PT  - JOURNAL ARTICLE
AU  - Jason Grabosky
AU  - Nina Bassuk
TI  - Testing of Structural Urban Tree Soil Materials for use Under Pavement to Increase Street Tree Rooting Volumes
AID  - 10.48044/jauf.1996.039
DP  - 1996 Nov 01
TA  - Arboriculture & Urban Forestry (AUF)
PG  - 255--263
VI  - 22
IP  - 6
4099  - http://auf.isa-arbor.com/content/22/6/255.short
4100  - http://auf.isa-arbor.com/content/22/6/255.full
SO  - JOA1996 Nov 01; 22
AB  - Quercus robur seedlings were grown in compacted stone-soil mixes known to meet engineering standards for pavement base compaction and strength. Root penetration into these materials was greatly increased in comparison to an equally compacted clay loam, which was also a component of the test material. Oak root penetration in the clay loam decreased 50%, from 6 to 3 g dry root weight, as the bulk density increased from 1.24 to 1.55 Mg/m3. Severe root impedance was observed when clay loam bulk densities exceeded 1.5 Mg/m3 (90% standard AASHTO peak density),a situation produced after 20% of the standard compaction effort was imposed on the soil profile. At the standard AASHTO peak density for the clay loam (1.67 Mg/m3), which would be the norm in a sidewalk installation, root growth was entirely stopped. In contrast, structured stone-soil mixes compacted to 100% of their respective standard AASHTO peak densities (between 1.85 and 2.07 Mg/m3) did not restrict root penetration with mean root dry weights between 4 and 6 g and demonstrated satisfactory bearing strength (California bearing ratios between 40 and 80).