Modyfication of the grain size distribution and geotechnical properties of the non-cohesive soil by the addition of the silt

Agnieszka Lal

Abstract

Frequent issue in the practice of soil engineering is the fi ll soil compactibility. The uniformity coeffi cient Cu of the Sand, Sand-Gravel and Gravel, that are the most common fi ll soil, is relatively low and usually is in the range of 2.5 – 4.0. These values allow to describe Sand, Sand-Gravel and Gravel as uniformly graded. The aim of the paper was to determine the impact of modifi cation of the grain size distribution of the non-cohesive soil – Medium Sand (MSa) on its compactibility. The loess silt, sampled in the territory of the Lublin city was used to modifi ed the Sand particle size distribution. Loess silt cover the considerable area of the Lublin, frequently in the surface zone. This ensures that loess silt could be reckoned as the easily accessible material. Laboratory tests were conducted on prepared samples of three kinds of soils – Medium Sand, Medium Sand combined with loess silt in the volume proportion of 1:1 and Medium Sand combined with loess silt in the volume proportion of 2:1. There were sieve and hydrometer analysis performed to quantify the percent fi ner by weight of grain size of prepared samples of the soils. As the result of grain size analysis particle size distribution curves were obtained. Estimated effective size D10 and D60 were used to determine the uniformity coeffi cient. The value of coeffi cient Cu for the Medium Sand was equal to 1.71 and it rose up to 21.8 (in case of Medium Sand combined with loess silt in the volume proportion of 1:1) and 13.3 (for the Medium Sand combined with loess silt in the volume proportion of 2:1). Obtained values suggest, that modifi cation of Sand grain size distribution with use of loess silt allows to classify received probes as soils with high compactibility. In order to prove this thesis Proctor tests were conducted. There were the same three kinds of the soil tested according to procedure I. Results indicate that Medium Sand with natural grain size distribution reached the maximum dry density of 1.751 g/cm3 at the optimum water content of 11.96 %. The maximum dry density of Medium Sand combined with loess silt in the volume proportion of 2:1 and 1:1 reached accordingly 2.079 and 2.076 g/cm3 at the optimum water content of about 7%. During Proctor test, there were plasticity of Medium Sand combined with loess silt in the volume proportion of 1:1 remarked, for the samples of water content greater than 14.25%. Increased plasticity prevents compaction of the examined soil with humidity above 14.25%, due to the deformations and cohesion. As the results of conducted laboratory tests, there were ascertained that modifi cation of the grain size distribution of Medium Sand with loess silt with volume proportion of 2:1 allows to reached the maximum compactibility. Therefore, combination of the Sand and relatively easily accessible loess could be used in soil engineering as the fi ll soil.