Research on a Critical Hydraulic Gradient of Piping in Noncohesive Soils

The critical hydraulic gradient of cohesive soil is an important condition for judging soil piping. For force analysis of movable particles in pore channels of soil, this study proposes to consider the influence of surrounding particles on the drag force of movable particles by water flow. According to the principle of relative motion, considering the interaction force between moving objects in still water, the value of the drag force of water flow that is affected by surrounding particles is calculated, to derive the method of the critical hydraulic gradient. This calculation method is suitable for the results of previous piping tests, and the method is accurate and concise.

Geophysical surveys integrated with rainfall data analysis for the study of soil piping phenomena occurred in a densely urbanized area in eastern Sicily

The occurrence of strong and abrupt rainfall, together with a wrong land use planning and an uncontrolled urban development, can constitute a risk for infrastructure and population. The water flow in the subsoil, under certain conditions, may cause underground cavities formation. This phenomena known as soil piping can evolve and generate the surface collapse. It is clear that such phenomena in densely urbanized areas represent an unpredictable and consistent risk factor, which can interfere with social activities. In this study a multidisciplinary approach aimed to obtain useful information for the mitigation of the risks associated with the occurrence of soil piping phenomena in urban areas has been developed. This approach is aimed at defining the causes of sudden soil subsidence events, as well as the definition of the extension and possible evolution of these instability areas. The information obtained from rainfall data analysis, together with a study of the morphological, geological and hydrogeological characteristics, have allowed us to evaluate the causes that have led to the formation of soil pipes. Furthermore, performance of 3D electrical resistivity surveys in the area affected by the instability have allowed us to estimate their extension in the subsoil and identifying the presence of further areas susceptible to instability.

Detection of soil pipe network by electromagnetic induction (EMI) in relation to the high resolution UAV data

<p>Subsurface erosion by soil piping is a widespread land degradation process that occurs in different soil types around the world. Recent studies have shown that piping erosion may lead to the significant soil loss and disturbances of ground surface. This process accelerates also gully erosion. However, it is still omitted in hydrological models of a catchment, as well as in soil and water erosion models. It seems that the main problem in soil piping studies lies on the basic issue, i.e., the detection of subsurface tunnels (soil pipes). As geophysical methods enable the exploration below the ground surface, they are promising in soil piping studies.</p><p> </p><p>This study aims to evaluate the suitability of the electromagnetic induction (EMI) to detect subsurface network of soil pipes. The detailed study was conducted in the small catchment (Cisowiec) in the Bieszczady Mts. (the Eastern Carpathians, SE Poland), where pipes develop in Cambisols. The measurements were carried out using a conductivity meter EM38-MK2 (Geonics) in both vertical and horizontal measuring dipole orientations. The EM38-MK2 provided simultaneous measurements of apparent electrical conductivity with two transmitter receiver coil separation (0.5 m and 1 m). In order to compare subsurface data with the surface response (i.e., depressions and collapses), the high resolution DEM and orthophotos have been produced. These data have been prepared using Structure from Motion (SfM) technique based on the images taken from the low altitude by an Unmanned Aerial Vehicle (UAV; DJI Phantom-4 equipped with a 1' camera). The UAV-derived products (orthophotos and DEM) have the resolution of 0.014 x 0.014 m and point density of 9240 per 1 m<sup>2</sup>.</p><p> </p><p>The EMI results are presented on the maps that gathered data at three depths (0.4 m, 0.75 m, 1.5 m). The results revealed the soil pipes as areas characterized by higher electrical conductivity than the surroundings. The spatial distribution of subsurface tunnels corresponds with the ground depressions and collapses detected in the field and seen on the high resolution DEM and orthophoto. The use of EMI in piping research has been evaluated.</p><p> </p><p>The study is supported by the National Science Centre, Poland within the first author’s project SONATINA 1 (2017/24/C/ST10/00114).</p>

Detection of Soil Pipes Using Ground Penetrating Radar

Soil piping leads to land degradation in almost all morphoclimatic regions. However, the detection of soil pipes is still a methodological challenge. Therefore, this study aims at testing ground penetrating radar (GPR) to identify soil pipes and to present the complexity of soil pipe networks. The GPR surveys were conducted at three sites in the Bieszczady Mountains (SE Poland), where pipes develop in Cambisols. In total, 36 GPR profiles longitudinal and transverse to piping systems were made and used to provide spatial visualization of pipe networks. Soil pipes were identified as reflection hyperbolas on radargrams, which were verified with the surface indicators of piping, i.e., sagging of the ground and the occurrence of pipe roof collapses. Antennas of 500 MHz and 800 MHz were tested, which made possible the penetration of the subsurface up to 3.2 m and 2 m, respectively. Concerning ground properties, antenna frequencies and processing techniques, there was a potential possibility to detect pipes with a minimum diameter of 3.5 cm (using the antenna of lower frequency), and 2.2 cm (with the antenna of higher frequency). The results have proved that soil pipes meander horizontally and vertically and their networks become more complicated and extensive down the slope. GPR is a useful method to detect soil pipes, although it requires field verification and the proper selection of antenna frequency.

Medium-scale laboratory model of mono-bucket foundation for installation tests in sand

Design implications of suction installation of bucket foundations are still not well understood. During suction installation, applied suction under the bucket lid results in seepage flow through the surrounding sand. Seepage flow plays a pivotal role in reducing the penetration resistance, allowing for full penetration despite the initial large soil resistance. However, loosening of the inside soil plug might be problematic when the soil approaches its failure stage, due to soil piping or extensive soil heave inside the bucket foundation. To better understand the interaction between the soil and bucket skirt during suction installation, this paper describes the results of medium-scale tests of bucket foundation installations in sand, comparing jacking and suction installations. Experimental measurements of the pore pressure around the bucket skirt are compared with the numerical simulation results, to validate the finite-element model and to enable analysis of the soil behavior around the skirt.

Mesquite bugs, other insects, and a bat in the diet of pallid bats in southeastern Arizona

The pallid bat (Antrozous pallidus) is a species of western North America, inhabiting ecoregions ranging from desert to oak and pine forest. They are primarily insectivorous predators on large arthropods that occasionally take small vertebrate prey, and are at least seasonally omnivorous in certain parts of their geographic range where they take nectar from cactus flowers and eat cactus fruit pulp and seeds. Until recently, mesquite bugs were primarily tropical-subtropical inhabitants of Mexico and Central America but have since occupied the southwestern United States where mesquite trees occur. Using a noninvasive method, we investigated the bats’ diet at the Cienega Creek Natural Preserve, Arizona, by collecting food parts discarded beneath three night roosts in soil-piping cavities in a mesquite bosque. We also made phenological and behavioral observations of mesquite bugs, Thasus neocalifornicus, and their interactions with the mesquite trees. We determined that the bats discarded inedible parts of 36 species in 8 orders of mainly large-bodied and nocturnal insects below the night-roosts. In addition, one partial bat wing represents probable predation upon a phyllostomid bat, Choeronycteris mexicana. About 17 of the insect taxa are newly reported as prey for pallid bats, as is the bat C. mexicana. The majority of culled insect parts (88%) were from adult mesquite bugs. Mesquite bug nymphs did not appear in the culled insect parts. After breeding in late summer, when nighttime low temperatures dropped below 21 °C, the adult bugs became immobile on the periphery of trees where they probably make easy prey for opportunistic foliage-gleaning pallid bats. Proximity of night-roosts to mesquite bug habitat probably also enhances the bats’ exploitation of these insects in this location.