RELATIONSHIP BETWEEN VOID RATIO AND PERMEABILITY FOR GYPSEOUS SOIL UNDER DYNAMIC LOAD

Abstract

ABSTRACT

The behavior of Gypseous soil under different frequencies encountered during a dynamic loading events like machine foundation, impact, explosions, seismic activity is very difficult to analyze, thus an attempt has been made to study the behavior of this type of soils subjected to dynamic loading. In this research a parametric study is carried out to investigate the effect of applying a vibrated loading during leaching process. The work is carried out by using an experimental model, designed and manufactured for this purpose. Two representative samples of gypseous soil which contain different gypsum contents with (65%, 46%) are brought from a local source in Salah-Aldeen governorate, in north of Iraq. The main objective of this research is to investigate the change in permeability of the samples with time (leaching), associated strains, dissolved salts and investigate the relationship between void ratio and the coefficient of permeability under static loading. Then after investigate these parameters under effect of wide range of vibrated loading to compare the results obtained with static state. Also the basic characteristics of vibrated loading have been measured during tests. They include, displacement amplitude, acceleration of motion, magnitude of dynamic force applied, and damping ratio. The results show that some frequencies of loading have a slight effect in permeability by increasing with percentage not exceeding 10 % from original value. While there is a set of frequencies produce a significant II increasing in permeability coefficient by magnitude exceeds nearly (30%) for the first sample and (45 %) for the second. As a result, the rate of dissolution is increased during process due to increase in volume of water collected. But the high frequencies have a different effect on permeability, where it has led to a significantly decreasing in its value. The change in this coefficient depends mainly on basic characteristics of vibration, which are, displacement amplitude, acceleration, and amount of dynamic force applied. Also the test results show that the vibrated loading leads to dangerous collapse, which increases strongly with increasing of frequency of loading. The collapse resulting from this loading reaches to 200 %, 210% from the soaking collapse for the two samples (S1, S2) respectively. The damping ratio calculation is performed according to bandwidth method for the system. The results show that the damping ratio for the first sample is greater than second sample. Also tests are carried to evaluate the wall reflective characteristics of the test container and to assess the isolating property of the rubber isolator which is used as absorbing layer. The results indicate that there are a significant effect on the settlement occur due to wall reflectance when the test is conducted without using absorbing layer in model test. The reduction factor in value of settlement due to using the absorbing layer is ranged between (15 - 28) % for frequencies of vibrated loading between (30 - 100) Hertz. Finally from the results, the relation between coefficient of permeability and void ratio is plotted with complex relation, the initially part of curve refers to increasing the permeability with decreasing of calculated void ratio, but the last part shows that the decreasing in void ratio led to decreasing in permeability of the soil samples.