particle flow code

Earth Pressure Balance (EPB) tunnel boring machines are widely utilized for the excavation of subway tunnels. These machines leverage the pressure generated by the excavated materials within the excavation chamber to stabilize the tunnel face. The pressure in the excavation chamber is modulated by varying the speed of the screw conveyor, making the precise control of this rotation speed critically important. Such adjustments facilitate the management of the tunnel face and influence the overall settlement of the tunnel structure. This study models the tunnel excavation of Tabriz Metro Line 2, employing an EPB shield that operates under earth pressure conditions. The excavated material is accumulated in a chamber located behind the cutter-head, which generates the requisite pressure at the work face. This pressure is regulated through the screw conveyor mechanism. The simulation was conducted using a three-dimensional particle flow code based on the discrete element method. The findings indicate that when the pressure at the face is decreased to 50% of the maximum pressure exerted by the horizontal jacks of the shield drive, significant and hazardous ground surface settlements occur. Conversely, at elevated pressures, a consistent settlement of 1.9 cm was recorded. Additionally, a reduction in the cutter-head rotation speed from 2 rpm resulted in a decline of the work face, while an increase in speed corresponded with the same 1.9 cm settlement. The discrete element method effectively models the drilling process. The validity of the modeling outcomes was corroborated by data acquired from instrumentation.

In this study, the effect of joints on rock breakage due to blast stress wave propagation in limestone has been investigated. The required rock strength properties were measured from limestone specimens extracted from Angooran lead-zinc mine located in the north-west of Iran. Also, geometrical properties of three joints were given from the benches of mine. The particle flow code in two dimensions (PFC2D) has been used to model applying blast pressure to inner walls of 6 holes; this code was based on discrete element method (DEM). The obtained results showed that producing large pieces of rocks and back break processes increased by making larger the distance between holes and free surface (B). Also, decreasing B caused to increase the producing powdered limestone around the holes. DEM models confirmed when the stress wave reached empty spaces between joint surfaces, it lost a large part of its energy and the wave passed from the joints could not break limestone well. Furthermore, creating a large number of cracks around the holes showed that the powdered areas started to develop by propagating the stress wave. Comparing the results obtained from DEM models with experimental data showed that the discrete element method was an appropriate method to simulate the rock fracturing process during the blast wave propagation. Also, the blast wave propagation was modeled well in the plane strain condition.

One of the most important issues in geotechnical studies is bearing capacity. It is also defined as the resistance when the maximum pressure is exerted from the footing to the foundation without creating shear failure therein. Since earing capacity is highly correlated with the stability of surface and subsurface structures, researchers have become interested in this subject. The area and geometry impacts on the footing are considered as the two important issues in this regard. In this research, a numerical model based on particle flow code was used in PFC3D software. To do experiments in numerical models, two triple-facet footings were utilized in square, rectangular and circular geometric shapes. Furthermore, these footings held a total area of 64 cm2 and other series included a full area of 49 cm2. In the modeling, the mechanical properties of granite were put into practice and the results of the numerical tests were scrutinized, as well. As a result, it was ascertained that the bearing capacity depends on both the footing geometry and the footing area.

In this research work, a 3D numerical modeling technique is proposed based on the 3D particle flow code in order to investigate the failure mechanism of rock foundations. Two series of footings with different geometries and areas are considered in this work. The failure mechanism obtained is similar to that of the Terzaghi’s but there is a negligible difference in between. Lastly, one equation is presented to calculate the bearing capacity based on the results achieved from the numerical model and the Mohr-Coulomb theory. The sensitivity analyses are performed on the friction angle, cohesion, and footing width. The results obtained are compared with the corresponding results given by the equations given by Terzaghi and Meyerhof. This comparison demonstrates a good agreement between them. In the friction angle sensitive analysis, the amounts of the bearing capacity diagram are very close to Meyerhof’s, which overlap with each other.

Nowadays acoustic emission (AE) testing based on the Kaiser Effect (KE) is increasingly used to estimate the in-situ stress in laboratories. In this work, this effect is assessed on cylindrical specimens in numerical simulations of the cyclic loadings including loading, unloading, and re-loading cycles using a 3D code called the particle flow code (PFC) based upon the distinct element method. To achieve this objective, at first, the numerical model is calibrated using a laboratory test performed on the selected sandstone specimens. The results obtained show that PFC and the distinct element code are useful tools used to investigate the damage and KE of a brittle rock. Also the results obtained by the triaxial modeling show that a combination of triaxial loading stresses change the results of uniaxial loading. Further, KE is influenced under confining stresses so that larger confining stresses lead to greater differences between the KE stress during the uniaxial and pre-stress loadings.