ENGINEERING GEOLOGY
Year:2018 | Volume:11 | Issue:3 |Papers Count:6

Chemical changes in the soil have a significant effect on its physical and mechanical properties and the rate of settlement. In this research, the effect of urban wastewater on chemical properties and soil engineering characteristics such as Atterberg limits, uniaxial compressive strength and consolidation parameters in central areas of Mashhad have been investigated. Based on the results, some chemical parameters such as Ca, Mg, Al and K decreased after the soil samples has been saturated by wastewater. Also, changing the chemical properties of the soil has changed its physical and mechanical parameters. For example, the consolidation parameters of the selected soil indicate that the (Cc) has increased over time with changes in the concentration of input wastewater. Also, the (Cs) has decreased over time and the rate of change in high concentrations is less. In addition, the results show that low concentrations of wastewater in short time have the greatest effect on reducing the uniaxial strength of soil. An examination of the electron microscope images shows that when the soil sample is saturated with wastewater, a layer of salt is accumulated around the soil particles, which expands the size and surface of the particles and also tends its structure towards the grain pattern. Therefore, simultaneously, the two factors of time and the change in concentration of wastewater affect the physical and mechanical parameters of the soil, and the effect of concentration on the time is more indicative.

Artificial stone is a mixture of natural aggregate and additives such as industrial gums (resin), cement and other polymer materials. In this research artificial stones with different additives and resins were designed to achieve high flexural capacity with mixing design, 84% aggregate, 10% resin and 6% additive completely manually without vacuum and pressure system. FESEM images were taken from specimens to determine fine cracks, elements, manufacturing atoms, weight percentages, and how to add and interconnect the additives used in making artificial rocks. To determine the ductility and evaluation of the quality of artificial rocks by their ability to withstand cracks or other surface roughness over a continuous bending period, artificial rocks made with additives (glass fiber, carbon fiber, polyester resin And vinyl ester) Three-point bending test Based on the three-point bending test, the sample made from wilin ester resin and the carbon fiber, had the most flexural strength and a sample made from wilin ester resin and the glass fiber tolerated the most strain during bending. Also, the type of fracture and cracks in the reinforced rocks are brittle and flexural respectively, and are ductile and shear-bending in rocks without reinforcing.

Nowadays, modeling of rock masses is widely used in order to accurately determine the properties of the rock mass and improve its behavior. In most cases, the geometric components of the fractures in the rock have a random nature. one of the most important methods to simulate the random nature of joints is the stochastic modeling of the fracture network of rock. The stochastic modeling of the fracture network makes the heterogeneous nature of rock mass with discrete elements, with geometrical properties and features that are statistically defined. In this study, the samples taken from the Liroo dam foundation are surveyed and analyzed. Then using the EasyFit that is a statistical software, the known distribution functions were determined by the maximum fitting on the surveyed geometric components and then their moments were determined. On the other hand, using the written code with Mathematica software, 3D-DFN three dimensional discrete fracture network method fractures simulated. Finally, the geometric model validated based on the comparison of the statistics of the distribution functions obtained from the model output with statistics of input distribution. The results in most cases indicate compliance of more than 90%. Also, P10, P21 and P32 values of the two-dimensional sections in a same strike with reality and in three-dimensional model were determined and compared with real values. The values of P10 and P32 showed more than 90% compliance and the P21 component was more than 75% consistent with actual data.

Determination of the optimum face support pressure is one of the fundamental tasks in a excavation using tunnel boring machines (TBM). The optimum face-stabilizing pressure ensures the safety of the excavation, helps to minimize a surface settlement and ultimately prevents the collapse of the entire tunnel. Existing methods have been presented only for homogeneous soil at the tunnel face. The heterogeneity or boundaries of the face layers have a significant effect on the stability of the tunnel face. Practical experiences show that the tunnel face stability in heterogeneous soil is relatively more difficult than homogeneous soils and it cannot be easily solved by the models proposed for homogeneous soil. This study investigates the infl uence of heterogeneity of the soil on the tunnel face instability in EPB TBM. Therefore, the numerical softwares (Plaxis 3D Tunnel and Phase2) and analytical methods (Broere and Carranza-Torres) were used for the stability analysis of tunnel face in heterogeneous soil. The results of comparing values of safety factor showed that analytical methods are conservative. Moreover, the numerical modeling results showed that when the soils with poor material properties are located in the upper part of the face, they can significantly increase the ground pressure and partial slide. From comparing the face support pressure for one layer (assumption of homogenous soil and averaging of physical and mechanical properties of soil) with multilayers of tunnel face, it can be concluded that assuming of tunnel face as a one layer, causes incorrect estimation of tunnel face support pressure.

In the current study, the effects of acid and alkaline rains on the physical properties of a particular type of clay with low plasticity is evaluated. In order to reproduce the process of interaction between artificial rain and soil, an infiltration setup was fabricated. Solutions of diluted sulfuric acid (H2SO4) and dissolved sodium hydroxide (NaOH) were used to create acidic or alkaline rains, respectively. Distilled water was also used as a reference pH value. Subsequently, the reconstituted samples in a mold are infiltrated by acid or alkaline rains in different pH levels and different fluxes of rainfall. Atterberg limits, Coefficient of permeability, California bearing ratio (CBR) test, and unconfined compressive strength (UCS) of the soil samples were evaluated, to investigate the changes of the mechanical properties of the soil after being exposed to acid or alkaline rain. The obtained results indicated that acidic contamination had a strong influence on the strength characteristics of soils, and the mineralogy of the clay fraction as well as the concentration of acid in the pore fluid could significantly influence the stress-strain behavior of studied soil. However, further decrease in pH (pH=3) and increase in rain fluxes (20 years) caused a significant reduction of the strength. Furthermore, the results indicate that the values of the LL, PI and the soil permeability has increased and the unconfined compressive strength and the CBR has decreased as the artificial rain become more acidic or alkaline, and precipitation years increased from one-year to twenty-years.

This study was conducted to analyze factors influencing the compressive strength test. The purpose is to introduce various factors affecting the accuracy of the compressive strength test in accordance with current standards and evaluate the effect of some effective parameters such as equipment (loading rate of automatic compression machine, jolting or vibrating), mortar preparation, sample preparation, etc. To check the reproducibility of the compressive strength test a program was developed to assess the possible modes through changes in loading rate, standard sand, sample preparation, and operator. The changes of each parameter were measured within 2, 7 and 28-day interval, while other conditions were considered as constant based on the EN 196-1 and ISIRI 393 standards. According to the test results, the most important factors in creating the difference in results are the type of the sand and loading rate. The changes in the reproducibility percentage using different sands with softer grains increases the coefficient of variation and reduced performance of the test. Also in some cases, with increasing the loading rate up to 40%, the compressive strength of 28 days is increased by 13%.