The National Building Research Organisation (NBRO) yesterday said that they have identified at least another 159 houses as risk-prone in the Meetotamulla area, where a 300-foot garbage mountain collapsed burying more than 30 people and a large number of homes last Friday.
NBRO Media Spokesman R.M.S.Bandara said the immediate vicinity of the garbage mountain remained an active zone and there were a likelihood of it further collapsing if the weight and the stress on the dump keep enhancing.
According to NBRO findings, the subsurface below the dump has several different soil layers. Prominent among them is a peat layer which is above a hard soil layer. Subsequent to heavy rains, rain water penetrated into the waste pile and the additional load caused by the infiltration of rain water in to the garbage mass may have caused the instability in soft soil underneath, resulting a deep seated failure in the garbage fill.
This resulted in a lateral movement of the peat layer in the direction of houses and the significant ground up heaving has taken place at the toe region and houses situated there were severely damaged.
There is still a possibility reactivating of such movement and with heavy rains, a similar situation can occur again. Therefore, people are advised to be cautious and keep away from danger zone.
Meanwhile, military authorities said those in the danger zone of the garbage mountain have been evacuated to safe shelters. Bandara meanwhile said that the NBRO believes at least 80 houses were completely destroyed due to the collapse of the garbage mountain after analyzing satellite images taken about one month back.
However, he said that the NBRO does not possess details whether any new structures had come up in the recent past in the area. When questioned whether these were unauthorised structures he noted that the NBRO did not have such details and it was upto those who administrated the district and the province.
Bandara further noted that the NBRO will come up with a detailed map of the danger zone surrounding the Meetotamulla garbage mountain today.
The NBRO stated that the disastrous slope failure occurred at the municipal solid waste disposal site at Pothuwilkumbura, Meethotamulla, Kolonnawa at about 2.45 p.m. on April 14.
NBRO staff conducted a ground survey and a drone survey to assess the impacts. These surveys are still continued in order to identify impact zones.