Asadul Haque

1-D Compression Behaviour of Acid Sulphate Soils Treated with Alkali-Activated Slag

Improvements of soft soils by mechanically mixing cementitious additives have been widely practised for construction of infrastructure. Mixing of additives improves strength and compressibility properties of soils through the development of soil structure. This study investigates the 1-D compression behaviour of alkali-activated slag treated acid sulphate soils (ASS) cured up to 365 days. The void ratio-logarithm of pressure (e-logσ′) behaviour of treated ASS, including the destructuration behaviour, with additive contents and curing time have been analysed. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses have been undertaken to explain the observed variations of the 1-D compression behaviour. This paper presents the results of these analyses in view of obtaining an insight into the 1-D compression behaviour of treated ASS with the help of mineralogical analysis.

Laboratory modelling of shear behaviour of soft joints under constant normal stiffness conditions

Shear behaviour of regular sawtooth rock joints produced from casting plaster are investigated under constant normal stiffness (CNS) conditions. Test results obtained in this investigation are also compared with the constant normal load (CNL) tests. It is observed that the peak shear stress obtained under CNL conditions always underestimates the peak shear stress corresponding to the CNS condition. Plots of shear stress against normal stress show that a nonlinear (curved) strength envelope is acceptable for soft rock joints subjected to a CNS condition, in comparison with the linear or bilinear envelopes often proposed for a CNL condition. Models proposed by Patton (1966) and Barton (1973) have also been considered for the predictions of peak shear stress of soft joints under CNS conditions. Although Pattons model is appropriate for low asperity angles, it overestimates the shear strength in the low to medium normal stress range at higher asperity angles. In contrast, while Bartons model is realistic for the CNL condition, it seems to be inappropriate for modelling the shear behaviour of soft joints under CNS conditions. The effect of infill material on the shear behaviour of the model joints is also investigated, and it is found that a small thickness of bentonite infill reduces the peak stress significantly. The peak shear stress almost approached that of the shear strength of infill when the infill thickness to asperity height ratio (t/a) reached 1.40. This paper also introduces an original, empirical shear strength envelope to account for the change in normal stress and surface degradation during CNS shearing.

Improvement of Problematic Soils by Lime Slurry Pressure Injection: Case Study

Lime slurry pressure injection (LSPI) is a stabilization operation used in problematic soils by transportation industries with the aim of improving the geotechnical properties and bringing excessive maintenance costs to an acceptable standard. This paper presents detailed field and laboratory studies of a lime/fly ash stabilized site at Breeza, NSW, Australia. The mixing of slurry into the soil with depths was investigated by excavating a trench while the improvement of geotechnical properties was determined in detailed field and laboratory tests. Visual observations of the surfaces of an excavated trench showed slurry to be distributed within the shrinkage cracks in the desiccated upper soil horizon whereas slurry was conveyed through planes of hydraulic fracture in the soils at greater depths. Laboratory swell tests on the stabilized soils demonstrated a statistically significant reduction of the intrinsic swell properties in the upper horizon of highly plastic clayey soils by LSPI. A gain in soil strength was observed in cone penetrometer test soundings conducted in stabilized soils. Scanning electron microscope and x-ray diffraction studies proved the underlying physicochemical and cementitious reaction processes in stabilized soils. Aggregation of the soils was observed with the outward diffusion of calcium cations within proximity of slurry seams and resulted in a subdued shrink/swell propensity.

Experimental study of shear behavior of rock joints under constant normal stiffness conditions

Abstract The shear behavior of synthetic soft rock joints (regular saw-tooth) was investigated in the laboratory under constant normal stiffness condition (CNS). A large-scale shear apparatus was designed and constructed which can test joints under both constant normal load (CNL) and CNS conditions. It is observed that CNL condition overestimates joint dilation compared to CNS condition and thereby, underestimates the peak shear stress of joints. Plot of shear stress against normal stress shows that a bilinear shear strength envelope is suitable for soft rock joints subjected to CNL conditions, while linear or bilinear envelopes are acceptable for CNS testing depending on the asperity angles. The shear behavior of infilled joints was also investigated under CNS conditions, and it was found that a very small thickness of bentonite infill reduced the shear strength significantly. The shear strength of joints almost approached that of pure infill, when the infill thickness to asperity height ratio reached 1.60.

Modelling of intact and jointed mudstone samples under uniaxial and triaxial compression

Rock mass is a highly complex entity where the strength and deformation behaviour can be significantly affected by its secondary structures such as joints, fissures and bedding planes. Whilst many research works have been conducted to study the behaviour of a specific rock mass, a thorough understanding of its strength and deformation behaviour incorporating different joint sets has not been established. In this study, a comprehensive numerical modelling using a three-dimensional distinct element code, 3DEC, was undertaken to study the strength and deformation behaviour of a mudstone, locally found in Melbourne, in unconfined and confined states. The initial unconfined model established for intact mudstone was calibrated against the well-established laboratory-based empirical strength relationships and subsequently compared with some strength test data available for field samples. The intact unconfined model was then extended to study the strength behaviour in the confined state. The results obtained from this confined intact model were compared with existing strength criteria and were found in good agreement. The confined model was extended further to investigate the effects of joint sets and dip angles on the rock mass strength and deformation behaviour by incorporating two different joint configurations (one-joint and two-joint) with varying dip angles (0°–90°). This study found that the rock mass strength in a confined state varied significantly between the two joint configurations.

X-ray Computed Tomography Imaging of the Microstructure of Sand Particles Subjected to High Pressure One-Dimensional Compression

This paper presents the results of X-ray CT imaging of the microstructure of sand particles subjected to high pressure one-dimensional compression leading to particle crushing. A high resolution X-ray CT machine capable of in situ imaging was employed to capture images of the whole volume of a sand sample subjected to compressive stresses up to 79.3 MPa. Images of the whole sample obtained at different load stages were analysed using a commercial image processing software (Avizo) to reveal various microstructural properties, such as pore and particle volume distributions, spatial distribution of void ratios, relative breakage, and anisotropy of particles.

New Pressure-Void Ratio Relationship for Structured Soils in the Virgin Compression Range

AbstractThe pressure–void ratio relationship of many structured soils in the virgin compression range is highly nonlinear. The initial part of the compression curve is characterized by the breakdown of structures, whereas the behavior in the postdestructuration range is influenced by soil mineralogy. A robust pressure–void ratio relationship should include parameters that account for the distinct mechanisms that control the behavior in the destructuration and postdestructuration ranges. A new pressure–void ratio relationship based on a modified secant compression index is proposed. It is shown that the variation of the proposed secant compression index with a logarithm of pressure can be approximated by a hyperbolic form with two parameters. The new relationship has been verified in a wide range of naturally structured soils. Parametric studies conducted show that one parameter controls the compression behavior within the stress range where the destructuration is dominant, and the other parameter controls...

A New Cluster Analysis-Marker-Controlled Watershed Method for Separating Particles of Granular Soils

An accurate determination of particle-level fabric of granular soils from tomography data requires a maximum correct separation of particles. The popular marker-controlled watershed separation method is widely used to separate particles. However, the watershed method alone is not capable of producing the maximum separation of particles when subjected to boundary stresses leading to crushing of particles. In this paper, a new separation method, named as Monash Particle Separation Method (MPSM), has been introduced. The new method automatically determines the optimal contrast coefficient based on cluster evaluation framework to produce the maximum accurate separation outcomes. Finally, the particles which could not be separated by the optimal contrast coefficient were separated by integrating cuboid markers generated from the clustering by Gaussian mixture models into the routine watershed method. The MPSM was validated on a uniformly graded sand volume subjected to one-dimensional compression loading up to 32 MPa. It was demonstrated that the MPSM is capable of producing the best possible separation of particles required for the fabric analysis.

A Study of the Particle-Level Fabric and Morphology of Granular Soils under One-Dimensional Compression Using Insitu X-ray CT Imaging

The particle morphology and fabric of a granular soil influence its mechanical behavior. This study focuses on the evolution of the particle-level fabric and morphology of a uniformly graded sand sample subjected to one-dimensional compression up to 64 MPa. The microstructural changes with increased stresses were captured using in situ high-resolution X-ray computed tomography (X-ray CT) imaging. The processed images of particles were separated using the Monash Particle Separation Method (MPSM) for subsequent fabric and morphological analyses. The variations of various fabric parameters were studied using the separated particle volumes. New methods of assessing the morphology and crushability of particles were introduced including a comprehensive algorithm for determining coordination number, branch and contact normal vectors. Results of all fabric parameters were analyzed and discussed with reference to observed changes. Potential mechanisms were identified and relevant correlations were developed where warranted.