Handheld CPT penetrometers are primarily used to determine the bearing capacity of the upper 2 – 3 meters of the soil. Using this device the penetration resistance is determined; this is representative for the bearing capacity of the soil. Since it is an easy to use measuring tool and it allows for quick and accurate assessment of soil conditions, it is used for various purposes, e.g.:
Suitability of Roads for Heavy Vehicles
Construction works depend on the use of heavy machinery, like dozers, excavators, crawler cranes, hydraulic cranes, and alike. These machines generate high ground pressures, whilst the access roads to the job sites and the job site itself are in general not paved. The risk exists that the bearing capacity of the soil is not sufficient and a machine subsides or even tips over. The handheld CPT penetrometer has proved to be an indispensable tool for assessing the roads and job site terrains.
Geotechnical Soil Investigation
Since the handheld CPT penetrometer is a useful tool to measure soil compaction and the bearing capacity of the ground, it can also be used for basic advise for the foundations of roads, small buildings, pedestrian bridges, and alike.
The agricultural industry could benefit from information provided by a hand-held CPT penetrometer, such as identification of areas of high compaction, plow pans, and clay zones to help determine appropriate irrigation, fertilization, and cultivation practices. Agronomists can use the penetrometer for the research of the (expected) growing circumstances of plants in the soil.
In farming the handheld CPT penetrometer is used to determine the settings for farming machinery.
The horticulture is an industry that is developing rapidly and becomes more and more automated. This high degree of automation is essential, since todays green-houses can be as large as several hectares. The transport inside the green-houses is primarily done by means of fully automated tube-rail-systems. Because of the dynamic forces to which this system is exposed and the fact that it is based on soft and during the growing process constantly changing mould, it is of paramount importance to have exact data available of the soil conditions. This to avoid any instability or even tipping over of the carts running on the tube-rail-systems.
Assessing the impact of logging operations on forest soil compaction is important. The hand-held CPT penetrometer helps soil scientists and contracting officers verify that specifications on soil compaction limits are being followed.
In civil engineering the hand-held CPT penetrometer can help pinpoint compaction problems that might require more extensive soil testing. It’s also useful for looking at variability or changes in soil strength caused by equipment, vehicles, and foot traffic.
Forest tree nurseries en landscape gardeners could benefit also from the hand-held CPT penetrometer. Soil compaction begins to inhibit the root growth of most plants when the soil’s strength is about 1,500 kPa. The roots of many plants quit growing when the soil’s strength reaches about 2,500 kPa. A hand-held penetrometer can help identify these areas fast and easy and help to enhance the (expected) growing circumstances of plants in the soil.
In cases where the soil was compacted artificially, the hand-held CPT penetrometer has proved to be an excellent tool to evaluate how well the compaction of the soil was done and at what rate.
To use, apply constant pressure on the built-in hand grips to push the sounding rods and conical tips perpendicularly into the ground. Resistance of the soil is determined by dividing the reading by the surface area of the selected conical tip. A drag pointer records the highest value measured. Avoid jerking pushes, since they yield values which are too high and which do not represent the soil.
The resistance measured by the cone can be read from the pressure gauge as indicated by the black pointer. The maximum resistance recorded during the entire test is indicated by the drag pointer. The resistance to penetration (kPa/cm²) of the soil can now be determined by dividing the recorded value by the surface of the conical tip. The value of the resistance to penetration to be expected determines the surface of the conical tip to be used. For high values a small conical tip is to be used and for low values a larger conical tip is to be applied. The larger the conical tip the more accurately the value of the resistance to penetration can be determined.
In order to acquire reliable data the sounding rods and conical tip are to be pushed into the ground at a consistent speed. An operator’s field notes are helpful when data require editing because of unusual conditions, such as very rocky soils, large roots, voids, buried organic materials, and very dry conditions. Conduct multiple tests at several locations in a given area to better understand variations in soil conditions and reduce the effects of operator inconsistency.
The handheld CPT penetrometer composes of:
- A measuring body with 2 push handles and an accurate hydraulic reading dial (range up to 10,000 kN/m2 (= 10,000 kPa), accuracy ± 8% of FS) equipped with drag pointer
- 3 stainless steel sounding rods (D = 15 mm, L = 450 mm)
- 1 stainless steel sounding rods (D = 10 mm, L = 450 mm) with a 1 cm² conical tip
- 3 conical tips, i.e. a 2 cm² (D = 16 mm), a 4 cm² (D = 22 mm), and a 6 cm² (D = 28 mm) tip
- 3 open ended spanners
- Cone wear gauge to check the dimensions of the conical tips
- Compact aluminium carrying case
- Measurement data conversion chart
- Calibration certificate and instruction manual
- Optionally extra sounding rods for testing to a depth of max. 3 meter and a hand operated auger