CEMENT STABILIZATION IN CLAYEY SOILS CONSIDERING CLAY TYPES, SAND … · 2018-03-08 · 19thInternational Conference on Soil Mechanics and Geotechnical Engineering, September 17-22,

19th International Conference on Soil Mechanics and Geotechnical Engineering, September 17-22, 2017, COEX Convention Centre, Seoul, TC217 Land Reclamation Session

CEMENT STABILIZATION IN CLAYEY SOILS CONSIDERING CLAY TYPES, SAND IMPURITIES AND CURING TEMPERATURE

Dr Darren SC Chian Assistant Professor, Civil & Environmental Engineering, National University of SingaporeVice President, Geotechnical Society of SingaporeContact: [email protected]


BACKGROUND• A quarter of Singapore is sited on Kallang Formation where soft ground

are present.

Kallang Formation


BACKGROUND• Underground construction has become the most popular alternative to

address land scarcity.• Soft ground often require improvement, commonly using deep soil

mixing (DSM) or jet grouting (JGP) techniques.• Recent land reclamation fill with use of cement treated clays• Huge incentives to optimise cement dosage to reduce wastage and cost

Deep Soil Mixing Jet Grouting

Land reclamation


OBJECTIVES• Performance of cement stabilised clay widely studied in the lab in the

past few decade (Bergado et al., 1996; Nagaraj et al., 1996; Uddin et al., 1997; Horpibulsuk et al., 2003, etc), however most were centered within their own limited database.

• Practical interest to validate and improve existing strength predictive models to cover a wide range of working conditions with different clays and cements.

• Study the effects of sand impurities and curing temperature in cement treated clay.

Singapore Marine ClaySand impurities found in ongoing reclaimed site


MATERIALS STUDIED• Soils used in this study are Singapore Upper Marine Clay (UMC) and

Kaolin Clay. • High plasticity clay (CH) according to the Unified Soil Classification System

(USCS).• Portland Blast Furnace Cement (PBFC) with 80% slag was used as

stabilizing additives. • The admixed sand used was uniformly graded fine sand with a mean

diameter (D50) of 0.25mm.

Properties UMC KaolinLiquid Limit (%) 84.0 60.5Plastic Limit (%) 45 42.5Specific Gravity 2.65 2.60

Properties ValueDensity 3000 kg/m3

Fineness 404 m2/kgInitial Setting Time ~189 minsFinal Setting Time ~225 minsSoundness < 1 mmConsistency 30%

Basic properties of claysPhysical properties of PBFC


EFFECT OF MIXING RATIO

6

Effect of Mixing Proportions on Unconfined Compressive Strength

Singapore Marine Clay + PBFC

• Significant influence of water/cement ratio on unconfined compressive strength. Minor effect of soil/cement ratio on strength.

• Uniform strength development, suggesting prospects of predicting later‐age strength (≥ 28‐day) with early age (< 7‐day) results.


EXISTING STRENGTH MODEL• Horpibulsuk et al. (2003) proposed an exponential function similar to the

Abrams’ Law commonly used for predicting strength of cementitiousmaterials (e.g. concrete):

• Proposed strength model inclusive of curing age and soil/cement effects:

• where a and b are the y‐axis intercept and slope of parameter X versus s/c respectively.

• Parameter Y at the denominator was found to be unaffected by s/c.

/

//

/[Chian et al. 2014 ASCE JGGE]


RESULTS –TYPES OF CLAY


COMPUTED VS ACTUAL

(Chian et al., 2015) (Horpibulsuk et al., 2003)

(Verastegui Flores et al., 2010) (Wu et al., 1998)


RESULTS –CLAY WITH

SAND IMPURITIES


LIQUID LIMIT• Determined using cone penetration test to assess water

holding capacity. • Measure of lower strength limit of shearing resistance.

[BS1377‐2 1990]• Composite effects of soil constituents and their interactions

with pore fluid are reflected in their liquid limit (wL). [Skempton 1953; Seed et al. 1964; Pandian and Nagaraj1990]

• Reference in the assessment of soil characteristics, having taken into account the presence of coarser fraction. [Casagrande 1932]


LIQUID LIMIT


EFFECT OF SAND CONTENT

(Chian et al., 2017) (Chian et al., 2017)

• Effect of sand impurities accounted for by replacing w/cwith (w/wL)/c parameter in the proposed strength model, where wL is the liquid limit of the soil.

• Good estimates of strength persist for clayey mixes with 0%, 20% and 40% sand impurities.

/


RESULTS –CURING TEMPERATURE


EFFECT OF TEMPERATURE

(Bi and Chian, 2017)

• No “cross‐over” unlike concrete, mortar & cement‐granular soil.• Ultimate strength under higher temperature significantly higher.• Higher temperature lowers pH requirement for pozzolanic reaction, thus produce more Ca(OH)2 by cement hydration to react with clay particles and produce strength enhancing materials (C‐S‐H).

Kaolin Clay + OPC 48 degrees

37 degrees

23 degrees


EFFECT OF TEMPERATURE

• Chitambira’s (2004) time‐based shift factor model based on Maturity theory and Arrhenius law :

1 1

• Zhang et al. (2014) introduced temperature‐enhancedstrength factor .


EFFECT OF TEMPERATUREShortcomings:• Both models underestimate short‐term strength. Calculated

at reference temperature is always 1 kPa at t =1 day for all cement soil mixture at all mixing ratios.

• Both models apply maturity method based on strength, (implies that cement treated soil with the same maturity index has the same degree of hydration and hence the same strength. However, different temperature develops different ultimate strength for cement treated clay).

• Applying the same shift factor to all curing ages and apparent activation energy is not accurate enough. Sensitivity to the temperature is different (Kada‐Benameur et al., 2000).


EFFECT OF TEMPERATUREProposed Temperature Model:• Apply maturity method based on relative strength /

(Tank & Carino, 1991). • Cumulative distribution function (CDF) of log‐normal

distribution. Shows a clear three‐phases development

12

12 erf

ln2

with an asymptotic value, which well matches the three‐phase strength development of cement treated clay.


• Proposed strength model shown to produce good estimates of strength development over a considerable range of water/cement ratio w/c, soil/cement ratio s/c, and curing time t, for different clays and cement types.

• Effect of sand impurities can be easily incorporated by replacing w/cwith (w/wL)/c parameter in the proposed strength model.

• Effect of curing temperature can be well presented with the proposed cumulative distribution function.

• With better understanding of the strength development of cement‐stabilized soils accompanied with the improved quality control measures, the dosage of cement could be minimized.

CONCLUSION

Documents

CEMENT STABILIZATION IN CLAYEY SOILS CONSIDERING CLAY TYPES, SAND … · 2018-03-08 · 19thInternational Conference on Soil Mechanics and Geotechnical Engineering, September 17-22,