Name: a bending test for determining the atterberg plastic limit in soils
Uploaded: 2016-06-28T15:00:00
Description: Watch this Scientific Journal Video about A Bending Test for Determining the Atterberg Plastic Limit in Soils at JoVE.com

This research has been partially funded by a grant (Beca de Investigaci&#242;n Ambiental) from the Servicio de Medio Ambiente de la Diputaci&#242;n Provincial de Toledo (gran number 133/10) and the research project PEII-2014-025-P of the Junta de Comunidades de Castilla-La Mancha.

1. Collect, Dry and Sieve the Test Sample
<ol>
	<li>Collect a soil sample in the field (use a shovel or a trowel) and store it in a polyethylene bag. 
	Note: The volume of the sample varies depending on the type of soil: in fine soils (clays and silts) between 100 and 1,000 g is generally sufficient, but in sandy soils and those containing gravel and pebbles, large amounts may be required, from a few to several kg.</li>
	<li>Reduce the sample by quartering in the laboratory if this is too voluminous (use a soil sp...

<ol>
	<li>Atterberg, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=&#220;ber+die+physikalische+Bodenuntersuchung+und+&#252;ber+die+Plastizit&#228;t+der+Tone.">&#220;ber die physikalische Bodenuntersuchung und &#252;ber die Plastizit&#228;t der Tone.</a> Internationale Mitteilungen f&#252;r Bodenkunde. 1, 10-43 (1911).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ASTM Standard ASTM D 4318. Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. , (2005).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> UNE 103-103-94. Determinaci&#242;n del l&#236;mite l&#236;quido de un suelo por el m&#233;todo del aparato de Casagrande. , (1994).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> BS 1377-2. Methods of test for soils for civil engineering purposes-Part 2: Classification tests. , (1990).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> UNE 103-104-93. Determinaci&#242;n del l&#236;mite pl&#225;stico de un suelo. , (1993).</li><li>Whyte, I. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soil+plasticity+and+strength:+a+new+approach+using+extrusion.">Soil plasticity and strength: a new approach using extrusion.</a> Ground Eng. 15 (1), 16-24 (1982).</li><li>Temyingyong, A., Chantawaragul, K., Sudasna-na-Ayudthya, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Statistical+Analysis+of+Influenced+Factors+Affecting+the+Plastic+Limit+of+Soils.">Statistical Analysis of Influenced Factors Affecting the Plastic Limit of Soils.</a> Kasetsart J. (Nat. Sci.). 36, 98-102 (2002).</li><li>Bobrowski, L. J., Griekspoor, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+the+Plastic+Limit+of+a+Soil+by+Means+of+a+Rolling+Device.">Determination of the Plastic Limit of a Soil by Means of a Rolling Device.</a> Geotech. Test. J., GTJODJ. 15 (3), 284-287 (1992).</li><li>Rashid, A. S. A., Kassim, K. A., Katimon, A., Noor, N. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Determination+of+Plastic+Limit+of+soil+using+modified+methods.">Determination of Plastic Limit of soil using modified methods.</a> MJCE. 20 (2), 295-305 (2008).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> ASTM Standard ASTM D 248. Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). , (2000).</li><li>Casagrande, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Research+on+the+Atterberg+limits+of+soils.">Research on the Atterberg limits of soils.</a> Public Roads. 13 (8), 121-136 (1932).</li><li>Casagrande, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Classification+and+Identification+of+Soils.">Classification and Identification of Soils.</a> Transactions, ASCE. 113, 901-991 (1948).</li><li>Sokurov, V. V., Ermolaeva, N., Matroshilina, T. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plastic+limit+of+clayey+soils+and+its+subjetive+determination.">Plastic limit of clayey soils and its subjetive determination.</a> Soil Mech. Found. Eng. 48 (2), 52-57 (2011).</li><li>Andrade, F. A., Al-Qureshi, H. A., Hotza, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+the+plasticity+of+clays:+A+review.">Measuring the plasticity of clays: A review.</a> Appl. Clay Sci. 51, 1-7 (2011).</li><li>Harison, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+the+BS+cone+penetrometer+for+the+determination+of+the+plastic+limits+of+soils.">Using the BS cone penetrometer for the determination of the plastic limits of soils.</a> G&#233;otechnique. 38 (3), 433-438 (1988).</li><li>Feng, T. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fall-cone+penetration+and+water+content+relationship+of+clays.">Fall-cone penetration and water content relationship of clays.</a> G&#233;otechnique. 50 (2), 181-187 (2000).</li><li>Feng, T. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+a+small+ring+and+a+fall-cone+to+determinate+the+plastic+limit.">Using a small ring and a fall-cone to determinate the plastic limit.</a> ASCE, J. Geotech. Geoenviron. Eng. 130 (6), 630-635 (2004).</li><li>Lee, L. T., Freeman, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dual-weight+fall+cone+method+for+simultaneous+liquid+and+plastic+determination.">Dual-weight fall cone method for simultaneous liquid and plastic determination.</a> ASCE, J. Geotech. Geoenviron. Eng. 135 (1), 158-161 (2009).</li><li>Sivakumar, V., Glynn, D., Cairns, P., Black, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+method+of+measuring+plastic+limit+of+fine+materials.">A new method of measuring plastic limit of fine materials.</a> G&#233;otechnique. 59 (10), 813-823 (2009).</li><li>Sivakumar, V., O'Kelly, B. C., Henderson, L., Moorhead, C., Chow, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Measuring+the+plastic+limit+of+fine+soils:+an+experimental+study.">Measuring the plastic limit of fine soils: an experimental study.</a> P. I. Civil Eng. - Geotec. 168 (GE-1), 53-64 (2015).</li><li>Wroth, C. P., Wood, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+correlation+of+index+properties+with+some+basic+engineering+properties+of+soils.">The correlation of index properties with some basic engineering properties of soils.</a> Can. Geotech. J. 15 (2), 137-145 (1978).</li><li>Haigh, S. K., Vardanega, P. J., Bolton, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+plastic+limit+of+clays.">The plastic limit of clays.</a> G&#233;otechnique. 63 (6), 435-440 (2013).</li><li>Barnes, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+apparatus+for+the+plastic+limit+and+workability+of+soils.">An apparatus for the plastic limit and workability of soils.</a> P. I. Civil Eng. - Geotec. 162 (3), 175-185 (2009).</li><li>Barnes, G. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+apparatus+for+the+determination+of+the+workability+and+plastic+limit+of+clays.">An apparatus for the determination of the workability and plastic limit of clays.</a> Appl. Clay Sci. 80-81, 281-290 (2013).</li><li>Moreno-Maroto, J. M., Alonso-Azc&#225;rate, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+accurate,+quick+and+simple+method+to+determine+the+plastic+limit+and+consistency+changes+in+all+types+of+clay+and+soil:+The+thread+bending+test.">An accurate, quick and simple method to determine the plastic limit and consistency changes in all types of clay and soil: The thread bending test.</a> Appl. Clay Sci. 114, 497-508 (2015).</li><li>Bain, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+plasticity+chart+as+an+aid+to+the+identification+and+assessment+of+industrial+clays.">A plasticity chart as an aid to the identification and assessment of industrial clays.</a> Clay Miner. 9 (1), 1-17 (1971).</li></ol>

The Atterberg plastic limit1 is a very important parameter in soils, mainly because it is widely used for geotechnical purposes10,11,12. The standard thread rolling test for PL determination has been widely criticized because it is highly dependent on the skill and judgment of the operator who is conducting the test and consequently new approaches to obtain the PL are claimed6,7,9,13,15-20, 23-25. However the simplicity, low cost and quick performance of the standard PL test give it an ad...

Liquid Limit (LL) and Plastic Limit (PL) are the two most important soil consistency limits of those defined by Atterberg in 19111. LL marks the boundary between liquid and plastic states, and PL between plastic and semisolid states. LL is obtained around the world according to several standards through the Casagrande method2,3 or the penetration test4. Both methods are conducted mechanically by devices; thereby, minimal operator interference is involved. In the case of PL, the so called &#34;thread rolling test&#34; is the most popular and standardized method for its determination2,5. This test is based on rolling soil into 3 mm threads by hand until the operator considers the soil to be crumbling. For this reason it has been widely criticized because the skill and judgment of the operator play a critical role in the outcome of the test. Standard rolling test is importantly affected by many uncontrolled factors, such as the pressure applied, the contact geometry, the friction, the speed of rolling, the size of the sample and the type of soil6,7. The American Society for Testing and Materials (ASTM) developed the ASTM D 4318 standard which includes a simple device in order to minimize the operator interference2,8, however significant differences have been reported in some soils when comparing the manual rolling test against the test performed by the ASTM D4318 device9.
PL is a very important parameter for geotechnical purposes, since Plasticity Index (PI) is obtained from it (PI = LL - PL); PI is used to classify the soil in accordance with the Plasticity Chart shown in ASTM D 248710, based on the research of Casagrande11,12. Errors in the PL affect negatively this classification13, and for this reason, a new test for PL determination is required.
Pfefferkorn test, cone penetrometer, capillary rheometer, torque rheometer or stress-strain tests are some examples of alternative methods for measuring soil plasticity14, but these are not adequate to obtain the PL. With the special instance of fall cone tests, a large number of researchers have attempted to define a new methodology for PL determination using different penetrometer designs15-20, but without reaching any real agreement. Furthermore, all of it is based on the assumption that the shear strength at the PL is 100 times that at the LL21, which is not true22.
Barnes23,24 developed an apparatus that emulated the rolling conditions of soil cylinders in an attempt to lay down a clear criterion for PL determination. Nevertheless, some shortcomings are identified with this approach, such as its complexity, test duration and mainly the questionable means of calculating the PL25. The success of the standard rolling test lies in its simplicity, quick performance and low cost, so no alternative method will be able to replace it, unless it meets these three requirements and other ones, such as high accuracy and low operator interference.
In a previous study by the authors, a new PL approach was proposed25: the original thread bending test (or simply bending test) allowed the PL to be obtained from a graph in which it was represented the relationship between water content and bending deformations. The authors obtained and plotted several experimental points for each soil (the protocol followed to get these points was the same as that indicated in the present paper), so that the correlation of the points could be defined in two ways without compromising in any way the correct definition of the point path: as a parabolic curve, named the bending curve (Figure 1A), and as two intersecting straight lines with different slope, named the stiff-plastic line and the soft-plastic line. The stiff-plastic line is the steepest one, and PL was calculated from it as the moisture percentage corresponding to the cutoff point of this with the y-axis (Figure 1B). In this cutoff point the bending produced is zero, which is in accordance with the concept of plastic limit, i.e., PL is the moisture content at which the soil is not capable of withstanding deformations below this threshold (semisolid state) but it does bear them above it (plastic state). Although in the original study, the PL could not be obtained directly by the bending curve (this does not intersect the y-axis), this line was very useful because considering that the bending curve and the intersecting lines follow very similar paths, the bending curve equation obtained from the experimental data was used to obtain extra points to, firstly, correct any deviation, and, secondly, to carry out the test with just a few points as shown in Figure 1B.
<img alt="Figure 1" src="/files/ftp_upload/54118/54118fig1.jpg" /> 
Figure 1. Graphical representation of the B-W points in a tested soil by the original bending test. (A) The correlation of the points is represented as a parabolic curve, named the bending curve whose equation is included. (B) The correlation of the points is defined by two intersecting lines and other extra points are added (they were calculated from the bending curve equation). B values are obtained as B=52.0-D (where D is the average distance measured between the tips at the time of cracking in mm) and the PL is calculated as the water content corresponding to the cutoff point of the stiff-plastic line with the y-axis. This figure has been modified from Moreno-Maroto &#38; Alonso-Azc&#225;rate25. <a href="https://www.jove.com/files/ftp_upload/54118/54118fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
All the results were in excellent agreement with those achieved through the traditional thread rolling method by a highly experienced operator. However, the original bending test remained slower than the standardized thread rolling test. In an attempt to further economize test time, a one-point version was put forward. It was based on the average bending slope (m) obtained in the 24 tested soils, which was 0.108 (m is the slope of the bending curve when it is represented in double logarithmic scale; m appears on the bending curve equation in Figure 1A). By means of an equation where this factor was included, both the stiff-plastic and soft-plastic lines were graphically drawn, and thus the PL was estimated. These results were also highly correlated with both the multi-point bending test and the standard rolling test. In spite of this one-point version being even faster than the traditional test, the PL calculation was more complex because plotting was necessary. For this reason, on the basis of statistical criteria a new equation for PL calculation has been developed in this study, so that plotting is not required and results can be achieved with only one point, whereas the experimental protocol is the same as the original bending test. This new version meets the necessary requirements to replace the outdated thread rolling method.

<table border="0" cellpadding="0" cellspacing="0" width="978">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:244px;">Shovel</td>
			<td style="width:76px;">Any</td>
			<td style="width:117px;">NA</td>
			<td style="width:541px;">It is preferable a round point metal shovel so that it can penetrate easily in the soil.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Trowel</td>
			<td>Any</td>
			<td>NA</td>
			<td>It should be easy to handle both in field and laboratory, so approximately 500 g of soil should be the maximum of soil that could pick up.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Polyethylene bags</td>
			<td>Any</td>
			<td>NA</td>
			<td>The size of the bags depends on the collected soil volume. If we were interested in preserving the natural moisture, use sealing tape to close the bag.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Soil splitter&#160;</td>
			<td>PROETISA</td>
			<td>S0012</td>
			<td>It is not mandatory, because the quartering can be performed with the shovel, but in case of using it: it must be big enough to split several kg of sample in the cases of soils with large amounts of gravel or pebbles.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Oven</td>
			<td>SELECTA</td>
			<td>2001254</td>
			<td>The oven must be able to maintain constant temperature and should have some sort of slot or outlet opening to facilitate the release of water vapor.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Lab trays</td>
			<td>Any</td>
			<td>NA</td>
			<td>Metal trays are preferred over plastic because the first ones tolerate the oven temperatures better than the second ones.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mortar and pestle</td>
			<td>MECACISA</td>
			<td>V112-02</td>
			<td>A ceramic mortar is valid.&#160; It is recommended to use a rubber covered pestle because if the pestle was of other different materials (like metal or a ceramic), it could break the sand particles.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">0.40 mm sieve (or 0.425 mm sieve)</td>
			<td>FILTRA</td>
			<td>0,400 (or 0,425)</td>
			<td>Make sure that the sieve mesh is in perfect conditions of use (it should not be neither broken or worn).</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Brush</td>
			<td>Any</td>
			<td>NA</td>
			<td>It is useful for passing the soil during the sieving.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Wash-bottle</td>
			<td>Any</td>
			<td>NA</td>
			<td>It should have an approximate capacity of one litre and it should be easy to control the amount of water that it releases.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Distilled water</td>
			<td>Any</td>
			<td>NA</td>
			<td>Distilled water can be purchased or obtained by filtering from tap water (in this last case, a filtering system is necessary).</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nonabsorbent smooth glass plate&#160;</td>
			<td>Any</td>
			<td>NA</td>
			<td>The plate should have a minimum area of approximately 30 &#215; 30 cm.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Metal spatula</td>
			<td>Any</td>
			<td>NA</td>
			<td>The metal blade of the spatula must be flexible. Dry it with a paper after water-cleaning to prevent rusting.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Latex gloves</td>
			<td>Any</td>
			<td>NA</td>
			<td>Latex, vinyl, nitrile or other impermeable materials are valid. They should be thin enough to sense the soil with the hands.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cling film</td>
			<td>Any</td>
			<td>NA</td>
			<td>Normal cling film is valid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Airtight bags</td>
			<td>Any</td>
			<td>NA</td>
			<td>Remove the air before closing them.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Thread molder</td>
			<td>Any</td>
			<td>NA</td>
			<td>It is a tool designed in this experiment (drawings with dimmensions are included in this paper).</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Steel pushers</td>
			<td>Any</td>
			<td>NA</td>
			<td>It is a tool designed in this experiment (drawings with dimmensions are included in this paper).</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Damp cloth</td>
			<td>Any</td>
			<td>NA</td>
			<td>A normal damph cloth is valid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Roll of paper</td>
			<td>Any</td>
			<td>NA</td>
			<td>Normall rolls of paper used to dry hands are valid.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Caliper</td>
			<td>Any</td>
			<td>NA</td>
			<td>It must have an accuracy of at least 0.1 mm.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Paper and pen</td>
			<td>Any</td>
			<td>NA</td>
			<td>Paper and pen are used to write the results.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Containers with covers</td>
			<td>Any</td>
			<td>NA</td>
			<td>Small cylindrical glass containers are valid. If they do not have covers, watch glasses can be used as covers. Covers are useful to avoid the loss of water during the test and also to prevent the dry soil absorbs moisture from the air after oven drying.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Precision or analytical balance</td>
			<td>BOECO</td>
			<td>BPS 52 PLUS</td>
			<td>It must have an accuracy of at least 0.01 g.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Protective gloves</td>
			<td>Any</td>
			<td>NA</td>
			<td>Protective gloves are used to catch the metal trays from the oven.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tongs</td>
			<td>Any</td>
			<td>NA</td>
			<td>Tongs are used to catch the hot containers from the oven.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Desiccator</td>
			<td>MECACISA</td>
			<td>A036-01</td>
			<td>A normal glass desiccator with silica gel is valid to prevent the dry soil absorbs moisture from the air after oven drying.</td>
		</tr>
	</tbody>
</table>

a bending test for determining the atterberg plastic limit in soils

The thread rolling test is the most commonly used method to determine the plastic limit (PL) in soils. It has been widely criticized, because a considerable subjective judgment from the operator that carries out the test is involved during its performance, which may affect the final result significantly. Different alternative methods have been put forward, but they cannot compete with the standard rolling test in speed, simplicity and cost.
In an earlier study by the authors, a simple method with a simple device to determine the PL was presented (the &#34;thread bending test&#34; or simply &#34;bending test&#34;); this method allowed the PL to be obtained with minimal operator interference. In the present paper a version of the original bending test is shown. The experimental basis is the same as the original bending test: soil threads which are 3 mm in diameter and 52 mm long are bent until they start to crack, so that both the bending produced and its related moisture content are determined. However, this new version enables the calculation of PL from an equation, so it is not necessary to plot any curve or straight line to obtain this parameter and, in fact, the PL can be achieved with only one experimental point (but two experimental points are recommended).
The PL results obtained with this new version are very similar to those obtained through the original bending test and the standard rolling test by a highly experienced operator. Only in particular cases of high plasticity cohesive soils, there is a greater difference in the result. Despite this, the bending test works very well for all types of soil, both cohesive and very low plasticity soils, where the latter are the most difficult to test via the standard thread rolling method.

The PL equation shown in the step 6.1 of the protocol was achieved through a statistical study of the 24 soils tested in a previous study of the authors25 (Table 1). The objective was to know the most probable bending slope (the term m in the bending curve equation, which appears in Figure 1A) and the average value of B on the bending curve at which PL was obtained according to the original bending test (the original test was conducted...

Watch this Scientific Journal Video about A Bending Test for Determining the Atterberg Plastic Limit in Soils at JoVE.com

A Bending Test for Determining the Atterberg Plastic Limit in Soils

The traditional standardized test for determining the plastic limit in soils is performed by hand, and the result varies depending on the operator. An alternative method based on bending measurements is presented in this study. This allows the plastic limit to be obtained with a clear and objective criterion.

The thread rolling test is the most commonly used method to determine the plastic limit (PL) in soils. It has been widely criticized, because a ...

The overall goal of this new procedure is to determine the plastic limit in soils by measuring bending deformations. The traditional thread-rolling method is highly influenced by the skill of the laboratory operators, so an alternative approach is presented. This method allows the plastic limit to be obtained with a clear and objective criterion.Therefore the obtained results are highly reliable to classify and identify soils for botanical purposes. The main advantage of this technique is that it is not only quick, simple, and cheap, but also accurate and free of subjective interpretations. Beginning with a fine soil sample, dry it at 60 degrees Celsius or less, as needed.Next, disaggregate the soil manually using a mortar. Preferably, use a rubber-lined pestle to avoid breaking up the sand particles. Then, pass the sample through a 0.4 millimeter sieve and discard the soil collected in the sieve.Now, take about 20 to 40 grams of soil and wet it down on a non-absorbent glass plate. Then, knead the sample with a metal spatula until a homogeneous soil-water mixture is obtained. Wearing latex gloves, roll the mixture into a ball that is between three and five centimeters in diameter.Now, make a second ball with more or less water than the first, so the balls have different moisture content. Both soil balls must not crumble or stick when they are handled. Then, wrap each soil ball with cling film and place them in an airtight bag.Store the bag for 24 hours under hermetic conditions. After the tempering period, wearing latex gloves, flatten the soil ball on a smooth glass plate into a nearly three-millimeter thick patty. Keep the patty's surface covered with cling film to avoid moisture loss.Then, using a thread moulder, get the thickness down to precisely three millimeters. Now, cut the jagged edges of the flattened soil mass with a spatula, and make strips of soil that are at least 52 millimeters long, and three millimeters wide. Next, roll the soil strip with the thread moulder until the square section just becomes round, so it is three millimeters in diameter.If the strip is too dry and crumbly, or too sticky, repeat the test, using soil with more or less water content. Next, place the soil thread next to the front side of the thread moulder, and use the width of the thread moulder to make the cylinder exactly 52 millimeters long. Now, turn the thread moulder upside-down, and put the cylindrical piece in contact with the central part of the soil thread.Put the steel pushers in contact with the center of the soil thread. Then, carefully move the steel pushers towards the tips of the soil thread in a circular path. Repeat this motion, until the point of cracking.If the first crack appears near one of the thread tips, keep bending the other tip until the second crack appears at the opposite end. Now, remove the thread moulder and use a caliber to measure the distance between the central part of each tip to a precision of 0.1 millimeter. Now, put the soil thread into a container of known weight, and cover it to prevent moisture loss.If the bending deformations are so large that even the thread tips come into contact, remove the pushers and thread moulder, and continue bending the soil thread by hand, until the point of cracking. Then measure the distance between the thread tips, and record a negative value. From the excess soil, shape other additional threads, but do not cut their tips.Store these in the same container, and cover it again. Now, make a second soil thread that is 52 millimeters long, like the first. Repeat the bending process on the second soil thread.If the results are similar, do not bend more threads. If they differed, shape and bend at least one more soil thread, until agreeable measurements are obtained. Once a minimum of five grams of threads are obtained, record the weight of the container with the soil threads to a precision of at least 01 grams.Now, repeat the entire process for the second ball of soil. Begin with placing the two containers of soil threads uncovered in an oven at 105 degrees Celsius to dry the soil for at least 18 hours. The next day, put the containers in a desiccator.Once they have cooled to ambient temperatures, record their weights to a precision of at least 01 grams. Then, place the containers back into the same oven for at least six more hours. Again, cool them in a desiccator, and measure their weight.Continue repeating this process until two consecutive weight measurements are completely identical, which is the weight of the soil when dry. Now, for each soil ball, using the known water content, W, and its bending at cracking, B, calculate the plastic limit of each ball. Then, use the average value to characterize the soil.The number, minus 0.108, in the plastic limit equation, corresponds to the average value of ending a slope obtained in a previous study with a multiple inversion in which 24 soils were tested. The number 2.135 refers to the average bending value corresponding to the plastic limit in the bending curve for those 24 soils, in accordance with our original multi-point test. The plastic limits calculated from 30 soils with the described bending test, were compared to the original multi-point bending test, and the standard rolling test.Each test was executed by a highly experienced operator, and the results were very similar. The plastic limit results obtained through the new bending test were highly correlated with the original bending test, and the standard thread-rolling test. Most results were perfectly correlated, even with very low-plasticity soils.After watching this video, you should have a good understanding of how the plastic limit can be obtained instantly and accurately with a simple test in which the operator does not play a critical role in the final outcome. Once mastered, this technique can be done in five to ten minutes. So it can be even faster than the traditional test.In addition to its quick performance, the simplicity, low cost, and accuracy of this test, make it easily affordable for any laboratory. After its development, this technique paved the way for researchers and companies in the field of geotechnics, agriculture, ceramics, and soil science, to obtain more reliable plastic limit results.

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Determination of Microbial Extracellular Enzyme Activity in Waters, Soils, and Sediments using High Throughput Microplate Assays

Much of the nutrient cycling and carbon processing in natural environments occurs through the activity of extracellular enzymes released by microorganisms. Thus, measurement of the activity of these extracellular enzymes can give insights into the rates of ecosystem level processes, such as organic matter decomposition or nitrogen and phosphorus mineralization. Assays of extracellular enzyme activity in environmental samples typically involve exposing the samples to artificial colorimetric or fluorometric substrates and tracking the rate of substrate hydrolysis. Here we describe microplate based methods for these procedures that allow the analysis of large numbers of samples within a short time frame. Samples are allowed to react with artificial substrates within 96-well microplates or deep well microplate blocks, and enzyme activity is subsequently determined by absorption or fluorescence of the resulting end product using a typical microplate reader or fluorometer. Such high throughput procedures not only facilitate comparisons between spatially separate sites or ecosystems, but also substantially reduce the cost of such assays by reducing overall reagent volumes needed per sample.

Microplate based procedures are described for the colorimetric or fluorometric analysis of extracellular enzyme activity. These procedures allow for the rapid assay of such activity in large numbers of environmental samples within a manageable time frame.

Much of the nutrient cycling and carbon  processing in natural environments occurs through the activity of extracellular  enzymes released by ...

Integrated Field Lysimetry and Porewater Sampling for Evaluation of Chemical Mobility in Soils and Established Vegetation

Potentially toxic chemicals are routinely applied to land to meet growing demands on waste management and food production, but the fate of these chemicals is often not well understood. Here we demonstrate an integrated field lysimetry and porewater sampling method for evaluating the mobility of chemicals applied to soils and established vegetation. Lysimeters, open columns made of metal or plastic, are driven into bareground or vegetated soils. Porewater samplers, which are commercially available and use vacuum to collect percolating soil water, are installed at predetermined depths within the lysimeters. At prearranged times following chemical application to experimental plots, porewater is collected, and lysimeters, containing soil and vegetation, are exhumed. By analyzing chemical concentrations in the lysimeter soil, vegetation, and porewater, downward leaching rates, soil retention capacities, and plant uptake for the chemical of interest may be quantified. Because field lysimetry and porewater sampling are conducted under natural environmental conditions and with minimal soil disturbance, derived results project real-case scenarios and provide valuable information for chemical management. As chemicals are increasingly applied to land worldwide, the described techniques may be utilized to determine whether applied chemicals pose adverse effects to human health or the environment.

Field lysimetry and porewater sampling allow researchers to evaluate the fate of chemicals applied to soils and established vegetation. The goal of this protocol is to demonstrate how to install required instrumentation and collect samples for chemical analysis during integrated field lysimetry and porewater sampling experiments.

Potentially toxic chemicals are routinely applied to land to meet growing demands on waste management and food production, but the fate of these chemicals ...

Measurement of Greenhouse Gas Flux from Agricultural Soils Using Static Chambers

Measurement of greenhouse gas (GHG) fluxes between the soil and the atmosphere, in both managed and unmanaged ecosystems, is critical to understanding the biogeochemical drivers of climate change and to the development and evaluation of GHG mitigation strategies based on modulation of landscape management practices. The static chamber-based method described here is based on trapping gases emitted from the soil surface within a chamber and collecting samples from the chamber headspace at regular intervals for analysis by gas chromatography. Change in gas concentration over time is used to calculate flux. This method can be utilized to measure landscape-based flux of carbon dioxide, nitrous oxide, and methane, and to estimate differences between treatments or explore system dynamics over seasons or years. Infrastructure requirements are modest, but a comprehensive experimental design is essential. This method is easily deployed in the field, conforms to established guidelines, and produces data suitable to large-scale GHG emissions studies.

This article showcases the static chamber-based method for measurement of greenhouse gas flux from soil systems. With relatively modest infrastructure investments, measurements may be obtained from multiple treatments/locations and over timeframes ranging from hours to years.

Measurement of greenhouse gas (GHG) fluxes between the soil and the atmosphere, in both managed and unmanaged ecosystems, is critical to understanding the ...

Extraction and Analysis of Microbial Phospholipid Fatty Acids in Soils

Phospholipid fatty acids (PLFAs) are key components of microbial cell membranes. The analysis of PLFAs extracted from soils can provide information about the overall structure of terrestrial microbial communities. PLFA profiling has been extensively used in a range of ecosystems as a biological index of overall soil quality, and as a quantitative indicator of soil response to land management and other environmental stressors.
The standard method presented here outlines four key steps: 1. lipid extraction from soil samples with a single-phase chloroform mixture, 2. fractionation using solid phase extraction columns to isolate phospholipids from other extracted lipids, 3. methanolysis of phospholipids to produce fatty acid methyl esters (FAMEs), and 4. FAME analysis by capillary gas chromatography using a flame ionization detector (GC-FID). Two standards are used, including 1,2-dinonadecanoyl-sn-glycero-3-phosphocholine (PC(19:0/19:0)) to assess the overall recovery of the extraction method, and methyl decanoate (MeC10:0) as an internal standard (ISTD) for the GC analysis.

Phospholipid fatty acids provide information about the structure of soil microbial communities. We present methods for extraction from soil samples with a single-phase chloroform mixture, fractionation of extracted lipids using solid phase extraction columns, and methanolysis to produce fatty acid methyl esters, which are analyzed by capillary gas chromatography.

Phospholipid fatty acids (PLFAs) are key components of microbial cell membranes. The analysis of PLFAs extracted from soils can provide information about ...

Methods of Soil Resampling to Monitor Changes in the Chemical Concentrations of Forest Soils

Recent soils research has shown that important chemical soil characteristics can change in less than a decade, often the result of broad environmental changes. Repeated sampling to monitor these changes in forest soils is a relatively new practice that is not well documented in the literature and has only recently been broadly embraced by the scientific community. The objective of this protocol is therefore to synthesize the latest information on methods of soil resampling in a format that can be used to design and implement a soil monitoring program. Successful monitoring of forest soils requires that a study unit be defined within an area of forested land that can be characterized with replicate sampling locations. A resampling interval of 5 years is recommended, but if monitoring is done to evaluate a specific environmental driver, the rate of change expected in that driver should be taken into consideration. Here, we show that the sampling of the profile can be done by horizon where boundaries can be clearly identified and horizons are sufficiently thick to remove soil without contamination from horizons above or below. Otherwise, sampling can be done by depth interval. Archiving of sample for future reanalysis is a key step in avoiding analytical bias and providing the opportunity for additional analyses as new questions arise.

Repeated soil sampling has recently been shown to be an effective way to monitor forest soil change over years and decades. To support its use, a protocol is presented that synthesizes the latest information on soil resampling methods to aid in the design and implementation of successful soil monitoring programs.

Recent soils research has shown that important chemical soil characteristics can change in less than a decade, often the result of broad environmental ...

Extraction of Organochlorine Pesticides from Plastic Pellets and Plastic Type Analysis

Plastic resin pellets, categorized as microplastics (&#8804;5 mm in diameter), are small granules that can be unintentionally released to the environment during manufacturing and transport. Because of their environmental persistence, they are widely distributed in the oceans and on beaches all over the world. They can act as a vector of potentially toxic organic compounds (e.g., polychlorinated biphenyls) and might consequently negatively affect marine organisms. Their possible impacts along the food chain are not yet well understood. In order to assess the hazards associated with the occurrence of plastic pellets in the marine environment, it is necessary to develop methodologies that allow for rapid determination of associated organic contaminant levels. The present protocol describes the different steps required for sampling resin pellets, analyzing adsorbed organochlorine pesticides (OCPs) and identifying the plastic type. The focus is on the extraction of OCPs from plastic pellets by means of a pressurized fluid extractor (PFE) and on the polymer chemical analysis applying Fourier Transform-InfraRed (FT-IR) spectroscopy. The developed methodology focuses on 11 OCPs and related compounds, including dichlorodiphenyltrichloroethane (DDT) and its two main metabolites, lindane and two production isomers, as well as the two biologically active isomers of technical endosulfan. This protocol constitutes a simple and rapid alternative to existing methodology for evaluating the concentration of organic contaminants adsorbed on plastic pieces.

Microplastics act as vector of potentially toxic organic contaminants with unpredictable effects. This protocol describes an alternative methodology for assessing the levels of organochlorine pesticides adsorbed on plastic pellets and identifying the polymer chemical structure. The focus is on pressurized fluid extraction and attenuated total reflectance Fourier transform infrared spectroscopy.

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Optimized Procedure for Determining the Adsorption of Phosphonates onto Granular Ferric Hydroxide using a Miniaturized Phosphorus Determination Method

This paper introduces a procedure to investigate the adsorption of phosphonates onto iron-containing filter materials, particularly granular ferric hydroxide (GFH), with little effort and high reliability. The phosphonate, e.g., nitrilotrimethylphosphonic acid (NTMP), is brought into contact with the GFH in a rotator in a solution buffered by an organic acid (e.g., acetic acid) or Good buffer (e.g., 2-(N-morpholino)ethanesulfonic acid) [MES] and N-cyclohexyl-2-hydroxyl-3-aminopropanesulfonic acid [CAPSO]) in a concentration of 10 mM for a specific time in 50 mL centrifuge tubes. Subsequently, after membrane filtration (0.45 &#181;m pore size), the total phosphorus (total P) concentration is measured using a specifically developed determination method (ISOmini). This method is a modification and simplification of the ISO 6878 method: a 4 mL sample is mixed with H2SO4 and K2S2O8 in a screw cap vial, heated to 148-150 &#176;C for 1 h and then mixed with NaOH, ascorbic acid and acidified molybdate with antimony(III) (final volume of 10 mL) to produce a blue complex. The color intensity, which is linearly proportional to the phosphorus concentration, is measured spectrophotometrically (880 nm). It is demonstrated that the buffer concentration used has no significant effect on the adsorption of phosphonate between pH 4 and 12. The buffers, therefore, do not compete with the phosphonate for adsorption sites. Furthermore, the relatively high concentration of the buffer requires a higher dosage concentration of oxidizing agent (K2S2O8) for digestion than that specified in ISO 6878, which, together with the NaOH dosage, is matched to each buffer. Despite the simplification, the ISOmini method does not lose any of its accuracy compared to the standardized method.

This paper introduces a procedure to investigate the adsorption of phosphonates onto iron-containing filter materials, particularly granular ferric hydroxide, with little effort and high reliability. In a buffered solution, the phosphonate is brought into contact with the adsorbent using a rotator and then analyzed via a miniaturized phosphorus determination method.

This paper introduces a procedure to investigate the adsorption of phosphonates onto iron-containing filter materials, particularly granular ferric ...

The Plant Infection Test: Spray and Wound-Mediated Inoculation with the Plant Pathogen Magnaporthe Grisea

Plants possess a powerful system to defend themselves against potential threats by pathogenic fungi. For agriculturally important plants, however, current measures to combat such pathogens have proved too conservative and, thus, not sufficiently effective, and they can potentially pose environmental risks. Therefore, it is extremely necessary to identify host-resistance factors to assist in controlling plant diseases naturally through the identification of resistant germplasm, the isolation and characterization of resistance genes, and the molecular breeding of resistant cultivars. In this regard, there is need to establish an accurate, rapid, and large-scale inoculation method to breed and develop plant resistance genes. The rice blast fungal pathogen Magnaporthe grisea causes severe disease symptoms and yield losses. Recently, M. grisea has emerged as a model organism for studying the mechanisms of plant-fungal pathogen interactions. Hence, we report the development of a plant virulence test method that is specific for M. grisea. This method provides for both spray inoculation with a conidial suspension and wounding inoculation with mycelium cubes or droplets of conidial suspension. The key step of the wounding inoculation method for detached rice leaves is to make wounds on plant leaves, which avoids any interference caused by host penetration resistance. This spray/wounding protocol contributes to the rapid, accurate, and large-scale screening of the pathotypes of M. grisea isolates. This integrated and systematic plant infection method will serve as an excellent starting point for gaining a broad perspective of issues in plant pathology.

The Plant Infection Test: Spray and Wound-Mediated Inoculation with the Plant Pathogen Magnaporthe Grisea

Here, we present a protocol to test plant virulence with the plant pathogen Magnaporthe grisea. This report will contribute to the large-scale screening of the pathotypes of fungi isolates and serve as an excellent starting point for understanding the resistant mechanisms of plants during molecular breeding.

Plants possess a powerful system to defend themselves against potential threats by pathogenic fungi. For agriculturally important plants, however, current ...

Sampling Soils in a Heterogeneous Research Plot

Soils are highly heterogeneous. In general, the number of soil samples required for soil research has always been determined arbitrarily and the associated accuracy is unknown. Here, we present a detailed protocol for efficient and clustered soil sampling in a research plot and, relying on a pilot sampling using this design, for demonstrating soil spatial heterogeneity and informing reasonable sample sizes and associated accuracy for future study. The protocol mainly comprises four steps: sampling design, field collection, soil analysis, and geostatistical analysis. The step-by-step procedure is modified according to former publications. Two examples will be presented to demonstrate contrasting spatial distributions of soil organic carbon (SOC) and soil microbial biomass carbon (MBC) under different management practices. In addition, we present a strategy to determine the sample size requirement (SSR) given a certain level of accuracy based on the plot-level coefficient of variation (CV). The field sampling protocol and the quantitative determination of the sample size will assist researchers in seeking feasible sampling strategies to meet research needs and resources' availability.

The traditional soil-sampling procedure determines the number of soil samples arbitrarily. Here, we provide a simple yet efficient clustered soil-sampling design to demonstrate soil spatial heterogeneity and quantitatively determine the number of soil samples required and the associated sampling accuracy.

Soils are highly heterogeneous. In general, the number of soil samples required for soil research has always been determined arbitrarily and the ...

Combined Size and Density Fractionation of Soils for Investigations of Organo-Mineral Interactions

Combined size and density fractionation (CSDF) is a method used to physically separate soil into fractions differing in particle size and mineralogy. CSDF relies on sequential density separation and sedimentation steps to isolate (1) the free light fraction (uncomplexed organic matter), (2) the occluded light fraction (uncomplexed organic matter trapped in soil aggregates) and (3) a variable number of heavy fractions (soil minerals and their associated organic matter) differing in composition. Provided that the parameters of the CSDF (dispersion energy, density cut-offs, sedimentation time) are properly selected, the method yields heavy fractions of relatively homogeneous mineral composition. Each of these fractions is expected to have a different complexing ability towards organic matter, rendering this a useful method to isolate and study the nature of organo-mineral interactions. Combining density and particle size separation brings an improved resolution compared to simple size or density fractionation methods, allowing the separation of heavy components according to both mineralogy and size (related to surface area) criteria. As is the case for all physical fractionation methods, it may be considered as less disruptive or aggressive than chemically-based extraction methods. However, CSDF is a time-consuming method and furthermore, the quantity of material obtained in some fractions can be limiting for subsequent analysis. Following CSDF, the fractions may be analyzed for mineralogical composition, soil organic carbon concentration and organic matter chemistry. The method provides quantitative information about organic carbon distribution within a soil sample and brings light to the sorptive capacity of the different, naturally-occurring mineral phases, thus providing mechanistic information about the preferential nature of organo-mineral interactions in soils (i.e., which minerals, what type of organic matter).

Combined size and density fractionation (CSDF) is a method to physically separate soil into fractions differing in texture (particle size) and mineralogy (density). The purpose is to isolate fractions with different reactivities towards soil organic matter (SOM), in order to better understand organo-mineral interactions and SOM dynamics.

Combined size and density fractionation (CSDF) is a method used to physically separate soil into fractions differing in particle size and mineralogy. CSDF ...