CN114609005A - On-line measurement device and method of soil mechanical composition based on pressure detection - Google Patents

Abstract

The invention discloses an on-line measuring device and method for soil mechanical composition based on pressure detection, wherein the on-line measuring device comprises a sedimentation cylinder, a pressure sensor and a data acquisition and processing unit. Below the liquid level of the soil suspension in the cylinder, the pressure sensor is installed at one end of the valve, and the signal output end of the pressure sensor is connected to the data acquisition and processing unit. The present invention utilizes the pressure sensor to detect the pressure value of the soil suspension in real time, and transmits it to the data acquisition and processing unit for recording and analysis, which reduces the instability in manual operation, has a high degree of automation, and improves the detection precision and accuracy.

Description

On-line measurement device and method of soil mechanical composition based on pressure detection

technical field

The invention relates to soil detection technology, in particular to an on-line measuring device and method for soil mechanical composition based on pressure detection.

Background technique

Soil mechanical composition (soil particle composition) refers to the percentage of soil mineral particles of each particle size. Soil mechanical composition is the basic data for studying various physical and chemical behaviors of soil, and mechanical composition analysis is the basic work for soil texture classification. Accurate and efficient determination of soil mechanical composition is of great significance to soil research.

The current domestic methods for the determination of soil mechanical composition are mainly the straw method and the hydrometer method. In the detection and analysis of the pipette method, a certain amount of suspension is sucked at a certain time point and at a certain depth, and the suspension is dried and weighed to measure the content of particles of different particle sizes. Therefore, the time and depth of the suction suspension will greatly affect the accuracy of the measurement results. The pipette method has some disadvantages, including cumbersome operation steps, long time-consuming, and the measurement accuracy depends on laboratory conditions and operating proficiency. Compared with the straw method, the hydrometer method is relatively easier to operate, but has low precision, and is still a very time-consuming method that is difficult to accurately control by manual operation. Both the straw method and the hydrometer method are based on Stokes' law. The former has complicated operation steps and the latter has poor accuracy. Both are time-consuming, especially when measuring soil particles with smaller particle sizes. The more, the larger the error.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an on-line measuring device for soil mechanical composition based on pressure detection in order to overcome the above shortcomings of the prior art. This pressure detection-based on-line measurement device for soil mechanical composition can improve experimental precision and accuracy.

Meanwhile, another object of the present invention is to provide an on-line measurement method of soil mechanical composition based on pressure detection.

The object of the present invention is achieved through the following technical solutions: the soil mechanical composition on-line measuring device based on pressure detection includes a settling cylinder, a pressure sensor and a data acquisition and processing unit, and the cylinder wall of the settling cylinder is provided with a valve, and this valve is located in the settling cylinder. Below the liquid level of the soil suspension in the cylinder, the pressure sensor is installed at one end of the valve, and the signal output end of the pressure sensor is connected to the data acquisition and processing unit.

Preferably, the distance between the valve and the liquid level of the soil suspension is greater than or equal to 20 cm.

Preferably, the outer wall of the settling cylinder is wrapped by a constant temperature heating plate.

Preferably, the pressure sensor is a grade 0.075 high-precision differential pressure sensor.

Preferably, the barrel wall of the settling barrel is provided with a scale.

The method for on-line determination of soil mechanical composition based on pressure detection adopts the above-mentioned device for on-line determination of soil mechanical composition based on pressure detection, including the following steps:

S1. Pour the treated soil suspension into the sedimentation cylinder, and stir well;

S2. The pressure sensor detects pressure changes in real time to form a data set of time and pressure;

S3. Divide the soil particles in the soil suspension into i groups according to the diameter of the soil particles, wherein the diameters of the soil particles in each group are d ₁ , d ₂ ... d _i , and the proportions of the soil particles in each group are k ₁ , k respectively ₂ …k _i , the linear system of equations can be obtained:

为沉降时间对应的压力值，i为大于或等于1的自然数；Among them, T ₁ ~T _i is the settlement time for each group of soil particles to completely settle to a certain depth h , Q is a constant,

is the pressure value corresponding to the settling time, i is a natural number greater than or equal to 1;

S4. Based on the data set of step S2 and the linear equation set of step S3, the mechanical composition of each group of soil particles in the soil suspension is obtained.

Preferably, the diameters of the soil particles in each group are 0.05mm> d ₁ > d ₂ >...> d _i >0.002mm.

Preferably, in step S3, the steps for determining the settling time T _i for the soil particles of each particle group to completely fall to the depth h are as follows:

According to Stokes' law and Archimedes' principle, the descending speed of each group of soil particles is proportional to the square of the radius of the soil particles, namely

Then according to the relationship between speed, time and distance, the settlement time of soil particles with diameter d _i when they settle to depth h is:

where v is the sedimentation velocity of soil particles in the liquid, g is the acceleration of gravity, ρ _s is the particle density, ρ _w is the liquid density, η is the liquid viscosity coefficient, d and d _i are the diameters of the soil particles, v _i is the sedimentation _velocity of soil particles with diameter di in liquid.

Compared with the prior art, the present invention has the following advantages:

1. The on-line measurement device for soil mechanical composition based on pressure detection of the present invention is mainly composed of a sedimentation cylinder, a pressure sensor and a data acquisition and processing unit. The pressure sensor is used to detect the pressure value of the soil suspension in real time, and it is sent to the data acquisition and processing unit for recording. The analysis reduces the instability in manual operation, the automatic degree is high, and the detection precision and accuracy are improved.

2. The on-line measurement method of soil mechanical composition based on pressure detection of the present invention uses a pressure sensor to detect the pressure value of the soil suspension online in real time, and transmits the pressure value data to the data acquisition and processing unit for recording and analysis, thereby forming a time and pressure data set , based on the data set and the linear equation system to obtain the soil particle content (ie mechanical composition) of each particle group; it is in contrast to the traditional method that separates the settlement of large and small soil particles to detect and ignores the simultaneous settlement of large and small particles. It not only improves the detection accuracy, but also has simple operation steps and short time-consuming.

3. The on-line measurement method of soil mechanical composition based on pressure detection of the present invention adopts pressure sensor and data acquisition and processing unit to detect data and record and analyze it to form a data group, so as to obtain a continuous soil particle group distribution curve, which can be used for more Research.

4. The on-line measurement method of soil mechanical composition based on pressure detection of the present invention uses a pressure sensor to connect outside the sedimentation cylinder, eliminating the interference of particle sedimentation by immersing in the suspension in other methods using straws, hydrometers or other measuring equipment. more acurrate.

5. The present invention adopts a constant temperature device to make the suspension in a constant temperature state during the whole measurement process, eliminating the influence of temperature change on the sedimentation velocity of soil particles, and the measurement result is more reliable.

Description of drawings

FIG. 1 is a schematic structural diagram of an on-line measuring device for soil mechanical composition based on pressure detection according to the present invention.

Among them, 1 is the sedimentation cylinder, 2 is the pressure sensor, 3 is the data acquisition and processing unit, 4 is the valve, and 5 is the soil suspension.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments.

As shown in Fig. 1, an on-line measuring device for soil mechanical composition based on pressure detection includes a settling cylinder, a pressure sensor and a data acquisition and processing unit. The cylinder wall of the settling cylinder is provided with a valve, which is located at the bottom of the soil suspension of the settling cylinder. Below the liquid level, the pressure sensor is installed at one end of the valve, and the signal output end of the pressure sensor is connected to the data acquisition and processing unit. Among them, the settling cylinder adopts a transparent glass cylinder to facilitate observation.

The distance between the valve and the liquid level of the soil suspension is greater than or equal to 20cm. With the settlement of soil particles, at a certain depth, the hydraulic pressure of the soil suspension will gradually decrease. Setting a pressure sensor at an appropriate depth position can accurately detect the change of pressure value, thereby ensuring the accuracy of the detection result.

The outer wall of the settling drum is wrapped by a constant temperature heating plate. The constant temperature heating plate enables the soil suspension to be treated in a constant temperature state, which further improves the detection accuracy.

The pressure sensor is a 0.075-grade high-precision differential pressure sensor. Only using a high-precision pressure sensor can detect the pressure change caused by particle sedimentation, further ensuring the accuracy of the detection result.

The barrel wall of the settling barrel is provided with a scale. This design is convenient for the operator to directly observe the volume of the suspension to ensure the accurate volume of the suspension.

The method for on-line determination of soil mechanical composition based on pressure detection adopts the above-mentioned device for on-line determination of soil mechanical composition based on pressure detection, including the following steps:

S1. Pour the treated soil suspension into the sedimentation cylinder, and stir it evenly; specifically, first pour the dispersed treated soil suspension into the sedimentation cylinder to the constant volume liquid level to the 1L mark, and use stirring according to the requirements of the sedimentation method. Stir thoroughly.

S2. The pressure sensor detects the pressure change in real time to form a data set of time and pressure; with the settlement of soil particles, the hydraulic pressure of the soil suspension at the monitoring position gradually decreases with time, and the pressure sensor transmits the detected pressure value. In the collector, the collector analyzes and processes the received pressure value and the corresponding time to form a data set of time and pressure.

S3. Divide the soil particles in the soil suspension into i groups according to the diameter of the soil particles, wherein the diameters of the soil particles in each group are d ₁ , d ₂ ... d _i , and the proportions of the soil particles in each group are k ₁ , k ₂ respectively ...k _i , the linear system of equations can be obtained:

为沉降时间对应的压力值，i为大于或等于1的自然数；Among them, T ₁ ~T _i is the settlement time for each group of soil particles to completely settle to a certain depth h , Q is a constant,

is the pressure value corresponding to the settling time, i is a natural number greater than or equal to 1;

S4. Based on the data set of step S2 and the linear equation set of step S3, the mechanical composition of each group of soil particles in the soil suspension is obtained.

For the above system of linear equations:

,

,

This is formula (1).

The process of obtaining formula (1) is as follows:

According to Stokes' law and Archimedes' principle, the falling speed of each soil particle is proportional to the square of the radius of the soil particle, then:

，此为式（2），

, which is the formula (2),

According to the relationship between speed, time and distance, the time Ti required for soil particles with diameter d _i to descend to the depth h (the distance between the liquid level of the soil suspension and the plane where the pressure sensor is located ₎ is:

，此为式（3）。

, which is the formula (3).

where v and vi are the sedimentation _velocity of soil particles in the soil suspension, _g is the acceleration of gravity, d and di are the diameter of soil particles, _ρs is the density of soil particles, ρw is the _density of water, and η is Viscosity coefficient of the soil suspension, h is the distance between the liquid level of the soil suspension and the plane where the pressure sensor is located, and T _i is the sedimentation time of the soil particles.

During the measurement, the soil particles in the soil are divided into i groups according to the diameter d _i , and the mass ratio of the soil particles with the diameter d _i in the soil is k _i ,

。土粒的分组的划分应根据研究需要划定，由于直径大于0.05mm的土粒沉降过程不符合Stocks定律，由于0.05mm土粒筛分误差较大；而土壤颗粒分级一般以0.002mm为粘粒直径上限，且小于0.002mm的土粒沉降时间过长，无特殊需要，一般最小粒组上限选0.002mm。因此本实施例中土粒的直径d _i 的大小为0.002mm~0.05mm。测定时，划分粒组数不可过多，划分太多粒组时，会由于每个粒组的土粒含量少，对应相邻两个沉降时间的间隔过短，某些时段内悬液密度可能变化不大，导致压力传感器采集的压力值变化不大，出现读数不准的情况，也可以根据测量要求，选择不同精度的压力传感器。Divide the grain groups d ₁ ~ di _i , i is a natural number, set the proportion of each grain group to be k _i , k _i ≥ 0,

. The grouping of soil particles should be delineated according to the research needs. Since the settlement process of soil particles with a diameter greater than 0.05mm does not conform to Stocks' law, and the sieving error of soil particles of 0.05mm is large, the classification of soil particles generally takes 0.002mm as clay particles. The upper limit of the diameter, and the settlement time of soil particles less than 0.002mm is too long, and there is no special need. Generally, the upper limit of the minimum particle group is 0.002mm. Therefore, in this embodiment, the diameter d _i of the soil particles is 0.002 mm to 0.05 mm. When measuring, the number of grain groups should not be divided too much. When too many grain groups are divided, due to the small content of soil particles in each grain group, the interval between the corresponding two adjacent settling times is too short, and the density of the suspension may be in some time periods. If the change is not large, the pressure value collected by the pressure sensor does not change much, and the reading is inaccurate. You can also choose a pressure sensor with different precision according to the measurement requirements.

In the working and calculation principle of this embodiment, the soil grains are divided into i grain groups, and the proportions of each grain group are respectively k ₁ , k ₂ , k ₃ , k ₄ . . . k _i , while k ₁ , k ₂ , k i _The diameters _of the _i groups _of soil particles ₃ , k _{4 .} _ _ _{_ _} _ _{_} _ _{_} _ _{_} _ _{_} k ₁ + k ₂ + k ₃ + k ₄ +...+ k _i =1.

已经下降到h深度以下，h深度内直径小于d ₁ 的土粒占沉降开始时h深度内该粒级的比例为

，占沉降开始时h深度内所有土粒的比例为

，即此时h深度内，所有土粒的组成比例为When the settling time is T1 , the soil particles with the diameter d1 all settle to the depth h and below, the soil particles with the diameter less _than d1 are all within the depth h , and the average density _{ρ1 of} the _suspension within the depth h is determined by the diameter Soil particles smaller than d ₁ are produced. Since the soil particles with diameter smaller than d ₁ will also settle for T ₁ , the soil particles of each particle group with diameter smaller than d ₁ have

Has dropped below the h depth, the proportion of soil particles with a diameter smaller than d ₁ in the h depth to the particle size in the h depth at the beginning of settlement is:

, the proportion of all soil particles within h depth at the beginning of settlement is

, that is, within the h depth at this time, the composition ratio of all soil particles is

，此为式（4）。

, which is the formula (4).

已经下降到h深度以下，h深度内直径小于d ₂ 的土粒占沉降开始时h深度内该粒级的比例为

，占沉降开始时h深度内所有土粒的比例为

，即此时h深度内，所有土粒的组成比例为When the settling time is T2 , the soil particles with particle size larger _{than d2} will all settle to the depth h and below, that is, the soil particles in the d1 group will all sink to the depth h and below, and all the particles in the h depth are _{smaller than} d2 . The average density ρ ₂ of the suspension in the depth h is generated by the soil particles with a diameter smaller than d _2. Since the soil particles with a diameter smaller than d ₂ also have a settlement time of T ₂ , at this time, each particle with a diameter smaller than d ₂ granular soil particles

Has dropped below the h depth, the proportion of soil particles with a diameter smaller _than d2 in the h depth to this particle size in the h depth at the beginning of settlement is

, the proportion of all soil particles within h depth at the beginning of settlement is

, that is, within the h depth at this time, the composition ratio of all soil particles is

，此为式（5）

, which is the formula (5)

By analogy, at time T3 , within the depth h , the composition ratio _of all soil particles is

，此为式（6）。

, which is the formula (6).

时刻，h深度内，所有土粒的组成比例为

，此为式（7）exist

At time, within the depth of h , the composition ratio of all soil particles is

, which is the formula (7)

，为常数。因此沉降一定时间T _i 时，h深度内悬液中土粒的总质量则为

。In the initial stage of subsidence, that is, when the subsidence time T _i =0, the total mass of soil particles in the suspension within h depth is m _s . The proportional product of the total depth H is calculated, namely

, is a constant. Therefore, when settling for a certain time T _i , the total mass of soil particles in the suspension within h depth is

.

，此为式（8）；According to the liquid pressure formula, record the pressure measured by the pressure sensor as p , and the average density of the suspension in the depth h as ρ , then there are

, this is formula (8);

，此为式（9）。

, which is the formula (9).

，因此 f is the ratio of soil particle volume V _s to suspension volume V within h depth,

,therefore

，此为式（10）。

, which is the formula (10).

，此为式（11）。

, which is the formula (11).

At a certain subsidence time T _i , there is

，此为式（12）；

, this is formula (12);

在整个沉降过程中是不变的，可设常数

，则T _i时刻，式（12）可写为

，即

，此为式（13）。because

It is constant during the whole settlement process, and a constant can be set

, then at time T _i , equation (12) can be written as

,Right now

, which is the formula (13).

Then based on k ₁ + k ₂ + k ₃ + k ₄ +…+ k _i =1, equations (4)~(7) and (13), the linear equation system can be obtained:

Then, based on equations (1) and (3), combined with the data set obtained in step S2, the mechanical composition of each group of diameter soil particles can be obtained.

The above-mentioned specific embodiments are the preferred embodiments of the present invention, and do not limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solutions of the present invention are included in the protection scope of the present invention. within.

Claims (8)

1. Soil mechanical composition on-line measuring device based on pressure detection, its characterized in that: the device comprises a sedimentation cylinder, a pressure sensor and a data acquisition and processing unit, wherein a valve is arranged on the wall of the sedimentation cylinder, the valve is positioned below the liquid level of the soil suspension of the sedimentation cylinder, the pressure sensor is arranged at one end of the valve, and the signal output end of the pressure sensor is connected with the data acquisition and processing unit.

2. The soil mechanical composition on-line measuring device based on pressure detection as claimed in claim 1, wherein: the distance between the valve and the liquid level of the soil suspension is greater than or equal to 20 cm.

3. The on-line soil mechanical composition measuring device based on pressure detection as claimed in claim 1, wherein: the outer wall of the settling cylinder is wrapped by a constant-temperature heating plate.

4. The on-line soil mechanical composition measuring device based on pressure detection as claimed in claim 1, wherein: the pressure sensor is a 0.075-level high-precision differential pressure sensor.

5. The soil mechanical composition on-line measuring device based on pressure detection as claimed in claim 1, wherein: the wall of the sedimentation cylinder is provided with scales.

6. The online soil mechanical composition measuring method based on pressure detection is characterized in that the online soil mechanical composition measuring device based on pressure detection according to any one of claims 1 to 5 is adopted, and the online soil mechanical composition measuring method based on pressure detection comprises the following steps:

s1, pouring the treated soil suspension into a settling cylinder, and fully and uniformly stirring;

s2, detecting pressure change in real time by the pressure sensor to form a data set of time and pressure;

s3, dividing the soil particles in the soil suspension according to the diameter of the soil particlesiGroups, wherein the diameter of each group of soil particles isd ₁ 、d ₂ … d _i The proportion of each group of soil particles is respectivelyk ₁ 、k ₂ …k _i Obtaining linearityThe system of equations:

wherein,T ₁ ~T _i completely settling each group of soil grains to a certain depth hThe settling time of (a), Q is constant,

is a pressure value corresponding to the settling time,iis a natural number greater than or equal to 1;

s4, based on the data set of step S2 and the linear equation set of step S3, the mechanical composition of each group of soil particles in the soil suspension is obtained.

7. The method of claim 6, wherein the diameter of each group of soil particles is 0.05mm >d ₁ ＞d ₂ ＞…＞d _i ＞0.002mm。

8. The method for on-line measurement of soil mechanical composition based on pressure measurement as claimed in claim 6, wherein in step S3, each group of soil particles is completely dropped tohSettling time of depthT _i The determination steps are as follows:

according to Stokes 'law and Archimedes' principle, the falling speed of each group of soil particles is proportional to the square of the radius of the soil particles, i.e. the velocity of each group is proportional to the square of the radius of the soil particles

And then the diameter is as follows according to the relation among the speed, the time and the distanced _i The soil particles are settled to a depthhThe settling time was:

wherein,vis the settling velocity of the soil particles in the liquid,gin order to be the acceleration of the gravity,ρ _sis the density of the particles and is,ρ _wthe density of the liquid is the density of the liquid,ηin order to be the viscosity coefficient of the liquid,dandd _i all the diameters of the soil particles are the same,v _i is of diameter ofd _i The settling velocity of the soil particles in the liquid.

Images