PAVEMENT DESIGNERS AND ASSET MANAGERS - Access is now readily available to subgrade strength parameters throughout New Zealand, initially on State Highways and main centres, but being extended to local roads on a GIS database.

Historic testing (since 1993) and recent non-destructive testing of subgrade properties for pavement preliminary design is now readily available. It includes ongoing weekly updates while the latest laser deflectometer from Measure (the LMD) is carrying out its non-destructive surveys. GIS presentation includes the subgrade stiffness (CBR or resilient modulus) most at 10 or 20m intervals in each lane, but finer granularity is also available. Results from historic TSD and FWD are also being compiled. These parameters are quantified in the meta-data which also record the reliability associated with each parameter (subgrades at shallow depth with stress-softening characteristics have greater reliability than subgrades at considerable depth or where stress hardening subgrades are located).  The relativity of subgrade stiffness along each road is expected to be appropriate for the season of testing (contained in the meta-data) hence the optimum locations for any confirmatory test pits can be readily targeted.  

The subgrade stiffness for many soils can be dependent on the applied stress hence the plotted values are all standardised to a stress of 100 kPa.  Where soft subgrades are surcharged by the weight of thick pavements, some consolidation will occur hence stiffness will tend to be slightly greater than where the pavements are thin. The meta-data quantify the degree of stress sensitivity for each result.

Conversion of LMD Slopes to an FWD Equivalent Deflection Bowl

Preventative Maintenance Index (PMI) - Utilised in predicting potholing before visual surveys

Pavement Structural Maintenance using Laser Deflectometer Data Better Roads at Lesser Cost