Innovative ideas in Construction of Concrete Dams
(Construction of Gandikota Dam – a case study)
(Civil Engineering is the art of directing the great sources in nature for use and convenience of man)
The human mind is an active mechanism to innovate methods and means to utilize the bounties of nature. Inventing the wheels led to invention of roller bearings and then lubricating the same for a smoother ride. The point is the constant thirst to achieve an easier, smoother and better life. The idea of preserving water to meet requirement in scarcity period and area, have undergone refinements both in the mega and micro sectors and Dams to form reservoirs of sweet water is a natural development. The world is dotted with small to mega dams, serving mankind in various ways. Production of electricity and control of floods have been the major by products of building reservoirs.
Concrete dams play a major part in this scenario, and their construction has undergone a sea change over the years. The present article describes such a small mosaic in the large canvas.
1.1 The five elements of the body as enshrined in our scriptures are:
Kshiti, App, Tej Marut & Vyomo, (The elements Earth, Water, Energy, Air, and the Ether)
Out of the above, Earth and Water (App) are the two elements visible and accessible to the living beings. Again water is the element most conveniently harnessed, used and reused by man. A crude example is that man can control and manage a flood to a great extent, but not a cyclone nor an earthquake.
From time immemorial man kind has tried and succeeded in harnessing the rain water (which is nature’s own distillery to provide potable water from sea water) by various means and methods. The most common mode as catalogued in modern language are Dams across streams, to retain and form reservoirs to store the flowing water for leisurely use.
1.2 Historical Development of Dams:
Construction of Dams of different kind across small rivers, rivulets and valleys have started in India probably in the 6th century B.C by benevolent kings whose intention to benefit their subjects were paramount. The Romans had also contributed the idea and practice of constructing Dams for preservation of water in the late 2nd Century B.C. How ever the modern concept of construction of Dams started in the early 17th century at Europe and gradually improved to provide the ideas, methods, and technology a recorded and gradual refinement over the years.
1.3 Different kinds of Dams:
A general classification may be made for 2 categories of Dams. One is the Earth dam and the other being the concrete or Masonry Dams. Earth Dams can be further categorized to a Homogenous section earth Dam and Rock fill Dams of different kinds. Both the types can be divided in subcategories depending on material and mode of design and construction procedure followed.
Concrete or Masonry Dams on the other hand use predominantly rocks and rock products and
are generally constructed in sites where rigid rock strata is available for the foundation.
*Formerly Chief Engineer, Water resources, Government of Orissa
Now Advisor to Maytas Infra Pvt., Ltd., on Hydro projects.
1.31 Different types of Concrete Dams:
In general there are 3 types of Concrete Dams.
a) Gravity Dams
b) Arch Dams
c) Buttress Dams.
1.311 Gravity Dams:
Concrete Gravity Dams have more or less replaced the Masonry Gravity Dams in India recently. Where massive masonry gravity dams were the norm till end of ninety’s of the 20th Century, concrete has replaced masonry as construction material for various reasons after wards.
Gravity Dams are designed and constructed in blocks.(sometimes called Monoliths) the size of which are generally restricted to 15 m to 28 m (50 to 80 feet).
By choosing the right size of blocks or monoliths the dam can be aligned with great flexibility. Some of the biggest Hydro electric projects in the World and India are solid gravity concrete and masonry Dams.
Guri Dam in Venezuela, Grand coulee Dam forming the Columbia reservoir USA. Three Gorges Dam in China, Bhakra Dam, Sri Sailam Dam, Nagarjuna Sagar Dam, Narmada Sagar, Sardar Sarovar etc., in India, are a few solid Gravity Dams constructed.
2.0 Innovative methods for Dam construction in general:
2.1 With the passage of time construction of Dams have become a highly mechanized procedure and gradually replacing execution by manual means. In the process the age old wisdom in methodology and technique have taken a back seat, rather discarded.
2.2 With ever increasing demand to build higher, bigger and finer Dams quicker, the cost factor has been given a go by in some developed countries. In a developing country like India the cost factor has a significant role and some times prevent us from adopting the state of the art methods and machinery. However demand for accrual of benefits in a shorter period of time has galvanized Indian engineers to go for different proven innovative methods with due consideration to cost factor, for delivering bigger dams in shorter time frame.
3.0 Methods and Plant and Machinery available:
3.1 Highly efficient machinery available now can be listed boldly
a) Highly efficient and high capacity concrete batching and mixing plants, designed to meet
b) Concrete transport systems, like transit mixers, conveyor systems, containers, etc.
c) Equipment for quick and efficient placement of concrete, like cranes of different types (crawler mounted, track mounted, and tower cranes) and capacities, conveyors with telescopic and movable delivery heads, rope ways, various types of buckets etc.
d) Concrete compaction equipment, like needle vibrators operated by electrical and diesel or petrol motors, pneumatic vibrators, shutter vibrators, self propelled vibratory rollers big and small etc.
e) State of the art centering and shuttering material, including slip forms.
f) Reinforcement cutting and bending machines.
g) Mechanically/electrically operated, shaping and finishing tools etc.
4.0 The Case Study – Construction of Gandikota Dam in Kadapa District:
4.1.1 For case study the Dam across river Penna, under Construction by Maytas Infra Pvt., Ltd., in the vicinity of Gandikota Fort is chosen. The Dam is a part of the GNSS Project, which is again a part of the ambitious JALA YAGNAM scheme envisioned by the Honourable Chief Minister of Andhra Pradesh.
The GNSS project is planned to provide irrigation to 3.5 lakh acres in Kadapa and Chitoor districts, drinking water to a population of 5 lakh, along the course of the canal. Minor industrial use is not out of bounds of the projects.
Government of Andhra Pradesh have entered into an agreement and entrusted the work of Construction of the Gandikota Dam to Maytas Infra Nagarjuna Construction, a Joint venture company, as part of GNSS Package – I and being executed by Maytas Infra Pvt., Ltd., partners. The salient features of the project presented in table 1 below:
4.2 Table 1 – Salient features of Gandikota Dam
G.N.S.S Project is a major Irrigation Project intended to provide Irrigation facility to 3.25 lakhs Acres in the three districts of Kadapa, Chittoor, and Nellore and drinking water to a population of 5 lakhs living in 640 villages and towns enroute the canal.
The Project envisages the drawl of 38 TMC of surplus flood waters in 45 flood days from the foreshore of Srisailam Reservoir to convey them through Srisailam Right main canal from Pothireddypadu, Srisailam Right Branch canal, Proposed Gorakallu reservoir, Owk reservoir and proposed Gandikota Reservoir / and other 8 storage reservoirs to provide above irrigation and drinking water facilities.
Gandikota Reservoir is located across Pennar river near Mangapatnam Railway station near Muddanur (V & M ) in Kadapa District it is about 80 Kms from Kadapa located on Kadapa – Gooty Express High way. The project site is accessible from Muddanur town by road. Network roads are connecting to district head quarters Kadapa. The main canal from foreshore of Gandikota dam passes through Mangapatnam, Muddanur, and Uppaluru.
The longitude and latitude for head works are as follows:
Longitude : 780 25′ 02”
Latitude : 150 54′ 00”
Project area reference: – S. I. Sheet Nos. 57 I, J , N
Rain fall :
The normal rain fall of the district is 564 mm. The summer is from March to May. This is followed by South – West monsoon season which continues up to September. However there is some rainfall in November due to the North East return monsoon.
Hydraulic particulars of Gandikota dam:-
1. Maximum Flood Discharge :: 8180 Cumecs.
2. Driving Head Hd :: 6.80 Mts
3. F. R. L / M.W.L (Phase – 1) :: + 209.000 Mts
4. MDDL :: + 202.900 Mts
5. Crest Level :: + 202.200 Mts
6. Tail water Level :: + 202.650 Mts.
7. No and Size of Radial gate vents :: 14 Nos of 15 x 6.80 Mts
8. No and Size of River sluice vents :: 3 Nos of 1.5 X 2.25 Mts
9. Total length of Dam :: 315.00 m
10. Storage capacity of Dam :: 16.48 TMC
11. Top of Dam :: 215.000 m
12. No of village lands under submergence :: 21
13. No of village structures under submergence :: 14
4.3 Peculiarities and Specialities:
4.31 The most important peculiarity of the Dam is the site chosen. The dam spans across the river Penna just below the joining point of river Chitravati with it. The site is inside the spread of the Mylavaram reservoir located 10.0 km d/s. The Gandikota Dam is to serve only as a temporary storage and diversion of water received by a series of canals and tunnels from Srisailam reservoir through the GNSS Main canal.
4.32 The specialities can be listed as the high tail water, because the MWL of Mylavaram reservoir is
almost equal to the crest level of the spill way.
The other specialities is that almost the entire length of the Dam is in spillway section due to the narrowness of the gorge. The above two features in the high tail water level and the site being under the back water level of Mylavaram reservoir and narrowness of the gorge continued for a great length have caused great restriction on planning and execution of the dam in a normal manner. Innovative methods are found necessary to tackle the problem.
5.0 Planning to construct the Dam:
5.1 Sites for constructing a Dam are generally chosen by nature. Where ever more than one options are available the best site has to be carefully selected. Topography and foundation conditions are the major factors for selection of a site.
The next important act is to choose the material of construction, available in plenty and economically so as to select the type of Dam.
In the instant case the site of the dam has already been chosen and required studies made for the suitability. Also the type of dam has already been decided. Therefore the execution agency’s planning requirement is to prepare an action plan to deliver the project in the specified time frame and cost.
5.2 Scope of the present work:
The scope of work consists of Construction of Gandikota dam across Penna river in Cuddapah district including investigation, preparation of hydraulic particulars, design and drawings, fabrication and erection of Radial crest gate, Stop log gates and its accessories. River sluice gates Gantry crane etc., UNDER PACKAGE -1
5.21 The responsibilities of the executing agency as defined the agreement is to
The agreement is in the EPC format which puts the onus on the contractor for everything. This involves the following steps:
a) Conduct survey & investigation on reservoir inundation, site contouring, geological exploration and testing and evaluation.
b) Design the dam for both hydrological and construction requirement with details drawings for every component and get it approved by the Government design organization.
c) Plan, Survey, conduct tests for the materials to be used for construction.
d) Plan for approach roads, instalment of Plant and machinery.
e) Execute the work proper.
f) Hand over the project to the client, but remain in charge for 2 years after completion with full responsibility of running and maintenance. The entire responsibility is deemed to have been rested with the contractor, with whole host of specifications, guidelines pertaining to stiffest and highest standards conceivable being set for the work.
5.3 Requirements for the planning for the particular work:
5.31 Paper planning
The basic requirements f the Gandikota Dam can be listed as under.
a) Investigation and design and its approval.
The investigation and design work were entrusted to reputed organization like M/s Stup who are pioneers in the subject.
b) Quantify the requirement of construction material.
The quantity of concrete, steel for reinforcement, and gates which form the bulk of construction material it was found that approximately 200,000 cum of concrete of different grades, 1500 metric tones of reinforcement steel and 2000 MT of structural steel would be required for the work. 200,000 cum of concrete may roughly require about 55 to 60 thousand MT of cement.
The requirement of course aggregate is to the tune of 2,10,000 cum including wastage which in turn requires rock to be quarried, to get about 2.73 to 2.75 lakh cum of stone boulders. Excavation quantity at the quarry face will be around 4 lakh cum. Similarly, sand required to be quarried may be to the tune of 1.5 to 1.75 lakh cum. All these to be considered for choosing a quarry or quarries for stone and sand at a reasonably close distance from work site meeting the required specified quality.
Planning in the preconstruction stage necessitated to choose the right plant and equipment, layout of roads, working area, dumping area, power supply and water supply, accommodation for work force and engineers, office and recreational and medical facilities.
6.0 Planning and execution of the work proper.:
6.1 River diversion and dewatering of foundation:
6.11 As mentioned earlier the dam site being within the submersible area of the Mylavaram reservoir
idea of any diversion work is eliminated. The level of foundation grade rock indicated by the drill holes varied from RL 174.5 m in the centre to RL 185.5 m on the flanks, where as the reservoir bed was at an average level of 192.00. The strata consisted of sand upto a depth of 7 to 10 metres, a compact conglomerate of clay and boulders varying from 3 to 5 metre depth and about 1.5 to 2 metres of fractured and layered and disintegrated rock, before foundation grade rock was available. The foundation rock consists of Ferrogenius quartzite in layers of varying thickness impregnated with thin water tight shell layers which is the hallmark of rock strata in the region.
6.12 Dewatering the work area:
6.13 Coffer dam
Though the total quantity of rainfall is quite less in the area, the site, receives rainfall from both South West as well as North East monsoons. The working time therefore is greatly restricted if the full period is to be considered. However rainfall being scanty (average annual rainfall 504 mm). Calculated risks had to be taken to continue work during at least in the North East monsoon period.
Various options were considered for getting the dam foundation area confined and dewatered. In the first instance a semi circular coffer dam was constructed to protect 50% length of the dam on left side and dewater the working area. As the back water was very high, the coffer dam constructed was huge. However the confined pool could not be dewatered due to huge seepage through the under lying sand layer. The idea of driving of sheet piles was considered and abandoned, after the experiment failed due to big boulders present just below the sand bed and cost considerations.
The only option left was to lower the reservoir water upto 191.00 RL at least and then start dewatering the confined area. The reservoir level came down to RL 191.00 after water was released to farmers through canals in March 2006 and after nearly a year was lost before the commencement foundation excavation could be started.
For dewatering 12 numbers of high capacity and specially designed pumps with diesel engines of 68 HP were deployed. After the surface water was dewatered, specially patented method of total dewatering system was adopted to lower the water level by providing well points connected to a common suction main. In this method the water level went down and construction machinery could move for excavation of foundation.
7.0 Excavation of foundation:
7.1 Excavation of soil in all classification sand, and dis-integrated rock, has become quite easy after the large scale manufacture and easy availability of various kinds of excavators (back hoe type) and loaders and heavy duty tippers and dumpers. In the instant case the depth of excavation up to 17 metres in a limited area was the problem. Lot of rehandling and road making was necessary, which caused the excavation work uneconomical. The number of excavators and dumpers varied from 4 to 3 and 16 to 10 respectively at any given time to meet the requirement. In addition a dozer of 100 HP capacity was required to level dumping areas, and a water tanker to spray water on haul roads to suppress dust.
The foundation area thus roughly cleared bock by block were cleaned manually by wedging barring, chiseling, air and water jetting for inspection of geologists and engineers and passed for laying foundation concrete.
8.0 Concreting proper:
8.10 Total quantum of concrete to be poured is about 200,000 cum at different places, in different mix proportions. For this different options were considered.
8.11 Establishing a Ropeway across the river could have been the best solution. The option was considered and rejected for the following reasons.
a) Restricted area for installation – The hill slopes on both sides of the gorge being very steep there was virtually no area to install the head and tail masts, anchor blocks, and concrete delivery equipment.
b) Time factor – Rope ways generally take longer time to install and the time schedule of 30 months including investigation and design was very short.
c) Cost factor – The rope way also needed huge capital cost, which was not advisable spend considering the total cost component of the dam which is only 130 crores with a gate component of 31 crores inclusive.
8.22 The second option was to place concrete by cranes. Procuring tower cranes to cover entire length
of the dam necessitated 4 cranes which again was cost prohibitive. After much permutation and combination of ideas it was decided to use 2 numbers of crawler mounted cranes with a lifting and delivery capacity of 1.5 cum to 2.5 cum of concrete at a distance of 20 to 25 m, to cover the block width of 18.5 m. This with the option of one rail mounted tower crane for higher levels of concrete is the present method being adopted. A small conveyor system to pour concrete in restricted places is also in use.
The present arrangement is working successfully and with a programme of pouring concrete at 600 to 1000 cum a day the dam construction work is progressing well.
9.0 Machinery Equipment procured and in use at site:
9.1 All required plant, equipment, machinery, tool in use at the work site are shown in table 2.
Sl.No. Description Capacity Available 1 Crusher 120 tph 1 2 Batching plant & Mixing plant 64 cum/hr 1 3 Ice Plant & Chilling plant 60 T/day 1 4 Dozer D 80 1 5 Excavators Ex-350/200/70 5 6 Concrete placer 25 cum/hr 1 7 Transit Mixers 6.0 cum/mixer 6 8 Tippers 14 T/16 T 21 9 Loader 2 10 Concrete pump 1 11 Dewatering pumps 68 12 12 Hydraulic concrete buckets 2.5/1.25 cum/bucket 12 13 Diesel Generators 500 to 30 KVA 7 14 Compressors HP 450 / 350 CFM 3 15 Pavement breakers/Rock breakers 150 CFM 2 16 Jack hammers 80 CFM 3 17 Water tankers 12000 litres 1 18 Welding transformers 450 Amps 13 19 Vibrators (Diesel/Electrical-Pneumatic) 14 20 Vibrator needles 80/60/40 mm 24 21 Drilling and grouting equipment 5 sets 22 Mahindra Scorpio 1 23 Tata Victa (Sumo) 3 24 Mini Bus (tempo traveler) 1 25 Mahindra Jeep 3 26 Mahindra Bolero 1 27 Bajaj CT 100 two wheeler 11
10.1 The present manpower deployed at site are shown in table 3.
Manpower Experience Sr. Engineers having more than
10 years of experience 5 nos. Graduate Engineers 8 nos. Diploma Engineers 10 nos. Surveyors 2 nos. Supervisors, Foremen, electricians etc., 25 nos. Drivers and operators 50 nos. Skilled and semi skilled workmen 300 nos.
Proper planning for all aspects of a project is the hall mark of an efficient management. Maytas Infra Pvt., Ltd., who are executing the work are an ISO 9001:2000 company, who have taken care to plan meticulously, and have procured high quality plant and machinery, T & P with enough capacity to spare. They have also deployed adequate and competent engineers and work force to execute the work. The work is progressing ahead of the revised milestone programme, fixed by the clients well designed and constructed dam will be added to the list of Dams in Andhra Pradesh very soon.