Stabilization and modification of geotechnical characteristics of windy sand using polymer slurry

Dissertation

To receive a Master's degree

Civil Engineering - Soil and Foundation Mechanics

Abstract

The purpose of this research is to improve the mechanical and geotechnical properties of windy sand soils. Because one of the major problems of windblown sand is its low resistance under natural and saturated moisture conditions, a laboratory study was conducted to investigate the effect of adding polyvinyl alcohol polymer in improving the geotechnical properties of windblown sand. The results of compaction tests showed that the addition of this polymer up to 0.2% by weight increases the maximum dry weight and there is no significant change in the optimal moisture content. The results of the tests also showed that with the increase in the polymer percentage, the CBR resistance of the samples increases to a significant amount, so that in the samples made with 0.5% by weight of the polymer, the CBR value reached 185; This value is more than 5.7 times CBR for soil without additives. Considering the solubility of the above polymer in water, cement was used to protect the mixture of soil and polymer against scouring. Experiments showed that by adding 2% of cement to the above mixture, both the strength of the samples increased and their stability against scouring increased. The results of the direct shear test showed that the addition of polymer also causes a significant increase in the shear strength of the samples. Of course, soil failure in this case was observed as brittle and sudden failure. To prevent this situation and to make the samples more malleable, tire fibers were used. The optimal amount of fibers needed in this case was equal to 0.6% by weight. The results of uniaxial tests also showed that the addition of polyvinyl alcohol increases the compressive and shear strength of the soil to a very significant extent. It was also found that the simultaneous combination of polymer, cement and fibers to the soil has the greatest effect in modifying the characteristics of windy sand. For example, in the combination of 0.4% polyvinyl alcohol, 2% cement and 0.6% tire fibers with air sand, the compressive strength of the sample reached 15 kg/cm2; While the compressive strength for windblown sand with 2% cement was only 0.3 kg/cm2.

Chapter One Introduction

Work Prospects

Undoubtedly, one of the most preliminary and important principles in the implementation of construction projects is to have a resistant land for construction, which due to the increasing growth of the world's population in recent years, the area of ??suitable land for construction is gradually decreasing. is In such a situation, finding new and fundamental methods to improve and correct unsuitable land has created a fierce competition among civil engineers in developed countries, and in fact, it must be accepted that the development of specific techniques and methods as much as possible will be necessary for humans to achieve this goal. What makes one method superior to another method is economic parameters, implementation conditions and problems, available facilities, and time and place limitations. Basically, obtaining high-quality materials that are economical and can easily withstand the loads applied by the structure is the main motivation of soil modification[1]. Problematic soils, such as loose soils with low bearing capacity and high settlement, have two ways in front of geotechnical engineers: a) Using load-bearing elements in the soil. b) Improving and correcting the physical properties of the soil. Improvement (or modification) refers to a set of operations that lead to the removal of some inappropriate behavior of the soil or the imposition of appropriate behavior on it. Basically, the main goals of improvement are: increasing the soil resistance, reducing the general characteristics of deformation and removing some inappropriate behaviors or adding some appropriate behaviors to the soil. There are wide soil stabilization methods that are used in each case according to their specific conditions, but in general they can be divided into two categories: chemical stabilization and physical-mechanical stabilization. The purpose of chemical stabilization is to modify the desired properties of the soil with the help of additives, which are obtained in terms of chemical interactions resulting from these materials in the vicinity of the soil. The meaning of physical stabilization of soil is stabilization and modification of soil properties without changing the chemical properties of soil.. This type of stabilization can be implemented in different ways, soil reinforcement is one of these methods.

In Iran, taking into account the climate and geographical conditions, as well as the existence of vast areas of deserts, where most of the soils in these areas are fine-grained sands (windy sand), because one of the major problems of windy sand soils is their low resistance under natural moisture and saturation conditions, perhaps one of the major obstacles in the field of developing the country's road network and construction projects is the existence of this type of sand. in a wide area of ??the country. It is natural that if the loan sources are far away from the axis of the road or construction projects, as is the case in the Central Desert, Lut Desert or the southern deserts of the country, the cost of road construction and soil improvement in the region will be several times higher than usual. For this purpose, it is very important to study new methods that are able to improve the soil of the land covered with windy sand, and this research is in this direction.

3-1-Overview of the materials presented in this research

In the second chapter, the generalities and history of research related to improving the properties of sandy soils are reviewed.

The third chapter describes the research method and laboratory programs.

In the fourth chapter, the results of the experiments and their interpretation are discussed.

The fifth chapter includes conclusions and proposals, and at the end, the sources are introduced.

The second chapter, research background

Introduction to soil improvement, materials and methods used

In this section, various materials that have been used so far to improve sandy soils are briefly discussed. The materials used in general include the following:

Using waste materials

Using natural fibers

Using synthetic fibers

Using abandoned polymer and petroleum materials

2-2- Using waste additives in order to improve the properties of sandy soils

Producing a huge amount of worn materials with a long lifespan and not providing a principled and correct solution for Burial, recycling or optimal use is one of the issues and problems that have arisen in recent years. In addition to improving soil properties, adding waste materials can also be considered from the two perspectives of disposal of waste materials and reduction of operational costs. In this research, several things are briefly mentioned. 1-2-2- Improving the properties of sand stabilized with cement and waste glass shards. For the first time in 1917, Amis [2] registered the soil-cement mixture as an invention in Philadelphia, America, and after him in 1922, the State Highway Organization of South Dakota and Iowa and subsequently in the year In 1932, the South Carolina Road Department used this mixture to stabilize the roads and build highways [1]. During the years 1940-1950, research was conducted on the effective factors of compacted improved soil in the road bed [2]. Cementation [3] in its general meaning is cementing and sticking, and in geotechnical engineering, it refers to the sticking of soil particles to each other and creating a sticky mass with greater resistance. Artificial cementation has generally been investigated in relation to sands. Because coarser materials such as coarse-grained sands generally do not need to be improved and often have favorable geotechnical characteristics, for this purpose, in order to improve the soil by using its artificial cementation, researchers have focused more attention on sands and fine-grained materials[3].

After cement is added to the soil, various reactions take place between soil and cement. The most important of these reactions in the short term is the substitution reaction of positive ions and the accumulation-condensation reaction. In these two reactions, the soil texture changes with the accumulation of particles next to each other in a kind of granulation and its resistance increases. The finer the cement particles, the more hydration [4] is done and for a longer period of time, even for many years, and this goes back to the increase in the strength of the cement composition with time [4].

Dupas and Packer [5] in 1979, studying the static and mechanical properties of sand-cement in order to improve the sand and avoid the risk of liquefaction, showed that by increasing the amount of cementing agent, the adhesion of the soil increases and adding 5% of Portland cement 200-300 kPa creates adhesion in sandy soil [5].