tailieunhanh - Soil and Environmental Analysis: Physical Methods - Chapter 4

Các định luật vật lý mô tả động thái nước thông qua các vật liệu xốp bão hòa nói chung và đất đặc biệt đã được đề xuất bởi Darcy (1856) trong công việc của mình có liên quan với các nguồn cung cấp nước cho thành phố Dijon. Ông đã thiết lập pháp luật từ kết quả thí nghiệm với nước chảy xuống cột cát trong một sự sắp xếp thử nghiệm đưa ra sơ đồ trong hình. 1. Darcy phát hiện ra rằng khối lượng nước Q chảy trên một đơn vị thời gian tỷ lệ thuận với. | 4 Hydraulic Conductivity of Saturated Soils Edward G. Youngs Cranfield University Silsoe Bedfordshire England I. INTRODUCTION The physical law describing water movement through saturated porous materials in general and soils in particular was proposed by Darcy 1856 in his work concerned with the water supplies for the town of Dijon. He established the law from the results of experiments with water flowing down columns of sands in an experimental arrangement shown schematically in Fig. 1. Darcy found that the volume of water Q flowing per unit time was directly proportional to the crosssectional area A of the column and to the difference Dh in hydraulic head causing the flow as measured by the level of water in manometers and inversely proportional to the length L of the column. Thus KA Dh Q L 1 where the proportionality constant K is now known as the hydraulic conductivity of the porous material. The dimensions of K are those of a velocity LT 1. Typical values of K for soils of different textures are given in Table 1. Conversion factors relating various units are given in Table 2. Since the hydraulic conductivity of a soil is inversely proportional to the viscous drag of the water flowing between the soil particles its value increases as the viscosity of water decreases with increasing temperature by about 3 per C. The hydraulic head is the sum of the soil water pressure head the pressure potential discussed in Chap. 2 expressed in units of energy per unit weight and the elevation from a given datum level. It is measured directly by the level of water in the manometers above a datum in Darcy s experiment and is the water potential Copyright 2000 Marcel Dekker Inc. Q Fig. 1 Darcy s experimental arrangement. expressed as the work done per unit weight of water in transferring it from a reference source at the datum level. The potential may also be defined as the work done per unit volume of water in which case the potential difference causing the flow would be pgDh .