Submarine Groundwater Discharge From Sediments and Sand Boils Quantified by the Mean Residence Time of a Tracer Injection

To quantify submarine groundwater discharge, we developed an inexpensive automated seepage meter that applies a tracer injection and the computation of the mean residence time. The SGD-MRT is designed to measure a wide range of discharge rates from about 30 to 800 cm³/min and allows minimizing backpressures caused by pipe friction or flow sensors. By modifying the inner volume of the flow-through unit, the range of measurement is adjustable to lower or higher discharge rates. For process control and data acquisition, an Arduino controller board is used. In addition, components like temperature, conductivity, and pressure sensors or pumps extend the scope of the seepage meter. During field tests in the Wadden Sea, covering tidal cycles, discharge rates of more than 700 cm³/min were released from sand boils. Based on the measured discharge rates and numerical integration of the time series data, a water volume of about 400 dm3 with a seawater content of less than 12% was released from the sand boil within 7 h.

The preliminary inventory of coseismic ground failures related to December 2020 – January 2021 Petrinja earthquake series

The most recent major earthquake series struck near Petrinja (December 29th 2020 M 6.2), and triggered extensive ground failures in the wider area of Petrinja, Sisak and Glina. Coseismic ground failures including subsidence dolines, liquefaction and landslides have been documented over a large area by various experts and teams. These data are stored in the newly created inventory, which is openly presented in this paper. This inventory is administered and updated by the Croatian Geological Survey, and will be available online via a Web Map Service (WMS) (www.hgi-cgs.hr). The aim of the inventory is to not only provide data for the development of susceptibility maps and more detailed exploration for possible remediation measures, but also to define the priorities for immediate action. The earthquake triggered the rapid development of dropout dolines which endanger the local populations of the villages of Mečenčani and Borojevići. This is still an ongoing process in the vicinity of the houses and therefore in-situ exploration started immediately. Liquefaction related to alluvial sediments of the Sava, Kupa and Glina rivers occurred almost exclusively in loose and pure sands, and was accompanied by sand boils, subsidence and lateral spreading. Liquefaction also presents a greater hazard because settlement of houses and river embankments occurred. Lateral spreading caused failures of river flood embankments and natural river banks. According to the data known to date, the majority of the coseismic landslides were reactivated with minor displacements. Despite that, it has been recognised that houses at the edge, or in landslide colluvium suffered greater damage than other houses located outside the landslide impact zone.

Evaluation of liquefaction potentials based on shear wave velocities in Pohang City, South Korea

This study evaluates the potentials of liquefaction caused by the 2017 moment magnitude 5.4 earthquake in Pohang City, South Korea. We obtain shear wave velocity profiles measured by suspension PS logging tests at the five sites near the epicenter. We also perform downhole tests at three of the five sites. Among the five sites, the surface manifestations (i.e., sand boils) were observed at the three sites, and not at the other two sites. The maximum accelerations on the ground surface at the five sites are estimated using the Next Generation Attenuation relationships for Western United State ground motion prediction equations. The shear wave velocity profiles from the two tests are slightly different, resulting in varying cyclic resistance ratios, factors of safety against liquefaction, and liquefaction potential indices. Nevertheless, we found that both test approaches can be used to evaluate liquefaction potentials. The liquefaction potential indices at the liquefied sites are approximately 1.5–13.9, whereas those at the non-liquefied sites are approximately 0–0.3.

Field measurements on a large natural sand boil along the river Po (Italy)

Sand boils are the surface manifestation of an erosion process, known as backward erosion piping, which may take place beneath river embankments during high-water events. The risk of embankment failure greatly increases in locations affected by sand boils. Numerous studies have been carried out, mainly at the laboratory scale, providing significant advancements in this field. Nonetheless, there is still a gap between research and practice that needs to be filled.This study presents a set of field measurements carried out on a large sand boil reactivated near the toe of an embankment along the river Po (Italy). Hydraulic heads, velocity and discharge, concentration and pipe geometry were measured as a function of the water level in the river during the November 2018 flood. The collected data are compared to predictions of a theoretical model which provides the head loss in the vertical pipe. Furthermore, the local exit gradients, as deduced from measurements, are discussed, together with the operational critical gradients adopted in current design practice.The collected data provide important input parameters for the calibration of analytical and numerical models, typically implemented to investigate the sand boil evolution and then to assess the backward erosion piping risk at real scale.

Liquefaction and Related Ground Failure from July 2019 Ridgecrest Earthquake Sequence

ABSTRACT The 2019 Ridgecrest earthquake sequence produced a 4 July M 6.5 foreshock and a 5 July M 7.1 mainshock, along with 23 events with magnitudes greater than 4.5 in the 24 hr period following the mainshock. The epicenters of the two principal events were located in the Indian Wells Valley, northwest of Searles Valley near the towns of Ridgecrest, Trona, and Argus. We describe observed liquefaction manifestations including sand boils, fissures, and lateral spreading features, as well as proximate non-ground failure zones that resulted from the sequence. Expanding upon results initially presented in a report of the Geotechnical Extreme Events Reconnaissance Association, we synthesize results of field mapping, aerial imagery, and inferences of ground deformations from Synthetic Aperture Radar-based damage proxy maps (DPMs). We document incidents of liquefaction, settlement, and lateral spreading in the Naval Air Weapons Station China Lake US military base and compare locations of these observations to pre- and postevent mapping of liquefaction hazards. We describe liquefaction and ground-failure features in Trona and Argus, which produced lateral deformations and impacts on several single-story masonry and wood frame buildings. Detailed maps showing zones with and without ground failure are provided for these towns, along with mapped ground deformations along transects. Finally, we describe incidents of massive liquefaction with related ground failures and proximate areas of similar geologic origin without ground failure in the Searles Lakebed. Observations in this region are consistent with surface change predicted by the DPM. In the same region, geospatial liquefaction hazard maps are effective at identifying broad percentages of land with liquefaction-related damage. We anticipate that data presented in this article will be useful for future liquefaction susceptibility, triggering, and consequence studies being undertaken as part of the Next Generation Liquefaction project.

Enhanced landslide mobility promoted by liquefaction of underlying sediments: Evidence from detailed field, lab, and modelling investigations of the deadly Oso, USA landslide

<p>Enhanced landslide mobility can project devastation across extensive areas, greatly affecting hazard and risk. Despite this importance, assessing potential mobility can be challenging as underlying causes of enhanced mobility vary. Liquefaction can dramatically decrease shear resistance and promote mobility, and pervasive liquefaction is well known to boost the mobility of debris flows and other flow slides. However, liquefaction’s potential effect on more coherent slide masses can be difficult to identify in the field. The 2014 Oso, Washington (USA) debris avalanche provides an exceptional opportunity to understand specific causes of liquefaction and enhanced mobility. The slide was more mobile than typical debris avalanches, sweeping over 1 km across a flat alluvial plain to the opposite side of the river valley and killing 43 people as it travelled. Following the 2014 event, we performed detailed investigations aimed at illuminating the event sequence and the mechanisms promoting mobility, with a strong focus on the role of liquefaction.</p><p>The landslide initiated in stratified glacial materials and created a variety of landslide deposit types, including a widespread debris-avalanche hummock field covering much of the formerly flat river valley. Our field investigations revealed clear and widespread evidence for sub-bottom (basal) liquefaction as the cause for the slide’s long reach. Soon after the slide event, we mapped more than 350 sand boils – classic indicators of liquefaction – as both isolated vents and groups of multiple vents within the hummock field. We found sand boils in the depressions between hummocks; the hummocks themselves were not liquefied and commonly contained rafted materials such as intact pieces of glacial stratigraphy and forest floor on their surfaces. The sand boils erupted through a variety of glacial sediments, including lacustrine clays. Sand boil grain-size characteristics most closely matched the underlying alluvial sands, rather than the overriding glacial sediments. Evidence of sand boils was transient; most features were eroded from the landscape within a year.</p><p>Liquefaction can be induced by several mechanisms, including rapid loading, shearing of loose contractive sediment, and cyclical loading during ground shaking. Given these plausible mechanisms, we used a fully coupled fluid-sediment elastic deformation analysis, as well as triaxial geotechnical testing of the alluvium, to assess potential liquefaction of the materials overrun by the Oso slide. Our results demonstrate that the large failure rapidly loading loose, already wet alluvial sediments likely resulted in their liquefaction. The greatly reduced shear strength of the liquefied alluvium enabled enhanced mobility of the overriding landslide mass on a liquefied base. This process differs from liquefaction of the slide material itself and is therefore not directly dependent on slide-mass properties. Liquefaction of underlying sediments, similar to that observed at Oso, may have enhanced the mobility of other large, coherent landslides in Europe and Asia.</p>