By : M.S.Yatnatti Editor and Video Journalist Bengaluru : Reportedly A 55-year-old man was literally pulled out of the entrails of earth after the ground under his feet caved in, sending him hurtling into a 10-foot-deep pit on Old Post Office Road opposite the City Civil Court Complex recently .The cave-in happened on a pavement abutting a Namma Metro construction site. An underground Metro station is being built at the site.The cavity was one metre wide and one-and-a-half metres deep. The pit was filled up with concrete and its surroundings will be investigated and grouted, if necessary, to prevent any such mishap, reportedly said by metro official.
Blasting is blasting ,whether it is controlled blasting or non-controlled blasting. Its effect is disastrous and may make the affected buildings and roads vulnerable and weak .Let the metro officials stop fooling the public and cracks are proof of structural cracksand not just plaster cracks .The after effects might surface after some time. Let the BMRCL accepts the fact that though controlled blasting technique that may minimizes the ground vibrations and reduces the speed of fly rocks but it cannot 100% totally guarantee that buildings above it may not crack as many building might not withstand controlled vibrations also as they are not calculated to take such loads..
The cracks are fact and metro officials need to resolve the issue .It cannot be adamant and arrogant on the issue as in Bale Pete several buildings have surfaced the cracks and BMRCL itself have propped up several pillar inside the buildings and residents are living in constant fear of their lives in their residences. As the Tunnel Boring Machine (TBM) digs meters underneath, residents of Balepet, at the heart of old commercial areas of the city, are feeling the tremors while their buildings shake. Much of the evacuations have been in and around Chikpete, where many of the buildings are more than 50 years old. "Many of these buildings don't even have a foundation. And since it is a congested area, many buildings are inherently weak,” the report said. In Balepet and Chickpet areas, there are hard rocks underneath. Tremors are caused due to tunnel-boring. The tunnel-boring machine is at work 60 feet below the ground and there is a possibility of encountering uneven ground and topography. To ensure that there is no depression of land and formation of holes and craters, we are pouring concrete from above. There is a need to bore the tunnel over 750 metres between Chickpet and Majestic. Now, we have completed 522 metres. Right now, the machine is at the MLS building of Balepet. This area has nearly 70 to 80 per cent of hard rock. So, work is going on slowly,” BMRCL officials said.
Cracks in Roads: Some cracks also appeared on the road and metal mats have been place on the road as portions of the road can get cracked and sunk . .When starting tunneling work in a new place, cement-like mixture is sprayed at high pressure. The surrounding areas of soft soil will get hardened. Only after this, the tunneling work will start and function safely. However, when spraying of this mixture at high pressure was carried out inRoads, with the surrounding soil being very soft, the road started cracking and this mixture was spewed out.The vibrations may damage the structures and roads even after the metro starts running at roaring sound .These damages need to b e factored in while calculating compensation . Need to study effects of earth quake on metro stations : Government officials said that old and under-construction buildings as well as underground metro stations, being on the high-risk list, need to bemonitored on an hourly basis during earth quake .BMRCL should accept the fact and provide safety of life and solution to the problem by paying compensation: The effect of controlled blasting technique may not appear today but it might surface afterwards because it is synonymous to inner impact. Which may not be visible today but may cracks may surface latter. Let the Government take a policy decision on this matter. Development and Humanity should go hand in hand.
It is reported by experts that Ground vibrations due to blasting processes are one of the fundamental problems in the mining and civil excavation industry which may cause severe damage to the structures. It is mostly recommended that a detail comprehensive vibration control is required. This paper presents the results of ground induced vibration at a metro rail station excavation site in the heart-of-city of Bangalore. This study was carried out to control ground induced vibration, fly rock near to sensitive structures, mostly to the city civil court and the buildings of Sir M Visveswaraya college and like statue, school, public and private structures closed to 10-15m. More than 60 blasts were done under control supervision of government officials. The maximum charge/delay, charge per hole, delay in between holes and rows were established on basis geological rock mass. Ninety percent rock was excavated to construct underground metro stations. The fly rock was control by optimum stemming lengths and by using suitable fly control rubber mat.
According to press reports ,one of the last surviving historical vestiges of namma City that has provided millions of women and children medical relief and maternal care now finds itself under imminent threat.The nearly 200-year-old edifice has developed a crack in its foundation, raising safety concerns not only for those housed in it for receiving medical attention, but also for its very own survival.Today, it sadly stands a mute testimony to what skewed development does when authorities run roughshod over elementary issues of protection, preservation and caution. The relocation of the pediatric intensive care unit was done as The Metro in the north-south stretch is underground below the Vani Vilas Hospital and becomes elevated near BMC towards Vani Vilas Circle. Earlierdue to blasting at the work site on the Vani Vilas Hospital premises, cracks in the ceiling of the 70-year-old hospital building were noticed. "The children's block in Vani Vilas Hospital, Radiology Department with the cancer patients ward, the Virology Department and the Sirur Block are affected by the blasting. More than 100 beds each in the children's block and the cancer patients' ward were relocated."These are stone buildings without pillars and are more than 75 years old. Due to the decrease in the water table below Vani Vilas Hospital, the ceiling has been impacted,” is reported in the media.
CIMFR reportedly had said that "controlled blasting technique that minimizes the ground vibrations : Scientists from Nagpur made a quiet contribution in making of Bangalore Metro Rail Project safer. Scientists at the Nagpur regional office of Central Institute for Mine and Fuel Research Institute (CIMFR) have used a controlled blasting technique that minimizes the ground vibrations and reduces the speed of fly rocks in open blasting making the entire operation safer not only for the personnel at the site but also for nearby buildings and structures.Ramulu More, principal scientist from CIMFR who led the team, told that the controlled blasting technique was always there but it was never used on a mass scale for and in open blasting. 'We have modified the technique to control ground vibrations and also reduce the speed at which the rock pieces fly into the air. The Delhi metro rail project used an imported method of controlled blasting which was very expensive. Our method reduces the cost by one third and makes the entire process safe,' he said.Controlled blasting, as followed in developed world, uses fool-proof covering of holes in which explosives are filled before blasting. It uses a three layered of muffling of mesh made of rubber connected to wire ropes. CIMFR technology called as 'bottom hole decking technique' has been used at City Market, Chikpet and Majestic stations of Bangalore metro. Work on the first station is completed and on the second one, it is nearing completion. At Majestic, work is still on.Metro in Bangalore consists of both elevated and underground sections. Tunnels are being made using tunnel boring machines while the underground stations are excavated by drilling and blasting method, which is bound to generate environmental effects like ground vibrations, air blast and fly rock. Keeping in view of habitats and structures, it was decided to go for rock breakers and chemical expansion based rock excavation. But nothing could result in effective rock breakage and hence open blasting method, considered to be the most dangerous, had to be used. Rock excavation was carried out for the north-south corridor at City Market, Chikpet and Majestic stations. The distances from various sensitive and critical structures to periphery of these station areas are just 10 to 25m.In view of such close proximity, it was a great challenge to conduct blasting without disturbing the surrounding structures and running traffic. The work is being carried out by M/s Coastal-TTS JV, for whom CIMFR is the technical consultant. CIMFR provided technical guidelines for blasting and monitoring of ground vibrations, air overpressure and fly rock during rock excavation at underground stations.The sensitive and critical structures at City Market Station included children and maternity hospitals at 10m distance and historical museum at 100m distance. The sensitive and critical structures at Chikpet station included a temple at 15m and mosque at 10m. Also there are structures like tall buildings and residential structures at Chikpet station at 20m. Running traffic is the most sensitive part at Majestic Station and zero tolerance is the limitation for fly rock as the habitats are well in the vicinity. The single layer muffling used by CIMFR restricted the fly rock distance to within 10m.The CIMFR team, besides more who is the project coordinator, comprised P B Choudhury, B K Jha and A K Soni. The team had an overall guidance from Amalendu Sinha, CIMFR director at Dhanbad.