Patent Application
20070277598
The application of the hammering force causes the cone-shaped point of the DCP rod to penetrate into the soil at a controlled rate that is correlated with the strength of the soil. The depth of penetration is determined by noting the decrease in distance between the initial height of the rod and its lower position as it descends into the ground. This distance is measured, for example, by a time-of-flight laser rangefinder (emitting a laser beam) that is mounted with the electronic module on the side of the percussive module and pointed at a suitable reflective surface placed on the ground adjacent to the location of penetration. Measurements from the laser rangefinder are transmitted by wire, or wirelessly, to a portable computer, where a software algorithm can compute the rate of penetration and in turn the soil strength profile. Control software will adjust the hammering rate to a level appropriate for the strength of the soil.
In the percussive module, the hammering force is generated by electrically driving a small mass at a controlled rate. For example, the mass can be of approximately 100 gm weight, and the rate of impulse driving can be of 5-50 Hz. The faster the rate of hammering, the more impact applied, so higher rates are used for stronger soils and lower rates for weaker soils. Thus, the rod can be driven into the soil with high frequency blows (in the range of 50 Hz) with low impulse energy (0.5-10 J).
The control software is adapted to read the depth data in real time and adjust the impulse of the hammering to keep the rate of penetration within a desired range, or to keep the rate of penetration constant. The software can consequently calculate, in real time, the penetration rate in blows per minute and compute the strength of the formation in California Bearing Ratio or some engineering property, such as soil resistance.
The automatically acquired depth measurements greatly reduce the amount of operator error and also speed up the determination of the soil's strength profile. The real-time penetration data are also used to instantly adjust the hammering energy to a level appropriate for the soil being tested, unlike the prior art, which requires a judgment determination and then several minutes to change from one hammer to another. Furthermore, the hammering energy can be made very small, to provide a more accurate correlation to CBR in weak soils than the prior types of DCP or ADCP hammers. The use of very small hammer impulses, which are controlled so as to maintain a constant rate of penetration, also confers on the invention the ability to measure actual engineering properties of the soil.
This invention has advantages over the prior types of penetrometers in that it is much easier to operate, requiring the user only to orient the unit upright such that the rod remains vertical, turn the unit on, and then maintain a light pressure to keep the unit vertical. Its operation does not require the user to have superior physical strength and does not result in user fatigue. Additionally, the risk of injury to the user is much lower because the hammering mechanism is not exposed. The improved penetrometer only employs three easily assembled components. It is lightweight and portable enough to be carried by a single person, even to remote locations. It can be operated by a single person, while the prior art devices can require two or more. Use of the improved penetrometer, including set up, operation, and break down, takes significantly less time than the prior art devices. Being an automated device, the action of hammering the rod into the ground is subject to automated control, resulting in more consistent soil strength data and also less time for each individual test.
Other modifications and variations may be made in accordance with the circumstances of field use for which the penetrometer is to be employed. The control software may be encoded in a simplified form for rugged use, e.g., as a stored look-up table in read-only memory ROM, that is embedded with the electronic (control) module rather than operated on a separate computer. This would be advantageous for highly mobile use by a single operator over far-ranging distances.
The hammer mechanism can be powered pneumatically or by internal combustion, rather than battery-powered. A heavier hammer, in the range of 500-1000 gm, can be made to impact with higher energy, but at a slower rate, e.g., 1-5 Hz. This embodiment is referred to as an Accelerated Cone Penetrometer (ACP). The rod that is driven into the soil may be made of other materials, for example, titanium alloy or aluminum alloy, and other penetration point configurations may be used.
The method of measuring the depth of penetration can be with any other non-contact method, such as an ultrasonic rangefinder, or it can be mechanical, making use of a wheel traveling along a guided track, or a string that is anchored to the ground and is retracted by a string as penetration proceeds.
Instead of keeping impact energy or impulse the same and controlling the rate of penetration, an alternative approach is to keep the penetration rate constant by changing the impulse or impact energy. In this method, the impact energy or impulse could be correlated to either an engineering soil property or a physical soil property.
Instead of keeping the rate of penetration the same (or within the certain range) by controlling the impact energy or impulse, an alternative approach is to keep the impact energy or impulse the same and record the rate of penetration (as is done with the DCP and ADCP). In this method, the penetration rate could be correlated to either an engineering soil property or a physical soil property.
While certain embodiments and improvements have been described above, it is understood that many other modifications and variations thereto may be devised given the above description of the principles of the invention. It is intended that all such modifications and variations be considered as within the spirit and scope of this invention, as defined in the following claims.
This U.S. patent application claims the priority of U.S. Provisional Application No. 60/804076 filed on Jun. 6, 2006, entitled “Percussive Cone Penetrometer and Accelerated Cone Penetrometer”, of the same inventors.
The subject matter herein was developed for ERDC as part of the “Rapid In-Situ Soil Characterisation System”, funded through the Department of Defense SBIR Phase I program. The U.S. Government retains certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60804076 | Jun 2006 | US |
