Study Of Dynamic Properties Of Soil In Wollo-Kombolcha Town

Abstract

Dynamic load due to earthquakes, vibrations from traffic and machines, and blasting cause a major problem in engineering practices and it is required to study the dynamic properties of soil to provide dynamic soil information and to reduce future damages. Kombolcha is one of the earthquake-prone areas and recognized and selected as an industrial development center. However, the dynamic properties of soils have not been investigated in this town so far. The objective of this study is to determine the important dynamic soil parameters (shear modulus and damping ratio). To meet the objective, the representative samples from six excavated pits (a total of 18 samples) were collected and tested for the characterization of soil. From index property test results, classification was made using Unified Soil Classification Systems and American Association of State Highway and Transportation Officials classification systems, the town is dominated by Highly plastic or fat Clay (CH/A-7-5) (four test pits) and (SM/A-2-5) Silty Sand (for two test pits). For the cyclic simple shear test and one-dimensional consolidation test, soil samples were remolded in a field condition from the three selected pits at 3m depth. The cyclic simple shear test was conducted at a confining pressure of 100 kPa, 250kPa, and 400kPa, at a wider strain (0.01%, 0.1%, 1%, 2.5%, and 5%) and a Sinusoidal Shape with 1Hz frequency for 40 cycles. The results were also found in the range of (0.52 MPa to 24.9 MPa) shear modulus and (0.83% to 27.57%) damping ratio, in addition to these values, maximum shear modulus was also determined using an empirical equation. The major factors that influence the values of shear modulus and damping ratio values were discussed and the shear modulus values increased as confining pressure, number of cycles, and plasticity increased, but it decreased with cyclic strain amplitude and void ratio (for Gmax), whereas damping ratio in contrary for these factors, but not significant for a void ratio. Similar trends were observed by other researchers. The results were also normalized to compare with the curve developed for sand and saturated clay soils. A similar shape was determined and concluded that the result is in good agreement. However, some variations of values at different strain levels from the limits given were observed, these could be due to testing machine and sample preparation differences. On the other hand, results were also compared with local reports and showed a similar shape to all findings, but some variations of values were observed. These variations could be from plasticity, void ratio, and over consolidation ratio differences. From these findings, it is recommended that further work could be made by considering these factors.