To validate the coverage of the geotechnical survey, the NEN9997-1 3.2.3 states a minimum distance between CPT's (25 m, 20 m or 15 m) for different variations in the bearing capacity of the group. By doing so, the risk of heterogeneity in the subsurface is checked. In general, with a higher bearing capacity variation between CPT's, a smaller centre-to-centre is allowed.

Because the variation changes over depth and between groups, it affects the optimization of the grouper algorithm. One of the challenges to implement in the rule set was the use of squares to check the distance between the soil investigation points.

The previous blogpost by Johan Zwaan on the PileCore grouper showed that pile lengths can be reduces by optimizing subgroups. By including the centre-to-centre validation in the grouper, the scope intensity of the soil investigation is taken into account. When the check is not valid, either the scope needs to be extended by execution of additional CPT's or a deeper pile tip level is necessary.