The threshold silt content is well known as a key parameter affecting the mechanical response of binary granular assemblies considering particle characteristics (size and shape). In this context, the threshold silt content (TSC) is determined from different laboratory tests based on packing density response (emax and emin versus silt content «Sc») and theoretical approaches proposed by several researchers in the specialized published literature using the characteristics of host sand and silt [emax(sand), emin(sand) , emax(silt) , emin(silt) , Gs , Gf and x]. The analysis of the recorded data indicates that the TSC derived from the (emax) curve appears more reliable than that obtained from the (emin) one. Moreover, it is found that the proposed analytical methods are suitable to quantify the threshold silt content (TSC) than that determined experimentally using the packing density (emax and emin). In addition, the test results show that the new introduced ratios [(D50s×As)/(D50f×Af)] and [(Cus×As)/(Cuf×Af)] determined based on particle characteristics (shape and size) appear as appropriate parameters for predicting the threshold silt content (TSC) of sand-silt mixture of the compiled data from the published literature as well as that of the present research related to Chlef sand, Fontainebleau sand and Hostun sand mixed with Chlef silt.

In this study the behavior of buried pipes under impact loading was investigated by forming protective layers with geosynthetics in various combinations in single and double layers. For this purpose, experiments were performed using a HDPE pipe with a 160 mm outer diameter, which is frequently used in the laboratory. In the experiments, Geocell, Geogrid, Geotextile, and Geonet protective layers at a depth of 120 mm were tested by laying Geosynthetic in single and double layers and then tested under the effects of impact loading by using free-weight dropping test apparatus. In the experimental study, the protective layers' energy absorption capacities were calculated by using acceleration measurements over the pipe and then evaluated together with their costs. In the experiments with a single layer Geosynthetic as a protective layer, Geonet's most successful protection structure was a 72.9 % acceleration-damping capacity. In the experiments with the combination of double-layer reinforcement elements, the most successful performance with 88.0 %, in terms of acceleration damping capacity, was obtained from Geocell and Geonet's combination with a thickness of 1 mm at a depth of 50 mm. When all the experiments with single- and double-layer Geosynthetic protective elements were evaluated as an acceleration damping ratio per unit cost, it was found that the optimum application was achieved when using a single-layer Geogrid.

A series of 94 laboratory tests were conducted to measure the response of pile foundation when subjected to dynamic loads. Eight tests were conducted on single pile in dry soil at relative density 30 % (loose) and 50 % (medium); 66 tests on group of piles with different spacings and patterns. All tests were carried out under operating frequencies 0.5, 1 and 2 Hz under horizontal shaking. All tests were achieved with one embedment ratio (L/d = 30). These tests were grouped in three different numbers of piles; 2 piles in row and line patterns, 3 piles and 4 piles; and three pile spacing ratios (s/d = 3, 4 and 5). The results of dry soil indicating the mechanism of dynamic response of piles and soil subjected to dynamic horizontal shaking include the variation and distribution of acceleration with time in different states of soil in addition to the vertical and horizontal displacements, end-bearing load, peak acceleration and the peak velocity of foundation. It was concluded that for a dry soil bed, the acceleration amplitudes increase with frequency for both soil relative densities (loose and medium) and different pile patterns (number; single or group and different spacing ratios s/d). The maximum acceleration in the foundation is lower than in the soil bed for all operating shaking frequencies, pile spacing ratios and soil states. The decreasing of the maximum acceleration recorded in the foundation as compared to that in the soil bed is between 10-100 % for loose and medium state of soil, and the decrease in loose state is more than in medium state. This means that there is damping effect or attenuation of vibration waves. The amplitudes of recorded acceleration in the pile cap are much higher than in the soil bed for single pile and pile group with different pile spacing ratios, also these amplitudes are increasing with increase of shaking frequency and relative density of the soil.

For traditional slice methods of limit equilibrium used to analyze slope stability, some hypothetical conditions on interslice force are generally introduced to solve the problem. In order to reduce the defect theoretically due to the related hypothesis, more rigorous constraints of interslice force are completely considered in light of static equilibrium conditions and energy dissipation principle of the interface between two adjacent slices. Without hypothesis of interslice force, the slope stability analysis is transformed consistently into a non-linear programming problem to be solved. So, a generally improved solution of slice method of limit equilibrium to slope stability is put forward. In particular, influence of the dilation angle of soil on slope stability can be involved in the method. The proposed method can be utilized for any slopes with arbitrary slip surfaces.

The precise study of the response of earth dams to earthquakes is one of the most complex issues in the field of soil structures. In this research, dynamic analysis of earth dam structures (a case study: Doyraj dam in the west of Iran) have been performed using 2D Finite Difference Method (2D F.D.M.). The aim of this study is to investigate accelerations, lateral (horizontal) and vertical displacements (i.e. settlements) due to earthquake occurrence. The results of dynamic analysis indicate that the performance of the dam is satisfactory for each one of the seismic scenarios considered in this investigation. The maximum settlements at the dam crest is considerably smaller than that of the dam freeboard, with maximum value of 540 mm, which is comparable to recommendation of the Department of Safety of Dams (DSOD). Depth of sliding surfaces is better shown in the Finn model, and the settlements based on the Finn model is about 2.5 times higher than that of Mohr model. In contrast to what is commonly accepted about earthquake acceleration (the increase in earthquake acceleration from the base to the top of the dam), it cannot generalize to all cases, and it can be limited to very strong dams or can be related to poor earthquakes.

Abstract A stability analysis of soils prone to liquefaction based on their undrained shear-strength characteristics is an indispensable challenge in earthquake geotechnical engineering. This paper presents a laboratory study of the influence of relative density on the cyclic behavior of Chlef sand. The experimental program includes undrained, triaxial cyclic tests that were carried out for three different relative densities (Dr = 15, 50 and to 65 %) with various cyclic stress ratios (CSR = 0.15, 0.25 and 0.35). All the samples were consolidated under one initial effective confining pressure σ'c = 100 kPa. The main results show that the increases in the relative density led to significant increases in the shear strength established by an increase in the number of cycles and with an exponential rise. In contrast, it was demonstrated that the number of cycles was decreased when increasing the cyclic stress ratio due to the shearing frequency. The two main effects of the studied parameters did not have the same influence on the cyclic undrained response of the sandy soil submitted to seismic loading: an increase of the deviatoric stress due to the high relative density that participates in the increase of the loading capacity of the compacted soils by minimizing the void ratios, and an increase of the pore-water pressure that has a negative effect on the liquefaction of the soil. From the results obtained, it can be concluded that these two mechanisms led to a global increase of the maximum shearing stress.

Soft soils have a high compressibility, and low shear strength, and constructions on such soils often require the use of ground-improvement techniques. This paper compares the use of an electrokinetic (EK) treatment of soft soils using the ionic solutions calcium chloride and sodium carbonate. The effects of the ionic-solution type, the EK-treatment duration, the cation exchange capacity (CEC), the specific surface area (Sa), the pH, the electrical conductivity (σ), and the ionic strength (Is) were considered in this study. Examining the parameters and evaluating their effects on soil behavior are difficult and complex. The design of experiments (DOE) software program was used to evaluate the effects of the parameters and determine the significant input factors for the EK treatment on soft soils. The analysis and optimization of the data produced the threshold values using the design-expert® software. In this study, the EK-treated soil with CEC = 4.9 meq 100/g, Sa = 4.5 m2/g , pH = 9.5, σ = 6.0 S/m, Is = 1.55·10-4 mol/L, and electrolyte-type setup of CaCl2-Na2CO3 gave better soil strengthening. The gain in strength is attributed to the flocculation and aggregation of the EK-treated soil particles. The analysis of the data by DOE indicated that it could be used to assess the significant effects of the input factors on the unconfined compressive strength, qu of the EK-treated soft soils.