Key Engineering Materials Vol. 857

Abstract: There are many constitutive models that have been used to model the mechanical behavior of soils. Some of these models are either unable to represent important features such as the strain softening of dense sand or required many parameters that can be hard to obtain by standard laboratory tests. Because of that, a more reliable constitutive model, which is capable to capture the main features of the soil behavior with easily obtained parameters, is required. The Hypoplasticity model is considered as a promising constitutive model in this respect. It is considered as a particular class of rate non-linear constitutive model at which the stress increment is expressed in a tensorial equation as a function of strain increment, actual stress, and void ratio. The hypoplastic model required only eight material parameters (critical friction angle critical, maximum and minimum void ratio respectively), granular stiffness h_s and the model constants n, α, β). The appealing feature of the hypoplastic model is that the material parameters are separated from the state variables (void ratio and the initial stresses). This feature enables the model to simulate the soil behavior under a wide range of stresses and densities with the same set of material parameters. In this research, a brief description of the Hypoplasticity model is presented. Detailed discussions regarding the measurement and calibration of the model parameters of an Iraqi soil are then exposed. It is concluded that only Consolidated Drained (CD) triaxial test, oedometer test, and the well-known limit density tests are needed to get all the parameters of the hypoplasticity model.

Abstract: In this study investigates utilizing of slag as an additional material to improve engineering properties of contaminated soil by crude oil to changing the engineering characteristics to be satisfying and compatible, this is due to its pozzolanic reactivity. The aim of this study the impact of slag material in geotechnical engineering and to stabilize properties of contaminated soils. Two percentages of slag were utilized in this study, which is 0% and 6%. Compaction and direct shear strength tests had been conducted on the artificial contaminated prepared soil samples. In the results, showed that the increasing of slag leads to a decrease in the optimum water contents while the maximum dry density values increase. Furthermore, the shear strength is improved by utilizing slag so that slag can be considered as a stabilizing material to improve the properties of contamination soil.

Abstract: The civil engineering projects that includes soft clay within its activities has a serious concern of hazards, such hazards can be overcame by treating the existing soils by certain materials which are named as "stabilizers". The common materials that are highly used in this field are ordinary Portland cement, fly ash, lime and rice husk ash, etc. Each one of these stabilizers has its known shortcomings. The alkali activation of any alumina silicate source produces some kind of cost effective primary binding gel which is known as "Geopolymers". This study is devoted to investigate the role of liquid over fly ash ratio to some soil – FA based Geopolymers geotechnical properties. Such ratio is taken as 2.71, 3.167, 3.8 and 4.75 respectively within the experimental program and the investigated geotechnical properties are the specific gravity, liquid and plastic limit, compaction characteristics and California bearing ratio. The tests results showed that the maximum dry density decreased about 42 % at 2.71 liq/FA whereas this the specific gravity decreased 27 % at the same this ratio. In addition, the 3.8 and 4.75 of such limits revealed no plastic behavior due to the high presence of liquid.

Abstract: Dry density modeling is a valuable issue. Artificial neural networks (ANNs) have been used in many problems in geotechnical engineering and have demonstrated great success. In this paper, the ANN model is proposed to predict the dry density of the soil. The developed model is managed by the Matlab Neural Network Interface (R2016a). To create the ANN model, liquid limit, plastic limit, plasticity index, moisture content, specific gravity, finer accuracy than sieve 200, total suspended solids, organic and SO₃ were selected and used as input parameters. There are (9, 6,5 and 3) nodes, (10) nodes and (1) node used for input, hidden layers and output layers, respectively. The value of dry density obtained from three sources was sympathetic. The first source is the experimental results of 99 soil samples conducted in Al-Najaf Institution laboratory for this study. The second source was to propose the expected dry density using multiple linear regression analysis (MLRA) on the samples used in the first source; The results show, that the prediction of the use of ANNs was closely consistent with the experimental data. Correlation coefficient (R²) and mean square error (MSE) were 0.97368 and 3.19474 10^-3, respectively. The observed results of the proposed system were very comparable with those obtained from empirical analysis and the prediction obtained from multiple linear regression analysis, where the advanced ANN approach is applicable.

Abstract: The main aim of this research can be represented as a trail to computerize the most soil engineering properties to compute them automatically using many simple Microsoft Excel functions based on raw soil test experimental data. This work will be shortening the time and effort of the geotechnical engineers calculating different soil parameters with acceptable accurate values. Nine different Microsoft Excel formulas, some of the techniques by certain Excel expressions and normal designed algebraic equations were used to present the final spreadsheet. The main computed soil parameters were (ω, LL, PL, PI, ρ_d,max, ω_opt, k) soil classification AASHTO, (q_u and c_u) for unconfined compression test, (ø and c') for the direct shear test finally (Cc and Cs) for consolidation tests. To get a better understanding on how most of the programmed tools and to Microsoft Excel sheets work, the user should have knowledge about basic concepts of the certain soil parameter test and experimental steps and also the guidelines of the theory that depends to compute the parameter. Also, the user should have enough background about engineering soil properties laboratory experiments computation.

Abstract: Soft clayey soils cover wide Iraqi areas specially the regions close to rivers and the southern part of this country Heavy weight structures like: highways, dams, multiple story buildings are suffering unacceptable settlement, when constructing on soft soils. The high contamination of water in such soils decrease the effective stress and reduce bearing capacity. The need was appeared to improve such problematic soil by the use of new technique of stone column treated with different percentages of natural bentonite by a series of field tests using full scale concrete footing constructed on soft soil in addition to a laboratory model to investigate settlement with time at constant stress. The soil that used in this study is natural clayey soil, brought from a location south of Diyala governorate, from a farm area. The study includes also: The effect of stone column diameter treated with bentonite on the behavior of footing constructing on soft clayey soil, The effect of stone column length on the behavior of footing on such soils. Results of field and laboratory model tests reviled that the treated model by stone column mixed with 40% bentonite is the ideal one, which reduces the settlement by 55%. In other hand problems of uneven settlements appear when using 60% bentonite as a mix proportion. The Ideal slenderness ratio (Ds/Ls<25%). The effective depth of stone column treated with bentonite is (1/3H).

Abstract: The problematic soils have complex and irregular behavior such as gypseous soils, which concentrated mainly in the dry and semi-dry regions in the world. In Iraq, the gypseous soils cover about 30 to 35% of its total area in the west desert and extended to the southern parts of Iraq. The gypseous soils experience sudden collapse upon wetting. The present paper focuses on studying the effects of nano silica fume (NSF) on the collapsibility and shear strength of gypseous soil before and after soaking. Also, this study, the influence of NSF on the chemical and physical characteristics of gypseous soil have been investigated. A gypseous soil sample obtained from Al-Najaf Sea has gypsum content of 42%. The gypseous soil samples are mixed with three percentages of nano silica fume (1, 2, and 4) % calculated as ratio of the dry mass of soil to measure their influence on the geotechnical characteristics of soil samples. The collapse potential of gypseous soil is reduced with increasing the content of nano silica fume. Also, increasing the content of NSF and curing time resulted in increasing the shear strength of soil samples.

Abstract: Advanced developed technologies associated with people demands have caused production and expansion of different local wastes where the process of managing such waste becomes a real need for controlling the pollution risk. One of the procedures for recycling can be made through using local wastes in permeability control for sandy soil since the soil permeability plays a crucial function on the water drainage, pore water pressure buildup and dissipation, and ground movement for saturated sand during and after earthquake occurrences. In addition, any economical mixture should maintain hydraulic constraints for practice use. In this study, a laboratory experiment was prepared to perform tests for estimating the water movements and permeability in a pure sand column and treated sandy soil with different locally waste materials including plastic, glass, rubber, and aluminum. In addition, a numerical investigation including finite element method has been adopted to verify the experimental procedure. It was shown that the permeability could be controlled to different rates using these local wastes.

Abstract: This study aims to assess the impact of time on sawdust usage to enhance the behavior of the clay used in landfills. The soil used in this paper was brought from Büyükçekmece region / Istanbul. Four proportions (1, 2, 3 and 5) of the sawdust were added as a percentage of the dry weight of the soil. Soil-sawdust mixtures were compacted with the optimum water content corresponding to each percentage and samples were extracted. The extracted samples were divided into two groups, the immediate tests were performed on the first group while the second group was kept in special containers for long-term tests after 90 days. A series of undrained unconsolidated triaxial tests (UU) and unconfined compression tests (UCS) were performed on the specimens and compared with the row soil, in the immediate tests, the results from the UU triaxial test showed that the undrained shear strength was increased as the sawdust content increased and then decreased, it was conducted that the optimum sawdust content was 3%, it was increased the undrained shear strength by (39.5%) and (41.44%) for UU triaxial and Unconfined compression tests respectively. After 90 days of the curing period, it found that 2% is the optimum sawdust content, it was increased the undrained shear strength by (202.51%) and (176.64%) for UU triaxial and unconfined compression test respectively. In the immediate and long-term tests, the coefficient of permeability increased by (66.66) and (94.44%) as the sawdust increased from 0 to 5 % respectively. Sawdust increases the hydraulic conductivity of the clay. It can be concluded that the sawdust usage has a remarkable effect on the shear strength of the clay for both immediate and long-term tests.

Abstract: Stone columns have been used widely to improve the engineering properties of the weak soil. Most of the previous works considered a circular section for the stone columns. In the present study, finite element analysis has been carried out to investigate the effect of stone columns shape and length on the settlement and bearing capacity of soft soil. Accordingly, three types of cross sectional shape for stone columns have been selected which they are circular, rectangular, and square sections with equivalent area. Various length of columns are adopted with diameter of 0.75m that achieved length to diameter or equivalent diameter ratios (L/d=2, 4, 6, 8, and 10) of columns spacing (S/d=3). The results show that the stone columns has tangible effects on the settlement of the soil while has minor effects on the bearing capacity. The settlement of the treated soil with stone columns have L/d=2, reduces by 18.0, 17.3, and 19.3% for circular, rectangular , and square sections respectively. With increasing length of the columns to L/d=10, further reductions in the settlement obtained of (27.1, 28.1, and 27.0%). Bearing capacity of the soil increased slightly with length of the stone columns. Almost all cross sectional shapes of the columns give bearing capacity about same. The increased in the bearing capacity of the treated soil with stone columns have L/d=2, not exceeded 10% for all sectional types. The average increments in bearing capacity when L/d=10 are 12 and 15% at settlement 50 and 100mm respectively. Insignificant changes in bearing capacity upon increasing length of columns from L/d=2 to 10 of maximum 5%. The plastic zone recedes with the increasing length of the stone columns. Finally, from the results obtained, it can be concluded that the stone columns shape has negligible effects on the settlement and bearing capacity of the soil.