Ingreso de telecomunicaciones

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 Soil investigation is carried out at site and result of soil investigation are forwarded to Corporate Centre for design of various foundations.

 Detailed soil investigation is carried out at site to arrive at sufficiently accurate, general as well as specific information about the soil profile and necessary soil parameters of the site in order that the foundations of various structures can be designed and constructed safely & rationally.

 The soil investigation tests should be conducted at all the critical locations i.e. control room building, auto transformer, shunt reactor, lightening masts, 400 KV tower locations etc.

 Engineering department at Corporate Centre prepares the works at site. During this period, the site levelling work is carried out at site in order to smoothen the undulations.

2.2 Levelling

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The land acquired for substation may be barren/cultivated land. The soil may be rocky, black cotton, sandy or any other type. The acquired land may contain trees, bushes, crop, drains, etc. that require cleaning/

clearing before starting the levelling works in the yard.

i) Switchyard area is important and preferably it should be brought to a single level. However, in only unavoidable circumstances or where it is uneconomical to go for levelling the soil than keeping a multi-layered/in steps levels, the different levels may be kept.

ii) Levelling may also be required in township area for bringing the land to a single level for designing the drainage system and residential quarters. In case of too much level difference the residences (categories) may be designed at different uniform levels but with good drainage system to avoid water logging.

iii) Before starting the levelling works the marked area of switchyard is cleaned. Any crop, bushes, trees, shrubs and structure that may cause hindrance or that are undesired are cleared from the yard area.

iv) Any drain, telephone line, building structure is also removed from the switchyard area, to a nearby suitable place.

v) Now spot levels will have to be taken in the yard area before making an assessment for the levelling i.e. for assessing the requirement of soil for low level areas and cutting of soil from high level area to bring the whole yard area to a normal formation level.

vi) In the ideal case of levelling there is no requirement for borrowed earth and quantity of earth excavated from the high level and fill it in the low lying areas is equal. This is the most economical method of levelling. Care is to be taken such that the earth is not excavated below the formation level.

vii) For compaction earth is filled in the low lying areas in layers of 20 cm thickness then watered and compacted by rollers/ dozers.

viii)The method and equipment used to compact the fill material to a density that will give the allowable soil bearing pressure required for the foundations, roads, etc. In each layer of fill material. Each layer of earth embankment when compacted should be as close to optimum moisture as practicable. Embankment material which does not contain sufficient moisture to obtain proper compaction should be wetted. If the material contains an excess of moisture, then it should be allowed to dry before rolling by hand rollers/dozers. No compaction is carried out in rainy weather.

ix) Sometime in hills or in rocky soil, we may have to go for blasting the earth at higher levels. The blasting is done in the specified manner.

All safety precautions should be taken while blasting so as to avoid any injury/loss of life and property. The explosive material used for blasting should be handled very carefully. While applying the explosive material for blasting, one should take care such that the earth excavated/hole created by blasting is upto/very near the desired ground level.

x) The levels in the entire area (after finishing the levelling work) should be taken and checked up with the desired formation level.

Final dressing up and finishing should be done in case if levels are not found satisfactory. The care should however be taken during compaction. Measurement for levelling work (i.e. excavation &

filling) is a cumbersome process and it should be done strictly as per the specifications. All the level records must be noted in field levelling book duly signed by the concerned personnel of contractor of site. The drawings of level before starting the levelling and then final levels should be maintained. The measurements should be recorded very carefully as per the technical specifications. Care should be taken that with the movement of trucks, dozers etc. any other structure in the vicinity is not affected or uprooted.

2.3

Foundations

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Foundations in switchyard area the foundations are cast for:

i) Lattice Structure (Tower foundations) i.e. for gantries, lightening masts etc.

ii) Cable trenches

iii) Equipment in switchyard

 Based on the approved layout drawings furnished by Corporate Engineering the foundations are marked on the ground.

 While marking the foundations on the ground their layout should be strictly verified with the layout drawings as well as with the bench mark/grid lines on site with great accuracy.

 Layout of the various switchyard equipments is also verified with the layout drawings and with respect to gridlines on the ground.

For further confirmation, the control room building co-ordinates can be used and necessary rectification in the layout & orientation of various equipments and foundation can be made.

 Any changes in layout if desired should be brought in the notice of Corporate Engineering and necessary amendments should be approved. It is a good practice to have a second confirmation for marking the various foundations w.r.t. control room co-ordinates that are fixed and marked before hand.

 Foundations for various lattice structure are cast in the switchyard area. The type of foundation is decided based on the type of soil.

Engineering Department at Corporate Centre provides the provided at our substation sites. Transformer and shunt reactors are the major equipments in switchyard. Their transportation, storage, foundation and installation require special techniques and efforts.

ii) Transformer & shunt reactor foundation work includes the supply of a permanent track system to enable the replacement of any failed unit by the spare unit located at the site. It also includes the concreting, providing jacking pads, steel work for the MS grating and providing the anchoring arrangement.

iii) The foundations for transformer & shunt reactor should be ready in advance before actual receipt of the equipments. Proper co-ordination in the works are required so that the foundations are completed well in advance.

iv) For casting the foundation of Transformer & Shunt Reactor the marking is done as per the approved drawings from the Corporate

Engineering Department. The marking of co-ordinates should be checked properly and reconfirmed with the control room and switchyard layout co-ordinates. The pylon supports that are required to be laid before the concreting works is generally in the scope of fire fighting contractor. Scheduling of such works should be co-ordinated between the contractors for smooth working & to avoid any stoppages in work.