ES2301297A1 - Determining method for liquid limit, plastic limit and plasticity index, involves screening in two porous washers on extractor membrane, where water is poured on washers and is left for suction - Google Patents

Abstract

The method involves screening in two porous washers on an extractor membrane. The water is poured on the washers and is left for suction. The washers are put in airtight containers for two days and are introduced in extractor in one day. The pressure to measure humidity portions lies in a certain range. The weight of material has sieve number 40 American Society for Testing and Materials passing through the sieve number 200 American Society for Testing and Materials.

Description

Limit determination procedure liquid, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus".

Object of the invention

The present invention relates, as expresses the statement of the present specification, to a procedure for determining the liquid limit, limit plastic and plasticity index using a pressure extractor membrane or "Richards apparatus".

Field of the Invention

The field of the invention is that of engineering geotechnical and its application will be within any industry that require it.

Background of the invention

As is known, there are four possible states of consistency in which a grain soil may occur fine depending on its moisture content.

These states are solid, semi-solid, plastic and liquid.

At the humidity limits between these states they are called retraction limit, plastic limit and limit liquid respectively.

The plasticity index is called the difference between the liquid limit and the plastic limit.

Thus, projecting on the plasticity chart of Casagrande the liquid limit and the plasticity index of a sample and having a soil granulometry, a soil by the Unified Soil Classification System or A.A.S.H.T.O.

After the works of the Swedish scientist Albert Mauritz Atterberg and Professor Arthur Casagrande (1948) se defined the concepts of liquid limit and plastic limit, as well as his determination by the Casagrande spoon method (Standard NLT-105/72, equivalent to the A.S.T.M. D-423-66 / 72), and performing floor cylinders (Standard NLT-105/72), respectively.

Due to the inconveniences derived from use of dynamic methods, Casagrande (1958), proposed replace them with other static ones.

In 1949 the cone method was normalized to the determination of the liquid limit in the Soviet Union (Lomtadse, 1952).

Finally, Sowers et al . (1959) develop the cone of the Georgia Institute of Technology.

Explanation of the invention.

The present invention develops a method novel that serves to directly determine the limit liquid, plastic limit and plasticity index with the help of a membrane pressure extractor, commonly known as "Richards apparatus".

For this the following is followed process:

- Take about 50 g. of sample screened with a No. 40 sieve ASTM. and make two roughly equal parts with the same.

- Place them inside some washers Porous rubber clamp on extractor membranes Richards

- Pour distilled water abundantly on the membrane, not directly on the samples, and let these suck the water alone through the washers.

- Put the trays inside hermetically sealed polyurethane containers (wet chamber) for 2 days.

- Insert the samples in the extractor Richards for a day.

PF is the antilogarithm of the measured pressure in millibars to which a saturated sample is subjected in the inside the pressure chambers of a Richards extractor.

It is required to know the humidity that they have left two different portions of the same sample, after being subjected to pF 4.2 and pF 2.5, that is, 15848 millibars and 316 millibars respectively.

- Take out the samples, put them in containers glass covered with a closed lid and weigh accurately hundredths of a gram.

- Put the samples in an oven between 105 and 110 ° C for one day with the lid open.

- Close the covers and weigh the samples dry with the same precision.

The percentage of humidity (W) that they had be:

(1) W = \ frac {Pw - Ps} {Pw} x 100

Pw = wet weight

Ps = dry weight

The devices and elements that make up the Typical membrane pressure extractor consist of a compressor, about pressure gauges and two pressure chambers. Inside the extractors, it they place the samples inside porous rubber washers on the membranes of Richards, whose surface lets the Water, but not the air.

It is also necessary to know the percentage in material weight of samples previously screened with a sieve No. 40 ASTM passing through sieve No. 200 ASTM, hereinafter F.

Thus, to determine the liquid limit (Wl) it is necessary to determine pF 2.5 and pF 4.2 of a sample with a Richards apparatus by the above procedure, as well as the amount of fines in the sample (F).

To determine the plasticity index (Ip) it is necessary to determine pF 4.2 with a Richards device by Exposed procedure, as well as the amount of fines in the sample (F).

Finally, to determine the plastic limit (Wp) it is necessary to determine pF 2.5 and pF 4.2 with a device of Richards by the procedure set forth, as well as the amount of sample fines (F).

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determinación del límite líquido, límite plástico  e índice de
plasticidad, ya que:}

With all of the above, it follows that the invention presents a series of advantages thanks to the membrane pressure extractor method that advocates

 \ hbox {in the
determination of the liquid limit, plastic limit and index of
plasticity, since:} 

- it is a static method,

- not based on trial and error methods for his determination,

- determine the liquid limit, the limit plastic and plasticity index at the same time,

- is faster than current methods,

- is automated, allowing the staff of the laboratory perform other tests or work in the meantime,

- allows the analysis of several samples at time,

- lowers personnel costs,

- does not require expert personnel to use it,

- it is cheaper in the short term,

- additional information can be obtained, such as the ability to nourish plants that have a soil or the its permeability,

- and finally, it helps to classify a soil from the geotechnical and edaphological point of view to it weather.

The invention is illustrated with the following examples:

To determine the liquid limit (Wl) is it is necessary to determine pF 2.5 and pF 4.2 of a sample with a Richards apparatus by the procedure set forth, as well as the amount of fines in the sample (F). The X factor is defined as the sum (pF2.5 + pF4.2) / F. E is defined as the sum (0.318796 + 0.0000556924 * F * pF4.2). In function of E and X the liquid limit like this:

Example one

Wl = 1 / (0.01873287 + 7.31125 / F * pF4.2)

(X greater than 0.48 and E less than 0.432)

       \ vskip1.000000 \ baselineskip
    

Example 2

Wl = 1 / ((0.0461931-0.0000167475 * F * pF4.2)

(when the conditions of E and X are not met from example 2 at a time)

To determine the plasticity index (Ip) it is necessary to determine pF 4.2 with a Richards device by Exposed procedure, as well as the amount of fines in the sample (F).

       \ vskip1.000000 \ baselineskip
    

Example 3

Ip = -5.41288 + 0.0195629 * F * pF42

To determine the plastic limit (Wp) is it is necessary to determine pF 2.5 and pF 4.2 with a Richards by the procedure outlined, as well as the amount of sample fines (F).

       \ vskip1.000000 \ baselineskip
    

Example 4

Wp = 64.4826 + 0.0181707 * F * pF42-1.41075 * pF25-0.320004 * F

Claims (7)

1. Procedure for determining the liquid limit, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus" consisting of a compressor, pressure gauges and two pressure chambers, the samples being placed inside the washers of porous rubber on the membranes of Richards, whose surface lets the water pass, but not the air, characterized in that about 50 g are taken. of sample screened with a sieve No. 40 ASTM. and two approximately equal parts are made therewith; they are placed inside porous rubber clamping washers on Richards extractor membranes; abundantly distilled water is made on the membrane, not directly on the samples, and they are allowed to suck the water by themselves through the washers; the trays are placed inside hermetically sealed polyurethane containers (wet chamber) for 2 days; the samples are introduced in the Richards extractor for one day; in that pF being the pressure measured in atmospheres to which a saturated sample is subjected inside the pressure chambers of a Richards extractor, it is required to know the humidity that remains to two different portions of the same sample, after being subjected to pF 4.2 and pF 2.5, that is, 15 atmospheres and 1/3 of atmosphere respectively; samples are taken, placed in covered glass containers with a closed lid and accurately weighed hundredths of a gram; the samples are put in an oven between 105 and 110 ° C for a day with the lid open; the covers are closed and the dried samples are weighed with the same precision; knowing the percentage by weight of the material of the samples previously screened with a sieve No. 40 ASTM passing through the sieve No. 200 ASTM, sample (F). 2. Procedure for determining the liquid limit, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus", according to claim 1, characterized in that the liquid limit (Wl) is determined by determining the pF 2.5 and the pF 4.2 of a sample with a Richards apparatus by the procedure described, as well as the amount of fines in the sample (F). 3. Procedure for determining the liquid limit, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus", according to claims 1 and 2, characterized in that the plasticity index (Ip) is determined by determining the pF 4.2 with a Richards apparatus by the procedure described, as well as the amount of fines in the sample (F). 4. Procedure for determining the liquid limit, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus", according to claims 1 to 3, characterized in that the plastic limit (Wp) is determined by determining pF 2.5 and pF 4.2 with a Richards apparatus by the procedure described, as well as the amount of fines in the sample (F). 5. Procedure for determining the liquid limit, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus", according to claims 1 to 4, characterized in that it determines the liquid limit, the plastic limit and the index of plasticity at the same time. 6. Procedure for determining the liquid limit, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus", according to claims 1 to 5, characterized in that it is automated and allows the analysis of several samples at the same time . 7. Procedure for determining the liquid limit, plastic limit and plasticity index by means of a membrane pressure extractor or "Richards apparatus", according to claims 1 to 3, characterized in that it contributes to classifying a soil from a geotechnical point of view and Edaphological at the same time.