Energy analysis of hydraulic fracturing

In this paper, numerical simulations of circular boreholes under internal hydraulic pressure are carried out to investigate the energy transferred to the surrounding rock and the breakdown pressure. The simulations are conducted by using a micromechanical continuum damage model proposed by Golshani et al. (2006). The simulation results suggest that the borehole breakdown pressure and the energy transferred to the surrounding rock are dependent on the mechanical properties of the rock and borehole size. Although the energy transferred to the surrounding rock increases with increasing borehole size, the borehole breakdown pressure decreases

Impact on a water filled cylinder

The computational and experimental results of impact loading a water filled cylinder with a high speed piston are presented. Computational simulation of the impact process is performed by means of DIANA, a commercial finite element software package. In this simulation, water is modeled as a solid with very small shear modulus compared to the bulk modulus of water. The efficiency of the simulated impact is evaluated by the time dependent water pressure in the vicinity of the cylinder. Also, the shock pressure resulting from impact is detected by using a pressure transducer located in the middle of the water tube. Comparison of the computational and experimental results shows that the impact process on a water filled cylinder is well modeled. It is shown that the best way to increase the pressure peaks of the pressure profile curve is to increase the piston’s impact velocity

Amirkabir Natm Tunnel — A Case Study of Design Challenges in a Mega Project of Tunnel in Soft Ground

In spite of enhancement in modeling techniques as well as site investigation methods, uncertainty exists seriously in the process of construction of underground structure in soft soils. These uncertainties arise from limited data of geological data, measurement errors, interpolation of spatially geological properties, and extrapolation of results of experiments and natural analogue studies over times and conditions relevant to the project. Robust and optimize design of tunnel support pattern consists of many important parameters including advance rate and excavation method. However, quantitative definition of these parameters is difficult because of restricting in site investigation data and uncertainties related to them. Furthermore, erroneous evaluation in these parameters can affect in incorrect projection of tunnel stability or economic loss. The work reported in this paper specifically dealt with Amirkabib highway tunnel with approximately 1.5KM long in each tube (i.e., north and south tubes). It is one of the important projects excavating below one of the highest traffic region of Tehran, including the difficulty of excavating through a heterogeneous sedimentary basin mainly composed of recent alluvial. Construction has been performed by different methods i.e., Underground excavation, Cut and Cover and Top/Down methods in different section of the project. Deformations and settlements have been monitored during and after construction in order to avoid unpredictable deformations and as a result any possible failure. Similar to other part of the project, a probabilistic hypothetical elasticity modulus (PHEM) approach has been employed to evaluate the uncertainty in lining design of a horseshoe shape NATM (New Austrian Tunneling Method) tunnel in T4 section of the project. The hybrid model, PHEM, consisting two essential parts is used to evaluate the performance of the system. A MATLAB interface program for generating the ABAQUS-based parametric model in one hand; and a Monte Carlo algorithm (Latin Hyper Cube Sampling method) to simulate the uncertainty existed in the system on the other hand are applied to produce the probabilistic density function of surface settlement of tunnel excavation and lining phases. In comparison with the monitoring data, the numerical results show that the PHEM approach introduced has had an appropriate prediction in surface settlements, improved the classical deterministic approaches

Amirkabir NATM Tunnel- A case study of design challenges in a mega project of tunnel in soft ground

Seventh International Conference on Case Histories in Geotechnical Engineering and Symposium in Honor of Clyde Baker, Chicago, USA, 29 April 4 May 2013In spite of enhancement in modeling techniques as well as site investigation methods, uncertainty exists seriously in the process of construction of underground structure in soft soils. These uncertainties arise from limited data of geological data, measurement errors, interpolation of spatially geological properties, and extrapolation of results of experiments and natural analogue studies over times and conditions relevant to the project. Robust and optimize design of tunnel support pattern consists many important parameters including advance rate and excavation method. However, quantitative definition of these parameters is difficult because of restricting in site investigation data and uncertainties related to them. Furthermore, erroneous evaluation in these parameters can affect in incorrect projection of tunnel stability or economic loss. The work reported in this paper specifically dealt with Amirkabir highway tunnel with approximately 1.5Km long in each tube (i.e.,north and south tubes).It is one of the important projects excavating below one of the highest traffic region of Tehran, including the difficulty of excavating through a heterogeneous sedimentary basin mainly composed of recent alluvial. Construction has been performed by different methods i.e., Underground excavation, Cut and Cover and Top/Down methods in different sections of the project. Deformations and settlements have been monitored during and after construction in order to avoid unpredictable deformations and as a result any possible failure. Similar to other part of the project, a probabilistic hypothetical elasticity modulus (PHEM) approach has been employed to evaluate the uncertainty in lining design of a horseshoe shape NATM(New Austrian Tunneling Method) tunnel in T4 section of the project.The hybrid model, PHEM, consisting two essential parts is used to evaluate the performance of the system. A MATLAB interface program for generating the ABAQUS-based parametric model in one hand; and a Monte Carlo algorithm (Latin Hyper Cube Sampling method) to simulate the uncertainty existed in the system on the other hand are applied to produce the probabilistic density function of surface settlement of tunnel excavation and lining phases. In comparison with the monitoring data, the numerical results show that the PHEM approach introduced has had an appropriate prediction in surface settlements, improved the classical deterministic approaches

Modelling a borehole subjected to fluid pressure

Fluid pressure inside a borehole produces hydraulic fracture and damage zones in the vicinity of the borehole. These fractures result from stress concentrations around the borehole. The results of numerical simulation of a borehole subjected to fluid pressure using a micromechanical damage model [2] are presented in this paper. It is observed that tensional concentrated stresses are generated around the bottom of the borehole by the applied fluid pressure. Furthermore, fractures develop from the corners of the bottom of the borehole

Simulation of hydraulic fracturing in brittle rocks

[Abstract]: To investigate the breakdown pressure and the energy transferred to the surrounding rock, numerical simulations of circular boreholes under internal hydraulic pressure are carried out. For this purpose, a micromechanical continuum damage model proposed by Golshani et al. [1] is used. The simulation results show that the borehole breakdown pressure and the energy transferred to the surrounding rock are dependent on the mechanical properties of the rock, borehole size and far-field confining stresses. Although the energy transferred to the surrounding rock increases with increasing borehole size, the borehole breakdown pressure decreases. The analysis also shows that breakdown does not occur even if a crack initiated at a borehole wall. In fact, the breakdown occurs when the crack growth becomes unstable. In other words, breakdown pressure appears to correspond to the onset of unstable crack growth

Energy analysis of hydraulic fracturing

[Abstract]: In this paper, numerical simulations of circular boreholes under internal hydraulic pressure are carried out to investigate the energy transferred to the surrounding rock and the breakdown pressure. The simulations are conducted by using a micromechanical continuum damage model proposed by Golshani et al. (2006). The simulation results suggest that the borehole breakdown pressure and the energy transferred to the surrounding rock are dependent on the mechanical properties of the rock and borehole size. Although the energy transferred to the surrounding rock increases with increasing borehole size, the borehole breakdown pressure decreases

Structural Reliability Analysis of NATM Tunnel Face Stability in Soft Ground

TU-Seoul 2013: Tunnelling and Underground Space Construction for Sustainable Development, Seoul, Korea, March, 2013In spite of enhancement in modeling techniques as well as site investigation methods, uncertainty exists seriously in the process of construction of underground structure in soft soils. These uncertainties arise from limited data of geological data, measurement errors, interpolation of spatially geological properties, and extrapolation of results of experiments and natural analogue studies over times and conditions relevant to the project. Robust and optimize design of tunnel support pattern consists many important parameters including advance rate and excavation method. However, quantitative definition of these parameters is difficult because of restricting in site investigation data and uncertainties related to them. Furthermore, erroneous evaluation in these parameters can affect in incorrect projection of tunnel stability or economic loss. In this study, a probabilistic hypothetical elasticity modulus approach, based on Monte Carlo simulation algorithm (Latin Hyper Cube sampling), has been employed to evaluate the uncertainty in lining design of a NATM tunnel located in Tehran region. A parametric finite element model based on ABAQUS and a MATLAB interface program has been introduced to evaluate the performance of supporting system to limit the settlements induced by tunnel excavation in the different magnitudes of lifetime probability of failure. The tunnel has a horseshoe shape, excavating in a soft soil for subway purpose.Tehran Municipalit