شادمان محمدی بلبان آباد

The occurrence of settlement induced by tunneling operations in urban environments is an inevitable phenomenon. The risk of damage to nearby infrastructures and surface structures can be greatly reduced by predicting and controlling this event. This paper uses multiple linear regression (MLR) model and random forest (RF) algorithm to predict the maximum surface settlement (Smax) due to shallow tunnel excavation. Nine input parameters, including the distance of the tunnel center from the ground surface (H), height of the underground water level above the tunnel (W.T), tunnel diameter (D), elastic modulus of soil (E), undrained shear strength of soil (Cu), earth pressure coefficient (K0), unit weight of soil (γ), gap parameter (g), and stability number (N) were selected from 24 data sets related to 14 tunneling projects. The MLR and RF techniques were then implemented for predicting Smax. Three performance indicators of coefficient of determination (R2), root mean square error (RMSE), and mean absolute error (MAE) were employed for the training and test phases to evaluate the efficiency of the suggested models. The coefficient of determination values for MLR and RF for training data were 0.814 and 0.957, respectively, while for test data were 0.793 and 0.96, indicating that the RF approach is more efficient than MLR. Moreover, the findings reveal that the RF algorithm exhibits lower RMSE and MAE values in both the training and testing phases compared to the MLR method. This suggests that the RF algorithm exhibits reduced error and higher reliability and accuracy when compared to the MLR model. Also, the performance study demonstrates that among the input parameters, the gap parameter (g) and the undrained shear strength of soil (Cu) have the greatest and least influence on Smax, respectively.

The interaction between an internal hole and two surrounded joints under a uniaxial compression are examined using the experimental and discrete element procedures. Inside the concrete sample, two notches and an internal hole are created. The joint angle change from 0° to 90° with an increment of 30°. The distances between the joint and the internal hole are 2 cm and 3 cm. Also the numerical models are provided. The joint angle change from  0° to 90° with an increment of 15°. The distances between the joint and the internal hole are 2 cm, 3 cm, and 4 cm. The compressive strength is 7.2 MPa. The rate of loading is 0.005 mm/s. The experiment indicates that the failure process is significantly dependent on the notch angle and the joint distance from the hole. The pattern of fracture and mechanism of failure of joints affect the shear strengths of the samples. The models with joint angles of 30° and 60° have a less compressive strength since the pure tensile failure occurs in these configurations. The model strength decreases with decrease in the join spacing. In fact, in the case that the joint spacing is 2 cm, the interaction between the hole and the neighboring joint is so strong. Consequently, the compressive strength is declined. In both approaches of the numerical simulation and experimental methods, the pattern and strength of failure are identical.

In this work, we investigate the interaction between tunnel and surface foundation in two dimensions by the particle flow code. At the first stage, the PFC calibration is conducted using the experimental test results rendered by a biaxial test. Then the simulation of a biaxial test is performed by confining a rectangular sample inside four walls. The walls are located at the top and bottom simulated loading plates and the adjacent walls are located at the left and right simulated sample side confinement. The velocities of the top and bottom walls are determined, and they are used for loading the sample in a strain-controlled mode. The respond of the material is evaluated by following the diverse stress and strain quantities. The axial deviatoric stress versus the axial strain for biaxial test on the bonded granular material is drawn, and then the Mohr's circle is drawn in order to reach the failure envelope of laboratory. Secondly, a rectangular model with dimensions of 10 m 10 m containing a central tunnel and a surface foundation is built. The tunnel is situated in sixteen different positions below the foundation. The foundation moves downward with a velocity of 0.016 mm/s. The results obtained show the position of the tunnel controlling the failure volume. Also the vertical displacement at the roof of the tunnel decreases by increasing the vertical spacing between tunnel and foundation. The settlement beneath the foundation increases by reducing the vertical spacing between the tunnel and the foundation. The settlement beneath the foundation decreases by augmenting the horizontal spacing between the tunnel and the foundation.

In this paper, the influences of joint angle and joint spacing on the rock fragmentation have been investigated using Particle Flow Code in two dimensions (PFC2D). Firstly calibration of PFC has been done using proper micro parameters. For this purpose, both of the Uniaxial test and Brazilian test have been done on the NX samples. These tests were simulated by numerical method and then the proper micro parameters have been chosen by try and error. After calibration, 21 models with dimension of 11cm ×10 cm consisting one joint have been prepared. The joint angels were 0°, 15°, 30°, 45°, 60°, 75°, and 90°. The joint distances from cutter were 1cm, 2.5 cm and 4cm. Shear properties of joints have been determined using simulation of direct shear test on the modeled joints. One u shape cutter with diameter of 2 cm was in contact to the model surface. Axial force was applied to the model trough cutter.  The results show that both of the joint angle and joint spacing have important effect on the failure pattern and final failure load.

In this paper, the failure pattern of non-persistent joint under U shape cutter was studied by experimental test and numerical simulation. For this purpose, 4 gypsum sample with dimension of 5cm*10cm*10cm containing perpendicular non-persistent joint were prepared.  Samples have 2 vertical non-persistent joint with lengths of 1cm and 2 cm. the angle of small joint related to horizontal axis was 0°, 45°, 90° and 135°. This sample was subjected to U shape cutter loading. Concurrent with experimental test, numerical simulation was performed using Franc2d on the non-persistent joint. Totally 12 numerical model was built that some of them have similar configuration with experimental specimens. The results show that perpendicular non-persistent joint configuration has important effect on the failure pattern.  The compressive strengths have minimum value when small joint angle were 45° and 135°. The comparison between experimental results and numerical output shows that the good accordance was established between experimental tests and numerical simulation.

The aim of this paper is to study the effect of spacing of the joint from ‘u’ shape cutter on the fracture mechanism and to investigate the effect of joint angularity under ‘u’ shape cutter loading on the shear failure mechanism. For this purpose nine sample with dimension of 5 cm *10 cm*10cm consisting non-persistent joints were prepared. The first sets of three specimens have one non-persistent joint with length of 2cm and angularity of 0, 45 and 90. The spacing between joint and top of the sample was 2cm. The second sets of three specimens have one non-persistent joint with length of 2cm and angularity of 0, 45 and 90. The spacing between joint and top of the sample was 4cm. The third sets of three specimens have two non-persistent joint with length of 2cm and angularity of 0, 45 and 90. The spacing between upper joint and top of the sample was 2cm and the spacing between lower joint and upper joint was 2cm. the samples were tested under loading rate of 0.01 mm/s. concurrent with experimental investigation, numerical simulation were performed on the non-persistent joint using FRANC2D. the results shows that the spacing between joint and specimen edge and joint angularity have important effect on the crack growth mechanism. Also, failure mode and failure pattern in experimental test and numerical simulation are similar.