With regard to the safety, environmental impact and sustainability of carbon capture and storage (CCS) projects, the integrity of injection and production wells plays a major role. In a CCS project, mechanical integrity of well cement should be maintained to sustain the required mechanical strength throughout the life of an oil/gas and CO 2 sequestration well. One of the major issues with existing Portland cement based oil well cement is cement degradation in CO 2 -rich environment. On the other hand, geopolymer cement possesses excellent acid resistant characteristics, shows higher mechanical strength and durability and demonstrates lower permeability. Therefore, this research work focused on studying the mechanical integrity of geopolymers under two different down-hole conditions: (1) effect of CO 2 on mechanical behaviour of geopolymers and (2) hydraulic fracturing of geopolymers to study the mechanical integrity under down-hole stress conditions. To study the mechanical integrity under CO 2 rich environment, geopolymers were tested in CO 2 chamber at a pressure of 3 MPa for up to 6 months and compressive strength and microstructural testings were conducted. It was noted that strength values of geopolymers did not change significantly in CO 2 environment for 6 months. There were only about 2 % variations in compressive strength values in CO 2 compared to the initial strength value. Scanning electron microscopy (SEM) test results revealed that there is no significance variation in the microstructure of geopolymer after 6 months in CO 2 . For hydraulic fracturing experiment, four different tests were conducted with various injection pressure (P in ), axial stress (r 1 ), confining pressure (r 3 ) and tube length (30 and 40 mm). Geopolymers could not be fractured in any of the four tests, in which maximum values of P in of 23 MPa and r 1 of 59 MPa were used. There was no fracture development in geopolymers despite maximum ratios of P in /r 3 of 3.8 and r 1 /r 3 of 13.3 was tested. Tests could not be repeated with higher ratios of P in /r 3 and r 1 /r 3 due to the limitation with the triaxial set-up used. Since there is no fracture development in geopolymers at higher ratios of P in / r 3 and r 1 /r 3 , it is concluded that required mechanical integrity can be observed when geopolymers are used as well cement.

Abstract:Peat has several unfavourable characteristics such as low bearing capacity, high compressibility, high content of natural water and difficulty of access and thus is not suitable for Civil Engineering constructions. One of the widely used techniques for its improvement is its chemical stabilization through the addition of chemical admixtures such as ordinary Portland cement, lime, fly ash, natural fillers etc. This research was focused on stabilizing peat using low Ca fly ash (ASTM Class F) combined with well graded sand. An experimentally based approach was followed to analyse the stabilization of peat samples with different proportions of fly ash (10, 20 and 30 % by weight) and 125 kg/m 3 of well graded sand. With the increase in the fly ash content, the Maximum Dry Density (MDD) increased while the Optimum Moisture Content (OMC) decreased. The Unconfined Compressive Strength (UCS) increased with the addition of fly ash up to 10 % by weight and thereafter it began to reduce as more and more fly ash was added. The UCS increase with curing period for all of the stabilized samples. Rowe cell test results showed that there was an improvement in the compressibility of peat after stabilization. On the whole, it was found that the geotechnical engineering properties of peat can be improved by stabilizing it using fly ash and well graded sand.

Grazed pastures and cultivated fields are significant sources of greenhouse gas (GHG) emissions, in particular N 2 O emissions derived from fertilizer deposition and animal excreta. Net surface emissions rely on subsurface gas transfer controlled mainly by diffusion, expressed as the soil-gas diffusivity (D p /D o). The value of D p /D o is a function of soil air-filled porosity (ε) and gaseous phase tortuosity (Ʈ), both of which vary with soil physical properties including soil texture and structure. Agricultural soils are often structurally aggregated and characterized by two distinct regions (inter-and intra-aggregated pores), however, such soils are subjected to frequent compaction and tillage resulting in alteration to structural arrangement. In this study, a comparative analysis between the Currie (1960) and Taylor (1949) methods was performed to provide a computational insight into selecting an appropriate method for calculating D p /D o in agricultural soils. Currie's (1960) method was chosen for further analysis of the soils in this study. Results show that the D p /D o in aggregated soil cannot be expressed using a simple linear, power law or combined linear and power law functions due to the presence of two-region characteristics. A new "Two-Region model" was developed to parameterize the D p /D o of aggregated soils, and tested against repacked samples from two Sri Lankan agricultural soils. This Two-Region model clearly distinguished tortuosity effects on gas movement with respect to density and textural variations within and between aggregates and outperformed previous models. The fitting parameters (α 1 , α 2 , β 1 and β 2) varied correspondingly with soil density, and the weighting factor (w) clearly distinguished the boundary between the two regions (inter-and intra-aggregates) of structured soils. The model developed will be of interest to those seeking to model the diffusion of GHG emissions and gas exchange between the atmosphere and soils. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

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Abstract:The settlement behaviour of axially loaded piles is one of the prime factors that control the design of single and group piles. Therefore, this research focused on the settlement behaviour of a pile foundation located in sandy-silt under the load of a high-rise building, by simulating it using PLAXIS numerical package and giving consideration to interface effects. Four different types of analysis were investigated: (i) a Linear Elastic (LE) analysis where the soil was assumed as linear-elastic; (ii) a simple Non Linear (NL) analysis where the soil was completely assumed as a Mohr-Coulomb(MC) model; (iii) Non Linear (NL) analysis where the soil was completely assumed as a Hardening -Soil (HS) model; and (iv) a combined (NL-LE and NL-NL) analysis assuming that the soil close to the pile shaft is a nonlinear model and that the soil in the remaining area is made of either linear material or simple nonlinear material (MC). The results of the analysis suggest that the complete MC model shows good agreement with the settlement behaviour obtained from field static load tests at lower working loads. However, the incorporation of a nonlinear HS interface zone of soil is required to predict the settlement at higher working loads. In addition, it was noted that an interface thickness that is twice the pile diameter with the remaining soil modelled as MC would suffice to ascertain the load transfer mechanism of a typical pile.