Abstract
The unified soil classification system (USCS) first proposed by Casagrande and subsequently developed by the Army Corps of Engineers. It widely used in many building codes and books. An-Najaf city is the most important city in Iraq due to its religious and spiritual value in the Muslim world, so it is fast expanding and continuous developing city in Iraq. The data from 464 boreholes in the study area for depths of 0–26 m have been used. 13 Soil samples were collected from each borehole with 13 depths level (0–26) m with 2 m intervals. The USCS was applied to the soil samples from 13 depth levels borehole. This research aims to create a geodatabase for soil properties for An-Najaf. The ArcGIS 10.5 software was used to interpolate the spatial data to produce 33 geotechnical maps for fine soil, coarse soil and USCS for 13 depth levels. For numerical soil data, Ordinary Kriging has been used for interpolation mapping of Fine and Coarse percentage data for each depth. For non-numerical (nominal) soil data (USCS class), the Indicator Kriging method is used. The results show that the coarse soil occupied 85–95% for depth 0–16 m and consist of (SP, SP-SM, SM) while fine soil occupied 5–15% consisting of (OL, CH, ML) subsequently, this soil when compacted has a permeability of pervious to semi impervious, good shearing strength, low to very low compressibility and acceptable workability as a construction material. The results also show that after 16 m depths until 26 m, the fine soil percentage increased to 40% with a coarse soil percentage of 60%, indicating changes in soil characteristics as the permeability became semi-pervious to impervious, fair shearing strength, medium compressibility and fair workability as a construction material. The study results will provide help and saving time, efforts and money in preliminary engineering designs.
Highlights
Classifying soil is a way to arrange it into groups or subgroups to describe its characteristics concisely (Das 2013) (Das and Sobhan 2013; Das 2013)
The results show that the coarse soil occupied 85–95% for depth 0–16 m and consist of (SP, SP-SM, SM) while fine soil occupied 5–15% consisting of (OL, CH, ML) subsequently, this soil when compacted has a permeability of pervious to semi impervious, good shearing strength, low to very low compressibility and acceptable workability as a construction material
The results show that after 16 m depths until 26 m, the fine soil percentage increased to 40% with a coarse soil
Summary
Classifying soil is a way to arrange it into groups or subgroups to describe its characteristics concisely (Das 2013) (Das and Sobhan 2013; Das 2013). It is essential to clarify the soil classes before designing and constructing any project as the engineering characteristics of soil (stiffness, permeability, and strength) are influenced by the soil particles’ shape, size, arrangement and microscopic structure (Budhu 2015). Fine soils are determined by the percentage of the soil mass passing through a 0.075 mm sieve, while granular soils are the soil mass that retained in a 0.075 mm sieve, including sand, gravel, cobbles, and boulders. If the percentage of fine soil passes through the sieve at a predefined proportion, usually 50% (but this could be less according to the soil classification system used), the soil is considered as Fine-grained. Soils are subclassified according to their consistency (Reale et al 2018)
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