Experimental Determination of TDR Calibration Relationship for Pyroclastic Ashes of Campania (Italy)

Time domain reflectometry (TDR) is one of the most widely used techniques for indirect determination of soil volumetric water content (θ). TDR measures the relative dielectric constant (εr) which, in a three-phase system like the soil, depends on water, air, and solid matrix dielectric constants. Since dielectric constant of water is much larger than the other two, εr of bulk soil mainly depends on water content. In many cases, the application of TDR requires a specific calibration of the relationship θ(εr) to get quantitatively accurate estimates of soil water content. In fact, the relationship θ(εr) is influenced by various soil properties, such as clay content, organic matter content, bulk density, and aggregation. Numerous studies have shown that pyroclastic soils often exhibit a peculiar dielectric behavior. In Campania (Southern Italy) wide mountainous areas are covered by layered pyroclastic deposits of ashes (loamy sands) and pumices (sandy gravels), often involved in the triggering of landslides induced by rainwater infiltration. Reliable field measurements of water content of such soils are therefore important for the assessment of landslide risk. Hence, in this paper, the θ(εr) relationship has been experimentally determined on samples of typical pyroclastic soil of Campania, collected around Sarno, reconstituted with different porosities. The aim of the study is to identify specific calibration relationships for such soils based not only on empirical approaches. In this respect, a three-phase dielectric mixing model with a variable exponent is introduced, and the variable value of the exponent is related to the different dielectric properties of bond and free water within the soil pores.

[1]  Marco Valerio Nicotera,et al.  Unsaturated soil mechanics in rainfall-induced flow landslides , 2013 .

[2]  Andrew P. Whitmore,et al.  Effect of aggregate size on the water content estimated with time domain reflectance [TDR] , 2004 .

[3]  Magnus Persson,et al.  Using neural networks for calibration of time-domain reflectometry measurements , 2001 .

[4]  Michel Vauclin,et al.  Theoretical evidence for `Lichtenecker's mixture formulae' based on the effective medium theory , 1998 .

[5]  A. P. Annan,et al.  Electromagnetic determination of soil water content: Measurements in coaxial transmission lines , 1980 .

[6]  L. Olivares,et al.  Steep-slope monitoring in unsaturated pyroclastic soils , 2012 .

[7]  Brent Clothier,et al.  A Dielectric–Water Content Relationship for Sandy Volcanic Soils in New Zealand , 1999 .

[8]  Domenico Guida,et al.  Typical source areas of May 1998 flow-like mass movements in the Campania region, Southern Italy , 2008 .

[9]  G. Rolandi,et al.  Tectonic controls on the genesis of ignimbrites from the Campanian Volcanic Zone, southern Italy , 2003 .

[10]  R. Greco,et al.  Moisture Measurements in Masonry Materials by Time Domain Reflectometry , 2011 .

[11]  S. Dasberg,et al.  Time domain reflectometry field measurements of soil water content and electrical conductivity , 1985 .

[12]  C. Dirksen,et al.  IMPROVED CALIBRATION OF TIME DOMAIN REFLECTOMETRY SOIL WATER CONTENT MEASUREMENTS , 1993 .

[13]  L. Olivares,et al.  Shallow flowslides triggered by intense rainfalls on natural slopes covered by loose unsaturated pyroclastic soils , 2003 .

[14]  R. Greco.  Soil water content inverse profiling from single TDR waveforms , 2006 .

[15]  Domenico Calcaterra,et al.  Andic soils and flow‐like landslides: Cause–effect evidence from Italy , 2018, Land Degradation & Development.

[16]  Pierre Todoroff,et al.  Comparison of empirical and partly deterministic methods of time domain reflectometry calibration, based on a study of two tropical soils , 1998 .

[17]  F. Ulaby,et al.  Microwave Dielectric Behavior of Wet Soil-Part II: Dielectric Mixing Models , 1985, IEEE Transactions on Geoscience and Remote Sensing.

[18]  Yakov A. Pachepsky,et al.  Performance of TDR calibration models as affected by soil texture , 1999 .

[19]  A. R. Socorro,et al.  Time domain reflectometry models as a tool to understand the dielectric response of volcanic soils , 2003 .

[20]  D. Or,et al.  Time domain reflectometry measurement principles and applications , 2002 .

[21]  R. Plagge,et al.  Empirical evaluation of the relationship between soil dielectric constant and volumetric water conte , 1992 .

[22]  Vijay P. Singh,et al.  Momentum of flow in soils assessed with TDR-moisture readings , 1997 .

[23]  F. Guadagno,et al.  Preliminary report on the landslides of 5 May 1998, Campania, southern Italy , 1998 .

[24]  J. E. Campbell,et al.  Dielectric properties and influence of conductivity in soils at one to fifty megahertz , 1990 .

[25]  Jan W. Hopmans,et al.  Time Domain Reflectometry Calibration for Uniformly and Nonuniformly Wetted Sandy and Clayey Loam Soils , 1992 .

[26]  Christian Roth,et al.  Improving the calibration of dielectric TDR soil moisture determination taking into account the solid soil , 1996 .

[27]  R. Greco,et al.  Use of TDR to Compare Rising Damp in Three Tuff Walls Made with Different Mortars , 2017 .

[28]  R. De Mascellis,et al.  Landslide processes and Andosols: the case study of the Campania region, Italy , 2007 .

[29]  Roberto Greco,et al.  Soil water content and suction monitoring in model slopes for shallow flowslides early warning applications , 2010 .

[30]  O. H. Jacobsen,et al.  Comparison of TDR calibration functions for soil water determination , 1995 .

[31]  S. Dautrebande,et al.  A method of measuring soil moisture by time-domain reflectometry , 1986 .

[32]  S. Jones,et al.  A Review of Advances in Dielectric and Electrical Conductivity Measurement in Soils Using Time Domain Reflectometry , 2003 .

[33]  S. Dasberg,et al.  THE EFFECT OF SALINE IRRIGATION WATER ON SHAMOUTI ORANGES , 1988 .

[34]  G. Renella,et al.  Impact of river overflowing on trace element contamination of volcanic soils in south Italy: part I. Trace element speciation in relation to soil properties. , 2006, Environmental pollution.

[35]  Marcel G. Schaap,et al.  TDR calibration of organic forest floor media , 1997 .

[36]  Michael H. Young,et al.  Rapid Laboratory Calibration of Time Domain Reflectometry Using Upward Infiltration , 1997 .

[37]  G. Topp,et al.  Measurement of Soil Water Content using Time‐domain Reflectrometry (TDR): A Field Evaluation , 1985 .

[38]  Michael Keller,et al.  Calibration of time domain reflectometry technique using undisturbed soil samples from humid tropical soils of volcanic origin , 1997 .

[39]  T. Heimovaara.  Design of Triple‐Wire Time Domain Reflectometry Probes in Practice and Theory , 1993 .

[40]  A. Santo,et al.  Debris slides rapid earth flows in the carbonate massifs of the Campania region (Southern Italy): morphological and morphometric data for evaluating triggering susceptibility , 2005 .

[41]  Carlos M. Regalado,et al.  A physical interpretation of logarithmic TDR calibration equations of volcanic soils and their solid fraction permittivity based on Lichtenecker's mixing formulae , 2004 .

[42]  R. Schulin,et al.  Calibration of time domain reflectometry for water content measurement using a composite dielectric approach , 1990 .