Cost
Content
COST CUTTING MEASURES IN THE CONSTRUCTION OF UNDERGROUND HYDRO ELECTRIC POWER PROJECTS
C.PURUSHOTHAMAN
ASSISTANT EXECUTIVE ENGINEER/CIVIL TAMILNADU ELECTRICITY BOARD CHENNAI-2, INDIA
Email:[email protected] ABSTRACT India has made rapid strides in the last two decades in the development of underground hydroelectric power projects. Experiences gained so far from large number of underground hydroelectric power projects implemented in India shows that most of the projects have suffered from cost and time over-runs during construction. As a result, cost of the projects has increased many folds and resulted in increase in cost of generation. All efforts are to be made to complete the project within the estimated time and cost. This paper attempts to suggest certain measures for cutting down the cost of the underground hydroelectric power projects. 1.0 INTRODUCTION
India has made remarkable progress in the last two decades in the development of underground hydropower projects. Hydropower from underground powerhouses accounts about 20% of the total hydropower generated in India. Many underground projects have already been constructed. More and more hydropower projects are being planned and constructed underground. Experiences gained so far from large number of underground hydro power projects implemented in India shows that most of the projects have suffered from cost and time over-runs during construction. Thus the benefits have not been realised in expected time and consequently returns are smaller than anticipated. There is lots of scope for cutting down cost of hydro projects during pre-construction and construction stages. 2.0 COMPONENTS OF UNDERGROUND HYDRO ELECTRIC PROJECT Intake Structure, Gate Shaft, Headrace Tunnel, Surge Shaft, Pressure Shaft and Penstock, Valve House, Power House complex consisting of power house cavern, transformer cavern, bus duct tunnels, escape tunnel etc., Access tunnel to the underground power house, Cable Shaft, Tailrace Tunnel, Surge Cavern, Surface Switchyard and Transmission lines are salient components of underground hydroelectric project. 3.0 COST CUTTING MEASURES The following measures may be considered in different stages of implementation of the underground hydroelectric project for cutting down the time and cost of construction and to commission the project in time. The location of powerhouse cavern shall be fixed in such a way that the access tunnel, tailrace tunnel, headrace tunnel, pressure shaft etc., are as short as possible. The surface switchyard shall be finalized such that the length of cable tunnel/shaft is as short as possible
Sufficient number of construction Adits of shorter length are to be provided for long tunnels, inclined shafts, large caverns like powerhouse, transformer caverns etc, at suitable location(s) to facilitate as additional working faces and to cut down the construction time The construction Adits may be provided in the raising gradient from portal as far as possible to drain the seepage water if any by gravity. Such raising gradient avoids regular pumping of seepage water All the tunnels, inclined/vertical shafts and powerhouse cavern are to be routed/located in good quality of rock with sufficient rock cover as far as possible to minimise geological problems and quantum of rock supports The maximum width of the powerhouse and other caverns may be kept in the order of 20m. Sufficient width of rock cover shall be left between the underground cavities for better stability and minimising rock support The orientation of the underground caverns for powerhouse, transformer, valve house and surge caverns shall be oriented in such a way that the longer axis of the cavern lies parallel to the major in-situ principle stress and perpendicular to the joint sets. Such orientation will minimise the extent of over break and quantum of rock support Precise tunnel surveying instruments may be employed for fixing the alignment and sill levels of tunnels/shafts and checking the same at periodic intervals during tunneling All independent components of the project may be taken up for construction simultaneously. Suitable tunneling method may be selected based on the geology of tunneling media, rock cover, available construction time etc. Suitable drilling and blasting pattern may be adopted to obtain maximum pull with minimum charges and minimum over break depending upon size and shape of tunnel section and quality of rock to be excavated. Proper blasting technique may be adopted to obtain smooth wall in caverns Various tunneling operations may be overlapped to the extent possible to reduce the cycle time. Proper sequence of excavation for the underground powerhouse and Transformer caverns, valve house and surge caverns etc. may be adopted to cut down the excavation time Dumping yards for dumping of excavated tunnel muck may be located as near as possible to minimise lead distance and cycle time. Coarse aggregate from the excavated tunnel muck dumped at the nearest dumping yard may be collected and the same used for concreting works Rock participation may be considered in the design of steel liners for the pressure shaft and penstock wherever rock cover is sufficient. High yield strength steel plates conforming to ASTM grade not requiring stress relieving may be considered for fabrication of pressure shaft and penstock steel liners subjected to high pressure. The steel liners to be erected shall be prefabricated and assembled in long section of 5m to 7.5m lengths close to the work site so that the same may be available for erection immediately after completion of excavation for headrace tunnel, pressure shaft. Readymade spiral welded steel pipes available in the market may be considered for low-pressure penstock pipes, as it is cheaper and technically superior than the conventional longitudinal seam pipes Adequate proper rock supports as per the design requirement shall be provided immediately after excavation to avoid distress formation. Providing rock support after distress formation is a time consuming and costlier task. Rock supports may be installed immediately after excavation and before benching down the cavern. Similarly, the instruments required for instrumentation purpose may be installed immediately after excavation. Rock supports for the underground cavities may be optmised based on 2D/3D numerical modeling studies. Geological surprises occur in the form of shear zones or weak zones. Such zones may be foreseen in advance by detailed geo-technical investigation and negotiated carefully during tunneling. The rock supports as recommended by the engineering Geologist are to be carried out as a whole and not in piecemeal. Close interaction between the Geologists and the Engineers is essential during construction for substantiation and corrections in design decisions taken previously Rock ledges for supporting of Electrically Operated Traveling (EOT) crane in the powerhouse cavern, valve chamber etc., may be considered. In such case, columns may be terminated at the service bay level itself. Provision of rock ledges enables erection of EOT crane immediately after excavation.
Lake tapping/piercing technique may be considered for connecting the headrace tunnel/pressure shaft/penstock with the existing reservoir. In such case depletion of existing reservoir for construction of intake structure not required. Concrete lining may be restricted up to full supply level wherever rock is good in the case of free flow tunnel carrying water from the powerhouse Adequate safety measures to the workers may be planned and provided during construction Activities in critical path shall not be delayed on any account in order to keep up final commissioning date of the project. Any delay in one activity in the critical path, will affect the commencement of subsequent activities Periodical co-ordination meeting among the design consultants, contractors and the owner of the project are to be convened to sort out problems then and there Engineers and engineering Geologists having sufficient knowledge in the tunneling works and rock mechanics shall be posted in the planning, design and construction of the underground projects. Transfer of Geologists and Engineers involved in the execution of the project frequently may be avoided The civil works associated with erection of generating machinery, transformers etc., may be entrusted to the agency to whom the scope of supply, erection, testing and commissioning of such works awarded Incentives for completion of various project activities on or before scheduled completion date may be declared for the contractors The contract document shall be flexible in regard to decision making as per the real site condition and problems encountered during construction Disputes between the owner of the project and the contractors in respect of works under execution shall be settled immediately so that the progress of subsequent works are not affected Modern construction equipments which are more efficient, reliable and safe shall be deployed for execution of the project. Use of modern construction equipments should not be viewed as a costly proportion whenever such application can result in shortening the total construction period of the project Compressors, Alimak, Winch and other tunneling machinery and equipments shall be maintained properly to avoid frequent break down. Adequate spares parts for the equipments may be procured and kept ready for immediate replacement and repairs in the event of any break down The project authority shall maintain uninterrupted power supply to the tunneling works.
4.0 SUMMARY Most of the underground hydroelectric projects implemented in India have suffered from cost and time over-runs during construction. As a result, cost of the projects has increased many folds and resulted in increase in cost of generation. All efforts are to be made to complete the project within the designated time and cost. Measures suggested in this paper would be beneficial to the Engineers involved in the planning, design and construction of underground hydro electric projects to complete the project within the estimated cost and time.
REFERENCES
1. Hoek and Brown, Underground Excavation in Rock, Institution of Mining and Metallurgy, London, 1980. 2. Grimstand, E., and Barton, N., Updating of the Q system for NMT, Proceedings of the International Symposium on Sprayed Concrete – Modern use of Wet Mix Sprayed Concrete for Underground Support, Fagernes, Norway, 1993.
6. Purushothaman. C, Design and Construction of an Under Ground Power House Cavern for Pykara Ultimate Stage Hydro Electric Project, proceedings of Regional Symposium on Advanced Rock Mechanics Frontiers to meet the Challenges of 21st Century, New Delhi, India, September 2002.
BIO-DATA OF AUTHOR
C.PURUSHOTHAMAN graduated in Civil Engineering from the university of Madurai in 1988. He obtained master’s degree in Soil Mechanics and Foundation Engineering at the Anna University, Chennai, India in 1991. In 1991, he joined Tamil Nadu Electricity Board as Assistant Engineer and now he is serving as Assistant Executive Engineer. He has associated with planning, design, construction and commissioning of Pykara Ultimate Stage Hydroelectric Project (150MW) in the Nilgiris district of Tamil Nadu. He has been associating with construction of underground surface hydroelectric power projects and thermal power projects for the past eighteen years.
C.PURUSHOTHAMAN
ASSISTANT EXECUTIVE ENGINEER/CIVIL TAMILNADU ELECTRICITY BOARD CHENNAI-2, INDIA
Email:[email protected] ABSTRACT India has made rapid strides in the last two decades in the development of underground hydroelectric power projects. Experiences gained so far from large number of underground hydroelectric power projects implemented in India shows that most of the projects have suffered from cost and time over-runs during construction. As a result, cost of the projects has increased many folds and resulted in increase in cost of generation. All efforts are to be made to complete the project within the estimated time and cost. This paper attempts to suggest certain measures for cutting down the cost of the underground hydroelectric power projects. 1.0 INTRODUCTION
India has made remarkable progress in the last two decades in the development of underground hydropower projects. Hydropower from underground powerhouses accounts about 20% of the total hydropower generated in India. Many underground projects have already been constructed. More and more hydropower projects are being planned and constructed underground. Experiences gained so far from large number of underground hydro power projects implemented in India shows that most of the projects have suffered from cost and time over-runs during construction. Thus the benefits have not been realised in expected time and consequently returns are smaller than anticipated. There is lots of scope for cutting down cost of hydro projects during pre-construction and construction stages. 2.0 COMPONENTS OF UNDERGROUND HYDRO ELECTRIC PROJECT Intake Structure, Gate Shaft, Headrace Tunnel, Surge Shaft, Pressure Shaft and Penstock, Valve House, Power House complex consisting of power house cavern, transformer cavern, bus duct tunnels, escape tunnel etc., Access tunnel to the underground power house, Cable Shaft, Tailrace Tunnel, Surge Cavern, Surface Switchyard and Transmission lines are salient components of underground hydroelectric project. 3.0 COST CUTTING MEASURES The following measures may be considered in different stages of implementation of the underground hydroelectric project for cutting down the time and cost of construction and to commission the project in time. The location of powerhouse cavern shall be fixed in such a way that the access tunnel, tailrace tunnel, headrace tunnel, pressure shaft etc., are as short as possible. The surface switchyard shall be finalized such that the length of cable tunnel/shaft is as short as possible
Sufficient number of construction Adits of shorter length are to be provided for long tunnels, inclined shafts, large caverns like powerhouse, transformer caverns etc, at suitable location(s) to facilitate as additional working faces and to cut down the construction time The construction Adits may be provided in the raising gradient from portal as far as possible to drain the seepage water if any by gravity. Such raising gradient avoids regular pumping of seepage water All the tunnels, inclined/vertical shafts and powerhouse cavern are to be routed/located in good quality of rock with sufficient rock cover as far as possible to minimise geological problems and quantum of rock supports The maximum width of the powerhouse and other caverns may be kept in the order of 20m. Sufficient width of rock cover shall be left between the underground cavities for better stability and minimising rock support The orientation of the underground caverns for powerhouse, transformer, valve house and surge caverns shall be oriented in such a way that the longer axis of the cavern lies parallel to the major in-situ principle stress and perpendicular to the joint sets. Such orientation will minimise the extent of over break and quantum of rock support Precise tunnel surveying instruments may be employed for fixing the alignment and sill levels of tunnels/shafts and checking the same at periodic intervals during tunneling All independent components of the project may be taken up for construction simultaneously. Suitable tunneling method may be selected based on the geology of tunneling media, rock cover, available construction time etc. Suitable drilling and blasting pattern may be adopted to obtain maximum pull with minimum charges and minimum over break depending upon size and shape of tunnel section and quality of rock to be excavated. Proper blasting technique may be adopted to obtain smooth wall in caverns Various tunneling operations may be overlapped to the extent possible to reduce the cycle time. Proper sequence of excavation for the underground powerhouse and Transformer caverns, valve house and surge caverns etc. may be adopted to cut down the excavation time Dumping yards for dumping of excavated tunnel muck may be located as near as possible to minimise lead distance and cycle time. Coarse aggregate from the excavated tunnel muck dumped at the nearest dumping yard may be collected and the same used for concreting works Rock participation may be considered in the design of steel liners for the pressure shaft and penstock wherever rock cover is sufficient. High yield strength steel plates conforming to ASTM grade not requiring stress relieving may be considered for fabrication of pressure shaft and penstock steel liners subjected to high pressure. The steel liners to be erected shall be prefabricated and assembled in long section of 5m to 7.5m lengths close to the work site so that the same may be available for erection immediately after completion of excavation for headrace tunnel, pressure shaft. Readymade spiral welded steel pipes available in the market may be considered for low-pressure penstock pipes, as it is cheaper and technically superior than the conventional longitudinal seam pipes Adequate proper rock supports as per the design requirement shall be provided immediately after excavation to avoid distress formation. Providing rock support after distress formation is a time consuming and costlier task. Rock supports may be installed immediately after excavation and before benching down the cavern. Similarly, the instruments required for instrumentation purpose may be installed immediately after excavation. Rock supports for the underground cavities may be optmised based on 2D/3D numerical modeling studies. Geological surprises occur in the form of shear zones or weak zones. Such zones may be foreseen in advance by detailed geo-technical investigation and negotiated carefully during tunneling. The rock supports as recommended by the engineering Geologist are to be carried out as a whole and not in piecemeal. Close interaction between the Geologists and the Engineers is essential during construction for substantiation and corrections in design decisions taken previously Rock ledges for supporting of Electrically Operated Traveling (EOT) crane in the powerhouse cavern, valve chamber etc., may be considered. In such case, columns may be terminated at the service bay level itself. Provision of rock ledges enables erection of EOT crane immediately after excavation.
Lake tapping/piercing technique may be considered for connecting the headrace tunnel/pressure shaft/penstock with the existing reservoir. In such case depletion of existing reservoir for construction of intake structure not required. Concrete lining may be restricted up to full supply level wherever rock is good in the case of free flow tunnel carrying water from the powerhouse Adequate safety measures to the workers may be planned and provided during construction Activities in critical path shall not be delayed on any account in order to keep up final commissioning date of the project. Any delay in one activity in the critical path, will affect the commencement of subsequent activities Periodical co-ordination meeting among the design consultants, contractors and the owner of the project are to be convened to sort out problems then and there Engineers and engineering Geologists having sufficient knowledge in the tunneling works and rock mechanics shall be posted in the planning, design and construction of the underground projects. Transfer of Geologists and Engineers involved in the execution of the project frequently may be avoided The civil works associated with erection of generating machinery, transformers etc., may be entrusted to the agency to whom the scope of supply, erection, testing and commissioning of such works awarded Incentives for completion of various project activities on or before scheduled completion date may be declared for the contractors The contract document shall be flexible in regard to decision making as per the real site condition and problems encountered during construction Disputes between the owner of the project and the contractors in respect of works under execution shall be settled immediately so that the progress of subsequent works are not affected Modern construction equipments which are more efficient, reliable and safe shall be deployed for execution of the project. Use of modern construction equipments should not be viewed as a costly proportion whenever such application can result in shortening the total construction period of the project Compressors, Alimak, Winch and other tunneling machinery and equipments shall be maintained properly to avoid frequent break down. Adequate spares parts for the equipments may be procured and kept ready for immediate replacement and repairs in the event of any break down The project authority shall maintain uninterrupted power supply to the tunneling works.
4.0 SUMMARY Most of the underground hydroelectric projects implemented in India have suffered from cost and time over-runs during construction. As a result, cost of the projects has increased many folds and resulted in increase in cost of generation. All efforts are to be made to complete the project within the designated time and cost. Measures suggested in this paper would be beneficial to the Engineers involved in the planning, design and construction of underground hydro electric projects to complete the project within the estimated cost and time.
REFERENCES
1. Hoek and Brown, Underground Excavation in Rock, Institution of Mining and Metallurgy, London, 1980. 2. Grimstand, E., and Barton, N., Updating of the Q system for NMT, Proceedings of the International Symposium on Sprayed Concrete – Modern use of Wet Mix Sprayed Concrete for Underground Support, Fagernes, Norway, 1993.
6. Purushothaman. C, Design and Construction of an Under Ground Power House Cavern for Pykara Ultimate Stage Hydro Electric Project, proceedings of Regional Symposium on Advanced Rock Mechanics Frontiers to meet the Challenges of 21st Century, New Delhi, India, September 2002.
BIO-DATA OF AUTHOR
C.PURUSHOTHAMAN graduated in Civil Engineering from the university of Madurai in 1988. He obtained master’s degree in Soil Mechanics and Foundation Engineering at the Anna University, Chennai, India in 1991. In 1991, he joined Tamil Nadu Electricity Board as Assistant Engineer and now he is serving as Assistant Executive Engineer. He has associated with planning, design, construction and commissioning of Pykara Ultimate Stage Hydroelectric Project (150MW) in the Nilgiris district of Tamil Nadu. He has been associating with construction of underground surface hydroelectric power projects and thermal power projects for the past eighteen years.
