Groundwater fluctuations during a debris flow event in Western Norway – triggered by rain and snowmelt

Pore pressure is crucial in triggering debris slides and flows. Here we present measurements of ground water pore pressure and temperature recorded by a piezometer 1.6 m below the surface on a slope susceptible to debris flows in Western Norway. One of the largest oscillations in data collected over four years coincided with a debris flow event on the slope that occurred during storm Hilde on 15–16 November 2013. More than 100 landslides were registered during the storm. Rainfall totalled about 80–100 mm in 24 hours, locally up to 129 mm, and an additional trigger factor for the slides was a rapid rise in air temperature that caused snowmelt. On 15 November, the groundwater level in the hillslope rose by 10 cm per hour and reached 44 cm below the surface. At the same time, air temperature rose from 0 °C to over 8 °C, and the groundwater temperature dropped by 1.5 °C. The debris flow probably occurred late in the evening of 15 November, when the groundwater level reached its peak. Measurements of the groundwater in the hillslope in the period 2010–2013 show that the event in 2013 was not exceptional. Storm Dagmar on 25–26 December 2011 caused a similar rise in groundwater level, but did not trigger any failures. The data suggest that during heavy rainstorms the slope is in a critical state for a slide to be triggered for a short time – about 4–5 hours.

Numerical Analysis of the Influences of Water Level on Seepage Stability of Tailing Dam

Understanding the influences of water level on seepage stability of tailing bay is an important topics in hydraulic engineering design. The seepage stability of tailing bay under different water level was calculated with the numerical simulation software FLAC3D and the change laws of water pore pressure and saturation line in the dam was analyzed. The results show that the saturation line in the dam is a parabolic curve and the pore pressure changes in layers. With the increasing of water level, the saturation line in the heaping dam ups rather obviously while it is not obvious in the initial dam. The maximum pore pressure in the bottom of the dam increases with the relationship of water level up, the shallow of the saturation line is in the heaping dam heel.

Dynamic Consolidation Test Study on Silt and Silt Soil

A dynamic consolidation model of double layered foundation of saturated soil and unsaturated soil is proposed. Mechanism of dynamic compaction treating on double layered foundation is studied by the model. On the base of the mechanism a new technology called soil-mound dynamic consolidation can be applied to treat the ground of saturated silt and silty clay with high groundwater level. The water-pore pressure test, static cone penetration test, settlement plate test are applied to evaluate that of the new technology with different construction parameters. The treatment effect is more remarkable than that of plastic drain-dynamic consolidation.

Correlation of seismicity and water level in the Açu reservoir—an example from Northeast Brazil

Seismic monitoring of the Açu reservoir (31-m depth, 2.4 × 109 m3 in volume), in Rio Grande do Norte State, Northeastern Brazil, started in 1987 about 2 years after impoundment. The largest earthquake so far (magnitude 2.8) occurred in August 1994. From 1987 to 1989, the monthly number of induced events had a clear correlation with the water level, with a 3-month delay, and the activity occurred mainly inside the reservoir. Although no preimpoundment monitoring had been carried out, the correlation of the water level and the seismicity strongly suggests the activity was induced by pore pressure diffusion. Since 1990, the activity migrated toward the border of the reservoir, and the number of events no longer correlated with the water level. A seismographic network was deployed around the reservoir during two field campaigns (1989 and 1990/91), showing that the activity occurred preferentially with strike-slip mechanisms on NE oriented faults. The E-W orientation of the P axes, parallel to the regional maximum horizontal stress, and the presence of many NE trending faults and fractures in the Precambrian basement near the reservoir, suggest that the probably induced seismicity was a typical case of water pore pressure facilitating earthquake occurrence in pre-existing zones of weakness under high regional stresses.