Browsing by Author "Dharmaratne, PGR"

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item: Conference Full-text
Application of emulsion explosive and comparative study on water-gel explosives for rock quarrying in Sri Lanka
Dharmaratne, PGR; Hemalal, PVA; Rohitha, LPS; Herath, B; ; Abeysinghe, AMKB; Dassanayake, ABN; Elakneswaran, Y
Dynamite has been the premier and the only high explosive used for mining and construction activities in Sri Lanka for a long period of time. Negative environmental impacts, effect on health and security hazards led to the Government of Sri Lanka (GOSL) to issue directives to find a suitable substitute for Dynamite. Subsequently, Water-Gel explosive was introduced in the year 2011. The poor performance of Water-Gels in wet conditions and it’s low Velocity of Detonation encouraged the use of Emulsion explosives. This research was focused on performing a comparative study of the performance of both Water-Gels and Emulsion explosives by analysis of the ground vibration and the blast air over pressures. The methodology adopted was to conduct ten blasts at one single metal quarry site keeping all other parameters constant. Blasting tests were performed using Emulsion explosives and Water-Gel explosives and the resulting ground vibration and Air-Blast overpressures were measured with Blastmate 111model for each blast. Calculation of mean fragmentation was done and particle size distribution based on photographic evidence of each blast was analyzed. Analysis was carried out demarcating the resultant production pile of aggregates covering a cleared zone. Grid lines inserted on the muck pile facilitated particle counting using photographs and calculating the mean fragmentation.
item: Conference-Full-text
Assessment of environmental impacts resulting from ground vibrations due to piling activities and railway transport
(Department of Earth Resources Engineering, 2018-08) Piyarathna, HDAM; Godagama, GWADC; Maduranga, THT; Hemalal, PVA; Samaradivakara, GVI; Samaradivakara, GVI; Dharmaratne, PGR; Abeysinghe, AMKB; Samaradivakara, GVI
With the development of the country's economy, industrial activities close to urbanized areas have inceased tremendously. These activities are sources of ground vibrations impacting on human life. Resulting annoyance conditions near residential areas and possible human response to ground vibrations have been investigated in this study. Ground vibration have been monitored at precast pile driving sites and at a location close to Panadura-Moratuwa railway line using an A4-channel seismograph. Human perception and disturbance conditions associated with each location is discussed with the criteria given in British Standards. According to the ground vibrations levels measured at the piling site, up to 55 m distance from pile driving locations perceptible level of ground vibrations have been occurred thus caving annoyance to occupants. Zone with adverse comments, extends up to 37 m from the pile and adverse comment possible zone extend up to 50 m from the pile when using pile diver and piles with given specifications. According to ground vibration levels near the railway track, occupants in residential areas will experience annoyance as residential area contains ground vibrations in perceptible amount. Up to 27 m distance from the railway track, ground vibrations levels were measured up to a level of making complaints regarding annoyance made by train.The trench already existed near the railway track (parallel to the rail way track) is capable of reducing ground vibration levels up to 40%.
item: Article-Full-text
A comparison of global rare earth element (REE) resources and their mineralogy with REE prospects in Sri Lanka
(Elsevier, 2020) Batapola, NM; Dushyantha, NP; Premasiri, HMR; Abeysinghe, AMKB; Rohitha, LPS; Ratnayake, NP; Dissanayake, DMDOK; Ilankoon, IMSK; Dharmaratne, PGR
Rare earth elements (REEs), a group of 17 elements comprises 15 lanthanides, scandium and yttrium, are largely attracting the world’s attention due to their importance in a wide variety of advanced technological applications. Global REEs production is mainly sourced from resources, such as carbonatites, alkaline igneous rocks, placers, laterites, and ion-adsorption clays. Recently, REE demand has been escalating, especially due to the REE applications in renewable energy and defense sectors, expecting a worldwide shortage of REE supply in the future. Therefore, REEs have been widely accepted as strategic elements in the world, which compels to prospect for new and alternative REE resources. In this context, Sri Lanka has a favorable geological setting which implies the presence of REE mineralization. Previous geochemical studies in Sri Lanka have reported significant concentrations of REEs in different geological formations and mineral resources. Accordingly, Pulmoddai and other beach placer deposits, Eppawala carbonatite, alluvial placer deposits, and pegmatites have been identified as potential REE resources in Sri Lanka. Monazite, apatite, allanite, and zircon are the primary rare earth (RE) minerals found in the preceding resources. The Pulmoddai mineral sand deposit is considered as the most potential REE resource in the island, which is enriched in monazite containing more than 61% of light rare earth elements (LREEs). Similarly, Eppawala carbonatite contains high concentrations of LREEs. However, despite their significant REE enrichments, to date, no attempt has been made to recover these REE prospects, which essentially conceals their potential of catering for both local and global REE supply chains.
item: Conference-Full-text
Critical analysis of safety aspects of an underground graphite mine with reference to Bogala mines
(Department of Earth Resources Engineering, 2015-07) Karunarathne, KVP; Piyasena, DT; Marino, IJ; Sarvakaran, S; Hemalal, PVA; Dharmaratne, PGR; Hemalal, PVA
Trend analysis of occurrence of mine accidents was proposed to assess the risks associated with occurrence of underground accidents and human health in order to manage and control measures and support decision making. It provides the right balance between different concerns, such as safety and costs. For this purpose, information collected from Bogala graphite Lanka PLC located at Aruggammana in Kegalle district, Sri Lanka, was used to manage the risks affecting the health and safety of the miners. In order to categorize the data, various hazardous activities were identified and classified under eleven categories: Scaling, Hammering, Supporting, Lifting of weights, Drilling, Graphite transportation, Loading, Mucking, Machine/tool operating, Machine/tool repairing. The ranking process is accomplished by analyzing the past accident records. Further, four critical groups of body parts with different illnesses were obtained. These groups were; eye, limbs, back, head. From these groups, the most common injuries with the highest level of occurrence are sprains, cuts, bruises and contusions. According to the results, the proposed methodology can be a reliable technique for management of mine hazards and coping with uncertainties affecting the health and safety of miners when performance ratings are imprecise. The proposed recommendations can be primarily designed to identify potential hazards and help in taking appropriate measures to minimize or remove the risks before accidents occur in future mining activities in Bogala mines.
item: Conference-Full-text
Critical Evaluation of Blast- Induced Structural Damage Criteria for Buildings around Metal Quarries at Thudugala, Kaluthara
(2016-08-22) Hettiarachchi, MM; Priyasanka, IDP; Herath, HMWD; Mohanaruban, G; Dharmaratne, PGR; Hemalal, PVA
Quarrying can generate a number of on-site and off-site environmental effects as a result of blasting, excavation, crushing, screening, stockpiling and transport activities. Blasting is necessary for recovery of ore and production of aggregates in most underground and open cut mines, as well as in quarries. However, blasting can cause noise and ground vibration, which can have an impact upon nearby structures and people living close by. Hence, proper control of blasting practices is necessary to ensure both the safety of employees and the protection of the community from adverse effects. In Thudugala, in Kaluthura district, people those who are living close to quarries are highly subjected to these effects due to quarry blasting. In these circumstances, it was decided to conduct a research into the ground vibration impact in the area. Due to complexity of structures ranging from wattle-and-daub structures which do not have proper foundations to those built with good foundations, the applicability of single criteria of 5 mm/sec PPV level of vibration which is currently being used in Sri Lanka is inadequate. It is also noted that the above vibration criteria has been adopted in Sri Lanka without a proper theoretical foundation. In this research program, the propagation of cracks due to the blasting was assessed at the initial stage of the project. At the final stage, the optimum PPV values will have to be found for different types of structures by constructing them. In this area soil overburden is less. Therefore most of the structures have been constructed on rock. When blasting takes place, rock tends to vibrate and the intensity perceived is very high. Therefore crack propagation is high in these particular structures. It is also noticed that the cracks have further developed between the period between pre-blast crack survey and post-blast crack survey. It is due to large number of un-monitored blasts that have been conducted during that period. Therefore to solve this problem, it is recommended to carry out continuous monitoring of blasts.
item: Conference-Full-text
Critical evaluation of blast- induced structural damage criteria for buildings around metal quarries at Thudugala, Kaluthara
(Department of Earth Resources Engineering, 2016-07) Hettiarachchi, MM; Priyasanka, IDP; Herath, HMWD; Mohanaruban, G; Dharmaratne, PGR; Hemalal, PVA
Quarrying can generate a number of on-site and off-site environmental effects as a result of blasting, excavation, crushing, screening, stockpiling and transport activities. Blasting is necessary for recovery of ore and production of aggregates in most underground and open cut mines, as well as in quarries. However, blasting can cause noise and ground vibration, which can have an impact upon nearby structures and people living close by. Hence, proper control of blasting practices is necessary to ensure both the safety of employees and the protection of the community from adverse effects. In Thudugala, in Kaluthura district, people those who are living close to quarries are highly subjected to these effects due to quarry blasting. In these circumstances, it was decided to conduct a research into the ground vibration impact in the area. Due to complexity of structures ranging from wattle-and-daub structures which do not have proper foundations to those built with good foundations, the applicability of single criteria of 5 mm/sec PPV level of vibration which is currently being used in Sri Lanka is inadequate. It is also noted that the above vibration criteria has been adopted in Sri Lanka without a proper theoretical foundation. In this research program, the propagation of cracks due to the blasting was assessed at the initial stage of the project. At the final stage, the optimum PPV values will have to be found for different types of structures by constructing them. In this area soil overburden is less. Therefore most of the structures have been constructed on rock. When blasting takes place, rock tends to vibrate and the intensity perceived is very high. Therefore crack propagation is high in these particular structures. It is also noticed that the cracks have further developed between the period between pre-blast crack survey and post-blast crack survey. It is due to large number of un-monitored blasts that have been conducted during that period. Therefore to solve this problem, it is recommended to carry out continuous monitoring of blasts.
item: Conference Full-text
Critical evaluation of current environmental comfort conditions of Bogala underground
Lasantha, MML; Thushath, T; Somarathne, KGMS; Hemalal, PVA; Dharmaratne, PGR; Abeysinghe, AMKB; Dassanayake, ABN; Elakneswaran, Y
Ventilation is a basic part of all underground mine operations as fresh, cool air is required to remove stale, affected air from the workings. The inadequate ventilation often is the cause of lower worker efficiency leading to decreased productivity and increased accident rates. This study focuses on the evaluation of environmental comfort conditions in Bogala Underground, a medium-depth underground graphite mine located in Aruggammana, Sri Lanka. A detailed ventilation survey was carried out taking measurements of dry bulb temperatures, wet bulb temperatures, Dry Kata and Wet Kata thermometer values, air velocities, surface air temperature and barometric pressures at strategic points covering the entire mine. All results were compared with corresponding standard values which describe the standard conditions to be met for working underground. Recommendations were made to improve the present environmental comfort conditions by installing auxiliary fans in stopes where necessary which will enhance the immediate mine environment contributing to health and safety aspects of the underground working environment.
item: Conference-Full-text
Critical evaluation of industrial mineral mining methods in Sri Lanka
(Department of Earth Resources Engineering, University of Moratuwa, 2021-12) Jeewandara, JTP; Senarathna, MKT; Wickramarathna, CH; Sirisena, KMW; Hemalal, PVA; Lasantha, MML; Dharmaratne, PGR; Chaminda, SP; Jayawardena, CL; Dissanayake, DMDOK; Jayawardena, CL
Sri Lanka is rich in industrial minerals, including graphite, apatite, ilmenite, rutile, quartz, feldspar, kaolin, apatite, garnet sand, mica, calcite, and dolomite. Even though lots of mining methods are used to extract such minerals, only limited studies have been carried out in Sri Lanka to evaluate mining methods by means of main mining principles, such as safety, economy, and efficiency. This study focuses on the Bogala graphite mine, a narrow vein medium depth underground mine, and Aruwakkalu limestone open pit mine. To evaluate the overhand cut and fill mining method in Bogala mine, Equivalent Linear Overbreak or Slough (ELOS), which is a useful measurement for quantifying the unplanned dilution in narrow vein mining, is used. The favourability of the underground mining method is evaluated for a particular mine site using Key Deposit Indicators (KDIs), and it provides the best suited underground mine based on characteristics of the ore body. The fracture system presence in the Bogala mine requires a good support system to ensure the safety of underground workers. The efficiency of the loading and hauling equipment in the Aruwakkalu mine site is evaluated by Match Factor (MF).
item: Conference-Full-text
Delineation of potential sites for gemstone mining in Kura Ganga catchment, Ratnapura: a GIS approach
(Department of Earth Resources Engineering, 2015-07) Jaliya, RGC; Thotahewa, AHTTB; Palihakkara, CR; Siriwardena, PRR; Premasiri, HMR; Dharmaratne, PGR; Chaminda, SP; Senanayake, IP; Hemalal, PVA
Sri Lanka has been known as 'Ratnadeepa', which translates to 'Island of gems' because of the precious natural gemstones found in its gravelly soil. Even though the gem industry in Sri Lanka extends back to ancient times, studies on patterns of gemstone occurrences were rare. However, identification of potential gem bearing lands can provide guidelines in mining and land valuation. This study was carried out to identify the potential lands for gemstone mining in Kuru Ganga catchment, Ratnapura, based on patterns of gemstone occurrences and mining cost using integrated geo-spatial technologies. Fieldwork was conducted to collect gravel samples from riverbanks and gem mines. The samples were subjected to microscopic analysis to trace potential gemstones. The results obtained were combined with the data gathered from gem mines and mapped on a GIS platform to identify the occurrence patterns. Mining cost at each sampling location was estimated based on depth to the gem bearing gravel layer, "illamaSubsequently, potential lands for feasible gemstone mining were delineated through a knowledgedriven weighted analysis. The results depict that the South Western region of the Kuru Ganga catchment encompasses the highest feasibility of gem mining while North Eastern region of the catchment has the least feasibility of gemstone mining based on mining cost and values of potential gem varieties in the area.
item: Conference-Full-text
Design and fabrication of cable bolt for excavation in a fractured rock
(Department of Earth Resources Engineering, 2009-05) Dhanawardana, YLC; Siriwardana, HDPM; Henderson, SH; Kumara, HMCP; Indika, KAS; Dharmaratne, PGR; Welideniya, HS; Rohitha, LPS; Karunaratne, S
In fractured rock masses, large excavations have an unsupported stand-up times less than the minimum time required to support the roof after the excavation. Therefore, the principal objective in the design of a support system is to help the rock mass to support itself. The use of rock bolts is a very flexible supporting method that can be combined with wire mesh, shotcrete and concrete lining. During past years a wide variety of dowels and bolt types were developed but most of them failed within a short period and the cost were high. Advantages of cable strand supports have been well documented and include flexibility, strength, and ease of installation. Main objective of this project is to design rock bolts using discarded wire ropes or cables at a low cost. A detailed designing methodology was carried out to fabricate this bolt. The bolt consists of nearly 1.6m long cable and 16 cm of anchored part and cable tightening part. Outer diameter of bolt is 33 mm and inner diameter is 12 mm and used cable diameter is 5mm. Field data illustrated the amount of load measurements that the bolt can carry is 5 kN. Suggestions were made to improve the design, which will enhance bolt performance. Field tests carried out at Bogala Lanka Graphite Ltd proved that cable bolts are effective in Sri Lankan conditions.
item: Conference-Extended-Abstract
Design and fabrication of cable bolt for excavation in a fractured rock
(2009) Dhanawardana, YLC; Siriwardana, HDPM; Henderson, SH; Kumara, HMCP; Indika, KAS; Dharmaratne, PGR; Welideniya, HS; Rohitha, LPS
Most often in fractured rock masses, large excavations have an unsupported stand-up times less than the minimum time required to support the roof after the excavation. During past few years a wide variety of dowels and bolt types have been developed but most of them failed within a short period of time and the cost were high. Main objective of this research work was to design rock bolts using discarded cables at a low cost. The bolt consists of nearly 1.6m long cable and 16 cm of anchored part. Field data illustrated the amount of load that the bolt can carry as 5 KN. Suggestions were made to improve the design, which will enhance bolt performance. Field tests carried out at Bogala Graphite Lanka Ltd proved that cable bolts are effective in Sri Lankan conditions.
item: Conference-Abstract
Design and fabrication of cable bolt for excavation in a fractured rock
(2014-08-08) Dhanawardana, YLC; Siriwardana, HDPM; Henderson, SH; Kumara, HMCP; Indika, KAS; Dharmaratne, PGR; Welideniya, HS; Rohitha, LPS
In fractured rock masses, large excavations have an unsupported stand-up times Jess than the minimum time required to support the roof after the excavation. Therefore, the principal objective in the design of a support system is to help the rock mass to support itself. The use of rock bolts is a very flexible supporting method that can be combined with wire mesh, shotcrete and concrete lining. During past years a wide variety of dowels and bolt types were developed but most of them failed within a short period and the cost were high. Advantages of cable strand supports have been well documented and include flexibility, strength, and ease of installation. Main objective of this project is to design rock bolts using discarded wire ropes 01' cables at a low cost. A detailed designing methodology was carried out to fabricate this bolt. The bolt consists of nearly 1.6m long cable and 16 em of anchored part and cable tightening part. Outer diameter of bolt is 33 mm and inner diameter is 12 mm and used cable diameter is Smm. Field data illustrated the amount of load measurements that the bolt can carry is 5 kN, Suggestions were made to improve the design, which will enhance bolt performance. Field tests carried out at Bogala Lanka Graphite Ltd proved that cable bolts are effective in Sri Lankan conditions.
item: Conference-Full-text
Determination of depleted rock volume in open cast mines using photogrammetric techniques for the purpose of royalty calculation
(Department of Earth Resources Engineering, University of Moratuwa, 2021-12) Ariyarathne, RCDK; Samaraweera, SACV; Maduwantha, LSE; Insaf, MJM; Hemalal, PVA; Illankoon, IMTN; Dharmaratne, PGR; Chaminda, SP; Lasantha, MML; Dissanayake, DMDOK; Jayawardena, CL
In Sri Lanka, Geological Survey and Mines Bureau (GSMB) imposed royalty levy for aggregate production volume using an equation (indirect method) which utilises the quantity of explosives for the calculation. Since the equation resulted in higher deviations and the previous studies emphasise the advantages of photogrammetric 3-dimensional (3D) modelling (direct method) when determining production volume of bench blast, the present study focus on investigating its applicability to irregular faced dynamic quarry with uneven overburden. Pre and post 3D Digital Surface Models (DSMs) of the quarry were generated using the structure from motion (SFM) algorithm with Real-Time Kinematic (RTK) positioning system and Pix4D mapper software. Golden Software Surfer 16 was used to determine depleted rock volume as the difference between pre and post 3D DSMs. Results indicate a 5.50% deviation of the proposed method from true depleted rock volume determined by truck measurements due to uncleaned quarry face during the pre-Drone survey and unaccounted soil overburden removal. Presence of overburden while generating DSMs can be overcome by pile volume estimation of overburden and decreasing it from depleted rock volume when calculating production volume. GSMB equation calculated production deviate -32% from true production due to the unaccounted explosive amounts which contributed to the production and confirm the suitability of the proposed direct method (5.5% deviation) for determining the depleted rock volume in open-cast mines.
item: Conference-Full-text
Determination of the Specific Charge in Sri Lankan Quarrying Industry and Tunnelling Practice
(2015-08-14) Fainaz, MIM; Premathilaka, SDNN; Faslan, ACM; Gayan, WAMS; Gugathasan, N; Hemalal, PVA; Dharmaratne, PGR
At present, Sri Lanka is investheavily on the development of the country’s infrastructure., facilitating the vast demand for construction materials particularly, aggregate metals. Blast fragmentation is one of the most important aspects in open pit blasting. Blasted rock should be easily loaded and transported and the rock fragments should be adequately pre-conditioned (i.e. weakened) in order to reduce the energy requirements in down-stream processes such as, crushing and grinding. In Sri Lanka, the geological parameters of rocks vary throughout the island. Currently, there is a large number of metal quarries and mining activities operating all over the country, but the lack of optimum blasting practice and specific charge selection is a drawback to achieve the optimum benefits. In this research, an investigation on specific charge values have been carried out for the required level of fragmentation in quarrying industry and tunneling practice throughout Sri Lanka depending on geological parameters varying from region to region. Rock sample collection from various geological locations, determination of rock strength and hence, building-up a relationship between rock strength and specific charge values, experimentation of a fragmentation model have been carried out.
item: Conference-Full-text
Determination of the specific charge in Sri Lankan quarrying industry and tunnelling practice
(Department of Earth Resources Engineering, 2014-07) Fainaz, MIM; Premathilaka, SDNN; Faslan, ACM; Gayan, WAMS; Gugathasan, N; Hemalal, PVA; Dharmaratne, PGR; Hemalal, PVA
At present, Sri Lanka is inveslheavily on the development of the country's infrastructure., facilitating the vast demand for construction materials particularly, aggregate metals. Blast fragmentation is one of the most important aspects in open pit blasting. Blasted rock should be easily loaded and transported and the rock fragments should be adequately pre-conditioned (i.e. weakened) in order to reduce the energy requirements in down-stream processes such as, crushing and grinding. In Sri Lanka, the geological parameters of rocks vary throughout the island. Currently, there is a large number of metal quarries and mining activities operating all over the country, but the lack of optimum blasting practice and specific charge selection is a drawback to achieve the optimum benefits. In this research, an investigation on specific charge values have been carried out for the required level of fragmentation in quarrying industry and tunneling practice throughout Sri Lanka depending on geological parameters varying from region to region. Rock sample collection from various geological locations, determination of rock strength and hence, building-up a relationship between rock strength and specific charge values, experimentation of a fragmentation model have been carried out.
item: Thesis-Abstract
Durability of rocks under tropical conditions
Samaradivakara, GVI; Dharmaratne, PGR; Puswewala, UGA
Sri Lanka has a basement rock formation of metamorphic origin that the majority is gneissic type, which is intensively used in many of the civil engineering constructions. In addition, foundations of most of the important civil engineering structures are extended up to or into the fresh gneissic rock strata. Sri Lanka has a tropical climate. Therefore the study on durability of gneissic rocks under tropical conditions would be immensely beneficial to the construction industry of the country. The simulation of exact natural weathering conditions is quite complicated. This study concentrates mainly on how heat stress affects deterioration of index properties of gneissic rocks. When the rock mass gets heated, and cooled rapidly due to sudden rainfall, there is a possibility of propagating micro-fractures in the rock mass which will initiate weakening the strength properties of the rock mass. Most of the bridge abutments and dam constructions are associated with basement rock. In such locations rocks mass is alternately subjected to wetting and drying processes. Therefore the deterioration of rock resulting in its breakup, which is termed as "slaking" is also studied in this research. One hundred and sixty rock samples of gneissic rock of diameter 54mm (NX size) are tested in this research. Out of these 132 samples are fresh competent rocks and 28 are weathered to different degrees. These samples are selected from biotite gneiss and quartzo-feldspathic gneiss; the major two gneissic rock formations found in Sri Lanka. Fresh gneissic rock samples were subjected to heating and the weakening of their strength properties were studied upon cooling. Naturally weathered gneissic rock samples belonging to different weathering grades were also tested for their index properties. These were compared with the index properties of artificially weathered fresh gneissic rock samples and some correlations are established. The rate of deterioration of index properties of quartzo-feldspathic gneiss is seen to be more than that of biotite gneiss. Therefore more attention should be paid in the designing of foundations of important civil engineering structures in quartzo-feldspathic gneiss as far as the 'durability, is concerned, based on the project location..
item: Conference Full-text
Effect of trenching on bast-Induced ground vibration in Sri Lankan metal quarries
Samarakkody, SATI; Dharmaratne, PGR; Hemalal, PVA; Premasiri, HMR; Abeysinghe, AMKB; Dassanayake, ABN; Elakneswaran, Y
Problems due to ground vibration are a matter of serious concern for the users of explosives, as it is not possible to eliminate vibration totally or to contain them at the source. Efforts need to be made in controlling the vibration to fall within the safe level, without affecting the production schedules and economic viability of the project. If ground vibrations predicted or monitored exceed the statutory limit, control measures are taken by modifying the blast design parameters. In the research, digging a trench between the vibration source and the point of observation has been studied as a technique to reduce the transmission of the Rayleigh waves. The extent to which ground vibration could be reduced has been examined by field experiments carried out at an open cast quarry situated at Arankele, Sri Lanka. Blast vibration measurements have been carried out for active isolation, where the trench is excavated closer to the blasting point. An average of ten single shot hole blasts carried out correspondingly for four different depths of shot holes namely 1 m, 1.5 m, 2 m and 2.5 m with varying depths of trench shows ground vibration reduction percentages of 6.3%, 1.2%, 7.0% and 18.3% at a point immediately after the trench keeping the depth of the trench greater than that of the shot hole in each blast, and reduction percentages at a point closer to the observation point under the same conditions for the four shot hole depths were 72.2%, 54.4%, 55.1% and 45.1% respectively. The corresponding values after digging the trench show ground vibration reduction percentages as 57.8%, 53.9%, 40.5% and 36.7% at the point immediately after the trench location and vibration reduction percentages of 55.5%, 64.7%, 56.8% and 42.3% at the point closer to the point of observation for the corresponding four shot hole depths. Results indicate that after digging the trench, ground vibration reduction levels recorded were much higher, compared to those obtained before digging the trench. However, results obtained closer to the point of observation do not indicate a reduction for each shot hole depth. This leads to the conclusion that active isolation results in a considerable reduction in ground vibration level under given geological conditions.
item: Conference-Full-text
Effects of discontinuous properties on the stability of tunnels
(Department of Earth Resources Engineering, 2010-09) Nawarathna, THK; Kulathilake, LKNS; Perera, HDH; Premalal, PAM; Dharmaratne, PGR; Chaminda, SP; Rohitha, LPS; Ratnayake, NP; Abeysinghe, AMKB; Premasiri, HMR; Karunaratne, S
Many failures of underground openings during excavation are closely related to discontinuous properties of the surrounding rock mass and they affect differently to the stability of underground openings. In this research, attempts have been made to study the effect of discontinuities over the rock mass stability with various infilling materials, dip angles and strikes by using laboratory scaled models. Specimens were casted using cement concrete mixture and five different dip angles (30°, 45°, 60°, 75°, 90°) and three infilling materials (quarry dust, kaolin and graphite) have been selected for the study. Models were tested to determine their uni-axial compressive strength. The results indicate that the dip angle of the joints and the orientations of the tunnel axis have significant impacts on the stability of the tunnel. The dip angle at 90°, perpendicular to the tunnel axis shows a higher stability while the angle at 45°, shows the lowest stability. The tunnels excavated with axis parallel to the discontinuous plane should be avoided as much as possible. If it is unavoidable in any circumstances, well designed support system should be used. Types of infilling materials also affect the stability of the tunnel with graphite being the most unfavourable among the selected materials.
item: Conference-Full-text
Effects of joint orientation in tunneling
(2014-08-08) Selvasekaran, R; Appuhami, KAIS; Kumarasiri, SAI; Fernandopulle, SN; Lakmal, HMAG; Dharmaratne, PGR
This research is focused on the effects of joint orientation with respect to the direction of tunnel axis. It is expected that the stability of surrounding rock is affected by the strike and dip of the joints and the direction of the tunnel axis, whether it is with the dip or against dip etc. similarly the spacing of joints will also affect the stability. The orientation of joints in different directions can form blocks liable to fall. The objective of this research project is to determine the degree of influence of joints' strike and dip orientation in tunneling. Field works related to this project was carried out at the Bogala Graphite Lanka Ltd. Tunnel mapping and other observations related to the project were made at 489.6m level in Bogata mine. Models were made with joint spacing of 15mm with two joint sets (joint sets parallel to tunnel axis and joint sets perpendicular to tunnel axis). Tunnels were created with 90mm diameter with dip angles of joints are 00,300,600,and 900. The tunnels models are loaded using UCS machine and observed the behavior of rock mass around the tunnels during loading. From the results the most preferable dip angle for the joint strike perpendicular to the tunnel axis would be the 900 and for the joint strike parallel to the tunnel axis would be 00.
item: Conference-Full-text
Effects of joint orientation in tunneling
(Department of Earth Resources Engineering, 2009-05) Selvasekaran, R; Appuhami, KAIS; Kumarasiri, SAJ; Fernandopulle, SN; Lakmal, HMAG; Dharmaratne, PGR; Karunaratne, S
This research is focused on the effects of joint orientation with respect to the direction of tunnel axis. It is expected that the stability of surrounding rock is affected by the strike and dip of the joints and the direction of the tunnel axis, whether it is with the dip or against dip etc. similarly the spacing of joints will also affect the stability. The orientation of joints in different directions can form blocks liable to fall. The objective of this research project is to determine the degree of influence of joints' strike and dip orientation in tunneling. Field works related to this project was carried out at the Bogala Graphite Lanka Ltd. Tunnel mapping and other observations related to the project were made at 489.6 m level in Bogala mine. Models were made with joint spacing of 15 mm with two joint sets (joint sets parallel to tunnel axis and joint sets perpendicular to tunnel axis). Tunnels were created with 90 mm diameter with dip angles of joints are 0°, 30°, 60°, and 90°. The tunnels models are loaded using UCS machine and observed the behavior of rock mass around the tunnels during loading. From the results the most preferable dip angle for the joint strike perpendicular to the tunnel axis would be the 90° and for the joint strike parallel to the tunnel axis would be 0°.