GEOLOGICAL INVESTIGATION DAM AND RESERVOIR GEOLOGICAL INVESTIGATION

Dam Dam may be defined as a solid barrier constructed at a suitable location across a river valley that a view of impounding water flowing through the river. Dam are constructed for a achieving one or more of the following objective. i) Generation of hydropower Energy . ii) Providing water for irrigation facilities; iii) Providing water supply for domestic consumption and industrial uses; iv) Controlling of flood; v) Providing navigational facilities; Additional benefits coming from dam are development of fisheries and recreation facilities in reservoir created by them and also overall greenery effect all along the reservoir.

Types of dam Design of construction ,whether the load of the body of the dam is transmitted on the foundation or to the abutment rock ; such as gravity dam , arch dam buttress dam etc. Material of construction such as concrete ,rock fill or Earthen dam; Size of construction such as small dam and large dam. The well known main types of dam are the Gravity Dam, Arch Dam and Embankment

GRAVITY DAM A Gravity dam is a solid masonry or concrete structure, Generally of a triangular profile, Which is so designed that it can safely stand against a precalculated volume of water by virtue of its weight. All the forces arising in such a dam – As due to the thrust of the impounded water and the massive weight of the dam material are assumed to be directly transmitted on the foundation rock Hence the strength of the foundation rock is the most critical factor in their design .

A gravity dam,when properly designed and carefully constructed, is considered among the safest types . E.g.:- Buttress. Arch Dam :- An arch dam as the name implies ,is an arch- shaped solid structure mostly of concrete. Which is designed in such a way that major part of the thrust forces acting on the dam are transmitted mainly by the arch section.(and also cantilever action at the base ) The constant radius arch dam ,in which the radius of curvature throughout the structure is constant and upstream face is vertical.

Selection of Site for Dam The following are the requisite of good sites for various types of dam. Foundation:- Topography:- Site of Spillway :- Material:- Reservoir and catchment area:- Communication:- Locality:-

Geological characters for investigation For achieving the above object through and systematic investigation of following Geological character. Geological of the area. Preliminary geological survey of the entire catchment area followed by detailed geological mapping of the reservoir 1)Main Topographic Feature 2)Natural Drainage Pattern 3)General character and structure of the rock formation such as their stratification ,folding and faulting and igneous intrusion 4)The trend and rate of weathering and erosion in the area

2) Geology of the site a) Lithology :- The single most important feature that must be known thoroughly at the site and all round and below the valley up to reasonable depth is the lithology. b) Structure :- This involve detailed mapping of planes of weakness like bedding planes ,chistosity ,foliation ,cleavage, joint, shear zone, fault and fault zone ,folding i) Dip and Strike :- The strength of sound ,unfractured stratified rock is always greater when the stresses are acting normal to the bedding plane than if applied in other direction .As such gently upstream dipping layer offer best resistance to resultant forces in a dam ii)Fault :- These structure can be source of danger to the dam in a number of ways

iii) Folds:- The most notable effect of fold on rock are :shattering and jointing along the axial planes and stressing of limb Iv) Joints :- No sites are totally free from jointing ,Hence sites cannot be abonded ,even if proof usually jointed. However , the detailed mapping of all the aspect and character of joining as loping in the rock of proposed site has to taken up with greatest caution. The micro joint presented considerable difficulties in detention and treatment.

Relative suitability of Different Rock Igneous rock Sedimentary rock Metamorphic rock

Reservoir Reservoir may be broadly defined as artificially created water storage basin with storage capacity that may range from few thousand cubic meter to few thousand of million cubic meter. Depending on the purpose of storage ,reservoir are classified into three group. 1)Storage and conservation reservoirs 2)Flood control reservoir 3)Distribution reservoirs

Pool level Pool the level, indicate the designed level up to which the reservoir shall be full of water at a particular point of time . Storage Capacity :- Useful Storage :- Dead Storage :- Surcharge Storage:-

Geological Investigation Topographically :- Ground water condition :- Permiability :- Structural constitution:- Liable to failure by sliding ,creep or subsidence. Trend and rate of weathering :- In catchment area is of considerable importance

Causes of failure of reservoir or dam Erosion below spillway:- A simple method for producing such turbulence by creating the hydraulic jump below the spillway . Providing sloping apron

Selection site of reservoir The river valley at the site should be narrow . The surrounding hill which constitute the rim of the reservoir should be watertight. The site should be such that as per as possible land and property is submerged in the reservoir . The site must be such that adequate reservoir capacity is availability As far as possible dip reservoir must be formed The Quantity of water stored reservoir must be satisfactory for its intended

Bridge A bridge may be defined as a structure built over a river ,a dry valley, low land or any depressed part of the land to provide a link between the two opposite sides.

Geological consideration The depth of a bed rock The nature of the bed rock The structural deposition of rock