5
1.1 Average CBR value; calculation per penetration
The penetration depth (70 cm) is divided into 5 customer-specific,
adjustable depths. The CBR value (1 to 5) is measured at these depths.
CBR 1 (first value) and CBR 5 (last / deepest measurement) are the
determining CBR values and saved as individual values per cm. Values
2, 3 and 4 are supplementary information.
1.2 Inluence of the soil moisture content and the
content of the organic contents
The penetration resistance of the soil depends, among others, on the
soil moisture content. The higher the degree of moisture of the soil,
the lower its penetration resistance and the lower its carrying capacity.
In the comparison of penetration resistances that are measured at
dierent points in time (for instance before and ater a particular soil
processing), one must ensure that the soil moisture conditions during the
measurement are comparable. In practice, comparable moisture values
are best ensured in that the penetration resistance is determined at field capacity (pF-2). The soil moisture
content of the measuring point can be defined and saved with the aid of the optional soil moisture sensor
(Art.-No.: 061550).
1.3 Influence of the spatial variability
In the determination of the penetration resistance the spatial variability of the soil must also be taken into
account. The dierences with regard to texture, the structure or content of organic content can dier substantially
on a parcel level. As all these factors determine the penetration resistance, it is first necessary to make repeat
measurements in order to receive a representative value. The number of necessary repeat measurements is
oriented to the desired precision and the natural variability of the soil. The literature (for instance Campbell &
O’Sullivan, 1991) recommends 10 measurements per plot because of the soil formation due to the impression of
the cone. The spacing between the individual measuring points is at least 50 to 60 cm. The Netherlands standard
for electrical penetrations (NEN 5140, 1996) promotes a spacing of at least 100 cm between penetrations.
2. Description
The CBR penetrologger is normally supplied as a complete set for measurements to a depth of up to 70 cm. Such
a set is comprised of the penetrologger itself, suitable CBR cones, conecheck key, probe rods, a depth reference
plate, cable, sotware and a test protocol. Accessories such as soil moisture sensor (061550) are obtainable as
option. All these parts are packed into a carrying bag.
The complete penetrologger (see picture) consists of a housing (a) with GPS antenna (7), a LCD display (8), a key
pad (9), a level (10), and a force absorber (2). The logger has a spray-water protected housing with hand grips
(11). The penetrologger is provided with power by means of batteries.
The cone-shaped point or “Cone” (4) is screwed on below the three-part probe rod (3).
When the cone is forced into the soil, the penetrologger registers the depth up to 70 cm with great precision
by means of an internal ultrasound sensor whereby the depth reference plate (5) comes into use.
The measured penetration resistance, the GPS data and – if the optional soil moisture sensor is connected to the
communication port (6) – the percentage of soil moisture are saved into the internal Logger of the penetrologger.
The average value of the CBR values and the standard deviation can be calculated automatically. If the cable
(13) is connected to the communication connection port (6) and to the PC, then data can be exchanged between
the Logger and the PC. The accompanying sotware permits the reading out of the data to the PC, the graphic
and numerical representation and the printing out of the data.
The conecheck key (12) is used for checking the wear on the cones. The cone must be replaced when it fits
through the hole.
Measuring soil moisture
