Interpretation of sand state from cone penetration resistance

Abstract

The cone penetration test (CPT) is a widely used test for determining in situ state (or density) of cohesionless soils. The reliability of the estimated in situ state parameter, ł, is constrained, however, because intrinsic soil properties affect the CPT response (often called a 'compressibility' effect). Here, the limiting cavity expansion pressure is used as an analogue for CPT tip resistance, q c , to determine the effect of intrinsic soil properties on the q c versus ł relation. The limiting cavity pressure is computed by a large strain finite element code using a critical state-based soil model. This cavity expansion idealisation is then scaled to reference calibration chamber data with a universal shape function. The approach leads to a practically simple and theoretically sound method in which results from a few triaxial tests allow calculation of a sand-specific CPT q c -ł calibration. The method is tested against published reference studies on nine sands and recovers ł with a precision in void ratio of˜e 60 . 04 at approximately 80% confidence. This accuracy for soils with elasticity measured by bender elements is considerably greater,˜e 60 . 04 being obtained at approximately 95% confidence.

Determining silt state from CPTu

“…The formal mechanics were subsequently provided by Shuttle and Jefferies (1998) and broadly supported by Been et al's (1987b) work while adding some refinement and insight. Subsequently, Ghafghazi and Shuttle (2008) confirmed the universality of scaling the spherical cavity analogue to reference chamber data in sands. This paper builds on these computationally driven developments to consider undrained CPTu soundings, as required for silts, and with further reflection of scaling factors from Shuttle and Cunning (2007).…”

“…The hypothesis is that the effect of soil properties will be fully reflected in k sph and m sph , with the scaling factor C Q in Equation 7 being a consequence of the difference in deformation patterns between an actual CPT and the spherical analogue -and which logically requires that C Q not depend on soil properties. This hypothesis was thoroughly examined, and confirmed, for nine sands by Ghafghazi and Shuttle (2008). Here, that earlier work is updated to reflect the introduction of stress-dependent elasticity within the spherical code and the further enhancements (and simplifications) of NorSand since that time.…”

“…Here, that earlier work is updated to reflect the introduction of stress-dependent elasticity within the spherical code and the further enhancements (and simplifications) of NorSand since that time. A further important difference is that Ghafghazi and Shuttle (2008) used geophysically determined G max , whereas in this paper G = G max /4 is adopted across the cavity expansion simulations, both with drained sands and undrained silts, for consistency with the fitting of undrained silt behaviour presented earlier. Similarly to Equation 10 fitted to the chamber data, the finite-element results can be expressed as…”

Characterization of a gold tailings with hypersaline pore fluid

“…Dissipation tests carried out both above and below the sample depths at CPTu 1 and 2 gave t 50 values ranging from 10 to 15 s, suggesting partially drained penetration conditions (DeJong and Randolph 2012). Therefore, improved Ψ interpretation methods for drained (Shuttle and Jefferies 1998;Ghafghazi and Shuttle 2008) (Youd and Craven 1975;Zhu and Clark 1994) over time -an observation that forms the primary basis for typical recommendations to apply higher K 0 in Ψ interpretation in some hydraulic fills (Jefferies and Been 2015).…”

A novel analytical approach for predicting the noncylindrical pile penetration‐induced soil displacement in undrained soil by combining use of cavity expansion and strain path methods

“…Cavity expansion theory is originated by Bishop, who developed for the interpretation of the metal indentation test in the early stage. Subsequently, CET was first introduced to geotechnical engineering by Gibson and Anderson and applied to the interpretation of the in‐situ tests by using pressuremeters or cone penetrometers . Further applications in geotechnical engineering were attributed to Randolph et al, who used CET to evaluate the pile installation effect.…”