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Location Depth Free Swell . Tp6-1 1.5 116 Tp7-1 2 113 Tp8-1 2 114 Tp9-1 2 125 Tp10-1 2 108 Tp11-1 1.5 124 Tp12-1 1.5 114 Tp13-1 1.5 95 3.2.6 Cation Exchange Capacity (CEC) Clay minerals are platelets like in shape and have negative charges on their surface. These negative charges readily attract cations till the surface is balanced. The amount the clay particle attracts cations depends on the type of mineral it is made of and it is expressed by Cation Exchange Capacity (CEC). Thus, CEC is the quantity of exchangeable cations required to balance the negative charge on the surface of the clay particle. A high CEC value indicates a high surface activity and a higher swell potential [14 ]. Different clay minerals have different CEC .In Table 10 the different values are given [5]. Table 10: Range of CEC Values [5] Clay Mineral CEC (meq*/100gm) Kaolinite 3-15 Illite 10-40 Montmorilonite 70-80 * miliequivalent per 100 gm 28
For the study area the CEC is determined for all the samples and the values are compared to the ranges given in Table 8. This shows that except one sample which is taken from Kebele 15 all the rest showed CEC greater than 40. Another test is also conducted to determine the Na+ concentration in the soil of the study area. Na + , Ma 2+ and Ca 2+ ions have their own role in the shrink-swell property of expansive soil. These cations balance the negative surface charge of clay particles. Especially the cations are held close to the surface in air-dry soil. But when water is available the hydration energy opposes the inter particle force which held these cations to the clay surface. As the amount of water increases in the soil, the cations start to enlarge and they tend to diffuse to the more dilute solution. But at the same time the negative surface force of the clay particle increases and this phenomenon attracts more cations towards the surface and cations accumulate around the clay particle. This accumulation of cations forms a layer, which is called diffused double layer (DDL). The DDL formed around every other clay particles overlaps and this overlapping produces repulsion force which is expressed as swelling pressure. The thicker the DDL the more is the swelling potential. The thickness of the DDL is governed by the presence of cations with low valance. Thus more swelling would occur in a soil having exchangeable sodium (NA + ) cations than same soil with calcium (Ca 2+ ) or magnesium (mg 2+ ) cations [14]. For this reason the Na + concentration of the soil of the study area is determined through a laboratory analysis and the result is given in Table 11 29
Page 1 and 2: ADDIS ABABA UNIVERSITY SCHOOL OF GR
Page 3 and 4: DECLARATION I, the undersigned, dec
Page 5 and 6: List of Tables Page Table 1: Mean M
Page 7 and 8: List of Symbols A c = Activity ω l
Page 9 and 10: 1. Introduction 1.1 General Bahir D
Page 11 and 12: Recent Map of Bahir Dar Area Accord
Page 13 and 14: 1.4 Lithologic Units and Soils Resi
Page 15 and 16: 2. Literature Review 2.1 General Pl
Page 17 and 18: Soil water chemistry Soil water has
Page 19 and 20: 2.3.2 Direct Measurement This type
Page 21 and 22: 3. Identification of Soil in the St
Page 23 and 24: Location Color Depth Northing Easti
Page 25 and 26: Table 4. Atterberg and Shrinkage Li
Page 27 and 28: Swell Potential Plasticity Index Lo
Page 29 and 30: Location Depth Gs Tp4-1 1.5 2.78 Tp
Page 31 and 32: Location Depth Sand (%) Silt(%) Cla
Page 33 and 34: Location Depth ω 24 (%) Kebele 9 2
Page 35: Table 9 : Free Swell Test Results o
Page 39 and 40: 4. Soil Classification Soil classif
Page 41 and 42: 100 Plastic Index (%) 80 60 40 20 0
Page 43 and 44: I ) Clay Content and Plasticity Ind
Page 45 and 46: 5 Determination of Swelling Pressur
Page 47 and 48: 5.1 Swelling Pressure and Index Pro
Page 49 and 50: 3 Log Sp (Kpa) 2 1 1 1.2 1.4 1.6 Dr
Page 51 and 52: 600.00 Swelling pressure (Kpa) 500.
Page 53 and 54: 6.1 Models Developed by Various Res
Page 55 and 56: Table 13. Comparison of Previously
Page 57 and 58: Using the above new equations the s
Page 59 and 60: Equation 2 800 Calculated Value (Kp
Page 61 and 62: Equation 6 Calculated Value (Kpa) 9
Page 63 and 64: Conclusion and Recommendation 1. Th

SCHOOL OF GRADUATE STUDIES FACULTY OF TECHNOLOGY ...

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