CN102866077B - Device and method for measuring mass moisture content and volume density of soil by utilizing volume replacement measurement way - Google Patents

Abstract

The invention provides a device and a method for measuring mass moisture content and volume density of soil by utilizing a volume replacement measurement way. The device comprises a controller, a sampling vessel, a weighing device and a saturation system, wherein the controller is connected with the weighing device, and the saturation system comprises a pre-saturation pond and a water supply device. The method comprises the following steps that under the situation that the density of soil particles is known, a soil sample with a certain volume is taken, so initial mass of the soil sample can be measured, then pre-saturation treatment is conducted on the soil sample, water is continuously supplied to the soil sample so as to ensure the soil sample to be maintained at a saturated state, when the mass of the soil sample is constant, the mass of the soil sample at the saturation state is measured, and the mass moisture content of the soil sample can be calculated through a formula according to the volume of the soil sample, the soil particle density, the initial mass of the soil sample, the mass of the saturated soil sample and the water density. The volume replacement measurement way is used for directly measuring the mass moisture content and the volume density of the soil, so that simplicity and convenience in operation can be realized, the measurement precision is high, the instrument stability is good, time and labor can be saved, and the energy can be saved.

Description

Device and method for measuring soil mass moisture content and bulk density by volume displacement method

technical field

The invention relates to the field of soil mass moisture content and bulk density measurement, in particular to a device and method for measuring soil mass moisture content and bulk density by a volume displacement method.

Background technique

The direct measurement of soil moisture content and bulk density is the basis of related research and application, and is very important in the research and practice of soil mechanics, crop cultivation, farmland irrigation, ecological environment, etc. Especially with the increasingly prominent water resource crisis, the research on water-saving agriculture is highly valued at home and abroad, and the water content of soil quality has become a frequently measured item in the research of water-saving agriculture. In production and construction, agriculture, water conservancy and other projects, it is necessary to measure soil moisture easily and quickly.

At present, the methods for directly measuring soil moisture content mainly include drying weighing method or alcohol combustion method, which are the only methods for directly measuring soil moisture content, and drying weighing method is the standard method. These two methods are the basis of all other indirect measurement methods, and have incomparable advantages in measurement accuracy than other indirect measurement methods. The traditional drying method for measuring moisture content is time-consuming and not suitable for field operations; the alcohol burning method consumes energy and has relatively low measurement accuracy. Other indirect measurement methods (such as TDR, FDR, gamma ray, capacitive sensor, neutron meter, etc.) must be calibrated and calibrated by one of the above two direct measurement methods, which are expensive, difficult to operate, and may be harmful to the human body. Larger and many other defects. Therefore, a simple and convenient direct measurement method is very important.

Contents of the invention

(1) Technical problems to be solved

The object of the present invention is to provide a method and device for measuring soil moisture content and bulk density, so as to overcome the defects of the prior art, such as time-consuming, labor-intensive, waste of resources, expensive and difficult to operate.

(2) Technical solution

In order to solve the above technical problems, the present invention provides a device for measuring soil moisture content and bulk density by volume displacement method, the device for measuring soil moisture content and bulk density by volume displacement method includes a controller, a sampling container, and a weighing device and a saturation system, the controller is connected with weighing equipment, and the saturation system includes a pre-saturation tank and water supply equipment.

Preferably, a drainage branch pipe is provided at the bottom of the sampling container.

Preferably, the sampling container is a sampling ring knife.

Preferably, the controller is a computer, which is connected to the weighing device through a data line, and measurement control software is installed in the computer.

Preferably, the weighing device is an electronic scale.

Preferably, the water level in the pre-saturated tank is lower than the upper surface of the soil sample to be tested in the sampling container.

Preferably, the water supply equipment is a drip pipe.

The present invention also provides a method for measuring soil mass moisture content and bulk density by volume displacement method, comprising the following steps:

S1, under the condition of known soil particle density ρ _s , get the described soil sample of certain volume, record its initial mass;

S2, performing pre-saturation treatment on the soil sample;

S3. Continuously supply water to the presaturated soil sample to keep it in a saturated state. When the quality of the soil sample remains constant, measure its saturated mass;

S4. According to the volume V of the soil sample, the density of soil particles ρ _s , the initial mass of the soil sample M ₁ , the mass of the soil sample at saturation M ₂ and the density of water ρ _w , the mass water content of the soil sample is calculated by the formula rate and bulk density.

Preferably, the soil particle density ρ _s of the soil sample ranges from 2600kg/ ^m3 to 2800kg/ ^m3 . In the present invention, the density of conventional soil particles is set to 2653kg/ ^m3 , and the density of water is 1000kg/m3. m ³ .

Preferably, the formula is:

V _s ×ρ _s +V _w ×ρ _w =M ₁

V _s ×ρ _s +(V _w +V _a )×ρ _w =M ₂

V _s +V _w +V _a =V

In the formula, ρ _w represents the density of water, ρ _s represents the density of soil particles, V _a represents the volume of gas in the soil, V _w represents the volume of water in the soil, V _s represents the volume of soil particles in the soil, V represents the total volume of soil, M ₁ Indicates the initial mass, M ₂ indicates the mass after saturation; where ρ _s , ρ _w and V are known, M ₁ and M ₂ can also be obtained by weighing, V _s , V _w and V _a are unknown, through the above three The following formulas can be derived for V _s , V _w and V _a , resulting in:

Soil mass moisture content=[(M ₂ -1000V _a )/(V _s ×ρ _s )-1]×100%;

Soil bulk density = V _s × ρ _s /V.

When the density of soil particles is 2653kg/ ^m3 , then;

Soil mass moisture content=[(M ₂ -1000V _a )/(V _s ×2653)-1]×100%;

Soil bulk density = V _s × 2653/V.

(3) Beneficial effects

The invention uses the volume replacement method to directly measure the moisture content and bulk density of soil mass, which is simple and convenient to operate, high in measurement accuracy, good in instrument stability, time-saving, labor-saving and energy-saving, and overcomes the long-standing traditional drying scale for measuring soil moisture content. There are problems such as time-consuming, labor-intensive and waste of resources in the quality method and the alcohol combustion method.

Description of drawings

Fig. 1 is the schematic diagram of the device of measuring soil mass moisture content and bulk density by volume displacement method of the present invention;

Fig. 2 is the schematic diagram of the pre-saturated tank of the present invention;

Fig. 3 is a three-phase distribution diagram of a soil sample of the present invention.

In the figure, 1: computer; 2: electronic scale; 3: sampling ring knife; 4: drainage branch pipe; 5: drip pipe; 6: data line; 7: pre-saturated tank.

Detailed ways

Embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. The following examples are used to illustrate the present invention, but should not be used to limit the scope of the present invention.

As shown in Figure 1, the controller of the present embodiment is a computer 1, and measurement control software is installed in the computer 1; the sampling container is a sampling ring knife 3, and its bottom is provided with a drainage branch pipe 4; , which is connected to the computer 1 through the data line 6; the water supply equipment is the drip pipe 5.

As shown in Fig. 1 and Fig. 2, the working process of the embodiment of the present invention is: at first, put the soil sample of soil mass moisture content and bulk density into the sampling ring cutter 3, or obtain from the field with the sampling ring cutter 3 The undisturbed soil sample, the soil particle density of described soil sample is known, uses the electronic balance 2 to measure and obtain the initial mass of the soil sample, and transmits and stores in the computer 1; Then, the sampling ring cutter 3 is placed in the pre-saturation pool 7, The water level injected in the pre-saturation tank 7 is lower than the upper surface of the soil sample to be tested in the sampling ring knife 3, and the drainage branch pipe 4 at the bottom of the sampling ring knife 3 can be used for water communication with the pre-saturation tank 7, and the soil sample passes through the gap between the soil particles. The capillary action reaches a saturated state; after a period of pre-saturation, the sampling ring knife 3 containing the soil sample to be tested is taken out, the outer wall of the sampling ring knife 3 is wiped dry, and placed on the electronic scale 2, in order to prevent the soil sample from being unsaturated due to drainage. state, adopt the drip pipe 5 to continuously supply water to the soil sample, so that the soil sample remains in a saturated state, that is, water absorption and drainage reach a relative balance, and excess water will be discharged by the drainage branch pipe 4 at the bottom of the sampling ring knife 3, when the water in the sampling ring knife 3 The total mass of the soil sample is no longer changed, that is, when the electronic scale 2 shows a stable value, stop supplying water to the soil sample, and the quality at this time is transferred to the computer 1 by the electronic scale 2; finally, according to the volume of the soil sample , soil particle density, soil sample initial quality and the quality of soil sample when saturated, and the quality of sampling ring knife 3, calculate and output soil quality moisture content automatically by computer 1 and the measurement control software installed in the computer, also can calculate simultaneously The bulk density value of the soil sample.

As shown in Figure 3, the three-phase distribution diagram of the soil sample, the calculation principle of soil mass moisture content in the present invention is: soil is a three-phase system composed of soil particles, moisture and gas, and the volume and quality of soil include these three phases volume and quality. For the soil packed into the sampling ring knife 3 with a certain volume, the mass of air is very small, which can be ignored in the measurement and calculation. The quality of the wet soil to be measured is the sum of the quality of water and the quality of soil particles. By adding water to the soil to be measured to make the soil saturated, and replacing the volume of air-filled pores in the soil with a certain volume of water, the pore volume of the unsaturated soil can be obtained, that is, V _a in the figure. From the total soil sample volume and the calculated aerated void volume, the volume of soil particles and water contained in the soil can be calculated, that is, V _s and V _w in the figure. The total volume of soil V is the water volume V _w , soil The sum of particle volume V _s and gas volume V _a . After replacing the air-filled pores in the aerated soil with a certain volume of water, the soil mass moisture content and bulk density can be measured and calculated according to the mass density of water and soil particles and the mass of the initially wet soil sample.

The masses of soil particles and water in a soil sample are equal to the product of their respective volumes and densities. The bulk density of soil is related to the chemical and mineral composition of the soil. Generally, the particle density of soil is in the range of 2600kg/m ³ to 2800kg/m ³ , and the density of soil with high organic matter content is low. Fine-grained soil (clay soil) is generally 2700kg/m ³ to 2750kg/m ³ , and sandy soil is generally around 2650kg/m ³ . The average density value of 2650kg/m ³ is usually used for calculation. In the present invention, the system sets the density of conventional soil particles to 2653kg/m ³ , and the density of water to 1000kg/m ³ . The measurement process is controlled by computer and control software, and the initial mass of a certain volume of soil and the mass of the saturated soil sample are measured. Under the condition of known soil particle density (2653kg/m ³ ), the soil can be automatically calculated, output and stored. Mass moisture content and soil bulk density values.

Soil quality water content of the present invention and bulk density can calculate and obtain according to following three formulas:

V _s ×ρ _s +V _w ×ρ _w =M ₁

V _s ×ρ _s +(V _w +V _a )×ρ _w =M ₂

V _s +V _w +V _a =V

In the formula, ρ _w represents the density of water, ρ _s represents the density of soil particles, V _a represents the volume of gas in the soil, V _w represents the volume of water in the soil, V _s represents the volume of soil particles in the soil, V represents the total volume of soil, M ₁ Indicates the initial mass, M ₂ indicates the mass after saturation; where ρ _s , ρ _w and V are known, M ₁ and M ₂ can also be obtained by weighing, V _s , V _w and V _a are unknown, through the above three The following formulas can be derived for V _s , V _w and V _a , resulting in:

Soil mass moisture content=[(M ₂ -1000V _a )/(V _s ×ρ _s )-1]×100%;

Soil bulk density = V _s × ρ _s /V.

When the density of soil particles is 2653kg/ ^m3 , then;

Soil mass moisture content=[(M ₂ -1000V _a )/(V _s ×2653)-1]×100%;

Soil bulk density = V _s × 2653/V.

According to the specific experiments, three kinds of soil materials are used in the following, which are clay loess from Yangling, Shaanxi, silty loam in Beijing and clay red soil from Jiangxi (hereinafter referred to as T1, T2, T3 respectively) to test the measurement accuracy of this device for different soils .

T1, T2, and T3 are prefabricated into 6 kinds of moisture content: air-dried soil (moisture content 2~3%), 5%, 10%, 15%, 25%, 30% volume moisture content; 3 kinds of soil density: 1.25g /cm ³ , 1.35g/cm ³ , 1.45g/cm ³ . A total of 54 soil samples were prepared from the three types of soil. Each soil sample uses two methods to measure soil moisture content respectively: one is to adopt the traditional geotechnical measurement method, i.e. drying and weighing method (used to compare and illustrate the accuracy of measurement using the device of the present invention); the other is Measured with the device of the present invention.

For each kind of soil, the soil mass moisture content obtained by the drying weighing method under different soil bulk densities and the soil mass moisture content measured by this device is fitted with the following formula (1):

y=B×x+A (1)

In the formula: y is the moisture content value of the soil mass measured by this device; x is the measured value of the drying weighing method, and A and B are the regression coefficient and regression constant respectively.

Table 1. Fitting parameters of T1 under three soil densities

Soil density (g/cm ³ ) A B R ² 1.25 0.51794 0.99430 0.9994 1.35 0.24465 1.00937 0.9997 1.45 0.43037 1.00111 0.9997

Table 2. T2 fitting parameters under three soil densities

Soil density (g/cm ³ ) A B R ² 1.25 0.14402 1.00843 0.9997 1.35 0.23783 1.00898 0.9999 1.45 0.12348 1.02130 0.9998

Table 3. Fitting parameters of T3 under three soil densities

Soil density (g/cm ³ ) A B R ² 1.25 0.62819 0.99560 0.9974 1.35 0.26524 1.00626 0.9995 1.45 0.10163 1.02393 0.9998

It can be seen from Tables 1, 2, and 3 that for different mass moisture contents of each soil, the soil mass moisture content measured by this device has a good one-to-one correspondence with the results measured by the traditional drying weighing method , indicating the rationality of the measurement with this device. Parameter A is greater than zero, indicating that the moisture content of the soil mass measured by this device is greater than the result measured by the traditional drying weighing method. This is because when the traditional drying weighing method is used to measure, there are still There is 1~2% moisture remaining, and this part of the error is often ignored by the experimenter, resulting in the measured moisture content being smaller than the real moisture content. Therefore, the soil moisture content measured by the device is closer to the real value.

For every kind of soil, every kind of soil density, carry out error analysis and comparison with traditional drying weighing method and the soil mass water content that this device records, and comparison error is about 1%, shows that the measured value with this device has Higher precision, the results are shown in Table 4.

Table 4. The present invention compares (%) with the moisture content error that traditional method records

The soil bulk density measured by this device is compared with the three prefabricated soil densities in the test, and fitted according to the formula (1), where y is the density of the three prefabricated soils in the test, and x is the soil volume measured by the device Density and fitting parameters are shown in Table 5. ^R2 is the coefficient of determination, indicating the goodness of fit. The closer its absolute value is to 1, the higher the reference value of the relevant fitting equation is. The coefficients of determination in Table 5 are all greater than 0.99.

Table 5. Fitting parameters of prefabricated soil density and soil bulk density measured by this device

A B R ² Yangling clay loess 8.6341 1.0095 0.998 Beijing silt loam 1.5016 1.0164 0.998 Jiangxi Clay Red Clay 30.1841 0.9958 0.996

The parameter B in Table 5 is close to 1, indicating that the soil bulk density measured by this device has a good one-to-one correspondence with the prefabricated soil density; the parameter A is greater than 0, indicating that the prefabricated soil density is greater than the measured soil volume density, which means Further explain the influence of residual moisture by drying weighing method. The results show that the error between the soil volume density value measured by this device and the actual soil volume density value is less than 1%, which has high precision. This device can be applied to simultaneously measure soil mass moisture content and soil volume density.

The embodiments of the present invention have been presented for purposes of illustration and description, but are not intended to be exhaustive or to limit the invention to the form disclosed. Many modifications and changes will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to better explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention and design various embodiments with various modifications as are suited to the particular use.

Claims (5)

1. volume displaced method is surveyed a device for soil quality water percentage and volume density, it is characterized in that, comprises controller, sampling container, weighing equipment and saturation system;

Described controller is computing machine, is connected with described weighing equipment by data line, in described computing machine, measurement control software is installed;

Described saturation system comprises presaturation pond and supply equipment, and described supply equipment is weep pipe;

Described sampling container bottom is provided with branch drain, and in the time that described sampling container is placed in described presaturation pond, the water level in described presaturation pond is lower than the upper surface of soil sample to be measured in described sampling container.

2. volume displaced method according to claim 1 is surveyed the device of soil quality water percentage and volume density, it is characterized in that: described sampling container is sampling spoon.

3. volume displaced method according to claim 1 is surveyed the device of soil quality water percentage and volume density, it is characterized in that, described weighing equipment is electronic scales.

4. a method of utilizing in claim 1-3 device described in any one to realize volume displaced method to survey soil quality water percentage and volume density, is characterized in that, comprises the following steps:

S1, at known soil bulk density ρ _scondition under, the soil sample of getting certain volume, records its initial mass;

S2, described soil sample is carried out to presaturation processing;

S3, the described soil sample through presaturation processing is continued to supply water, make it keep state of saturation, in the time that the constant mass of soil sample is constant, record its quality when saturated;

S4, according to volume V, the soil bulk density ρ of described soil sample _s, soil sample initial mass M ₁, the mass M of soil sample when saturated ₂and the density p of water _w, calculating quality water percentage and the volume density of described soil sample by formula, described formula is,

V _s×ρ _s+V _w×ρ _w＝M ₁

V _s×ρ _s+(V _w+V _a)×ρ _w＝M ₂

V _s+V _w+V _a＝V

In formula, ρ _wrepresent the density of water, ρ _srepresent soil bulk density, V _arepresent gas volume in soil, V _wrepresent soil moisture volume, V _srepresent soil particle volume in soil, V represents soil cumulative volume, M ₁represent initial mass, M ₂represent the quality after saturated; Wherein ρ _s, ρ _wwith V be known, M ₁and M ₂also can obtain by weighing V _s, V _wand V _afor the unknown, can derive V by three formula above _s, V _wand V _athereby, obtain:

Soil quality water percentage=[(M ₂-1000V _a)/(V _s× ρ _s)-1] × 100%;

Soil volume density=V _s× ρ _s/ V.

5. volume displaced method according to claim 4 is surveyed the method for soil quality water percentage and volume density, it is characterized in that: the soil bulk density ρ of described soil sample _sspan is 2600kg/m ³to 2800kg/m ³, the density of water is 1000kg/m ³.