Experiment 5 Part a Permeability By Constant Head

Experiment # 5 Part a Permeability By Constant Head Method Soil Mechanics lab CE 350/01 1

Permeability u It is the measure of the soil's ability to permit water to flow through its pores or voids. Objective u To determine the coefficient of permeability of a cohesion less (granular) soil. Soil Mechanics lab CE 350/01 2

Darcy's Law The coefficient of permeability, k, is a product of Darcy’s Law. In 1856, Darcy established an empirical relationship for the discharge velocity of water through saturated soils. Soil Mechanics lab CE 350/01 3

u u If the cross sectional area, A, through which flow is occurring is known, the flow rate, q, can be determined as: q = ki. A If the time, t, over which flow occurs is also known, the total quantity of water, Q, flowing during this period can be found: Q = ki. At Soil Mechanics lab CE 350/01 4

Apparatus u u u u u Permeameter cylinder Perforated metal or plastic disks and circular wire screens A device for maintaining a constant-head water supply Timing device Graduated cylinder, 100 ml capacity Scale, graduated in centimeters Balance, sensitive to 0. 1 g. Oven. Centigrade thermometer, range 0 to 50 C Soil Mechanics lab CE 350/01 5

REQUIRED MEASUREMENTS Wet weight of soil specimen, Wwet. u Moisture content of soil specimen, w. u Diameter of soil specimen, D. u Length of soil specimen, L. u Reading of first piezometer, H 1. u Temperature of test water, T. u Elapsed time of test, t. u Weight of beaker and captured water, Wbw u Reading of second piezometer, H 2. u Soil Mechanics lab CE 350/01 6

Void Ratio Determination Wt. of dry soil + can Diameter of specimen, D Wt. of can Area of specimen, A Wt. of dry soil Ws Initial height of specimen, L Sp. Gravity, Gs Initial volume of specimen, V Vol. of solid (Vs = Ws/Gs) Initial void ratio, e Soil Mechanics lab CE 350/01 7

Coefficient of Permeability Test No. Initial height of specimen Void ratio, e = (AL – Vs)/Vs Red. lower piezometer, h 1 Red. upper piezometer, h 2 Head loss, h Quantity of flow, Q Elapsed time, t Water temperature, C Viscosity correction factor, RT Distance between piezometers, LT Soil Mechanics Coefficient of permeability, K 20 lab CE 350/01 8

Correction Factor, RT, for Viscosity of Water Soil Mechanics lab CE 350/01 9

POSSIBLE SOURCES OF ERRORS Non-uniform compaction of cohesionless soil, specially when there is an accumulation of fines on each compacted layer. u Incomplete initial saturation of the specimen. u Excessive hydraulic gradient that might cause the flow not to be laminar. u The presence of fine bubbles in the system. u Leakage along the circumference of the specimen in the permeameter. u Soil Mechanics lab CE 350/01 10