CBR testing of subsoil using Dynamic Cone Penetrometer
The installation of artificial pitches and floodlight columns usually requires CBR (California Bearing Ratio) testing of subsoils to confirm its stability under load. Suitable data may be obtained using our Dynamic Cone Penetrometer. We have found that a 'contour' map of the area of the pitch showing the varying soil strengths gives the best indication of whether and where soil reinforcement may by necessary.
More usually an issue for artificial sports surface developments, subsidence occurring within the subsoil once the construction has been put in place can be quite disastrous. This is a distinct possibility in many types of subsoil formation material. By mapping the strength of the subsoil surface before the rest of the construction is put in place those areas, if any, where an appropriate form of subsoil reinforcement is necessary can be identified. The consequences of subsidence can therefore be avoided.
The conventional unit of subsoil strength is the California Bearing Ratio (CBR) which is a percentage. Values of 5 % or more are normally to be preferred, for example, for a 3G football or artificial hockey pitch. Around 15 or 20 measurements are normally sufficient to determine the extent of variations in subsoil strength over the area of such a pitch. This takes around a day to collect.
Subsidence can also occur on natural turf constructions but this can often be put right by simply incorporating more topsoil and re-seeding. On particularly high value projects, however, for example a stadium pitch, consideration may also need to be given to subsoil strength. We have been using our DCP to try and identify tolerances for subsoil strength for natural turf which may be incorporated into design specifications where appropriate.
Discovering voids within a chalk subsoil after construction. Knowledge of the situation beforehand would have been useful!