It may sound incongruous, but developing a metro rail link in under-developed north Chennai may be faster than in other parts, thanks to the soil condition.
A geo-technical report released with tenders floated by CMRL for a section of the elevated stretch of the 9km phase-I extension has determined the soil from Washermenpet to Wimco Nagar is mostly silt, clay and fine sand.
More than 40 borewells were drilled and soil samples collected to a depth of 40 metres. "Excavation for an underground stretch and pile foundation for an elevated stretch can be faster if the soil is sand or clay," said an official. "The type of soil is crucial in deciding the depth of the foundation for the elevated stretch when calling for tenders."
The report was submitted to France-based Systra MVA Consulting, involved in design and alignment of the `3,770-crore WashermenpetWimco Nagar project with eight stations, including two on a 2km underground stretch. Boring underground tunnels is on since July . In fact, Russian firm Mosmetrostroy abandoned work along Anna Salai, claiming there was a change in alignment and that the rocky stretch was hard to break with the available equipment.
While sandy soil and clay can help in boring tunnels and laying the foundation for the elevated stretch at a faster pace, metro rail engineers said they had to carry out additional work on elevated lines where they encountered finer soil. In the case of silty sand or clay, they might have to drill to an extra depth to lay the foundation for the pile holding the viaduct. "When we lay the foundation, we drill till we reach a rock, then drill another metre into it and complete the foundation ," an engineer said. "If it is just sandy or clayey soil, we might have to drill down 150-180 metres. If we still don't hit a rock, we will have no choice but to rely on the friction around the pile." On underground stretches, the soil may not affect construction too much as blades in tunnel boring machines vary with the type of soil."Work becomes difficult only if it is mixed strata," an official said. Engineers had to slow down tunnel boring between the high court and Central after facing hard rock below and loose soil on top. Applying more pressure while drilling would have affected roads and heritage structures en route.
A geo-technical report released with tenders floated by CMRL for a section of the elevated stretch of the 9km phase-I extension has determined the soil from Washermenpet to Wimco Nagar is mostly silt, clay and fine sand.
More than 40 borewells were drilled and soil samples collected to a depth of 40 metres. "Excavation for an underground stretch and pile foundation for an elevated stretch can be faster if the soil is sand or clay," said an official. "The type of soil is crucial in deciding the depth of the foundation for the elevated stretch when calling for tenders."
The report was submitted to France-based Systra MVA Consulting, involved in design and alignment of the `3,770-crore WashermenpetWimco Nagar project with eight stations, including two on a 2km underground stretch. Boring underground tunnels is on since July . In fact, Russian firm Mosmetrostroy abandoned work along Anna Salai, claiming there was a change in alignment and that the rocky stretch was hard to break with the available equipment.
While sandy soil and clay can help in boring tunnels and laying the foundation for the elevated stretch at a faster pace, metro rail engineers said they had to carry out additional work on elevated lines where they encountered finer soil. In the case of silty sand or clay, they might have to drill to an extra depth to lay the foundation for the pile holding the viaduct. "When we lay the foundation, we drill till we reach a rock, then drill another metre into it and complete the foundation ," an engineer said. "If it is just sandy or clayey soil, we might have to drill down 150-180 metres. If we still don't hit a rock, we will have no choice but to rely on the friction around the pile." On underground stretches, the soil may not affect construction too much as blades in tunnel boring machines vary with the type of soil."Work becomes difficult only if it is mixed strata," an official said. Engineers had to slow down tunnel boring between the high court and Central after facing hard rock below and loose soil on top. Applying more pressure while drilling would have affected roads and heritage structures en route.