Shear resistance degradation of lime –cement stabilized soil during cyclic loading
Alex Gezahegn Gebretsadik
Master of Science Thesis 14/01 Division of Soil- and Rock Mechanics Department of Civil, Architectural and the Built Environment
Stockholm 2014
© Alex Gezahegn Gebretsadik Master of Science Thesis 14/01 Division of Soil and Rock Mechanics Royal Institute of Technology ISSN 1652-599X
i
ABSTRACT: This thesis presents the results of a series of undrained cyclic triaxial tests carried out on four lime-cement stabilized specimens and clay specimen. The shear resistance degradation rate of lime-cement column subjected to cyclic loading simulated from heavy truck was investigated based on stress-controlled test. The influence of lime and cement on the degradation rate was investigated by comparing the behavior of stabilized kaolin and unstabilized kaolin with similar initial condition. The results indicate an increase in degree of degradation as the number of loading cycles and cyclic strain increase. It is observed that the degradation index has approximately a parabolic relationship with the number of cycles. Generally adding lime and cement to the clay will increase the degradation index which means lower degree of degradation. The degradation parameter, t has a hyperbolic relationship with shear strain, but it loses its hyperbolic shape as the soil getting stronger. On the other hand, for unstabilized clay an approximate linear relationship between degradation index and number of cycles was observed and the degradation parameter has a hyperbolic shape with the increase number of cycles. It was also observed that the stronger the material was, the lesser pore pressure developed in the lime-cement stabilized clay.
Keywords: undrained cyclic triaxial test ;lime-cement stabilized column; shear resistance; shear strain; degradation index; degradation parameter; pore pressure
ii
SAMMANFATTNING : I detta examensarbete presenteras resultat från en serie odränerade cykliska triaxialtest som utfördes på fyra kalk- och cementstabiliserade prov och ett ostabiliserat lerprov. Nedbrytningen av skjuvmotståndet hos kalkcementpelare vid cyklisk belastning undersöktes med hjälp av spänningskontrollerade triaxialförsök. Inverkan av inblandning med kalk och cement på nedbrytningen av skjuvmotståndet undersöktes genom att jämföra beteendet hos stabiliserad och ostabiliserat kaolin med liknande initiala förhållanden. Resultaten visar på en ökad grad av nedbrytningen allteftersom lastcykler och cyklisk töjning ökar. Det framgår att nedbrytningsindex har ungefär ett paraboliskt förhållade till antalet cykler. Att tillsätta kalk och cement till leran ökar i allmänhet nedbrytningsindex vilket innebär en lägre grad av nedbrytning. Nedbrytningsparametern t har ett hyperbolisk förhållande med skjuvtöjningen, men den förlorar sin hyperboliska form när jorden blir starkare. Å andra sidan observerades för ostabiliserad lera ett ungefärligt linjärt samband mellan nedbrytningsindex och antalet belastningscykler och nedbrytningsparametern har en hyperbolisk form med ökande antalet cykler. Det framgår också att ju starkare material, desto mindre utvecklades porvattentrycket i kalk- och cementstabiliserad lera.
Nyckelord: odränerade cykliska triaxialtest, kalkcementpelare, skjuvmotstånd, spänningskontrollerade triaxialförsök, skjuvtöjning, nedbrytningsindex, nedbrytningsparameter, porvattentryck
iii
Acknowledgement
I would like to express the deepest appreciation to Almir Draganovic for tremendous support and help throughout the process of this master thesis. Without his guidance and persistent help this dissertation would not have been possible. I would like to express my gratitude to my supervisor Stefan Larsson for introducing me to the topic as well for the useful comments and remarks on the process of this master thesis. Furthermore I would also like to thank Stefan Lagerquist from IMCD Group and Håkan Wernersson, plant manager of Nordkalk Corporation for their support in delivering necessary materials for the laboratory test. I would like to thank my friends, family and colleagues who have supported me throughout entire process.
Alex G.Gebretsadik Stockholm, February 2014
iv
In memory of my dad, Rest In Peace
v
TABLE OF CONTENTS
1 INTRODUCTION ...... 1
1.1 Aim and objective ...... 2
1.2 Limitations ...... 3
2 LITERATURE REVIEW ...... 4
2.1 General ...... 4
2.2 Post-cyclic response of soils ...... 4
2.3 Factors affecting the degradation of soils ...... 8
2.4 Soil stabilization ...... 10
2.4.1 Mass Stabilization ...... 10
2.4.2 Deep soil mixing (DSM) ...... 10
2.5 Stabilization effect on degradation of soils ...... 11
2.6 Cyclic triaxial shear test ...... 14
2.7 Summary ...... 14
3 METHOD AND MATERIALS...... 16
3.1 Degradation model ...... 16
3.2 Column stress, σcol and confining pressure, σ3 ...... 17
3.3 Experimental Procedure ...... 19
3.4 Unconfined Compression (UC) test ...... 22
3.5 Cyclic triaxial tests - test set-up and test procedure ...... 23
4 TEST RESULTS AND ANALYSIS ...... 28
4.1 Uniaxial compression test result ...... 28
4.2 Cyclic Triaxial test results and discussion ...... 29
vi
5 CONCLUSIONS AND COMMENTS ...... 36
6 REFERENCES ...... 37
vii
List of figures
Figure 1: A plot of degradation index versus number if cycles in log-log scale (Basack and Purkayastha, 2009) ...... 6 Figure 2: Variation of degradation parameter with cyclic shear strain amplitude for different marine clays (Basack and Purkayastha, 2009) ...... 6 Figure 3: The effect of frequency, f on cyclic degradation ( Mortezaie, A. and Vucetic, M. ,2013) ...... 9 Figure 4: Shear strength of different soils mixed with two quantities of lime and cement at three curing times (Hartlen and Holm, 1995) ...... 11
Figure 5: Variation of degradation index with N/N f, (a) uncemented sample, (b) 1.5 % cemented sample and (c) 3 % cemented sample (Haeri et al., 2002) ...... 13 Figure 6: Layout of lime-cement column under the embankment ...... 18 Figure 7: Position of point A of in lime-cement column under moving vehicle load ...... 18 Figure 8: Stress distribution at point A due to a track passing the road ...... 19 Figure 9: GDS triaxial testing system ...... 20 Figure 10: The four components used to prepare the specimens; (a) cement (b) lime (c) clay (d) water ...... 21 Figure 11: Unconfined uniaxial compression test ...... 22 Figure 12: Sample is covered with a rubber membrane and sealed before putting the chamber. 24 Figure 13: Typical example of test plan during testing a sample ...... 26 Figure 14 : Stress-strain during uniaxial compression test...... 28 Figure 15: Variation of axial strain with number of cycles (a) for samples cured for 7 days and (b) for samples cured for 28 days ...... 31 Figure 16: Variation of shear strain with number of cycles; (a) for samples cured for 7 days and (b) for samples cured for 28 days ...... 31 Figure 17: Degradation index plotted against number of cycles in log-log scale; (a) for samples cured for 7 days and (b) for samples cured for 28 days ...... 32 viii
Figure 18: Degradation parameter plotted against cyclic shear strain; (a) for samples cured for 7 days and (b) for samples cured for 28 days ...... 32 Figure 19: Pore pressure variation with number of cycles; (a) for samples cured for 7 days and (b) for samples cured for 28 days ...... 33 Figure 20: Plot results for a clay soil sample for 28 days curing time ...... 34 Figure 21: (a) Degradation index plotted against number of cycles and (b) degradation parameter plotted against cyclic shear strain for unstabilized clay sample for 28 days ...... 35
ix
List of tables
Table
1. Stabilizer combination scheme for stabilized soils ...... 20 2. General input data summary for each specimen ...... 24 3. Test conditions ...... 25
x
List of symbols and abbreviations
δ Degradation index
G Shear modulus
Gmax maximum shear modulus