مجله زمین شناسی مهندسی
سال شانزدهم شماره 1 (Spring 2022)

The goal of this study was improvement of sandy soil using a combination of polystyrene foam container waste and Portland cement. For this purpose, Babolsar sand was used as the base soil. Strips of disposable polystyrene foam container waste in “chips” of 50 ´ 5 mm and 50 ´ 10 mm were added to the soil at 0.0%, 0.1%, 0.2% and 0.3% by weight along with 3% Portland cement at a relative density of 70%. All samples were cured for 7 days under saturated conditions and then tested using a large-scale direct shear apparatus. The results showed that, in both cemented and uncemented samples, the addition of foam chips increased the cohesion and internal friction angles, which increased the shear strength of the soil. At higher percentages and using larger-sized foam chips, the shear strength increased even more. In uncemented samples, the stiffness did not change with the addition of foam chips, yet the final dilation of the samples decreased. In cemented samples, both the stiffness and softening behavior after the peak strength point decreased. The final dilation of the cemented samples increased at higher foam chip contents and for the larger sized chips. The results of numerical analysis showed that the use of foam chips increased the safety factor of a slope improved in this manner. It also was found that the foam chips with a lower length-to-width ratio had a greater effect on increasing the safety factor of the tested slopes.

The salty running water from Gachsaran Formation in Robat Namaki region, north of Khorramabad city, has caused salt weathering of some rocks in the region. Salt weathering due to the salty running waters of the region is one of the reasons for changing the geomechanical properties of rocks, and as a result reducing their durability. In current research, the effect of salty running waters on the geomechanical properties of outcropping rocks in Robat Namki region has been studied by conducting salt weathering tests. For this purpose, two samples of limestone and sandstone have been prepared and salt weathering tests have been performed on them for 30 cycles in salty running water, spring water and saturated salt solution. After every 5 cycles, the point load index and porosity of the samples were determined. Fitting curves between salt weathering test cycles with point load index and porosity were developed for all three test solutions, and parameters of decay constant and half-life were obtained from them. The effect of the three test solutions on the samples has been evaluated using these parameters, as well as the percentage of changes of the point load index and porosity. The results show that saturated salt solution, spring water and salty running water had the greatest to least effect on the changes of point load index and porosity of the samples, respectively. Also, data analyses shows that sandstone is more affected by salt weathering due to its higher porosity and layered than limestone.

Many researches have been currently conducted on the effects of fault distance on structures revealing that their seismic response can differ according to their distance from the fault. Suspension bridges due to their long period and high flexibility can be more sensitive to this phenomenon, especially in vertical vibration. Since the engineers tend to use longer spans, the length factor should be studied more accurately. In this paper, the effects of length factor on the seismic response of the suspension bridge under near and far-fault ground motions were addressed. The Vincent Thomas and Golden Gate suspension bridges as short and long ones, respectively, are selected as the case studies. The seismic responses of two bridges under five main worldwide ground motions contained both near and far-fault ones, with the same peak ground’s acceleration, are evaluated. The results indicated that the response of both bridges to the near and far-fault ground motions are perfectly different. Short span suspension bridges are vulnerable to near-fault ground motions, whereas long span ones are completely susceptible to both near and far-fault ground motions, and by increasing the length of span, the sensitivity of bridge was increased against far-fault low frequency excitations. Also, maximum displacement responses of spans in both bridges did not increase by maximizing peak ground’s acceleration.

The soil’s natural period has been simulated in more realistic conditions in recent years using complex equations. In previous studies, the natural period of soils made of bilayer soils with different characteristics has been determined and formulas have been presented. For three-layer soils, the proposed relations are complex and performed by approximate methods. Those methods are inappropriate to fast and precise calculation. In this study, the natural period of the soil has been solved using explicit and closed solution of wave propagation method. The final equations are simplified to utilize the advantages of this method are providing simple relations and high accuracy of answers. Likewise, the natural period of twolayer soil is determined based on the proposed method. the natural ground period of the layers around Karaj alluvium has been determined using the above method. Additionally, considering a few ordinary conditions (depth of layers and soil qualities), the natural period of the soil has been determined and introduced by graphs. As indicated by the outcomes, weak layer cause to increase the ground natural period, while stiff layer decreases the period. The rate of ground period sharply reduces by considering the strong soil in bottom of the layers. In general, increasing the layers specification ratio, reduce ground natural period; excluding the case where the order of the layers is strong to weak. The difference between the values of period in both states are significant.

In geotechnical engineering, rock mechanics and engineering geology, depending on the project design, uniaxial strength and static Youngchr('39')s modulus of rocks are of vital importance. The direct determination of the aforementioned parameters in the laboratory, however, requires intact and high-quality cores and preparation of their specimens have some limitations. Moreover, performing these tests is time-consuming and costly. Therefore, in this study, it was tried to precisely predict the desirable parameters using physical characteristics and ultrasonic tests. To do so, two methods, i.e. principal components regression and support vector regression, were employed. The parameters used in modelling included density, P- wave velocity, dynamic Poisson’s ratio and porosity. Accordingly, the experimental results conducted on 115 limestone rock samples, including uniaxial compressive and ultrasonic tests, were used and the desired parameters in the modelling were extracted using the laboratory results. By means of correlation coefficient (R2), normalized mean square error (NMSE) and Mean absolute error (MAE), the developed models were validated and their accuracy were evaluated. The obtained results showed that both methods could estimate the target parameters with high accuracy. In support vector regression, Particle Swarm Optimization method was used for determining optimal values of box constraint mode and epsilon mode, and the modelling was conducted using four kernel functions, including linear, quadratic, cubic and Gaussian. Here, the quadratic kernel function yielded the best result for UCS and cubic kernel function yielded the best result for Es. In addition, comparing the results of the principal components regression and the support vector regression indicated that the latter outperformed the former.

In this study, it is attempted to analyze sensitivity and reliability in order to evaluate the liquefaction potential in soil layers in Tabriz. 62 boreholes that had possible conditions for liquefaction were selected. Seismic mapping was simulated using finite fault method and then the effect of soil layers on PGA was estimated. In continue, the liquefaction potential index was estimated and the zoning map of liquefaction risk was presented. In final, through sensitivity and reliability analysis of the Monte Carlo method, the rate of density function against safety factor of the soil layers versus to liquefaction was determined.

Earth dams are geotechnical structures constructed on various shapes of a valley. The Vanyar Dam is a rock-fill dam located on a narrow valley. Concerning the geometry of the canyon, three-dimensional modeling was utilized to analyze this dam. According to the numerical analysis, the maximum settlement is 88.14 cm, which corresponds to 48 m above the bedrock in cross-section C, that is, a little less than 1% of the dam height. Besides, the total vertical stresses recorded by the pressure cells are about 28% less than those obtained from the numerical analysis. It is assumed that the difference is caused by local arching due to lower compaction and consequently a low stiffness area around the pressure cells. In terms of pore water pressure, there is good agreement between the pore water pressure obtained from the numerical analysis and the piezometers, such that the results are restricted to less than 1%. In general, the difference between the numerical analysis results and those recorded by the instruments is acceptable. Furthermore, the dam shows a suitable level of performance at the end of construction.