Sand Based Structural Soil (SBSS) is a mix of organic material and a uniformly graded sand. Uniformly graded sand means that the sand grains are of similar size. Rapid gas exchange takes place between these sand grains because of the many small openings. This is the reason for the development of Amsterdam tree soil in the Netherlands (Amsterdam), the first structural soil in the world. The rapid gas diffusion also means rapid drainage, not a problem if the groundwater is within reach of the tree roots as in Amsterdam. The sand grains should have an angular structure allowing the grains to interlock for greater stability.
SBSS is applicable under paving with minimal load, such as a walkway, bicycle path or shopping area without vehicular traffic. To promote rooting of the SBSS, the SBSS should not be maximally compacted. As a result, the SBSS will gradually sink over the course of several years. The standard for this (accepted in the Netherlands) is 3% post-sagging in the first few years. During this period, the tree roots are supposed to have found their way around, because once subsided, the SBSS is difficult for tree roots to penetrate. Consideration should therefore be given to re-surfacing after about 3 years so that the post-settlement can be filled. In order to prevent re-surfacing, SBSS is therefore often used in combination with a sandwich construction. In order to minimalize both the visual damage caused by subsidence in the first few years and later to reduce the visual damage to the pavement caused by increased root thickness.
Benefits of Amsterdam Tree Sand
The difference between sand and gravel is simply the size of the material in question. Sand particles are larger than silt but smaller than gravel. Gravel and sand are both a granular material derived from rock erosion. Depending on which classification you use, the boundary between sand and gravel is or 2mm in most classification protocols. In most, because some protocols use 4,75mm as the line between sand and gravel.
But whichever classification we use, the transition from the less load-bearing SBSS and the considered load-bearing GBSS is not a sharp one. There are different angles to determine this boundary, but all angles give a different value. Practically speaking, I am aware of only 1 product that can fit into both categories hence this product is included in both SBSS and GBSS.
