Cone penetration testing in deltaic soils

Abstract

A multichannel electric cone penetrometer was used to perform a variety of in-situ tests in saturated deltaic deposits. Factors affecting the tip bearing, friction sleeve stress, and pore-water pressures and their interpretation are studied and discussed. Pore pressure measurements were essential to evaluate the in-situ test results. The effect of rate of penetration is discussed and the concept of effective bearing introduced as an attempt to interpret cone bearing in undrained or partially drained soil. Field values of consolidation characteristics from pore pressure decay are compared with traditional laboratory consolidation test results on undisturbed samples.The advantages of continuous electric cone logging to evaluate soil stratigraphy are demonstrated. Field and laboratory test results are presented from a test site where stabilization was used to reduce liquefaction potential of hydraulically placed sand and silt. The importance of pore pressure measurements is demonstrated along with examples and recommendations for the location of the porous element.

Hydraulic and mechanical properties of glacial sediments beneath Unteraargletscher, Switzerland: implications for glacier basal motion

“…From the solution of Equation (2) (e.g. Carslaw and Jaeger, 1959), applying to a harmonically varying pressure at the surface of a semi-infinite aquifer, it follows that pressure fluctuations with angular frequency ω are propagated into the aquifer with velocity v D…”

“…If R is small, there is insufficient time for pore pressures to equilibrate as the sediment is compressed, and the potential for local excess pore pressure is enhanced. The threshold value for R, below which excess pore pressure should arise, can be estimated from a cone penetration study conducted by Campanella et al (1983), in which a cone was forced downward through a silty clay at different but constant velocities, and pore pressure was recorded by a transducer in the cone. All parameters relevant to Equation (12) were either measured or could be estimated reliably.…”

Characterization of deltaic sediment bodies based on in situ CPT/CPTU profiles: A case study on the Llobregat delta plain, Barcelona, Spain

“…In this case, the cone tip records a stress that is less than the applied allaround pressure because of the unequal area at the tip. Because of this effect, often referred as the bunequal area effectQ, it is recommended for q c values to be reported as total resistance q t whenever possible (Campanella et al, 1983). This correction Eq.…”

“…CPT/CPTU tests provide high resolution estimates of grain size vertical variations in a way that the resulting logs can be directly compared with sedimentary successions in terms of coarsening and thickening sequences and cyclicities (Moran et al, 1989). This allows characterizing sedimentological trends and sequence boundaries, both aspects highly relevant to sedimentology and sequence stratigraphy as shown by Campanella et al (1983), Moran et al (1989), Robertson (1990), Robertson et al (1996), Amorosi and Marchi (1999) and Devincenzi et al (2003). In addition, distributed grids of CPT/CPTU profiles allow the 3D reconstruction of the geometry of sediment bodies.…”

Condicionantes geológicos na interpretação de ensaios de piezocone para identificação estratigráfica na investigação geotécnica e geoambiental

“…Outro aspecto que torna impreciso o uso dos resultados de fs é a freqüente ausência de correção de posição devido a simultaneidade de medição no sensor da luva de atrito em relação ao sensor de resistência de ponta do cone. Jaksa et al (1997) estudando o efeito das correções de posição, concordam com Campanella et al (1983), que para a maioria dos tipos de solos uma correção de 100 mm para a posição da luva de atrito é recomendada. Estes mesmos autores concluem que ignorar a correção dos resultados de f s com relação a posição implica em erros significativos na razão de atrito (R f ) e consequentemente na identificação do perfil estratigráfico.…”