 So up to now, we've been mainly interested in the total consolidation of the total settlement but We're also interested in the time it takes for soils to settle and that's what these set of videos are going to be about so if we return to this graph again from our one-dimensional odometer test Where we have void ratio on the y-axis and time on the x-axis Before we put any load on the soil has an initial void ratio, and then we when we stick a load on The void ratio will decrease until it reaches a new a new level a new level of equilibrium And I'm here now if we If we say that well at this point what we've got is a soil that's zero percent Consolidated and at this new level we describe as a hundred percent Consolidated what we're defining is something called a degree of consolidation. So that's the value you so the value you can be between zero and a hundred percent Now we can ask two questions of this we can the same question in two different ways we can say Given the certain length of time Let's say ten days What would be the degree of consolidation that we would expect Alternatively, we might say okay. Well, how long does it take for a soil to reach a certain degree of consolidation? so that's the Those are the two sort of well the same question, but the two different ways we're interested in in asking it and trying to find answers for So what controls this relationship this consolidation relationship? Well, we invoke Tizagi's one-dimensional consolidation theory for this You derived a parameter for describing the time it takes For a soil to consolidate and that's the coefficient of consolidation through CV is the coefficient of consolidation Now your CV value is a function of a number of different things But as you can imagine, it's directly proportional to the permeability of the soil Okay The unit weight of water and the coefficient of volume compressibility The proof of this this this formula is a combination of Dalsey's law and the conservation of mass and Suggest if you're interested you go through the proof But we can derive CV from a Nodometer test and I'll go through that in a later video But how is how is that that value related to consolidation? relationships a solution of Partial differential equations and I'm not going to go through the the the proof of that But what actually pops out of that is an equation that Relates something called a time factor, which is TV with your CV value Multiplied by the time of consolidation all over the the drainage pathway squared so that the time factor is related to you the degree of consolidation, so You can relate you To the time factor and you can do it either through formulae and there's a bunch of different formulae available for that there's also Some tables that help you relate those two things together and I've stuck both on on my website on the link below But what this is saying is that the essentially the TV which is related to the you the degree of consolidation is equal to this coefficient of consolidation the time it takes Or the time that we're examining this consolidation and the drainage pathways squared So before we move on the relationship between TV and your degree of consolidation looks something like this where there's a curve that relates the two together and you see that it's not linear and there's a bunch of equations that govern This relationship so you can draw more than one curve and I've provided a link on my website to to a more detailed explanation of those curve so if TV or your time factor is related to your degree of consolidation and your coefficient of consolidation is some sort of function of permeability Then and T is the time span that we're interested in or we're looking at what is ID? What is the drainage pathway? Well, there are two simple examples that you can give a drainage pathways within soils the first one is if you have a Soil that you're you're interested in it's consolidation So let's say we have a clay and it's overlying an impermeable material like a bedrock So this material here is impermeable There's only one way for this the water to get out of the the soil once it's been loaded and that's through the the top of the Stratham so we have And we might have a permeable layer above the clear here This might be permeable Or this might just be the ground surface, but in this case There's only one way the water can flow so we take the drainage path here to be the thickness of the layer So D in this case is equal to the thickness of the layer H An alternative example is if instead of we had an impermeable bedrock But this was now permeable and water could flow out of both sides of the Stratham Then our drainage pathway would be equivalent to H over 2 So half the thickness of the layer So it's important when we're using this equation to know What situation we've got in terms of the drainage pathway whether the clay is lying on an impermeable bedrock Or an impermeable material or permeable material