Na montmorillonite with porewater that is poor in electrolytes has a swelling pressure even for bulk densities at saturation below 1300kg/m 3 and that Ca montmorillonite shows no swelling pressure for less than about 1500kg/m 3 at saturation. Since steric interlamellar water does not contribute to the pressure at these low densities it is believed that the discrepancy results from errors in using concentrations rather than activities of the exchangeable cations and from neglecting formation of clay gels of tactoid type between dense aggregates of stacks, yielding a swelling pressure even after complete expansion of the stacks. The swelling pressure at this stage is largely due to double-layer interaction. SKB TR-01-07, 16

10 Swelling pressure components Osmotic pressure The swelling pressure at this stage is largely due to double-layer interaction. SKB TR-02-20, 88

Bentonite Characteristics Cations-Exchange and Swelling Behaviour dry Calcium-Bentonite in Suspension 2 2 2 2 d 001 : 2,0 nm 2 = Ca 2 + -Ions : 1,5 nm d 001 (Hydration shell of 6 water-molecules ) +

11 Bentonite Characteristics Cations-Exchange and Swelling Behaviour dry Calcium-Bentonite in Suspension d 001 : 2,0 nm 2 = Ca 2 + -Ions : 1,5 nm d 001 (Hydration shell of 6 water-molecules ) + Na 2 CO 3 (Activation) Hydrated Kations Na-Bentonite (2g) in Water: 32 ml Ca-Bentonite (2g) in Water: 5 ml Hydrated Kations Natrium-Bentonite d 001 : = Na + -Ionen d : 1,2 nm 001 Kolloidal dispersion of particels Water molecule Dietrich Koch, S&B, ABM Projectmeeting, Äspö,

12 SKB TR-01-07, 18

13 Interlamellar hydration The interlamellar space offers large amounts of hydration sites due to the crystal lattice constitution, which determines the charge and coordination of adsorbed cations and water molecules. The hydration properties control the swelling potential, plasticity and rheological behavior and are hence of fundamental importance. The coordination of interlamellar cations, the crystal lattice and the water molecules depends strongly on the size and charge of the cations and of the charge distribution in the lattice. 3 hydrate layers in montmorillonite can only be formed when sodium, lithium or magnesium are in interlamellar positions. One finds that montmorillonite is the only smectite mineral that can expand by forming 3 interlamellar hydrates. This means that montmorillonite clay can swell more than other smectite minerals, which gives it better sealing properties. However, this is the case only when Li+, Na+ and Mg 2 + are in interlamellar positions. With K+ or Ca 2 + in these positions a third hydrate does not form in this or any other smectite mineral because of the charge and size of these ions. When submerged in free water, the hydration of an initially dry montmorillonite crystallite proceeds until the maximum number of hydrates is formed, provided that there is no geometrical restraint. In humid air, the number of hydrates depends on the relative humidity. SKB TR-01-08, 18

14 Extralamellar hydration External surfaces are basal planes and edges of the stacks of lamellae. The firstmentioned consist of hexagonal arrangements of oxygens or hydroxyls and can attach water molecules by establishing hydrogen bonds. However, diffuse electrical double-layers are formed here with a relatively high concentration of cations near the surface, which affects the organization and physical state of the hydrates. There are reasons to believe that the viscosity of the adsorbed water is higher than that of free water but that the mobility of the molecules is higher than that of interlamellar water. It is assumed that no more than 3 hydrate layers are adsorbed at the free surfaces and that only the first of them has physical properties that deviate significantly from those of free water. At low bulk densities the fraction of interlamellar, immobile water is naturally higher than at high bulk densities. The impact of the type of adsorbed cation in the diagram is explained by the difference in numbers of interlamellar hydrates. SKB TR-01-08, 18

15 Theoretical relationship between bulk dry density in g/cm 3 and the content of interlamellar ( internal ) water expressed in percent of the total porewater content SKB TR-01-08, 18

16 Börgesson et. al., SKB IC 122

17 Hydraulic conductivity Once constant flow is achieved, the volume of water passing throw the sample (V) is determined over a given period of time (t). Evaluation of hydraulic conductivity k is according to Darcy s Law, calculated as: k V l A t h k hydraulic conductivity [m/s] Δl length of the sample [m] A the surface area of the cell [m 2 ] Δh hydraulic head [m] Δt time [s] ΔV volume of water [m 3 ]

18 Hydraulic conductivity When hydraulic gradient is defined as: i h l i hydraulic gradient Δh hydraulic head [m] Δl length of sample [m] and injection pressure can be substituted by hydraulic head: h p g Δh hydraulic head [m] Δp hydrostatic (injection) pressure [Pa] ρ density of liquid (water) [kg/m 3 ] g gravitational acceleration [m/s 2 ]

19 Börgesson et. al., SKB IC 122

21 Influence of Pore Water Salinity Friedland Ton bentonite SKB TR-02-12, 132

22 Influence of Pore Water Salinity Friedland Ton bentonite SKB TR-01-07, 21

23 Determination of Swelling Pressure The base of test is measurement of sample deformation and stress.

24 Type I oedometric bench Test method with usage of classical oedometric bench is similar to compressibility test, where sample is loaded (or unloaded) gradually and sample deformation is measured. It is possible to perform the test in two ways: - initial loading is maximal and sample is unloaded in steps - at beginning sample is without loading and it is loaded in steps.

25 Test procedure: Type I oedometric bench 1. Sample with known water content w and known weight m is put into oedometer with known volume V. 2. First reading on indicator watch (which measure deformation) is performed. 3. Sample is loaded by initial loading according to the type of test, loading is zero (test with loading) or loading is maximal (test with gradual unloading). 4. Sample is watered and is waited till stabilization in deformation is reached. 5. Reading of deformation and stress (e s1 and s 1 ) is performed. 6. Loading/unloading (according to test type) to stress for further step is performed. 7. It is waited till stabilization of deformation is reached. 8. Reading of deformation and stress (e si and s i ). 9. If final stress is reached (maximal or zero according to test type) test is finished, otherwise is continued from step No.6.

26 Type I oedometric bench Both types of test can be combined. Directly after one type, the second type can continue. Result of test is always couple stress deformation from particular steps.

27 Type I oedometric bench Swelling pressure is determined as follows: s sw, di = s i - swelling pressure corresponds to stress in particular step di = m/(e i.v. (1+w)) - dry density is calculated from initial weight, water content, volume and ratio of final and initial height (ε i )

28 Type II using oedometer in rigid frame Test with usage of oedometer in rigid frame is used for materials with higher swelling pressure. Measured values during test: sample deformation, frame deformation and pressure - by dynamometer. Although the frame deformation is not used during test evaluation it is important to control part of system.

29 Type II using oedometer in rigid frame Test procedure: 1. Sample with known water content w i and known weight m i is put into oedometer with known volume V. 2. The initial reading for reference values of frame deformation, sample deformation and stress (force on dynamometer) is performed. 3. Sample is watered. 4. Is waited till stabilization of deformation and stress (checking by regular readings on indicator watch). 5. The last reading is done and resulting frame deformation, sample deformation e f and stress s w is read. 6. Oedometr is dismantled. Weight of sample m f and its water content w f are determined.

30 Type II using oedometer in rigid frame s sw, d = s sw swelling pressure corresponds to stress at the end of the test d = m i /(e f.v. (1+w i )) dry density is calculated from initial weight, water content, volume and final deformation. d = m f /(e f.v. (1+w f )) dry density is calculated from final weight, water content, deformation and initial volume. Dry densities calculated from initial and final values must not differ. w sat, d = w f water content for fully saturated state for determined density

31 Type II using oedometer in rigid frame s sw k. A σ sw - Swelling pressure [MPa] k - Dynamometer calibration constant [N/mm] Δ - Dynamometer deformation [mm] A - Sample surface [mm 2 ] Dynamometer 300kp = 3kN 500 kp = 5kN 1Mp = 10kN 50kN 100kN 500kN k kn/mm Pressure (d =120 mm) MPa/mm

32 Type III specialized device Custom built device for determination of permeability and swelling pressure of samples. Measures simultaneously: - Swelling pressure up to 30 MPa - Permeability of very low permeable materials

33 Type III specialized device SKB TR-02-20, 194

1 koncový uzávěr měřicího okruhu 2 vstupní uzávěr měřicího

kapiláře) 4 uzávěr přemostění měřicího okruhu Zkratka 5

tlakovou nádobu 7 výpustní kohout pro měřicí smyčku 8 výpustní

34 1 koncový uzávěr měřicího okruhu 2 vstupní uzávěr měřicího okruhu 3 přepínač směru měřicí smyčky (pohybu rozhraní v kapiláře) 4 uzávěr přemostění měřicího okruhu Zkratka 5 výpustní kohout pro měřicí smyčku 6 výpustní kohout vody pro tlakovou nádobu 7 výpustní kohout pro měřicí smyčku 8 výpustní kohout plynu pro tlakovou nádobu 9 uzavírací kohout plynu (z tlakového rozvodu)

35 Type III specialized device Direct measurement of force induced by swelling by force sensor Zero deformation = constant volume test Pressurised water used for sample saturation and steady state flow establishment The injection presure up to 6MPa Bear in mind ratio of injection and expected swelling pressure when injection pressure level is set Hydraulic conductivity water volume reading manually on thin, calibrated pipe

36 Swell index

37 Swell index Free swelling in distilled water Plus: Relatively fast Easy No special equipment needed Minus: Informative test only ASTM D Standard Test Method for Swell Index of Clay Mineral Component of Geosynthetic Clay Liners

38 Swell index How: 100ml calibrated cylinder with distilled water Dried Sample, 2-3g Pour 0,1g to water in 10min. interval CAREFULLY pour slowly to avoid clotting Reading (volume) on cylinder after 24h (after last pouring) is Swell index for certain amount of sample divide volume by weight of sample

39 Ca-Mg clay, Deposit Stránce natural material Na bentonite MX80 pure bentonite

40 It can occur

41 It can occur

Clay-isolation of chemical waste in mines

Clay-isolation of chemical waste in mines R. Pusch Geodevelopment AB, IDEON Research Center, SE-22370 Lund, Sweden Abstract Surrounding and mixing of solid waste by low-permeable expansive clay very effectively