Influence of Microbial Activities in Reducing Erodibility of Sand
S. Datta and D. Roy
ABSTRACT: Microbe-induced reduction of soil erodibility, since natural, is expected not to disrupt the natural environmental system. Although the role of bacteriogenic EPS in aggregating soil particles is widely recognized but the impact of various environmental parameters e.g., groundwater velocity and nutrient availability on bacteriogenic EPS in reducing the erodibility of soil is not very clear. In this study, a species of EPS producing soil bacteria Bacillus megaterium RB-05 isolated from a naturally cemented intertidal silt site was used to investigate the influence of flow velocity and nutrient availability on microbially mediated reduction of erodibility of sand. Durations of nutrient availability and media circulation velocity were observed to influence the bacterial population, amounts and composition of EPS found within sand specimens. Drained shear strength of loose sand samplers was found to increase due to EPS-related interparticle aggregation. EPS produced under fluvial activities seems to be more capable in aggregating sand grains as well as reducing erodibility of sand. Results of model sand erosion test further strengthen this conclusion.
KEYWORDS: Extracellular polymeric substance (EPS), Bacillus megaterium RB-05, Erodibility, Flow velocity, Nutrient availability.
Effective Treatment Technique for Producing a Highly Pozzolanic Clay in a Construction Work
A. Poowancum, P. Kotkhangphlu, and J. Ayawanna
ABSTRACT: A high reactivity pozzolanic clay was developed in this work as a partially replacing cement material for eco-friendly construction. Kaolinite clay was treated at a transformation temperature range of meta-kaolin formation for 6 h in a simple electric furnace. The heated kaolinite clay was separately cool down with 2-different techniques, a normal cool down using a free-cooling rate and a quenching cool down, to make an active phase in a pozzolanic activity. The pozzolanic activity of the treated kaolinite clay was evaluated via the Frattini test, and the compressive strength of the treated clay-cement mixed samples was reported. In comparison to the normal cool down technique, the quenching cool down technique in the heat treatment process generated a higher reactivity clay with a higher degree of reactive metakaolin phase. The Frattini test revealed a decrease in Ca2+ and OH- ions in the Ca(OH)2 solution, which confirmed the pozzolanic reaction between the Ca(OH)2 and the high reactive kaolinite clay from the quenching technique. The replacement of cement with a highly reactive pozzolanic kaolinite clay effectively enhanced the compressive strength above the standard requirements within 2-days curing. Also, the compressive strength of the treated clay-cement mixed samples after 2-days curing was comparable to the strength after 7- days curing of the cement samples. This study thus revealed a new effective technique to produce a high potential clay as a cement replacement material in the construction works.
KEYWORDS: Pozzolanic materials, Kaolinite clay; Cooling treatment technique, Compressive strength, Construction.
Estimating Hydraulic Conductivity Assisted with Numerical Analysis for Unsaturated Soil – A Case Study
Md Rajibul Karim, David Hughes, and Md Mizanur Rahman
ABSTRACT: Meteorologically induced pore water pressure changes and associated changes in effective stress often affect the behaviour of geotechnical structures such as slopes. Seasonal fluctuations in pore water pressure can lead to stiffness degradation which is also known to have caused a number of failures across the world. These effects are likely to become more severe in the future as dryer summers and wetter winters are expected to become more frequent climate scenario in many parts of the world. To analyse the behaviour of a slope subjected to atmospheric boundary interactions, a number of parameter may be used including the soil water characteristics curve, saturated and/or unsaturated hydraulic conductivity of soil, and strength parameters. Some of them (e.g., hydraulic conductivity) are very difficult to deduce with high degree of certainty because of natural variability of soils and limitations in testing procedure. This paper outlines how numerical techniques combined with conventional field or laboratory investigation can serve as a useful technique to overcome some of these limitations specially in deducing hydraulic conductivity. The effectiveness of these techniques will be tested using a well-documented case study form the United Kingdom.
KEYWORDS: Pore water pressure, Atmospheric boundary, Climate change, Effective stress, Shear strength, Slopes, Soil water characteristics curve.
Development of a Stress-Strain Path Controlled Triaxial Apparatus to Understand the Behaviour of Silty Sand
A. T. M. Z. Rabbi, M. M. Rahman, K. Mills, and D. A. Cameron
ABSTRACT: Triaxial tests are widely used to determine the shear strength, material properties and instability behaviour of soil. The conventional isotropically consolidated drained and undrained triaxial compression tests under constant confining stresses, fail to simulate many field stress conditions such as K0-consolidation for zero radial strain or the reduction of lateral confinement at constant shear stress and associated instability behaviour of slopes. Such strain or stress path controlled tests need special arrangements and control systems. In this paper, a newly developed triaxial apparatus, capable of stress-strain path controlled test, is described. The main feature of this apparatus is the precise measurement and control system, which permits individual control of the cell pressure, pore water pressure, vertical stress and axial strain. The apparatus was used to study the stress-strain behaviour of a South Australian silty sand under different stress-path testing such as isotropic and K0-consolidated undrained and drained shear, constant shear drained (CSD) and constant mean stress (CMS) tests. Critical state conditions were achieved with uniform soil deformation at large axial strains, except in the case of the constant shear drained (CSD) tests where a gradual reduction of lateral confinement accelerated sample failure.
KEYWORDS: Stress-path, Triaxial apparatus, Critical state, Constant shear drained, Constant mean stress.
Laboratory Investigations on the Shear Behaviour of Sand-Tyre Derived Aggregate Mixtures
J.S. Vinod, M. Neaz Sheikh, Soledad Mashiri, and Dean Mastello
ABSTRACT: A significant amount of research has been carried out in recent years to investigate possible options on the reuse of scrap tyres in civil engineering applications. One of the sustainable options is to utilise scrap tyre as tyre shreds/tyre chips (generally called as Tyre Derived Aggregate, TDA) and sand mixture as a lightweight fill material in the construction of infrastructure. Utilising TDA in infrastructure projects has multiple benefits including environmentally sustainable recycling and reuse of the scrap tyre thereby easing the consumption of natural fills, reduced material costs and enhanced geotechnical properties of the soil. Understanding the shear and volume change behaviours of TDA and sand mixture is critical before recommending the mixture as a suitable lightweight-reinforcing structural fill. In this study, the effect of the addition of TDA on the shear behaviour of sand was investigated using large scale direct shear and triaxial apparatus. It has been observed that TDA has significant influence on the shear and volume change behaviours of sand. Also, overall improvements in the soil characteristics, such as enhanced shear strength, can be achieved by the addition of TDA in sand.
KEYWORDS: Tyre derived aggregates, Sand, Triaxial testing, Direct shear testing
Stress-Strain and Deformation Characteristics of an Unsaturated Soil-Cement Interface under Different Overburden Stresses and Grouting Pressures
M. A. Hossain and J. H. Yin
ABSTRACT: The most important parameters, by which the shear strength of any interface may be affected, are overburden stress and degree of saturation. Nowadays, grouting pressure is considered as another important parameter, which affects the interface behavior. In addition to gravity grouting, pressure grouting has been widely used to grout insitu soil-cement grout interfaces, like interfaces of soil-nail, soil-pile, and soil-anchor. In the present study, a series of interface direct shear tests were performed between a compacted completely decomposed granite (CDG) soil and cement grout under different overburden stresses, matric suctions, and grouting pressures. The stress-strain and deformation characteristics of the pressure grouted interface are similar to that of the CDG soil. However, the dilation values of soil-cement interface under different grouting pressures are smaller compared to CDG soil. The interface shear strength envelopes are approximately linear, and the apparent interface friction angle and adhesion intercept increase with matric suction for particular grouting pressures. On the contrary, the apparent interface friction angle decreases with pressure grouting for different matric suctions except saturated condition at which it remains constant.
KEYWORDS: CDG soil, Direct shear, Matric suction, Grouting pressure, Overburden stress, Cement grout, Interface.
Influence of the Sample Preparation on the Mechanical Characteristics of Hostun Sand
Q. Gu, D. König, and M. Goudarzy
ABSTRACT: The paper assesses the effect of sample preparation on the small and large strain characteristics of Hostun sand that has been widely used for many years in model tests and researches. For approaching to this goal, experimental efforts were conducted on fully saturated samples prepared using the dry air pluviation (AP) and moist tamping (with various initial water contents) (MT) methods. The experiments were conducted using bender elements for small strain level (e.g. the maximum shear modulus Gmax) and triaxial device for large strain level. The results show that the initial fabric of specimens can be affected by sample preparation. For an example, loose specimens prepared by the AP method show larger maximum shear modulus in comparison with those prepared by the MT method. On the other hand, dense specimens compacted using the AP method show less maximum shear modulus in comparison with those compacted using the MT method. However, the experiments showed the negligible effect of sample preparation on the large strain characteristics of the adopted sand under drained condition. The experiments revealed that the dry deposition method provides samples with the more isotropic fabric in comparison with those prepared by the moist tamping. This effect can be obviously seen in dense samples.
KEYWORDS: Stiffness, Critical state line, Hostun sand, Triaxial device, Bender elements, Wave velocity.
Piled Raft on Sandy Soil – An Observational Study
V. Balakumar, Min. J. Huang, Erwin Oh, Nilan S. Jayasiri, Richard Hwang, and A. S. Balasubramaniam
ABSTRACT: The increasing recognition of the combined piled raft foundation system is mainly due to the economics and the savings that can be achieved in the foundation design without compromising the safety and serviceability requirements. While detailed investigations through field monitoring of the piled raft supporting several tall and heavily loaded structures have been reported (Hooper, 1974; Cooke et al., 1981; Poulos, 2008; Yamashita, 2012), it appears, not so many case histories exist on the applicability of piled raft in the case of moderately loaded structures. The present study is related to the monitoring of the piled raft supporting a 12 storied apartment building and the results have been subjected to validation through numerical analyses. The results have been compared with the published results for a similar structure. As a practical problem, the study also discusses the effect of a compressible layer sandwiched between two competent layers obtained from an analytical study.
KEYWORDS: Piled raft, ANSYS, Compressible layer.
Lateritic Soil Stabilization by Addition of Steel Slags
S. Chaiyaput and J. Ayawanna
ABSTRACT: The addition of electric arc furnace slag and ladle furnace slag on strength improvement of lateritic soil was studied in this work. Liquid limit, plasticity index, and the California bearing ratio of lateritic soil mixed with the slags were determined in comparison to those of ordinary lateritic soil. A scanning electron microscope was used to confirm the effect of those two slags on microstructures related to chemical components of raw materials and the strength of lateritic soil. The deterioration of California bearing ratio, liquid limit, and plastic index values were obtained when the electric arc furnace slag was mixed in lateritic soil. Meanwhile, the California bearing ratio of lateritic soil was highly improved with the addition of ladle furnace slag, owing to the hydration reaction between water and excess lime in ladle furnace slag with free silica in lateritic soil. The values of the plasticity index were also comparable to the ordinary lateritic soil. Microstructures confirmed a highly compacted surface of mixed lateritic soil with ladle furnace slag. The ladle furnace slag is therefore one of the promising alternative low-cost materials for the soil-stabilizing application.
KEYWORDS: Steel slags, Soil stabilization, Construction, Mechanical properties, Improvement.
