Use of geophysical methods to assess the quality of compaction of fill soils

Abstract

Using the procedure of backfill and replacement of soils for the construction of water-development works and the beds of special-purpose structures in the Trans-polar region, quality control over their compaction is an inherent part of the overall production process of the construction. The potential for internal freezing of soil, the formation of ice lenses during the winter and their thawing in the summer, and the effect of groundwater and marine tides render the problem of localization of zones of loosenening of the compacted layer rather urgent during construction. Currently accepted direct point methods of evaluating the strength characteristics of soils by the extraction of samples, and boreholes do not provide desirable information on the distribution of density characteristics within the soil stratum and over the entire fill area. When the layer of fill is more than 2–3m thick, use of on-going methods of surface seismic-prospecting tomography based on the interrelation between the velocity of longitudinal seismic waves and compaction of the soil is effective [1]. Here, however, we are speaking of relative estimates of compaction in a monitoring regime that ensures undisturbed monitoring of significant areas and depths of inspection. In this statement, it is methodically necessary to solve two basic problems: establishment of the interrelation between the velocity of longitudinal seismic waves and the compaction of the soil, and the influence exerted by saturation of the soils on the results of estimates of the quality of their compaction. According to the recommendations set forth in the Construction Rules and Regulations [2], the coefficient (degree) of compaction m — the ratio of the density of the dry soil nid of the rock mass to the maximum density of the dry soil nd max, which can be attained during compaction, should be used for quality control of layer-by-layer placement of a rock mass, which is a mixture of rubbly stony soil and crushed rock in various proportions. To avoid incomplete compaction, the control scheme adopted should satisfy the condition m mdes, (1)