Field scale determination of the aquifer–aquitard boundary in Joso Clay by cone penetrometry

Abstract

A few number of soil profile studies have pointed out that Joso Clay, a thick clayey layer underlying the shallow groundwater bodies in the diluvial uplands of southern Ibaraki and northern Chiba prefectures, Japan, has a structured surface layer in which the hydraulic conductivity is one to several orders of magnitude higher than that of the underlying massive layer. The spatial distribution of the boundary between the structured and massive clay layers should be determined as the aquifer-aquitard boundary; however, such attempts have not been made. In the present study, dynamic cone penetrometry was used to determine the spatial distribution of the aquifer-aquitard boundary in Joso Clay at a field scale in Tsukuba-Inashiki Upland, Ibaraki prefecture, Japan. The dynamic cone penetration index N d5 , every 5-cm depth average of the number of hammer strikes required for the tip cone to enter into the soil per unit of depth, was determined to a depth of 3.1-3.7 m at 54 rectangular grid points with approximately 5-m spacing in a field with an area of 943 m 2 . The field-scale N d5 profile data suggested that prismatic structures with N d5 values of up to 50-60 m -1 are widely distributed in the uppermost layer of the Joso Clay. Accordingly, a criterion of N d5 > 60 m -1 was proposed for determining the underlying aquitard in this field. The depth to the aquifer-aquitard boundary was determined to be 2.58 m on average, ranging from 2.40 to 2.89 m. Furthermore, annual water table monitoring at each grid point showed that the thickness of the structured layer, varying from 0.30 to 0.75 m, occupied 61-100% of the annual average shallow aquifer thickness, which varied from 0.40 to 0.87 m. These results demonstrate the significance of the uppermost structured layer in the Joso Clay as the major part of the shallow aquifer at a field scale in this upland.

Toward improved prediction of the bedrock depth underneath hillslopes: Bayesian inference of the bottom‐up control hypothesis using high‐resolution topographic data

“…Examples of direct measurement methods include rod penetrometers [ Kuriakose et al ., ; Tesfa et al ., ; Fu et al ., ; Lanni et al ., ; Lucà et al ., ], excavated pits [ Boer et al ., ; Heimsath et al ., ; Pelletier and Rasmussen , ; Catani et al ., ; Pelletier et al ., ], hand and gasoline or electric‐powered augers [ Fernandes et al ., ; Ziadat , ; Liu et al ., ], road cuts, and erosion gullies [ Kuriakose et al ., ; Wilford and Thomas , ], and dynamic cone penetrometers [ Kosugi et al ., ; Fujimoto et al ., ; Ohnuki et al ., ; Tsuchida et al ., ; Askarinejad et al ., ; Wiegand et al ., ; Athapaththu et al ., ; Liang and Uchida , ]. This last measurement device is particularly promising as it can help delineate soil stratigraphy and layers with contrasting hydraulic properties [ Eguchi et al ., ; Masaoka et al ., ]. Examples of indirect bedrock depth measurement methods include the use of gravity survey [ Stewart , ; Bohidar et al ., ], geophysical exploration [ Dahlke et al ., ], seismic refraction [ Zhou and Wu , ], electrical resistivity tomography [ Zhou et al ., ; Lucà et al ., ], and airborne electromagnetic [ Christensen et al ., ].…”

Wellbore‐Wall Compression Effects on Monitored Groundwater Levels and Qualities

“…The upper Joso Clay is also a part of the shallow aquifer and lower down it becomes the underlying aquitard. The boundary depth ( η ) between the shallow aquifer and underlying aquitard in the Joso Clay is about 2.6 m (Eguchi et al 2009b). Further descriptions of the study site are included in Supporting Information (Study Site).…”

Modelagem Da Interface Solo-Rocha Utilizando Inferência Bayesiana

“…Exemplos de métodos diretos incluem penetrômetros manuais de aço (Kuriakose et al, 2009;Tesfa et al, 2009;Fu et al, 2011;Lanni et al, 2012;Lucà et al, 2014), trincheiras escavadas (Boer et al, 1996;Heimsath et al, 2001;Pelletier e Rasmussen, 2009;Catani et al, 2010;Pelletier et al, 2011), trados manuais e mecânicos (Boer et al, 1996;Heimsath et al, 2001;Pelletier e Rasmussen, 2009), taludes rodoviários e voçorocas (Kuriakose et al, 2009;Wilford e Thomas, 2013), e penetrômetros dinâmicos de cone (Ohnuki et al, 1997(Ohnuki et al, , 2008Shanley et al, 2003;Uchida et al, 2003;Katsuyama et al, 2005;Kosugi et al, 2006Kosugi et al, , 2009Fujimoto et al, 2008;Ohnuki et al, 2008;Springman et al, 2009;Tsuchida et al, 2011;Askarinejad et al, 2012;Wiegand et al, 2013;Athapaththu et al, 2014;Liang e Uchida, 2014;Masaoka et al, 2016). Esteúltimo dispositivoé particularmente promissor pois pode delinear a estratigrafia do solo e camadas com propriedades hidráulicas contrastantes (Eguchi et al, 2009;Masaoka et al, 2012). Exemplos de métodos de investigação de campo indiretos incluem o levantamento gravimétrico (Stewart, 1980;Bohidar et al, 2001), Georadar (D...…”