MOHAMMAD HADI MEHRANPOUR
 
 
Improvements for the Smooth Joint Contact Model of the Particle Flow Code and its applications
This project deals with two shortcomings of the smooth-joint contact model (SJCM) used in the particle flow code (PFC). The first shortcoming is the increase of the shear strength of the joint when the shear displacement of the joint exceeds a specific value that is related to the particle size. This problem is named as the interlocking problem, which is caused by the interlocking particles. It occurs due to a shortcoming of the updating procedure in the PFC software related to the contact conditions of the particles that lie around the intended joint plane during high shear displacements. This problem also increases the dilation angle and creates unwanted fractures around the intended joint plane. To solve this problem joint sides checking (JSC) approach is proposed. In this approach contacts between the particles in the opposite sides of each joint are being checked to be the smooth-joint contact. The other shortcoming of the SJCM dealt within this project is its inability to capture the non-linear behavior of the joint closure varying with the joint normal stress. This problem is solved in this paper by proposing a new modified smooth-joint contact model (MSJCM). MSJCM uses a linear relation between the joint normal stiffness and the normal contact stress to model the non-linear relation between the joint normal deformation and the joint normal stress observed in the compression joint normal stiffness test. For more information you can check Mehranpour and Kulatilake (2017a) and Mehranpour and Kulatilake (2017b). Morover the fish codes which are used in this project will be available soon in the PFC codes page on this website.
Finding the best intact rock failure criteria for FPC models under polyaxial stress condition
Suitability of six major intact rock failure criteria: Mohr-Coulomb, Hoek-Brown, Modified Lade, Modified Wiebols and Cook, Mogi and Drucker-Prager in representing the intact rock strength under the true-triaxial stress condition is examined in this project. Because the true-triaxial experimental test data available in the literature are limited and do not cover a wide range of confining stresses, the Particle Flow Code (PFC3D) software was used to simulate synthetic rock material failure of cubic samples. This project is performed in the Rock Mass Modeling and Computational Rock Mechanics Laboratories of the University of Arizona. For more information you can check Mehranpour and Kulatilake (2016). Morover the fish codes which are used in this project are available in the PFC codes page on this website.
Study on shear behavior of rock joints by direct shear test under CNL & CNS boundary
The aim of this project is to investigate on shear behavior of rock joints under constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. For this reason, a direct shear test device has been developed in the rock mechanics laboratory of the University of Tehran under the supervision of Dr. Moosavi and in collaboration with F. Saffarian. This device can conduct direct shear tests on the rock joints and continuously acquire data within the test. On the other hand, in order to study the effect of rock joint roughness, a 3D laser distance measurement device with accuracy of 25 microns, has been designed and built in collaboration with H. N. Rafsanjani. Additionally, the 2-dimensional new roughness parameters (Cl and Ci) and the 3-dimensional new roughness parameter (Ci3D) were introduced using Fourier analysis. The Cl parameter is representative of the variance of the actual length of the profile as a result of applying a low pass filter on the profile and Ci and Ci3D are also representative of the variance of the average dip angle of the profile in shear direction as a result of applying a low pass filter. For more information you can read Mehranpour (2016) and moosavi et al. (2013).
Impression relaxation test as a new time-dependent test method
In this project the relaxation impression technique was designed and introduced as a novel relaxation test in which a cylindrical flat ended indenter penetrates into a small region of the sample and after keeping the displacement constant at a certain point, the decrease in the stress level will be recorded. Conventional relaxation test is a time consuming and expensive technique when a large number of samples need to be tested. In contrast, the impression relaxation test requires only a small number of samples which makes this method cheaper. This project is conducted in the rock mechanics laboratory of the University of Tehran under the supervision of Dr. Moosavi and with the collaboration of F. S. Rassouli and F. Tavanaei. For more information please check Mehranpour et al. (2012) and Tavanaei et al. (2014).
An investigation on the loading rate effect on the three point bending single-edge notch test
This study aimed to investigate the influence of loading rate on fracture toughness in the three point bending notched test as well as loading rate effects on induced joint surfaces roughness which are created by fracturing sample. This study shows that the fracture toughness increases by increasing the loading rate. However, the surface roughness is reduced by increasing the loading rate. Moreover the results of this project show that the surface roughness is higher near the notch tip and this value reduces as the distance from the notch tip increases. This project was conducted in the rock mechanics laboratory of the University of Tehran under the supervision of Dr. Moosavi and with the collaboration of H. Nayebvali.
Indentation creep behavior of salt rock
Since conventional creep testing requires many specimens to establish stress and temperature effects, a new indentation creep test called "impression creep" is introduced in which a cylindrical, cubical or conical punch is used to produce a shallow impression on a specimen surface under the action of a constant load. This method had been used on rocks for the first time by Moosavi et al. (2008) in the rock mechanics laboratory of the University of Tehran. In this project the effect of indentation shape and temperature changes are investigated. Moreover these test are modeled in Ansys software by M. H. Mehranpour. For more information you can read Rassouli et al. (2012a), Rassouli et al. (2012b).
Investigation on creep behavior of soft rocks by compression tests
This project was defined to investigate the creep behavior of claystone and salt rock under the uniaxial compression test. Creep is a plastic deformation under constant stress. In order to perform this test an apparatus is designed to measure sample displacement in axial and lateral directions under constant stress in the rock mechanics laboratory of the University of Tehran under the supervision of Dr. Moosavi.