MANILA - A damage in a half-century-old drainage line has been pinpointed by city engineers in Pasig City as the root of the cracks that appeared on Topaz Road in Ortigas Center.
Water seepage from the ruined pipe caused the topsoil beneath the street to erode, Mayor Vico Sotto said in an online post on Tuesday, citing the findings of the city engineering department.
The cracks that ran 50 meters along the road—some going 10 feet deep—opened up amid heavy rain on Sunday that also saw pressurized water escaping from drainage openings.
The affected portion of Topaz Road has since been closed to motorists.
The pipe is part of an original drainage system constructed in the 1960s and later turned over to the local government, Sotto said.
However, the engineers have yet to determine how the line gave way.
The drainage line has already been plugged and diverted.
Investigators have ruled out soil liquefaction and a fault line as factors behind the cracks, Sotto added.
The Philippine Institute of Volcanology and Seismology (Phivolcs) earlier stated there were no fault lines in the area and no seismic activity at that time.
Weather bureau PAGASA also refuted lightning strikes as the cause of the cracks.
The probe into the cause of the cracks also included a survey by the Mines and Geosciences Bureau (MGB) of the Department of Environment and Natural Resources (DENR).
The MGB ran ground-penetrating radar across the road on Tuesday to analyze the soil and other utilities underground.
Sotto said aside from the city’s rapid assessment and planning, they are also waiting for soil testing results before they begin fixing the drainage and road.
The city engineer’s report also said the high-rises surrounding Topaz Road are safe.
The buildings had not been evacuated after the cracks appeared, with residents and tenants still allowed to enter the road.
However, a new water line was installed Tuesday to service the 4 buildings after the damaged pipe was cut off.
The assessment found the foundation of the building within 5 meters of the road went deeper than the excavation of the adjacent construction site.
Part of the excavation has been flooded for 2 days since the appearance of the cracks.
The retaining wall of the site is set to be reinforced to stop soil erosion.
Sotto said the city engineering department and the office of the building official are looking into possible violations at the excavation site that may have caused complications in the incident.
The private developer and contractor have told the city they would cooperate with the probe, he added.
They would also help with the rehabilitation and repair expected to be done in the coming days.