Rheology of Foam-conditioned Sands: Transferring Results from Laboratory to Real-World Tunneling

Transcription

1 9 th International Symposium on Geotechnical Aspects of Underground Construction in Soft Ground IS Sao Paulo 2017 Rheology of Foam-conditioned Sands: Transferring Results from Laboratory to Real-World Tunneling Sascha Freimann, Mario Galli, Markus Thewes 4. April 2017

2 Motivation Investigation of the flow behavior of conditioned soil with different testing methods MICRO-SCALE Real scale MACRO-SCALE Measuring system plate-plate / cone-plate cylinder, vanes (material cells) ball slump (flow) tests large-scale tests machine data Sample volume ca. 1 ml ca ml ca. 0,25-20 l ca. 20 l ca. 500 l > 500 l Preciseness Anton Paar MCR 301 HOMOGENEOUS EXPERIMENTS Anton Paar MCR 301, Anton Paar Rheolab QC, Schleibinger Viskomat NT Anton Paar Rheolab QC COSMA HETEROGENEOUS EXPERIMENTS INDEX TESTS, BACK ANALYSIS EPB shield 1 ml Sample size > 500 l 2

3 Index 1. Soil conditioning and rheological behavior of soil foam mixtures 2. Materials 3. Examination Methods Slump test 4. Examination Methods Ball Measuring System (BMS) 5. Comparison to index tests 6. Outlook 3

4 Soil conditioning and rheological behavior of soil foam mixtures Requirements for the excavated soil for effective face support EPB shields use excavated ground for face support Properties of supporting medium are decisive for effective advance and face support Suitable flow behavior essential but also sufficient stiffness for transport Even pressure transfer resulting of homogeneous earth muck in the excavation chamber Reducing water permeability Increasing of the compressibility for reduction of pressure fluctuation at the tunnel face Reducing inner fraction Soil conditioning affects the properties of the excavated soil, especially the flow behavior 4

5 Soil conditioning and rheological behavior of soil foam mixtures Extended application range for EPB shields: (Budach & Thewes 2015) 5

6 Materials Test series on different soil-foam-mixtures: sample composition Investigated soils: fine sand (fs) fine sandy middle sand (msfs) middle sand (ms) Sand (S) fine sandy coarse sand (gsms) coarse sand (gs) Foam parameters: Concentration c f = 3% Volume flow: 60 l/min Variation: Water content Foam Expansion Ratio (FER) Foam injection ratio (FIR) 6

7 Examination Methods Slump Test Valuable tool to evaluate flow behavior (index test) Modified setup with guiderails All soil-foam mixtures could be foam-conditioned to suitable flow behavior (10-20 cm range) Slump S [cm] Slump tests of soil-foam mixtures Fine sand and Sand, w=var., FIR=var FIR [vol%] FS w2 S w2 FS w4 S w4 FS w6 S w6 FS w8 S w8 FS w10 S w10 FS w12 S w12 (Galli 2016) (Galli 2016) 7

8 Examination Methods Slump Test Influence of the different parameters on the workability of soil-foam-mixtures Variation of FIR: Variation of water content: Variation of FER: Freimann: Rheology of Foam-conditioned Sands IS - Sao Paulo

9 Examination Methods Ball Measuring System (BMS) Eccentrically rotating sphere through sample Flow principle: flow around sphere Calibration with different fluids to find suitable flow curve model: Silicon oil (Newtonian) Shaving foam (Non-Newtonian fluid without yield-stress) Bentonite slurry (Non-Newtonian fluid with yield-stress) Sample volume: 500 cm³ M, N L Sphere BMS 10, 12 and 15 (different diameter) Six rotations in the sample Analysis of averaged data from rounds 2-6, because of the influence of the ball immersion in round 1 η, ρ d Sphere 9

10 Examination Methods Ball Measuring System (BMS) Typical set of "flow curves" (Fine sand, w=10%, FIR=var.) Shear stress [Pa] 1,0E+03 1,0E+02 Rheolab QC BMS12 - Flow curve tests on soil-foam mixtures Soil 1, w=10%, FIR=var.; Fit : Bingham, Round 2-6 FIR50 FIR60 FIR70 FIR80 FIR90 FIR100 fit FIR50 fit FIR60 1,0E+01 fit FIR70 fit FIR80 fit FIR90 fit FIR100 1,0E-02 1,0E-01 1,0E+00 1,0E+01 1,0E+02 Shear rate [1/s] Shear stresses almost independent of shear rate Significant shear stresses, low viscosity values Influences from FIR clearly determinable (same for w) Data fit with Bingham model (Galli 2016) 10

11 Comparison to index test Mixtures with same slump possess similar yield stresses Goes along with findings from slump models Suitable yield stress range: 130 Pa (Slump20) Pa (Slump10) BMS yield stress [Pa] BMS yield stresses corresponding to soil 1 mixtures with FIR 10 and FIR 20 FS FIR 10 : 250 Pa FIR 20 : 130 Pa BMS08 BMS12 BMS15 FS FS FS FS 8 90 FS 6 70 FS FS 4 80 FS FS 2 90 (Galli 2016) 11

12 Comparison to index test Variation of yield stresses for desired slump of 10 and 20 cm for BMS 12 Fine Sand and Sand were investigated more extensively Further investigations with other soils have to be performed to generate an encompassing range for foam conditioned sands Yield stress range can be used to calibrate larger test device (COSMA) Soil Yield stress Slump10 Yield stress Slump20 Fine sand 250 Pa 130 Pa Fine sandy middle sand 310 Pa 190 Pa Middle sand 270 Pa 190 Pa Sand 250 Pa 130 Pa Middle sandy coarse sand Pa Coarse sand Pa 12

13 Outlook BMS scaling to EPB shield Investigations should concentrate on the extension of the scaling of the rheological tests to larger applications Development of a BMS for large test set up COSMA Extension of investigated soils including required conditioning agents Investigation under realistic pressurized conditions Install a BMS in the excavation chamber of an EPB z M, N η(z,p), ρ(z,p) p(z) shield Information on the efficiency of the soil conditioning (flow behavior) in the excavation chamber Develop an evaluation system for the conditioning behavior in the excavation chamber M, N (Galli 2016) 13

14 Thank You for your attention