Journal of Engineering Geology

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This paper presented the feasibility of developing and using artificial neural networks (ANNs) for modeling the monotonic large scale triaxial tests over angular, rounded rockfill and materials contained various percentages of fines as a construction material in some dams in Iran. The deviator stress/excess pore water pressure versus axial strain behaviors were firstly simulated by employing the ANNs. Reasonable agreements between the simulation results and the tests results were observed, indicating that the ANN is capable of capturing the behavior of gravely materials. The database used for development of the models comprises a series of 52 rows of pattern of strain-controlled triaxial tests for different conditions. A feed forward model using multi-layer perceptron (MLP), for predicting undrained behavior of gravely soils was developed in MATLAB environment and the optimal ANN architecture (hidden nodes, transfer functions and training) is obtained by a trial-and-error approach in accordance to error indexes and real data. The results indicate that the ANNs models are able to accurately predict the behavior of gravely soil in CU monotonic condition. Then, the ability of ANNs to prediction of the maximum internal friction angle, maximum and residual deviator stresses and the excess pore water pressures at the corresponding strain level were investigated. Meanwhile, the artificial neural network generalization capability was also used to check the effects of items not tested, such as density and percentage smaller of 0.2 mm.

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This paper describes triaxial compression tests conducted to determine the effect of fiber inclusion on stiffness and deformation characteristics of sand-gravel mixtures. Tested soil was a mixture of Babolsar sand from the shores of the Caspian Sea and Karaj River gravel. Portland cement was used as the cementing agent and fibers 12mm in length and 0.023mm in diameter at 0%, 0.5% and 1.0% were added to the mixtures. Triaxial tests were performed on saturated samples in consolidated drained and undrained conditions at confining pressures of 100, 200 and 300 kPa. Deviatoric stress-axial strain, volumetric strain-axial strain, pore pressure-axial strain curves with deformation and stiffness characteristics were investigated. Tests results show that fiber addition increased peak and residual shear strength of the soil. Fiber addition resulted in an increase of the maximum positive and negative volumetric strains. In undrained condition, fiber inclusion caused increase in initial positive pore pressure and final suction. It has also been observed that fibers decreased initial tangent stiffness of the cemented sand-gravel mixture.

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Collapsible soils could widely be found in central part of Iran and has caused lots of problems for roads and railroads in that region. Appearance of wide cracks in the collapsible soil near the Tehran-Semnan railroad tracks has caused some worries regarding the safety and performance of the railroad. However, due to the high traffic of the railroad, it is impossible to block the road for remedy. Therefore using injection method was found the most suitable alternative to improve the soil along railroad. The results of field and laboratory tests revealed that the injection of lime has better effects on improving soil characteristics than the other materials. It will significantly decrease the collapsibility potential of soil in saturated condition and will cause an increase in loading capacity of soil. Lime injection was suggested as the most appropriate solution for projects with similar geological condition. 

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Consolidated-drained triaxial compression tests were conducted to compare the stress-strain and volume change response of sands and clayey sands reinforced with discrete randomly distributed poly-propylene fibers. The influence of various test parameters such as fiber content (0.0%, 0.5% and 1.0% by weight), clay content (0%, 10% and 20% by weight), relative density (50% and 90%) and confining pressure (100 kPa, 200 kPa and 300 kPa) were investigated. It has been observed that addition of clay particles to the sands decreased the shear strength of samples. Also, increase in clay content reduced dilation and increased compressibility of the mixed soil. Addition of the fiber to both sands and clayey sands samples improved the shear strength and increased ductility and axial strain at failure point. 

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of initial texture and plastic fine content has been investigated. In order to model the different deposition condition four different specimen preparation methods are used. The tests are conducted on sands and its combination with to 25 fine percent using static and cyclic method. Four different specimen preparation methods are used consisting of Dry Funnel Deposition (DFD), Water Sedimentation (WS), Moist Tamping (MT) and Air Pluviation (AP). Each method may be useful to model the behavior of some special deposited soils. For example, DFD is the best method to model the natural deposition of silty sands, while the WS method is suitable for simulating the sands natural deposition in the rivers. MT method is the best method to simulate the behavior of compacted embankments while SD method is suitable to prevent the segregation of particles with respect to other methods like Water Pluviation. Effect of sample preparation methods on the sands and silty sands behavior is investigated to some extent, while the clayey sands are rarely considered. The results show that water sedimentation method, Air pluviation method and Dry funnel deposition method tends to create dilative textures with continuous dilative behavior even in high clay fine content. In contrast, the wet tamping method shows the dilative behavior only for clean sands specimens and increasing fines will results in instability and complete strain softening behavior. In cyclic loading the difference between different methods are less with respect to static loading. It seems that the results of different methods tends to be identical with increasing in fine content. In general, increasing fine content up to 20 percent results in more instability. After that a threshold value can be estimated bout 2 percent, after that the instability becomes less with continuous increase in fines content. The valuable result is that the threshold value is not dependent on the specimen preparation method or initial texture of specimens. 

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Materials such as waste tire chips were widely used to improve the strength of soil. The objective of this study is to discuss the residual strength or steady-state behavior of sand-waste tire chip mixtures. A series of undrained monotonic triaxial compression tests were conducted on reconstituted saturated specimens of sand and sand-tire chip mixtures with variation in the tire-chip contents from 0 to 4 percentages by dry weight of soil. The specimens are prepared using dry deposition method of preparation. The influence on residual resistance of varying confining pressure (100, 200, and 300 kPa) and sand mixture relative density (40, 65, and 80%) were evaluated. Tests results showed that by increasing the tire chip contents, the residual strength increased and steady-state lines move to the right of log S_us-e diagram. Also, the residual resistance improvement induced by tire chip inclusions was found to be sensitive to the relative density of samples and applied confining pressure.

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Introduction
One-dimensional site response analysis is widely performed to account for local site effects during an earthquake. Most of these approaches assume that dynamic soil properties are frequency independent. Laboratory test results as well as in-situ testing show that shear modulus and damping ratio are dependent on the frequency of loading. Although the amplification factor at ground surface with respect to frequency dependent dynamic properties of mixed alluvium materials under different near-fault motions with various velocity period is recognized, it is not well characterized and quantified.
Material and analysis methods
In this study, the tests results of samples which obtained from the drilling borehole (BH14) form Pardis city in Iran, are used. The soil is classified as clayey of high plasticity/clayey sand (CH/SC) and almost uniform and similar in the whole log profile.
Shear modulus and damping ratios versus shear strain curves (ASTM D3999) of CH/SC natural materials at effective confining pressures of 1, 2 and 5 kg/cm² with frequency of 0.5, 2, 5, and 10 Hz were used in one dimension response analyses using EERA Code.
Generally the damping ratio versus shear strain of the studied materials under low loading frequency (i.e. 0.5 Hz) almost falls in the range identified in literature. However, at higher loading frequencies (5 and 10 Hz) the damping ratios completely fall above the known upper bound trend. It is observed that, in general, the G and D values increase as loading frequency increases. Moreover, at certain strain G/G_max ratio decreases as loading frequency is increased.
Different dynamics behaviour curves were used in analyses, in isotropic consolidation conditions. In order to assess the amplification, acceleration spectra, acceleration spectra ratio, coefficient of B, at ground surface under eight well-known near-fault ground motions, 1728 one dimensional analyses were carried out with EERA code. The analyses have been performed for three base acceleration levels, namely, 0.1 g, 0.35 g and 1 g, using the simple time history scaling method. Field and laboratory test results of shear wave velocity were used in the analyses.
In this study, several well-known near-fault motion records are utilized for ground response analyses. Near-fault earthquakes records were selected from the strong motion database of the Pacific Earthquake Engineering Research Center (PEER) and Iran Strong Motion Network (ISMN) for specific reasons of location of the near faults sites.
In current building codes, the upper 30 m soil deposits overlying the higher impedance earth crust are regarded as the most relevant and significant in characterizing the seismic behavior of a site. Therefore, it is useful to accomplish investigations for obtaining their amplification and spectral acceleration for 30 m and even thicker (e.g. 60 m, for usual deep excavation in Iran), in order to have economical and safe designs and constructions.
Results and discussion
Figure 1 presents a comparison of normalized spectral acceleration (B factor) versus period for 30 m and 60 m thick profiles and Vs testing for frequencies dependent and independent analyses under input base acceleration of 0.35g for longitudinal component of used earthquakes. B factor of Iranian Standard 2800 and UBC97 also has been presented in the figure. The spectral acceleration at short period for frequency dependent analysis is higher than that of the frequency independent analysis. The  increases in frequency dependent analysis and higher thick profile (i.e. 60 m).
Conclusion
Results show that the effect of loading frequency has a considerable influence on the acceleration response at the ground surface. For both 30 m and 60 m soil columns, the increase of the loading frequency, decreases the amplification factor especially in the short period zone of the spectra. Based on the acceleration response spectra of near field strong motions derived for soils types of I and IV in this study, the period corresponding to  in the design spectrum of Iranian Standard 2800 should increase to 0.5 and 1.4, respectively. Therefore, selection of the appropriate G and D curves measured at frequency similar to those of the anticipated cyclic loading (e.g. seismic) has a paramount importance../files/site1/files/134/1.pdf