Physical Properties of Gypseous Soil after Gypsum Removal using EDTA Solution

Farouk Majeed Muhauwiss

doi:10.25130/tjes.25.2.09

Abstract

The main structural problem in construction on gypseous soils is due to the melting of the gypsum when exposed to water. This may be creating voids in the soil leading to rearrangement of the soil structure and moving the soil particles to more stable positions. This can cause excessive settlement which directly affects superstructures. This study, investigates the influence of gypsum removing on granular soil classification. Four gypsum soil specimens were taken from Al-Qadisiyah district in Tikrit at different depths from the natural ground surface. The depths adopted were 0.75, 1.10, 2.00 and 3.30 m. The corresponding gypsum content was 42.23%, 32.50%, 8.75% and 19.82%, respectively. The EDTA solution was used to disassemble and remove the gypsum particles by washing using distilled water. The results showed that EDTA solution and washing with distilled water was an effective method to remove gypsum from granular soils. Gypsum ratio was reduced to less than 2% in all tested specimens. The percentage of organic matter was not affected, and the specific gravity of the specimens increased between 2% and 12%. The gypsum removal process affected the granular distribution curves of the soil specimens and led to a decrease in the rate of soil grain diameters. In general, classification process of the soil before and after the washing of gypsum from the soil was not affected.

Highlights

Gypseous soils contain high concentrations of salts; some of these salts are soluble in water, called gypsum salts
It was concluded that: (a) the washing process decreases the weight by 20-22%, (b) the values of Atterberg limits reduced due to the washing process, whereas the longitudinal contraction increased, (c) the compressibility index increased whereas the coefficient of consolidation decreased, and (d) the shear strength of soil decreased after gypsum removal from the soil, these results matched with those obtained from AlBusoda [5]
The pH values for all specimens increased by percentages ranged from 0.26 to 0.76, relative to the increasing in gypsum content of specimens. - Effect of gypsum removal on the physical properties: As show in Table 4, all specimens have values for the liquidity limit, whereas the plasticity limit did not obtain for specimens before washing process

Summary

Introduction

Gypseous soils contain high concentrations of salts; some of these salts are soluble in water, called gypsum salts. As a result of the washing process, the voids ratio increased, that leading to an increase in the value of the compression index (cc) compared to untreated soil. It was concluded that: (a) the washing process decreases the weight by 20-22%, (b) the values of Atterberg limits reduced due to the washing process, whereas the longitudinal contraction increased, (c) the compressibility index (cc) increased whereas the coefficient of consolidation (cv) decreased, and (d) the shear strength of soil decreased after gypsum removal from the soil, these results matched with those obtained from AlBusoda [5]. It was noticed that the washing process led to: (a) significant reduction in the soils volume, (b) increasing the compressibility index (cc) and (c), the shear strength of the soil reduced by the washing process, the permeability decreases with time until the decrease reaches a low value after nine hours of washing

Results

Discussion

Conclusion