New Device to Measure Soil, Rock Strength Wins WIPO Award.

The H-Ometer, granted the World Intellectual Property Organization's (WIPO) annual gold medal award for best invention by a national from a developing country, is a new strength-measuring device developed by a group of researchers at the Mountainous Terrain Development Research Centre, Faculty of Engineering, Universiti Putra Malaysia. It has been developed to measure the indirect tensile strength of hard soil and weak rock. The H-Ometer is a cylindrical probe with an expandable flexible membrane, designed to apply a uniform pressure to the walls of a cavity. The probe consists of a steel tube, 12 millimetres in diameter and 74 mm in length, with a hole in the mid-portion of the main body. There are six main components of the H-Ometer, namely, the main body, head connector, special clip, tail, tubing and membrane. The head connector joins the main body to the tubing, which is attached to a control unit. The special clip consists of a ring that secures the membrane to the main body, which represents a major pa rt of the measuring device and has a hole in its mid-portion. The tail, located at the lower end of the probe, fastens the membrane to the probe. The membrane is made from rubber of high elasticity and is between 0.5 mm to 1.0 mm thick. The illustration at right shows the schematic diagram of the H-Ometer.

Generally, when measurements of tensile strength of rock and hard soil are carried out, there is a need to cut samples to a particular shape using the appropriate equipment. This is sometimes difficult to achieve, especially on weak materials such as weak rock and hard soil. It is also time-consuming and costly. To overcome these problems, it is necessary to have a measuring device that is reliable, simple to use, small, light, portable and inexpensive. The H-Ometer is designed to measure indirectly the tensile strength of weak rock and hard soil, and is reliable, simple to use, portable and can even be used in the laboratory. It is mainly for use in civil engineering works, especially in testing weak materials to gauge their strength. The strength parameters obtained from the H-Ometer tests can then be used in the design of the foundation.

As we know, weak materials and hard soil are difficult to test as they break easily, and they always pose problems to design engineers when their strength parameters are being taken. Weak rocks are often characterized by difficulties in obtaining intact and reliable samples for laboratory testing. With these problems in mind, the H-Ometer has been developed to surmount the difficulties encountered by design engineers. It has been designed to be portable so that it can be used in the field. In situ testing will give more accurate results.

In addition, its development is relevant to two major disciplines in engineering:

(1) Mechanical/manufacturing engineering--the designing of the equipment, testing and material selection need mechanical input. In the development of the H-Ometer components, material selection is performed prior to other procedures such as detailed design, design analysis, tool design, manufacture and assembly (see diagram at right). The CAD/CAM application and the finite element study are carried out to determine a suitable form, size and material for the H-Ometer;

(2) Civil engineering-- the H-Ometer is used to gauge the strength properties of the materials. It is mainly used in geotechnical, as well as geological engineering. The new approach, procedures and method for testing weak material, especially weak rock and hard soil, using the H-Ometer, have now been developed.

As there is no need to cut core specimens to a particular shape for testing, the H-Ometer is an attractive and convenient option for measuring the tensile strength of weakly bonded rock and hard soil. A small hole is pre-drilled for the insertion of the H-Ometer. Once inserted, it is inflated using a suitable fluid (e.g. water) until the test specimen fails. Its volume and pressure are monitored at the same time.

Calibration of the H-Ometer is an essential operation required for obtaining the corrected pressure-volume curve. It is calibrated before a test is conducted. This must be carried out correctly so that the true response of the weak rock and hard soil can be determined from the test. As a general rule, the calibration test should always be conducted before the H-Ometer is used.

For testing, the device is installed in the pre-drilled hole of a piece of weak rock or hard soil. It is connected by tubing to the control unit, where pressure s applied and the volume changes between 30 and 60 seconds are recorded. It is important to keep a dose watch on the rate of volume change during testing. An increase in pressure by 50 or 100 kPa is recommended for safety and to achieve a better result. The quality of the test can be judged by inspecting the H-Ometer curve. At left is a typical H-Ometer curve.

The development of the H-Ometer provides an inexpensive, reliable, simple and portable means for indirect measurement of the tensile strength of earthen materials.

Husaini Omar, from the Mountainous Terrain Development Research Centre, Faculty of Engineering, Universiti Putra Malaysia, is the recipient of the WIPO Gold Medal Award for the best invention by a national from a developing country. He wishes to thank the Ministry of Science, Technology and Environment, Malaysia for funding this project.