A thesis submitted to the Civil Engineering Department of Daffodil International University (DIU) in partial fulfillment of the requirements for the degree of. Daffodil International University iii Thesis entitled "Effect of Water Content on Unconfined Compressive Strength of Clay". It is hereby declared that this research work has been carried out under the supervision and guidance of Mohammad Mominul Hoque, Assistant Professor in the Department of Civil Engineering at Daffodil International University, Dhaka Bangladesh.
Authors would like to express their appreciation to Mohammad Mominul Hoque, Assistant Professor, Department of Civil Engineering, Daffodil International University, for continuous assistance and guidance throughout the process of completing this research. Hussainuzzaman, Associate Professor and Head, Department of Civil Engineering, Daffodil International University for his valuable advice and support. In this research, the effect of water content on unconfined confined compressive strength of two different clays is investigated.
In unconfined compressive strength tests, cylindrical specimens of 38 mm diameter and 76 mm height are prepared at 90% of the maximum dry unit weight with different water contents in the plastic limit region. The experimental results showed that the water content has remarkable effects on the reduction of the unconfined compressive strength, and this reduction is dominant while the water content reaches almost the liquid limit. It is also observed that the unconfined compressive strength of the clay is linearly related to the water content.
It is expected that the result of this research can be used to predict the reduction of unconfined compressive strength with changes in water content.
GENERAL
THESIS BACKGROUND
OBJECTIVE OF THE STUDY
SCOPE OF THE STUDY
Based on this result, unconfined compression tests were performed for both clay with different combinations of water and plotted on a log graph.
ORGANISATION OF THE THESIS
GENERAL
UNCONFINED COMPRESSIVE STRENGTH
Daffodil International University 6 The shear strength (su) of clay is equal to half of the unconfined compressive strength (qu) when the clay is below φ = 0, where (φ = is the angle of internal friction).
APPLICATION OF UNCONFINED COMPRESSIVE STRENGTH
INFLUENCING FACTORS OF UNCONFINED COMPRESSIVE STRENGTH
SPECIMEN SIZE
The result of these studies mainly agreed that the strength properties are affected by the sample size. Yoshinaka (1976) and LO, (1970) mentioned that the strength properties are affected by the sample size for fractured clay and stone materials respectively. From this research, they obtained that there is no effect of sample size on deformation characteristics and strength if the ratio of sample length to diameter is 2, for the diameter greater than 20 mm.
SAMPLE RECONSTITUTION
SAMPLE DISTURBANCE
PREVIOUS RESEARCH
Daffodil International University 10 Finally, previous studies regarding the effect of water content on clay are presented and it appears that a very limited number of studies have been conducted to find out the effect of water content in clay.
GENERAL
In this study, the liquid limit of the representative sample is mainly used to find the approximate range of water content for reshaping the clay sample for unconfined compressive strength test, where clay liquid played a crucial role. Moreover, the water content at which the behavior of clay changes from plastic limit to liquid limit is also based on this experiment. The plastic limit of representative clay is mainly used to find the water content at which clay samples change from plastic state to semi-solid state.
The plasticity limit of the specimen is an essential parameter for the unconfined compressive strength test. Given the phenomenon that cohesive soils become plastic as their water content increases, this also leads to a loss of shear strength and stability. For this study, nine series of unconfined compression tests are conducted on reshaped clay samples made from a representative clay sample and at three different water contents for clay-1 and seven different water contents for clay-2 to capture different clay wettities under different conditions at the field. The unconsolidated undrained shear strength of the cohesive is equal to half of the unconfined compressive strength.
Second, test specimens are prepared at different water contents for clay-1, such as moisture content is 25%). The unconfined compaction test was conducted for two different types of clay with different water contents and the results are shown in Figure 4-1 and Figure 4-2. It is also observed that the unconfined compressive strength of the clay has a linear relationship with the water content in Fig 4-3 and Fig 4-4.
The water content has extreme effects in the reduction of unconfined compressive strength, and this reduction is predominant while the water content reaches close to the liquid limit. It also observed that the unconfined compressive strength of clay has a linear relationship with water content. The result of this research can be used to predict the reduction of unconfined compressive strength with changes in water content.
Currently, determining the allowable structural strength of clay is a difficult task, but the effects of water content must be taken into account. Typically, laboratory samples used to determine the shear strength of soils are prepared at the same water content and dry density as field conditions, regardless of the fact that the conditions may not remain the same in the future. Pore water pressure measurements were developed to determine their effect on the saturated strength of clays.
LABORATORY TEST FOR INDEX PROPERTIES
SPECIFIC GRAVITY
HYDROMETER ANALYSIS
ATTERBERG LIMIT TEST
- LIQUID LIMIT
- PLASTIC LIMIT
Therefore, in this study, plastic limits test will perform significant amount on unconfined compressive strength test.
COMPACTION TEST
UNCONFINED COMPRESSIVE STRENGTH TEST
APPARATUS
To perform the unconfined compressive test in the laboratory, a number of apparatuses are used according to the testing machine and the reformed sample, such as unconfined mold, wooden dowel about 2 inches in diameter, compression device, dial gauge, strain indicator, number comparator, balance, timer, oven, spatula and many more. Where, for cohesive soil with an unconfined compressive strength of less than 1.0 tsf, the compaction equipment is capable of measuring the compressive stress to within 0.01 tsf and the unconfined compressive strength of the soil 1.0 tsf or moreover, the compression device also has the ability to measure compressive stress to the nearest 0.05 tsf. The deformation indicator shall be a dial indicator graduated to 0.03 mm or better and having a travel range of at least 20 % of the length of the test specimen.
In this study, the maximum travel range of 15% of the length is sufficient to obtain accurate results. The dial gauge shall be capable of measuring the physical dimensions of the specimen to within 0.1 % of the measured dimension. The balance used for weighing the specimens shall determine the weight of the specimen to within 0.1% of its total weight.
For reshaping the disturbed specimen, the ideal mold impact on the specimen, in this specimen to avoid any effect of specimen size the ratio of diameter to height is 2.0 is used, here the mold size is 38 mm in diameter and 76 mm in height.
EQUATIONS FOR CALCULATIONS
LIMITATIONS OF UNCONFINED COMPRESSIVE STRENGTH
Daffodil International University 19 number of bladders is applied to achieve targeted density and sample height. To perform an unconfined pressure test, extruded clay sample is placed in a loading frame on a metal plate (fixed between the end plate) by turning a crank and then raising the level of the bottom plate. Then the top of the sample is held by the top plate, which is attached to the calibrated test ring.
As the bottom plate is lifted, an axial load is applied to the specimen. Then the load is gradually increased to the sample and the readings are periodically taken of the force applied to the sample and the resulting deformation. Then all the measured data is used to determine the stress vs strain characteristics of the clay samples.
This chapter discussed about the unconfined compressive strength result of representative samples, which are evaluated from laboratory investigation. It was found that the unconfined compressive strength of clay continues to decrease with increasing water content, in the case of both clay-1 and clay-2 specimens. There is no one specific reason for a decrease or increase in strength of the representative sample tested.
The effects of water content on clay strength have been presented to highlight the fact that moisture, which is always present in the field with variation of water content and the variation of water effects on clay, must be considered in future soil mechanical design. It may also become economical to dewater a zone which shows a pronounced weakening with the presence of water or, on the other hand, to saturate an area where pitting is desired. The effect of water and strength on open pit mining and tunneling and slope stability design must also be considered.
The shear strength of soils is greatly affected by water conditions, especially if the soil contains clayey materials. 34;Effects of moisture content in compression on the shear strength of an unsaturated clay." Geotechnical and Geological Engineering.
SAMPLE PREPARATION
TEST PROCEDURE
DATA CALCULATIONS
GENERAL
RESULTS AND DISCUSSION
CONCLUSION
SIGNIFICANCE OF RESEARCH
RECOMMENDATIONS
34;Secondary mechanical disturbance; Effects in Cohesive Soil Sampling, Proceedings of Special Session, Quality in Soil Sampling.” Fourth Asian Conference, International Society for Soil Mechanics and Foundation Engineering, Bangkok.
