Evaluation of Dispersion Potential for Some Problem Soils in Central Myanmar

Dispersive soils which occur in central region of Myanmar are easily erodible and serious problem of stability of embankments, earth dams, earths and earth retaining structures. These soils are found in where the annual rainfall is less than 800 mm. Dispersive soil is structurally unstable and the presence of dispersive soil is indicated by occurrence of erosion gullies, sink holes, spew holes and piping. In some parts of the central Myanmar, disp have to be used for construction purpose since no other soil material is available. Dispersion only occurs in non-saline or rain water. If dispersive soils have been used in the construction of earth embankments, serious piping and f occurred. In Myanmar, some problems are found in central region of Myanmar. The study soil is investigated by emersion test in field and then physical tests are done in Yangon Technological University and chemical tests are done in Irrigation and Management of Water Utilization Department in Myanmar. According to these tests results, most of the study soils are dispersive. This paper presents the results of study soils, soil structural problems along Yangon-Mandalay Express Way, dispersive poten rating for the study soils and the correlation between Exchangeable sodium percentage (ESP) and Atterberg’s limits.


I. INTRODUCTION
Many earth dams, hydraulic structures and other structures like road way embankments have suffered serious erosion problems and have failed due to the presence of the dispersive soils. Though the problem has been identified in many parts of the world in recent times, design advances and technical preventive measures are yet to be fully developed and practiced. As the scope and magnitude of the problem which can result from the use of dispersive soil is very high, preventing the failures caused by the dispersibility of the soils has become one of the major concerns of the geotechnical engineers.
In the past, clay soils were considered to be highly resistant to erosion by flowing water, however, in the last few years it was recognized that highly erodible clay soils exist in nature. The tendency for dispersive erosion in a given soil depends on variables such as mineralogy and chemistry of the clay, as well as dissolved salts in the water in soil pores and in the eroding water. Such clays are eroded rapidly by slow moving water, even when compared to cohesionless fine sands and silts. When dispersive clay soil is immersed in water, the clay fraction behaves like single-grained particles; that is, the clay particles have a minimum of electrochemical attraction and fail to closely adhere to, or bond with, other soil particles. Thus, dispersive clay soil erodes in the presence of flowing water when individual clay platelets are split off and carried away. Such erosion may start in a drying crack, settlement crack, hydraulic fract crack, or other channel of high permeability in a soil mass. Dispersive soils are clayey and silty soils which Evaluation of Dispersion Potential for Some Problem Soils hydraulic structures and other d way embankments have suffered serious erosion problems and have failed due to the presence of the dispersive soils. Though the problem has been identified in many parts of the world in gn advances and technical preventive measures are yet to be fully developed and practiced. As the scope and magnitude of the problem which can result from the use of dispersive soil is very high, preventing the failures caused by the soils has become one of the major concerns of the geotechnical engineers.
In the past, clay soils were considered to be highly resistant to erosion by flowing water, however, in the last few years it was recognized that highly erodible n nature. The tendency for dispersive erosion in a given soil depends on variables such as mineralogy and chemistry of the clay, as well as dissolved salts in the water in soil pores and in the eroding water. Such clays are eroded rapidly by slowter, even when compared to cohesionless fine sands and silts. When dispersive clay soil is immersed in water, the clay fraction behaves like grained particles; that is, the clay particles have a minimum of electrochemical attraction and fail to ely adhere to, or bond with, other soil particles. Thus, dispersive clay soil erodes in the presence of flowing water when individual clay platelets are split off and carried away. Such erosion may start in a drying crack, settlement crack, hydraulic fracture crack, or other channel of high permeability in a soil mass. Dispersive soils are clayey and silty soils which International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456 @ IJTSRD | Available Online @ www.ijtsrd.com | Volume are highly susceptible to erosion. The dispersion occurs when the repulsive forces between individual clay particles exceed the attractive fo Waals attraction) so that when the clay mass is even in contact with still water individual clay particles are progressively detached from the surface & go into suspension.
The principal difference between dispersive clays and ordinary erosion resistant clays appears to be the nature of the cations in the pore water of the clay mass. Dispersive clays have a preponderance of sodium cations, whereas ordinary clays have a preponderance of calcium, potassium, and magnesium cations in the pore water.

II. PROBLEMS DUE TO DISPERSIVE
STUDY AREA The problems related to dispersive soils are common throughout the world. In Myanmar, some of the problems due to dispersive soil are occurred in central region of Myanmar and on the Yangon Express Way embankment. In the past, clay soils were considered to be highly resistant to erosion by flowing water, however, in the last few years it is recognized that highly erodible clay soils exist in nature. Some natural clay soils are dispersed or deflocculated in the presence of relatively pure water and are, therefore, highly susceptible to erosion and piping. Piping failure in embankment is caused by water flowing through the pores of the soil. The erosion occurs mainly in cohesionless soils which have little resistance to the plucking forces of seeping water. With dispersive clay, piping is due to a deflocculating process where water travels through a concentrated leakage channel then occurs along the entire length at the same. Erosion damage in embankments constructed with dispersive soils have generally occurred in areas of high crack potential such as long conduits, in areas of large differences in compressibility of foundation materials. When a concentrated leak starts through embankment constructed of dispersive clay, either of falling two actions may occur: (a) .If the velocity is sufficiently low, the clay surrounding the flow channel swells and progressively seals off the leak. (b) If the initial velocity is sufficiently rapid, the dispersed clay particles are carried away, enlarging the flow channe at faster channel at faster rate than it is closes by swelling leading to progressive piping failure. Some of the failures due to dispersive soil on Yangon International Journal of Trend in Scientific Research and Development (IJTSRD) ISSN: 2456 @ IJTSRD | Available Online @ www.ijtsrd.com | Volume -2 | Issue -4 | May-Jun 2018 are highly susceptible to erosion. The dispersion occurs when the repulsive forces between individual clay particles exceed the attractive forces (Vander Waals attraction) so that when the clay mass is even in contact with still water individual clay particles are progressively detached from the surface & go into The principal difference between dispersive clays and on resistant clays appears to be the nature of the cations in the pore water of the clay mass. Dispersive clays have a preponderance of sodium cations, whereas ordinary clays have a preponderance of calcium, potassium, and magnesium

DISPERSIVE SOIL IN
The problems related to dispersive soils are common throughout the world. In Myanmar, some of the problems due to dispersive soil are occurred in central on the Yangon-Mandalay Express Way embankment. In the past, clay soils were considered to be highly resistant to erosion by flowing water, however, in the last few years it is recognized that highly erodible clay soils exist in nature. Some oils are dispersed or deflocculated in the presence of relatively pure water and are, therefore, highly susceptible to erosion and piping. Piping failure in embankment is caused by water flowing through the pores of the soil. The erosion occurs ohesionless soils which have little resistance to the plucking forces of seeping water. With dispersive clay, piping is due to a deflocculating process where water travels through a concentrated leakage channel then occurs along the entire length at me. Erosion damage in embankments constructed with dispersive soils have generally occurred in areas of high crack potential such as long conduits, in areas of large differences in compressibility of foundation materials. When a rough embankment constructed of dispersive clay, either of falling two occur: (a) .If the velocity is sufficiently low, the clay surrounding the flow channel swells and progressively seals off the leak. (b) If the initial velocity is sufficiently rapid, the dispersed clay way, enlarging the flow channel at faster channel at faster rate than it is closes by swelling leading to progressive piping failure. Some of the failures due to dispersive soil on Yangon-Mandalay Express Way embankment are shown in Figure (1), (2) and (3).

Identification of Dispersive Soil by Emerson Field Test
Field testing is able to identify dispersive soils by observing the behaviour of air dried aggregates soil samples in distilled water or rainwater. The Emerson crumb test is used as an initial test to identify dispersive soil in the field.
Step 1 Collect soil aggregates (2 or 3 pea sized soil aggregates / 1-2cm in diameter) from each layer in the soil profile representative of the soil layers.
Step 2 If moist, dry the aggregates in the sun for a few hours until air-dried (Note: aggregates may not disperse when they should if they have not been sufficiently dried).
Step 3 Gently place the selected aggregates in a shallow glass or jar of distilled water or rain water.
Step 4 Leave the soil aggregates on a stable surface without shaking or disturbing them for 2 hours.
Step 5 Record the results to determine the level of dispersion observed (refer to Figure (5 Figure 6.