主要区别——孔隙度与渗透率

孔隙度和渗透率都是岩石和土壤的特性。孔隙度和渗透率之间的主要区别在于孔隙度是岩石之间空间的度量，而渗透率是流体在岩石之间流动的容易程度的度量。

什么是多孔性(porosity)？

孔隙度测量岩石之间的空隙。它被认为是岩石中的空隙（或孔隙）体积与总体积的比值，通常用分数或百分比表示。由于流体可以占据岩石之间的自由空间，孔隙度也是衡量岩石能容纳多少流体的一个指标。

There are several methods to measure the porosity of a sample of soil. One method used to measure porosity is called the Archimedes method. To test porosity using this method, the mass of a sample of soil is first measured when the soil is dry. Let us call this mass . Then, water is added to the sample until the soil sample is saturated and the mass of the soil sample and water,  is measured. Next, the saturated sample is immersed in water, and the “mass” of the submerged sample,  is measured again. (Note that in fact we are measuring weights, however, the factors of  cancel out, so you can treat the mass readings taken from a spring balance as readings of weight).

Then, the mass of water added to the sample is  . If the density of water is  , then the volume of pores in the soil sample is  .

The total volume of soil is the volume of the fluid displaced when the sample is submerged in water. From the Archimedes’ Principle, the total volume is given by  . Then, the porosity  is given by  . Therefore,

另一种测量孔隙度的方法是使用波义耳定律。在这种方法中，气体被用来填充土壤颗粒之间的孔隙。根据波义耳定律，对于在恒定温度下质量固定的气体，气体的压力与其体积成反比。为了利用波义耳定律确定孔隙度，使用了两个相连的腔室。这些腔室的容积是已知的，这些腔室中气体的压力可以用压力计测量。

Initially, the two chambers are separated by closing a valve between them. A container with a known volume, called the core, is filled with the soil sample. Let us call the volume of the core . The core is placed inside one of the chambers and  the air is taken out of this chamber. Gas is still present in the other chamber, and the air pressure inside this chamber is measured. Let us refer to the volume and pressure in this chamber as  and  .

Measuring Porosity using the Boyle’s Law method.

Next, the valve between the two chambers is opened, allowing for air from the first chamber to fill up the second chamber as well. The pressure in the chambers is measured again, and let this pressure be  . Using Boyle’s law, the total volume occupied by the gas, which we will call  , can now be calculated:

The volume  can be given by,

where includes the volume of the second chamber and the tubing between the two chambers. Now, the above expression allows us to calculate the volume of pores  . gives the total volume of the soil sample. The porosity  is then given by,

什么是渗透(permeability)？

渗透率是测量流体在岩石之间流动的容易程度。具有高渗透性的土壤样品允许液体容易地流过，而液体更难流过具有低渗透性的土壤。例如，可以用具有高渗透性的材料建造路面，这样水就不会积聚在路面上的水坑中。

Material forming “permeable pavements”.

Mathematically, permeability is described in Darcy’s law. Darcy’s law is a formula describing the flow rate of fluid through a porous medium. According to this law, if a fluid with a viscosity of  flows through a volume of porous material with a cross-sectional area   for a distance  , then the total volume of fluid discharged per second is given by:

where  is the pressure at the start and  is the pressure of fluid after flowing through length .  The c***tant  in this formula is defined as the permeability of the medium. The unit of  is square metres (m2).

多孔性(porosity)和渗透(permeability)的区别

它测量什么

孔隙度测量岩石之间或土壤中的空隙量，作为总体积的一部分。

渗透率衡量流体流经物质的容易程度。

单位

孔隙度是体积的比率，所以它没有单位。

渗透率以面积为单位（在国际单位制中为m2）。

Image Courtesy:

“A permeable paver dem***tration, Austin’s Ferry, Ta**ania, Australia” by JJ Harrison ([email protected]) (Own work) [CC BY-SA 3.0], via Wikimedia Comm***