Question

A construction company specializing in drilling horizontal holes across rivers or lakes with diameter ranging from 12 to 24 inches is currently engaging in a construction project in Dallas/Fort Worth Area. According to the regulations of the municipality where the projects locates, construction activities cannot be carried out during weekends and holidays. Therefore, during the coming Thanksgiving, the construction will be suspended. The construction company could resume its work after Thanksgiving. As a construction project engineer for the project, what kind of problem can you predict? Please write briefly about your prediction BASED ON THE CONCEPT OF EFFECTIVE STRESS? Please explain how effective stress would affect the drilling procedures after a long lay-off

Answer 1

As a construction project engineer for drilling holes across rivers or lakes,a thorough examination and detailed report of the project is essential. Sub-surface works such as excavation, drilling must be executed with deep scrutiny, as slight change in the atmospheric behavior may lead to devastating effects.

During the weekends / off days for the duty, their might be the risk of surge or draw down of the water level in the river, which might effect the altered soil profile. As a result, this might be added benefit or burden for the engineer.

As we know that, fluctuations in the water level will effect the pore water pressure on the soil.

As an instance, if water table is up to a certain level in the river or water body. if it is allowed to withhold for a particular duration, pores in the soil are occupied by water beyond the water level. This will lead to increased upliftment pressure in the form of pore water pressure, which directly reduces the value of effective stress over the time. So, drilling can be carried with faster pace after a particular depth and duration.

This might not be the scenario at mild cool conditions. Due to the effect of freezing and thawing, pores filled by the water may freeze which may cease the upward percolation of water leading to confined pore water pressure. So, the effective stress is altered from expected value to increased value. drilling requires additional efforts to make a bore hole in this scenario.

Therefore, prediction of following climatic conditions and site behavior is essential to halt the work or prolong it. Dallas climatic conditions are being moderately cool, works are carried usually at this season and delay of work for thanksgiving is acceptable,