From this guide, you will know more about the fundamentals of cone penetrometer test soundings and insitu testing in Australia.
Cone penetration testing Sydney soundings can be effective in the characterisation of the site, especially with discontinuous lenses or stratigraphic horizons. Today, most of the commercially available cone penetrometer test rigs operate piezocone penetrometers and electronic friction cones, whose testing procedures are explained in this article.
Rate of advance and shape of cone tip
The standardised cone penetrometer test involves pushing a cone through the underlying ground at a rate of 1cm/sec to 2 cm/sec. The cone tip is a 60 degree cone.
Sleeve versus tip resistance
Tip and sleeve resistance instruments yield a computerised log of sleeve and resistance of the tip, the ratio between these two devices, induced pore pressure behind the cone tip, lithologic interpretation of each two-centimetre interval and pore pressure ratio.
CPT rigs employ one-meter-long rods. They can penetrate consolidated soils and colluvium but have been employed to characterise weathered quaternary. They have also been used to characterise tertiary age strata. Unweathered or cemented horizons, such as conglomerate, sandstone or massive volcanic rock can also impede the advancement of the probe.
The cone is capable of delineating even the smallest low strength horizons, missed in traditional subsurface investigation projects.
The resistance of the tip
The resistance of the tip is measured by the load cells located behind tapered cone. The resistance of the tip is related to the undrained shear strength of the cohesive material, while the sleeve friction is closely related to the friction of the horizon being penetrated. During insitu testing, the tapered head of the cone forces failure of the soil ahead of the tip and the resistance is usually measured with an embedded load cell in millivolts that is converted to load.
The cone penetrometer’s tip senses out ahead of itself as it leads to a local bearing failure of soil it passes through. The resistance of the tip recorded by the equipment is averaged across the tip influence zone. This means that it is important to proceed with caution when evaluating insitu strength.
Sleeve or local friction
The local friction is often measured by the tension load cells that are embedded in the testing sleeve about four inches behind the tip. They are used to measure the average skin friction as the probe is pushed through the soil. If the cohesive soils are partially saturated, it means they can exert appreciable skin friction and negate the interpretive program.
The friction ratio
The friction ratio is recorded in percentage. This is the ratio of the skin friction divided by the resistance of the tip. It is used to classify the soil by its reaction to the cone. High ratios indicate clayey materials while low ratios indicate sandy materials. Typical friction of the skin to tip friction ratios are one percent to ten percent. The ratio rarely exceeds 15 percent.
Pore pressure
During cone penetration testing Sydney, when using the cone equipment to penetrate dense layers such as dense sand, cemented siltstone, or conglomerate, a piezo filter element can get compressed to induce high pore pressures. However, the plastic filters don’t exhibit this tendency although they become brittle with time and they may need replacement periodically, IGS uses a new filter for every test.
