A new simple shear apparatus which is capable of applying monotonic and cyclic load on soil specimens is fabricated. Cylindrical specimens are placed in a special triaxial type cell where confining pressure, pore air and pore water pressures can be controlled. The apparatus consists of an inner part and an outer portion. The inner portion that is inside the triaxial cell consists of a pedestal attached to a movable base. The movable base is mounted on a pair of horizontal rolling tables, which makes the inner portion capable of moving back and forth, horizontally. The outer portion consists of a cylindrical frame that holds the top cap and prevents its lateral movement. A high air entry ceramic disk is sealed into the pedestal using an epoxy resin. The specimen is sheared in a simple shear mode. The horizontal load required to shear the specimen, divided by the nominal area of the specimen gives the shear stress. Soil suction can be measured using the so-called axis-translation technique [1] by increasing the pore air pressure through the top low air entry disk and recording the pore water pressure through the high air entry ceramic disk. Using the fabricated apparatus it is possible to measure and control the vertical normal stress as well as the all-around confining pressure applied to the soil specimen. Hence, testing the soil under initial isotropic or anisotropic confining pressure could be easily achieved. In this paper, the main features of the apparatus are discussed via some test results carried out on unsaturated soil specimens.

One of the methods for investigating the mechanical properties of rocks is direct shear test. It is considered as the simplest and the most commonly used methods for the shear testing of rock specimens containing a weakness plane or a discontinuity. This kind of test is normally carried out in the laboratory, but it may also be performed in the field, using a portable shear box to test discontinuities contained in a piece of drill core. As the normal and shear stresses are applied by hand pumps in the portable shear tests, there are some doubts on the accuracy of results. These ambiguities may be eliminated when using electrical hydraulic pumps instead of mechanically controlled hand pump for applying shear stress on the specimen. The shear stress increasing rate would be regular and may be controlled and changed by means of electrical pumps. As the power supplier will be a 12 volts battery, the developed shear apparatus will also be portable. A series of shear tests have been conducted using both conventional and developed direct shear test apparatus. To be able to have a close comparison, artificially made specimens containing a discontinuity have been tested. The results obtained from these apparatus show some discrepancies which makes one think about the results of the conventional portable shear box.

Shear modulus and confined modulus are important parameters for static and dynamic analysis in geotechnical applications. Cyclic simple shear apparatus had been developed by mounting bender element and ultrasonic sensors to measure continuous shear wave and pressure wave velocities for determination of Gmax and M. For this purpose two new pedestals have been fabricated on which HAE ceramic disc and sensors were mounted. A pressure control panel and a hanging column system have been designed to apply high and low matric suction values with high accuracy. Finally, some tests was conducted to verify the result of device performance and to compare with the theoretical results of unsaturated soils.

Over the past few years, liquefaction phenomena have always been one of the challenging issues in geotechnical engineering. The occurrence of liquefaction is due to cyclic tensions resulting from zero effective stress in the soil mass. Carbonate sands are significantly different in static and dynamic resistance than silicate sands. In this research, this phenomenon has been studied by studying the liquefaction behavior of Bushehr carbonate sand. In this paper, the liquefaction of Bushehr carbonate sand in multiple relative densities, different cyclic stress ratios (CSR), and different overburden stresses are studied and investigated. The liquefaction status of this sand is investigated in dry conditions and volume control situations in the simple shear apparatus. The results indicated that in the same conditions and a low cyclic stress ratio, by reducing overhead stress from 300 to 50 kPa, resistance to liquefaction in Bushehr carbonate sand will be 35 times more. This is not true in the higher cyclic stress ratio, in which liquefaction occurs in very low cycles (up to three cycles). The results also indicated that carbonate sand shows lower liquefaction resistance compared to silica sand.

This paper presents the effect of geogrid tensile strength by calculating the pullout resistance and the geogrid-soil interaction mechanism. In order to investigate this interface, a series of pullout tests have been conducted by a large scale reformed direct shear test apparatus in the both cohesive and granular soils. In numerical, the finite difference software FLAC3D has been carried out on experimental tests and the results are compared with findings from laboratory tests and to complete investigation results. The results show tensile strength of geogrids has an important role in the interface behavior. The effect of the soil type also is discussed. The obtained results show that the geogrids with low tensile strength have higher pullout resistance in the low normal stress on the surface, this effect reversed as the normal applied stress is increased. Numerical analysis only estimates the pullout strength with good agreement in the high normal stresses. Furthermore, it is found that the effective particle size of soil is close to the geogrid thickness by comparing two sands with different grain size.

Carbonate sediments are among the problematic soils in geotechnical engineering. These soils are different from quartz soils both in terms of production origin and engineering behavior. In this paper, for comparison of shear strength parameters, Bandar Abbas carbonate sand and Firoozkooh quartz sand were studied by common triaxial and simple shear tests. Experiments were performed under the same conditions of grain size, relative density and stress level. Parameters such as physical properties, shear behavior, stress path, modulus of elasticity, shear modulus, internal friction angle and dilation angle were compared. The results showed that Bandar Abbas carbonate sand had higher shear strength than quartz sand. The maximum internal friction angle ​​of carbonate sand was higher than quartz sand due to its intrinsic interlocking in both triaxial and shear tests. The dilation angle decreases with increasing stress level for both experiments. Also, the internal friction angle obtained from the triaxial test was higher than the simple shear test for about 10 to 15% due to different stresses paths and the presence of a pre-shear in the simple shear test.  Also, the presence of shear stress in simple shear tests reduces more the internal friction angle versus stress level compared to the triaxial test.

In this paper, results of a series of static and dynamic tests performed on Shiraz silty clay, are presented. Using these test results, the effect of dynamic loading in reducing the stiffness and consequent degradation of the soil is illustrated. Different factors affecting the rate of reduction of soil stiffness are investigated. Among these factors the effects of reconsolidation pressure, cyclic strain amplitude and number of load cycles on the soil behavior are studied and empirical relationships correlating the soil stiffness to these factors are derived. Variation of soil damping ratio during cyclic loading is also highlighted. The normalized behavior of Shiraz silty clay, under both static and dynamic loading is investigated.