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1.	INTRODUCTION

There are chances of collapsing the sides of the trenches which may cause accident which may cause serious harms to working persons and damage to the tools, equipments and plants inside the trench. It aldo disturbs the desirable profile of the work. It is necessary to make arrangement to prevent the sides of the trench from collapsing when the depth of excavation exceeds 1.50m.

2.	NECESSITY OF TIMBERING IN TRENCHES

Main object of timbering are as under : -	Safety of workers employed for excavation. -	Maintain safety and proper alignments of some public services like electric cables, water lines, telephone cables, drainage lines etc. -	To protect vehicles and other traffic elements passing (Travelling) near by the trenches. -	To ensure safety to the adjoining properties. -	To maintain correct profile of the work. 3. TECHNICAL TERMS RELATED TO TIMBERING Wooden planks and struts are arranged in some systematic order to provide appropriate working space with desirable safety, So timbering is some times known as “planking or strutting”. According constructional arrangement, locations and functions of various components timbering are given their technical names.

There are some important technical terms related to timbering described as under and shown in figure down : (FIG. 1 )

1)	Polling Boards/Sheeting/lancing : Vertical planks which transmit the load form polling boards to status are known as ‘Wales or waillings’. Sometimes in case of excavation in hard soil (only wailings are provided directly ).

2)	Struts : The timer pieces which provided to maintain fixed distance between wailing or polling boards are known as struts.

3)	Bracing : The indined compounds which are provided to import rigity to formwork of strutting process.

4)	Runners : It is used when soil to be timbered is very bed it is similar in aiear to boric timbering. In this are only runners are used in the place of vertical shadings runners are long whonden planks having iron shear at bottom each.

The Soil whater and struts fixed between runners.

4. STAGES OF TIMBERING The chances of collapsing the sides of trench depend upon the type of soil and also on depth of the trench so the type farms work of timbering is decided accordingly. Incase of soft or collapsible soils timbering is down in single stage upto 2m depth, to import the strength of the timbering additional inclined struts are provided. These inclined members are known as struts. If depth of excavation is more than 3m than width of the trench upto 3m is kept wider in such a way that about 25 to 30cm wide offsets can bee provided and the width of tranch after 3m depth is kept same as that of the footing of the foundation and suitable type of timbering is provided upto 1.50m depth of excavation. This types of timbering is known as ‘double stage timbering’. Similarly for future excavation additional offsets are given at each of 1.50m depth, then the types of timbering is called as “multistage timbering”. 1)	Timbering in Firm Soil In this system only vertical shatting and strut are used to only strut are used to give support to the tranch sides excavation is done in proderately form ground and depth of tranch does not excludes is to 20 meter vertical sating’s are rolling boardsare put agoinst the tranch sides apposite to each other with the help of stets. In moderately form soil they may be placed at an internch of about 2.03m for trench one new of stret is sufficient for larger depths more than onw now of tarts may be used. ( FIG. 2 ) 2)	Timbering in moderately firm soil If there is moderately firm soil in the trench then timbering up to 1.5 mt depth consists of vertical polling boards supported by horizontal wales parallel to side of the trench and they are strutted. If the depth of tranch is more then 1.5m then polling boards are supported by double wales and shown in fig.

3)	Timbering Loose Soil If the nature of soil is loose, sandy or gravel they then it is necessary to provide vertical sheeting with polling nearer at reasonaaale distance of at vey closed distance to prevent blowing or sleeping of the soil. Vertical sheeting are supported by walls strus as shown in if depth of trench in more than 1.5 mt then additional braces are provided to import more strength to the timbering. Necessary steppings (offsets) are given to the trench if depth exceeds 3m and timbering with that type of stepping is known as single stage, double stage or multistage timbering as discussed in topic ( Fig.)