A serious problem, however, yet lies in the early identification of dispersive soils . In spite of all the knowledge obtained over the years, there is still no fast, simple and dependable mean of conclusively recognizing dispersive soils. Many methods have been suggested including the pinhole, double hydrometer, crumb and chemical tests, individually or in group. These, but, have not always been totally credible and it looks like that the cause sets in the factual testing procedures. The standard testing procedures for the Soil Conservation Service double hydrometer test, the pinhole test, crumb test and chemical analyses have lately been studied and problems/abnormalities identified. Although no discussion concerning these anomalies has been discovered in the literature, the recent testing proposes that many of these deficiencies may have been looked out during past routine investigations. This paper summarizes a proportional study including the testing of three specimen utilizing one standard laboratory test, namely the SCS double hydrometer test and discusses some potential means of conquering the problems identified.
The other tests have been discussed separately. SCS double hydrometer or dispersion soil test has been identified as one of the most suitable tests for classifying dispersive soils. The test assesses the dispersibility of a soil by measuring the natural propensity of the clay fraction to go into annotate in water. The procedure involves the estimation of the percentage of particles in the soil that are finer than 0.005 mm utilizing the standard hydrometer test. A parallel test is also carried out, in which no chemical dispersant is added and the solution is not mechanically excited. The quantity of particles finer than 0.005 mm in the parallel test is explicit as a percentage of this fraction determined in the standard test, which is defined as the dispersion ratio or dispersivity of the soil . Dispersion ratios greater than 50% are observed extremely dispersive, between 30% and 50% are moderately dispersive, between 15% and 30% are a little dispersive and less than 15% are non-dispersive . Similar systems with various limits were used by, and the dispersion test was first described by Volk as a means of determining the potential dispersive of soils.
The test has since been utilized extensively in this concern with minor modifications. Volk’s test contrasts the weight of soil grains, 0.005 mm or smaller that slaked free when air-dried lumps of soil were soaked in silent distilled water with that of the complete soil. This was shown as the percentage dispersion. The pipette method itself was announced by Middleton in 1930 as a means of determining the erosion potential of a soil. The difference in the methods was that the samples collected in the pipette depend on particles of a maximum diameter of 0.05 mm . Volk’s method was, however, chosen because studies in the southwest of the United States point out that the dispersion of the clay fraction was more significant in assessing the piping potential of soils . The SCS involvement in earth dam construction in the United States reproduces in the 1940’s and early 1950’s. It was during this time that the test procedure was appropriate to utilize a hydrometer to instate a pipette .This study was performed in Sulaimani Governorate to determine the effect of ten land use and clay content on dispersion ratio. The soil samples from 0 – 30 cm depth were collected from different locations. All soil samples were air dried, sieved through a 2 mm physical properties were measured such as particle size distribution by the pipette method, bulk density by Clod method. A single point using water under isothermal condition was measured the according to . Chemical properties were measured like soil organic matter which determined by the Walkley-Black method and calcium carbonate by titration method. Correlation and regression were used to analyze the relationship between land use and some soil parameters of the samples .
Analysis of variance for complete randomized design was used to compare the influence of the land usage types on the measured soil properties. DUNCAN at P < 0.5 level was used to separate the mean where applicable.The soil texture of the study area was significantly affected by land use. Data obtained in Table 1 showed the variation in sand, silt and clay fraction of the soil. The result shows that the textural class across all the land use types of the study area is different soil texture, indicating the different of parent material. The result is in agreement with . However, over a very long period of time, paedogenesis processes such as erosion, deposition, eluviations, and weathering can change the soil texture.