Miniature Pressuremeter and Miniature Cone Penetrometer Testing in Calibration Chamber with Unsaturated Soil Beds By Norman K. Tan

Outline Introduction Objective Research task Why calibration chamber? OU calibration chamber Preparation of soil beds Test results Research question.

Introduction Cone Penetrometer (CPT) & Pressuremeter (PMT) –Popular in situ testing devices –Give estimates of in situ soil properties –Methods developed to interpret results focus around: Saturated soil Dry sand About 1/3 of earth ~ arid/semi arid regions Behavior of unsaturated soil is different from saturated soil Motivation: No methods for interpreting CPT & PMT in unsaturated soil

Objective Develop a method to predict PMT and CPT responses for various matric suction based on one test result

Research Task Calibration chamber testing Numerical and analytical analysis and modeling Laboratory testing

Research task Calibration Chamber Testing ModelingLaboratory Testing ~Soil properties

Why Calibration Chamber? Field Testing –Easy and cheaper –Lack of control over the boundary conditions –Heterogeneous of soil –Unknown stress history, stress state, etc. Calibration Chamber Testing –Controlled environment Boundary condition Stress state Homogeneous soil beds Etc.

OU Calibration Chamber (OUCC) Allows independent control of radial & axial stress (BC1) Designed working pressure ~ 1380 kPa Capable to perform axis translation Pore air & pore water can be controlled independently Burettes system: measure water volume change DAVI: measure diffused air volume

LVDTs ~ measure total volume change Soil beds –diameter: 610 mm –Height: 450 mm to 1350 mm

Preparation of Soil Beds Soil used: –Minco Silt –From Tuttle, OK –CL-ML soil –PI: 8 Soil bed preparation: –Statically compacted –152 mm/layer Soil preparation: –Oven dried –Pass #10 sieve –Mixed with water in large concrete mixer –Store in 5 gallon pails for minimum of 1 day Soil bed consolidation –35 kPa increment –Up to 103 kPa

OU Miniature Pressuremeter (MPMT) Diameter: 15.2 mm Length: 130 mm H/D: 8.5 D soilbed /D probe : 40 Test Depth: –267 mm (center of probe) –495 mm (center of probe)

OU Miniature Cone Penetrometer (MCPT) Diameter: 8.9 mm D soilbed /D probe : 68.5 Penetration rate: 0.5 cm/sec

Typical MPMT Results Limit Pressure ~ defined as pressure at which vol. of the cavity is twice of initial soil cavity volume ~ determined using 1/v vs P plot From test: CCT6 PMT 6-2

Summary of MPMT Results

MPMT Results

MCPT Results w: 6%

MCPT Results w: 8%

MCPT Results w: 10%

MCPT Results CPT 1 A ~ w: 8%

MCPT Results: q c Histogram

MCPT Results:  0 of q c

MCPT Results CCT3B

MCPT Results

Research Questions ??? What is the true value of H, v for Minco Silt? Does c`,  `,  b varies with initial water content, dry unit weight? How significant? Are the interpreted matric suctions the true matric suctions? Explanations for the PMT response: ~ trend in u a -u w vs. P l plot

Thank you !!!