Simulation of dilatometer tests by neural networks

Rock rigidity may be experienced in a wide range depending on several factors, and different methods can be used to consider their load-deformation behaviors. In this context, dilatometer tests (DTs) can be applied to obtain the modulus of elasticity of rock masses; therefore, it is possible to evaluate in-situ stress-strain behavior of rock masses realistically. Nevertheless, the application of this test is expensive as well as time-consuming, and necessitates mobilization of the equipment to construction site by trucks. The aim of this study is to simulate the load-deformation curve obtained of DT by neural networks (NNs). Therefore, the dilatometer test can be modeled as well as synthetic simulation of the test enables analyzers to characterize the material behavior. In order to investigate this, 50 different stress-deformation curves are obtained from DTs conducted on limestone formation underlying a dam (Dim dam) construction site in the Southern part of Turkey. The developed database by the curves was used for training and testing of the NN models. The results revealed that NN technique is quite successful for modeling the stress-deformation behavior of specific rocks based on DT results. It is therefore possible with the help of this alternative tool developed for the simulation of DT i) to model DT numerically, ii) to simulate the stress-strain behavior successfully, iii) to calculate the modulus of deformation efficiently, iv) to generate additional DT data synthetically, v) to develop material model alternatively, and vi) to make assumptions on the characterization of the rock mass behavior using previous information gathered by DTs. Copyright © Association for Scientific Research

Estimation of the local void ratios of compacted sands [Sikiştirilmiş kumlarin yerel boşluk oranlarinin tahmini]

In this study, the variation of local void ratio in granular soils is investigated within an experimental study. In this regard, 2D local void ratios of sands compacted under three energy levels and corresponding optimum water contents are determined via image analyses performed on images obtained from certain cross-sections. Afterwards, it was investigated whether the variation of the void ratios in horizontal and vertical direction is proper or not. Moreover, the effect of particle shape on the variation of the local void ratio is scrutinized by employing statistical analyses on these parameters. Although it is inferred that increasing particle angularity results denser structures, a mathematical expression identifying the relationship between particle shape parameters and relative densities or void ratios is not obtained. As a consequence, multiple variable linear and nonlinear regression equations are employed to obtain the local void ratios at certain points in terms of a number of particle shape parameters, compaction energy level and global void ratio

Relationships between shape characteristics and shear strength of sands

In the Mohr-Coulomb criterion, the shear strength of sands is typically characterized by the internal friction angle, which depends on many factors such as grain size and distribution, the mineralogical origin of the particles, particle shape, unit weight, geological history, cementation, saturation, and overburden pressure. In this study, the empirical relationships among three particle shape indices, different fractal dimension definitions, and internal friction angles were investigated. Within this context, direct shear tests were conducted on 38 different types of sands from different origins and with various grain sizes. For each type of sand, image analyses were performed to find out the roundness, sphericity, regularity parameters belonging to individual grains. Additionally, several statistics of these parameters for different types of sands were determined. The results revealed that particle shape has a limited effect on the friction angle of sands in comparison to grain size distribution. Furthermore, it was found that decreasing regularity in particle shape caused an increase in the internal friction angle of uniform sands. These findings agree with the empirical relationship between the internal friction angle and particle shape suggested in the literature

Estimation of the permeability of granular soils using neuro-fuzzy system

5th IFIP Conference on Artificial Intelligence Applications and Innovations, AIAI 2009 -- 23 April 2009 through 25 April 2009 -- Thessaloniki -- 100720Determination of the permeability coefficient is crucial for the solution of several geotechnical engineering problems such as modeling of underground flow, determination of the hydraulic properties of leachate water in waste disposal areas, calculation of the compressibility, and so on. Constant head permeability test, which is usually performed for the determination of the permeability, is easy to apply; however, it is not easy to obtain undisturbed sand specimens from field. Therefore, the tests are usually employed on specimens having similar relative densities to those from the field. An alternative approach to permeability tests for granular soils is the prediction of permeability levels in terms of a number of particle size distribution and shape parameters. Although these methods are capable of making reasonable predictions for permeability coefficient, they have certain limitations. In this study, the approximation ability of neuro-fuzzy systems is utilized for the prediction of the permeability coefficient. Permeability test results on 20 different types of granular soils are used to generate a database to train adaptive neuro-fuzzy inference system (ANFIS), which is considered to predict the results of eight different permeability tests. It is concluded that ANFIS structure is superior in the prediction of permeability tests considering particle shape and grain size distribution information