مرتضی احمدی

Compressed air storage is one of the methods of energy storage. One of the most important parts of a compressed air storage system is the storage cavern. In this study, the behaviour and the long-term stability of the salt cavern as a storage site for compressed air were investigated. Due to the construction and operation of the salt cavern, the in-situ stress conditions around the cavern will change. The difference between induce stress and pressure of compressed air will cause the cavern to converge and damage around it. In this study, the salt rocks from one of the regions of Iran were used to test creep. To investigate the creep behavior of salt rock, creep test was performed in three stress levels in a stepwise manner. Lubby2 model parameters were calculated. Then, using LOCAS finite element software, the compressed air storage cavern was simulated and its behavior and stability were investigated. The results of these experiments and modelling have shown that with increasing stress in each stage, the slope of the secondary part of the creep increases. Therefore, it can be concluded that with increasing stress, the Maxwell viscosity coefficient decreases. In addition, the amount of movement in the lower half of the cavern was more than the upper half of it. Value of the cavern safety factor according to the Devries dilation criterion also decreased with increasing depth and the probability of dilation in the cavern wall increased.

This research has been achieved at the aim of recognizing the type of dominant rationality on the Vision Plan of Tourism in Iran. Tourism planning has experienced noticeable changes under the influence of transformations in the philosophical and social paradigms in recent decades. The research based on interpretive epistemology and regarding the methodological aspect considered as a qualitative research. Archival studies and thematic analysis with the exploratory purpose were used for data gathering as well as analysis. On the basis of this study findings, Instrumental rationality with 48 themes out of 71 and its correspondent theory that is rational planning has been dominant on the Vision Plan of Tourism in Iran. Also, we observed the slight share of other types of rationality among the themes recognized in the Vision Plan. Analysis and comparison of the share for each type of rationality made it clear that coordinative rationality has been ignored.

One of the practical issues leading to the success or failure of tourism development plans is the type of rationality that dominates the country’s planning system in each era and the corresponding planning theory. This article has been compiled to analyze the position of rationality in planning as an epistemological framework in Iran’s strategic tourism development plan. This research’s conceptual framework of rationality is based on Alexander’s Rationality Model (2000) and the new approaches to tourism planning. The philosophical paradigm of the study is based on interpretive epistemology, and its methodology is based on qualitative research. Archival Studies and Thematic Analysis methods have been used for gathering and analyzing data in this research. The study’s statistical population for the content analysis comprises the qualitative texts of Iran’s strategic tourism development plan. The findings of this research indicate that, for the first time, coordinative rationality has become dominant in Iran’s strategic tourism development plan (Approved in 2020). The components of rationality were recognized, and the share of each type of rationality was outlined by analyzing 85 themes and thematic networks in the strategic plan in this research.

In structure of rocks, there are a number of pores, joints and small cracks which called discontinuities. Studies showed that these discontinuities propagate under load and emit acoustic wave (signals). Acoustic emission (AE) method is used to study these signals. In AE method, a rock sample is loaded and a number of sensors are placed around it. Then during the loading test by growing the cracks signals emit and collecting by sensors. By collecting and analyzing these signals in the frequency dimension, mechanism of crack propagation could be studied. In this research, frequency bandwidth of the waves emitted from a rock sample under increasing load has been investigated. Data which obtained from an experiment on rock sample have been used for study. A sample of granite with dimensions of 1*3*6 inches was subjected to uniaxial loading. A code was written to change the data and executed in MATLAB. By execution the code, initially, raw data is transmitted into domain-time signals. Then, time-amplitude dimension signals converted to the frequency dimension using wavelet transform. Analyses were carried out with outputs of code and in form of diagrams and figures are presented. Analysis showed that by elapse of time and crack growth in the experiment, there was an inverse relationship between the length of the growing crack and frequency bandwidth of the emitted wave, and the frequency bandwidth decreased.

The aim of this study is microstructure modeling and deformation and damage analysis of aluminum-based metal matrix reinforced by Tic particles by using the Peridynamic theory and experiment. The particulate composite was fabricated by mixing aluminum and TiC powder and then the mixture was hot-extruded. Tensile tests were carried out to validate the Peridynamic model. Four representative volume elements were extracted from surface images of specimens. The location of Particles in the matrix was obtained by image processing. Due to restrictions on bond-based Peridynamic, state-based Peridynamic was utilized for modeling. Overall stress-strain curve, the destitution of equivalent stress and plastic strain, distribution of damage parameter, the total plastic stretch of all interactions, and the number of damaged interactions were used to analyze the results. At matrix surrounded by particles, matrix/particle interface, and narrow particles stress concentration were detected. The damage was initiated at these regions, but the damage was mostly propagated in matrix and matrix/particle interfaces. In the loading process, several damage mechanisms were initiated and propagated, and finally, a principal crack was created that led to the final fracture. By comparing scanning electron microscope images of the fractured surface, modeling, and experimental result, it is shown that the developed Peridynamic model can precisely predict the progressive damage behavior of particulate composites.

Determination of seismic response of geotechnical structures is important for safe design in a seismically active area. The dynamic behavior of geotechnical structures is complex, and therefore the use of different methods helps to understand this dynamic behavior. Numerical methods allow to well describe the complex dynamic behavior of geotechnical structures. However, the time-consuming, determination of several different parameters, radiation conditions, and difficulty in interpreting the results are the reasons for limiting the use of these methods in the technical community. The pseudo-static method is the most common method for analyzing seismic stability in geotechnical engineering. This method is independent of time and does not consider the dynamic nature of the earthquake load. Also, some soil parameters such as damping or compressive and shear wave velocity are not considered. To overcome these drawbacks, the pseudo-dynamic method was developed by Steedman and Zeng [1]. Sarangi and Ghosh [2] used the pseudo-dynamic method to determine the seismic stability of nailed vertical excavations in medium dense to dense sand. However, the boundary conditions are not included in the pseudo-dynamic method. Therefore, the pseudo-dynamic method has been modified again to satisfy the boundary conditions [3]. Recently, Kokane et al. [4] using the modified pseudo-dynamic method presented a solution for nail tensile force and inertial forces acting on failure wedges. However, the formulation used in this article is very difficult to develop. In this paper, the modified pseudo-dynamic method is used to analyze the seismic stability of nailing soil walls. Because the modified pseudo-dynamic formulation has been formulated to calculate the seismic pressure of a nail-free wall, the modified pseudo-dynamic formulation first is rewritten for the wall system with nail reinforcement, to calculate the seismic active pressure. Using pseudo-dynamic acceleration components derived by Belleza [3] and conducting an analytical process, the proposed formulation is obtained for the active seismic soil pressure coefficient and the safety factor corresponding to the general stability of soil-nailed walls. In the proposed formulation both Qh and Qv as horizontal and vertical inertial forces of the failure wedge are considered. Then, using the try and error iteration method, the critical angle of failure, seismic active pressure, and seismic safety factor are obtained. The main innovation of this study is to apply the modified pseudo-dynamical method for a nailed soil wall, however, as another innovation, seismic pressure on the wall is calculated taking into account the tensile force of the nails. It should be noted that in the available analytical methods, the seismic pressure of the wall has been calculated without regard to the nail tensile force. In the following, to validate and verify the proposed analytical method, a comparison between the presented analytical results with the results of the shaking table and the available analytical methods is carried out, which shows the high accuracy of the proposed method than other analytical methods. Finally, with a numerical example, a parametric study is carried out to verify the effect of various soil and nail parameters on the seismic stability of the nailed walls, and the coefficient of seismic active pressure. References 1. Steedman, R. and Zeng, X. (1990) The influence of phase on the calculation of pseudo-static earth pressure on a retaining wall. Geotechnique, 40(1), 103-112. 2. Sarangi, P. and Ghosh, P. (2016) Seismic analysis of nailed vertical excavation using pseudo-dynamic approach. Earthquake Engineering and Engineering Vibration, 15(4), 621-631. 3. Bellezza, I. (2015) Seismic active earth pressure on walls using a new pseudo-dynamic approach. Geotechnical and Geological Engineering, 33(4), 795-812. 4. Kokane, A.K., Sawant, V.A. and Sahoo, J.P. (2020) Seismic stability analysis of nailed vertical cut using modified pseudo-dynamic method. Soil Dynamics and Earthquake Engineering, 137, 106294.

In this work, the entanglement of a superposition of bipartite qubit coherent states with non-phased coherent parameters is studied. We use Generalized-concurrence as the measure to quantify the entanglement and drive analytical results in terms of the effective parameters involved. Analyzing the results, we conclude that such states may attain maximum entanglement or no entanglement at all, depending on the choice of the parameters involved.

One of the methods used to investigate the damaged zone in rock structure is the acoustic emission method. This method is based on receiving the elastic waves that are produced by deformation and cracking of the rock mass around the underground excavation. In this research, a study is conducted on the rock samples by a numerical method to investigate the damaged zone caused by the excavation of circular space on it. For this purpose, 33 cube samples of three different material types including sandstone, concrete, and cement-plaster mortar are prepared. A circular hole is drilled in the center of each sample. The hole diameter is 20 or 25 mm. The samples are loaded uniaxially or biaxially with different stress rates. It is tried to study the acoustic events occurring in the samples during the test, and their locations are investigated. Then the experiments are evaluated by a numerical method using the FLAC3D software and some developed codes. The relation between the sample damaged zone where the acoustic events have occurred during the loading period and the numerical elements that reach a degree of tensile and shear yield is studied. The results obtained show that the amount of cumulative acoustic parameters in cement-plaster mortar specimens is more than the others. In fact, the finer grains, the more amounts of energy and counts will be produced. Also, the results show that with increase in the lateral pressure and loading rate, the amount of cumulative energy and counts decreases.

During an earthquake, the better performance of segmental tunnel lining, compared to the continuous in-cast concrete lining, is generally related to the joints between segments. In order to better understand the influence of the segment joints, their effect on the internal forces induced in tunnel lining simultaneously with the effects of the other influential parameters should be considered. In this work, the segmental joints were simulated by the representative stiffnesses and effects of these characteristics in relation to the other parameters such as the soil-liner interface behavior, number of segments in each ring and thickness of segments on the internal forces induced in structure were investigated. For this purpose, 2D numerical analyses were performed and the results obtained were discussed. Results showed that under the seismic condition, the components that had the most significant role on the internal axial forces induced in the segmental lining were rotational stiffness and axial stiffness of joints. Also the bending moments were more affected by the rotational stiffness. Generally, the radial joint stiffness had a less effect on the induced internal forces. With increase in the number of segments and their thickness, the effect of joint stiffness on the internal forces increases and the design of joints should be given more attention; however, the effects of joint stiffness and frictional behavior at the soil-liner interface on the maximum induced forces are almost independent from each other. Also in a specified joint behavior, by variation in each one of the other parameters including the soil-liner interface condition, number of segments and their thickness, the absolute magnitude of the maximum induced internal forces sometimes change significantly.

Excavation of tunnels and construction of underground safe facilities are always faced with numerous challenges and problems that often hinder or stop the work progress. Excavation of loose media is such a challenge which creates a special structure in weak strata. Therefore, in such conditions, it is important to be aware of proper method for improving the condition of the ground and the excavation methods in order to achieve the maximum safety and operational efficiency. The present study aimed to investigate excavation method of Glass water transmission tunnel in the alluvial section of the path.The present study aimed to investigate excavation method of Glass water transmission tunnel in the alluvial section of the path. The stability of this tunnel has been investigated during the implementation of NATM, EPB, TBM and ADECO-RS excavation methods. Studies have shown that the study field is a high-risk area. Excavation of the tunnel was studied through the ADECO-RS method. The tunnel and the project conditions were designed using the FLAC3D software. With regard to the pre-constraints imposed on the face, the obtained displacements were within an acceptable range. On the other hand, the predicted support systems in the tunnel have the capacity to withstand the loads and moments. Therefore, implementation of the ADECO-RS method is recommended in deep alluvial condition.

Feasibility studies of pumped storage power plant in Azad dam has been carried out. This project includes underground spaces such as tunnels, shafts and two big caverns including; power house and transformer. So, in this research long term stability of the powerhouse cavern is studied numerically. To determine the time-dependent behavior of the surrounding rock mass of cavern which includes sandstone layers with phyllite interlayers, was used instrument curves which obtained from one of the access tunnel. To simulate the cavern time dependent behavior, numerical method and Flac3D software have been used. Results of the numerical model showed a good agreement with results of convergent pins of the access tunnel. Long term stability analysis of support system of Azad dam main cavern was objective of research. The study was numerically and Flac3D software was used. Bergar’s time dependent model was considered for rock mass periphery of cavern. Numerical model of cavern was built. Long term stability analysis for 100 years was reviewed. Data which obtained from convergent pins of access tunnel was used for conformity to numerical results. Results of the time dependent analysis showed that the cavern will be stable for a 95-year period with a safety factor of 1. In this research, due to importance of the subject and the sufficient knowledge of conducted studies in similar cases, the long-term behavior of the main cavern in Azad dam pumped storage has been investigated. Hence, identification and description of time-dependent behavior of surrounding rock mass is important, as it is possible to calculate and analyze time dependent deformation and, consequently, long term stability of the cavern. To understand such behavior, creep parameters should be calculated by creep tests or using instrument curves which obtained from installed convergent pins in underground space. Finally, with time-dependent analysis, it can be examined the stability of the cavern for different time periods. In this study time-dependent behavior of rock surrounding cavern which consists of sandstone with interlayer phyllite, have been studied using instrumentation data that were installed in one of access tunnels. Viscoplastic model (CVISC) was selected for the rock mass periphery of cavern. To simulating CVISC model, finite difference software (FLAC3D-V5.01) is applied. Results of numerical method were verified with instrumentation data. Capacity diagrams of support system were drawn. Results of numerical model are in good agreement with the results of convergence pins data which show accuracy of the numerical model. According to long term stability analysis, powerhouse cavern structure will be stable for a period of 95 years with safety factor of one.

Hydraulic fracturing is one of the conventional and common methods to stimulate oil and gas formations with low permeability. This method is widely used for creating artificial fractures and stimulate fluid flow in oil and gas wells. In this paper, fracture propagation process was simulated by using a Discrete Fracture Network (DFN) in UDEC software. Discrete Element Method (DEM) is a key for simulating hydraulic fracturing which is capable of performing a fully coupled hydromechanical analysis to model fluid flow through a network of fractures. In this regard, fictitious joints were used for modeling fracture propagation in a medium with equal to intact rock properties. To achieve this goal, the mechanical and strength properties of discontinuities were considered equal to mechanical and strength properties of intact rock. Then, the role of rock mechanics parameters including elastic modulus, cohesion and friction angle were studied in the process of fracture propagation. The results of numerical simulations showed that the extended fracture length is increased by increasing the elastic modulus and decreasing the friction angle. Also, increasing in the cohesion does not have a significant effect on the extended fracture length, but it reduces the hydraulic fracture opening.

Different methods are being used for monitoring of crack growth and failure mechanism in rock fracture. Acoustic Emission (AE) is one the methods used for micro crack monitoring in samples under pressure. Existence of porosity and humidity in rock and soil structure cause different effects on process of micro cracks and growth of micro cracks and finally their fracture. In this study, effects of porosity and humidity in micro crack growth and rock fracture are being analyzed. Four parameters which are highly effective in AE method namely hit, count, wave durability and fracture energy are used. Mortar (synthetic rock) was used to have a constant porosity ratio in samples. Cylindrical samples with 54 mm diameter and 110 mm length with 5 different porosity ratios ranging from 17 to 35 percent were made using Panplast lubricant. Samples were subjected to uniaxial compression test in two dry and saturated conditions and AE data were recorded. Data analysis showed that the dominant failure mode on samples of dry mortar with increasing porosity, increase toward the tension mode. With increasing of porosity and moisture content the numbers of micro crack decreases. Different methods are being used for monitoring of crack growth and failure mechanism in rock fracture. Acoustic Emission (AE) is one the methods used for micro crack monitoring in samples under pressure. Existence of porosity and humidity in rock and soil structure cause different effects on process of micro cracks and growth of micro cracks and finally their fracture. In this study, effects of porosity and humidity in micro crack growth and rock fracture are being analyzed. Four parameters which are highly effective in AE method namely hit, count, wave durability and fracture energy are used. Mortar (synthetic rock) was used to have a constant porosity ratio in samples. Cylindrical samples with 54 mm diameter and 110 mm length with 5 different porosity ratios ranging from 17 to 35 percent were made using Panplast lubricant. Samples were subjected to uniaxial compression test in two dry and saturated conditions and AE data were recorded. Data analysis showed that the dominant failure mode on samples of dry mortar with increasing porosity, increase toward the tension mode. With increasing of porosity and moisture content the numbers of micro crack decreases. Different methods are being used for monitoring of crack growth and failure mechanism in rock fracture. Acoustic Emission (AE) is one the methods used for micro crack monitoring in samples under pressure. Existence of porosity and humidity in rock and soil structure cause different effects on process of micro cracks and growth of micro cracks and finally their fracture. In this study, effects of porosity and humidity in micro crack growth and rock fracture are being analyzed. Four parameters which are highly effective in AE method namely hit, count, wave durability and fracture energy are used. Mortar (synthetic rock) was used to have a constant porosity ratio in samples. Cylindrical samples with 54 mm diameter and 110 mm length with 5 different porosity ratios ranging from 17 to 35 percent were made using Panplast lubricant. Samples were subjected to uniaxial compression test in two dry and saturated conditions and AE data were recorded. Data analysis showed that the dominant failure mode on samples of dry mortar with increasing porosity, increase toward the tension mode. With increasing of porosity and moisture content the numbers of micro crack decreases.

Summary : Wellbore instability can increase drilling time and sometimes leads to wells being side-tracked. Appropriate estimation of the weight of drilling mud can be mentioned as the key designing factor to ensure the mechanical stability of wellbores. Considering the elastoplastic behavior of the medium, yield criterion plays a key role in this analysis and estimation. Applying the Mohr-Coulomb criterion leads to underestimation of rock strength due to ignoring the effect of the intermediate principal stress. On the other hand, the Mogi-Coulomb yield criterion is able to consider the effect of the intermediate principal stress, while preserves the simplicity of the Mohr-Coulomb model. In this study, the elastic - perfectly plastic constitutive model is developed based on the Mogi-Coulomb criterion. Model predictions for some triaxial tests are compared with experimental data, and reasonable agreement is achieved. The proposed model is also applied for analyzing a wellbore stability problem and results are compared with two popular models, Mohr-Coulomb and Drucker-Prager, to investigate the effect of the intermediate principal stress.
The simplicity of the Mohr-Coulomb criterion makes it as one the most popular models in geomechanical analysis. However, ignoring the effect of the intermediate principal stress can be mentioned as the main shortcoming of this model. On the other hand, the effect of the intermediate principal stress has been widely studied in experimental and analytical investigations. The Mogi-Coulomb yield criterion, not only overcomes this shortcoming, but also conserves the simplicity of the Mohr-Coulomb model. Alajmi and Zimmerman (2005) analytically showed the ability of Mogi-Coulomb criterion in considering the effect of the intermediate principal stress. This investigation showed that this criterion can introduce a more realistic estimation of rocks strength.
Methodology and Approaches : An elastic-perfectly plastic constitutive model is developed based on the Mogi-Coulomb yield criterion. The proposed model is implemented to “FLAC”. Verification is done by simulating some triaxial test data. Numerical example is also conducted to investigate the efficiency of the model.
Results and Results of the numerical study shows that the Mohr-Coulomb criterion results in underestimation of rocks strength by ignoring the effect of the intermediate principal stress. On the other hand, the Drucker-Prager criterion leads to overestimation of the strength by considering identical effects for both intermediate and minimum principal stress. While the Mogi-Coulomb criterion introduces a more realistic estimation of the strength by moderating the effect of the intermediate principal stress.

Summary: Modelling and simulation have increased in the study of rock engineering in the past decades. Numerical simulation is an important tool for analysis that is impossible to do in the laboratory. The main reasons for using numerical modeling in laser drilling which can be mentioned are lack of access to high confining pressure in the existing laboratory condition, increase in the cost of drilling in large diameter, differentiation mechanical and thermal stresses and strain caused by the laser in the laboratory, as well as important secondary effects in laser drilling on rock. In this study, a Finite Element Method (FEM) is used for understanding the thermal and mechanical stresses caused by the ND: YAG laser drilling in the reservoir rocks. For this purpose, ABAQUS code was employed to analyse the thermal and mechanical stresses. A numerical model of a core rock was simulated and thermal properties of a reservoir rock such as thermal conductivity, heat capacity and density were imported into the code. By entering drilling rate to the model, tests carried out in the lab were simulated and after conformity with them, high confining pressures were imposed.
Laser perforating is a new scientific approach to the generation of uniform holes in oil and gas reservoir wells at a selected pitch to improve the permeability of rocks. Thermal stress generated by differential thermal expansion of minerals and high-temperature gradient, breaks the bonds between the grains. In this range of temperature, physical and chemical changes occur that are associated with the process of spallation. Hence, Laser rack spallation is a complicated phenomenon depending on many factors. Using experimental studies to comprehend this phenomenon is merely expensive and time-consuming. Since there are not enough techniques to appraise some of the factors, they should be studied in the laboratory. On the other hand, numerical modelling provides simulative action of the factors which are difficult to be considered by experimental research. Many researchers have been examined the laser cutting process. In previous studies, researchers focused mainly on some factors to improve the cutting quality and assess the thermal stress levels around the cutting section. However, these studies were limited mainly laser cutting of rock and has not been examined the thermal and mechanical stress analysis in detail.
Methodology and Approaches: The finite element model has been used to simulate the thermal and mechanical stresses induced by laser drilling ND: YAG. For this investigation, some samples have been taken from a hydrocarbon reservoir in Ahvaz. For this purpose, ABAQUS software was used and thermal properties of reservoir rocks, such as thermal conductivity, density and heat capacity were considered.
Results and Results of the numerical study show that the model has good agreement with the lab tests. Around the drilled holes, thermal stress induced by the laser is lower than the mechanical stress caused by confining pressure. And the distribution of the stress concentration has a high correlation with the amount of confining pressure.

The present study sought to test the efficacy of the Ohlson model (1995) combination with Piotroski index (2000) to predict stock returns in Stock Exchange and OTC companies in Iran. The dependent variable is stock returns in the next period, and the independent variables are changes in net profit, changes in equities, changes in Piotroski index in both current and prior periods as well as the first lag in dependent variable which is using data from the Panel during the years 2007 to 2013 and Eviews software and Generalized Method of Moments (GMM) statistical technique, to test research hypotheses. The results indicate that considering significance of all other independent variables and the results of the Wald test, combination of the Ohlson model and Piotroski index, is efficient in predicting stock returns. Piotroski index changes in the current and prior period is significantly correlated with stock returns, as well.

The in-situ stress is one of the most important parameters in the design of underground structures. Conventional methods such as in-situ stress measurements using hydraulic fracturing method has two main disadvantages are time and cost of this methods. Acoustic emission is one of the indirect in-Situ stress measurement methods which is based on the theory of the Kaiser effect. When a rock is stressed, it release acoustic signals this phenomenon is called acoustic emission. Kaiser Effect is defined as lack of acoustic signals in the lower stress levels than the previous maximum stress level. In other words, as long as rock is not reached to the previous maximum stress level, do not show significant acoustic emission. Several factors affect on Kaiser Effect such as delay time, temperature, rock fabric, porosity, discontinuities, joints and geological structure. In this paper, effect of the delay time on Kaiser Effect has been presented. The time between coring operations and acoustic emission test is called delay time. The limestone rock is selected as main samples of test and after preloading, reloading and acoustic emission test were carried out with different delay times. The results showed that the felicity ratio is less than 1, when delay time is about 20 days and after three months has increased to be more than one.

Laser perforating in rocks is a very complex phenomenon that its performance depends on many factors. Since it’s not possible to consider all of these factors in laboratory, numerical modeling is used. In this study, a finite element code (FEM) have been taken to model the thermal and mechanical stresses induced by laser drilling ND:YAG in the hydrocarbon reservoir rock samples. For this purpose the software ABAQUS was used to analyze the thermal and mechanical stresses induced by laser. It is found that Numerical models, show good agreement with the actual observation for holes with diameter of 2 millimeter. In addition, the larger the diameter of the hole is, the vaster the effective zone of stress concentration is. Therefore fracturing occurs in larger zone around the hole.Laser perforating in rocks is a very complex phenomenon that its performance depends on many factors. Since it’s not possible to consider all of these factors in laboratory, numerical modeling is used. In this study, a finite element code (FEM) have been taken to model the thermal and mechanical stresses induced by laser drilling ND:YAG in the hydrocarbon reservoir rock samples. For this purpose the software ABAQUS was used to analyze the thermal and mechanical stresses induced by laser. It is found that Numerical models, show good agreement with the actual observation for holes with diameter of 2 millimeter. In addition, the larger the diameter of the hole is, the vaster the effective zone of stress concentration is. Therefore fracturing occurs in larger zone around the hole.