Mercury (Hg) intrusion is widely used for determining soil pore size distribution (PSD) in the range 7.5-3xl05 nm of diameter. The reliability of the method for air dried samples is well established. For soils at moisture levels commonly found in the field, samples have to be dehydrated in such a way as to preserve the original features of the swollen material. Greene-Kelly (1973) suggested the CO2 critical point (CP) drying as the most suitable method for this purpose. Murray and Quirk (1980) observed that a CP dried red brown soil, with high clay content, collapsed on Hg int1usion,The aim of this study is: to check the finding of Murray and Quirk for a number of clays and soils of different nature and to describe and understand the dynamics of soil pores collapse. The experiments were performed on different soils and pure clays. A number of small clods of about 3-4 cm3 were separated from each sample, conditioned at pF2, and dried by CO2- CP technique. Total volume of samples was measured by kerosene method (Monnier 1973). This same determination was carried out also after the Hg intrusion, at different pressure values, to evaluate the samples collapse, For comparison, PSD of CP dried samples was also determined in the range 7.5 - 60 mn by N2 desorption at 77° K. An estimation of the size distribution, for pores from 0.2 to 300 um, was obtained by scanning electron microscopy (SEM). Therefore the size of pores, not measured also by a reference method, is limited to the range 60 - 200 nm. The pores volume of CP dried samples decreases as Hg intrusion pressure increases. The different classes of pores are affected in relation to their volume and at a value of pressure close to that requested for penetration of Hg. The collapse occurs to a different extent (from 15% in an Alfisol to 90% in a Na-bentonite) depending on the nature of the sample. The comparison between the "apparent" PSD shown by Hg porosimetry, and the effective PSD obtained by N2 desorption or estimated by SEM observations, evidences a very good agreement. It seems reasonable to assume that the Hg PSD measurement could be reliable also in the range of porosity of 60 - 200 run. Ours results show that Hg porosimetry can be an useful tool for characterization of soil microstructure even in swollen CO2-CP dried samples.
Reliability of mercury intrusion for pore size distribution measurement in different soils and clays dehydrated by CO2-critical point dried technique
Sparvoli E;D'Acqui L P;
1992
Abstract
Mercury (Hg) intrusion is widely used for determining soil pore size distribution (PSD) in the range 7.5-3xl05 nm of diameter. The reliability of the method for air dried samples is well established. For soils at moisture levels commonly found in the field, samples have to be dehydrated in such a way as to preserve the original features of the swollen material. Greene-Kelly (1973) suggested the CO2 critical point (CP) drying as the most suitable method for this purpose. Murray and Quirk (1980) observed that a CP dried red brown soil, with high clay content, collapsed on Hg int1usion,The aim of this study is: to check the finding of Murray and Quirk for a number of clays and soils of different nature and to describe and understand the dynamics of soil pores collapse. The experiments were performed on different soils and pure clays. A number of small clods of about 3-4 cm3 were separated from each sample, conditioned at pF2, and dried by CO2- CP technique. Total volume of samples was measured by kerosene method (Monnier 1973). This same determination was carried out also after the Hg intrusion, at different pressure values, to evaluate the samples collapse, For comparison, PSD of CP dried samples was also determined in the range 7.5 - 60 mn by N2 desorption at 77° K. An estimation of the size distribution, for pores from 0.2 to 300 um, was obtained by scanning electron microscopy (SEM). Therefore the size of pores, not measured also by a reference method, is limited to the range 60 - 200 nm. The pores volume of CP dried samples decreases as Hg intrusion pressure increases. The different classes of pores are affected in relation to their volume and at a value of pressure close to that requested for penetration of Hg. The collapse occurs to a different extent (from 15% in an Alfisol to 90% in a Na-bentonite) depending on the nature of the sample. The comparison between the "apparent" PSD shown by Hg porosimetry, and the effective PSD obtained by N2 desorption or estimated by SEM observations, evidences a very good agreement. It seems reasonable to assume that the Hg PSD measurement could be reliable also in the range of porosity of 60 - 200 run. Ours results show that Hg porosimetry can be an useful tool for characterization of soil microstructure even in swollen CO2-CP dried samples.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
