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AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT BARBARA COSANTI N. SQUEGLIA D.C.F. LO PRESTI University of Pisa – D.E.S.T.eC.

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AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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Improving soil strength by increasing the unit weight Increasing the bearing capacity of foundations Decreasing the undesirable settlement of structures Control undesirable volume changes Reduction in hydraulic conductivity Increasing the stability of slopes AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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CAUSES of FAILURE CAUSES of FAILURE DESIGN ASSESSMENT of the SAFETY DEGREE ASSESSMENT of the SAFETY DEGREE Saturated for only a short period of time POOR ATTENTION Different erosion mechanisms and slope instability POOR DEGREE OF COMPACTION = PREDISPOSING FACTOR Definition of design values for strength and permeability characteristics DEPENDENCY ON THE DEGREE OF COMPACTION AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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EVALUATION OF THE DEGREE OF COMPACTION OF RIVER EMBANKMENTS CPT tests in situ CPT TESTS IN LABORATORY in a mini CC with a mini CPT using samples at given densities TIP RESISTANCE TARGET PROFILE q c LAB Vs QUALITY CONTROL After completion In situ stress state when relevant Existing embankments: evaluation of the degree of compaction Embankments under construction: it is possible (a ‒ priori) to establish which is the expected q c corresponding to a prescribed density AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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q c from CPT (d= 35.7 mm) q cLAB from mini-CPT (d= 8 mm) The tip resistance is not affected by the tip diameter Normalized velocity (Finnie & Randolph, 1994) Where: v: velocity of the penetrometer d: diameter of the penetrometer c v : coefficient of consolidation of the soil Even if: UNSATURATED SILT MIXTURES AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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FOR DRY SAND → IN SITU STRESS STATE → (Jamiolkowski et al. 1988) (Baldi et al. 1986, Jamiolkowski et al. 1988, Garizio 1997, Jamiolkowski et al. 2000, 2001) Estimate of the vertical effective stress component v At-rest earth pressure coefficient → DMT test AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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CC diameter Mini-CPT diameter = 40 Diameter of the biggest particle Mini-CPT diameter 4 The effects of the mini–chamber sizes can be considered negligible if: DMT blade location CPT at 30d distance CPT at 15d distance When the horizontal distance between DMT and CPT is 20 times the cone diameter the DMT is no more sensitive to the passage of the cone It is acceptable: AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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The method has been successfully used in some case histories AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT q cLAB,80% q cLAB,90% CPT n°1 CPT n°2 CPT n°3 (Modified Proctor)

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AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT q cLAB,80% q cLAB,90% CPT n°1 CPT n°2 CPT n°3 CPT n°4 partially disturbed samples

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AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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Developed by the Geotechnical Laboratory of the University of Pisa in partnership with Pagani Geotechnical Equipment AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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Diameter = 320 mm; Height = 210 mm Top boundary → rigid Lateral and bottom boundaries → flexible → provided with latex membranes THE EQUIPMENT AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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THE EQUIPMENT All the possible chamber boundary conditions can be applied: - BC1 = h = cost; v = cost - BC2 = h = 0; v = 0 - BC3 = h = 0; v = cost - BC4 = h = cost; v = 0. The membranes allow the independent application of horizontal and vertical stresses through a compressed air system. AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT Manual air pressure regulators for the vertical and horizontal stresses.

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THE EQUIPMENT AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT aluminum frame locking system step by step electric motor

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Mini CPT: - 60° conical tip - cone diameter = 8 mm - external sleeve - standard rate of 20 mm/s - load cell external to the cone THE EQUIPMENT AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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d 50 = 0,5 mm C u = 2 min = 1,419 kg/dm 3 ; max = 1,663 kg/dm 3 A6; dmax = 20.5 kN/m 3 ; w opt =9.43% A4; dmax = 18.2 kN/m 3 ; w opt =13.2% A4; dmax = 19.5 kg/m 3 ; w opt =10.8% CRUSHED SAND (Calibration material) FINE GRAINED SOILS (Building materials) Dry sand samples are reconstituted inside the CC to a given D R by pluvial deposit. AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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Fine grained soil samples are reconstituted in 5 layers at a known unit weight using static compaction (hydraulic ram) in a mold The compaction effort, required to consolidate each layer and the sample, is registered: FINE GRAINED SOILS AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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TIP RESISTANCE STRESS DEPENDENCE AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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TIP RESISTANCE STRESS DEPENDENCE AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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TIP RESISTANCE STRESS DEPENDENCE AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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DD; PC; → d = 80 92% dmax (Modified Proctor) w = w opt Suction → evaluated according to Aubertin et al. (2003) FR → d = 80% dmax (Modified Proctor) w= 4; 8; 12% AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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There is a clear relationship between tip resistance ‒ degree of compaction ‒ compaction energy, while, confinement pressures and suction have little effect on the tip resistance

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AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT FR → d = 80% dmax (Modified Proctor) w= 4; 8; 12% (w opt 10%)

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AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT Very high values of q c in the shallower layers of the embankments EVAPO - TRANSPIRATION PHENOMENA (DESSICATION) Variation of tip resistance with water content

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AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT Laboratory tests

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Correlation between E d and q c CPTu LFWD Average q c measured within the influence depth for the LFWD (approximately 1.5 times the diameter of the loading plate = 45cm) AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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As the water content decreases, E d value increases AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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a correlation exists between q c and soil density that can be used to define a target tip resistance profile it is possible to predict the dry density from the measured q c irrespective of the boundary stresses For a given soil and water content: AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT

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