# 3.9: Specific Cutting Energy Esp

In the dredging industry, the specific cutting energy is described as:

The amount of energy, that has to be added to a volume unit of soil (e.g. sand, clay or rock) to excavate the soil.

The dimension of the specific cutting energy is: kN/m2 or kPa for sand and clay, while for rock often MN/m2 or MPa is used.

For the case as described above, cutting with a straight blade, the specific cutting energy can be written as:

$\ \mathrm{E}_{\mathrm{sp}}=\frac{\mathrm{P}_{\mathrm{c}}}{\mathrm{Q}_{\mathrm{c}}}=\frac{\mathrm{F}_{\mathrm{h}} \cdot \mathrm{v}_{\mathrm{c}}}{\mathrm{h}_{\mathrm{i}} \cdot \mathrm{w} \cdot \mathrm{v}_{\mathrm{c}}}=\frac{\mathrm{F}_{\mathrm{h}}}{\mathrm{h}_{\mathrm{i}} \cdot \mathrm{w}}\tag{3-78}$

So the specific cutting energy equals the cutting power divided by the cutting volumetric production. Once the specific cutting energy is known and the installed cutting power is known, this can be used to determine the theoretical cutting production according to:

$\ \mathrm{Q}_{\mathrm{c}}=\frac{\mathrm{P}_{\mathrm{c}}}{\mathrm{E}_{\mathrm{s p}}}\tag{3-79}$

It should be noted here that there may be other factors limiting the production, like the hydraulic transport system of a cutter suction dredge, the throughput between the blades of a cutter head or the capacity of the swing winches.