Tevere river banks protection

Italy, Roma
Geocontainers and soil reinforcement geogrids for river banks protection

Problem:
river banks are often characterized by their highly variable boundary and mechanical properties of their soil, by their conditions of partial saturation as well as by the high variable surrounding hydraulic conditions in space and time, especially during floods.
Specifically, the condition of partial saturation of the soil causes a reduction in the permeability of the soil with the increase in soil suction, defined as the difference between the air pressure (ua) and the porosity water pressure (uw). It follows that, in a fully (or almost) submerged bank, due to the effect of a flood, very high hydraulic gradient values and/or neutral pressure can develop, with drastic degradation of the bank’s stability in time.
This occurred in a section of the banks on the Tevere River, about 10 m high with a slope of about 30°, consisting of loamy sand, that is loamy sand deposited in layers varying from 2 to 5 m thick. During the flood on November 14-15, 2012, the water level of the Tevere River rose over a 60 hour period from its ordinary level of 8.52 m above sea level to a maximum of 16.20 m above sea level.
This level held constant for about 24 hours, and returned to its ordinary value in only 12 hours. This time sequence was critical for the bank, which underwent instability phenomena, with a local slip surface about 4 m deep and 15 m long.

Solution:
following, the top surface of this section of the bank was reshaped using granular aggregates and six layers of Edilgrid 35/20, polyester woven geogrid with PVC coating, with a vertical space of 0.8 m.
At the base of the river bank, on top of a lean concrete layer, two layers of 4-ton Ecogreen Filter Units were placed for control of the foot erosion, providing soil reinforcement, stabilization and filtering.
After performing the works, specifically on February 1-2, 2014, another flood occurred, with similar levels to those recorded in November 2012. On this occasion, there was no slide, nor was there any relevant deformation of the river bank or surface erosion recorded.