Time-dependent physicochemical characteristics of Malaysian residual soil stabilized with magnesium chloride solution

The effects of non-traditional additives on the geotechnical properties of tropical soils have been the subject of investigation in recent years. This study investigates the strength development and micro-structural characteristics of tropical residual soil stabilized with magnesium chloride (MgCl2) solution. Unconfined compression strength (UCS) and standard direct shear tests were used to assess the strength and shear properties of the stabilized soil. In addition, the micro-structural characteristics of untreated and stabilized soil were discussed using various spectroscopic and microscopic techniques such as X-ray diffractometry (XRD), energy-dispersive X-ray spectrometry (EDAX), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR) and Brunauer, Emmett and Teller (BET) surface area analysis. From the engineering point of view, the results indicated that the strength of MgCl2-stabilized soil improved noticeably. The degree of improvement was approximately two times stronger than natural soil after a 7-day curing period. The results also concluded the use of 5 % of MgCl2 by dry weight of soil as the optimum amount for stabilization of the selected soil. In addition, the micro-structural study revealed that the stabilization process modified the porous network of the soil. The pores of the soils had been filled by the newly formed crystalline compounds known as magnesium aluminate hydrate (M-A-H).Ministry of Education Malaysia under the Fundamental Research Grant (FRGS) (R.J130000.7822.4F658); Universiti Teknologi Malaysia (UTM); Construction Research Centre UT

Simulation of seismic liquefaction: 1-g model testing system and shaking table tests

In this paper, we focus on the development and performance of the 1-g model testing system to monitor the liquefaction occurrence of saturated soils, under subsequent one-dimensional shake table tests. The system is composed of one-dimensional laminar box, cone penetration system, soil model, system for hydraulic soil pumping to achieve loose soil deposit, instrumentation and associated testing hardware. In order to simulate the free-field conditions in the laboratory, the laminates slide on each other using rollers placed between each laminate. The static calibration test results demonstrate that the friction effects between the laminates and the rollers are satisfactorily low. The loosest and the most liquefiable sand deposit is prepared inside the laminar box by hydraulic filling process and subjected to four subsequent shaking tests at different intensities. First, the laminar box and shake table performance is verified by using time-histories of acceleration and displacement test results. Then, the measured data inside the soil and on the laminates are compared with the numerical model. The previously calibrated numerical model UBCSAND which shows the seismic loading conditions in the free field is used in the simulations. Those shake table test results and the numerical simulations of the box and the soil indicate that the usefulness of the laminar box system for shaking table tests is satisfactory for dynamic model tests in 1-g gravity.European Union Marie Curie Fellowship (IRG248218); TUBITAK (111M435

The use of neural networks for CPT-based liquefaction screening

This study deals with development of two different artificial neural network (ANN) models: one for predicting cone penetration resistance and the other for predicting liquefaction resistance. For this purpose, cone penetration numerical simulations and cyclic triaxial tests conducted on Ottawa sand–silt mixes at different fines content were used. Results obtained from ANN models were compared with simulation and experimental results and found close to them. In addition, the performance indices such as coefficient of determination, root mean square error, mean absolute error, and variance were used to check the prediction capacity of the ANN models developed. Both ANN models have shown a high prediction performance based on the performance indices. It has been demonstrated that the ANN models developed in this study can be employed for predicting cone penetration and liquefaction resistances of sand–silt mixes quite efficiently

The use of neural networks for the prediction of cone penetration resistance of silty sands

In this study, an artificial neural network (ANN) model was developed to predict the cone penetration resistance of silty sands. To achieve this, the data sets reported by Ecemis and Karaman, including the results of three high-quality field tests, namely piezocone penetration test, pore pressure dissipation tests, and direct push permeability tests performed at 20 different locations on the northern coast of the Izmir Gulf in Turkey, have been used in the development of the ANN model. The ANN model consisted of three input parameters (relative density, fines content, and horizontal coefficient of consolidation) and a single output parameter (normalized cone penetration resistance). The results obtained from the ANN model were compared with those obtained from the field tests. It is found that the ANN model is efficient in determining the cone penetration resistance of silty sands and yields cone penetration resistance values that are very close to those obtained from the field tests. Additionally, several performance indices such as the determination coefficient, variance account for, mean absolute error, root mean square error, and scaled percent error were computed to examine the performance of the ANN model developed. The performance level attained in the ANN model shows that the ANN model developed in this study can be employed for predicting cone penetration of silty sands quite efficiently.European Union (IRG248218); TUBITAK Project (111M602

Influence of non-/low plastic fines on cone penetration and liquefaction resistance

Uncertainties prevail at the current liquefaction screening method based on the cone penetration test (CPT) as to whether the existence of fines increases liquefaction resistance or decrease cone penetration resistance. In this study, field-based data are used to evaluate the effects of non-/low plastic fines on liquefaction resistance at the current CPT-based liquefaction assessment method. The first part of this paper examines the effects of the coefficient of consolidation or drainage characteristics of soils containing fines on cone penetration resistance. The coefficient of consolidation is influenced by the fines content and the relative density of the soil. The second part of this paper investigates the contribution of fines content less than 30% by weight on the liquefaction resistance of soils at different relative densities. Fines content over 30% by weight and/or high plasticity of fines can cause additional complications; therefore, it needs different valuation methods, which is beyond the scope of this paper. The liquefaction resistance of sands and silty sands is reinterpreted from the current CPT-based liquefaction assessment method. The trend, which presents the change of liquefaction resistance with fines content at the same relative density, is compared with the available laboratory-based data in the literature. The results show that the interpreted trend is not consistent with the laboratory-based correlations obtained by several previous researchers. Therefore, there will be probably some inaccuracies in estimation of liquefaction potential of silty sand using the current CPT-based liquefaction assessment method.TUBITAK (110M602); European Union (PIRG05-GA-2009-248218

Feasible packing of granular materials in discrete-element modelling of cone-penetration testing

This paper explores how the discrete-element method (DEM) was found to play an increasingly important role in cone penetration test (CPT) where continuum-mechanics-based analysis tools are insufficient. We investigated several crucial features of CPT simulations in the two-dimensional DEM. First, the microparameters (stiffness and friction) of discrete material tailored to mimic clean, saturated sand, which is used in cone-penetration tests, were calibrated by curve-fitting drained triaxial tests. Then, three series of cone-penetration simulations were conducted to explore (1) top boundary conditions, (2) reasonable size of discrete particles at different initial porosities, and (3) limit initial porosity of the model for a balance between accurate representation and computational efficiency. Further, we compared the cone-penetration resistance obtained in the laboratory and numerical simulations for the range of relative densities.TUBITAK (111M435

Influence of consolidation properties on the cyclic re-liquefaction potential of sands

The relative density can be used as the main indicator to assess the liquefaction resistance of clean sands. As relative density of the sand deposit increases significantly following the initial liquefaction, one should expect that the soil can improve its liquefaction resistance. However, earthquake records indicate that densified sand can be liquefied again (re-liquefied) at smaller cycles by the similar seismic loadings. This work aims to clarify the counterintuitive finding that, after the first liquefaction, the resulting significant increase in relative density (induced by settlements and variation of the water level) do not necessarily imply an increase in the number of loading cycles for re-liquefaction. In this paper, we present a series of experimental results concerning the cyclic liquefaction and the following re-liquefaction of clean sand deposits. The experimental setup is performed by a shaking table, transmitting one-degree of freedom transversal motion to the soil within the 1.5 m high laminar shear box. At four different seismic demands, the input excitation was imposed three times to examine the influence of the initial distributions of the relative density and the consolidation characteristics on the liquefaction potential of the sand. The re-liquefaction cycles of the sand, which previously experienced liquefaction under the same seismic loadings, show that post-liquefaction reconsolidation of the sand deposits affects the re-liquefaction resistance.TUBITAK Project 111M43

Laminar box system for 1-g physical modeling of liquefaction and lateral spreading

Details of a large scale modular 1-g laminar box system capable of simulating seismic induced liquefaction and lateral spreading response of level or gently sloping loose deposits of up to 6 m depth are presented. The internal dimensions of the largest module are 5 m in length and 2.75 m in width. The system includes a two dimensional laminar box made of 24 laminates stacked on top of each other supported by ball bearings, a base shaker resting on a strong floor, two computer controlled high speed actuators mounted on a strong wall, a dense array advanced instrumentation, and a novel system for laboratory hydraulic placement of loose sand deposit, which mimics underwater deposition in a narrow density range. The stacks of laminates slide on each other using a low-friction high-load capacity ball bearing system placed between each laminate. It could also be reconfigured into two smaller modules that are 2.5 m wide, 2.75 m long, and up to 3 m high. The maximum shear strain achievable in this system is 15 %. A limited set of instrumentation data is presented to highlight the capabilities of this equipment system. The reliability of the dense array sensor data is illustrated using cross comparison of accelerations and displacements measured by different types of sensors. Copyright © 2009 by ASTM International