Investigating changes in elastic modulus, bed reaction coefficient and bearing capacity in soil improved by lime, lime, cement, geogrid using plate loading test.

Civil Engineering Master's Thesis - Soil and Foundation Mechanics

Abstract

From the past until now, one of the most economical methods to improve the mechanical properties of clay soils has been stabilization by means of additives such as lime and cement in construction projects such as road construction and building bed consolidation. Also, with the passage of time and the emergence of synthetic and polymer materials such as geosynthetics and their combination with cement and lime in the last few decades, such materials have also helped and improved the soil resistance parameters, and the reason is that adding lime to clay will change the behavior of the soil from ductile to brittle, and this is while adding a percentage of cement and using Geosynthetics between stabilized soil layers can be considered as flexible soil behavior. Also, according to the conducted research, the use of geosynthetics will increase the bearing capacity of the stabilized layer in foundations of different dimensions. In this situation, the desired features can be obtained by performing a page loading test using a small page and generalizing the results. According to the preliminary studies that have been done, the dimensions of the loading plate as well as the thickness of the stabilized layer will be effective in the obtained results.

However, in this research, we will examine the effect of additives: lime, cement and geosynthetics such as geogrid and their combination on characteristics such as stress-strain behavior, compressive strength, modulus of elasticity, reaction coefficient and settling rate of clay soil using various laboratory and in situ tests (relying on plate loading test).

Key words: consolidation, clay, test Loading plate, lime, cement, geogrid.

General research:

Establishing various construction structures on weak or soft soils is often unavoidable. In this situation, it is necessary to choose appropriate methods to improve the physical and mechanical properties of the soil.

One of these methods is soil stabilization using a variety of additive materials such as lime, cement and geosynthetic materials such as geogrid and geotextile. Calcium hydroxide is mixed and condensed at the optimum moisture content. In this situation, according to extensive research conducted in the past, many geomechanical properties of clay can be improved, including: increasing the uniaxial resistance and bearing capacity of California, and as a result, increasing the bearing capacity, reducing the range of dough, as well as reducing the swelling ability, but increasing the brittleness and brittleness of the soil. The increase in brittleness in earthquake-prone areas will create risks for the structure due to the production of shear waves and the failure of stabilized soil. Therefore, with the advancement of technology and the production of materials such as cement, the use of the combination of both additives or the use of cement has increased day by day. The first cement stabilized soil was in 1935 on a road in southern California that is still in service. The main reasons for using cement in stabilization are its effectiveness in dealing with soils with different characteristics, easy access, simplicity and ease of use in implementation and cost savings.

In general, soil is a material that resists pressure and shear well, but does not show much resistance to tensile forces. In ancient times, it has been experimentally seen that the roots of trees or plants have been used to strengthen the soil mass, and from ancient times until now, people built their houses with a mixture of straw and mud, which in this mixture of straw has a reinforcing role and acts like a tensile element. to be A major category of these elements are geogrids. In fact, by using these elements, the shear resistance of the soil mass increases. Investigating the action of soil-reinforcing element is one of the most important factors in the design of reinforced soil. The efficiency of this system depends on the mobilization of the frictional resistance between the soil and reinforcement elements.

Despite proving the efficiency of these additives, it is necessary to accurately determine the amount of changes in the basic parameters depending on the bearing capacity of the foundation.

Despite proving the effectiveness of these additives, it is necessary to accurately determine the amount of changes in basic parameters depending on the bearing capacity of the foundation and the amount of settlement, such as: the substrate reaction coefficient (Ks) and the modulus of elasticity (Es). One of the best methods to determine these values ??is the Plate Load Test, which in this research we will get to know the principles of conducting and interpreting this important test. In general, this research includes 2 The chapter is:

•       Chapter 1: Application, method and interpretation of plate loading test on the soil mass

In this chapter, we will discuss concepts such as: scope of application, cases of use, preparation, method of performing and interpretation of plate loading test results, as well as generalization of the test results to obtain the permissible bearing capacity and foundation settlement of structures. to types of additives such as: lime, cement and geogrid

This chapter includes: reviewing the history of research presented in this field and presenting their results. How to conduct the test, determine the findings and interpret the test findings. The test is done with various layouts and arrangements as well as different loading methods, which should be considered in each case, the limitations and interpretive aspects of the test. Of course, building a foundation with real weight and loading it is undoubtedly the best way to determine the earth's resistance. But it is not desirable to do this for two reasons. First, it is very expensive, and second, the ground resistance can only be obtained for foundations of one size, and if the foundations of the building have more than one size, multiple tests are needed. In this situation, by conducting the test on a small plate and generalizing the results (taking into account the necessary aspects), the desired characteristics can be obtained: 1-1-1- Purpose: The purpose of this test is to help determine important parameters such as Young's modulus, substrate reaction coefficient, and allowable resistance of the tested materials, and finally to determine the earth's resistance during foundation construction. 1-1-2- Scope of application:

The loading test consists of: placing a rigid plate (often steel) on the soil and applying pressure on it, along with measuring the amount of plate sinking into the soil, according to the amount of pressure applied. Normally, round plates with diameters of 60, 45, 30 cm are used. The use of larger screens (even the size of the main foundation) is also common and customary. [1] Often, the coarser the soil size (non-homogeneous soil), the better the use of larger screens, and it is preferred that the diameter of the screen is greater than 10 times the size of the largest soil grain. It should be noted that the screen can be placed on the ground, deep on the floor or on the walls and ceiling.  Considering that the dimensions of the loading test plate are often small compared to the dimensions of the original foundation and the stress penetration depth is smaller than the original foundation (Figure 1-1), if there is stratification or difference in geotechnical characteristics in the influence range of the foundation, generalization of the test results for the foundation should be avoided. It is obvious that the results obtained from the test are valid in line with the applied load, and especially in heterogeneous and heterogeneous soils, this point should be taken into account when generalizing the results. Settlement estimation

1-3- Test preparation

1-3-1- Prerequisites

Before starting any workshop study in the field of plate loading test, all the necessary equipment, including: jacks, pressure gauges and measuring devices, must be measured. This should be done at least once every six months. Ensuring the proper functioning of the gauges is more important than starting any test. 1-3-2- Preparation of the test site In tests that are performed on soft soil and clay, the test site must be completely intact and any damaged or loosened materials must be removed. The surface to be tested should be smooth and if possible, it is better to prepare it by hand. It is suggested to smooth the test surface with plaster or cement mortar. If the tested surface is very hard, it is necessary to use several layers of plaster or cement mortar to obtain a completely smooth surface.