Excavation works :
- TBM : For starting excavation works, for any structure, we need some reference points to proceed, hence, first and foremost thing is to establish Temporary Bench Marks (TBM) all round the project site. These TBMs are permanent in nature and should clearly visible. Once these points are established, then by using paint and brush mark Reduced Levels (RL) on its surface.
- Grid levels : For maintaining accuracy in earthwork, it is important to take grid levels at 5 meter regular intervals before going for mass excavation. But earth having sloping terrain or rolling terrain then it is very much necessary to take grid levels at close intervals, say at 3 m for greater accuracy.
- It is highly advisable to go for earthwork, in a phased manner, to avoid any practical difficulties of excavation likely to occur in future.
- Collection of data : Collect as much as possible, all data regarding water table, period of monsoon, density of rain fall in particular location and make arrangements for dewatering pumps with discharge point accessible.
- Keep these pumps ready, when once the depth of excavation crosses the existing water table level. (Fig 1 & Fig 2).
Earth benching :
- It is necessary to provide shore slopes or step cut of sides called “earth benching,” as we excavate below 1.2 meters to ensure stability of sides. Wherever the depth of excavation is beyond 1.2 meter, provide barricading all around the excavated area at a distance of one meter from the edge of excavation. Safety measures to be strictly followed.(Fig 3 & Fig 4)
- Since the cost of hire charges of machinery and equipment used for excavation is very high, planning is very much essential.
- Hence combination of manual and mechanical means of earthwork should be matched in order to avoid unnecessary idling of equipment.(Fig 5)
Safety Measures during excavation :
- It is better to avoid earthwork during night times. Due to lack of visibility errors may occur, even under artificial lights. Also from safety point of view it is unsafe for workers and supervisors working under poor lighting conditions.
- With reference to the TBM (Temporary Benchmark) located around the site, depth of excavation is carefully monitored with dumpy level and carried out as per the required depth.
- Back filling : Always plan earthwork well in advance for balance cutting and filling. So that excavated earth can be stocked in site itself, and later same can be reused for back-filling, thus by minimizing cost of transportation and time.
- Blasting : With the help of compressed air jack hammer, chiseling, wedging etc., hard rock can be removed from the excavated area, likewise try to avoid blasting as much as possible.(Fig 6 & Fig 7)
- Blasting operations : Under unavoidable circumstances, if blasting is essential, then work should entrusted to experienced and authorized blasting contractor. After obtaining necessary statutory clearances then Controlled blasting should be resorted to. Enough safety Signage, deployment of safety supervisor with constant monitoring is absolutely required during blasting operations.
Carefully ascertain the location of all permanent main services namely Water supply lines, Underground cable line, sewer lines, telephone cables, OFC etc. It is very much necessary to protect these lines throughout earthwork, back-filling and compaction.
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Excavation, basement, footing, excavation works, Temporary Bench Marks (TBM), Reduced Levels (RL), grid levels, mass excavation, sloping terrain, rolling terrain, water table, density of rain fall, dewatering pumps, depth of excavation, existing water table level, shore slopes, step cut the sides, earth benching, stability of sides, equipment used for excavation, dumpy level, cutting and filling, excavated earth, backfilling, bottom level of excavation, blinding,sand filling, excavated surface, crushed and compacted stone, compressed air jack hammer, chiseling, wedging, hard rock, blasting, authorized blasting contractor, statutory clearances, Controlled blasting, safety Signage, Water supply lines, Underground cable line, sewer lines, telephone cables, OFC.