Video for Students of Soil Technology - Measurement and Data Evaluation

>> [Background Music] This video is designed to be used as a pre-course assignment for the Soil Technology-Measurement and Data Evaluation Course conducted by the Natural Resources Conservation Service. It contains demonstrations and explanations of the use of seven tools or methods for collection of soil data. These data will be used to populate databases, primarily, the National Soil Information System database commonly referred to as NASIS. This video also provides the student instruction in

a format that can be easily reviewed as the need arises. For example, if the student is asked to provide data using the compliant cavity-bulk density method, the student can use the tape to review the procedure used to gather this data. The seven methods or tools to be reviewed are compact constant head permeameter, double ring infiltrometer, bulk density-compliant cavity method, bulk density-core method, EM soil electrical conductivity meter or EM-38, ground penetrating radar, and aggregate sta

bility field office method. [ Music ] >> We're here today to talk about and to demonstrate a variety of measurement techniques for acquiring quantitative data for some of the common variables that we encounter to describe, to quantify water movement through soil or across landscapes. One of the most common challenges is to choose immediately and to think about carefully what it is that you're really after because that will affect your site selection, where you are going to measure and what you'r

e going to measure. We've chosen a site here in Southeastern Nebraska that's representative of typical landscapes and shows a variety of different land use activities. And any one of which can be chosen to base your measurements upon. For example, if you want to talk about and quantify or validate map unit content or design, you will find yourself placed in a different location in the landscape than you would if you were saying focusing on a particular cropping technique or a specific site inves

tigation. If you want to look at the influence of mapping a design, oftentimes, you have to take in to account breaks in slope or geomorphic position, and that will affect whether or not you're up on a ridge top position, if you're here somewhere on a middle of a side slope, or whether you're down hill in a foot slope position. If you're after a particular site investigation, the boundaries are going to be determined by that particular application and maybe irrespective of the map unit you're in

. So site selection is a critical aspect of what you do. Choosing a site that's representative of your primary purpose is the foremost activity that you have to consider. Once having done that, you're in business to actually begin the process of opting between various measurement techniques and then pursue with the actual methodology of how you actually execute and acquire the data. >> One of the field instruments used to measure in situ saturated hydraulic conductivity is the compact constant h

ead permeameter, also known as the Amoozemeter. This tool would be demonstrated by Dr. Aziz Amoozegar, Professor, North Carolina State University, Raleigh, North Carolina. >> Today, we are talking about measuring saturated hydraulic conductivity of the unsaturated zone or vadose zone. There are a number of techniques that can be used to measure in situ hydraulic conductivity. One of the technique is referred to as constant-head well permeameter method, shallow well pumping method, borehole perme

ameter method. These are all referred to the same technique in which you dig a small diameter hole into the ground to the desired depth, you maintain a constant depth of water at the bottom of the hole, and you measure the steady state flow rate of water into the hole. And then based on the steady state flow rate of water, the depths of water in the hole and the diameter of the hole, you calculate the saturated hydraulic conductivity, which is an index or a number that will define the rate of mo

vement of water in the soil. So it's a measure of the ability of the soil to transmit water. The technique that I'm going to talk to you about specifically today is the constant-head well permeameter method and the device that will be used to maintain a constant depth of water at the bottom of the hole is referred to as the compact constant-head permeameter that is available to you to make a measurement. To make the measurement, you need a minimum number of equipment. First, you need a set of au

ger. The best that we can use would be a two inch auger. And the reason that we use a two inch auger which will give you about a six centimeter diameter hole is that you don't need as much water as you use a larger diameter hole. This device has a five liter water capacity and can make measurement in most soils with one filling of the permeameter. Cleaner or hole cleaner, or cleaner, and also you need a brush to brush the side of the auger hole that you've made in case that there is any smearing

. The planer auger is use to square the bottom of the hole to form it into a cylinder. You also need a measuring tape or meter stick. You need a permeameter. You need water. Those are the basic parameters, equipment that you need. You also have to have datasheet that you would need to prepare before hand. And you also need to have your manual handy in case that you need to refer to it if you have any problem with any of the device. I'm going to explain the compact constant-head permeameter here.

This device is made of five parts. That these parts, I will explain to you so you know what the system function, how it operates, and then you can work with it better and easier. The first part of this, there are four constant head tubes that are referred to. These constant head tubes, each one is capable of providing 50 centimeters of vacuum or negative pressure for you. Inside three of these are constant head tubes. They are fixed air tubes that are fixed and they do not move. And one of thes

e constant head tubes has an air tube that is adjustable. That is that you can move it in and out. Before you start your measurements, you want to put some Vaseline or some vacuum grease on this tube so it can move up and down very easily. And we will later explain how you set these up when you are actually doing the run. So these are the four constant head tubes. In the middle, you have a four liter capacity reservoir that's referred to it as main reservoir. Next to it, you have the flow measur

ing reservoir which has one liter capacity, and then it has a meter stick next to it that you can use that meter stick to measure the water level in the flow measuring reservoir. Then you have a water dissipating unit that this unit will go to the bottom of the hole, there is a ring at the bottom of the hole, so when it sits at the bottom at the hole, it would not block any of the surface area at the bottom of the hole. And this is refer to as the water dissipating unit and you have, in this cas

e, you have about two and a half meters of flexible plastic tubing that will assist you with putting the unit down at the bottom of the hole. And then finally, the last part of this is the base with a three-way valve, and this three-way valve has three positions. At the positions that you are seeing right now, the unit is connecting the main reservoir to the flow measuring reservoir here. And then when you put that on the two on position, you're connecting the main units to the flow measuring re

servoir, to the water dissipating unit. And when it's on one position, you have the flow measuring reservoir connected to the water dissipating unit. [ Pause ] >> After you've chosen a representative site, the next step is to clear an area, any unnecessary debris or obstruction so that you're prepared to clearly and cleanly auger a hole to the desired depth. [ Noise ] I'd like to add a comment here. With these small diameter augers, it's often helpful to take very small bite size bits rather tha

n to try to fill the auger completely because they tend to jam up with soil material and makes it difficult to extract it. So it's far simpler, just to simply take a one or two turns, taking small bite size pieces rather than go at trying to fill the entire auger. You want to collect the last bucket full of soil material and set it aside in a sealed container for soil moisture determination. Soil moisture content can affect the conductivity of the soil or at least there's a potential for it, and

so we're trying to collect that information along with the actual Ksat measurements. When you've bored your hole to the desired depth and verified your placement, there's a couple of fine adjustments that need to be made. And if there's a question about this-- the location-- the shape of the hole, one has a flat bottom planer auger that's-- whose purpose is simply to shape the bottom of the hole into a perfect cylinder. The objective here is not to-- when one is augering, is not to compact the

bottom of the hole, but merely to seat the plane auger lightly on the bottom and rotate it a few times so that it may simply shape the bottom hole. You're not attempting to dig any greater depth. [ Noise ] When you're done shaping the hole, if there's concern about smearing of the sidewalls due to moisture content or the type of clay in the soil, you can use an optional brush attachment to simply insert it and to lightly scuff the sidewalls a time or two to minimize the smearing. The main horizo

nation at this site consist of a darkened AP horizon which overlies a series of BT layers. By augering-- by boring a pilot hole, you can assess the actual horizonation and layering sequence at your specific site because-- and this will help you account for microcide variability. Once you've targeted a specific layer that you want to measure the Ksat for, you can then focus on saying and measuring what-- determining what the midpoint is for the main horizon or layer you want to measure and then d

etermining the associated depth. That depth is the bottom of the borehole that you want to auger into the ground. At this particular site, we want to measure the conductivity, the saturated hydraulic conductivity of a lower BT horizon. So our borehole, the maximum depth of the borehole is approximately 80 centimeters. [ Noise ] >> Before we make the measurement, we make sure that we have water in the four constant head tubes. There's a water level mark on the constant head tubes that you fill th

e hole of the tubes with the water to that level that is marked on the tubes. And then from the top port of the main reservoir which is a large port in here, you can fill the two tubes together, making sure that the valve is on off position, that is this tube and these tubes are connected with one another. After we fill the permeameter with water, we bring the permeameter, set it up next to the hole, and we just put it in here so we can use the level in here as a reference level for measuring th

e depth of the hole. The reference level for the permeameter is the top of this coupling tube that is in here. So we have to measure from the top of this tube down to the bottom of the hole. This is about nine centimeter above the base in here, and we make measurement of the depths of the hole from the bottom of the hole to the top in here, that is 82 centimeters, and that will give you 91 centimeters from the bottom of the hole to the reference level on the reservoir. Then we have to set the co

nstant head tubes so it will give us the water level that would be at about 76 centimeters which is 15 centimeter depth of the water at the bottom of the hole. So we need to use two of these tubes. The second tube is fixed and the first tube, we need to move this air tube from here. So it is approximately 25 centimeter below the bottom of the-- below the top of the water in here. So the distance from the bottom of this tube to the top of the water in here would be approximately 25 centimeters. 2

5 centimeter and 50 centimeters, that will give us a total of 75 centimeter depth vacuum. For this tube system to function, air has to get to the top of this tube in here for that air goes through this tube in here, it bubbles, comes up in here, goes through the second reservoir, and there is a quick connects-- connect the first one to the second one, air goes to the bottom of this tube and then comes on top. And from the top, has to go to the flow measuring reservoir, goes through the air tube

in here, air bubbles up in here. We also connect the top of the two reservoirs together so the air pressure on top here and on top here will be equal. After the system is set up, we are ready to make the measurement. For that, we have to fill this tube with water so there will be no air entrapped in it. For that purpose, you hold the water dissipating unit up with all of the tubes in it and change the valve from the off position to two on position, that will allow the water to come from these tu

bes. Make sure that the air on top is open so the top, we have atmospheric pressure right now. And the water comes out of this tube and what you do is that, eventually, you're going to remove all the air out of it. You don't want to let this one to come too fast because you may bring air bubbles in here and air bubbles will cause problem. Then you lay it down on the ground and let some water to go out of it and close the valve. Now, we are ready to put the tube back in the hole but before we do

that, I like to just mention that it's always better to push this tube a little bit further down and make sure that all the tubes are connected with one another before you put this tube at the bottom. Then you put the tube at the bottom quickly and turn it to the two on position. You will see that the water that starting going out of in here. And now, air is coming from the top in here into this tube, it goes-- bubble comes up, goes to the next tube, it bubbles from the second tube, it comes bac

k to the bottom in here, and the air is coming in here and water is going out of the tube in here. At that stage, you let the bubbling go until the bubbling becomes more stable. And as the bubbling comes more stable and perhaps will be a little bit slower, then you know that you have reached the head that you have at the bottom. You measure the head then and you go and do any adjustment that you like to have. As I mentioned, we like to start with the lower head in there read and having 15 centim

eter, we will have 10 or 12, and then we can always increase it to 15 centimeters or higher. I have to also mention that you do not need to have exactly 15 centimeters water at the bottom of the hole. You can have 15, 16, all the way to 30 centimeters of water at the bottom of the hole. However, you need to measure exactly how much water you have at the bottom and that's what we do after the permeameter has come into an equilibrium. And right now, we see that the bubbling has slowed down quite a

bit so we have established a constant head that we want at the bottom of the hole. There are a number of ways that you can measure the depth of water at the bottom of the hole. One way is to stick a rod or a wooden dowel or a meter stick if you have it all the way to the bottom of the hole, and then bring it out, see where the water mark is. But make sure that if you are doing that, use the thinnest and the smallest diameter rod that you have because you are not going to raise the water level t

hat much. The other option is that we-- if you remember, the bottom of the hole to this level here was 82 centimeters. So if I want to have 15 centimeters, that means that the water level to the top of this base in here, we want it to be 67 centimeters. So anything around 67 centimeters will do it. So what I will do is that, basically, I insert the meter stick or my measuring tape here and bring it to 67 centimeter there, and then I'll bring it out. If I haven't touched any water in here, that m

eans the water level is below this level in here. So what I will do is that I very slowly pass the 67 and I will go to somewhere like 75 centimeter in here and bring it out to see how much water we have. We have very little bottom, at the bottom of the hole, so what I have to do is that raise this one another five or six centimeters and let more water go into the hole, in that way, we start increasing the water level to the depth that we want. Once the water level reaches 15 or 16 centimeters, w

e measured that water level exactly. We determined exactly what depths of water level we have. We put it in our datasheet. And then we are ready to go. We'll let the permeameter run for a period of time depending on the soil texture, the time that you have on your hand, and how fast the steady state is going to reach. The amount of time may vary from 10 or 15 minutes all the way to maybe a couple of hours. Generally speaking, if you have time, you want to let this one go to come to steady state

so you don't have to sit here and babysit this unit in here, but you can always sit in here and keep making measurements. So we'll let this one go. Now, it's becoming more stable. I'll go back again and measure the depth of water in here again and see how much water we have in the hole and raise that level accordingly. So it seems that we have to raise this one maybe a few more centimeters in there until the steady state-- the water level reaches the depth that we want. You notice that anytime t

hat I remove-- move this tube up in here, I'm raising the water level at the bottom of the hole, the unit starts bubbling for a period of time, and then it will slow down. And once the bubbling becomes more uniform in here, I'll probably-- I'm getting there to have 15 centimeters. So I have at the bottom of the hole right now 16 centimeters of water because once I have put this meter down in there, I have the one centimeter bottom in here that gets wet. So 67 minus one, 66 centimeter from here t

hat means that I have 16 centimeter depth of water at the bottom of the hole. Now, all I have to do is wait until steady state is reached. And for that purpose, I'll go ahead and make measurements in here. And right now, you can use a stopwatch or you can use your own watch and determine, you know, what the depth of the water will be here. As an alternative, what we can do is that instead of directly going in here and making measurement of the meter stick in here, some people like to use a tape,

a removable tape, not masking tape, not any other tape that will stick to the tube. There are removable tape that you can buy from scientific supply stores and you use that measuring-- that tape and put it on the side of the tube and you can make all your marks on it and then you have to remove that tape and put it in your data book. And now, all we have to do is wait until steady state is reached. Generally speaking, we keep making measurements until three consecutive measurements are the same

. Once we reach that level, we assume that we have reached a steady state level. Now, here we have the unit on two on position. That means that both reservoirs are connected to the water dissipating unit. Every centimeter drop in here and this tube corresponds with 105 milliliters or cubic centimeters of water going out. So basically, what we measure in here per unit time, we multiply by the 105 and that is in your datasheet, and that will give you the quantity of water that has gone up per unit

of time. You choose the unit of time that you want to use for measurement. It's best to fix the time and make the measurements, so you don't need to do any calculation. All you have to do is measure these distances and if three distances in a fix period of time, three consecutive ones are the same, you assumed that you have reached the steady state. Now, if you are in a soil that that the conductivity is not high, then what you need to do when you have reached a steady state or you think you ha

ve reached a steady state, put the valve, rather than being on two on position, put it on one on position so you only will get water out of this other tube in here. And this other tube, every centimeter drop correspond to 20 milliliters or two 20 cubic centimeters of water, so you can fine tune to your measurements. Another option that you have is increase the length of the time. Rather than making measurement every 10 minutes or every 15 minutes, you may want to make measurement every hour. But

that means that you have to run the system for three hours to get three consecutive ones. So you put it in the other tubes and you can measurements. And perhaps within 45 minutes after the steady state is reached, you can have the number of the data that you want in order to do the appropriate calculations. But this permeameter, you can make measurement from the soil surface, that is the water level will be at the soil surface all the way to two meters depth. If there is any need to go beyond t

wo meters depth, you can go to four meters depth by using a set of constant head tubes that will be an addition to the four that you have in here. So using another full constant head tube, you can go to four meters depth. For that purpose again, you take the top and set it on the side in here and you fill the water to the water level that you have indicated in here is there, and then you make sure that these are all tightly attached to one another. And depending again on the depth of the hole an

d the depth of the water that you want inside of the hole and from the top of the water level to the reference level, you connect the appropriate number of these. And each one of these, as I mentioned, will give you 50 centimeters. And you can put this one to the side, attach it. [ Noise ] And connect these tubes appropriately in a series, and then the final one will go to the flow measuring reservoir here to achieve the number of constant head tubes that you need to get to the depth that you de

sire beyond two meters depth. [ Pause ] >> An example of a completed data sheet is included at the end of this section in your student training manual which you'll receive with this video. There are also exercises containing problems which you are expected to have completed before you attend the training session. Infiltration is the rate at which water enters the soil. In comparison to saturated hydraulic conductivity, infiltration is affected by properties of the immediate surface, including cr

ust, biopores and cracks. The double ring infiltrometer is a tool used to measure the infiltration rate. The measurement is strongly affected by soil use and may change through the year. Infiltration is measured under conditions where free water is on the ground surface. After several hours, the soil profile becomes saturated to a depth of about three feet and the rate becomes fairly constant. This is referred to as the steady ponded infiltration rate. >> Knowledge of infiltration is extremely i

mportant because it determines how much of the water that falls on the soil, how much of the precipitation actually gets in to the soil where it can be used. It's important for irrigation as it is for dry land agriculture. And the various models that have been developed for prediction of erosion for our agency all have estimates of infiltration, because it's the water that doesn't infiltrate, so water then that runs off in the soil that determines the-- or look-- it's very important in determini

ng the amount of erosion. And the method we have here is the classical approach. It has been used for 75 years for measuring this so-called steady ponded infiltration rate. There's an aspect of the set up here that's very important and that is how deep the-- you insert the rings in the soil. I think you can visualize that in order to measure the infiltration rate, you need to have the rings down in the layer of the soil that limits the infiltration rate. And in this soil, that will be what we ca

ll the plow layer. And we'll want to insert these rings, the order of four to six inches into the soil. [ Noise ] I want to talk to you just a moment about the water source for the outer ring. You have water in this barrel and in it, you have a garden hose which is hooked to a float device. And this float device then will be mounted on the outer ring. And we will then be able to keep the water level in the outer ring at the-- at the level that we desire. And the water, I should have mentioned, f

eeds by gravity from the water source here over to the outer ring. Here, we insert the float on the outer ring thusly. And now, we're in position and ready to go. Now, we're going to fill the inner ring with water bringing it up to approximately the same level as in the outer ring. And just to recapitulate, the water in the outer ring is being controlled by this float valve that we talked about. And you see, we've put an energy breaker there of straw because we don't want water impacting directl

y on the soil because it will cause dispersion, perhaps. So we just pour this in. [ Noise ] And I just check very quickly the height of the water in there, and that's-- make sure that that's about the same as the level in the outer ring, and which it is. So now, we're ready to attach the device for measuring now the rate at which the water moves into the soil from the inner ring buffered, as you can see, by the envelope of water in the outer ring which reduces and prevents lateral water flow. We

want to talk to you about measuring the rate of water movement out of the inner ring, and that is really what we're after here. You recall, we have a float device that we use for metering the water into the outer ring, but that is really too crude an approach. And what we're going to be using here is a compact constant head permeameter. And here, we have the water source from the permeameter. It's placed in the inner ring, as you see. And the bubbles now that you will see periodically in the--

in this device then mark the movement of water from the device to the inner ring to replace water that has moved out of the inner ring into the soil. So with this device, we can keep the water level constant in the inner ring and we're then getting a measure of how fast the water moves into the soil from the inner ring. >> For a description of how to properly set up the compact constant head permeameter, please refer to the demonstration of the use of that instrument, or to the instruction manua

l. >> Now, we want to initiate the measurement of the rate at which the water is moving out of the inner ring. And we do that by finding an even minute to time here and marking this tape, as you see here. And then, we will come back and after a known time interval, we'll mark it again and we'll know the height of the-- or the distance between the two marks and we know the diameter of the tube, and so we know how much water has moved from the inner tube into the soil in a given time. And now, her

e, we have almost 3 minutes elapsed and when it has, we're going to mark this, as you see here, and we now have-- write three minutes on there so we won't forget. We now have the height of the column of water and actually the cross sectional area and we can get the volume of water that's moved into the soil in three minutes. And I think you could see from this that if you know the diameter of this tube and you know the diameter of the inner ring that we then can calculate the infiltration rate,

the inches per hour of water that has moved into the soil from the inner ring. [ Pause ] >> One of the methods used for measuring bulk density is the compliant cavity method. This method is designed to measure the bulk density of weak or loose soil material for which the clod or core methods are unsuitable. The method is particularly applicable to the nearest surface including fragile tillage zones. It also may find application for deeper zones through sampling on top of horizons exposed in a so

il pit, zones as thin as two centimeters maybe measured and the immediate surface need not be disturbed. Bulk density is a very important measurement in soils and can be used to predict the rate at which water moves through the soil, the water holding capacity of the soil, and the air-filled porosity of the soil. >> We have here a wheat stubble, two rows of wheat, or at least they were wheat three or four or couple of months ago, and this device is very simple. It consists of an annulus, a spong

e which is placed on the soil, and then a rigid annulus is placed over the sponge. And though not shown here, you drive in posts and mount this annulus on the-- sponge annulus on the soil surface. The size of the device is dictated by agricultural practice. Here, you have about eight inch rows and-- so the device is designed so that you can then measure between two rows. The-- it's very important in designing the device to have a scale that both permits you to make measurements of features and y

et not lap over to a three inter row so you know what you're actually measuring. This is-- it's called a compliant cavity because you actually make a cavity on the soil surface which complies to the irregularities in the soil surface. Here's where we're going to make the actual measurement. We have the sponge annulus with a rigid annulus over it, already mounted, and we're going to put in these threaded rods so we can mount the assembly on the soil surface. [ Noise ] There are many ways to do th

is but one thing you don't want to do is pound directly on the plastic. So you see what I'm doing here, I'm pressing it down for-- so I don't pound the plastic. And I fit-- I make sure that the sponge annulus coincides then with the opening in the rigid annulus. So we're done. We're already to-- we've mounted the compliant cavity on the soil surface. And we use tough plastic film. This is about half mil diameter. And we have here a volume of water already metered out, it's 500 cc's in a graduate

d cylinder, and we pour that in to here, to the cavity and kind of seat it a little bit. Now, this is a hook gauge. This is a bar with literally a hook gauge on it which is just a hook that we can use to measure the water level. So we put that in the device. So, I can get it right. And now, we have a situation where the tip of that hook gauge establishes a datum plane from which we can get the volume to the soil surface. Pour water in to exceed the level of the hook gauge. And then I take a 60 c

c syringe and come in and remove water until you just see the tip of the hook gauge breaking the surface. And then that water goes back in here. So now, we have a measure of the dead space in the soil and that volume is 500 cc's which we started with. Now, it has to take the water out of the compliant cavity and you might say that if you hiked in a mile with your water into the woods or otherwise you might throw it to-- you might throw the water away. Now, we're going to excavate to the depth de

sired. I have a bag here and a lot of different tools depending on what you want to use for excavation. You need knives and spoons and you'll soon gain experience just to-- tools that are needed for your soil. Now, a very important point here and distinguishes this method from most of the methods is that the depth which we excavate is not arbitrary. It's determined by how the soil feels or the color. It's determined by the morphology of the soil. A second important point is that we can measure t

hin zones, centimeter and a half or so, much thinner than we can do with the usual core procedure or the clod procedure. Now, this is something you don't want to do. Remove the soil quantitatively. And we're going to get down about a centimeter and a half and the reason we're going to stop there is because the soil feels firmer down there. So that suggests that there's another little bit that I got. I think maybe we'll just take a little more out. [ Noise ] You see in the usual core method, you

might press in the core maybe three inches into the soil and you may have gone through most of the really important changes that have occurred, whereas with this method, you would not. You'd feel the differences. Now, the excavation should be a cylinder. It shouldn't be a little soup bowl. It should be a cylinder that coincident then with the edge of this hole and that rigid plate because we want the cross sectional area of the hole to be constant. So, again, try and don't make soup plates, make

cylinders and keep the excavation about the diameter of the rigid plate or the hole on the rigid plate. So working our way then, we would take this back to the office and we would oven-dry it. We would make a correction for rock fragments probably if there were and then we'd have the weight. And to get the volume, where the bulk density, which again is the ratio of the weight, the oven-dry weight to the volume, we make a second measurement here of that volume, same way as for the first, and we

use a thousand cc graduate, usually, because more water is involved. And here, we're filling that graduate with the-- the hole with the water from the thousand cc graduate. We put the hook gauge across. Remember I said that this is a datum plane and the apparatus is so set up that you have to put the gauge in the same place each time. So what you're doing then is measuring the volume twice and the difference between the second volume and the initial volume, which is the volume of the dead space,

is the volume that you've excavated. And I'm going to go over here. Well, I have to add a little more water. I'm going to go over here and take this out and measure it, and we started with a thousand cc and we ended up with 280 cc's, so we have a net volume then of 720 cc's. And from that, we have to subtract the dead space which was 400 cc's, so we have a net volume of the hole of 320 cc's. >> Another method used to collect bulk density measurements is the core method. The method demonstrated

is a variation of other core methods in that the core does not have to be inserted to a specified depth. This increases the probability that soil compaction within the core will not distort the bulk density measurement. >> We're going to talk here about a core method of bulk density which we found very practical in the field under conditions where we can't get clods and where the excavation compliant cavity method is inappropriate. We have here a small exposure. And the first step is to slice it

down, get it flat, yup. And of course then in the process, you decide where you're going to make the measurement. And we're going to make it in just the lower part of the plow layer. We have here these cores. They're made of aluminum. They're sharpened a bit on one end and they're about 13 centimeters high and about 8 centimeters diameter. So we take the core and place it against the soil, like this, and then you have to use a little muscle and come in and push this the depth that you want into

the soil. What we can do, if really necessary, is tap it a little bit carefully. There, you have to make a judgment whether you maybe disturbing the soil too much. But we don't have to insert it a full distance. We can composite more than one core. That's a nice advantage to this procedure. Now, we have to re-cut away the soil and the objective is to get it broken out so there's excess soil at the bottom. So it goes something like so, and each end go like that. There you have it and now I will

cut it away. So we're square with the base of the core. [ Noise ] And get rid of the excess soil around the edge. And that's pretty good. And we can put it on a flat surface. And we know the volume of this core but the question then is to get the volume of the soil inside. And there are several ways you can do this. One way that I do is just take a ruler and maybe I'll just work it this way and drop it and then measure the height there. It's 35.1, maybe I should have centered this a little bit.

And then the next one is 35 right on the button, and then the third one is a 35.3. So then you write those numbers down. And I won't necessarily do it here. Then you turn it so that you can get another set of three numbers from the-- going the other way, this is 35, 35.2, and 35.3. And that-- these little pieces of tape here are-- ruler so-- design so that I can-- I keep the measuring tape more or less vertical when I'm making these measurements. Okay, so I know then-- let's say it's 35 centimet

ers to the top of the soil. And then I know if that the total height from here to here is 37 centimeters. This hits this core height plus this bar that I have it resting here plus four centimeters of this ruler here that's attached. So the difference between 37 and 35 is two centimeters, that's the average height of the soil. I know the cross sectional area of the core, and so-- and that's about 40 square centimeters, so I multiply 40 squared centimeters by two centimeters and I get 80 cubic cen

timeters as the volume. And then I take the soil and-- if I can find my bag, here we go-- I put the-- transfer the soil and transfer it quantitatively now to the bag. [ Noise ] Sometimes, like in this soil which is kind of wet, you got to go in and maybe use your fingers even a little bit-- to get it all transferred. This is a soil with about 40 percent swelling type clays and it sticks to everything. Well now, we've taken the sample and we can take more than one and-- core and some composite it

if we wish. Once we go back to the laboratory with the sample, we have to oven-dry it and we have to make a correction for the weight and the volume of the rock fragments if there are any. And that gives us then the bulk density in grams per cc. You see, we have the weight in a known volume, and so the weight divided by the volume then is the bulk density. One major advantage of this procedure, and we've used it in a number of circumstances, is that it's something that can be done with simple e

quipment and it is something that a person in a soil survey with rather rudimentary laboratory equipment can run. [ Pause ] >> Another tool for measuring the electrical conductivity of earthen materials is the EM-38. The EM-38 is handheld instrument that has an effective observation depth of about one and a half meters. It differs from the GPR unit demonstrated earlier in that it is self-contained and very portable. >> Electrical magnetic measurements have been used in soil survey program to mea

sure sinkholes and karst topography, as well as to measure the distribution and extent of sodium effect to soils. It's also been used to measure the depth of the hardpan, as well as to measure soil quality. I will briefly explain how the instrument operates. At this end of the instrument is located a transmitter. The transmitter emits circular loops of electricity. The size of these loops is directly proportional to the electrical conductivity in the soil. At this end of the instrument is a rece

iver which intercepts a portion of the current loops. The current loops that are intercepted are translated into an analog reading that can be measured using this meter. The measurements on this meter are directly proportional to the amount of electrical conductivity that is found in the soil. These dials and switches are used to set up the instrument. Electrical conductivity is read at-- on this meter. The next dial is used to set the correct range depending upon the scale of the reading in the

electrical conductivity meter. This dial turns the instrument off and on, and also is used to check the battery. These two-- these next two dials are used to set the I/P 0 or the in-phase null. The next-- the next dial is set at the factory and usually is not altered. This dial is used to set the Q/P 0. It is a locking dial with the locking on this side. This toggle switch switches between Q/P and I/P. During normal reading, the Q/P position is used. This button is used to transmit data to a da

ta logger if it is connected. At the beginning of each measurement session, you must make sure that all metallic objects are removed from your pockets and hands, and that you are fairly far away from vehicles, fences, and power lines. There are several parts to zeroing or setting up the instrument. There is the in-phase nulling, setting the vertical and horizontal measurements, and finally, nulling the in-phase measurement again. The battery is checked by turning this knob to batt and observing

that the needle goes all the way to the top, indicating that the battery has sufficient voltage to make measurements. The I/P switch is used for the in-phase nulling. This is done by changing this toggle switch to I/P and adjusting the scale to this highest number which is a thousand. These two knobs are used to zero the dial. First, adjust the course dial until the reading as near zero, and to make it exactly zero by using the fine adjustment. This must be done for each one of the scale, so tur

n it to 300. Again, use the fine and the course to bring the needle to zero, move this to 100, zero the instrument again, and then move it to 30 for the final in-phase zeroing. The next step is to-- is to set the instrument so that the vertical mode equals two times the horizontal. This is done by switching the toggle switch to the Q/P position and then unlocking the Q/P 0 and adjusting this knob so that the dial reads approximately halfway between zero and one. And then turning the instrument i

nto the vertical mode and ensuring that it is at least twice that reading. If it is not, you must continue to adjust this dial and tell the vertical mode equals two times the horizontal mode at which point you lock the dial. In order to set the instrument so that the horizontal reading is equal to twice the vertical, you must hold up the instrument about five feet off the ground and then set the Q/P 0 so that the scale reads about half the distance between the highest and lowest reading and then

turn the instrument vertically and check to see if that reading is twice the horizontal reading. If it is not, then you must turn the instrument in the horizontal position and decrease or increase the reading and then check the vertical reading to see if it is twice the horizontal reading. You must continue to check vertical and horizontal until that relationship is true that vertical equals two times the horizontal. The last step to setting up the instruments is to again check that the in-phas

e nulling is zero. We do this by placing the instrument on the ground, changing the toggle to I/P, and then check to see that the meter reads zero. If it does not, we use the course or fine I/P 0 knobs and adjust them until they're-- until the meter reads zero. And then we turn the meter into its horizontal position and check to see if it also reads zero. If it does not, we adjust this slightly so that it does. Now, we're ready to make measurements. The last step to initialize the instrument is

to again check that the in-phase nulling is set to zero. We do this by moving the toggle switch to I/P, making sure the [inaudible] per meter knob is set to zero. And then, we check the meter. If it is not zero, we adjust the course or fine zero dials until the meter reads zero. Then we turn the instrument to its horizontal position. Again, check the meter to see if it reads zero, and make the slight adjustments until it does read zero. To make measurements, we turn the toggle switch back to the

Q/P position. Now, we're ready to make measurements. [ Music ] Try to understand how electrical conductivity measurements relate to soil properties. >> Electromagnetic induction techniques measure the apparent conductivity of earthen materials. Though seldom diagnostic in themselves, lateral and vertical variations in apparent conductivity have been used to infer changes in soils and soil properties, and to detect surface anomalies. One of the tools used to measure electrical conductivity is th

e ground-penetrating radar. The purpose of this video is not to show the viewer how to use ground-penetrating radar, but rather, to introduce the principles and concepts of using and interpreting ground-penetrating radar. >> The radar circuitry inside the ground unit generates a sequence of trigger pulses. These pulses are sent via the control cable to the antenna where each trigger pulse is transformed into a bipolar transmit pulse. [ Pause ] The transmit pulses are then directed into the subsu

rface by the antenna which is pulled along the surface. The energy is radiated in a conical pattern, roughly 90 degrees front to back and 60 degrees side to side. The transmit pulse encounters different materials in the subsurface, each with different dielectric properties. Where the different subsurface materials meet or interface and the dielectric constant changes, some energy is reflected back to the subsurface and detected by the receiving antenna. The received signals are then sent back to

the control unit where they are processed. The data are displayed on the color monitor and can be stored on the internal hard drive for later playback or printed on a thermal plotter. The horizontal axis on the display represents the distance along the ground surface. The vertical axis indicates the time it takes for the transmitted pulses to enter the ground, reflect from an interface, and return to the antenna receiver. This is called travel time and can be converted to depth once the velocit

y of the radar pulses is known. The strength of the returned pulses determine the darkness or color on the display when in line scan format. How well ground-penetrating radar or GPR will solve a particular problem at a certain site mainly depends on two electrical properties of the subsurface materials, electrical conductivity and relative dielectric permittivity, or the dielectric constant. These properties are important to understand in order to acquire good data. Let's first look at the diele

ctric constant. This is a measure of the capacity of a material to store a charge when an electric field is applied. Different subsurface materials have different dielectric constants. The value of the dielectric constant ranges between one for air and 81 for water. You'll find a table in your SIR-2 manual that gives the approximate values for a variety of typical subsurface materials. At the subsurface interface, some part of the radar signal passes through the interface to the underlying mater

ial while some is reflected back to the antenna. How much signal is reflected and how much passes through depends upon the difference of the dielectric constants between the two layers. In GPR, it is important that the change in the dielectric constant occurs over a short distance in order to produce a good reflection. If the dielectric constant changed gradually in the subsurface, reflections from the boundaries will be weak, discontinuous or non-existent. For example, the ability to detect the

water table is highly dependent upon the sharpness of the water boundary. A fine grained sand layer could have steadily increasing water saturation with depth. In another words, no sharp water table boundary. This gradual change from dry to saturated sand is barely detectable. However, coarse grained sands would have a sharp water table boundary which would be easily detectable. The next property to understand is electrical conductivity, a measure of the ability of a material to conduct an elec

tric current. This will determine the depth of penetration of the radar signal. The lower the conductivity of the materials, the deeper the radar signal can penetrate. Conductivity is controlled by the water, mineral and clay content in the subsurface. The conductivity of water saturated clay is high enough that it will greatly limit the penetration of the radar signal. Salt water is so highly conductive, it effectively blocks the radar signal from penetrating. On the other hand, dry sand, limes

tone, granite, asphalt and concrete have low conductivity and allow good radar penetration. The chart in your manual also lists the electrical conductivity of typical subsurface materials. The depth of penetration is also dependent on the antenna selected. GSSI manufactures several antennas with ranges from 20 megahertz to 2.5 gigahertz. The lower the frequency, the greater the penetration depth. The higher the frequency, the better the resolution. [ Pause ] Now, let's take a look at the process

of conducting an actual survey. Before conducting any survey, you should first try to find out as much information as you possibly can about the site you'll be surveying. >> The radar operator will need to know some of the following information. Taxonomic family, geologic setting, terrain conditions; wooded, cropland, urban; size of the area to be covered, location of the site. The use of the terms you and your 1:05:24.9 in the remainder of GPR segment of this video refers to the radar operator

. This section is included to give the viewer an overview of what is involved in conducting the survey. >> So first, we need to estimate target characteristics. Here are some questions to answer. How deep is the object that we want to see? What are the overall dimensions of the objects? What are the other subsurface materials surrounding the objects? How well are the boundaries of the objects defined? To illustrate the importance of knowing as much as possible about your target, there is a very

general guideline that can sometimes be applied if you're looking for metal cylindrical objects. The object should have about one inch of diameter for every foot of depth. So, you should be able to find a three inch metal pipe to a depth of about three feet. Beyond that, it would be increasingly difficult to see. If a pipe is at a five foot depth, it would need to be no less than about five inches in diameter to be visible. Remember, this is only for metal pipe. Other materials with different di

electric constants would have different requirements. And of course, the surrounding subsurface materials will also affect your data. The possible depths of your survey will decrease as the electrical conductivity of the subsurface material increases, the water content increases, the clay content increases, scattering of the radar signal increases and conductive contaminants increase. Once your target characteristics are identified, you can select an antenna. The two main factors to consider are

, first, what is the maximum target depth, and second, what is the size of the target? This difference in penetration depths and resolution make selecting the proper size antenna crucial to the success of the GPR survey. The next step before surveying is to estimate the two-way slowness of the radar signal in the area we are working. At this point the SIR-2 can be set up. If you'll be powering your system with the vehicle as you see here, be sure the engine is running before you power the system

up. Also, be sure you turn the system off before you turn the engine off. When the equipment is hooked up and the parameter is set, conduct some preliminary test lines. The survey area should be gridded with flag stakes or paint placed at measured distances. The longer the test lines, the better. When surveying the ground, a minimum test line is about 30 feet. With a handheld antenna, make the line as long as is practical. It's also a good idea to do several test lines before doing the actual s

urvey. When you are ready to do a test line, press the marker switch at the antenna to start data collection, then, double click the marker switch when you start walking. If you're not using a survey wheel, try to pull the antenna at a constant speed, slightly slower than a normal walking pace. Press the marker switch once each time the center of the antenna passes the marked distances along the line. When you reach the end of the line, hold the marker switch down for two seconds to stop the dat

a scrolling and close the file. If you know the location of some buried objects in the area, this is the time to use these targets to check the system settings and make necessary adjustments. Once you are satisfied with the settings, you can conduct the survey. You should try to not change the settings once you have started the survey. Again, remember to pull the antenna at a constant speed. Use the strain relief clips on the control cable and don't pull the antenna if the cable gets stuck. Neve

r let the cable run underneath the antenna during the survey. It's best to have the cable drag behind the antenna as you pull it. Finally, be sure to keep a detailed log of the survey and keep accurate notes of the file saved on your hard disk. You now know how to setup your SIR system 2 and how to conduct a survey. You're armed with a tremendous tool, and a key to your success is how well you interpret the data you acquire. In earlier sections of this training video, we covered the principles o

f subsurface interface radar. We touched on how the electrical characteristics of the soil affect wave propagation, types of soil where radar will be most useful, and how reflections from various interfaces occur. This will all be helpful in data interpretation. Let's now look at a basic ground penetrating radar concept. Here, the radar pulses enter the subsurface and reflect off interfaces or targets. On the records we receive, the vertical axis is depth and time. Later, we'll learn how to conv

ert these to feet or meters. Our horizontal axis is distance traveled by the antenna across the area of investigation. When interpreting radar data, you'll be considering three characteristics of the data. One, how does the strength of the reflections vary? Two, do the targets or zones of interest have unique reflection patterns? Three, what is the vertical and lateral extent of the unique patterns or reflections of interest? What determines reflection strength? Basically, the reflection strengt

h is determined by the change in electrical characteristics between two layers or the difference between a target and its surrounding medium. As we showed in the beginning, if water saturation occurs gradually with depth, you will not see a response from the water table. But if the change is abrupt, a sharp response will occur. This is also true in regard to changes in electrical characteristics. For example, a change from dry sand to loam represents a significant change in dielectric properties

from four for sand to 19 for loam. Let's review the following equation where E sub 1 equals the dielectric of the first layer, E sub 2 equals the dielectric of the second layer, R equals the reflection coefficient. For our example of dry sand to loam, the equation looks like this. The reflection coefficient ranges from 0 to 1 and 0 to minus 1. The closer to 1 or minus 1, the stronger the reflection, and the closer to 0, the weaker the reflection. A reflection coefficient of 0 to plus or minus 0

.2 is a weak response. Plus or minus 0.2 to plus or minus 0.35 is a medium response, and greater than plus or minus 0.35 is a strong response. Our example of dry sand to loam will produce a relatively strong signal response. Now, let's look at responses from targets. Let's consider where six inch diameter PVC pipe air-filled buried four feet deep in saturated sand. The dielectric of saturated sand is approximately 30 and the dielectric of air-filled PVC pipe is approximately one. The equation no

w looks like this. Again, we receive a strong signal from this target because of the significant contrast in dielectric values. Here is a tougher situation. Let's examine what happens when a concrete pad is buried in dry sand. The dielectric of dry sand is approximately four and the concrete pad is approximately six. In this scenario, the concrete pad would be virtually invisible. Understanding the dielectric values of the materials you are working with prior to starting a survey can help plan w

hat to expect from your data. Let us divide interpretation into three general objectives and discuss what characteristic reflection patterns may exist. First, looking from manmade targets. Second, mapping the structure of the subsurface. Third, non-destructive evaluation of concrete structures. A cylindrical target such as a pipe, tank or a drum will produce a distinct response due to its shape. Thus, this is the first characteristic that we look for in the data. The strength of the hyperbolic r

eflection will depend upon the material as discussed above. Water-filled PVC or metal targets produce strong reflections. Air-filled PVC and concrete targets typically produce weaker reflections. When looking for utilities, you should expect to see the hyperbolic on several lines. In addition to observing the target reflections, you can also look for secondary features, in particular, trenching. This often shows as a disruption in the horizontal subsurface layering. When interpreting natural str

atigraphy, the continuity of reflections and their signal strength is an important consideration. For example, a wet clay underlying a dry sand will provide a large dielectric contrast and a strong reflection. In contrast, a silt overlying granite bedrock would not produce a strong reflection. If the pattern of continuity of reflectors change, we can interpret that as indicative of subsurface change. The water table will sometimes show as a strong reflection cutting across sediment reflections.

While in fine grained materials, it will often not be observed. Air-filled voids in bedrocks have a strong dielectric contrast, and thus, produce strong reflections. Non-destructive evaluations of concrete structures normally focuses on one or more of the following objectives. Location of reinforcing, determining thickness, and identifying various defects. Metal reinforcing bars show in the data as high amplitudes, small hyperbolas in a regular pattern. Voids at the base of concrete, if large en

ough, will show as high amplitude reflections due to the dielectric contrast. The reflections from the bottom of concrete can vary in strength depending on the underlying material. The reflection's continuity will vary depending upon the amount of metal reinforcing above. Once you have identified your targets or layers of interest, you'll want to determine their depth. Determining depth is an important capability of GPR. Depth is the vertical axis of the profile view. It is labeled in terms of t

ime and can be converted to depth. There are four methods to estimate depth. The method used will depend on the required precision for depth measurements, available equipment, and site conditions. Method one, use assumed radar velocities from tables in your manual. Method two, locate object of known depth. Method three, geometric scaling. Method four, simple CDP. Methods one and two are the simplest and most commonly used methods. We'll discuss these two methods. Method one, estimating velocity

from the dielectric constant requires that you know something about the materials that you're working with. If you can determine the dielectric of the materials, you can use this equation. Method two, locate objects of known depth. Caution must be exercised because the velocity calculated is only an average to the target depth of that location. Lateral changes and moisture content of soil and rock composition will affect radar velocities. First, acquire a line of GPR data perpendicular to the lo

ng access of the target of known depth such as a tank or a pipe. Second, determine the travel time to the target from the GPR data. Third, estimate the velocity of the subsurface material using velocity equals travel time over depth. Four, the depth of unknown targets can now be estimated using depth equals travel time over velocity. You now understand how certain targets will be presented in your radar data, why reflection strengths vary and how certain targets or interfaces can appear invisibl

e to GPR. And finally, how to determine depth to a target or interface. Proceed cautiously, never over interpret your data. An anomaly is only an anomaly and becomes an identified feature only after proper ground truthing. Each situation you encounter will be slightly different. By now, you can see that used properly, the SIR system 2 is an extremely versatile and easy to use tool. Even though you now have all the basic information you need to conduct your own surveys, you'll find that every sur

vey will become a learning experience. And the more you used your SIR-2, the more familiar you'll become with its wide ranging potential for gathering invaluable data. Use it as much as you can and experiment with different settings in different environments. >> The aggregate stability test is a method to determine the stability of soil aggregates under wetting and drying conditions associated with saturation by rainfall and subsequent drying of the soil surface. The procedure is based on visual

observation rather than numerical measurement. It does not require weighing and takes very little distilled water. It is suitable for field office use and can be run on small samples such as are collected for correlation. >> Here, we are demonstrating an aggregate stability procedure that depends on the degree of reconstitution of aggregates when they're placed abruptly in distilled water. It has a big advantage in that we don't have to do any weighing. It's based on a visual assessment and pla

cement of the soil into classes which of course is not as quantitative as if you are going to weigh the soil material. But it's very well designed for the usual field office. Here, we have number 10 sieve, a two millimeter sieve, and one millimeter sieve, number 18, and that's the base. I'm going to put them together, like so, with the smaller sieve below the other. And here, we have soil that was taken from the field and brought to the office and dried. And now, we're going to take a part of it

and pass it through this number 10 or two millimeter sieve and catch it on the one millimeter. And we'll use a heavy hammer here. This is a part of it that's kind of fun. [ Noise ] And you want to pass most of these raw materials through the-- through the number 10 sieve. [ Noise ] I think that's pretty good. Now, we'll take it and we have the material retained on the one millimeter sieve here. And now, we'll proceed to determine its aggregate stability. Now, we have the two to one millimeter f

rom the soil in the field that we're in. We have here a cell which has a half a millimeter screen at the bottom which will let the water in real rapidly and we take some of these two to one millimeter aggregates and we place it-- the cell with the aggregates in them abruptly into this distilled water. The water rushes up pass them and effectively, we have almost instantaneously immersed the aggregates in distilled water. We'll leave this overnight. And we'll take the cell out, drain it, and it w

ill be air-dried. And then we will determine the degree of reconstitution and place that degree into a set of classes. Now here, we have two cells. One contains a sample from native grass, long-term native grass, and the other from long-term cultivation. And actually, the two sites are across the road from each other, so-- and they would be mapped the same soil. They are not from the field that we're in. The reason we selected them is because we'll see a large difference in aggregate stability,

quite a striking difference, and that that we wish to make a point. Okay, now, I'm going to invert these. These would be-- these samples then in a sequence of measurement would've been air-dried as we talked to earlier. And now, we're all ready to look at them. This is the-- from the long-term native grass and this is from the cultivated field across the way. And you can see that it's been relatively little reconstitution. The sample after being inundated in water looks to be about what we start

ed with, two to one millimeters discrete aggregates, whereas in this case, the-- we formed a kind of a plate and there's been considerable degree of reconstitution. Maybe I can just reach in here and open this up. And I know it maybe hard to see, but this is almost a devoid of any aggregate-- of aggregates. It's more like a mass. Now, we take these two samples in after we performed the measurement we discussed and then we place them into classes. This would be a high class of aggregate stability

and this would be a low class. And we have a set of class definitions in which we've tried to be as quantitative as we could, though, we have, as we've said earlier, it's a visual test, not a measurement. So there will be some variation in the placement made by one person versus another. And we ended up with 280 cc's, so we have-- [ Silence ]