AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION

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. e. C.

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT Presentation outline 1 2 3 4 5 6 7

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 1 2 3 4 5 6 7

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 1 Introduction Compaction = üImproving soil strength by increasing the unit weight üIncreasing the bearing capacity of foundations üDecreasing the undesirable settlement of structures üControl undesirable volume changes üReduction in hydraulic conductivity üIncreasing the stability of slopes

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

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 1 2 3 4 5 6 7

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 2 The method EVALUATION OF THE DEGREE OF COMPACTION OF RIVER EMBANKMENTS CPT TESTS IN LABORATORY in a mini CC with a mini CPT using samples at given densities After completion ( In situ stress state when relevant TIP RESISTANCE TARGET PROFILE ) CPT tests in situ qc LAB Vs QUALITY CONTROL ü Existing embankments: evaluation of the degree of compaction ü Embankments under construction: it is possible (a‒priori) to establish which is the expected qc corresponding to a prescribed density

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 1 2 3 4 5 6 7

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 3 Hypotheses The tip resistance is not affected by the tip diameter qc from CPT (d= 35. 7 mm) qc. LAB from mini-CPT (d= 8 mm) Even if: Normalized velocity (Finnie & Randolph, 1994) Where: v: velocity of the penetrometer d: diameter of the penetrometer cv: coefficient of consolidation of the soil UNSATURATED SILT MIXTURES

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 3 Hypotheses FOR DRY SAND → (Baldi et al. 1986, Jamiolkowski et al. 1988, Garizio 1997, Jamiolkowski et al. 2000, 2001) IN SITU STRESS STATE → Estimate of the vertical effective stress component v At-rest earth pressure coefficient → DMT test (Jamiolkowski et al. 1988)

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 3 Hypotheses The effects of the mini–chamber sizes can be considered negligible if: CC diameter Mini-CPT diameter DMT blade location CPT at 30 d distance It is acceptable: CPT at 15 d distance = 40 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 Mini-CPT diameter Diameter of the biggest particle 4

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

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

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 1 2 3 4 5 6 7

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 4 The equipment 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 THE EQUIPMENT Diameter = 320 mm; Height = 210 mm Top boundary → rigid Lateral and bottom boundaries → flexible → provided with latex membranes

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT THE EQUIPMENT The membranes allow the independent application of horizontal and vertical stresses through a compressed air system. Manual air pressure regulators for the vertical and horizontal stresses. All the possible chamber boundary conditions can be applied: - BC 1 = h = cost; v = cost - BC 2 = h = 0; v = 0 - BC 3 = h = 0; v = cost - BC 4 = h = cost; v = 0.

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

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

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

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 1 2 3 4 5 6 7

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 5 Laboratory tests y l l ia ed t r pa urat t a s y r d CRUSHED SAND (Calibration material) d 50 = 0, 5 mm Cu = 2 min = 1, 419 kg/dm 3 ; max = 1, 663 kg/dm 3 Dry sand samples are reconstituted inside the CC to a given DR by pluvial deposit. FINE GRAINED SOILS (Building materials) Only the particle size fraction which pass the 2 mm sieve DD PC A 4; FR A 6; A 4; dmax = 18. 2 k. N/m 3; wopt=13. 2% dmax = 19. 5 kg/m 3; wopt=10. 8% dmax = 20. 5 k. N/m 3; wopt=9. 43%

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

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT 1 2 3 4 5 6 7

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT y dr d n sa TIP RESISTANCE STRESS DEPENDENCE

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT y dr d n sa TIP RESISTANCE STRESS DEPENDENCE

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT TIP RESISTANCE STRESS DEPENDENCE AT A GIVEN DR VALUE h IS THE MOST INFLUENTIAL PARAMETER ON qc. LAB

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

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

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

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

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

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPTu LFWD Correlation between Ed and qc Average qc measured within the influence depth for the LFWD (approximately 1. 5 times the diameter of the loading plate = 45 cm)

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

AN INNOVATIVE METHOD TO EVALUATE DEGREE OF COMPACTION OF RIVER EMBANKMENTS USING CPT Conclusions qc = f (σ’h) qc = f ( ) COMPACTION ENERGY w For a given soil and water content: ü a correlation exists between qc and soil density that can be used to define a target tip resistance profile ü it is possible to predict the dry density from the measured qc irrespective of the boundary stresses

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