Method for laboratory determination of optimum moisture content and maximum density of soil under compaction

Abstract

The invention relates to the field of technical analysis and to determining for construction purposes the optimum moisture content and maximum density of natural and man-made soils under static compaction. The essence of the invention consists in compacting a first soil specimen after first determining the initial moisture content thereof and, if necessary, adjusting same by adding water in accordance with recommended values for the given type of soil. A compaction mold cylinder and a lower liner are then placed on 18-20 mm high support stands on a level surface, a weighed amount of the soil under examination is placed in the compaction mold cylinder, the cylinder is positioned on a base plate of a compactor, a top plate of the compactor is brought into contact with the upper end of the cylinder and the compactor is set to a 20 mPA loading mode which is maintained for 5-10 minutes. Loading is ceased, the compaction mold is removed from the compactor, the compacted specimen is extruded and the volume thereof is calculated, the specimen is broken up, a representative sample is taken and weighed on electronic scales with an accuracy of up to 0.01 before being dried and reweighed. On the basis of the data obtained, the damp soil density and the dry soil density are calculated according to given formulae, and the data obtained are entered into a table and noted on a graph. A second soil specimen is compacted, the moisture content of which is increased by 1%, the specimen is placed in the compaction mold, placed under a 20 mPA load in the compactor and held for 5-10 minutes, after which loading is ceased, the compaction mold is removed from the compactor, the compacted specimen is extruded, the volume thereof is calculated, the specimen is broken up, a representative sample is taken and weighed on electronic scales with an accuracy of up to 0.01 before being dried and reweighed, the moisture content of the soil and the dry soil density are calculated and the d

Description

[0001] Name of the invention

[0002] Laboratory method for determining optimal moisture content and maximum soil density during compaction.

[0003] Field of technology

[0004] The invention relates to the field of technical analysis and determination of optimal moisture content during compaction and maximum density of natural and man-made soils for construction during static compaction.

[0005] Prior art

[0006] A well-known method for determining the optimal moisture content during soil compaction and the maximum dry soil density is the Proctor method. According to GOST R 70456-2022, determining the optimal moisture content and maximum soil density under dynamic loading involves layer-by-layer compaction of the soil using a dropped weight of the calculated mass from a specified height. The diameter of the dropped weight is equal to 50% of the diameter of the mold in which the soil is compacted, and the dropped weight is displaced during compaction.

[0007] A method is known for determining the optimal moisture content during soil compaction and the maximum density of dry soil using the SoyuzDorNII device in accordance with the requirements of GOST 22733-2016 for determining the optimal moisture content and maximum density of soils under dynamic loading, wherein the anvil diameter is no more than 5 mm smaller than the diameter of the mold.

[0008] Prior art shows that methods employing dynamic drop loads are used to determine the optimal soil moisture content during compaction and the maximum dry soil density. However, with any dynamic loading, it is difficult to control the uniformity of each impact, resulting in varying pressures at different points in the soil sample, complicating the soil compaction process, leading to partial destruction of mineral particles in the soil and changes in the particle size distribution of the soil being tested, and requiring the use of sophisticated equipment. Furthermore, the dynamic method is not suitable for compaction achieved with modern equipment and technology.

[0009] Disclosure of invention

[0010] The technical objective of the present invention is to increase the reliability of the obtained results and to simplify the method for determining the maximum density of dry soil and the optimal moisture content during compaction in the studied samples of natural and man-made soils under laboratory conditions using a mathematical calculation model using static loading.

[0011] When using static compaction of the soil samples being studied in the claimed invention, uniform pressure is achieved on the entire surface of the soil sample, while the density is uniform throughout the entire volume of the soil sample, which corresponds to the indicators obtained during construction work using modern road construction compaction equipment.

[0012] The invention is implemented as follows.

[0013] A sample of the original natural or man-made soil is taken and its moisture content is determined. If the natural moisture content of the original soil sample is below the recommended values: 6% for sandy loam, 8% for clay loam, 4% for gravel-crushed stone-sand mixtures, 4% for RAP, 6% for sedimentary rock sand, the moisture content of the original soil is adjusted to the recommended values ​​during the first test by adding water to the original sample.

[0014] Then the first soil sample is compacted, for which purpose the cylinder of the press mold and the lower insert are placed on a flat surface on support stands 18 - 20 mm high, a sample of the soil being tested is placed in the cylinder of the press mold, installed on the lower plate of the press, the upper plate of the press is brought up to contact with the upper base of the cylinder, the press load mode of 20 MPa is turned on and held for 5 - 10 minutes, after which the loading is stopped, the press mold is removed from the press, the compacted sample is squeezed out, its volume is calculated, it is destroyed, an average sample is taken, weighed on an electronic scale with an accuracy of 0.01, dried, and weighed again, based on the data obtained according to the formulas and The soil moisture content and dry soil density are calculated, the obtained data are entered into a table and plotted on a graph; the second soil sample is compacted, increasing its moisture content by 1%, placed in a press mold, loaded with a press to 20 MPa, and held for 5-10 minutes., after which the loading is stopped, the mold is removed from the press, the compacted sample is extruded, its volume is calculated, it is destroyed, an average sample is taken, weighed on an electronic scale with an accuracy of 0.01, dried, and weighed again, the soil moisture content and the dry soil density are calculated, the obtained data are entered into a table and marked on a graph; compaction of soil samples in the mold is carried out until the point of optimal moisture content and maximum density is exceeded, that is, until a small amount of water from the mold is released onto the bottom plate of the press during the compaction process, after which the previous indicators are taken as the indicators of maximum soil density and optimal moisture content according to the mathematical calculation model using static loads.

[0015] We provide an example of a mathematical calculation model for determining the optimal moisture content during compaction and the maximum dry soil density for a sand and gravel mixture in stages.

[0016] Example.

[0017] 1. Determine the maximum size of mineral particles in the sand-gravel mixture (hereinafter referred to as soil) using sieves. It was determined that the maximum size of the soil mineral particles was 20 mm. According to Table 1, it was determined that a mold with a diameter of 71.4 mm and a sample surface area of ​​40 cm would be used for testing. 2 .

[0018] Table 1.

[0019] 2. A sample weighing at least 100 g is taken from the total soil sample, dried, and the moisture content is determined with an accuracy of 0.1% using formula (1):

[0020] INCORPORATE BY REFERENCE (RULE 20.6) W = (mi - mo) / mo x 100%, (formula 1), where: W is the soil moisture content, %; mi is the mass of the wet soil sample, g; mo is the mass of the dried soil sample, g. (100g - 97.3g) / 97.3g x 100% = 2.8% The soil moisture content is 2.8%.

[0021] 3. A sample is taken from the total soil sample for testing in accordance with GOST R 70456-2022, GOST 22733-2016 and the data in Table 2.

[0022] Table 2

[0023] Since the soil moisture content is 2.8%, we adjust the soil sample weight based on the soil moisture content to obtain the calculated dry soil weight. This adjustment is made by adding the required amount of soil according to formula (2): 2), where is the mass of the soil sample, taking into account the correction for moisture content, g; is the mass of the soil sample, g; moisture content of the original soil, %

[0024] 5000 g + 5000 g x 2.8% * 0.01 = 5140 g

[0025] The soil sample mass required for testing is 5140 g.

[0026] 4. We increase the soil moisture content for the first test in accordance with GOST R 70456-2022 and the data in Table 3. The recommended moisture content for the first test for this type of soil is 4%.

[0027] Table 3

[0028] INCORPORATE BY REFERENCE (RULE 20.6)

[0029] Using formula 3, we calculate the amount of water required to achieve the soil moisture content required for the first test. 0 is the amount of water, g; is the mass of the soil sample, g; is the moisture content of the original soil, %; - required soil moisture content, %.

[0030] 5140 g x (4% - 2.8%) x 0.01 = 62 g

[0031] The amount of water required to achieve the required moisture content of the soil sample is 62 g.

[0032] To evenly distribute water in the soil sample, water is added to the soil, it is thoroughly mixed and left for 5 minutes, after which it is mixed again.

[0033] 5. Next, we compact the first soil sample. To do this, we place the mold cylinder and lower insert on 20 mm high supports on a level surface.

[0034] From the soil sample we select a sample weighing 500 g, in accordance with GOST R 70456-2022, GOST 22733-2016 and Table 4.

[0035] Table 4 The soil sample is gradually poured into the mold cylinder and tamped with a knife or spatula to evenly distribute the large soil particles throughout the entire volume. The upper liner is then installed into the mold cylinder. Pre-compact the soil manually so that after removing the supports from under the mold cylinder, the lower liner protrudes more than 15 mm below the cylinder. This ensures uniform soil compaction throughout the entire mold.

[0036] The mold with the soil is transferred to the lower plate of the press without the support stands. The upper plate is moved until it contacts the upper insert of the mold and the press loading mode is turned on. The press loading is increased to 20 MPa (200 kg / cm). 2) , which for this particular mold is 80 kN (8000 kg). The mold is held at this load for 3 minutes, after which the loading is stopped and the mold is removed from the press.

[0037] The compacted soil sample is pressed out of the mold, preventing destruction or damage to the sample, then the protruding edges of the soil on the end parts of the sample are removed.

[0038] We measure the height of the compacted soil sample using a caliper, with a measurement accuracy of up to 0.01 cm, and calculate the volume of the soil sample using formula (4):

[0039] V = h x F (formula 4), where V is the volume of the compacted soil sample, cm 3 , h - height of compacted soil sample, cm;

[0040] F is the cross-sectional area of ​​the soil sample according to Table 1, cm 2 .

[0041] The sample volume was:

[0042] 6.13 cm x 40 cm 2 =245.2 cm 3

[0043] We then determine the mass of the compacted soil sample (m, g) by weighing it on an electronic scale. The mass of the compacted sample was 498 g.

[0044] We calculate the density of wet soil using formula (5): p w mi V (formula 5) , where p w - density of wet soil, g / cm 3 ; t, 1 — mass of compacted sample, g;

[0045] V is the volume of the compacted soil sample, cm 3 . 498g 245.2cm 3 =2.03 g / cm 3

[0046] The soil density was 2.03 g / cm3

[0047] We determine the moisture content of compacted soil. We crush the compacted soil sample, take a sample weighing at least 100 g from the center of the sample, dry it, and determine the moisture content using formula (1). The soil moisture content is 4.2%.

[0048] The remaining soil from the destroyed sample is disposed of and not used for further testing.

[0049] Based on the obtained results, we calculate the values ​​of dry soil density {pd, g / cm 3 ), with an accuracy of 0.01 g / cm 3 according to formula (6): ' (formula 6) where is the density of dry soil, g / cm 3 ; wet soil density, g / cm 3 ; soil moisture content during testing, %.

[0050] 2.03 g / cm 3 - (1 + 4.2% x 0.01) = 1.95 g / cm 3

[0051] The dry soil density is 1.95 g / cm 3 .

[0052] Soil moisture content is 4.2%, wet soil density is 2.03 g / cm 3and dry soil density of 1.95 g / cm 3 We record this in the table and on the graph.

[0053] 6. To compact the second soil sample, increase the moisture content of the original soil by 1% (+ / - 0.3%) by adding the amount of water calculated using formula (7): = (TPo-Shx) * 0.01, (formula 7) where QH2O is the amount of water, g;

[0054] ТП - initial mass of soil sample, g; t х - the total mass of soil samples taken from the soil sample for testing, g.

[0055] (5000 g - 500 g) x 0.01 = 45 g Add 45 g of water to the soil sample.

[0056] To evenly distribute water in the soil, mix the soil thoroughly and leave for 5 minutes, then mix again.

[0057] The sample is compacted in the mold under a load of 20 MPa (200 kg / cm 2 ) within 3 minutes and remove it from the mold.

[0058] We then measure the height of the compacted soil sample using a caliper, with a measurement accuracy of up to 0.01 cm, and calculate the volume of the soil sample using formula (4):

[0059] V = h x F (formula 4), where V is the volume of the compacted soil sample, cm 3 , h - height of compacted soil sample, cm;

[0060] F is the cross-sectional area of ​​the soil sample according to Table 1, cm.

[0061] The sample volume was:

[0062] 5.99 cm x 40 cm 2 = 239.6 cm 3

[0063] We then weighed the compacted soil sample on an electronic scale. The mass of the compacted sample was 498 g.

[0064] The density of wet soil is calculated using formula (5): p w mr- V (formula 5) , where p w - density of wet soil, g / cm 3 ; t 1 - - mass of the compacted sample, g;

[0065] V is the volume of the compacted soil sample, cm 3 .

[0066] 499 g - 239.6 cm 3 = 2.08 g / cm 3

[0067] The soil density was 2.08 g / cm3:

[0068] We again determined the moisture content of the compacted soil. To do this, the compacted soil sample was broken up, a sample weighing at least 100 g was taken from the center of the sample, dried, and the moisture content was determined to the nearest tenth using formula (1). The soil moisture content was 5.1%.

[0069] The remaining soil from the destroyed sample is disposed of and not used for further testing.

[0070] Based on the obtained results, the values ​​of dry soil density (pa, g / cm) are calculated. 3 ), with an accuracy of 0.01 g / cm 3 according to formula (6): ' (zф, formula 6) where d is the density of dry soil, g / cm 3 ; w - density of wet soil, g / cm 3 ; - soil moisture content during testing, %.

[0071] 2.08 g / cm 3 - (1 + 5.1% x 0.01) = 1.98 g / cm 3

[0072] The dry soil density is 1.98 g / cm 3 :

[0073] Soil moisture content is 5.1%, wet soil density is 2.08 g / cm 3 and dry soil density of 1.98 g / cm 3 are recorded in the table and on the graph.

[0074] 7. The third soil sample is compacted by increasing the moisture content of the original soil by 1% (+ / - 0.3%) by adding the amount of water calculated using formula (7):

[0075] QH2O = (to- t х ) * 0.01 , (formula 7) where QH2O is the amount of water, g; to is the initial mass of the soil sample, g; is the total mass of the soil samples removed from the soil sample for testing, g.

[0076] (5000 g - 500 g - 500 g) x 0.01 = 40 g

[0077] Add 40 g of water to the soil sample, mix and leave for 5 minutes, then mix again.

[0078] The soil sample is compacted in a press mold under a load of 20 MPa (200 kg / cm 2) for 3 minutes. After which the sample is removed from the mold, the height of the compacted soil sample is measured using a caliper, with a measurement accuracy of 0.01 cm, and the volume of the soil sample is calculated using formula (4):

[0079] V = h x F (formula 4), where V is the volume of the compacted soil sample, cm 3 , h - height of compacted soil sample, cm;

[0080] F is the cross-sectional area of ​​the soil sample according to Table 1, cm.

[0081] The sample volume was:

[0082] 5.7 cm x 40 cm 2 = 228 cm 3 The mass of a compacted soil sample (m, g) is determined by weighing it on an electronic scale. The mass of the compacted sample is 498 g.

[0083] We calculate the density of wet soil using formula (5): (formula 5), ​​where p w - density of wet soil, g / cm 3 ; mi - mass of the compacted sample, g;

[0084] V— volume of compacted soil sample, cm 3 .

[0085] 498g - 228 cm 3 = 2.18 g / cm 3

[0086] The soil density is 2.18 g / cm 3

[0087] We determine the moisture content of compacted soil by destroying the compacted soil sample, taking a sample weighing at least 100 g from the center of the sample, drying it, and determining the moisture content using formula (1).

[0088] Soil moisture content is 6.2%.

[0089] The remaining soil from the destroyed sample is disposed of and not used for further testing.

[0090] Based on the obtained results, the values ​​of dry soil density (pa, g / cm) are calculated. 3 ), with an accuracy of 0.01 g / cm 3 according to formula (6): ' (formula 6) where d is the density of dry soil, g / cm 3 ; w - density of wet soil, g / cm 3 ; - soil moisture content during testing, %.

[0091] 2.18 g / s m3 - (1 + 6.2% x 0.01) = 2.05 g / cm 3

[0092] The dry soil density is 2.05 g / cm 3

[0093] Soil moisture content is 6.2%, wet soil density is 2.18 g / cm 3 and dry soil density of 2.05 g / cm 3 We record this in the table and on the graph.

[0094] 8. We compact the fourth soil sample by increasing the soil sample’s moisture content by 1% (+ / - 0.3%) by adding the amount of water calculated using formula (7):

[0095] QH2O = (to— t х ) х 0.01 (formula 7) where He 20 is the amount of water, g; to is the initial mass of the soil sample, g; t х - the total mass of soil samples taken from the soil sample for testing, g.

[0096] (5000 g - 500 g - 500 g - 500 g) x 0.01 = 35 g

[0097] Add 35 g of water to the soil sample, mix and leave for 5 minutes, then mix again.

[0098] The soil sample is compacted again in the press mold under a load of 20 MPa (200 kg / cm 2 ) for 3 minutes. After which the sample is removed from the mold.

[0099] We measure the height of the compacted soil sample using a caliper, with a measurement accuracy of up to 0.01 cm. We calculate the volume of the soil sample using formula (4):

[0100] V = h x F (formula 4), where V is the volume of the compacted soil sample, cm 3 , h - height of compacted soil sample, cm;

[0101] F is the cross-sectional area of ​​the soil sample according to Table 1, cm.

[0102] The sample volume was:

[0103] 5.59 cm x 40 cm 2 =223.6 cm 3

[0104] We determine the mass of a compacted soil sample weighed on an electronic scale. The mass of the compacted sample is 499 g.

[0105] We calculate the density of wet soil using formula (5): p w= mi V (formula 5), ​​where pw is the density of wet soil, g / cm 3 ; mi - mass of the compacted sample, g;

[0106] V is the volume of the compacted soil sample, cm 3 .

[0107] 499g - 223.6 cm 3 = 2.23 g / cm 3

[0108] The soil density is 2.23 g / cm 3

[0109] The soil sample is crushed, a minimum 100 g sample is taken from the center of the sample, dried, and the moisture content is determined to the nearest tenth using formula (1). The soil moisture content is 7.0%. The remaining soil from the crushed sample is discarded and not used for further testing.

[0110] Based on the obtained results, we calculate the values ​​of dry soil density (pd, g / cm 3 ), with an accuracy of 0.01 g / cm 3 according to formula (6): ' (formula 6) where pd is the density of dry soil, g / cm 3 ; p w - density of wet soil, g / cm 3 ;

[0111] W – soil moisture content during testing, %.

[0112] 2.23 g / cm 3 - (1 + 7.0% x 0.01) = 1.95 g / cm 3

[0113] The dry soil density was 1.95 g / cm 3

[0114] Soil moisture content is 7.0%, wet soil density is 2.23 g / cm 3 and dry soil density of 2.08 g / cm 3 We record this in the table and on the graph.

[0115] 9. We increase the moisture content of the soil sample by 1% (+ / - 0.3%) by introducing into the soil the amount of water calculated using formula (7): (formula 7) where QH20 is the amount of water, g; to is the initial mass of the soil sample, g; t х - the total mass of soil samples taken from the soil sample for testing, g.

[0116] (5000 g - 500 g - 500 g - 500 g - 500 g) x 0.01 = 30 g

[0117] Add 30 g of water to the soil sample, mix and leave for 5 minutes, then mix again.

[0118] Then the soil sample is compacted in a press mold under a load of 20 MPa (200 kg / cm 2 ) for 3 minutes. After which the sample is removed from the mold.

[0119] We measure the height of the compacted soil sample and calculate the volume of the soil sample using formula (4):

[0120] V = h x F (formula 4), where V is the volume of the compacted soil sample, cm 3 , h is the height of the compacted soil sample, cm; F is the cross-sectional area of ​​the soil sample according to Table 1, cm.

[0121] The sample volume was:

[0122] 5.47 cm x 40 cm 2 =218.8 cm 3

[0123] We determine the mass of the compacted soil sample (m, g) by weighing it on an electronic scale. The mass of the compacted sample is 500 g.

[0124] We calculate the density of wet soil using formula (5): (formula 5) , - density of wet soil, g / cm 3; - mass of compacted sample, g; volume of compacted soil sample, cm 3 .

[0125] 500 g - 218.8 cm 3 = 2.28 g / cm 3

[0126] The soil density is 2.28 g / cm3.

[0127] To determine the moisture content of compacted soil, the resulting sample is crushed, a minimum 100g sample is taken from the center of the sample, dried, and the moisture content is determined to the nearest tenth using formula (1). The soil moisture content was 8.1%.

[0128] The remaining soil from the destroyed sample is disposed of and not used for further testing.

[0129] Based on the obtained results, the values ​​of dry soil density (pd, g / cm) are calculated. 3 ), with an accuracy of 0.01 g / cm 3 according to formula (6): ' (formula 6) where pd is the density of dry soil, g / cm 3 ; p w - density of wet soil, g / cm 3 ;

[0130] I' - soil moisture content during testing, %.

[0131] The dry soil density was 1.95 g / cm 3 :

[0132] 2.28 g / cm 3 - (1 + 8.1% x 0.01) = 2.11 g / cm 3

[0133] Soil moisture content is 8.1%, wet soil density is 2.28 g / cm 3 and dry soil density of 2.11 g / cm 3 We record it in the table and on the graph. 10. We increase the soil moisture by 1% (+ / - 0.3%) by adding the amount of water calculated using formula (7): (formula 7) where O is the amount of water, g; is the initial mass of the soil sample, g; is the total mass of the soil samples removed from the soil sample for the process conducting the test, g.

[0134] = (5000 g - 500 g - 500 g - 500 g - 500 g - 500 g) x 0.01 = 25 g

[0135] Add 25 g of water to the soil sample, mix and leave for 5 minutes, then mix again.

[0136] We compact the soil sample in a press mold under a load of 20 MPa (200 kg / cm 2) for 3 minutes. During compaction, a small amount of water from the mold was released onto the bottom plate of the press, indicating that excess moisture was being released from the soil and the optimum moisture content and maximum dry soil density had been exceeded.

[0137] We use the previous values ​​for the maximum dry soil density and optimal moisture content during compaction. The data is entered into Table 5 and the graph (Fig. 1).

[0138] Table 5

[0139] Based on the values ​​given in Table 5, we construct a graph (Fig. 1) in which the dry soil density values ​​obtained in the experiment are plotted along the Y-axis, and the soil moisture values ​​obtained in the experiment are plotted along the X-axis. Thus, in this sample of sand and gravel mixture, the optimal moisture content is 8.1%, and the maximum density is 2.11 g / cm 3 .

[0140] Industrial applicability

[0141] The claimed method allows one to obtain indicators of the maximum density of dry soil and the optimal moisture content of samples of natural and man-made soils in laboratory conditions using a mathematical calculation model under static loading, which correspond to the indicators obtained during construction work using modern road construction compaction equipment.

Claims

Invention formula A method for laboratory determination of optimum moisture content and maximum density of soil during compaction, characterized in that the first soil sample is compacted, having previously determined its initial moisture content and, if necessary, corrected by adding water in accordance with the recommended values ​​for a given type of soil, then the cylinder of the press mold and the main insert are placed on a flat surface on support stands 18 - 20 mm high, a sample of the soil being tested is placed in the cylinder of the press, installed on the lower plate of the press, the upper plate of the press is brought into contact with the upper base of the cylinder, the load mode is turned on at 20 mPa and held for 5 - 10 minutes, after which the loading is stopped, the press mold is removed from the press, the compacted sample is squeezed out, its volume is read, destroyed, an average sample is taken, weighed on an electronic scale with an accuracy of 0.01, dried, and weighed again, based on the data obtained according to the formulas and calculate the soil moisture and the dry weight density, where p w — density of wet soil, g / cm 3 , ТП1 - mass of compacted sample, g, V - volume of compacted soil, cm 3 , pd - dry soil density, m 3, W - soil moisture content during testing, %, the obtained data are entered into the table and marked on the graph; the second soil sample is compacted, increasing its moisture content by 1%, placed in a press mold, loaded with a 20 mPa pressure and held for 5-10 minutes, after which the loading is stopped, the press mold is removed from the press, the compacted sample is squeezed out, its volume is read, destroyed, an average sample is taken, weighed on an electronic scale with an accuracy of 0.01, dried, and weighed again, the soil moisture content and the density of dry soil are calculated, the obtained data are entered into a table and marked on the graph; Compaction of soil samples in a press is carried out until the point of optimal importance and maximum density is exceeded, after which the previous indicators according to the mathematical calculation model using sthetic loads are taken as the indicators of maximum soil importance and optimal moisture content.