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Optimization of Sand-Bentonite Mixture for the Stable Engineered Barriers using Desirability Optimization Methodology: A Macro-Micro-Evaluation

  • Environmental Engineering
  • Published:
KSCE Journal of Civil Engineering Aims and scope

Abstract

In this paper, Desirability Optimization Methodology (DOM) is employed to achieve optimum sand bentonite mixture (SBM) based on multiple antagonist macro-geotechnical responses of the compacted SBM prepared using poorly graded sand with the mean grain size around 0.2 mm and bentonite with plasticity index around 157% for the stable engineered barriers (EBs). For this purpose, varying mix designs of SBM compacted at compaction energy of 2,700 kN-m/m3 are initially tested to determine their mechanical properties, volumetric-change behavior, and hydraulic conductivity. The unconfined compressive strength, cohesion, angle of internal fiction, swell pressure, compression index, and hydraulic conductivity are taken as the geotechnical design parameters for the SBM. Mathematical models are developed and statistically validated for these design parameters using sand content (SC) and bentonite content (BC) as the predictors. In addition, models are also developed to predict compression curves for compacted SBMs. Moreover, microstructural evaluation is conducted through scanning electron microscope (SEM) analysis to determine the SBM having a desirable microstructure for stable EB. It is observed that a major shift in the microstructure from medium pores to micro-pores occurs for the BC between 20% and 30%. Afterward, optimization of SBM is carried out by integrating developed models for the geotechnical design parameters in a desirability function (D) algorithm, which is subsequently simulated by setting maximization of strength and minimization of swell pressure, compressibility and hydraulic conductivity of compacted SBM as the goals. A reasonably high D-value is achieved for the SBMs having SC:BC in a range of 74:26 to 78:22 with the highest at 75.63:24.37 against the set goals. This study manifests an effective and pragmatic strategy for designing the SBM for a stable EB considering its antagonist hydraulic, volumetric change, and mechanical responses.

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Abbreviations

ANOVA:

Analysis of variance

BC:

Bentonite content

c :

Cohesion

C c :

Compression index

C v :

Coefficient of consolidation

D :

Desirability

DOM:

Desirability optimization methodology

e :

Void ratio

EB:

Engineered barriers

e 0 :

Initial void ratio

e 100 :

Void ratio at 100 kPa pressure

e 1000 :

Void ratio at 1,000 kPa pressure

e 2000 :

Void ratio at 2,000 kPa pressure

EICL :

Extended intrinsic compression line

HLW:

High-level radioactive waste

ICL :

Intrinsic compression line

I P :

Plasticity index

I v :

Void index proposed by Burland (1990)

I vc :

Void index proposed for compacted clay-bentonite mixture

I vs :

Oid index proposed for compacted sand-bentonite mixture

k :

Hydraulic conductivity

m ben :

Mass of bentonite

m sand :

Mass of sand

m v :

Coefficient of volume compressibility

MSW:

Municipal solid waste

NCCL :

Normalized compacted compression line

q u :

Unconfined compressive strength

SB:

Sand bentonite

SBM:

Sand bentonite mixture

SC:

Sand content

SR:

Subsurface repositories

USCS:

Unified soil classification system

w L :

Liquid limit

w opt :

Optimum moisture content

w p :

Plastic limit

σ v′:

Effective consolidation pressure

σ y :

Yield stress

ϕ :

Angle of internal friction

γ dmax :

Maximum dry unit weight

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Acknowledgments

Laboratory of Geotechnical Engineering, Civil Engineering Department, UET Lahore, is acknowledged for providing technical support during this study.

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Correspondence to Zia ur Rehman.

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Farooq, K., ur Rehman, Z., Shahzadi, M. et al. Optimization of Sand-Bentonite Mixture for the Stable Engineered Barriers using Desirability Optimization Methodology: A Macro-Micro-Evaluation. KSCE J Civ Eng 27, 40–52 (2023). https://doi.org/10.1007/s12205-022-2088-8

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  • DOI: https://doi.org/10.1007/s12205-022-2088-8

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