Numerical simulation of settlement behaviour of axially loaded piles used for high-rise building

The reliable prediction settlement of pile foundation at typical working load remains one of the major geotechnical engineering problems. In this research, settlement behaviour of a pile foundation located in sandy-silt, under the loads from high-rised building is simulated in 2D using a finite element program (PLAXIS). Three different types of analysis were investigated: a linear elastic (LE) analysis where the soil was assumed as linear-elastic material, a simple nonlinear analysis where the soil was completely assumed as Mohr- coulomb (MC) model and an advanced nonlinear analysis where the soil was completely assumed as Hardening-Soil (HS) model. A comparison was done between the predicted settlement from Finite element analysis and field settlement values. Based on the results of analysis, it is suggested that although complete MC model shows good agreement with the settlement behaviour obtained from field static load test at lower working loads, MC model is not adequate to capture the settlement prediction at higher working loads. In addition, modelling the soil completely using HS model is required to capture the safe settlement prediction at higher working loads. Finally, this scenario can be applied for the similar problems in settlement prediction using numerical methods

Compressibility behaviour of peat stabilized with low calcium fly ash an experimental study

Peat is a kind of soft organic soil having partially disintegrated plant remains hence it is not good for constructions. Chemical stabilization is the commonly used ground improvement technique by adding chemical admixtures such as ordinary Portland cement, fly ash, natural fillers etc. In Sri Lanka, annually 150 metric ton of fly ash is produced in Nuraicholai coal fired power plant and only about 20 % is usable for cement production, leaving huge amount of fly ash ends up in landfills. Thus, our research focused on stabilizing peat using a combination of fly ash and well graded sand. An experimental study was conducted to analyse the stabilization of peat with 125 kg/m3 dosage of well graded sand and fly ash at three various proportions 10, 20 and 30 % by weight. A series of experiments including Unconfined Compressive Strength (UCS) and Rowe cell test were conducted to evaluate the compressibility behaviour of stabilized peat. UCS increases up to 10 % fly ash addition and increases with curing period for all sample types. There is an improvement in settlement behaviour of peat after the stabilization using fly ash and well graded sand

Effect of low calcium fly ash (ASTM class f) on the stabilization behaviour of expansive soil

Expansive soil experiences swelling with the addition of water and then shrink after the removal of water. These alternate wetting and drying impose lot of problems to the structures built on expansive soils. Ground improvement techniques for expansive soil include chemical and mechanical method of soil stabilization. In this paper, chemical stabilization has been used as a ground improvement technique. Testing such as compaction, unconfined compressive strength (UCS) and swell pressure were conducted for expansive soil stabilized with ASTM Class F fly ash as a chemical stabilizer at 8%, 16% and 24% of total weight. Based on the outcome of this study, it was noticed that maximum dry density (MDD) increases up to 16% and then decreases beyond that. Effect of fly ash on variation of UCS value was observed with three different curing periods (7, 28 and 45 days) as well as three different percentages of fly ash (8%, 16%, 24%). UCS values increase up to 16% and then they decrease with any further addition of fly ash. Further, increment of curing period helps to increase the UCS value for a given percentage of fly ash mixture. Reduction of swell pressure was observed with addition of fly ash. On the whole, fly ash can be successfully used as soil stabilized to improve the geotechnical engineering properties of expansive soil

Geopolymer as well cement and its mechanical behaviour with curing temperature

Carbon capture and storage (CCS) technique is found as a best solution to reduce the emission of CO2 to the atmosphere. In this technique, the CO2 emitted from large industries is captured, and pressurized, and finally injected into deep underground reservoirs. In a geological sequestration project, integrity of injection well play an important role. It means the well cement is a key factor that affects the well integrity. In typical injection wells, Ordinary Portland cement (OPC) based cement is used as well cement and it has been found that it undergoes degradation in CO2 rich environment. Geopolymer can be a good alternative to existing OPC based well cement as it has been found that geopolymer possess high strength and durability compared to OPC. Geopolymer is a binder produced through the process called geopolymerization of alumino- silicate materials and alkaline activators. In the sequestration wells, well cement is exposed to different curing temperatures with a geothermal gradient of 30°C/km. Therefore, it is important to study the mechanical behaviour of well cement with curing temperatures expected deep under the ground. Therefore, this research aims to study geopolymer as well cement and its mechanical behaviour at different curing temperatures (25, 40, 50, 60, 70, 80 °C). In addition, effect of ageing on the mechanical behaviour was also studied. The OPC samples were tested for the comparison of results with geopolymer. The results showed that the optimal curing temperature for higher strength of geopolymer and OPC are 60 °C and 50 °C respectively. Geopolymer possess highest strength at elevated temperatures whereas OPC possess higher strength at ambient temperatures. Moreover, at elevated temperature curing, geopolymer develops ultimate strength within short curing period and it does not gain significant strength with further ageing

Effects of “soil-like” particle size on gas transport and water retention properties in aged municipal solid waste from a Sri Lankan open dumpsite

Open dumps constitute a major source of greenhouse gases (GHGs), predominantly methane and carbon dioxide, in developing countries. In an aged dump, typical waste composition is dominated by the “soil-like” fraction of which physical, hydraulic and gas transport characteristics markedly affect GHG emissions. This study characterized soil-gas diffusivity (Dp/D0), soil-water characteristics (SWC), and particle size distribution in “soil-like” fractions of aged solid waste retrieved at 2.5–5 m depth from an old open dumpsite situated at Kurunegala, Sri Lanka. The “soil-like” fraction was proportioned into three groups based on particle size (0–4.75, 4.75–9.5, and 9.5–25 mm) to investigate the particle size effect on Dp/D0 and SWC. The simulated methane concentration profiles in different size groups were also examined using the transport simulator TOUGH2-EOS7CA based on the multiphase flow of multicomponent gas mixture (methane, water vapour and air) under dry and half-saturation conditions across a predefined temperature gradient. The results highlighted distinct two-region characteristics (i.e., inter-aggregate and intra-aggregate pore regions) in all three size fractions which could be adequately parameterized with existing and modified bimodal functions. We proposed a useful practical tool for estimating Dp/D0 for known mean particle size and volumetric water content in the absence of direct measurements. The results further revealed that Dp/D0 is particle-size dependent; however, Dp/D0 remained invariant across all size fractions at the volumetric water content of ∼0.22–0.25 cm3 cm−3. Numerical results further showed a pronounced effect of particle size and soil moisture on gas transport properties