Normally Trench will have less width and more length and depth as rightly explained by Raghu and the link given by Mr. Simhan. First time I heard the word Trench in Defence. When they proceed for field area, the soldiers make their toilets by excavating a trench, which is called as DTL (Ditch Trench Latrine) and on completion of their camp at the location they will close the trench and pack up.
The excavation carried out deeply to protect (Tanjavur Brahadeeswara Temple surrounded with trench) is called Trench. 1000 years back the kings of Chola dynasty used to excavate in outer side of the important places (Palaces Temples, Forts, etc.,) from enemies invasion and fill the same with water and crocodiles, so that the enemy cannot access easily to their places.
The questions you have at hand:
1. why trench should always be deeper than its width?
It is a classification to show the importance and there by employ more stringent safety precautions specified.
2. Say an example if the width is 4 meter and the depth is also 4 meter, should it be called as trench or excavation?
It will be called “excavation” only.
Your most interesting question is “What is the logic of setting up this definition for trench? Why it is so binded?
We have to think about it in the specific context of construction industry.
Kindly differentiate the safety precautions required separately for 1) excavation and 2) trench excavation.
Even then if the problem is not resolved kindly advise for me to give you all the explanations to satisfy your enthusiasm.
First of all thanks to Dipil for triggering such an topic for discussions. I happeneed to go through the site after almost a month so missed this discussion. Any way I would like to contribute from my knowledge and experience in three perspective..
1. Technical aspects
1.1 Technically this activity comes under "Earthwork" which comprises of excavation & backfiling (cut & fill) and disposal of excavated earth. Cut is to lower the elevation and fill to raise the elevation.
1.2 Depending on the soil condition and purpose, excavation is classified into excavation in soil, soft rock and hard rock. Further classified in to depth of excavation like upto 3mts, 3 to 6 mts, etc in general and trench excavation again depth wise.
1.3 The excavation also gets classified based on soil types as type A,B and C whether it is clay, silt, gravel, sand etc.
1.4 Other soil characteristics considered are soil saturation level - dry or wet for stability, loose or hard, etc.
1.5 The difference between excavating and trenching broadly is trench digging always involves digging undergroung, where as excavtion can involve moving earth above the ground like digging in to mountain to mine for coal. Trenching is also a type of excvation
1.6 Depending on the type of excavation the methods, machineries, and controls are defined. When excavating in deep and trenches depending on soil condition, water level, etc, sloping, benching, shoring, side supports, sheet piling, trench shields, etc are provided
2. Health & Safety aspect
2.1 OSHA defines an excavation as any man-made cut, cavity, trench, or depression in the earth's surface formed by earth removal. This can include excavations for anything from cellars to highways. A trench is defined as a narrow underground excavation that is deeper than it is wide, and no wider than 15 feet (4.5 meters). This is in line with your statement.
2.2 Risks involved in actvities for various conditions and levels as explained above varies. Trenching work involves more hazards. Cave-ins pose the greatest risk and are much more likely than other excavation related accidents to result in worker fatalities. Other potential hazards include falls, falling loads, hazardous atmospheres, and incidents involving mobile equipment, access and egress, etc
2.3 Also weight of 1 cubic foot of soil is around 100-125 lbs and upto 2 foot of soil on chest or back weighs around 700 to 1000 lbs
2.4 For access and egress we provide ladders at every 7 mts for longer trenches
3.0 Legal aspects
3.1 Most of what I stated in ! & 2 are common known aspects and we follow.
3.2 In my opinion, the definition of not more than 15 foot wide deep trench is derived for legal purpose absed on case study nd scientific study. This may be similar to the study and conclusion on the legth of safe harness length as in 0.5 sec one falls upto 1.2 mts
3.3 Although I could not find any document to substantiate the 15 ft requirement, I believe, this is defined on legal aspects in case of accident, investigation should lead to control measures taken for trenches and not addressing mere excavation.
3.4 In case I get any more information, I will share with you all. However, pl. find two attachments which may be useful
3.3 By classifying the trench
Another important aspect could be the pattern of earth collapse and the extend of its affect. It could dangerously risk the people working in trench if the width at the bottom of the trench is 15ft or less. This could be worst in case of working near water ponds or where ground water level is high. The affect of loose soil with water seepage or water pressure leading to collapse of soil + follding of water there may not be any place for those in the trench to move, run or escape easily.
Together with average height of man + worst type of soil collapse + extent of the soil covering the part of the people in the trench + types of control + Evacuation + cost of such activities considering all H & S aspect may be considered in defining the width factor for a trench
Thanks for writing to OSHA and get me the answer.
I am not fully satisfied with this answer from OSHA also as its still fails to answer why this limitation of 4.6m at the bottom of trench.
Really simple question but not able to get accurate answer even from OSHA.
Once again thanks a ton to take pains for me and even to write to OSHA. Great help Raghu and please keep up the great enthusiasm.
Thanks for participating into the thread with detailed inputs.
The attachments are really good and an add on collection to the technical references..
You try to differentiate between excavation and trenches and come up with a conclusion that the binding of 4.5 meter is might be some legal requirements. But as per even Raghu's reply which was from OSHA the logic or exact thought process of why this binding of 4.5 or 4.6 meter not defining.
To satisfy a participant of training I can't say an answer stating "Might Be" , hope you understand and will appreciate my concern...
Please try to pull out the exact logic which everyone of us can use in future, if so required and really it shall be a great help to me...
Looking forward to hear from you...
First of all sorry for being this much late. Mentioning the reasons in this forum doesn't make any sense, hence not going to that part...
As advised by you, I have prepared the attachment after careful reading and understanding of various study materials... Whatever and wherever I studies, I am not able to read why this classification of trench and it's limitation of width at bottom as 4.5meter.
Request you to review the attachment and please advice further.
Looking forward to hear from you with curiosity of learning.
@All: Request to participate. If any one can add upon the differentiation with a certain heading against each excavation and trench, we can make this as a great ready reference, small and apt document. Also correct me if I am wrong in any of the point been refereed in the attached document.
Please review the same and
Understand your concern. My reasoning was based Firstly on ANSI standard which I purchsed only yesterday to get clarity. The trench definition given there is does not mention on bottom width.
"1.2.32 Trench (Trench Excavation). A narrow excavation (in relation to its length) where the depth is greater than the bottom width. If forms or other structures are installed or constructed in an excavation so as to reduce the dimension measured from the forms or structure to the side of the excavation (measured at the bottom) to less than the depth, the area between the forms and the excavation wall is also considered to be a trench".
Second, the OSHA response also did not satify the concern. One of my friend also has written to OSHA and let us see the second response.
Normally in Engineering practice we also go with assuptions and prove that they are correct. Here in this case yes it can not be proved. Till such time that we dig proper answer for this subject some more thoughts
1. If it says a trench has to be deeper than its width, and the set width is 4.5 meter at bottom, that means say it is minimum 5 meter depth. If you have a hole that is 4.5 meter wide and 5 meter deep I would note this as being an excavation not merely a trench.
2. For width factor, more possible way to look at it might be the typical max dimensions of trench boxes. Typically these are wedged by acro props / screw jacks and may be the max typical length of these is around the 4.5 meter mark? I will also check. The reason, if you cannot adequately prop a trench box, you can't have a trench box, hence cant be a trench.
3. Also I need to check the maximum bucket size of an excavator. Will it be 4.5 meter?
4. If all reasoning fails, does OSHA standards applicable in India? It is not in UAE here. Never the less our aim is to find the right answer. I will keep trying all available avenues
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