CN102928575B - A device for keeping the saturation of test soil constant - Google Patents

Abstract

The invention provides a device capable of keeping saturation of experimental soil mass constant. The device comprises a sealed box with an upper cover, a calculation unit and a display unit, wherein the sealed box is provided with a water replenishing device; a temperature sensor, a humidity sensor and a dew point sensor are arranged on the upper portion of the box; the calculation unit is used for receiving temperature, humidity and dew point temperature data of air sent by the temperature sensor, the humidity sensor and the dew point sensor, calculating moisture content of air at initial time and moisture content of air at a subsequent time and figuring out the difference therebetween, and controlling the water replenishing device to replenish water at the difference into the soil mass; and the display unit is used for displaying temperature, humidity and dew point temperature of air and the difference. The device can accurately replenish water to the soil mass, simply and effectively keep saturation of soil mass constant, so that the test results of experiments are objective, real and reliable.

Description

A device for keeping the saturation of test soil constant

technical field

The invention relates to a test device for unsaturated soil in the field of civil engineering geotechnical tests, in particular to a test device for keeping the saturation of unsaturated soil constant.

Background technique

Natural soil is a complex three-phase material system, in which soil particles form a solid soil skeleton, and the gaps in the soil skeleton are filled with liquid and gas. When the gaps between the skeletons are all filled with liquid, saturated soil is formed; if the soil If the pores inside the body are partially filled with liquid, it is an unsaturated soil. Unsaturated soil is a heterogeneous porous medium material composed of soil particles and immiscible fluids (such as water-air, water-oil, water-pollutants, etc.), which are widely distributed in soil slopes, Earth-rock dams, roadbed fills, landfills and arid - semi-arid areas. With the continuous improvement of the national economy's demand for transportation, the construction of roads and railways is expanding, and unsaturated soils such as fine-grained soil (silty soil and clay soil), expansive soil, loess, and collapsible soil are gradually increasing as roadbed materials. In recent years, with the rapid development of my country's economy and the intensification of human social transformation activities, more and more engineering problems related to unsaturated soils need to be solved.

Subgrade engineering, hydraulic engineering, and municipal engineering built in unsaturated soil areas are affected by factors such as climate, and the properties of shallow unsaturated soil engineering change, which is manifested as changes in water and heat distribution in construction projects. This change has a major impact on the stability of the project, and often leads to subsidence, vertical expansion, and ditch sinking in subgrade engineering, frost heaving, bank collapse, and masonry cracking in water conservancy projects, and frost heaving, subsidence, and other damage in municipal engineering. Disorders such as fissures. The cause of the disease is that the water content in the soil increases to cause collapsing, the strength decreases, the volume of the soil itself changes due to freezing and thawing, and the difference in water and heat on the yin and yang surfaces causes deformation differences, etc. The main index affecting the stability of shallow unsaturated soil engineering is the water content. and temperature.

In order to accurately grasp the influence of unsaturated soil with a certain degree of soil saturation on the stability of roadbed engineering, water conservancy projects, etc., people need to use the unsaturated soil as the experimental object to conduct experiments on hydraulic parameters such as soil consolidation and viscoelasticity. . During the various tests of the soil, the change of the ambient temperature will lead to the loss of water in the soil, which will lead to changes in the saturation of the soil and affect the accuracy of the test results. Therefore, it is very important to keep the soil saturation constant during the experiment.

In order to keep the saturation of the soil constant, in the prior art, water is generally added directly to the test soil to maintain the saturation of the soil. However, this approach has greater randomness, and the soil saturation is not stable enough, which is not conducive to obtaining accurate experimental results.

Contents of the invention

The object of the present invention is to provide an experimental device for keeping the saturation of the test soil constant, so as to overcome the arbitrariness of maintaining the saturation of the soil in the prior art and improve the accuracy of the test.

The inventor finds through a large number of experiments:

1. The physical process of soil moisture evaporation

The conditions for the continuous evaporation of soil water are: heat often reaches the soil surface to provide the heat of vaporization required for water vaporization; the water vapor pressure on the soil surface is higher than the atmospheric water vapor pressure; the soil surface can continuously obtain moisture in the soil. According to the movement of various forms of water, the evaporation process of soil water is divided into three stages:

① In the stage of capillary operation, when the soil is wet, the water fills the internal pores of the soil, and the water moves continuously and rapidly to the surface through capillary action. The water vaporizes and diffuses on the surface, and the soil water evaporates strongly. the

② In the film operation stage, when the evaporation water consumption reduces the water content of the soil and is less than the capillary water breakage water content, the capillary water is disconnected, the capillary conduction stops, and the soil moisture is in the form of film water, from the place where the water film is thick to Movement where the water film is thin. Due to this slow movement, water evaporation is significantly reduced. At this time, evaporation is not only carried out on the surface, but also the water inside the soil can be vaporized and diffused to the atmosphere through the pores of the soil. the

③ In the diffusion operation stage, when the water content of the soil decreases and approaches the withering coefficient, the thin film movement of soil water from the bottom to the soil surface has basically stopped, and only gaseous water in the surface soil diffuses, and the evaporation rate is very small. the

2. Influencing factors of soil moisture evaporation

In addition to the same factors that affect water surface evaporation, there are soil water content, groundwater depth, soil structure, soil color, and soil surface characteristics. the

① When the water content of the soil is close to saturation, since the irregular soil particles constitute a larger total evaporation surface, the evaporation opportunities are more than those of the free water surface with the same horizontal area. The water content in the range of 3 to 5 cm on the surface of the soil plays a decisive role in evaporation, and the downward influence is small. the

② If the buried depth of the groundwater is small and the phreatic level is always kept within the range of capillary action, the water content of the soil can be permanently replenished and the evaporation will be uniform; on the contrary, if the buried depth of the groundwater is large, the evaporation rate will decrease greatly. the

③Soil with aggregate structure has small evaporation; soil with non-aggregate structure has large evaporation. the

④The soil color changes the reflectance of the soil surface, thereby affecting evaporation. The darker the soil color, the greater the evaporation. The evaporation of brown soil is 19% larger than that of white, and the evaporation of black soil is 32% larger than that of white. the

⑤Soil surface characteristics affect the turbulence of wind, the evaporation of rough ground is larger than that of smooth ground; the wind speed is higher at high terrain, and the evaporation of highland is larger than that of basin; the slope of the surface affects the absorption of radiation, and the evaporation is also different. different.

It can be seen that, as shown in Figure 1, with the increase of the external temperature, the water in the upper part of the soil continuously enters the air in the form of water vapor under the action of evaporation; as the water in the upper part of the soil decreases, the water in the lower part of the soil moves to the air under capillary action. The movement of the upper part of the soil causes the groundwater table to drop continuously. As shown in Figure 2, as the temperature rises, more and more water enters the air, and the humidity of the air increases accordingly. The water loss in the soil is serious, which directly causes the saturation of the soil to drop. Therefore, it can be considered to keep the soil saturation constant by adjusting the humidity of the air.

Accordingly, the device of the present invention includes the following components: a closed box with a top cover for encapsulating the test soil; The upper part of the body is provided with a temperature sensor, a humidity sensor and a dew point sensor, which are used to detect the temperature, humidity and dew point temperature of the air on the upper part of the soil body; a calculation unit is used to receive the air sent from the temperature sensor, humidity sensor and dew point sensor temperature, humidity and dew point temperature data, and calculate the moisture content of the air at the beginning and the moisture content of the air at a certain time later, calculate the difference, and control the water supply device to replenish the moisture of the difference and a display unit for displaying the temperature, humidity, dew point temperature and difference of the air.

According to the device of the present invention, the water supply device is preferably arranged on the upper cover of the box body.

According to the device of the present invention, the water replenishing device is preferably a spraying device, which is used to evenly spray water on the surface of the soil.

According to the device of the present invention, the lower part of the box body can also be provided with a water tank and a water-permeable plate for simulating the groundwater layer, so that the experimental results are closer to the natural state.

According to the device of the present invention, the computing unit is made of a single-chip computer.

The device of the invention can accurately replenish water to the soil, and can simply and effectively keep the saturation of the soil constant, so that the test results of the experiment are more objective, real and reliable.

Description of drawings

Figure 1 is a schematic diagram of soil water migration under high temperature;

Fig. 2 is a schematic diagram of soil water migration after water replenishment according to the method of the present invention;

Fig. 3 is a structural diagram of a specific embodiment of the device of the present invention.

Detailed ways

Below in conjunction with accompanying drawing, the specific implementation of the method of the present invention is described in detail as follows: the test device of the present invention comprises casing 1 and loam cake 2, and described airtight casing 1 top is provided with shower device 3, and the top of casing top One side is provided with a temperature sensor 4 , a humidity sensor 5 and a dew point sensor 6 , and a computing unit 7 is used to control the spraying device and a display unit 8 .

The device according to the present invention comprises the following components: a box body 1 with a loam cake 2 for encapsulating the test soil; the lower part of the airtight box body is provided with a water tank 9 for containing water, and the water tank 9 is provided with The water-permeable plate 10 separates the water in the water tank from the soil; the upper cover 2 is provided with a spray device 3 for uniformly spraying and replenishing water on the surface of the soil; the upper part of the airtight box 1 is provided with There are temperature sensor 4, humidity sensor 5 and dew point sensor 6, which are used to detect the temperature and humidity of the air on the upper part of the soil in the casing and the dew point temperature; the calculation unit 7 is made by a single-chip microcomputer, and is used to receive data from the temperature sensor 4, The temperature, humidity and dew point temperature data of the air sent by the humidity sensor 5 and the dew point sensor 6, and calculate the initial moisture content of the air and the moisture content of the air at a certain time thereafter, calculate the difference, and pass the control The spraying device 3 is used to fill the water of the difference into the soil; and the display unit 8 is used to display the difference.

During use, water is filled into the water tank 9 earlier, and the permeable plate 10 is covered; then an appropriate amount of test soil is placed on the permeable plate 10 to form the soil; the loam cake 2 is covered with the casing 1; the temperature sensor 4, the humidity Sensor 5 and dew point sensor 6 test the initial temperature and humidity of the air above the soil, and calculate the initial moisture content V1 of the air; when the temperature rises to a certain level, temperature sensor 4, humidity sensor 5 and dew point sensor 6 test the current air The temperature, humidity and dew point temperature corresponding to the current air humidity, calculate the current water content V2 of the air; calculate the difference ΔV between the current water content V2 and the initial water content V1, which is the evaporation of water in the soil; calculate The unit 7 controls the spraying device 3 to replenish the moisture of the ΔV amount of water into the soil body through uniform spraying to keep the saturation of the soil body constant; at the same time, the display unit 8 timely displays the temperature, humidity, and dew point temperature of the air. And the difference is displayed for the user to judge the amount of water replenishment.

The present invention may be embodied in other specific forms without departing from the spirit or main characteristics of the invention. Therefore, no matter from which point of view, the above-mentioned embodiments of the present invention can only be considered as illustrations of the present invention rather than limiting the present invention. The claims indicate the scope of the present invention, but the above description does not indicate the scope of the present invention. Therefore, any changes within the meaning and scope equivalent to the claims of the present invention should be considered to be included in the scope of the claims.

Claims (5)

1. A constant device for keeping the saturation of the test soil is characterized in that it comprises the following parts: a closed box with a loam cake for packaging the test soil; the box is provided with a water replenishing device for The test soil is replenished with water; the upper part of the box is provided with a temperature sensor, a humidity sensor and a dew point sensor, which are used to detect the temperature, humidity and dew point temperature of the air on the upper part of the soil; The temperature, humidity and dew point temperature data of the air sent by the sensor and the dew point sensor, and calculate the initial moisture content of the air and the moisture content of the air at a later time, calculate the difference, and control the water supply device, filling the water of the difference into the soil; and a display unit for displaying the temperature, humidity, dew point temperature and the difference. 2. The device according to claim 1, characterized in that: the lower part of the closed box is provided with a water tank and a water-permeable plate. 3. The device according to claim 1 or 2, characterized in that the water supply device is arranged on the upper cover of the closed box. 4. The device according to claim 3, characterized in that: the water replenishing device is a spraying device for evenly spraying water on the surface of the soil. 5. The device according to claim 4, wherein the computing unit is made of a single-chip computer.