The penetration resistance of the ground can be determined in the field, using a penetrometer. One of the range of penetrometers is the mechanical recording penetrograph.

The penetration resistance is a means of determining the ground load-bearing capacity, and the ease with which roots will grow through the ground. Determining the load-bearing capacity is of the greatest importance in the design of foundations for civil engineering works.

The penetrograph is a devise for determination of the penetration resistance of the ground. Continuous measurements can be made with the penetrograph, recording each layer of the ground profile up 0.80 m on the chart. In addition, the penetrograph is self-recording, i.e. during the measurement the resistance is immediately graphically recorded. This greatly reduces the amount of work to be done afterwards. The principle of the measurement is based on the compression of a calibrated spring, while at the same time the chart is moved in proportion to the depth by the drive pulley.

Applications:
The penetrograph is used for:
· general soil science examinations;
· checking the suitability of soils for carrying vehicles or pedestrians;
· checking artificially-made compactions;
· checking load-bearing capacity for the installation of underground tanks;
· the detection of compacted sub-soil layers;
· research into poor growing conditions, including those for trees in urban streets and parks;
· research into the connection between the intensity of rooting of specific crops and the resistance to penetration of the soil
  layers present.

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