Laboratory study on the effects of hydraulic and granulometric parameters on the response of granular soil to internal erosion

Erosion is a major environmental problem to agricultural land as well as to civil engineering infrastructures. Rainwater infiltration into granular soils can lead to the migration of fine particles by suffusion. This experimental study is conducted to evaluate the susceptibility to erosion of cohesionless soils. The soil under investigation was collected from the coastal region of Mostaganem (West of Algeria) where erosion has recently caused several damages. To assess soil instability to erosion, two approaches have been proposed in the literature: the geometric approach and the hydraulic approach. Few studies have examined the combination of the two methods. The objective of our study is the combination of the two approaches by determining the critical hydraulic load responsible for triggering erosion as a function of soil characteristics. An experimental parametric study was conducted to determine the influence of initial amount of fines, hydraulic gradient and axial stress on the initiation and evolution of suffusion. A combination of the interactions between these parameters allowed us to express the critical hydraulic gradient and to identify the hydraulic behavior of the soil according to the studied parameters. This approach can better estimate the erodibility of cohesionless soils. It can be used in future development studies at this site to reduce the risk of erosion

Dynamics of loess mass deformations due to technogenic load

По результатам анализа энергетических и фильтрационных свойств техногенно нагруженного лессового массива определен интервал глубин, и геологические слои, характеризующиеся наиболее интенсивным развитием деформационных и суффозионных процессов. Приведенная методика оценки устойчивости массива, позволяет прогнозировать поведение склона с учетом нарушения его сплошности, произошедшего вследствие суффозионных про- цессов. Дана количественная оценка момента перехода массива в неустойчивое состояние, а также связь фильтрационных процессов с формированием оползней течения.За результатами аналізу енергетичних і фільтраційних властивостей техногенно навантаженого льосового масиву визначені інтервал глибин та геологічні шари, що характеризуються найбільш інтенсивним розвитком деформаційних та суфозійних процесів. Наведена методика оцінки стійкості масиву дозволяє прогнозувати поведінку схилу з врахуванням порушення його цілісності внаслідок суфозійних процесів. Наведена кількісна оцінка моменту переходу масиву в нестійкий стан, а також зв'язок фільтраційних процесів з формуванням зсувів течії.Analysis of energetic and filtration properties of loess with technogenic loads helps determine depth interval and geological layers characterized by maximum development of deformation processes and suffusion ones. Mass stability evaluation technique shown in the paper helps predict a slope behaviour involving its discontinuity as a result of suffusion processes. Moment of a mass transition into unstable condition is estimated quantitatively as well dependence of filtration processe on stream landslides formation

Phreatic seepage flow through an earth dam with an impeding strip

New mathematical models are developed and corresponding boundary value problems are analytically and numerically solved for Darcian flows in earth (rock)–filled dams, which have a vertical impermeable barrier on the downstream slope. For saturated flow, a 2-D potential model considers a free boundary problem to Laplace’s equation with a traveling-wave phreatic line generated by a linear drawup of a water level in the dam reservoir. The barrier re-directs seepage from purely horizontal (a seepage face outlet) to purely vertical (a no-flow boundary). An alternative model is also used for a hydraulic approximation of a 3-D steady flow when the barrier is only a partial obstruction to seepage. The Poisson equation is solved with respect to Strack’s potential, which predicts the position of the phreatic surface and hydraulic gradient in the dam body. Simulations with HYDRUS, a FEM-code for solving Richards’ PDE, i.e., saturated-unsaturated flows without free boundaries, are carried out for both 2-D and 3-D regimes in rectangular and hexagonal domains. The Barenblatt and Kalashnikov closed-form analytical solutions in non-capillarity soils are compared with the HYDRUS results. Analytical and numerical solutions match well when soil capillarity is minor. The found distributions of the Darcian velocity, the pore pressure, and total hydraulic heads in the vicinity of the barrier corroborate serious concerns about a high risk to the structural stability of the dam due to seepage. The modeling results are related to a “forensic” review of the recent collapse of the spillway of the Oroville Dam, CA, USA

New species and records of Rhyssa and Rhyssella (Hymenoptera: Ichneumonidae: Rhyssinae) from Florida and Central America

Rhyssa neotropicae n. sp. is the first Rhyssa to be recorded from the New World tropics, where it was collected in cloud forest at 1800 m on Monte Uyuca near Zamorano, Honduras. It is closely related to the Nearctic R. hoferi Rohwer and R. howdenorum Townes but differs from all other Rhyssa by its complexly yellow and black marked head and body, whose color pattern mimics that of aggressive social vespid wasps (Agelaia) which occur in the same habitat. Rhyssa howdenorum Townes is recorded for the first time from Florida and Oklahoma. The genus Rhyssella, previously unknown in Florida, is represented in that state by R. perfulua n. sp., distinctive in its mostly orange brown coloration, and by R. humida (Say), a black and white species with fulvous on the thoracic pleura and propodeum.Rhyssa neotropicae n. sp. es la primera especie de su genero de ser senalada para la Region Neotropical, donde se la colecciono en selva humeda de alta montana a 1800 msnm en la cima del Monte Uyuca cerca de Zamorano en Honduras. Se trata de una especie muy afin a R. hoferi Rohwer y a R. howdenorum Townes, las cuales se distribuyen en el sur y centro de la Region Neartica, diferenciimdose, no obstante, R. neotropicae de todas las demas Rhyssa por su bello esquema de coloracion con intrincados dis enos amarillos y negros, a semejanza del que osten tan unos vespidos sociales agresivos (Agelaia), que abundan en los mismos ambientes. Se cita pol' primera vez a Rhyssa howdenorum Townes para Florida y Oklahoma. El genero Rhyssella, antes no conocido en la Florida, cuenta de hecho en este estado con 2 especies, R. perfulua n.sp., que destaca pOl' tener el cuerpo casi uniformemente de color castano claro anaranjado, y R. humida (Say), especie negra con dis enos blancos y las pleuras toracicas junto con el propodeo en gran parte de color claro, entre anaranjado y rojo

Antlions of Hispaniola (Neuroptera: Myrmeleontidae)

Twelve extant species of antlions are known from Hispaniola including four new species (Eremoleon petrophila, Eremoleon phasma, Purenleon nunezi, Purenleon woodruffi) and one new genus (Peruveleon). Five New World species are transferred into Peruveleon resulting in new combinations: Peruveleon bruneri (Alayo), Peruveleon camposi (Banks), Peruveleon dolichogaster (Navás), Peruveleon dorsalis (Banks), Peruveleon indiges (Walker). Vella fallax haitiensis Smith is considered a new synonym of Vella eggerti Esben-Petersen. Descriptions and records for the species are provided as well as keys to the adults and larvae. The larvae of eleven species were found and reared.Se documentan doce especies de Myrmeleontidae de Hispaniola incluyendo cuatro especies nuevas (Eremoleon petrophila, Eremoleon phasma, Purenleon nunezi, Purenleon woodruffi) y un género nuevo (Peruveleon). Cinco especies son transferidos al género Peruveleon resultando nuevas combinaciones: Peruveleon bruneri (Alayo), Peruveleon camposi (Banks), Peruveleon dolichogaster (Navás), Peruveleon dorsalis (Banks), Peruveleon indiges (Walker). Vella fallax haitiensis Smith es considerado como un sinonimo nuevo de Vella eggerti Esben-Petersen. Se proporcionan descripciones y registros para las especies y claves para los adultos y larvas. Las larvas de once especies fueron descubiertas y asociadas con adultos

Tomographic Study of Internal Erosion of Particle Flows in Porous Media

In particle-laden flows through porous media, porosity and permeability are significantly affected by the deposition and erosion of particles. Experiments show that the permeability evolution of a porous medium with respect to a particle suspension is not smooth, but rather exhibits significant jumps followed by longer periods of continuous permeability decrease. Their origin seems to be related to internal flow path reorganization by avalanches of deposited material due to erosion inside the porous medium. We apply neutron tomography to resolve the spatio-temporal evolution of the pore space during clogging and unclogging to prove the hypothesis of flow path reorganization behind the permeability jumps. This mechanistic understanding of clogging phenomena is relevant for a number of applications from oil production to filters or suffosion as the mechanisms behind sinkhole formation.Comment: 18 pages, 9 figure

Variability of the grain size distribution of a soil related to suffusion

Risk and Reliability in Geotechnical Engineerin

Laboratory study on the effects of hydraulic and granulometric parameters on the response of granular soil to internal erosion

Erosion is a major environmental problem to agricultural land as well as to civil engineering infrastructures. Rainwater infiltration into granular soils can lead to the migration of fine particles by suffusion. This experimental study is conducted to evaluate the susceptibility to erosion of cohesionless soils. The soil under investigation was collected from the coastal region of Mostaganem (West of Algeria) where erosion has recently caused several damages. To assess soil instability to erosion, two approaches have been proposed in the literature: the geometric approach and the hydraulic approach. Few studies have examined the combination of the two methods. The objective of our study is the combination of the two approaches by determining the critical hydraulic load responsible for triggering erosion as a function of soil characteristics. An experimental parametric study was conducted to determine the influence of initial amount of fines, hydraulic gradient and axial stress on the initiation and evolution of suffusion. A combination of the interactions between these parameters allowed us to express the critical hydraulic gradient and to identify the hydraulic behavior of the soil according to the studied parameters. This approach can better estimate the erodibility of cohesionless soils. It can be used in future development studies at this site to reduce the risk of erosion

The Effect of Suffusion Phenomenon in the Increasing of Land Subsidence Rate

Land subsidence is defined as gradually ground surface settlement in an aquifer due to the compaction of unconsolidated sedimentary deposits. Since in an aquifer, deposits consist of cohesive or non-cohesive alluvial soil layers. The consolidation theory cannot be explained as the only reason for land subsidence. According to the susceptibility of alluvial soils to suffusion, internal erosion is also considerable to enhance the rate of the local settlement. Suffusion is explained as a process of soil particle movement in the soil body due to the effect of seepage flow on it. The subsidence rate in southwest and south of Tehran in Iran is very considerable whereby some structures have suffered significant damages due to this phenomenon. In this research, the contribution of suffusion and land subsidence was investigated in damaged building located at Ghale Morghi Street in southwest of Tehran, as a case history. Because of the incapability of available methods, in this article, a probability pattern is also proposed using statistical analysis for determination the likelihood of internal instability in alluvial soils in regard to soil cohesiveness