Key Engineering Materials Vol. 857

Abstract: The effect of adding sand on clayey soil compressibility is investigated in this study. Four different percentage of clay-sand mixtures are used; 100% clay with 0% sand named 100C, 30% clay with 70% sand named 30C-70S, 15% clay with 85% sand named 15C-85S, and 100% sand named 100S. The used clay was obtained from Baghdad city in Iraq and classified as CH soil, while the used sand was taken from the sand quarry in Al-Khider area from Al-Muthana Governorate in Iraq and classified as SW soil. The initial dry unit weight for all mixtures is 18 kN/m³. The results show that the variations of the soil compressibility properties with soil components content changes almost linearly The results show that the preconsolidation stress (P_c) decreases with 19% and 38% and the rebound index (C_r) decreases with 4 and 53% and the compression index (C_c) decreases with 39 and 68% as the sand percentage increases with 70 and 85% respectively. Finally, predicted (fitting) Equations are achieved for the change of the soil compressibility properties with clay content with good agreement.

Abstract: The purpose of this study is to discuss which constitutive law can describes at best the observed behavior of Silt and Gravelly Clay on the basis of experimental and analytical results. To find numerical solution for saturated soils in oedometer test Plaxis 2D the finite element software was used. In order to obtain the compressibility, excess pore pressure and degree of consolidation curves; two constitutive laws were used in this work: the Soft Soil Model ‘SSM’ and the Modified Cam Clay Model ‘MCC’. Predicted results were found in good agreement with measurements obtained from experimental test and analytical solutions. The Soft Soil is in good agreement with experimental results in the compressibility curve; however the Modified Cam Clay Model is the most appropriate if compared with the analytical solution.

Abstract: This article aims to study the Performance footing on loose sand soil reinforced with geogrid layers The Load Settlement behavior of the footing under various conditions such as different eccentric value (e), depth of the first geogrid layer (u/B), and vertical spacing between geogrid layers (z/B) was studied. This study presents, the numerical modeling utilizes the finite element package (PLAXIS version 8.2). The soil vertical stress displacement, axial force and footing displacement are discussed by means of a set of finite element results and the validation. The Load carrying decrease with increasing eccentricity values were shown. The optimal spacing between any successive reinforcement layer (z/B) is equivalent to (0.5) for different eccentricity value (e). The PLAXIS output show the failure mechanism developed, and maximum axial force that will be reached in geogrid and footing and the total stress distribution at failure.

Abstract: Road specialists in the world often suffer the huge challenge in designing a stable road on very soft saline soils, these soils in arid zones have a low bearing capacity with high compressibility and very sensitive to moisture and synchronized with complete collapse. The case study concerned by the deterioration of main road linking between ‎Alsamawa town and Sawa lake approximately 20 km away from Alsamawa town. There are sections of roads affected by converges of nearby local artificial ‎lakes , water drawn from several good drain down to (80) meters depths and causing the deterioration in the road sections , swell-collapse test results represented by a little swell potential values were appeared for zero applied stress, while aggressive collapse were happened with increasing in applied stress, and the increasing in degree of collapsibility corresponding to increasing of applied stress of (50,100,200) KPa, and sodium chloride (NaCl%) in soil layers range between (0.613-16.468) % and slightly to moderately gypseous soils, the case study included several recommendations to treating the deteriorated significantly of road to protect the sub-grade and subbase layer .

Abstract: Many methods have been used for soil improvement at site, one of these methods is grouting. Cement grouted soils consist of particulate soil media and cementation agents. Such soils have been widely used to improve the shear strength and stiffness of weak soils and for preventing of water seepage through soils. The modulus of subgrade reaction may give a good indication about the soil bearing capacity and stiffness. This geotechnical parameter can be measured by using the plate load test. In this study, an experimental work is done to assess the improvement in the stiffness of sandy soils by injection two different cementing agents (cement and colloidal silica). The work includes plate loading tests with two different plate diameters (B= 150 and B= 250 mm). The effects of plate size, depth of the grouted zone (0-B and B-2B) as well as the effect of grouting material type on the performance of the grouted soil are investigated. The results show that the colloidal silica grout is more effective in increasing the modulus of sub grade reaction (k_s) than the cement grout. Also, the use of plate with 150 mm diameter gives higher value of (k_s) than that of 250 mm diameter. Furthermore, grout injection at depth (from 0 to B) gives a higher value of (k_s) than that for deeper grouted zone.

Abstract: The interest in expansive soils goes as far as they were considered as a new phase of soil mechanics. Problems associated with potential volume change of soils occur worldwide, mainly in the arid and semi-arid climatic region, as is the case of the country of this research. These problems are particularly existed in regions where the variation in the moisture content can cause a potential expansiveness of the soil. In fact, Bentonite/Sand mixture represents one of the available answers for the geotechnical engineering problems such as heaves, cracks and other damages caused by swelling and shrinkage. This mixture may be used to 1) reduce the settlement time of structures, and 2) increase the permeability of soils. The main target of the present work is to demonstrate the influence of adding sand on an expansive soil (bentonite) behavior. This includes an investigation to the effect of the amount and the particles size of sand on the physical properties of the expansive soil. The reduction in swelling and swelling pressure of the expansive soil by the addition of different percentages and different particles size of sand and the consequent effect on strength characteristic were also studied. Thirteen samples of Bentonite/sand mixture were used in this study to evaluate the effect of the sand percentages on the swelling behavior. To implement the laboratory program, many tests were used which were sieve analysis, Atterberg’s limits, compaction, and free swelling test with swelling pressure test. The results indicated a reduction in the liquid limit of around 55% and in the plastic limit of around 54%, where the increase in the maximum dry density was 46%. On the other hand, the reduction in the swelling pressure was 87.5%.

Abstract: The present research has been conducted to trace the various effects of Mosul city demolition waste materials (DMs), on the geotechnical properties of clay. The properties of the samples have already been investigated and evaluated. Moreover, cement has been added to upgrade these properties. Finally, the fine demolition has been added to a highly expansive soil selected from the site of the University of Mosul to reduce the swelling potential. In fact, the experimental work includes: The Abrasion, index and compaction properties, swelling and strength of stabilized and treated expansive soil. The laboratory tests include the testing of consistency limits, unconfined compressive strength (UCS), compaction (standard and modified), swelling, consolidation, and Abrasion test by Los Angeles Machine. The Results show that, increasing the old and new demolition (OD and ND) percentages lead to a decrease of liquid limit and plasticity index of clay, respectively. The increase in maximum γ_dry for the clay has been noticed when the OD and ND content has been added from 5 to 25%. A reduction of optimum water content (opt) for clay was optimized also by increasing the demolitions percentage to 25%. Also, the UCS strength values of the clay have been increased by increasing the demolition materials (DMs) percentage from 5 to 25%. The odometer characteristics, including the swelling and consolidation of DMs-clay mixtures, were controlled mainly by the type of the demolition. The final result indicates that the presence of old and new demolition waste could improve the clay engineering properties of the stabilized soil. Untreated and cement treated (OD) and (ND) materials could be successfully used as a base or sub-base for road.

Abstract: This study focuses on investigating the impacts of kerosene on the physical, mechanical, and chemical characteristics of clay soil. The soils specimens are contaminated artificially with six ratios of kerosene (5, 10, 20, 30, 40, and 50) % calculated according to the dry weight of soil. The artificial contamination includes air drying of the disturbed soil, then placed in plastic containers and mixed with the field water content and the specified concentration of kerosene to ensure getting homogenous contaminated soil specimens. The contaminated soil specimens left for 30 days in plastic containers covered by nylon sheets to control the water content and prevent volatility of contaminant. The results of tests proved that different ratios of kerosene have different impacts on the engineering and chemical characteristics of soil specimens. The specific gravity, percentages of fine particles, optimum water content, the initial and final void ratio, coefficient of consolidation, swelling index, permeability, the undrained shear strength, effective shear strength parameters, and the rate of reduction of initial pore water pressure are reduced significantly with increasing the content of kerosene in soil. Generally, the concentration of kerosene less than 10% has slight impacts on the studied characteristics of soil specimens.

Abstract: Swelling soil is a type of problematic soils. It always causes different types of failures such as cracks experienced by structures founded on this soil due to swelling. A residential compound has been built as one-story houses in Sargalu (Kurdistan region, Iraq) experienced cracks. These failures appear in different shapes of cracks mainly diagonal in walls under the window openings and hair cracks in walkways. The soil of site is clay soil with moderate to high plasticity and swelling potential. This classification of the soil was investigated by taking specimens form pits so closed to the foundation of the structures. The soil properties were studied: soil grain size distribution, plasticity indices, unconfined compression strength, and water content. The diagnose gives the cause of the deterioration to the houses, which is as a result of swelling potential of the clay soil due to the seasonal variation of moisture content.

Abstract: In the present study, 24 laboratory models on soft clay treated with stone columns were carried out. The results for each case are analysed for the purpose of constructing a statistical model linking the variables studied. The experiments showed that the stress concentration and bearing capacity of soil treated with stone column increase with increasing the undrained shear strength (cu), number of columns and L/d ratio. The models represent a single stone column and a group of stone columns. The studied variables are three dependent variables, the stress concentration ratio (n), bearing capacity of soil treated with stone column (q) and the settlement improvement ratio (S_r) due to the existence of stone columns. The independent variables are six: the undrained shear strength of clay soil, with three values (6, 9 and 12 kPa), the number of stone columns (1, 2, 3 and 4 columns) and the length (L) to the diameter (D) of the stone column or (L/D) ratio in two values (6 and 8). Besides, the bearing capacity of the soil treated (q) with stone columns and the settlement improvement ratio were used in some statistical models as independents. After regression analysis, a set of equations that correlate the previous variables have been suggested. The incepted values for dependent variables are close to the laboratory results.