Ahmad Safuan A. Rashid

Developing a hybrid PSO---ANN model for estimating the ultimate bearing capacity of rock-socketed piles

Rock-socketed piles are commonly used in foundations built in soft ground, and thus, their bearing capacity is a key issue of universal concern in research, design and construction. The accurate prediction of the ultimate bearing capacity (Qu) of rock-socketed piles is a difficult task due to the uncertainty surrounding the various factors that affect this capacity. This study was aimed at developing an artificial neural network (ANN) model, as well as a hybrid model based on both particle swarm optimisation (PSO) and ANN, with which to predict the Qu of rock-socketed piles. PSO, a powerful population-based algorithm used in solving continuous and discrete optimisation problems, was here employed as a robust global search algorithm to determine ANN weights and biases and thereby improve model performance. To achieve the study aims, 132 piles socketed in various rock types as part of the Klang Valley Mass Rapid Transit project, Malaysia, were investigated. Based on previous related investigations, parameters with the most influence on Qu were identified and utilised in the modelling procedure of the intelligent systems. After constructing and modelling these systems, selected performance indices including the coefficient of determination (R2), root-mean-square error, variance account for and total ranking were used to identify the best models and compare the obtained results. This analysis revealed that the hybrid PSO–ANN model offers a higher degree of accuracy compared to conventional ANN for predicting the Qu of rock-socketed piles. However, the developed model would be most useful in the preliminary stages of pile design and should be used with caution.

Effect of magnesium chloride solution on the physico-chemical characteristics of tropical peat

Abstract The stabilization of soils with additives is a chemical method that can be used to improve soils with weak engineering properties. Although the effects of non-traditional additives on the geotechnical properties of tropical soils have been subject of investigation in recent years, the effects of magnesium chloride (MgCl2) on the macro- and micro-structural characteristics of peat soil have not been fully studied. This study investigates the effect of MgCl2 on the physico-chemical characteristics of tropical peat. Unconfined compression strength tests were performed as an index of soil improvement in treated samples. In addition, the micro-structural characteristics of untreated and treated peat were investigated using various spectroscopic and microscopic techniques such as X-ray diffractometry, energy-dispersive X-ray spectrometry, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and Brunauer, Emmett, and Teller surface area analysis. From an engineering point of view, the results indicated that the strength of MgCl2-stabilized peat improved significantly. The degree of improvement was approximately six times stronger than untreated peat, after a 7-day curing period. Additionally, the micro-structural study revealed that the stabilization process led to a few changes in the mineralogical, morphological, and molecular characteristics of the selected peat. The pores of the peat were filled by newly formed crystalline compounds known as magnesium aluminate hydrate (M–A–H).

Behavior of Weak Soils Reinforced with End-Bearing Soil-Cement Columns Formed by the Deep Mixing Method

This article reports on a series of small-scale, plane strain, 1 g physical model tests designed to investigate the bearing capacity and failure mechanics of end-bearing soil-cement columns formed via Deep Mixing (DM). Pre-formed soil-cement columns, 24 mm in diameter and 200 mm in length, were installed in a soft clay bed using a replacement method; the columns represented improvement area ratios, ap, of 17%, 26%, and 35% beneath a rigid foundation of width 100 mm. Particle Image Velocimetry (PIV) was implemented in conjunction with close-range photogrammetry in order to track soil displacement during loading, from which the failure mechanisms were derived. Bearing capacity performance was verified using Ultimate Limit State numerical analysis, with the results comparing favorably to the analytical static and kinematic solutions proposed by previous researchers. A new equation for bearing capacity was derived from this numerical analysis based on the improvement area ratio and cohesion ratio of the soil column and ground model.

Sustainable Improvement of Tropical Residual Soil Using an Environmentally Friendly Additive

Many tropical residual laterites have relatively poor engineering properties due to the significant percentage of fine-grained soil particles that they contain, which are formed by the soil weathering process. The widespread presence of laterite soils in tropical regions often requires that some form of soil improvement be performed to allow for their use in various civil engineering applications, such as for road base or subbase construction. One of the most commonly utilized stabilization techniques for laterite soils is the application of additives that chemically react with the minerals that are present in soil to enhance its overall strength; effective soil stabilization can allow for the use of site-specific soils, and can consequently result in significant cost savings for a given project. With an increasing focus on the use of more environmentally friendly and sustainable materials in the built and natural environments, there is an emerging interest in eco-friendly additives that are an alternative to traditional chemical stabilizers. The current study examines the viability of xanthan gum as an environmentally friendly stabilizer that can improve the engineering properties of tropical residual laterite soil. Unconfined compressive strength (UCS) tests, standard direct shear tests, Brunauer, Emmett, and Teller (N2-BET) surface area analysis tests and field emission scanning electron microscopy (FESEM) tests were used to investigate the effectiveness of xanthan gum for stabilization of a tropical laterite soil. The UCS test results showed that addition of 1.5% xanthan gum by weight yielded optimum stabilization, increasing the unconfined compressive strength of the laterite soil noticeably. Similarly, direct shear testing of 1.5% xanthan gum stabilized laterite specimens showed increasing Mohr–Coulomb shear strength parameters with increases in curing time. From the FESEM results, it was observed that the stabilization process modified the pore-network morphology of the laterite soil, while also forming new white layers on the surface of the clay particles. Analysis of the test results indicated that xanthan gum stabilization was effective for use on a tropical residual laterite soil, providing an eco-friendly and sustainable alternative to traditional soil stabilization additives such as cement or lime.

Xanthan gum biopolymer: an eco-friendly additive for stabilization of tropical organic peat

Biogeotechnology is a recently established branch of geotechnical engineering, associated with the practical uses of microbiological techniques to improve the engineering properties of geomaterials. This study explores the utility of xanthan gum, an eco-friendly biopolymer obtained from microbial sources, for stabilization of tropical organic peat, using a series of macroscale and microscale test approaches. At the macroscale, the shear strength characteristics of both untreated and stabilized peat were evaluated using unconfined compression strength (UCS) and standard direct shear tests. Microscopic techniques, including field emission scanning electron microscopy (FESEM), Brunauer, Emmett, and Teller (N2-BET) surface area analysis, and particle size analysis, were also utilized to examine changes in the microstructural characteristics of stabilized peat that are caused by the chemical reaction that occurs between the xanthan gum and peat particles. UCS test results showed that the xanthan gum stabilization significantly improved the shear strength of the peat in its natural condition, with the 28-day strength of the stabilized peat being six times higher than the strength of the untreated peat. Microstructural analysis showed that the morphological characteristics of the peat are changed due to the chemical reaction that occurs during the curing process, as indicated by the FESEM results. Over time, formation of cementitious products was clearly observed, which welded peat particles and filled the pores in the soil structure, yielding a denser soil fabric with less pore volume and stronger attractive forces. From the testing that was performed, xanthan gum stabilization is recommended for peat as an eco-friendly and sustainable alternative to traditional soil stabilization additives such as cement or lime.

Settlement prediction of the rock-socketed piles through a new technique based on gene expression programming

The settlement design of bored piles socketed into rock has received considerable attention. Although many design methods of pile settlement are recommended in the literature, proposing new/practical technique(s) with higher performance prediction is of advantage. A new model based on gene expression programming (GEP) is presented in this paper for predicting the settlement of the rock-socketed pile. To do this, 96 piles socketed in different types of rock (mostly granite) as part of the Klang Valley Mass Rapid Transit project, Malaysia, were studied. In order to propose a predictive model with higher performance prediction, a series of GEP analyses were conducted using the most important factors on pile settlement, i.e. ratio of length in soil layer to length in rock layer, ratio of total length to diameter, uniaxial compressive strength, standard penetration test and ultimate bearing capacity. For comparison purpose, using the same dataset, linear multiple regression (LMR) technique was also performed. After developing the equations, their prediction performances were checked through several performance indices. The results demonstrated the feasibility of GEP-based predictive model of settlement. Coefficients of determination (CoD) values of 0.872 and 0.861 for training and testing datasets of GEP equation, respectively, show superiority of this model in predicting pile settlement while these values were obtained as 0.835 and 0.751 for the LMR model. Moreover, root mean square error (RMSE) values of (1.293 and 1.656 for training and testing) and (1.737 and 1.767 for training and testing) were achieved for the developed GEP and LMR models, respectively.

The contribution of particle swarm optimization to three-dimensional slope stability analysis.

Over the last few years, particle swarm optimization (PSO) has been extensively applied in various geotechnical engineering including slope stability analysis. However, this contribution was limited to two-dimensional (2D) slope stability analysis. This paper applied PSO in three-dimensional (3D) slope stability problem to determine the critical slip surface (CSS) of soil slopes. A detailed description of adopted PSO was presented to provide a good basis for more contribution of this technique to the field of 3D slope stability problems. A general rotating ellipsoid shape was introduced as the specific particle for 3D slope stability analysis. A detailed sensitivity analysis was designed and performed to find the optimum values of parameters of PSO. Example problems were used to evaluate the applicability of PSO in determining the CSS of 3D slopes. The first example presented a comparison between the results of PSO and PLAXI-3D finite element software and the second example compared the ability of PSO to determine the CSS of 3D slopes with other optimization methods from the literature. The results demonstrated the efficiency and effectiveness of PSO in determining the CSS of 3D soil slopes.

A New Model for Determining Slope Stability Based on Seismic Motion Performance

The factor of safety is one of the major aspects for designing specific structures like embankment, landslide, and artificial slopes. In this context, some huge damages are particularly reported due to the effect of earthquakes. In this paper, 700 slopes were designed based on the limit equilibrium method, and relevant factor of safety values were obtained. In the modelling process, the parameters with the greatest effect (slope height, slope degree, soil cohesion, and internal angle of friction with peak ground acceleration), were considered as predictors or model inputs. As a result, the factor of safety under the impact of seismic motion is significantly reduced when the peak ground acceleration increases. A multiple regression model was developed. Coefficients of determination for the training and testing datasets indicate the excellent ability of the proposed model to estimate the seismic factor of safety. Peak ground acceleration and soil cohesion were obtained as the parameters with the most and least effect on the factor of safety, respectively.

Strength and morphological characteristics of organic soil stabilized with magnesium chloride

Organic soil causes major problems in infrastructure development. It has high compressibility and low shear strength, and requires chemical stabilization if it is to be a sustainable geomaterial. This research investigated the strength and microstructural properties of organic soil stabilized with magnesium chloride (MgCl2). Unconfined compressive strength tests were undertaken to assess shear strength properties, and microstructural changes were monitored via field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectrometry (EDAX). The results confirm that MgCl2 improves the compressive strength of organic soil. The strength of MgCl2-stabilized organic soil is increased to around 3 – 5 times that of untreated soil during the first 7 days of curing. FESEM results show that the porosity of organic soil is filled by a new cementitious compound, identified as magnesium silicate hydrate (M-S-H).

The Consequence Assessment of Gas Pipeline Failure due to Corrosion

In this paper, a qualitative consequence assessment method for damaged urban natural gas pipelines is proposed. It focuses on identifying reputation loss factors according to stakeholders’ (investors, customers, employees, and communities) perceptions. The analytical hierarchy process (AHP) method is applied to prioritize these factors. Results show that the loss of customer confidence ranks as the highest contributor to an operator’s reputation loss due to a pipeline accident. Thus, better risk assessment of pipeline damage due to corrosion will be achieved with the inclusion of reputation loss in the consequence assessment. Hence, decision making in pipeline repair, inspection, and maintenance can be improved as well as a company’s annual profit margin.