Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Distributive type parameters
Reexamination Certificate
1999-04-27
2001-04-10
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Distributive type parameters
C324S637000, C324S690000
Reexamination Certificate
active
06215317
ABSTRACT:
This invention was made with Government support from the Indiana Department of Transportation/Federal Highway Administration. The Government has certain rights in the invention.
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to scientific measurement methods and apparatus and, more particularly, to a method and apparatus for measuring in-place soil density and moisture content.
BACKGROUND OF THE INVENTION
For the past 20 years, time domain reflectometry has been used to measure the volumetric moisture content of soils (volume of moisture per unit volume of soil), mostly in the field of soil science. As shown in
FIG. 1
, these measurements involved the insertion of a probe
10
comprising a central rod
12
and two or more peripheral rods
14
into the soil
16
to be measured. The peripheral rods
14
(which are preferably three in number) are spaced equidistant from the central rod
12
and equidistant from each other. A coaxial transmission line
18
is then coupled to the structure with the center conductor of the coaxial cable
18
coupled to the center rod
12
and the exterior shield (outer conductor) of the coaxial cable
18
coupled to each of the peripheral rods
14
. In this way, the peripheral rods
14
simulate the effects of a continuous outer coaxial shield in the soil
16
, without the requirement of attempting to drive a cylindrical probe into the soil
16
. Time domain reflectometry analysis equipment
20
is then coupled to the coaxial cable
18
, and the reflections of high frequency electrical signals from the soil
16
are measured using the analysis equipment
20
. These reflections will change in predictable ways depending upon the dielectric constant of the soil
16
, which has been found to be strongly correlated with the volumetric moisture content of the soil
16
. Therefore, time domain reflectometry has been established as a viable tool for measuring volumetric moisture content of a soil.
The prior art probes such as those illustrated in
FIG. 1
are intended for permanent installation at a measurement location with periodic measurements being made through the probe
10
over a period of time. Physically, the prior art probes
10
are not rugged enough to withstand repeated insertion into and extraction from hard soils. The prior art robes
10
are not suitable as portable probes to be used for rapid insertion and removal following one-time soil measurement at a variety of locations within a soil field to be measured. There is therefore a need for a probe design which is rugged enough to withstand repeated insertions and extractions from dense soil, thereby facilitating the taking of one-time measurements at multiple locations. The present invention is directed toward meeting this need.
Although time domain reflectometry techniques are useful in measuring volumetric moisture content of soils, they cannot be presently used to measure gravimetric moisture content of soils (weight of moisture per unit weight of soil solids). Many applications in geotechnical engineering require a knowledge of the gravimetric moisture content of soil. In order to convert from the volumetric moisture content measured by time domain reflectometry to the gravimetric moisture content, it is necessary to know the density of the soil. There are several prior art methods for measuring in-place density in moisture content of soils, such as the sand-cone method, the rubber balloon method and the drive tube method. These methods are difficult and time consuming and are usually accompanied by the oven drying method of measuring moisture content in order to measure in-place dry density and moisture content of the soil. The oven drying method of measuring moisture content requires a significant waiting time before measurement results are available. Another method, the nuclear method of measuring in-place soil moisture content and density requires extensive calibration. Moreover, the nuclear method is potentially hazardous because it utilizes radioactive materials. There is therefore a need for a technique to measure in-place gravimetric moisture content and density quickly, precisely, and preferably in a non-destructive manner. The present invention is directed toward meeting this need.
SUMMARY OF THE INVENTION
The present invention relates to a method and apparatus for measuring in-place soil density and moisture content. A cylindrical cell is disclosed which may be used to measure the density and the dielectric constant of a soil sample placed within the cylindrical cell. Also disclosed is a multiple rod probe which is designed to contact spikes driven into the ground to measure the in-place dielectric constant of soil. The multiple rod probe includes adjustable studs which ensure complete contact with the spikes. Both measurements are performed using time domain reflectometry. The present invention develops equations for determining the density of the soil in-place from the measured dielectric constant of the soil in-place and the measured density and dielectric constant of the soil in the cylindrical cell.
In one form of the invention an apparatus for measuring a moisture content of a soil sample is disclosed, comprising a container having a closed first end, an open second end and a substantially cylindrical conductive sidewall defining an interior volume adapted to receive the soil sample; a template having a central opening therethrough that is coaxial with a longitudinal axis of the sidewall, the template adapted to be removable mounted to the open second end; a hand penetrometer having an elongated rod sized to be inserted through the template central opening and into the soil sample such that a hollow shaft is created along the longitudinal axis; and a cap adapted to be removably mounted to the open second end after the hollow shaft has been created and after the template has been removed from the open second end, the cap comprising: a conductive head adapted to contact the sidewall; a conductive central rod; and a first annular non-conductive spacer coupling the conductive head to the conductive central rod; wherein the central rod substantially fills the hollow shaft when the cap is mounted to the open second end; wherein the assembled container, soil sample and cap form a coaxial transmission line wherein the soil sample serves as a dielectric.
In another form of the invention a method of preparing a soil sample for measurement of a moisture content of the soil sample is disclosed, comprising the steps of: (a) providing a container having a closed first end, an open second end and a substantially cylindrical conductive sidewall defining an interior volume adapted to receive the soil sample; (b) removably mounting a template to the open second end, wherein the template has a central opening therethrough that is coaxial with a longitudinal axis of the sidewall; (c) inserting an elongated rod through the template central opening and into the soil sample such that a hollow shaft is created along the longitudinal axis; (d) removing the elongated rod; (e) removing the template; (f) providing a cap, comprising: a conductive head adapted to contact the sidewall; a conductive central rod; and an annular non-conductive spacer coupling the conductive head to the conductive central rod; and (g) mounting the cap to the open second end such that the central rod substantially fills the hollow shaft, wherein the assembled container, soil sample and cap form a coaxial transmission line wherein the soil sample serves as a dielectric.
In another form of the invention an apparatus for measuring moisture content of an in-place soil sample is disclosed, comprising a template having a central hole therethrough and a plurality of peripheral holes therethrough, the plurality of peripheral holes being substantially equidistant from the central hole; a plurality of spikes adapted to be driven through the central and peripheral holes of the template and into the soil sample; and a probe head, comprising: an annular conductive body; a plurality of conductive peripheral
Drnevich Vincent P.
Siddiqui Shafiqul I.
Kerveros J.
Metjahic Safet
Purdue Research Foundation
Woodard Emhardt Naughton Moriarty & McNett
LandOfFree
Method and apparatus for measuring in-place density and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for measuring in-place density and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for measuring in-place density and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2552621