Influence of drainage state on direct-push permeability profiling methods

Open Access
Author:
Fitzgerald, Michael Robert
Graduate Program:
Energy and Geo-Environmental Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
February 04, 2009
Committee Members:
  • Derek Elsworth, Dissertation Advisor
  • Derek Elsworth, Committee Chair
  • Kamini Singha, Committee Member
  • Zuleima T Karpyn, Committee Member
  • Jamal Rostami, Committee Member
Keywords:
  • soils
  • hydraulic conductivity
  • permeability
  • direct-push
Abstract:
This dissertation is composed of three articles that examine the influence of drainage condition on the measured magnitudes of mechanical and fluid transport properties of soils obtained using direct-push tools. The two tools that were used within this work are the Hydraulic Profiling Tool (HPT) and the Cone Penetration Test (CPT). The influence of drainage state originates from the coupled soil strain rate, which is prescribed by the penetrometer radius and advance rate along with diffusivity, which controls the induced fluid pressure dissipation rate through the soil, was examined for both instruments through a combination of field and laboratory experiments with numerical and analytical models developed to assist in understanding the resulting data trends. Through out, the analyses were conducted to first evaluate the role of drainage state on the magnitudes of induced fluid pressures and strength magnitudes; then advanced to utilize this information to develop methods for recovering depth-continuous magnitudes of permeability from the data. Detailed abstracts for each article are provided below. Depth-continuous permeability profiling using an active source permeameter: A method is developed to recover a depth-continuous hydraulic conductivity (K) profile of an unconsolidated saturated aquifer using an active source penetrometer, the Hydraulic Profiling Tool (HPT). The tool yields estimates of through continuous injection of fluid in the subsurface from a small port on the probe shaft while controlled measurements of net applied fluid pressure (∆P) required to maintain a specified flow rate (Q) (typically 350 mL/min) are recorded. The tool gathers these data of flow rate and measured applied pressure during halted and constant-rate penetration (typically 2cm/sec) of the probe. The analysis is developed in two parts: first to explore the interplay between advective effects controlled by penetration rate, and second to examine flow volume effects controlled by the targeted flow rate. These two effects are analyzed through their respective influence on the measured applied pressure response in space, which shows a linear relationship for the flow rate to applied pressure response when and when the response tends towards an asymptotic limit representing soil failure limits as ∆P/effective stress. The analysis shows that penetration rate does not significantly influence the applied pressure response at the tested penetration rates (U = 0, 2, 4 cm/s ). The targeted applied flow rate does however influence the applied pressure response as flow rates less than ~300 mL/min show a scattering of the data in space, where above 300 mL/min the data begin to form a linear response. A targeted flow rate of is suggested as a suitable flow rate based on this analysis. Measurements of hydraulic conductivity are then obtained for the HPT data through the derivation of an equation based on a recast form of Darcy’s law where considerations of the flow geometry as . profiles obtained for the HPT system are then compared against profiles obtained from an independent method (PSU permeameter) and yield a good correspondence between the two methods. Influence of drainage condition on CPTu ‘On-the-Fly’ metrics with relation to permeability profiling: Magnitudes of end-bearing , sleeve friction and penetration-induced pore pressure are reported for steady penetration of a one-quarter-scale miniature-CPT probe in a kaolinite-sand (75:25) mixture spun at 100-g in a beam centrifuge. Penetration rates in the range 0.004 to 3.00 (fast) mm/s span the spectrum of fully-drained to fully-undrained loading and represent maximum and minimum penetration and frictional resistances, respectively. Cavity expansion solutions are developed to calculate magnitudes of and as drainage state changes based on normalized pore pressure data. These confirm relationships between normalized end bearing (Qt) pore pressure ratio (Bq) and dimensionless hydraulic conductivity (KD ) magnitudes as . New independent relationships linking end bearing and pore pressures and linking sleeve friction (Fr ) and pore pressures are able to constrain independent relationships between dimensionless permeability and the metric pairs QtFr and Bq/Fr . These observations provide additional evidence and correlations in support of the direct recovery of depth-continuous hydraulic conductivity magnitudes from steady profiling by CPT. Analysis for a variable rate penetrometer – Scanning drainage states to better recover soil behavior in the partial drainage transition: An analysis is presented to examine the pore pressure relationships that develop as a function of variable rate penetration of a standard CPT probe advanced in a homogeneous elastic-perfectly plastic and fully saturated soil. Dimensionless penetration rate is conditioned as oscillating between and on selected oscillation frequencies ranging from . Pore pressure trends are calculated for couplings of dimensionless parameters, and , using a finite-element analysis model following a Lagrangian framework. A parametric analysis conducted shows that for low magnitudes, representing drained conditions, the peak pore pressure response is very low in magnitude compared with high magnitudes, which represent undrained conditions. Oscillation frequencies ( ) are shown to control stroke length of the penetrometer advance per cycle, independent of selected values of or , with low magnitudes ( ) yielding longer penetration strokes then high magnitudes ( ). Steady state pore pressures, on the oscillating cycle, are found to develop after a length of the penetrometer radius, and for a standard CPT rods equates to steady state occurring after approximately 1/3 of each rod leaving 2/3’s per rod for data collection at steady state conditions. Soil strength moduli are shown to influence the area of influence surround the advancing cone tip with low magnitudes ( ), presented as high undrained strengths, having the smallest zone of influence, and largest peak magnitudes of pore pressure, compared with high magnitudes ( ) that result in the lowest peak magnitudes of pore pressure and yield the largest zone of influence. This analysis was advance to examine the ability to recover (coefficient of) permeability magnitudes from the oscillating pore pressure data and yielded a unique solution for permeability as a function of dimensional net pore pressure , penetration rate ( ), and dimensionless pressure ( ) obtained from the finite-element analysis.