Reply to the discussion by Chapuis and Aubertin on “Influence of relative compaction on the hydraulic conductivity of completely decomposed granite in Hong Kong”Appears in Canadian Geotechnical Journal, 47(6): 704–707.

Abstract

(1) Both the standard Proctor test and the modified Proctor test are used in Hong Kong for compaction of fills. (2) The author agrees with the discussers that the completely decomposed granite (CDG) fill compacted in the mould and soaked for a few days was not fully saturated. The author used the symbol k for the permeability measured under the test condition in the original submission of the paper under discussion, which was later changed to ksat as suggested by one reviewer. It is pointed out that the values of the permeability were obtained from standard falling-head tests following a standard testing procedure. The permeability values measured were valid under the test condition. (3) Completely decomposed granite is widely used and compacted in site formation projects. The initial condition of the CDG fill is normally unsaturated. Even during and after rains, the compacted CDG fill is still unsaturated. The condition of the CDG fill in the field was close to the test condition in the laboratory during our testing. To obtain fully saturated CDG fill, backpressure would have to be applied to the compacted fill at the site (which is not feasible) or the CDG fill would have to be under the water table permanently. However, most CDG fill is above the water table and is in an unsaturated condition. (4) In addition, the relative compaction (RC) is commonly used as an indication of the degree of compaction of the CDG fill in the field in Hong Kong and in many other parts of the world. The correlation established between RC and the permeability measured in the test condition is very useful to engineers to make a quick estimation of the permeability of the CDG fill.