75_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011

75_CEG 4012 Notes Fall 2011 CEG 4012 Notes Fall 2011 -...

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X16 Borehole Pressuremeter Test (PMT) o from France - inflate balloon (with fluid) in ground (ASTM 04719). Figure from McCarthy 1998. Contlol unit 150,----------;-:-:==== Limit pressun.: G" 0.376 £ Boring -""""1 P,obe lubing (gas and water f-i'd---I lines) Basic components ot pressuremotor Menard { G",d~" P bo Measuringor_=j!'> .0 lest cell Guard cell PAF (self-boring) o 01<::----:'-::0 ------::40;;------:6~0:-------,;8'0 6V 1/(%) 50 100 o Measure pressure~volume relationship. Corrections for expansion of hose, membrane stiffness, and height of control unit above probe. D Most tests performed within a borehole - with significant disturbance effects (see s-shaped PV o Probe diameter, iength/diameter ratio, and borehole clearance are important. Gravel and shell may damage membrane. o Original Menard PMT is a stress controlled test- apply pressure, measure volume change. Very complicated plumbing. o More recent PMTs (Texam probe) are strain
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Unformatted text preview: controlled - insert slug of fluid, measure pressure. o Self-boring PMT has cutting head with jets to make its own hole. Overjetting and small roots and gravel create big problems but the data is potentially very good. o Push-in PMTs (Pencel) similar in size to CPT. These eliminate hole disturbance but cause penetration disturbance - lose early part of PV curve. Remedy with unload-reload loop. o Determine shear modulus from straight-line portion of PV curve. Analyze radial expansion of probe (assumed equal in all directions). Correlate E vs. G using theory of elasticity and assumed fl. o Estimate lateral stress based on pressure, Po, the pressure at start of straight-line portion of curve. o Estimate shear strength based on failure at limit pressure, PI, where pv curve flattens out (assuming failure is achieved)....
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