When required to assess the strength of a road or to design improvement / remedial works, your civil engineer needs to know the strength of the existing pavement layers and their condition. When a traditional Plate Bearing Test is not possible due to time or space constraints, the TRL Dynamic Cone Penetrometer (DCP) is an cheap and flexible alternative which can be used in large numbers by a single operative.
The DCP consists of a cone fixed to the bottom of a vertical rod. A 8 kg slide hammer is repeatedly lifted and dropped onto the rod to deliver a standard ‘blow’, to the cone and drive it into the subgrade. The penetration per blow, is recorded as the cone is driven into the ground and then used to calculate the strength of the material through which it is passing. A change in strength of the soil allows layers to be identified and the thickness and strength of each to be determined. These layers are then grouped together into the pavement layers of base, sub-base and subgrade and The strengths of Test layers are calculated by converting the penetration rate (mm per blow) to a California Bearing Ratio (CBR) value.