Browsing by Author "Sastry, V.R."

Now showing 1 - 20 of 45

A Critical Comparison of Regression Models and Artificial Neural Networks to Predict Ground Vibrations
(Springer International Publishing, 2017) Ram Chandar, K.; Sastry, V.R.; Hegde, C.
Blasting is important and an essential prerequisite in any opencast mine for fragmenting hard deposits. Blasting always produces unwanted effects like ground vibrations, noise and fly rock; among which ground vibrations effect is more on surrounding structures. Propagation of ground vibrations can lead to destruction of surrounding structures. Prediction of ground vibrations especially in terms of peak particle velocity is beneficial as opposed to conventional data monitoring techniques which can be expensive as well as time consuming. This paper uses predictors to estimate the intensity of ground vibrations and compares different methods of prediction methods like linear regression, multiple linear regression, non linear regression (NLR) and artificial neural networks. Intensity of ground vibrations generated from blasting operations was monitored in three different mines of limestone, dolomite and coal; obtaining about 168 ground vibration recordings in total. The statistical modelling or data-driven modeling has shown promise in the prediction of blast vibrations. Proposed a system of introducing site specific rock parameters like poison’s ratio, uniaxial compressive strength of rock and Young’s modulus to improve the correlation coefficient using statistical modelling (commonly called feature engineering in machine learning circles). © 2016, Springer International Publishing Switzerland.
A Numerical Modelling Approach to Assess Deformations of Horseshoe Cavern on Account of Rock Mass Characteristics and Discontinuities
(Materials and Energy Research Center, 2023) Kuili, S.; Sastry, V.R.
Caverns are massive underground openings excavated for purposes like defense installations and nuclear waste disposal which becomes challenging for weak strata consisting of fractured rock masses and may result in future calamities. This study is dedicated to ascertain stability of a horseshoe cavern in different types of granitic rock masses as well as fractured rocks. Two different types of granitic formations are accounted and displacements obtained along cavern periphery have been illustrated in the preliminary part of this study. An increment in vertical displacement at the crown of 260% and lateral displacement of almost 170% for both walls were observed for moderately weathered rock. Further, implications due to orientation and frequency of joint sets on the displacements incurred has also been explored. This study acquires its novelty by considering combinations of joint sets with varying spacings for investigating their implications on cavern walls. Presence of discontinuities depicted that horizontal joint spaced closely increased the deformation magnitude which reduced with decrement in joint frequency. Subsequently, along with horizontal joints at 4m interval, vertical and oblique joints sets were also incorporated at different frequencies. Consideration of vertical joints at 2m spacing with horizontal joints resulted in 313.2% increase in vertical displacement at cavern crown as well as 340% and 363% increase in lateral deformation at the left and right wall, respectively in comparison to intact rock. In case of oblique joints spaced at 2m with horizontal joints, increment in vertical deformation at the crown proliferated to 329% in comparison to intact rock. © 2023 Materials and Energy Research Center. All rights reserved.
A numerical modelling approach to assess the behaviour of underground cavern subjected to blast loads
(China University of Mining and Technology, 2018) Kuili, S.; Sastry, V.R.
The paper gives an insight into the behaviour of large underground caverns which are subjected to blast loads. Caverns are generally constructed in hard rock formation which compels us to use blasting methods for the excavation works. Comparative study was done between models with intact rock mass and discontinuities to assess the stability of cavern as a result of blast loads. Numerical modelling was performed with 3 dimensional distinct element code (3DEC) to analyse the performance of cavern walls in terms of displacement and to compute peak particle velocities (PPV) both around the cavern periphery and at surface of models. Results showed that the velocity wave with higher frequency exhibited large displacements around the periphery of cavern. Computation of PPV showed that model with horizontal joint sets showed lower PPV in comparison to model with intact rock mass. PPV values were also analysed on the surface for model consisting vertical joints spaced at 4 m intervals. Comparative study of PPV on surface vertically above the blast location between models with horizontal joints spaced at 4 m and vertical joints at 4 m intervals were conducted. Results depicted higher magnitudes of PPV for model with vertical joints in comparison to model with horizontal joints. © 2018
An approach to tap electrical energy from ground vibrations
(American Institute of Physics Inc. subs@aip.org, 2018) Garimella, G.R.; Sastry, V.R.
Electrical Energy Generation has become an important aspect in Power Systems because of incremental demands from citizenry in Electrical Distribution System. Electrical power generation using piezo sensors can efficiently convert unwanted vibrations into direct electricity as a renewable energy source. Blasting operations in mines and quarries always result in ground vibrations, which are of major environmental concern. Studies were carried out in three different limestone mines and two different sandstone formations of coal mines, situated in Southern India, to assess and analyze the seismic energy resulting from the blast induced ground vibrations. In addition, Piezo generator circuits were developed and used in addition to the seismographs at different distances, from short to long range, in all mining locations, to tap the ground vibrations. In total, Electrical energy was tapped from 66 blast induced ground vibrations in limestone formation and 41 blast induced ground vibrations in sandstone formation, using piezo sensor based piezo generators developed. The range of voltage tapped from ground vibrations is up to 4531.42mV in limestone formation and 4277.51mV in sandstone formation. Â© 2018 Author(s).
Analysis of stress distribution in longwall barrier: a case study
(2010) Sastry, V.R.; Nair, R.
This paper presents results of a detailed study on the stress distribution in longwall barriers during extraction of coal in an underground mine. Analysis was carried out on the stress obtained at different locations in the barrier using finite element modelling and field monitoring. Results indicated that the zone of barrier lying in goaf experienced higher stress when compared with barrier lying in the solid zone. Stress in the region of barrier lying between 10 m ahead of face and 40 m behind the face (barrier section lying in goaf) was found to be the most critical in the design of barrier. © 2010 Inderscience Enterprises Ltd.
An approach to tap electrical energy from ground vibrations
(2018) Chandra, G.R.; Sastry, V.R.
Electrical Energy Generation has become an important aspect in Power Systems because of incremental demands from citizenry in Electrical Distribution System. Electrical power generation using piezo sensors can efficiently convert unwanted vibrations into direct electricity as a renewable energy source. Blasting operations in mines and quarries always result in ground vibrations, which are of major environmental concern. Studies were carried out in three different limestone mines and two different sandstone formations of coal mines, situated in Southern India, to assess and analyze the seismic energy resulting from the blast induced ground vibrations. In addition, Piezo generator circuits were developed and used in addition to the seismographs at different distances, from short to long range, in all mining locations, to tap the ground vibrations. In total, Electrical energy was tapped from 66 blast induced ground vibrations in limestone formation and 41 blast induced ground vibrations in sandstone formation, using piezo sensor based piezo generators developed. The range of voltage tapped from ground vibrations is up to 4531.42mV in limestone formation and 4277.51mV in sandstone formation. � 2018 Author(s).
Assessment of blast performance based on energy distribution
(2008) Sastry, V.R.; Ram Chandar, K.
Effective utilization of explosive energy in and around the blasthole gives better fragmentation with reduced unwanted results. Ineffective utilization of energy leads to dissipation of energy in the form of ground vibrations, noise, fly rock, back break etc. An attempt is made in this paper to present the results of the study on blast performance based on the energy dissipated into ground vibrations by analyzing the wave forms and estimating the energy distribution around blastholes by simulating blast patterns using JkSimBlast software.Generally, ground vibrations generated due to blasting operations are monitored at a known distance from blast site with a geophone / ground vibration monitor, in three mutually orthogonal, i.e longitudinal, transverse and vertical directions. Using such wave forms, the work done (energy) was estimated for all the signals in three directions, based on the principle that the area within the curve is 'work done'. Summation of energy in all three directions was considered to estimate the total work done (energy) from each blast event. Fourteen blasts were conducted in a limestone mine in southern India in 7 pairs. In each pair, one blast was conducted with shocktube initiation and other one with detonating cord initiation, keeping initiation patterns and all other parameters constant. Ground vibrations monitoring distance was also kept constant in each pair of blasts. The events were analyzed and the work done was estimated for each event. It was found that the detonating cord initiated blasts dissipated higher energy in the form of ground vibrations compared to shocktube initiated blasts. The blast performance was assessed based on the energy distribution around the blastholes. A comparative analysis was done with both the initiation systems. Once the blasthole is initiated, the explosive energy dissipates into the rock mass in the form of strain waves. The energy will be high at the vicinity of the blastholes, and it dissipates gradually with distance. If the energy is higher than the breaking strength of the rock mass the rock mass gets fragmented. Based on this concept, the blast patterns were simulated using JkSimBlast software. Around the blastholes, the energy distribution was divided into four zones / ranges. It was found that the area of highest energy zone around the blastholes is larger for shock tube initiated blasts than the detonating cord initiated blasts, which indicates effective energy utilization with shocktube initiation system.
Assessment of blast performance based on energy distribution
(2008) Sastry, V.R.; Ram Chandar, K.
Effective utilization of explosive energy in and around the blasthole gives better fragmentation with reduced unwanted results. Ineffective utilization of energy leads to dissipation of energy in the form of ground vibrations, noise, fly rock, back break etc. An attempt is made in this paper to present the results of the study on blast performance based on the energy dissipated into ground vibrations by analyzing the wave forms and estimating the energy distribution around blastholes by simulating blast patterns using JkSimBlast software.Generally, ground vibrations generated due to blasting operations are monitored at a known distance from blast site with a geophone / ground vibration monitor, in three mutually orthogonal, i.e longitudinal, transverse and vertical directions. Using such wave forms, the work done (energy) was estimated for all the signals in three directions, based on the principle that the area within the curve is 'work done'. Summation of energy in all three directions was considered to estimate the total work done (energy) from each blast event. Fourteen blasts were conducted in a limestone mine in southern India in 7 pairs. In each pair, one blast was conducted with shocktube initiation and other one with detonating cord initiation, keeping initiation patterns and all other parameters constant. Ground vibrations monitoring distance was also kept constant in each pair of blasts. The events were analyzed and the work done was estimated for each event. It was found that the detonating cord initiated blasts dissipated higher energy in the form of ground vibrations compared to shocktube initiated blasts. The blast performance was assessed based on the energy distribution around the blastholes. A comparative analysis was done with both the initiation systems. Once the blasthole is initiated, the explosive energy dissipates into the rock mass in the form of strain waves. The energy will be high at the vicinity of the blastholes, and it dissipates gradually with distance. If the energy is higher than the breaking strength of the rock mass the rock mass gets fragmented. Based on this concept, the blast patterns were simulated using JkSimBlast software. Around the blastholes, the energy distribution was divided into four zones / ranges. It was found that the area of highest energy zone around the blastholes is larger for shock tube initiated blasts than the detonating cord initiated blasts, which indicates effective energy utilization with shocktube initiation system.
Assessment of objective based blast performance: Ranking system
(2013) Sastry, V.R.; Ram Chandar, K.
Rock fragmentation using chemical energy is commonly followed for fragmenting and displacing the rock mass in mining, civil and other excavation projects. In case of mines, the objective of rock fragmentation is to get a uniform sized material to suit the subsequent operations like loading, hauling and crushing. In case of civil engineering projects like canals, tunnels, it is to provide the space for some facilities and the material produced may not be having a specific use. In case of blasting near to the human habitats or important structures like dams, ground vibrations generated should be within permissible safe limits, along with proper fragmentation. Cost reduction is also a prime factor in all the cases. In general, assessment of blast performance refers to fragmentation assessment. However, based on the objective, the approach to blast design may be different. An attempt is made through this paper to discuss different blast performance assessment methods, through a case study and a ranking system is proposed. Field studies were carried out in a limestone mine in southern India, using eight controlled blasts by changing the initiation system, initiation pattern and maintaining same blast geometry parameters. Blast performance was assessed based on fragmentation using digital image processing technique, energy distribution, and productive yield and powder factors resulting from the blasts. Rankings were given to different blasts as per the performance.
Assessment of objective based blast performance: Ranking system
(CRC Press, 2012) Sastry, V.R.; Ram Chandar, K.R.
Rock fragmentation using chemical energy is commonly followed for fragmenting and displacing the rock mass in mining, civil and other excavation projects. In case of mines, the objective of rock fragmentation is to get a uniform sized material to suit the subsequent operations like loading, hauling and crushing. In case of civil engineering projects like canals, tunnels, it is to provide the space for some facilities and the material produced may not be having a specific use. In case of blasting near to the human habitats or important structures like dams, ground vibrations generated should be within permissible safe limits, along with proper fragmentation. Cost reduction is also a prime factor in all the cases. In general, assessment of blast performance refers to fragmentation assessment. However, based on the objective, the approach to blast design may be different. An attempt is made through this paper to discuss different blast performance assessment methods, through a case study and a ranking system is proposed. Field studies were carried out in a limestone mine in southern India, using eight controlled blasts by changing the initiation system, initiation pattern and maintaining same blast geometry parameters. Blast performance was assessed based on fragmentation using digital image processing technique, energy distribution, and productive yield and powder factors resulting from the blasts. Rankings were given to different blasts as per the performance. © 2013 Taylor & Francis Group, London. © 2013 by Taylor & Francis Group, LLC. All rights reserved.
Assessment of objective based blast performance: Ranking system
(2013) Sastry, V.R.; Ram Chandar, K.R.
Rock fragmentation using chemical energy is commonly followed for fragmenting and displacing the rock mass in mining, civil and other excavation projects. In case of mines, the objective of rock fragmentation is to get a uniform sized material to suit the subsequent operations like loading, hauling and crushing. In case of civil engineering projects like canals, tunnels, it is to provide the space for some facilities and the material produced may not be having a specific use. In case of blasting near to the human habitats or important structures like dams, ground vibrations generated should be within permissible safe limits, along with proper fragmentation. Cost reduction is also a prime factor in all the cases. In general, assessment of blast performance refers to fragmentation assessment. However, based on the objective, the approach to blast design may be different. An attempt is made through this paper to discuss different blast performance assessment methods, through a case study and a ranking system is proposed. Field studies were carried out in a limestone mine in southern India, using eight controlled blasts by changing the initiation system, initiation pattern and maintaining same blast geometry parameters. Blast performance was assessed based on fragmentation using digital image processing technique, energy distribution, and productive yield and powder factors resulting from the blasts. Rankings were given to different blasts as per the performance.
Assessment of seismic energy obtained from blast induced ground vibrations using signal processing computation techniques
(2017) Sastry, V.R.; Chandra, G.R.
Enhanced demand for coal and minerals in the country has developed an interest on the environmental problems, which may have potential harm and cause disturbance. Ground vibrations generated due to blasting operations in mines and quarries are very important environmental aspect to be looked into by the researchers. It is clear that a small amount of total explosive energy is being utilized in blasting for breakage of rock mass while the rest is being wasted. The amount of energy which is wasted causes various environmental issues such as ground vibrations, air over pressure and fly rock. Ground vibrations caused by blasting cannot be totally eliminated, yet they can be minimized as far as possible through a suitable blasting methodology. Considerable amount of work has been done to identify ground vibrations and assess the blast performance in terms of the intensity of ground vibrations. However, not much research has gone into the seismic energy and utilizing this energy in understanding performance of blast rounds. In this paper, an attempt was made for the estimation of seismic energy dissipated at different distances from the blast site using Signal Processing Techniques with the help of DADiSP and Advanced Blastware software in three different formations, viz. Limestone, Sandstone and Underground Coal Mine. In total, 116 blast vibration events from Limestone Mines, 96 blast vibration events from Underground Coal Mine and 43 blast vibration events from Sandstone Mines were collected using ground vibration monitors for Signal Processing Analysis of Seismic Energy. Blast induced ground vibrations were recorded in three orthogonal directions collecting 2100-2500 particle motion samples for each. � 2016 IEEE.
Assessment of seismic energy obtained from blast induced ground vibrations using signal processing computation techniques
(Institute of Electrical and Electronics Engineers Inc., 2017) Sastry, V.R.; Garimella, G.R.
Enhanced demand for coal and minerals in the country has developed an interest on the environmental problems, which may have potential harm and cause disturbance. Ground vibrations generated due to blasting operations in mines and quarries are very important environmental aspect to be looked into by the researchers. It is clear that a small amount of total explosive energy is being utilized in blasting for breakage of rock mass while the rest is being wasted. The amount of energy which is wasted causes various environmental issues such as ground vibrations, air over pressure and fly rock. Ground vibrations caused by blasting cannot be totally eliminated, yet they can be minimized as far as possible through a suitable blasting methodology. Considerable amount of work has been done to identify ground vibrations and assess the blast performance in terms of the intensity of ground vibrations. However, not much research has gone into the seismic energy and utilizing this energy in understanding performance of blast rounds. In this paper, an attempt was made for the estimation of seismic energy dissipated at different distances from the blast site using Signal Processing Techniques with the help of DADiSP and Advanced Blastware software in three different formations, viz. Limestone, Sandstone and Underground Coal Mine. In total, 116 blast vibration events from Limestone Mines, 96 blast vibration events from Underground Coal Mine and 43 blast vibration events from Sandstone Mines were collected using ground vibration monitors for Signal Processing Analysis of Seismic Energy. Blast induced ground vibrations were recorded in three orthogonal directions collecting 2100-2500 particle motion samples for each. Â© 2016 IEEE.
Assessment of Structural Damage Due to Blasting in Hydro Power Tunnel
(Springer Science and Business Media Deutschland GmbH, 2022) Naveen, G.C.; Sastry, V.R.; Ram Chandar, K.R.
Excavation is a major activity in construction of mega underground hydropower project. Successful excavation of access and water conducting tunnels and caverns of different size and shapes by adopting highly economical and efficient method of excavation like drilling and blasting in extreme geological conditions makes the hydropower project a manmade marvel. The national codes which regulates the safety of structures while using explosives are successfully adopted where the tolerable limits for blast induced seismic waves are provided for different type of structures. This paper deals with impact of 9Â m(W) and 8Â m(H) tunnel blast induced seismic vibrations on the underground and surface concrete structures. The outcome of tunnel blasting with reference to peak particle velocity and related displacements gave a unique results where the seismic wave produced displacements up to 0.04Â mm at large underground openings (250Â m(L) Ã— 18Â m(W) Ã— 59Â m(H)) when compared to displacements of 0.016Â mm in small openings of 9Â m(W) Ã— 8Â m(H) with similar peak particle velocity levels of 20Â mm/sec. These results subjected the structures which are located in the larger underground openings to lose their strength easily when compared to the structures located in small openings. Further, the structures located in the surface are more vulnerable to get damaged due to higher displacement recordings up to 0.123Â mm. Experimental outcome was recorded for various blast design and results were further analyzed to optimize the blast parameters for successful control of blast induced vibration zone within 60Â m. The relation between the structure locations where blast induced seismic wave propagates seems to play a key role in influencing on the structural damage, where less influence of peak particle velocity is observed. Â© 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
Behaviour of large underground cavern during construction in himalayas - a case study
(CAFET INNOVA Technical Society cafetinnova@gmail.com 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2014) Naik, S.R.; Sastry, V.R.
Construction of large underground caverns in Himalayas is challenging due to complex geological and insitu stress conditions. Understanding the behaviour of such caverns during construction stage is possible only with extensive instrumentation. A case study of a large cavern under construction in Himalayan region in Bhutan is considered. Results from various types of instruments are discussed in this paper. Instrumentation data shows that Himalayan rock mass particularly with phyllitic quartzite exhibits large deformations thus requiring careful selection of support and excavation methodology. © 2014 CAFET-INNOVA TECHNICAL SOCIETY.
Behaviour of tunnel and surrounding strata using 3Dec numerical modelling: Case study of an U/G metro rail project
(CAFET INNOVA Technical Society cafetinnova@gmail.com 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2012) Rebello, R.; Sastry, V.R.; Shivashankar, R.; Laksmi, S.
Tunnel serves various purposes including transportation. A case study of an underground metro rail project involving considerable length of the tunnel was taken up for this study. This paper presents the analysis carried out for a stretch of 350m long tunnel being constructed for an underground metro. Modeling was carried out at seven different cross sections of tunnel, using 3DEC software, incorporating the strata characteristics. Study was carried out for the stability of tunnel with and without support. Observations were made about the behaviour of tunnel under given conditions for Vertical Stress, Vertical Displacement, at points like crown of tunnel and at the surface. Minute displacement of 0.05mm was observed particularly at the chainage where the tunnel is completely passing strong rock at Chainage 9345m. Tunnel is passing through Moderately Weathered Rock at Chainage 9295m, and the analysis resulted in a displacement of 4mm without support which has reduced to 0.5mm after placing the lining. Higher displacements were observed at chainages where the tunnel is passing through Silty sand, Highly Weathered Rock and Sandy Silt. Displacement at the tunnel crown increased to 18.6mm where the tunnel is passing through Silty sand (Chainage 9495m). © 2012 CAFET-INNOVA TECHNICAL SOCIETY.
Blast vibration signal analysis using S-transform
(2016) Teja, V.V.S.A.; Chaitanya, S.V.; Akula, U.; Srihari, P.; Sastry, V.R.
Rock blasting in mines and quarries is an important operation meant for fragmenting and displacing the hard rock mass / strata. The unavoidable environmental effect is the ground vibration, resulting from the wastage of explosive energy. Ground vibrations travelling to far off distances may have effect on the structures. Signal processing techniques play a vital role in analyzing the velocity of ground vibration signals in rock blasting. So far, time-frequency domain is being used for analyzing the ground vibration signals. However, usage of S-Transform, we get frequency dependent resolution of time-frequency domain. It is possible to simultaneously analyze the signal using time, frequency and amplitude values obtained by applying S-transform. A case study is presented in this paper, wherein the S-Transform is applied to the ground vibration velocity signals, which helps in better understanding and analysis of the signal compared to Fourier transform and Wavelet transform techniques. � 2016 IEEE.
Blast vibration signal analysis using S-transform
(Institute of Electrical and Electronics Engineers Inc., 2016) Teja, V.V.S.A.; Chaitanya, S.V.; Akula, U.; Srihari, P.; Sastry, V.R.
Rock blasting in mines and quarries is an important operation meant for fragmenting and displacing the hard rock mass / strata. The unavoidable environmental effect is the ground vibration, resulting from the wastage of explosive energy. Ground vibrations travelling to far off distances may have effect on the structures. Signal processing techniques play a vital role in analyzing the velocity of ground vibration signals in rock blasting. So far, time-frequency domain is being used for analyzing the ground vibration signals. However, usage of S-Transform, we get frequency dependent resolution of time-frequency domain. It is possible to simultaneously analyze the signal using time, frequency and amplitude values obtained by applying S-transform. A case study is presented in this paper, wherein the S-Transform is applied to the ground vibration velocity signals, which helps in better understanding and analysis of the signal compared to Fourier transform and Wavelet transform techniques. Â© 2016 IEEE.
Computer aided slope stability analysis
(2006) Sastry, V.R.; Ram Chandar, K.; Santosh, M.
Primary purpose of slope stability analysis in most of the engineering applications is to provide safe and economic design of slopes that prevent failure. The analysis technique chosen depends on both site conditions and potential mode of failure which depends upon the rock mass characteristics. Various slope stability analysis techniques include physical, numerical and analytical methods. Physical modeling is a time consuming process and a costly affair, while analytical method involves past experiences, it is site specific and depends upon various parameters which are difficult to quantify. Numerical analysis with sophisticated softwares provides an accurate solution within short duration. This paper presents an in-house developed software package called "V-slope" to analyze and interpret the slope with options for suggesting suitable safety measures based on the nature of slope. Slip circle and tension crack techniques were considered for analysis. The slope profile for different factor of safety (FOS) values will be displayed on the screen for easy understanding. In case the FOS is lower than the required, the V-slope gives suggestive measures. In case of temporary slopes the only way by which slope failure can be prevented is by decreasing the slope angle and in such cases the program gives additional volume of material to be excavated and the likely additional cost incurred for various slope angle options. For permanent slopes, option is provided for designing the soil nails, i.e. number of bolts required, length, diameter and spacing of the bolts etc. Finally the V-slope is compared with a comprehensive commercial software package Slide and the results were found very much satisfactory.
Effect of lower seam old workings on longwall powered supports in upper seam
(2007) Sastry, V.R.; Nair, R.; Venkat, Ramaiah, M.S.
Load bearing capacity of powered roof supports is a key issue in the design of longwall panels. The existence of multiple seams in a given project may involve over mining or undermining operations across different seams. The paper envisages variation in stress distribution and load on powered supports in the upper seam longwall panel due to the presence of already mined out bottom seam consisting goaf, pillars and openings through detailed field investigations in an underground coal mine followed by finite element modeling study. Studies revealed that for every 40 m of face retreat, the load from the roof gradually gets transferred from the panel to the goaf. Stress distribution over chock shields was considerably affected when the face in upper seam reached 15-25m zone above the openings in lower seam. The presence of barrier in the bottom seam increases load on the chock shields in longwall panel of upper seam. � 2007 Taylor & Francis Group, London.