Ahmad Mahir Makhtar

A Novel Approach for Blast-Induced Flyrock Prediction Based on Imperialist Competitive Algorithm and Artificial Neural Network

Flyrock is one of the major disturbances induced by blasting which may cause severe damage to nearby structures. This phenomenon has to be precisely predicted and subsequently controlled through the changing in the blast design to minimize potential risk of blasting. The scope of this study is to predict flyrock induced by blasting through a novel approach based on the combination of imperialist competitive algorithm (ICA) and artificial neural network (ANN). For this purpose, the parameters of 113 blasting operations were accurately recorded and flyrock distances were measured for each operation. By applying the sensitivity analysis, maximum charge per delay and powder factor were determined as the most influential parameters on flyrock. In the light of this analysis, two new empirical predictors were developed to predict flyrock distance. For a comparison purpose, a predeveloped backpropagation (BP) ANN was developed and the results were compared with those of the proposed ICA-ANN model and empirical predictors. The results clearly showed the superiority of the proposed ICA-ANN model in comparison with the proposed BP-ANN model and empirical approaches.

Critical State of Sand Matrix Soils

The Critical State Soil Mechanic (CSSM) is a globally recognised framework while the critical states for sand and clay are both well established. Nevertheless, the development of the critical state of sand matrix soils is lacking. This paper discusses the development of critical state lines and corresponding critical state parameters for the investigated material, sand matrix soils using sand-kaolin mixtures. The output of this paper can be used as an interpretation framework for the research on liquefaction susceptibility of sand matrix soils in the future. The strain controlled triaxial test apparatus was used to provide the monotonic loading onto the reconstituted soil specimens. All tested soils were subjected to isotropic consolidation and sheared under undrained condition until critical state was ascertain. Based on the results of 32 test specimens, the critical state lines for eight different sand matrix soils were developed together with the corresponding values of critical state parameters, M, λ, and Γ. The range of the value of M, λ, and Γ is 0.803–0.998, 0.144–0.248, and 1.727–2.279, respectively. These values are comparable to the critical state parameters of river sand and kaolin clay. However, the relationship between fines percentages and these critical state parameters is too scattered to be correlated.

CYCLIC BEHAVIOUR OF JOHOR SAND

Series of laboratory testing on the investigation of soil liquefaction using cyclic triaxial test had been carried out by researchers around the world but many of the results are contradictory. Thus, it is important to first determine the condition in which the clean sand is most susceptible to liquefaction, then only the liquefaction susceptibility of sand matrix soils could be compared and discussed under this specific condition. This paper presents the undrained behaviour of Johor sand and sand mixed with fines (kaolin) from cyclic triaxial tests. Stress controlled triaxial test apparatus was used to shear the isotropically consolidated soil samples under undrained two-way cyclic loading until the initiation of liquefaction. The liquefaction was defined based on: (i) excess pore pressure was equal to effective confining pressure or (ii) double amplitude strain of 5 % was reached, whichever was achieved first. The results of two-way cyclic triaxial tests on clean sand showed that besides the cyclic stress ratio, the liquefaction resistance of the sand under undrained loading was proportional to effective consolidation pressure and density index. The Johor sand was more liquefiable at its loose state and under low effective consolidation pressure, when subjected to earthquake loading.

Effect of fines content on critical state parameters of sand matrix soils

Natural sand does always contain significant amounts of fine particles, known as sand matrix soils. The development of critical state for sand and clay are both well established. However, limited researchers focused on the sand matrix soils. This paper discusses the effect of fines content on the critical state parameters of sand matrix soils. Two types of plastic fines with different plasticity (kaolin and bentonite) were mixed into poorly graded Johor clean sand at different percentages to form the sand matrix soils. The critical state was obtained from the strain controlled triaxial compression test. All tested soils had been isotropically consolidated to four different effective confining pressures and sheared under consolidated undrained condition until the critical state was ascertained. The critical state line was plotted for each sand matrix soils on space and compression spaces. Based on linear regression analysis, the critical state parameters, M, λ and Γ were obtained and the ranges are from 0.807 to 1.102, 0.062 to 0.160 and 1.732 to 2.431, respectively. The trend of the critical state lines of sand matrix soils in both stress and compression space coincides with the concept of threshold fines content. The threshold fines content identified for sand-kaolin mixtures is 25 % kaolin while it is 20 % bentonite for sand-bentonite mixtures.

Plasticity Behaviour of Sand Matrix Soils

Natural sand does always contain significant amounts of fine particles, but previous study always assumes that the typical engineering characteristic of clean sand was remarkably representing as to all types of sand matrix soils. Studies reported that additional of plastic fines could either impose additional or reduce the liquefaction resistance of sand matrix soils. Therefore, the aim of this paper is to examine the plasticity behaviour of sand matrix soils through experimental study. The Atterberg Limit test was carried out on plastic fines mixtures and sand matrix soils. Results show that the plasticity behaviour is depending on the type of presenting plastic fines. The absorption of clay mineral is the key element to in manipulating the plasticity behaviour of plastic fines. It can be concluded that the absorption of montmorillonite is better compare to kaolinite.

Effect of Fines Content on Liquefaction Susceptibility of Sand-Kaolin Mixtures

Recent empirical observations reveal that not only the clean sand is susceptible to liquefaction hazard, both silty sand and clayed sand are also liquefiable. This paper presents the cyclic behaviour of sand-fines mixtures at various fines content. The sand-fines specimens were reconstituted by mixing clean sand with different percentages of plastic fines (kaolin) by weight to a constant relative density of 20 % using dry tamping method. The specimen had been tested with stress controlled cyclic triaxial test under consolidated undrained condition with effective confining pressure of 100 kPa, cyclic load of 0.1 kN and cyclic frequency of 0.5 Hz. The results show that the liquefaction resistance of sand matrix soils increased as fines content increased from 0 to 25 %, whereas this trend was reversed for value of fines content greater than 25 %. In fact, the 25 % of kaolin by weight is also the threshold fines content of sand-kaolin mixtures. Hence this finding justifies that the concept of fines threshold content could be used to significantly explain the influence of fines content on the liquefaction susceptibility of sand-fines mixtures.

Effect of Plasticity on Liquefaction Susceptibility of Sand-Fines Mixtures

The usability of the clay fraction as one of the criteria in the assessment of liquefaction susceptibility is questionable since year 2001. The use of plasticity index to replace clay fraction as a controlling parameter in the criterion is proposed. This paper aims to compare the usability of different parameter in describing the cyclic behaviour of sand-fines mixtures with various plasticity characteristics. The sand-fines mixtures were reconstituted by mixing clean sand with two types of plastic fines at different percentages by weight, at a standardized ratio of 80% of clean sand with 20% of plastic fines. All soil samples were mixed using the dry tamping method to achieve a constant relative density of 20% throughout the specimen. The soil specimens are tested with stress controlled cyclic triaxial apparatus under consolidated undrained condition, with an effective confining pressure of 100kPa. The soil specimens were considered liquefy when the value of pore pressure is equivalent to the initial cell pressure, resulting zeroes effective stress in soil specimen. The results showed that the liquefaction resistance of the sand-fines mixtures increased as the value of plasticity index increased. The plasticity index is a better indicator to describe the liquefaction susceptibility of sand-fines mixtures compare to clay content, plastic limit and activity.