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Laboratory investigation of the freezing point of oil-polluted soils
Cold Regions Science and Technology 32 Ž2001. 183–189 www.elsevier.comrlocatercoldregions
Laboratory investigation of the freezing point of oil-polluted soils S.E. Grechishchev a , A. Instanes b,),1, J.B. Sheshin a , A.V. Pavlov a , O.V. Grechishcheva a a
b
Earth Cryosphere Institute, Russian Academy of Sciences, Moscow, Russian Federation Norwegian Geotechnical Institute (NGI), P.O. Box 3930, UlleÕaal Stadion, N-0806 Oslo, Norway Received 4 August 2000; accepted 27 April 2001
Abstract This paper presents the results from an experimental laboratory investigation studying the volumetric and unidirectional freezing of oil-polluted soils. The experiments are a part of a larger laboratory programme where the objective is to understand how oil pollution affects the phase transition velocity and how the phase transition is dependent on the oilrsoil structure, the temperature near the points of crystallisation and the orientation of the ice crystals. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Freezing point; Oil-polluted soils; Phase transition
1. Volumetric freezing 1.1. Experimental set-up In order to study the structural changes in frozen oil-polluted soils and the crystallisation of the pore water, special laboratory instruments were developed ŽFigs. 1 and 2.. The soil samples are placed in a special cylindrical brass cell ŽFig. 2.. The cylindrical cell has a diameter of 15 mm and a height of 20 mm. The cell has a lid with an opening in the centre for
)
Corresponding author. Present address: University Courses on Svalbard ŽUNIS., P.O. Box 156, N-9171 Longyearbyen, Norway. Fax: q47-7902-3301. E-mail addresses: [email protected], [email protected] ŽA. Instanes.. 1 Fax: q47-2223-0448.
thermocouples. The cell is then placed in a AmicrorefrigeratorB. The working volume of the micro-refrigerator is approximately 120 cm3. The micro-refrigerator is filled with a non-freezing liquid up to 0.6 of the height of the refrigerator. This creates homogenous temperatures in the cell and improves the heat exchange between the cell and the surrounding environment. The cylindrical brass cell is airtight and completely immersed in the liquid. After the sample has reached an isothermal temperature regime, initiation of ice formation is caused by shaking the cell. The temperature inside the sample, in the middle of the sample and along the walls of the cell, is measured with thermocouples. Temperature variations do not exceed "0.28C. Typical temperature change inside the sample can be described by the following three phases ŽFig. 3.. Ži. Super cooling. The temperature in the sample decreases below the temperature of icerwater equilibrium Žwithout any ice crystals forming..
0165-232Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 2 3 2 X Ž 0 1 . 0 0 0 3 0 - 1
184
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
Fig. 3. Sample temperature Ž t . changes versus time Žt ..
Fig. 1. Device for freezing point measurements Ž1—power and rectifier, 2—automatic temperature regulators, 3—micro-refrigerator, 4—micro-ampermeter, 5—thermocouple switcher..
Žii. Ice formation. Ice nucleation is produced by shaking the sample. Crystallisation commences and the temperature abruptly increases to the temperature of icerwater equilibrium.
Žiii. Constant temperature. In the course of time, the temperature will remain constant till unfrozen water content attains the value corresponding to the icerwater equilibrium temperature and until the ice and water distribution become homogenous. After this moment, the change of phase continues in the frozen soil and the temperature decreases. 1.2. Preparation of samples Two types of soils were used in the experimental study of volumetric ice crystallisation in oil-polluted
Fig. 2. Bath for freezing point measurement.
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
185
Fig. 4. Grain size distribution curves.
soils: Ži. quartz sand and Žii. kaolinite clay. The characteristics of the soils are presented in Fig. 4 and Tables1–3: The oil used to pollute the soil was from the oil deposit Zapadnoy in Siberia. The dry soil was moisturised by mixing 30–50 g of soil with distilled water and then, for the oil-polluted samples, a fixed quantity of oil was added to the sample and the mixture was thoroughly mixed. To ensure even distribution of moisture Žmoisture and oil for oil-polluted samples. within the clay samples, the samples were placed in a mixer for 24 h prior to testing. The maximum water content Žwater and oil for oil-polluted samples. for the sand samples did not exceed
saturation and the maximum water content for the clay samples did slightly exceed the plastic limit. Oil concentration is defined as millilitres of oil per grams of dry soil. In order to study the influence of oil pollution on the ice formation in samples, tests were first carried out on clean soil samples without any addition of oil. By comparing the results from the clean samples to the results of the oil-polluted samples, the effect of oil on ice formation can be derived. All experiments were repeated three times with the same soil, water content and oil content. A total of 58 tests were carried out. 1.3. Results
Table 1 Soil properties Soil type
Specific gravity ŽkNrm3 .
Liquid limit, w l Ž%.
Plastic limit, wp Ž%.
Plasticity index, Ip Ž%.
Sand Clay
26.0 26.1
– 45.8
– 34.0
– 11.8
1.3.1. Sand Fig. 5a shows the effect of water content on the freezing point icerwater equilibrium temperature of pure sand without oil pollution for three different water contents: 7.2%, 16% and 25%. It can be observed from the figure that the freezing point
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
186
Table 2 Composition of pore water, anodic Soil type
Dried remainder Ž%.
pH
HCO 3 Ž%.
Ž%. COy2 3
Cly Ž%.
SO4y2 Ž%.
Ž . NOy 2 %
Sand Clay
0.0170 0.0515
7.1 6.9
0.0046 0.0076
– –
0.0009 0.0027
0.0029 0.0195
– 0.0002
Table 3 Composition of pore water, cathodic Soil type
Caq2 Ž%.
Mgq2 Ž%.
Kq Ž%.
Naq Ž%.
Feq3 Ž%.
Ž . NHq 4 %
Other minerals
Sand Clay
0.0005 0.0020
– 0.0012
0.0018 0.0007
0.0014 0.0085
0.0001 0.0001
0.0002 0.0005
0.0124 0.0430
icerwater equilibrium temperature decreases with decreasing water content for the sand. Fig. 5b shows the effect of oil pollution on the freezing point of a sand with three different water contents: 7.2%, 16% and approximately 25%. It can be observed from the figure that for water content of 7.2%, the freezing point Žtemperature of ice formation. decreases with increasing oil concentration. For higher water contents, oil pollution does not show a significant influence on the freezing temperature Žtemperature of ice formation. of sand.
1.3.2. Clay Fig. 6a shows the effect of water content on the freezing point of pure clay without oil pollution for three different water contents: 23%, 34% and 48%. From the figure, the same trend that was observed for sand is evident: The freezing point Žtemperature of ice formation. decreases with decreasing water content. For water contents less than the liquid limit, there is no significant influence of oil pollution on the freezing temperatures of the clay Žsee Fig. 6b.. For water content of 48%, there is a slight reduction
Fig. 5. Freezing temperature Žfreezing point icerwater equilibrium. Ž8C. in sand versus moisture content ŽW%. and oil concentration ŽC, mlrg dry soil..
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
187
Fig. 6. Freezing temperature Žfreezing point icerwater equilibrium. Ž8C. in clay versus moisture content ŽW%. and oil concentration ŽC, mlrg dry soil..
in freezing temperature for oil concentration of 2 mlr30 g Ž0.07 mlrg. and then an increase to above that of pure clay for oil concentration of 4 mlr30 g Ž0.13 mlrg..
2. Unidirectional freezing
soils, we used two couples of the samples. First couple was one sample without oil and another sample with oil concentration of 4–100 g of wet soil Žweak concentration.. The second couple was one sample without oil and another sample with oil concentration of 14–100 g of wet soil Žstrong concentration..
2.1. Experimental set-up The special laboratory device was developed and used for studies of unidirectional freezing of oil-polluted soils ŽFig. 7.. The device is placed into a refrigerator and provides a freezing of soil samples like in open system with warm lower end Ždue to heater. and water supply from below and cooling from upper surface of sample. Some details are clear from Fig. 7. 2.2. Samples Silt from Yamal Peninsula, West Siberia was used in the experimental study of oil-polluted soils. Sample height was 100 mm, diameter was 70 mm. Initial moisture content of the silt was 21.5%, initial bulk density was 2.0 g to 1 cm3. The temperature of upper end of the sample was y5 " 1.08C. The temperature of lower end of the sample was q3 " 1.08C. The oil used to pollute the soil was the same one as mentioned above. To compare clear and polluted
Fig. 7. Device for measurements of ice segregation in freezingr thawing soils Ž1—strain gauge, 2—soil sample, 3—fiberglass wall, 4—foamplastic box, 5—fiberglass filter, 6—thermistor, 7 —flat heater, 8—metal plate, 9—foamplastic cover, 10—paper filter, 11—bath cover, 12—bath..
188
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
Fig. 8. Ice segregation in silt versus oil concentration; Ža. —without oil, Žb. —with oil concentration of 4–100 g of wet soil. ŽA. —sample surface elevation Ž ´ , mm. versus time Žt , days., ŽB. —photo after experiment.
2.3. Results The results are shown in Figs8–10. They are as follows: Ø oil pollution reduces ice segregation and frost heave ŽFigs. 8a and 10.; Ø oil pollution decreases the strength of frozen polluted soils; Ø there are many small Ž; 0.1 mm. vacuum bulbs in oil-polluted samples; Ø there are no significant differences in cryogenic structure of frozen soils with or without oil pollution ŽFigs. 8b and 9..
3. Summary and conclusions The experimental results on volumetric freezing presented in this paper shows that the freezing point Žicerwater equilibrium temperature. is strongly de-
pendent of the sample water content and weakly dependent of the oil concentration. The experiments with unidirectional freezing show the similarity of cryogenic structures of oil-polluted and unpolluted frozen soils if the initial moisture contents are the same. Both groups of experiments—volumetric and unidirectional freezing—give us the basis to form the virtual structure of Aoil –water–ice–soil particlesB mixture ŽFig. 11. as an initial step for model development. Observation of the soil behaviour during the laboratory tests must be used also as basis for a mathematical thermodynamic model. Indeed, the model is necessary to Ža. estimate transport of oil pollution in soils subjected to freeze–thaw cycles and Žb. estimate the possible negative effects of oil pollution on geocryological processes in the zone of transport Žincrease in the depth of seasonal thaw, slope instability.. With assistance of the model, it will be possible to change the oilrsoil structure and estimate the
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
Fig. 9. Photo of ice segregation in silt versus oil concentration Ž1—without oil, 2—with oil concentration of 70 ml to 500 g of wet soil..
189
Fig. 11. Model fabric of Aoil –water–ice–mineral particlesB mixture Ž1—water, 2—ice, 3—mineral particles, 4—oil, 5—gas, 6 —vacuum..
variation in pore pressure caused by annual temperature cycles. If an oilrsoil mixture is subjected to several temperature cycles, segregation is observed and formation of alternate layers of ice and oil inside the frozen oilrsoil mixture. Near summer thaw, it is possible that the pore pressure in the oil layer increases and the effective stress decreases. A consequence of this effect could be instability of oil-polluted slopes. Acknowledgements
Fig. 10. Sample surface elevation Ž ´ . due to ice segregation in silt versus oil concentration Ž1—no oil, 2—oil concentration of 70 g wet soil. and time Žt , days..
The research presented in this paper has been partly funded by the Norwegian Geotechnical Institute ŽNGI. and the Programme for Research and Higher Education, Co-operation Programme for Eastern Europe, administered by the Norwegian Council of Universities and the Research Council of Norway.
Laboratory investigation of the freezing point of oil-polluted soils S.E. Grechishchev a , A. Instanes b,),1, J.B. Sheshin a , A.V. Pavlov a , O.V. Grechishcheva a a
b
Earth Cryosphere Institute, Russian Academy of Sciences, Moscow, Russian Federation Norwegian Geotechnical Institute (NGI), P.O. Box 3930, UlleÕaal Stadion, N-0806 Oslo, Norway Received 4 August 2000; accepted 27 April 2001
Abstract This paper presents the results from an experimental laboratory investigation studying the volumetric and unidirectional freezing of oil-polluted soils. The experiments are a part of a larger laboratory programme where the objective is to understand how oil pollution affects the phase transition velocity and how the phase transition is dependent on the oilrsoil structure, the temperature near the points of crystallisation and the orientation of the ice crystals. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Freezing point; Oil-polluted soils; Phase transition
1. Volumetric freezing 1.1. Experimental set-up In order to study the structural changes in frozen oil-polluted soils and the crystallisation of the pore water, special laboratory instruments were developed ŽFigs. 1 and 2.. The soil samples are placed in a special cylindrical brass cell ŽFig. 2.. The cylindrical cell has a diameter of 15 mm and a height of 20 mm. The cell has a lid with an opening in the centre for
)
Corresponding author. Present address: University Courses on Svalbard ŽUNIS., P.O. Box 156, N-9171 Longyearbyen, Norway. Fax: q47-7902-3301. E-mail addresses: [email protected], [email protected] ŽA. Instanes.. 1 Fax: q47-2223-0448.
thermocouples. The cell is then placed in a AmicrorefrigeratorB. The working volume of the micro-refrigerator is approximately 120 cm3. The micro-refrigerator is filled with a non-freezing liquid up to 0.6 of the height of the refrigerator. This creates homogenous temperatures in the cell and improves the heat exchange between the cell and the surrounding environment. The cylindrical brass cell is airtight and completely immersed in the liquid. After the sample has reached an isothermal temperature regime, initiation of ice formation is caused by shaking the cell. The temperature inside the sample, in the middle of the sample and along the walls of the cell, is measured with thermocouples. Temperature variations do not exceed "0.28C. Typical temperature change inside the sample can be described by the following three phases ŽFig. 3.. Ži. Super cooling. The temperature in the sample decreases below the temperature of icerwater equilibrium Žwithout any ice crystals forming..
0165-232Xr01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 5 - 2 3 2 X Ž 0 1 . 0 0 0 3 0 - 1
184
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
Fig. 3. Sample temperature Ž t . changes versus time Žt ..
Fig. 1. Device for freezing point measurements Ž1—power and rectifier, 2—automatic temperature regulators, 3—micro-refrigerator, 4—micro-ampermeter, 5—thermocouple switcher..
Žii. Ice formation. Ice nucleation is produced by shaking the sample. Crystallisation commences and the temperature abruptly increases to the temperature of icerwater equilibrium.
Žiii. Constant temperature. In the course of time, the temperature will remain constant till unfrozen water content attains the value corresponding to the icerwater equilibrium temperature and until the ice and water distribution become homogenous. After this moment, the change of phase continues in the frozen soil and the temperature decreases. 1.2. Preparation of samples Two types of soils were used in the experimental study of volumetric ice crystallisation in oil-polluted
Fig. 2. Bath for freezing point measurement.
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
185
Fig. 4. Grain size distribution curves.
soils: Ži. quartz sand and Žii. kaolinite clay. The characteristics of the soils are presented in Fig. 4 and Tables1–3: The oil used to pollute the soil was from the oil deposit Zapadnoy in Siberia. The dry soil was moisturised by mixing 30–50 g of soil with distilled water and then, for the oil-polluted samples, a fixed quantity of oil was added to the sample and the mixture was thoroughly mixed. To ensure even distribution of moisture Žmoisture and oil for oil-polluted samples. within the clay samples, the samples were placed in a mixer for 24 h prior to testing. The maximum water content Žwater and oil for oil-polluted samples. for the sand samples did not exceed
saturation and the maximum water content for the clay samples did slightly exceed the plastic limit. Oil concentration is defined as millilitres of oil per grams of dry soil. In order to study the influence of oil pollution on the ice formation in samples, tests were first carried out on clean soil samples without any addition of oil. By comparing the results from the clean samples to the results of the oil-polluted samples, the effect of oil on ice formation can be derived. All experiments were repeated three times with the same soil, water content and oil content. A total of 58 tests were carried out. 1.3. Results
Table 1 Soil properties Soil type
Specific gravity ŽkNrm3 .
Liquid limit, w l Ž%.
Plastic limit, wp Ž%.
Plasticity index, Ip Ž%.
Sand Clay
26.0 26.1
– 45.8
– 34.0
– 11.8
1.3.1. Sand Fig. 5a shows the effect of water content on the freezing point icerwater equilibrium temperature of pure sand without oil pollution for three different water contents: 7.2%, 16% and 25%. It can be observed from the figure that the freezing point
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
186
Table 2 Composition of pore water, anodic Soil type
Dried remainder Ž%.
pH
HCO 3 Ž%.
Ž%. COy2 3
Cly Ž%.
SO4y2 Ž%.
Ž . NOy 2 %
Sand Clay
0.0170 0.0515
7.1 6.9
0.0046 0.0076
– –
0.0009 0.0027
0.0029 0.0195
– 0.0002
Table 3 Composition of pore water, cathodic Soil type
Caq2 Ž%.
Mgq2 Ž%.
Kq Ž%.
Naq Ž%.
Feq3 Ž%.
Ž . NHq 4 %
Other minerals
Sand Clay
0.0005 0.0020
– 0.0012
0.0018 0.0007
0.0014 0.0085
0.0001 0.0001
0.0002 0.0005
0.0124 0.0430
icerwater equilibrium temperature decreases with decreasing water content for the sand. Fig. 5b shows the effect of oil pollution on the freezing point of a sand with three different water contents: 7.2%, 16% and approximately 25%. It can be observed from the figure that for water content of 7.2%, the freezing point Žtemperature of ice formation. decreases with increasing oil concentration. For higher water contents, oil pollution does not show a significant influence on the freezing temperature Žtemperature of ice formation. of sand.
1.3.2. Clay Fig. 6a shows the effect of water content on the freezing point of pure clay without oil pollution for three different water contents: 23%, 34% and 48%. From the figure, the same trend that was observed for sand is evident: The freezing point Žtemperature of ice formation. decreases with decreasing water content. For water contents less than the liquid limit, there is no significant influence of oil pollution on the freezing temperatures of the clay Žsee Fig. 6b.. For water content of 48%, there is a slight reduction
Fig. 5. Freezing temperature Žfreezing point icerwater equilibrium. Ž8C. in sand versus moisture content ŽW%. and oil concentration ŽC, mlrg dry soil..
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
187
Fig. 6. Freezing temperature Žfreezing point icerwater equilibrium. Ž8C. in clay versus moisture content ŽW%. and oil concentration ŽC, mlrg dry soil..
in freezing temperature for oil concentration of 2 mlr30 g Ž0.07 mlrg. and then an increase to above that of pure clay for oil concentration of 4 mlr30 g Ž0.13 mlrg..
2. Unidirectional freezing
soils, we used two couples of the samples. First couple was one sample without oil and another sample with oil concentration of 4–100 g of wet soil Žweak concentration.. The second couple was one sample without oil and another sample with oil concentration of 14–100 g of wet soil Žstrong concentration..
2.1. Experimental set-up The special laboratory device was developed and used for studies of unidirectional freezing of oil-polluted soils ŽFig. 7.. The device is placed into a refrigerator and provides a freezing of soil samples like in open system with warm lower end Ždue to heater. and water supply from below and cooling from upper surface of sample. Some details are clear from Fig. 7. 2.2. Samples Silt from Yamal Peninsula, West Siberia was used in the experimental study of oil-polluted soils. Sample height was 100 mm, diameter was 70 mm. Initial moisture content of the silt was 21.5%, initial bulk density was 2.0 g to 1 cm3. The temperature of upper end of the sample was y5 " 1.08C. The temperature of lower end of the sample was q3 " 1.08C. The oil used to pollute the soil was the same one as mentioned above. To compare clear and polluted
Fig. 7. Device for measurements of ice segregation in freezingr thawing soils Ž1—strain gauge, 2—soil sample, 3—fiberglass wall, 4—foamplastic box, 5—fiberglass filter, 6—thermistor, 7 —flat heater, 8—metal plate, 9—foamplastic cover, 10—paper filter, 11—bath cover, 12—bath..
188
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
Fig. 8. Ice segregation in silt versus oil concentration; Ža. —without oil, Žb. —with oil concentration of 4–100 g of wet soil. ŽA. —sample surface elevation Ž ´ , mm. versus time Žt , days., ŽB. —photo after experiment.
2.3. Results The results are shown in Figs8–10. They are as follows: Ø oil pollution reduces ice segregation and frost heave ŽFigs. 8a and 10.; Ø oil pollution decreases the strength of frozen polluted soils; Ø there are many small Ž; 0.1 mm. vacuum bulbs in oil-polluted samples; Ø there are no significant differences in cryogenic structure of frozen soils with or without oil pollution ŽFigs. 8b and 9..
3. Summary and conclusions The experimental results on volumetric freezing presented in this paper shows that the freezing point Žicerwater equilibrium temperature. is strongly de-
pendent of the sample water content and weakly dependent of the oil concentration. The experiments with unidirectional freezing show the similarity of cryogenic structures of oil-polluted and unpolluted frozen soils if the initial moisture contents are the same. Both groups of experiments—volumetric and unidirectional freezing—give us the basis to form the virtual structure of Aoil –water–ice–soil particlesB mixture ŽFig. 11. as an initial step for model development. Observation of the soil behaviour during the laboratory tests must be used also as basis for a mathematical thermodynamic model. Indeed, the model is necessary to Ža. estimate transport of oil pollution in soils subjected to freeze–thaw cycles and Žb. estimate the possible negative effects of oil pollution on geocryological processes in the zone of transport Žincrease in the depth of seasonal thaw, slope instability.. With assistance of the model, it will be possible to change the oilrsoil structure and estimate the
S.E. GrechishcheÕ et al.r Cold Regions Science and Technology 32 (2001) 183–189
Fig. 9. Photo of ice segregation in silt versus oil concentration Ž1—without oil, 2—with oil concentration of 70 ml to 500 g of wet soil..
189
Fig. 11. Model fabric of Aoil –water–ice–mineral particlesB mixture Ž1—water, 2—ice, 3—mineral particles, 4—oil, 5—gas, 6 —vacuum..
variation in pore pressure caused by annual temperature cycles. If an oilrsoil mixture is subjected to several temperature cycles, segregation is observed and formation of alternate layers of ice and oil inside the frozen oilrsoil mixture. Near summer thaw, it is possible that the pore pressure in the oil layer increases and the effective stress decreases. A consequence of this effect could be instability of oil-polluted slopes. Acknowledgements
Fig. 10. Sample surface elevation Ž ´ . due to ice segregation in silt versus oil concentration Ž1—no oil, 2—oil concentration of 70 g wet soil. and time Žt , days..
The research presented in this paper has been partly funded by the Norwegian Geotechnical Institute ŽNGI. and the Programme for Research and Higher Education, Co-operation Programme for Eastern Europe, administered by the Norwegian Council of Universities and the Research Council of Norway.