Cone Penetration Testing (CPT) for Geotechnical Investigations (Legion Drilling Webinar #7)

⏰Thu, 01/02 09:46AM · 61mins

Transcript

Well, let me first quickly introduce myself. As Jonas has already said, my name is Ernst Wassenaar and I'm the regional manager for Geomil in Asia Pacific. I've started working in the CPT industry more than 30 years ago.

I have an electronics background and I started in our electronics department working with cones and calibrating equipment and that sort of stuff. So that's where I come from originally and throughout the years I've learned more about geotechnics and about the use of CPT in practice, basically.

So to start off with, why do we actually do CPT? Well, I think it's an obvious thing that if we want to. something if we want to construct something that we need to understand the subsoil and therefore ground investigation is a must in any of these cases.

If not things can go wrong like you can see here on this picture from I think it is China. This building collapsed. Of offshore applications same story apparently here a punch through of one of the legs resulted in this platform collapsing with all sorts of damage as a result.

Another typical example you are very familiar with in Australia is the mine tailings storage facilities and dams that can fail and that can lead to a lot of damage and even casualties. So, if we look into ground investigation and the definition of that, we could summarize that as sampling, testing, logging, and modeling of the physical and chemical properties of the ground.

There are many different methods of ground investigation, for example, drilling, sampling, geophysical testing, and then there's the in-situ tests, and the common penetration test, the CPT, is one of those.

Peter Robertson, a name I will mention a couple of times today, is one of the leading academics in the field of CPT. He wrote up this table, comparing the different in-situ test methods, and then sort of assessing how applicable they are for the different geotechnical parameters and the different ground types.

And what you can see here is that the CPT, the CPTU, so the CPT with pore pressure measurement, and the SCPTU, the S for seismic, how they sort of rank compared to these other methods. And what you can see is that the CPT has a pretty favorable, or the outcome is pretty favorable compared to other methods.

So this was a good reference to use. The book from which this table comes, which is the guide to CPT, is downloadable from the Robertson CPT website, if you are interested in more background reading.

So where does the CPT come from, and how did it develop over the years? So a very brief overview of the history and the technical progress around the field. 1932 in the west of Holland where we had a lot of issues with soft organic soils and railway lines that we tried to construct and that failed.

Mr. Peter Barnes invented a device to measure the bearing capacity of the soil and that was dubbed the compenetration test. Around 1935 we then see the first 10 TON penetration tests being carried out and you can see a picture here on the right hand side showing how that was conducted.

It was all manually operated by means of cranking systems, additional counterweights to help push in the gun. Around 1948 then we see the introduction of the mechanical conia. The first cones were all mechanically or mechanical designed.

um around 1948 we see the introduction of the comically shed jacket behind the comb tip that prevented soil entering the gap between the comb tip and the rest of the rods and that improved the measurements.

Then in 1953 we see uh Professor Beggemann, another Dutch engineer, he introduces the friction sleeve just behind the comb tip and that allowed for not measuring just the comb resistance and the tunnel push force but also to measure local sleeve friction.

Then around 1965 we see Fugro, probably the largest geotechnical contractor in the world. They developed the first electrical counts and this electrical comb still is the basis for today's counts in terms of dimensions, in terms of how it was designed.

And then around 1980 we see the introduction of the piezocone where the piezometer was integrated into an electrical cone allowing for measurement of pore pressure in addition to the cone resistance and the sleeve friction.

So what is the CPT? It's a ground investigation technique used in soils. It's not suitable for rock but in soils it can almost always be used. It constitutes advancing a comically shaped tip into the soil and while you do that you measure the data.

This provides soil strength and behavioral characteristics of the soil. It's done with standardized speed which is determined as 20 millimeters per second. you use a reaction force that is required, otherwise you cannot push the cone into the ground, and typically you would use hydraulic ramps to push that cone into the soil.

You have an electro-pokone, which is what we will focus on today, although the mechanical cone is still used in some parts of the world, but in more modern societies the electro-pokone is prevailing.

So when you have an electro-pokone you do a downhole in-situ measurement and it provides real-time data. It measures three basic parameters. So cone resistance Qc is the force acting on the projected area of the cone tip.

The sleeve friction is the friction along the sleeve that is positioned just behind the cone tip. and then there's the pore pressure can be measured in different positions. There's a U1 and a U3 position as well but the most common position for the filter is the U2 position that's in the shoulder of the contib and that measures the pore pressure there.

So if we look at typical projects and applications then you can say that the CPT is suitable for any geotechnical problems as long as the soils are testable by CPT. Very prominent use of the CPT especially in countries like Holland where a lot of pile foundations are being designed for many of the buildings or constructions then the CPT is a unique tool to design a pile.

It is essentially a miniature pile that you push into the ground so it sort of resembles the same loading criteria as the pile itself does. So it's a very simple straightforward method to do pile foundation design.

Soil improvement, think of compacting soil, think of mixing soil especially in land reclamations such as the one here on the picture where you have a sand fill which is not immediately suitable to build on so the soil needs to be compacted and the CPT is a unique tool to measure the grade of compaction.

There's a direct relationship between become resistance QC and the compaction grade. Settlement prediction if you deal with soft soils with load on top of it can be a rub. can be industrial park and be buildings anything of that sort and for example when installing vertical weak drains then settlement will occur and the CPT can be used as a profiling tool to determine how much settlement will to be expected CPT is not probably not the best tool to predict settlement but it will help in profiling the soil and then with more focused methods such as lab tests on samples or maybe using a DMT you can determine or you can estimate the settlement well the original use of the CPT embankment and type profiling this was what it was invented for embankments carrying a railroad back in the 1930s the profiling capabilities with the CPT lots of data in relatively short amount of time.

Stability issues especially around mine tailings, the result of such failures are well known and mining companies nowadays invest a lot of money in preventing this sort of thing to happen again. So a lot of research or a lot of testing is being done and the CPT is used there a lot as well.

Seismic survey especially for liquefaction, a potential liquefaction analysis. Think of for example the situation in Christchurch in New Zealand 10 years ago where due to the earthquakes a lot of liquefaction took place and after that has happened a lot of testing has been done to determine which areas of Christchurch are safe to build on and which areas are not.

Environmental issues the CPT can be used for a lot of other testing methods so for example here is an example from Kuwait where the research institute in Kuwait is installing a source of sampling and remediation tools to handle oil contamination in the soils which occurred after the first Gulf War.

What I mean to say with this is that the CPT equipment can be used to install other sorts of testing equipment or other sorts of tooling, more about that later. Very prominent use of the CPT especially in today's age where we see the green energy booming so a lot of places around the world these big wind farms are constructed offshore and again the CPT is the excellent tool here to determine or to design the foundation for these wind turbines.

Offshore construction, oil and gas related, think of these sort of platforms but there's a lot more sitting on the seafloor that you may not see processing stations, pumping stations, valves, all that sort of equipment needs to be safe on the seafloor and therefore needs a proper foundation and therefore needs proper testing.

So the CPT is used there a lot as well. And then if we look at the wind farms and also the offshore constructions then Obviously, infrastructure is going to and from these constructions offshore. So, pipeline cable routing requires also testing before these are installed.

This is an overview of different applications. There are obviously a ton more, but this is just a brief overview. Again, a table from the same book I referred to earlier. So, Robertson has sort of listed all the different methods in different types of soil and has then indicated whether the CPT is reliable for this sort of application in this sort of soil.

And you can see here, like for pile design, there is the CPT is very suitable. Same for bearing capacity settlement, as I already mentioned, not the best tool probably, but a good help in profiling the soil mass.

Compaction control and sand, that's where the CPT really excels and for the perfection analysis. The CPT is also used very, very widely. Again, if this is of interest, then I would suggest that you download that book.

It's free to download, so you can always use that as a reference. If we look at the use of CPT data, we can essentially subdivide it into three categories. The first and most simple one is the stratification, where you do an interpretation based on fundamental characteristics of the soil.

Essentially you look at is it soft or is it hard, is it drained or is it undrained, is it cohesive, is it uncalhesive, that sort of fundamental characteristics you can gain from the CPT data. Here's an example where you see the typical CPT plot and you can immediately identify three different sort of soil types.

The top one being sandy, gravelly, where friction ratio is low, high cone resistance, then the second layer, the green colored layer. You can see that the cone resistance is still reasonable around 10 MPa but this indicates it's lower than above and you see slightly higher friction ratio.

This indicates that it also contains finer material. And then the third layer is the clay layer, a soft clay where you have low cone resistance. Also low sleeve friction but relatively speaking higher than in the other layer, so you see a higher friction ratio here.

And that clearly indicates that we are dealing with a cohesive soil. So that is a soft clay layer. So again the very essential entry use of CPT data where you can very clearly identify the different soil types.

Or sophisticated use is the soil classification where empirical charts are used to compare known soil profiles with the data at hand. So that leads to this sort of classification charts. This is the probably the most commonly used one which is from again from Robertson 1990 and uses or it uses normalized cone resistance and friction ratio and pressure ratio to come to a classification D sub divided over nine different zones.

So we have two charts, the one on the left is based on the cone resistance, normalized cone resistance and normalized friction ratio, the one on the right is based on normalized cone resistance and poor pressure ratio.

So you get two different charts, you get two numbers out of this chart and well if it's nice if they both they're both the same or at least come close. This is then how that looks in a typical CPT plot, where on the right-hand side you see the soil behavior type index with a classification.

Now this is just software-based, you just just input the data and software outputs these sorts of plots. Now there is obviously always some engineering judgment required here because it's not an exact science, the soil classification, I always say it's a guideline.

It's a guideline that indicates how the soil behaves and that it is most likely a sand or clay or whatever, but it's always important to keep in mind and it is their software that these charts are based on samples from all over the world that soil is never the same in any place.

So always keep in mind that you have to be careful with these sorts of classifications. Then the most prominent use of CPT data is getting soil design parameters straight out of the CPT data. So empirical formulas are used to sort of output soil design parameters purely based on the basic parameters that we measured, which are the cone resistance, sleeve friction and pore pressure.

Robertson again listed some of these parameters in a table and indicated how how reliable or how applicable these are for how applicable the CPT is for these parameters. And as you can see here, it's not always perfect.

It's not a perfect, most of the CPT is not a perfect tool. For some things it is, for some things it's very good, but for other stuff it might be not the best tool. So it's important to keep that in the back of your mind.

It's not the magic tool that gives you perfect data for every single one of these parameters. So some words of caution there. So when you look at soil classification, make sure that you use all the information that is available.

Never over rely on one classification chart. It's best to use the combination of the two as I've shown in one of the previous slides. and use the QC and FS1 and the QC and U21. If you have samples or other ground investigation methods then use that data or use those samples to correlate your data, correlate your CPT data I mean, and be careful when you use differently sized counts.

If you use 10 square centimeter counts and 15 if you mix those you expect slightly different readings. So especially if you're if you're working with very small numbers be careful not to careful when you compare those numbers.

When you look at soil design parameters there are numerous semi-empirical correlations as was shown in the previous table. It is important to understand the reliability And the applicability of these different parameters, as they vary greatly, as was indicated in that same table, and also understand that seismic measurements, if you have those that they improve the ability to estimate soil stiffness parameters greatly.

So that is to keep in the back of your mind. Now, look at the practical side of things. How do we push the county to the ground? Well, we can do it in a very, very simple way. As you can see here on the left hand side is a picture from Indonesia, where the local contractor is still using a hand cranked CBT device.

He uses that in combination with electrical CBT, which is clearly illustrated by the rods and the cable you see in the same picture. But this is obviously not the most high tech way of pushing a gun.

But if it works, it works. On the right hand side, a picture that was shared with me by Jonas, where you see one of the NUMAK rigs, which is a combined, or a hybrid, the GeoPro rig that can do all sorts of testing, but also CBT.

So that's obviously a more high tech and more versatile kind of rig. Another two examples. I won't list all the different options because then we would be here for another two hours. But on the left hand side, a very simple rig that is attached to the boom of an excavator.

The excavator pushes it down to the ground, so that is the reaction force that is achieved that way. And you can do this in a very quick manner, as long as you have that excavator. and the excavator can position you on the location where you need to be.

On the right-hand side, a dedicated CPT rig completely fitted out for the use of CPT remote controls here on the reclamation side where it is used for compaction control mainly. Just to illustrate these different things, because in the end I always say that the pushing equipment itself is basically irrelevant from a data perspective.

What I mean with that is that there is no impact on the quality of the data as long as you make sure that your cone and your data position system are in good working order within the calibration parameters etc.

As long as that cone is pushed in at a constant speed which is 20 millimeters per second. plus or minus five according to the standards, that's tolerance. As long as it is pushed in with that speed, it's okay, as long as your pushing system is stable, it's capable of generating necessary push force, then it doesn't matter as long as your cone and your data acquisition system are up to today's standards or then your data will be reliable.

Obviously, this is not to be confused that the pushing equipment does play a significant role when you talk about, okay, how much CPT can I do in a day? So how productive is it? How efficient is it? Pick the right tool for the right job.

Pick the right type of CPT equipment. What sort of developments do we see recently as a manufacturer, but I mean, this is obviously market driven. So what do we see happening in the market? We see a diversification.

So where a CPT maybe 20, 30 years ago, there was just one type of cone, maybe two or three, but not that many. And every CPT was more or less considered to be the same, whether it was in very soft materials or for pile foundation, whether it was for compaction control or for settlement prediction.

We are moving away from that. So the latest standards, but also the market is driving this. So we move away from the one size fits all philosophy. So it means that for different applications, we see that different cones are being used, different cone types and different classes of cones, or about that in a minute.

Is obviously driven by the purpose or the objective of the. investigation and the soil conditions that you are testing. In other words, if it's very soft, if it's a mind-tailing, where we're talking about the shear strains of a few kPa, it's a totally different type of test if you compare that to compaction incense that have cone resistance of maybe 25, 30 MPa.

So what sort of selection criteria are then used? Well, if you work according to a standard, if you work according to the ISO standard, then there are application classes in this standard. And the application classes more or less indicate what the accuracy is that your cone or your CPT has to apply to.

In the latest draft, so there will be a new ISO standard fairly soon, the draft for that has been released last year, and in this new ISO standard, the application class is now subdivided into different subjects, so the cone is looked at separately from the CPT itself.

So the cone is basically assessed, like how accurate is the cone, in what class does that fall, and then the test itself, so the CPT in the field is assessed separately, and when these two are combined, you come to a certain test category.

So based on the application, the objective of the investigation, etc, etc, you pick the right cone size and the range of load cells and transducers. You pick the cone type, there are two different cone types on the market, either compression or subtraction, I will explain that to you in the next couple of slides.

So which one do you pick? Well it depends again on your investigation and your soil conditions. So if we look at the cone design, very briefly, then the most commonly used sizes are the 10 and the 15 square centimeter cone.

When I started 30 years ago, the number of 15 square centimeter cones was very very limited, maybe 5 percent of the production that we did. Nowadays it's about 50-50, so the 15 square centimeter cone is being used more and more.

As I already mentioned, two different cone designs. One is a compression cone, which is a relatively accurate cone and sensitive, and then there's the subtraction cone, which is more solid and robust type of cone.

So once again very quickly the difference is the way that the friction sleeve is measured. So in a compression cone we have an independent measurement of the cone resistance and the local sleeve friction.

On the left hand side you can see a cutaway drawing of a compression cone with two separate load cells. The orange colored cutaway part is the cone resistance load cell and the red colored one is a very thin line so it's a very thin load cell measures the local sleeve friction.

So you get two independent different measurements and because of that there is no further processing required. What you can immediately recognize if you look at that drawing on the left which is to scale then you can see that the cone load cell is much thicker, essentially, than the friction load cell, indicating that the range of these load cells is very different.

That is because the loads in the stresses in the soil are so different. So standard cone, what used to be standard cone, has a capacity of cone resistance of around 100 MPa, whereas the friction typically has a capacity 1 MPa.

So there's a factor 100 different. If you look purely to forces, so kilonewtons, not because of the different areas, the other cone is smaller than the friction sleeve. If you look at that, then it's 100 kilonewton for the tip versus 15 kilonewtons for the friction.

So it's about a factor 7 different. Summarizing the cone load cell for the friction load cell is 7 times more sensitive, or needs to be 7 times more sensitive than the cone load cell. Hence the two different thicknesses, and with that, two different sensitivities.

Look at the subtraction cone. The cone is also used a lot. You have one load cell, and that one load cell measures both cone resistance and the friction. So we have one combined load cell. You can see that on the left again.

In that cutaway drawing, you see all the orange. There's only one load cell. There is no second load cell. But you do see two strain gauge bridges, one at the bottom of the cone, and one at the top of the load cell.

Sorry, one at the bottom of the load cell, one at the top of the load cell. so you can also see that in the picture on the right hand side. You can see the two strain gauge bridges there. The upper strain gauge bridge, so the top one, measures the cone resistance plus the friction.

How come? Because the friction sleeve is attached to the middle of the load cell. You can very clearly see that on the picture on the right hand side. You can see the friction sleeve is screwed on in on the middle bit of the load cell.

The lower part of the cone load cell only measures the cone resistance because the friction sleeve is attached above it. So what you get is that the lower strain gauge bridge measures my cone resistance only and the top one measures my cone resistance and the local sleeve friction.

Because of that further processing is required to get to the sleeve friction. You have to subtract the output from the lower bridge from the output of the upper bridge because of this subtraction, we call this a subtraction curve.

What is clear from this is that you are, in order to arrive at sleep friction, you are subtracting two relatively big numbers because the cone resistance is a higher number as I explained earlier. So you are subtracting two relatively large numbers to arrive at a relatively small number.

So in general you can say that the subtraction cone will be less accurate when it comes to friction measurements. So which one to use? You have a compression cone which has a smaller dimension load cell for sleep friction and based on the book's law the same force will result in larger deformation.

So it's more sensitive to small strains and therefore more delicate. The subtraction cone on the other hand it's a one larger dimension load cell which measures both the cone resistance and sleep friction.

Same force will result in smaller deformation and therefore it's less sensitive to small strains. The upside is it's less delicate. The subtraction cone is typically used in harder soils and it's used in situations where, for example, the cone cannot be cleaned after each test.

The compression cone is more sensitive, needs more cleaning. We recommend to clean it after each test for the subtraction cone that is less critical. Anyway, all of these differences only relate to how the sleep friction is measured.

It does not affect the measurement of the cone resistance for the show. So back to the developments. So we see more sensitive cones entering the market to meet the strictest of requirements. Class one plus is a class that was introduced in Holland three four years ago for dike assessments as a big program big government funded program to assess all the dikes because of the expected rise of the sea level.

All the dikes in Holland had to be reassessed and for that in order to get very accurate shear strength estimates the industry introduced or the government agency introduced a new testing class which was dubbed one plus.

This one plus class is now in the new ISO draft is dubbed class zero just for your reference. but it's basically the same numbers or the same accuracies, but it is considered class zero instead of class one plus.

These more sensitive cones, that's what we see more and more nowadays. And I have an example here where we have some testing done with an ultra-sensitive cone that we introduced last year, three megapascal capacity cone.

On the right-hand side, what you can see is the friction readings, the difference in friction readings. So we have comparing a conventional 10 MPa cone, which is already a more sensitive cone, 10 MPa, versus an ultra-sensitive 3 MPa cone in blue and red or orange.

This is a mind-tailing, the 10 MPa cone, as I already mentioned, is a very sensitive cone. The FS readings, however, are lagging in this soft material of the 10 MPa cone, likely because of the friction of the seals and because there's insufficient material deformation in the cone itself.

So the load cell itself is not deforming enough under these very, very small loads. Ultra-sensitive cone, which is made from a different load cell material, deals with this better. This meets the class one plus or the class zero if we follow the latest ISO draft.

Another example is a comparison of a conventional 100 MPa cone, the gray and yellow plots, versus the ultra-sensitive cone. This is in the marine sediment, apparently this is in Tasmania, used 100 MPa cones of compression and subtraction.

designed just to compare everything. The QC errors that you see on the left-hand side are likely attributable to temperature effects. It was in the cold season, and we assume that the guns had to be bumped off basically before they were used.

So that's the differences you see in regular guns and the more sensitive guns that we see more and more nowadays. But we also see additional parameters being measured. So seismic testing is becoming what is starting to become the norm in various applications, especially when you look at things like liquefaction analysis.

It looks like this. There are different systems on the market, but this is how the system looks like that we. manufacturer. So we have a standard cone and on top of that there's an add-on module which has in this case a dual array set of sensors.

So we have a bottom receiver and a top receiver either one receiver only measuring the shear wave velocity or the double set of receivers where we do not really measure the shear wave velocity but also compression wave.

The surface source wave is generated typically that's just done using a hammer big hammer and a plate steel plate or steel beam something like that it doesn't really matter it's not that critical as long as you can get that energy that source wave into the ground and then the typical measurement looks like this where the usual testing interval is every one meter so in this case you see on the left hand side here the tests are done at 4.19 meter 5.19 6.19 so one meter interval you can see on the left hand side the data is recorded so the source wave arrives at the top receiver first logically then arrives a little bit later at the bottom receivers and the difference between the two is my is my or essentially leads to my shear wave velocity we know the distance between the two sets of receivers we know the difference in arrival time and then we can calculate the difference in or we can calculate the shear wave velocity over that distance between the top receiver and bottom receiver on the right hand side the data is rephased just to check for quality this is to determine the quality of the testing It's a very common method that's being used more and more.

Other equipment that can be efficiently used with the CPT, for example the field train tester, you can use an up-hole system as the one you see in this picture, this is what GMU offers. There are also systems on the market that measure down-hole, but essentially the system looks the same in the sense that you have a set of outer tubes and inner rods, everything is pushed to the test depths where you want to do a vane shear test.

You extend the blade, different sizes of blades available, you extend the blade, you do your test and then you continue to the next testing depth, so you can do multiple vane tests in one location. Samplers can be used with CPT equipment, so there are dedicated samplers designed for the use with CPT rigs.

So a sampler like this is attached to the bottom of the rods, is pushed to the depth where the sample needs to be taken, so that can be 20 meters, so you don't lose any time or not much time, you can just push it down to 20 meters.

When it arrives at the testing depth you can open it up by lowering a unlocking mechanism through the rods, you open it up and then essentially you keep the piston, the tip, you keep stationary and you push the outer rod or you push on the rods and then the the sample tube penetrates deeper, then you can take a sample this way, it's essentially piston second.

And another testing method that we see is the flat dilatometer or the DMT made by Marchetti from Italy, this can be pushed in using the same CPT equipment, using the same CPT rods, you can push it in and then every, I believe every 20 centimeters, I'm not 100% sure, every 20 centimeters you can do a DMT test and get more information about the stiffness parameters, soil stiffness parameters.

Another thing we see nowadays, especially offshore, but we've also seen people using these in mine tailings, if it's very soft, are the full flow penetrometers, where you use a T-bar or a bowl that is attached to the cone and is then essentially pushed in with the CPT rig and using a regular cone, but with a different base.

So instead of a cone tip, you attach a bowl or a T-bar and the soil flows around this sensing mechanism, which is the T-bar or the ball, hence the name full flow. Gets you a more precise measurement or estimate of shears on-drain shear strength.

So what do we see in, we look at practical challenges in the field, what goes wrong? Very often it has to do with the cone condition. So it could be that the zero readings and the location where the zero readings are taken is incorrect.

So the zero readings of the cone are the main key for the operator to control the condition of the cone. If the zero readings are stable, it is the sign that the cone is in good condition and within the calibration parameters.

Still the zero readings need to be taken at the proper location meaning above the ground when it's fully unloaded. Sometimes this goes wrong, unfortunately. The straightness of a cone is important. There is a direct relationship between the straightness of a cone in the zero readings, meaning that if a cone is no longer straight, if it's bent, then this will result in a drift of the zero readings immediately.

The cleanliness and the dirt seals are these in place and are they in a proper condition? As you can see here on this picture, here the dirt seals and the cleanliness of the cone is not good. As long as you clean the cone afterwards, you make sure that the dirt seals are properly positioned again, then everything should be fine for the next test.

If the cone is not clean and if the dirt seals are not in place or they are not properly positioned, then that can lead to negative or equal to zero friction readings. Or what you can also see is what we call crosstalk, where the friction readings are affected by the cone resistance.

So if there's a load on the cone, that load is immediately transferred onto the sleeve, hence the name crosstalk. Water seals inside the cone. The cone is full of electronics. Electronics and water are not the best combination.

So in order to keep the water out, the cone is provided with water seals. These need to be in place and the integrity has to be okay. The wear of a cone, it's all determined by the standards, the mix.

dimensions the minimum dimensions just check that make sure everything is okay here on the right hand side a picture of how we sometimes get cones back from use and I can guarantee you this is far far far beyond the beyond the tolerances as set out by that.

These are cone saturation this is sometimes a problem if the saturation of the cone and the filters is not conducted properly then that will lead to a desaturated system air in the system. Air is compressible as a gas is compressible whereas a fluid isn't obviously so what we want to see is the pressure of the water so we want to see the pressure of the fluid not the pressure on the gas the gas inside the system because it is compressible,

it will act as a shock absorber. And what you can see here on the right hand side is three different CTTs with three, I should say, differently saturated cones. One was made with cone not saturated at all.

That's the black line. The red colored line was a cone where the filter was saturated and replaced, but not the complete cone saturated. So you can see the effect of that on the data. The blue line is obviously how it should have been.

Temperature differences can play a role. You saw that in one of the earlier plots that I showed about the ultra sensitive cone in Tasmania. Temperature shocks. So if the temperature difference between the outside air and the ground, if that difference is very high, that can lead to jumps in readings.

And most cones, our cones are all temperature compensated. And I would like to think that most cones on the market are temperature compensated. But the temperature shock will always lead to a slight jump in readings.

And it will take time for the cone to acclimatize to the new surrounding temperature. So it's very important to give the cone the time to do that or to prevent temperature shock. So make sure the cone is not outside in the direct sunlight or something like that.

Keep it in the shade. Put it in a bucket of water, just to keep it at a moderate temperature. Make sure the penetration speed is okay. 20 millimeters per second, as already mentioned a few times today.

All the literature, all the research, everything is based on the speed. So make sure you maintain that. And finally, something that is usually underestimated or gets unnoticed, make sure that your depth measurement is correct.

It's lovely if your cone is in a perfect condition, gives you perfect data, but if the depth measurement is incorrect, then all the data given by the cone is essentially worthless. Because you think that cone resistance is at 10 meters, is so and so much at 10 meters, but in reality the cone was at 12 meters.

So all your engineering, all your calculations are erratic and essentially worthless. What other challenges do we see on a day-to-day basis? Well, unfortunately the CPT is still not always an established method, especially in countries where the SPT, the standard penetration test, prevails.

that way not benefiting from efficiencies and the more accurate parameters that the CPT can provide. This is not so much true for Australia but for other countries. This is often still the case. Think of countries like India or for the US even where the CPT is not that established.

For understanding of standards, unfortunately we see a market-wide lack of understanding of the objective of these application classes that we see in the ISO standard. The idea of these classes is to distinguish between the different tests.

So for a very soft material we need a different type of cone. It's a different test than in a hard material. It doesn't mean that class one is always what you need. If you think I want the best so I need class one is incorrect.

It depends on what sort of project are you dealing with. If you want to design a pile foundation there's no reason for class one test. Unfortunately it's extremely difficult to accurately assess the class that you've achieved because it's not only about the cone.

It's the total CPT that needs to comply to the test standards. So how are you going to determine if you've done everything right in the field and in the field no inaccuracies have occurred. That is extremely difficult.

Also it's not that easy for us as cone manufacturers to exactly assess or measure the application class for a particular cone. Why? Because it was not in the ISO 2012. It was not indicated how this should be measured or how this should be assessed.

among the different cone manufacturers there was a different interpretation on how to do that, so you get a lot of miscommunication about that as well. Fortunately, the new ISO draft that will come out hopefully later this year or maybe next year, it deals with most of these issues, so it has, there's a better distinction between the cone and the test itself, so the practical side of the thing and the instrument,

also it indicates how to assess the petatrometer class, how to measure that, so there is, there will be less of debate about that. Another challenge we see is that sometimes there is uncertainty and debate about the quality of the data, especially around the ski friction.

pore pressure and these patient tests, if those are conducted. Not so much about common resistance. Y is a relatively simple measurement, which is less sensitive to error. But the sleep friction and the pore pressure are more sensitive to things like dirt, to talk about pore pressure saturation, desaturation.

So the quality of that data is not always what it should be, maybe. And therefore, there is also more debate about it. And therefore, it is important that there is more understanding about how things work.

And there's more appreciation for how cones are being prepared so that they are properly cleaned, properly saturated, etc. That leads to less uncertainty and therefore less debate. And the other side of the coin is that we sometimes see that consultants or clients or engineers are too focused on the data and fail to understand what I've mentioned, what I've called here the bigger picture.

What I mean with this is, for example, when we think back of the soil classification charts that we looked at earlier, that is not an exact science. So if the soil classification says you're in a zone 3 material, it doesn't necessarily mean it is a zone 3 material.

It is a guideline. Unfortunately, some consultants, especially the ones that do not really understand the practical side of things, they are looking at the numbers and they take it as gospel, which is not the best approach.

And unfortunately, and there's obviously a relationship with the other issues we've discussed here, that is that CPT operating companies, CPT contractors sometimes cover it. corners and do not adhere to quality standards or to standards to begin with to CPT standards.

That is often also a problem that we see in practice. So that brings me to the end of this presentation. I've done well time-wise, exactly one hour. So I hope it was informative. It is very basic and a summary.

As I said to Jonas earlier when we discussed this webinar upfront, what I said to him is that I can talk about CPT for days on end. So if there is the need for some more in-depth information, then I'm happy to run one or two more webinars.

That's not a problem at all. Um, but in order to give you a brief overview in an hour, then obviously you have to limit yourself. So this is what I came up with. And once again, I hope it was informative.

And if there are any questions, then I'm happy to answer those, or I will try to answer.