Climatic Changes Challenge Construction Design

If the UK climate continues to get wetter, design engineers will need to ensure they allow for rising groundwater and the looming threat of retaining wall and earthworks slope failure.

That’s the stark warning from HBPW’s geoenvironmental engineer, Jay Fox, following record rain falls that left Britain wallowing in flood water earlier this year, and homes in Somerset sandbagged or evacuated.

He said: “According to the Met Office 2012 was the second wettest year ever since records began, and 2013 / 14’s looking pretty bleak as well judging from the weather we have experienced in recent months.

“Groundwater – held underground in the soil and crevices in rock – is now the highest for many years which is leading to a number of issues affecting the construction industry.”

Jay said that rising groundwater levels not only created difficulties during construction work, such as a greater requirement for de-watering and pumping out of excavations in order to keep them dry, but also impacted ground stability.

“As groundwater levels rise piezometric pressures in soil also increase, particularly where the ground cannot drain due to flooding or ineffective drainage, placing added strain on ground and slope stability. The result can be that slopes become unstable.”

He said there had been a noticeable increase in slope failures on the UK’s rail and highways network, particularly in the south west.

“Many structures, particularly retaining walls, are designed on the assumption of a certain groundwater level. However, whilst prudent design assumes a worst case scenario – namely where the soil behind the wall is saturated – this is not always the case meaning many retaining walls move, or even fail, due to groundwater levels building up behind them over time.

“The resulting movements can cause major structural damage, and ground subsidence can occur many meters away from the actual retaining walls,” added Jay.

He said that if the climate continued to get wetter designers would need to start thinking differently.

“Invariably drainage measures are designed and installed but many are designed in such a way that they cannot be accessed for maintenance or cleaning and, as a result, become silted, blocked and ineffective at reducing groundwater pressure build-up. Resulting retaining wall failure can have catastrophic implications,” he added.