CN108572189A - Static and dynamic comprehensive test system considering soil body expansion and contraction characteristics under temperature gradient - Google Patents

Abstract

The invention discloses a static and dynamic comprehensive test system considering the expansion and contraction characteristics of the soil under the temperature gradient. The temperature-controlled circulation chamber at the upper end of the sample realizes the low-temperature freezing and temperature-rising freeze-thawing of the sample, and realizes the freezing and thawing of the actual project in combination with the actual situation. Simulate the phenomenon of expansion, melting and sinking; use water vapor to accurately control the change of sample humidity, and better simulate the phenomenon of shrinkage and swelling in actual engineering; and design an electron microscope that can rotate and lift freely to fully monitor the side of the sample The azimuth scanning is helpful to observe the change of the internal structure of the sample due to the change of the external environment, and provides theoretical support for the analysis of the change of physical and mechanical properties; the creative design of the double-layer silicone oil ring is proposed to improve the test accuracy, so that Effective expansion force; in addition, by arranging optical fibers on the side wall of the sample, the precise monitoring of temperature can be realized, and combined with the local strain sensor outside the sample, the comprehensive monitoring of the overall strain of the sample can be realized; the practical value and promotion value of the design of the present invention It is of great significance to simulate the freeze-thaw-expansion and contraction of expansive soil indoors and monitor the changes of various indicators.

Description

A static and dynamic comprehensive test system considering the expansion and contraction characteristics of soil under temperature gradient

technical field

The invention belongs to the field of geotechnical engineering, and specifically relates to a static and dynamic comprehensive test system considering the expansion and contraction characteristics of soil under a temperature gradient, which is applied to the indoor simulation of freezing and thawing and expansion and contraction of expansive soil to monitor the changes of various indicators.

Background technique

my country is a country where expansive soil is widely distributed, and the expansion or contraction of expansive soil can bring serious harm to engineering construction. At the same time, permafrost areas are widely distributed in my country, and the problem of permafrost diseases is prominent, which has seriously affected the speed of infrastructure construction and regional development in permafrost areas in my country. A reasonable model urgently needs the support of experimental technical conditions.

The invention patent with application publication number [CN106644750A] discloses an open system freeze-thaw soil dynamic and static triaxial tester, which can realize conventional frozen soil tests, one-way freeze-thaw tests of samples under different stress states under dynamic load, etc. However, the existing test instruments are still lacking in test accuracy, application range and practicability. It is urgent to propose a static and dynamic frost heave-expansion test system using an open system to carry out dynamic tests of soil under various dynamic loads. Experimental research on response and dynamic characteristics, including stability, damage identification and health diagnosis of foundation engineering, dams, road engineering, marine engineering, pipeline engineering and other types of engineering and equipment, as well as soil-structure interaction test research and highway/ Seismic test research on railway engineering structures. In order to greatly promote the construction capacity of major projects and make greater contributions to the country's economic construction.

Contents of the invention

The technical problem to be solved by the present invention is to propose a static and dynamic comprehensive test system considering the expansion and contraction characteristics of the soil under the temperature gradient in order to accurately simulate the actual situation. Changes of various physical and mechanical indexes of expansive soil, and observe the change of soil mesostructure with the external environment.

The present invention is realized by adopting the following technical solutions:

A static and dynamic comprehensive test system considering the expansion and contraction characteristics of soil under temperature gradients, including a steel frame, a central dowel bar, a loading system, a temperature control system, a moisture content control system, and a main control system. The central dowel bar is set at On the steel frame, the loading system, temperature control system and moisture content control system are all connected to the main control system;

The loading system includes a static load loading device and a dynamic load loading device to apply a static load or a dynamic load on the central dowel bar, and the static load loading device includes a counterweight and is applied through a counterweight; the dynamic load The loading device is applied by a vibrator; the temperature control system includes a water bath device, a circulation pipeline, a temperature-controlled circulation chamber and a silica gel membrane, the silica gel membrane is wrapped on the outside of the sample, and the temperature-controlled circulation chamber is located above the sample and surrounds the sample. The central dowel bar is set, and the water bath device is connected with the temperature-controlled circulation chamber through the circulation pipeline to realize the temperature control of the sample and simulate the phenomenon of frost heaving and thawing in actual engineering;

The moisture content control system includes an optical fiber, an optical fiber demodulator and an ultrasonic steam generating device. The optical fiber is arranged on the inner wall of the silica gel membrane, and the optical fiber is connected with the optical fiber demodulator to detect the humidity of the sample. There is a ring-shaped local strain sensor connected to the main control system, which can be combined with an optical fiber to realize all-round monitoring of the overall strain of the sample; a steam conduit is provided under the silicone membrane, and the steam conduit is connected to an ultrasonic steam generating device to realize the monitoring of the overall strain of the sample. The uniform humidification treatment of the sample controls the change of the humidity of the sample by controlling the content of water vapor in the circulating gas, and simulates the phenomenon of shrinkage and swelling in actual engineering;

The outer side of the silicone membrane is surrounded by a first silicone oil ring cavity and a second silicone oil ring cavity connected to the temperature control circulation cavity, the second silicone oil ring cavity is located outside the first silicone oil ring cavity, and the first silicone oil ring cavity and the second silicone oil ring cavity A vacuum ring cavity is set between the silicone oil ring cavities, and an electron microscope is set in the vacuum ring cavity to realize omni-directional scanning of the side of the sample. It can observe the mesoscopic structure changes of the soil caused by the change of the external environment of the sample, so as to deeply explore the mechanism of the influence of the physical and mechanical properties of the soil under different temperature gradients and stress conditions; through the design of the double-layer silicone oil ring cavity, the second silicone oil The ring cavity is not under pressure, and the bottom pressure is only controlled by temperature. The side of the first silicone oil ring cavity transmits the lateral expansion force of the sample, and the difference between the two can offset the pressure change caused by the temperature, thereby obtaining the effective expansion force.

Further, the bottom of the vacuum ring cavity is provided with an annular track, and the annular track is arranged around the circumference of the sample. The electron microscope is arranged on the annular track through a lifting device and rotates along the annular track. And the height adjustment realizes all-round scanning of the sample, which is convenient for observing the change of the internal structure of the sample due to the change of environment, and provides a theoretical basis for analyzing the change of physical and mechanical properties.

Further, the lifting device includes a lifting rod and a driving motor. The bottom of the lifting device is provided with a pulley matching the circular track. The lifting rod adopts a motor lifting rod to realize the free lifting of the electron mirror. The driving motor is connected with the pulley , to control the lifting device to move along the circular track.

Further, a pressure difference sensor is also provided between the first silicone oil ring cavity and the second silicone oil ring cavity to detect the pressure difference between the first silicone oil ring cavity and the second silicone oil ring cavity, and the lateral expansion force can be obtained directly, Calculate the lateral displacement of the sample by corresponding calculation.

Further, a positioning piece is provided on the central dowel bar, and a distance measuring sensor is provided above the temperature control circulation chamber, and the real-time recording of the height change of the sample is realized through the cooperation of the distance measuring sensor and the positioning piece. The sensor adopts laser displacement sensor.

Further, the test system also includes a vacuum pump and a glass cover arranged on the steel frame, the vacuum pump makes the inside of the glass cover form a vacuum during the test, reduces temperature transfer, and improves cooling and heating efficiency.

Compared with prior art, advantage and positive effect of the present invention are:

The soil frost heave-expansion open test system proposed by the present invention has a simple and novel structure design:

(1) Through the design of the temperature control system, the temperature-controlled circulation chamber at the upper end of the sample realizes the low-temperature freezing and freezing-thawing of the sample, and realizes the simulation of the phenomenon of frost heaving and thawing in actual engineering in combination with the actual situation;

(2) Through the design of the moisture content control system, the humidity change of the sample is accurately controlled by means of water vapor, and the shrinkage and swelling phenomenon in the actual project can be better simulated;

(3) By designing an electron microscope that can rotate and lift freely, scan the side of the sample in all directions, and observe the changes in the internal structure of the sample due to changes in the external environment, providing theoretical support for the analysis of changes in physical and mechanical properties;

(4) Design a double-layer silicone oil ring cavity, the outer silicone oil ring cavity is not under pressure, the bottom pressure is only controlled by temperature, the inner silicone oil ring cavity transmits the lateral expansion pressure of the sample, and the difference between the two can be the pressure brought by the temperature Change the offset to get the effective expansion force;

(5) By arranging optical fibers on the side wall of the sample, the precise monitoring of the temperature is realized, and combined with the local strain sensor on the outside of the sample, the all-round monitoring of the overall strain of the sample is realized;

(6) Since the test equipment needs to simulate temperature changes, a toughened glass cover is designed on the outermost side and equipped with a vacuum pump to form a vacuum inside the glass cover during the test, reduce temperature transfer, and improve cooling and heating efficiency.

Description of drawings

Fig. 1 is the overall structure schematic diagram of soil frost heave-expansion open test system described in the embodiment of the present invention;

1. Vacuum pump; 2. Main control system control panel; 3. Vacuum exhaust pipe; 4. Positioning plate; 5. Central dowel rod; 6. Glass cover; , Silicone membrane; 10, Local strain sensor; 11, Second silicone oil ring cavity; 12, Circulation pipeline outlet pipe; 13, Electron microscope; 14, Optical fiber; 15, Base; 16, Optical fiber demodulator; 17, Pressure difference sensor 18. Water bath device; 19. Power supply; 20. Ultrasonic steam generating device; 21. First silicone oil ring chamber; 22. Temperature control circulation chamber; 23. Steam conduit.

Detailed ways

In order to understand the above-mentioned purpose, features and advantages of the present invention more clearly, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be noted that, in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways than those described here. Therefore, the present invention is not limited to the specific embodiments disclosed below.

A static and dynamic comprehensive test system considering the expansion and contraction characteristics of soil under temperature gradient, as shown in Figure 1, including a steel frame, a central dowel bar 5, a loading system, a temperature control system, a moisture content control system and a main control system , the bottom of the steel frame is provided with a base 15, and the central dowel 5 is provided on the steel frame, and the loading system, the temperature control system and the moisture content control system are all connected to the main control system, specifically, the loading system Including a static load loading device and a dynamic load loading device (not shown in the figure), to apply a static load or a dynamic load on the central dowel bar 5, the static load loading device includes a counterweight, applied by a counterweight The dynamic load loading device is applied by a vibrator; the temperature control system includes a water bath device 18, a circulation pipeline (circulation pipeline water inlet pipe 8 and circulation pipeline water outlet pipe 12), a temperature control circulation chamber 22 and a silica gel membrane 9, The silica gel membrane 9 is transparent and wrapped around the sample. The temperature-controlled circulation chamber 22 is located above the sample and arranged around the central dowel 5. The water bath device 18 is connected to the temperature-controlled circulation chamber 22 through a circulation pipeline to realize The temperature control of the sample simulates the phenomenon of frost heaving and thawing in actual engineering; the water content control system includes an optical fiber 14, an optical fiber demodulator 16 and an ultrasonic steam generator 20, and the optical fiber 14 is arranged on the inner wall of the silica gel membrane 9 (on the outer wall of the sample), the optical fiber 14 is connected to the optical fiber demodulator 16 to detect the humidity of the sample, and the outer wall of the silica gel membrane 9 is also provided with a ring-shaped local strain sensor 10 connected to the main control system, which can be connected with the optical fiber 14 combined to realize the all-round monitoring of the overall strain of the sample; a steam conduit 23 is provided under the silica gel membrane 9, and the steam conduit 23 is connected with the ultrasonic steam generating device 20 to realize uniform humidification of the sample. The content of water vapor controls the change of the humidity of the sample, simulating the phenomenon of shrinkage and swelling in actual engineering.

In this embodiment, the outer side of the silicone membrane 9 is surrounded by a first silicone oil ring cavity 21 and a second silicone oil ring cavity 11 connected to the temperature-controlled circulation cavity. Outside, and a vacuum ring cavity is set between the first silicone oil ring cavity 21 and the second silicone oil ring cavity 11, and an electron microscope 13 is arranged in the vacuum ring cavity to realize omni-directional scanning of the side of the sample, and the electron microscope 13 can be used to test The mesoscopic structure of the soil caused by the change of the external environment, so as to deeply explore the mechanism of the influence of different temperature and stress conditions on the physical and mechanical properties of the soil, between the first silicone oil ring cavity 21 and the second silicone oil ring cavity 11 A pressure difference sensor 17 is also provided to detect the pressure difference between the first silicone oil ring cavity 21 and the second silicone oil ring cavity 11, so that the lateral expansion force can be obtained directly, and the lateral displacement of the sample can be obtained through corresponding calculation. And the important thing is to creatively propose a double-layer silicone oil design scheme. By designing the double-layer silicone oil ring cavity, the second silicone oil ring cavity is not under pressure, and the bottom pressure is only controlled by temperature. The side of the first silicone oil ring cavity transmits the lateral expansion force of the sample. , the difference between the two can offset the pressure change brought by the temperature, so as to obtain the effective expansion force.

Continuing to refer to Fig. 1, the bottom of the vacuum ring cavity is provided with an annular track, and the annular track is arranged around the circumference of the sample. The rotation and height adjustment of the electron microscope can scan the sample in all directions, which is convenient for observing the changes in the internal structure of the sample due to environmental changes, and provides a theoretical basis for analyzing changes in physical and mechanical properties; in this embodiment, the lifting device includes A lifting rod and a driving motor. The bottom of the lifting device is provided with a pulley matching the circular track. The lifting rod adopts a motor lifting rod to realize the free lifting of the electron mirror 13. The driving motor is connected with the pulley to control the lifting device along the circular track. sports.

In addition, a positioning piece 4 is arranged on the central dowel bar 5, and a distance measuring sensor 7 is arranged above the temperature control circulation chamber 22, and the real-time recording of the height change of the sample is realized through the cooperation of the distance measuring sensor 7 and the positioning piece 4 , the distance measuring sensor adopts a laser displacement sensor. In order to reduce temperature transmission and improve refrigeration and heating efficiency, the test system also includes a vacuum pump 1 and a glass cover 6 arranged on a steel frame. The vacuum pump 1 is connected to the glass cover 6 through a vacuum exhaust pipe 3, so that A vacuum is formed inside the glass cover 6 .

This test device is mainly used for static dynamic frost heave-expansion test in an open system, and is used to simulate the changes of various physical indicators of the soil under real conditions. Specifically, the following tests can be carried out:

(1) Sample expansion and contraction displacement monitoring:

Place the configured cylindrical sample with a radius R ₁ =50.0mm and a height h ₁ =200mm in a cylindrical space wrapped by a silica gel film, and assemble the instrument; take the initial volume V ₁ =V _instrument -V _sample , according to the instrument Instructions Calculate the value of V ₁ , feed the cooling liquid from the inlet of the temperature control system, the constant temperature liquid flows through the temperature control circulation chamber, and realize the cooling or heating of the sample through the heat transfer through the silicone oil, and at the same time, the sample can be cooled or heated by the optical fiber demodulator. The temperature data measured by the optical fiber is fed back to the water bath device in real time to achieve precise temperature control. When the temperature of the sample reaches the required temperature, it is left to stand for 1-2 minutes.

The optical fiber distributed on the side surface of the sample during the dry-wet cycle can monitor the change of the water content ρ of the sample in real time, and at the same time maintain the change of the water content of the sample through the water content control system; the frost heaving-expansion coupling process can be carried out many times. Provide samples after different times of frost heave-expansion cycles; adjust the static force and dynamic force of the loading system through the main control system to make the loading system drop slowly, and record the numerical changes Δh and Δp of the displacement sensor and pressure sensor at the same time, and record the atmospheric pressure P ₁ ; After the system is stable for 1-2 minutes, check the value ΔP of the differential pressure sensor. Through the formula PV=nRT, it can be deduced that P ₁ V ₁ =P ₂ V ₂ , where (P ₂ =P ₁ +ΔP), then formula It can be concluded that: The average lateral displacement of the sample can be obtained by this formula.

(2) Lateral local strain:

The lateral strain ΔR _i at the i-th point in the vertical direction can be measured by the local strain sensor arranged outside the silicone membrane (the i-th point is the corresponding position of the local strain sensor, which is set at an interval from top to bottom outside the silicone membrane There are i local strain sensors, i=1, 2, 3,...), the data can be used as the review data of the lateral average displacement while providing data for the experiment as the local strain.

(3) Changes in internal structure characteristics of soil samples:

The electron microscope can be started to scan the sample. Because the electron microscope is in contact with the bottom circular slide rail through the freely retractable control rod, it can realize 360° rotation and scan the sample in all directions.

In a word, this test system adopts full digital control system and high-precision sensor technology. The main control system adopts full digital controller and has multiple measurement channels. Each measurement channel can perform separate control or several measurements of load, deformation, etc. Joint control of channels. The vertical static force is applied by the counterweight method, and the vertical dynamic force is applied by the vibrator; it can carry out: ① Frost heave test, ② Melting settlement test, ③ Expansion test, ④ Dry shrinkage test, ⑤ Expansion-frost heave coupling test, ⑥ Melting settlement-drying shrinkage coupling test realizes detection of the following parameters: ① vertical frost heave displacement (top of sample), strain, earth pressure; ② vertical thawing displacement (top of sample); ③ vertical expansion displacement, Strain, earth pressure, ④ vertical shrinkage displacement (top of sample); ⑤ vertical displacement, strain, earth pressure under expansion-frost heave coupling, ⑥ vertical displacement under thawing-drying shrinkage coupling; ⑦ frost heave , thawing, expansion, drying shrinkage, expansion-frost heave coupling, thawing-drying shrinkage test and other lateral deformation; ⑧ water displacement, local volume deformation, vertical deformation (strain and displacement) , local lateral deformation (strain and displacement); ⑨ changes in internal pore structure; the design of the present invention has high practical value and promotion value, and is of great significance for indoor simulation of expansive soil freeze-thaw-expansion and contraction conditions, and monitoring changes in various indicators.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention to other forms. Any skilled person who is familiar with this profession may use the technical content disclosed above to change or modify the equivalent of equivalent changes. The embodiments are applied to other fields, but any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention still belong to the protection scope of the technical solutions of the present invention without departing from the content of the technical solutions of the present invention.

Claims (6)

1. a kind of force model comprehensive test system considering soil body harmomegathus characteristic under temperature gradient, including steel framework, center pass Power bar, loading system, temperature control system, moisture control system and master control system, central transmission rod are arranged on steel framework, institute Loading system, temperature control system and moisture control system is stated to be connected with master control system, it is characterised in that：

The loading system includes static load loading device and dynamic load loading device, quiet to apply on central transmission rod Power load or dynamic load；The temperature control system includes water bath device, circulation line, temperature control torus and pellosil, the silicon Glued membrane is wrapped on the outside of sample, and temperature control torus is located at the top of sample and is arranged around central transmission rod, and water bath device passes through Circulation line is connected with temperature control torus；

The moisture control system includes optical fiber, optical fibre interrogation instrument and ultrasonic wave steam generation facility, and the optical fiber setting exists On pellosil inner wall, optical fiber is connected with optical fibre interrogation instrument, and the ring-type being connected with master control system is additionally provided on the outer wall of pellosil Local train sensor；Steam lead is provided with below pellosil, steam lead is connected with ultrasonic wave steam generation facility, with It realizes to the uniform humidification process of sample；

Wrapping around for the pellosil is provided with the first silicone oil ring cavity and the second silicone oil ring cavity, and the second silicone oil ring cavity is located at first The outside of silicone oil ring cavity, and a vacuum ring cavity is set between the first silicone oil ring cavity and the second silicone oil ring cavity, the vacuum ring intracavitary It is provided with Electronic Speculum, realizes the comprehensive scanning to sample side.

2. the force model comprehensive test system according to claim 1 for considering soil body harmomegathus characteristic under temperature gradient, special Sign is：The bottom of the vacuum ring cavity is provided with a circular orbit, and the circular orbit is arranged around sample circumference, the electricity Mirror is arranged by a lifting gear on circular orbit, and is rotated along the circular orbit.

3. the force model comprehensive test system according to claim 2 for considering soil body harmomegathus characteristic under temperature gradient, special Sign is：The lifting gear includes an elevating lever and driving motor, and the bottom of lifting gear is provided with and circular orbit The pulley matched, the elevating lever use motor elevating lever, the driving motor to be connected with pulley.

4. the force model comprehensive test system according to claim 3 for considering soil body harmomegathus characteristic under temperature gradient, special Sign is：It is additionally provided with differential pressure pickup between the first silicone oil ring cavity and the second silicone oil ring cavity, to detect the first silicone oil ring The pressure difference of chamber and the second silicone oil ring cavity.

5. the force model comprehensive test system according to claim 4 for considering soil body harmomegathus characteristic under temperature gradient, described Be provided with a locating plate on central transmission rod, distance measuring sensor be provided with above temperature control torus, by distance measuring sensor with The real-time monitoring to specimen height change is realized in the cooperation of locating plate.

6. the force model comprehensive test system according to claim 5 for considering soil body harmomegathus characteristic under temperature gradient, special Sign is：It is characterized in that：The pilot system further includes a vacuum pump and the cloche that is arranged on steel framework, described Vacuum pump is connected by vacuum exhaust pipe with cloche.