WO2018161866A1 - 一种能源桩桩 - 土界面力学行为特性试验设备及方法 - Google Patents

一种能源桩桩 - 土界面力学行为特性试验设备及方法 Download PDF

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Publication number
WO2018161866A1
WO2018161866A1 PCT/CN2018/077952 CN2018077952W WO2018161866A1 WO 2018161866 A1 WO2018161866 A1 WO 2018161866A1 CN 2018077952 W CN2018077952 W CN 2018077952W WO 2018161866 A1 WO2018161866 A1 WO 2018161866A1
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WIPO (PCT)
Prior art keywords
pile
soil
hollow cylinder
concrete hollow
soil interface
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PCT/CN2018/077952
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English (en)
French (fr)
Inventor
张丹
刘子文
施斌
程健
刘春�
丁大勇
陈卓
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南京大学
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Publication of WO2018161866A1 publication Critical patent/WO2018161866A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/24—Investigating strength properties of solid materials by application of mechanical stress by applying steady shearing forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0001—Type of application of the stress
    • G01N2203/0003—Steady
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014—Type of force applied
    • G01N2203/0025—Shearing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/003—Generation of the force
    • G01N2203/005—Electromagnetic means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/022—Environment of the test
    • G01N2203/0222—Temperature
    • G01N2203/0224—Thermal cycling
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/022—Environment of the test
    • G01N2203/023—Pressure
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/026—Specifications of the specimen
    • G01N2203/0262—Shape of the specimen
    • G01N2203/0266—Cylindrical specimens
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/06—Indicating or recording means; Sensing means
    • G01N2203/067—Parameter measured for estimating the property
    • G01N2203/0676—Force, weight, load, energy, speed or acceleration
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/06—Indicating or recording means; Sensing means
    • G01N2203/067—Parameter measured for estimating the property
    • G01N2203/0682—Spatial dimension, e.g. length, area, angle
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/06—Indicating or recording means; Sensing means
    • G01N2203/067—Parameter measured for estimating the property
    • G01N2203/0694—Temperature

Definitions

  • the invention belongs to the technical field of geotechnical engineering test, and in particular relates to a test device and method for mechanical behavior characteristics of an energy pile pile-soil interface.
  • Energy piles also called energy piles
  • energy piles are a new type of energy development and utilization technology that uses underground pile foundations as shallow geothermal heat exchangers.
  • shallow geothermal energy has received extensive attention and development as a green and sustainable new energy source.
  • the technology utilizes the heat capacity of the earth to store indoor heat in the ground for winter heating in the summer, and also achieves the purpose of indoor indoor cooling. Since the traditional ground source heat pump technology needs to be drilled outside the construction site, it not only occupies additional sites, but also has high construction cost, resulting in a large investment in the initial stage of the project.
  • the energy pile has the dual role of bearing the upper load and exchanging heat. Part or all of the bearing capacity of the energy pile comes from the lateral friction of the pile and the surrounding soil. During the process of energy pile cooling and thermal cycling, the thermal expansion and contraction of the pile and surrounding soil will affect the stiffness of the pile-soil interface and the lateral stress of the surrounding soil, thus affecting the bearing capacity of the friction pile. At present, there are few studies on the normal stress of pile-soil interface under variable temperature conditions. Because of the unclear understanding of the variation law of normal stress, it is difficult to accurately judge the maximum static friction force at the pile-soil interface. In addition, under the condition of temperature change, the shear behavior of the pile-soil interface is also a hot issue in current research.
  • the present invention proposes a normal stress test and shear test equipment for pile-soil interface under variable temperature conditions. Through laboratory tests, the variation of normal stress and shear behavior of pile-soil interface during temperature cycling is studied. .
  • the invention has the important theoretical research and engineering application value for grasping the variation law of the mechanical properties of the energy pile-soil interface with temperature, revealing the characteristics of the energy pile bearing capacity, and promoting the promotion and application of the energy pile technology.
  • the technical problem to be solved by the invention is to provide a test device and method for the mechanical behavior characteristics of an energy pile-soil interface, which considers different constraints and simulates the normal stress and side friction of the pile-soil interface at different temperatures.
  • the changes of parameters such as force, normal direction and tangential deformation provide a theoretical basis for studying the mechanism of the mechanical behavior of pile-soil interface under cold and thermal cycles.
  • a test device for mechanical behavior characteristics of pile-soil interface including frame, pile-soil interface simulation system, vertical pressure loading system, cycle temperature control system, and data acquisition system.
  • the frame is used to support other systems of the test equipment.
  • the pile-soil interface simulation system includes a base, a ring-shaped soil sample, a concrete hollow cylinder, a pressure plate, a hollow ring, and a servo stepping motor.
  • the upper part of the base is used for placing concrete hollow cylinders and annular soil samples. .
  • the precast concrete hollow cylinder is mounted in a hollow ring.
  • a test soil is placed between the concrete hollow cylinder and the hollow ring to form an annular soil sample.
  • the pile-soil interface is simulated by the contact surface of the concrete hollow cylinder and the annular soil sample.
  • the servo stepping motor is mounted on the base for pushing the concrete hollow cylinder, and can also be propelled by other means. The servo stepping motor is not necessary for the test equipment of the present invention.
  • the annular soil sample remains stationary, so that the contact surface of the concrete hollow cylinder and the annular soil sample is relatively shear-displaced, and the deformation of the pile-soil interface is simulated.
  • the outer wall of the concrete hollow cylinder is provided with mounting holes for placing the earth pressure gauge and the first temperature sensor, measuring the normal stress and temperature of the pile-soil interface, and the hollow portion is for taking out the sensor signal line.
  • the heat exchange tube is pre-buried in the concrete hollow cylinder, and the circulating hollow liquid is used to heat or cool the concrete hollow cylinder.
  • the upper part of the soil sample is covered with a pressure plate, and the soil sample is vertically loaded by the pressure plate to simulate the natural geostress state of the soil around the pile.
  • the hollow ring is installed in the upper space of the base of the frame, and the lower part of the bottom plate of the hollow ring is provided with a pressure transmitting chamber.
  • the pressure transmitting chamber and the base can be engaged to fix the hollow ring.
  • Concrete hollow cylinders can realistically simulate the interaction between piles and soils, and facilitate the shear test, which is convenient for placing sensors and avoiding the sensor's disturbance to soil samples.
  • a steel cylinder is mounted on the upper and bottom of the concrete hollow cylinder.
  • the vertical pressure loading system is used to apply a vertical load to the annular soil sample.
  • the circulating temperature control system is used to simulate the temperature change process of the pile body, including the heating process of the pile in summer and the cooling process of the pile in winter.
  • the data acquisition system comprises a earth pressure gauge and a first temperature sensor.
  • the earth pressure gauge and the first temperature sensor are arranged in a mounting hole of the outer wall of the concrete hollow cylinder, and the normal stress and temperature data of the pile-soil interface are collected.
  • the hollow ring is an indium steel ring, and the indium steel has a low thermal expansion coefficient at a normal temperature and a low thermal conductivity, which can well meet the test requirements. It can also be made of plexiglass.
  • the data acquisition system further comprises a distributed optical fiber sensor, and a distributed optical fiber strain sensor is attached to the outer wall of the concrete hollow cylinder for measuring the radial deformation of the pile under variable temperature conditions.
  • the data acquisition system further comprises a load sensor and a displacement sensor, the load sensor and the displacement sensor are installed between the vertical pressure loading system and the concrete hollow cylinder, and are used for obtaining the thick-walled concrete hollow cylinder when the servo stepping motor is working. Displacement, velocity and friction at the pile-soil interface.
  • the energy pile-soil interface mechanical behavior characteristic test equipment further includes a water injection drainage system.
  • the water injection drainage system includes a water passage hole, a water injection and drainage valve, and an exhaust valve.
  • the water-passing hole is opened at the bottom of the base, and the pressure plate is in close contact with the steel cylinder and the hollow ring at the upper part of the upper end of the hollow cylinder through the rubber ring, and the hollow ring and the lower pressure-transmitting cavity are in close contact with the rubber ring, and the base and the concrete hollow cylinder
  • the lower steel cylinder is in close contact with the rubber band to prevent the annular soil sample from leaking during the test and achieve the purpose of sealing.
  • the water injection and drainage valve is installed outside the water outlet hole, and the soil sample can be saturated by the water outlet hole and the water injection drainage.
  • a pore water pressure gauge is installed outside the water passing hole to measure the change of the pore water pressure during the test in real time.
  • An exhaust hole is formed in the pressure plate, and the exhaust valve is connected to the pressure plate on the pressure plate.
  • the circulating temperature control system comprises a cryostat, a circulating water pump, a heat exchange tube, a throttle valve, and a flow meter; and the data acquisition system further includes a second temperature sensor for monitoring the temperature of the circulating fluid.
  • the cryostat includes a warmer and a desuperheater, and has a temperature adjustment function.
  • the thermostat is wrapped around a thermal insulation material (such as polystyrene foam) to prevent heat loss.
  • the circulating water pump pumps the circulating fluid in the constant temperature tank through the water conduit into the heat exchange tube in the simulated pile body (concrete hollow cylinder) to provide power for circulating fluid flow.
  • a throttle valve is arranged on the water conduit for adjusting the flow rate of the liquid in the heat exchange tube to make the liquid in the tube turbulent.
  • a second temperature sensor is disposed at the inlet and the outlet of the heat exchange tube for measuring the temperature of the circulating fluid at the inlet and outlet of the heat exchange tube.
  • a flow meter is also provided for measuring and controlling the flow rate of the circulating fluid. The temperature rise and temperature drop process of the simulated pile body is controlled by the inlet and outlet temperature and the circulating fluid flow rate.
  • the water-based antifreeze of ethylene glycol is used as the circulating liquid in the test.
  • the water-based antifreeze of ethylene glycol has the advantages of high boiling point, low volatility, moderate viscosity, small change with temperature, good thermal stability, etc. At -45 ⁇ 155 °C, meet the test requirements.
  • the vertical pressure loading system employs a lever loading system
  • the lever loading system includes a lever, a weight, a threaded rod, and a force transmission rod.
  • the vertical pressure loading system is provided with a plurality of levers arranged in a radial shape with a threaded rod in the middle, and a steel shaft is arranged around the threaded rod.
  • One end of the lever is connected to the threaded rod through the steel shaft, and the weight is applied to the other end through the lever.
  • the principle applies a vertical load to the annular soil sample.
  • the threaded rod is threaded at one end and connected to the lever by a nut, and the threaded rod can move up and down.
  • the lower end of the force-transmitting rod is concave, which is in contact with the bearing point of the pressure plate and transmits the vertical load.
  • the data acquisition system further includes a force-transmitting rod axial force sensor for measuring the pressure applied vertically on the annular soil sample.
  • an energy pile-soil interface mechanical behavior test equipment including a bracket, a vertical pressure loading system, a pile-soil interface simulation system, a circulating temperature control system, a data acquisition system;
  • the bracket includes a pillar, an upper connecting beam and a lower connecting beam;
  • the pile-soil interface simulation system comprises a base, a concrete hollow cylinder, a pressure plate and a hollow ring; the upper part of the base is used for placing a concrete hollow cylinder and an annular soil sample; and the prefabricated concrete hollow cylinder is installed on the hollow ring Inserting a test soil between the concrete hollow cylinder and the hollow ring to form an annular soil sample; the outer wall of the concrete hollow cylinder is provided with a mounting hole for placing the earth pressure gauge and the first temperature sensor; the annular soil
  • the upper part of the sample is covered with a pressure plate;
  • the hollow ring has an edge along the mouth, the base and the edge are both made of a hard polyvinyl chloride plate, the hollow ring is mounted on the base; the pillar passes through the edge of the base; the bottom of the base has a water-permeable hole; a steel cylinder is mounted on the upper and bottom of the concrete hollow cylinder;
  • the vertical pressure loading system comprises a cylinder and a pressure transmitting block; the cylinder is installed under the upper connecting beam, and the pressure transmitting block is placed on the pressing plate; the pressure transmitting block is formed into a "convex" shape, the convex portion is a hollow structure, and the top portion has a threaded hole.
  • the cylinder and the pressure transmitting block are coupled to the threaded hole through the cylinder shaft head; the two steel cylinders are respectively installed inside the inner hole of the base and the convex portion of the pressure transmitting block, and the inner hole and the pressure transmission of the base
  • An annular ball groove is disposed on an inner wall of the convex portion of the block, and a ball is placed in the ball; an inner annular hole of the base and an inner wall of the convex portion of the pressure transmitting block are provided with an annular sealing groove, and the sealing groove is disposed in the sealing groove Place the seal.
  • the vertical pressure loading system may need to load tens of thousands of cattle into the annular soil sample during the test using the test apparatus and method of the present invention, the application of the weight in the first embodiment obviously cannot meet such test requirements. . Therefore, the way to load the vertical force of the weight is replaced by the cylinder loading mode.
  • a method for testing the mechanical properties of a pile-soil interface under variable temperature conditions using the above test equipment comprising the following steps:
  • Steps 4) and 5) are carried out according to the test requirements, regardless of the order.
  • the invention relates to an energy pile-soil interface mechanical behavior characteristic test equipment and method, which has the advantages of using a lever loading system, applying vertical pressure to the soil sample, and applying pressure to the pile-soil interface according to the static side pressure principle of the soil,
  • the actual stress conditions are the same as those of the pile.
  • the circulating fluid temperature control system is used to regulate the temperature of the thick-walled concrete hollow cylinder, and the temperature rise and temperature reduction process in the heat exchange process of the energy pile is simulated.
  • the water-injection drainage system was used to saturate and drain the annular soil samples, and simulate the change process of the normal stress pore water pressure at the soil around the pile and the soil-pile-soil interface under different temperature conditions.
  • the relevant sensors are arranged on the outer wall of the thick-walled concrete hollow cylinder, and the normal pressure and temperature data of the pile-soil interface are collected.
  • the frictional force and relative shear deformation of the pile-soil interface are collected by the force sensor axial force sensor and the displacement sensor.
  • Figure 1 is a schematic view showing the structure of an embodiment of the test apparatus of the present invention.
  • Figure 2 is a layout view of a heat exchange tube in a concrete hollow cylinder
  • Figure 3 is a schematic view showing the installation of a fiber optic sensor, a earth pressure gauge, and a temperature sensor;
  • Figure 4 is a partial view of the pile-soil interface
  • Figure 5 is a cross-sectional view of the base
  • Figure 6 is a top view of the base
  • Figure 7 is a three-dimensional view of the base
  • Figure 8 is a front view of the hollow ring
  • Figure 9 is a bottom view of the hollow ring
  • Figure 10 is a schematic view of the top of the hollow ring
  • Figure 11 is a top plan view of the vertical loading system
  • Figure 12 is a front elevational view of another embodiment of the testing apparatus of the present invention.
  • Figure 13 is a top plan view of the test apparatus shown in Figure 12 (only some of the components are shown).
  • Embodiment 1 is a diagrammatic representation of Embodiment 1:
  • an energy pile-soil interface mechanical behavior test equipment includes a frame, a vertical pressure loading system, a pile-soil interface simulation system, a circulating temperature control system, and a data acquisition system.
  • the frame 1 is preferably a steel frame device, which functions to provide support points for other systems of the device.
  • the steel frame structure is seamlessly welded by channel steel and steel plate, and the bottom plate is widened and treated along the length direction of the main beam and the secondary beam.
  • the steel frame provides sufficient space for simulation experiments. Other materials that can support the test equipment are also available.
  • the pile-soil interface simulation system includes a base 6, a concrete hollow cylinder 7, a permeable stone 8, a pressure plate 9, a hollow ring 10, a heat insulating material 11, and a rubber band 12.
  • the concrete hollow cylinder 7 is made of thick-walled, thick-walled concrete hollow cylinder 7 which can realistically simulate the pile in the actual project.
  • the hollow structure is mainly for guiding the signal line of the sensor.
  • the middle portion of the upper portion of the base 6 is a cylindrical space for mounting a thick-walled concrete hollow cylinder 7, the thick-walled concrete hollow cylinder 7 is installed at an intermediate position, and the lower portion of the base 6 is provided with water.
  • the hole 13 has a hollow lower portion and a right side opening for placing the servo stepping motor 14.
  • a steel cylinder is installed on the upper part and the bottom part of the concrete hollow cylinder 71, and the steel cylinder can be placed on the upper and lower ends of the concrete hollow cylindrical mold when the concrete hollow cylinder 71 is prefabricated.
  • the thick-walled concrete hollow cylinder 7 has a hollow structure, and the outer wall is provided with a plurality of mounting holes for mounting the earth pressure gauge 16 and the first temperature sensor 17, and the number of mounting holes can be determined according to the number of sensors to be laid.
  • the inner diameter of the mounting hole is matched with the outer diameter of the sensor.
  • the earth pressure gauge and the temperature sensor are fixed in the mounting hole by epoxy resin, and the signal line is led out through the thick-walled concrete hollow cylindrical hollow structure, connected to the external demodulator 28, and then connected.
  • To the computer used to collect the normal stress and temperature data of the pile-soil interface.
  • a heat exchange tube 15 is pre-embedded in a thick-walled concrete hollow cylinder and connected to an external heat exchange tube.
  • the prefabricated concrete hollow cylinder is installed in the hollow ring, and the centers of the two are coincident.
  • the test soil is placed between the concrete hollow cylinder and the hollow ring, and is compacted to form a ring-shaped soil sample.
  • the pile-soil interface is simulated by the contact surface of the concrete hollow cylinder and the annular soil sample.
  • the bottom part of the bottom plate is provided with a pressure transmitting cavity, and the water passing hole of the base is tightly connected by a rubber ring, the middle of the bottom plate is a hollow structure, the hollow inner diameter is matched with the outer diameter of the thick-walled concrete hollow cylinder, and the rubber ring is used for sealing purpose, and the upper part of the bottom plate has a circle.
  • the groove groove can fully saturate the soil sample to eliminate the air in the pore when water is injected.
  • the hollow ring 10 is surrounded by a heat insulating material 11 to prevent heat loss.
  • the bottom heat insulating material 11 has five circular holes, and the lower protruding steel column supports the upper load through the heat insulating material 11, which has both heat insulation and upper load.
  • the hollow ring 10 is made of an indium steel ring.
  • the indium steel ring has a low coefficient of thermal expansion, does not deform under variable temperature conditions, can restrain the expansion deformation of the soil sample, and has a low thermal conductivity and a certain degree. Adiabatic effect.
  • the thick-walled concrete hollow cylinder 7 can realistically simulate the actual engineering pile, and its hollow structure facilitates the signal line of the sensor.
  • the rubber band 12 is installed at the relevant position to achieve the purpose of sealing.
  • the thick-walled concrete hollow cylinder 7 will expand outward and compress the soil.
  • the thick-walled concrete hollow cylinder will shrink inward, causing the stress state between the pile and the soil to change. The interaction between pile and soil caused by the thermal energy cycle of the simulated energy pile.
  • the circulating temperature control system comprises a heat exchange tube 15, a cryostat 18, a circulating water pump 19, a throttle valve 20, a flow meter 21, and a second temperature sensor 22 for simulating the temperature drop and temperature rise of the pile during summer and winter geothermal exchange.
  • the cryostat 18 includes a warmer and a desuperheater.
  • the circulating fluid is a water-based antifreeze solution of ethylene glycol, and has the characteristics of high boiling point, low volatility, moderate viscosity, small change with temperature, and good thermal stability.
  • the surrounding of the cryostat 18 can be wrapped with a heat insulating material polystyrene foam to prevent heat loss.
  • the circulating water pump 19 pumps the circulating fluid into the simulated pile body to provide power for the circulating fluid to circulate in the water conduit 15 and the heat exchange tube.
  • a throttle valve 20 is disposed on the water conduit 15 near the water pump outlet for adjusting the flow rate of the circulating fluid in the water conduit, so that the water flow in the pipe is turbulent, and the throttle valve 20 can also be installed on other portions of the water conduit 15.
  • a second temperature sensor 22 is disposed at the inlet and outlet of the water conduit.
  • the flow rate meter 21 is additionally arranged, and the throttle valve 20 is adjusted according to the flow rate meter 21 to achieve the control flow rate, and the temperature rise and the temperature decrease process of the simulated pile body are controlled by the inlet and outlet temperature and the circulating fluid flow rate.
  • the data acquisition system includes a pile-soil interface micro-earth pressure gauge 16, a temperature sensor 17, an axial force sensor 23 on the force-transmitting rod 4, a base pore water pressure gauge 24, a distributed fiber-optic sensor 25, a load sensor 26, and a displacement sensor 27.
  • a soil pressure gauge 16 and a temperature sensor 17 are arranged around the outer wall of the thick-walled concrete hollow cylinder 7, and the normal stress and temperature data of the pile-soil interface are collected, and the vertical applied load is measured by the axial force sensor 23 on the force transmission rod 4. .
  • the base pore water pressure gauge 24 collects the saturated soil sample pore water pressure data.
  • a distributed optical fiber strain sensor 25 is attached to the outer wall of the thick-walled concrete hollow cylinder 7 and connected to an external demodulator 28 to monitor the radial deformation of the thick-walled concrete hollow cylinder.
  • a load sensor 26 and a displacement sensor 27 are installed between the thick-walled concrete hollow cylinder 7 and the connecting device 5 and between the servo stepping motor 14 and the upper connecting rod for monitoring the friction and shear of the pile-soil interface during the shearing process. Cut displacement.
  • the water injection drainage system includes a water passage hole 13, a water injection and drainage valve 29, and an exhaust valve 30.
  • the water passage hole 13 passes through the base 6, and is connected to the lower pressure transmission chamber of the indium steel ring 10, and the water injection and drainage valve 29 is installed outside the water passage hole 13. .
  • the soil sample can be saturated by the water passing hole 13, the drain valve 29, and the exhaust valve 30, and a pore water pressure gauge 24 is installed outside the water passing hole 13 to monitor the change of the pore water pressure.
  • the vertical pressure loading system can adopt the method of directly loading the vertical force or the method of indirectly loading the vertical force.
  • a lever loading system is adopted, including a lever 2, a weight 3, a threaded rod 4, and a force transmission rod 5.
  • a lever loading system including a lever 2, a weight 3, a threaded rod 4, and a force transmission rod 5.
  • the threaded rod 4 is threaded at one end and connected to the frame through the nut to move up and down. .
  • the force-transmitting rod 5 is connected to the lever 2 through a steel shaft, and the lower end is in contact with the steel plate to transmit a vertical load.
  • the weight of the corresponding weight is placed at one end of the lever to accurately control the vertical pressure, and the stability is good, and the lateral load caused by the compression of the soil sample and the deflection of the lever is filtered by the force transmission rod and the connecting device.
  • the radiant loading system can provide a higher vertical load, and the loading is uniform, and the operation is simple.
  • the soil samples were tested for sand, assuming an indoor temperature of 20 °C.
  • Preparation Install the base 6, fix the base 6 bolts, check the water valve 29 and the water passage hole 13, run the servo motor 14, check whether it can operate normally, and then install the displacement sensor 27 and the load sensor 22 at the relevant positions.
  • the heat insulating material 11 is placed around the bottom and the bottom before placing the soil sample, and the earth pressure gauge 16, the temperature sensor 17 and the distributed optical fiber sensor 25 are arranged in the thick-walled concrete hollow cylinder, and then the indium steel ring 10 and the permeable stone 8 are placed and installed.
  • the thick-walled concrete hollow cylinder of the good sensor is installed on the base, and the soil samples are layered and compacted around the soil.
  • the water-permeable stone 8 and the pressure plate 9 are placed and the insulating material 11 is placed on the pressure plate.
  • a displacement sensor 27 and a load sensor 26 are installed between the threaded rod 4 and the thick-walled concrete hollow cylinder, the force transmission rod 5 is mounted at a predetermined position, the threaded rod 4 is adjusted, and the pressure sensor 23 is placed at a lower portion thereof.
  • a pore water pressure gauge 24 and a water valve 29 are installed outside the base 6, and the temperature control system is inspected.
  • the vertical load is applied to the annular soil sample by placing the weight, and the normal stress of the pile-soil interface is brought to a certain value by the static side pressure principle.
  • the normal stress setting value is specifically set according to the experimental needs, such as 50 kPa, 100 kPa, 200 kPa, and the like.
  • the water injection drainage system is enabled to saturate and drain the annular soil sample.
  • Saturation After the exhaust valve 24 is opened, the water is slowly injected into the annular soil sample through the water-passing hole 13, the air in the soil sample space is removed and the soil sample is saturated, and then the exhaust valve 24 and the drain valve 23 are closed (it can also be loaded) Before the soil sample is saturated and loaded); drainage: always open the injection valve 23 during the test;
  • the circulating fluid pump 19 is used to pump the circulating liquid in the cryostat 18 into the thick-walled concrete hollow cylinder, and the temperature of the thick-walled concrete hollow cylinder 7 is regulated by the circulating temperature control system, the value of the flow meter 21 is recorded, and the throttle valve is adjusted according to the inlet and outlet water temperature. 20 controls the flow rate.
  • the servo motor 14 is started to push the concrete hollow cylinder to move at the design rate, such as 0.02 mm/min, so that the pile-soil interface is relatively sheared, and the actual pile is simulated.
  • the mechanical behavior of the soil interface under variable temperature conditions, and the friction between the pile-soil interface is obtained.
  • it is also possible to control other aspects of the movement of the concrete hollow cylinder such as round-trip shear or one-time linear shear, such as spiral shearing.
  • the data acquisition system was used to collect the normal stress of the pile-soil interface at different temperatures, temperature, pore water pressure, displacement of the thick-walled concrete hollow cylinder, radial deformation, friction with the annular soil sample and other related data.
  • Embodiment 2 is a diagrammatic representation of Embodiment 1:
  • the vertical pressure loading system may need to load tens of thousands of cattle into the annular soil sample during the test using the test apparatus and method of the present invention, the application of the weight in the first embodiment obviously cannot meet such test requirements. . Therefore, the way to load the vertical force of the weight is replaced by the cylinder loading mode.
  • the specific structure is as follows:
  • an energy pile-soil interface mechanical behavior test equipment includes a bracket, a vertical pressure loading system, a pile-soil interface simulation system, a circulating temperature control system, and a data acquisition system.
  • the bracket includes a strut 31, an upper connecting beam 32, and a lower connecting beam 33.
  • the pile-soil interface simulation system includes a base 66, a concrete hollow cylinder 71, a pressure plate 91 and a hollow ring 101; the upper portion of the base 66 is used for placing the concrete hollow cylinder 71 and the annular soil sample.
  • the precast concrete hollow cylinder 71 is installed in the hollow ring 101; the test soil body is installed between the concrete hollow cylinder 71 and the hollow ring 101 to form an annular soil sample; the outer wall of the concrete hollow cylinder 71 is provided with a mounting hole for placing The earth pressure gauge 161 and the first temperature sensor 171.
  • the upper part of the annular soil sample is covered with a pressure plate 91; the hollow ring 101 has an edge along the mouth, the base 66 and the edge are both made of a hard polyvinyl chloride plate, and the hollow ring 101 is mounted on the base 66.
  • the struts 31 pass through the rim position of the base 66.
  • the bottom of the base 66 has a water permeable hole.
  • the upper and bottom portions of the concrete hollow cylinder 71 are fitted with steel cylinders which can be placed on the upper and bottom portions of the concrete hollow cylindrical molds in the precast concrete hollow cylinders 71.
  • the vertical pressure loading system includes a cylinder 34 and a pressure transmitting block 35; the cylinder 34 is mounted below the upper connecting beam 32, and the pressure transmitting block 35 is placed on the pressing plate; the pressure transmitting block 35 is formed into a "convex" shape, and the convex portion is a hollow structure.
  • the top has a threaded hole, and the cylinder 35 and the pressure transmitting block 35 are coupled to the threaded hole through the cylinder shaft head. The vertical force applied by the cylinder 35 is transmitted to the annular soil sample through the pressure transmitting block 35 and the pressure plate.
  • Two steel cylinders are respectively installed in the inner hole of the base 66 and the convex portion of the pressure transmitting block, and the inner hole of the base 66 and the inner wall of the convex portion of the pressure transmitting block are respectively provided with annular ball grooves 36 in the annular ball groove 36.
  • the ball is placed to facilitate the installation of the concrete hollow cylinder 71 with the steel cylinder and to reduce the friction of the steel cylinder when moving up and down.
  • An annular sealing groove is disposed in the inner hole of the base 66 and the inner wall of the convex portion of the pressure transmitting block, and a sealing ring is placed in the sealing to prevent water leakage in the annular soil sample.
  • the energy pile-soil interface mechanical behavior characteristic test device of the present embodiment further includes a water injection drainage system, a circulation temperature control system, a water injection drainage system and a data acquisition system.
  • a displacement sensor 271 is mounted on the pillar 31, and the displacement sensor 271 The probe is placed at the top of the pressure transmitting block 35, one displacement sensor 271 is mounted between the pressure transmitting block 35 and the steel cylinder, the other displacement sensor 271 is mounted on the lower steel cylinder, and the other load sensor 231 is mounted on the lower steel cylinder.
  • the installation of other components is also installed in accordance with the installation method of the first embodiment.

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Abstract

一种能源桩桩-土界面力学行为特性试验设备及方法，包括框架（1）、竖向压力加载系统、桩-土界面模拟系统、循环控温系统、注水排水系统以及数据采集系统。所述试验设备和方法通过循环控温系统调控混凝土空心圆柱（7）的温度，真实模拟能源桩的热交换过程。采用注水排水系统，控制土样饱和程度、模拟饱和土样在不同温度条件下桩周土和桩-土界面法向应力孔隙水压力的变化过程。在混凝土空心圆柱（7）外壁布置相关传感器，采集桩-土界面法向压力及温度数据。通过荷载传感器（26）和位移传感器（27），采集桩-土界面的摩擦力和相对剪切变形。通过数据的采集和分析，为冷、热循环作用下桩-土界面的力学行为特征及其演化过程的研究提供试验数据。

Description

一种能源桩桩-土界面力学行为特性试验设备及方法 技术领域
本发明属于岩土工程试验技术领域，具体是一种能源桩桩-土界面力学行为特性试验设备及方法。
 背景技术
能源桩，也称能量桩，是将地下桩基础作为浅层地温能换热器的一种新型能源开发利用技术。近年来，随着能源危机和环境污染问题的日益严重，浅层地温能作为一种绿色、可持续新能源得到了广泛的关注和发展。该技术利用大地的热容量，在夏季将室内的热量贮存在地下用于冬季的采暖，同时也达到了夏季室内制冷的目的。由于传统地源热泵技术需要在建筑场地外钻孔，不仅占用了额外的场地，且施工成本较高，造成项目初期投资大。21世纪80年代，工程师们尝试将换热管置于建筑物的桩基、基础底板以及地下连续墙等结构内用来代替传统的地埋管换热器，不仅节省了场地而且大大地降低了地源热泵系统的造价。能源桩是将换热管置于桩基中，它通过管内的循环流体实现向大地中提取和存贮热量。在节约地下空间、保证施工质量的同时，桩体混凝土热交换效率高，具有更好的经济效应。
能源桩具有承担上部荷载和进行热量交换的双重作用。能源桩的承载力部分或全部来自于桩与周围土体的侧摩阻力。在能源桩冷、热循环过程中，桩体和周围土体的热胀冷缩会影响桩-土界面的刚度及桩周土的侧向应力，从而影响摩擦桩的承载力。目前，关于变温条件下桩-土界面法向应力的研究较少，由于对法向应力的变化规律认识不清，给桩-土界面最大静摩擦力的准确判断造成了困难。此外，变温条件下，桩-土界面的剪切特性也是目前研究的热点问题。基于此，本发明提出一种变温条件下桩-土界面法向应力测试及剪切试验设备，通过室内试验，研究在温度循环过程中，桩-土界面法向应力、剪切特性的变化规律。本发明对于掌握能源桩桩-土界面力学性能随温度的变化规律，揭示能源桩承载能力的特征，推动能源桩技术的推广和应用，具有重要的理论研究和工程应用价值。
 技术问题
本发明要解决的技术问题是提供一种能源桩桩-土界面力学行为特性试验设备及方法，该试验设备和方法考虑不同的约束条件，模拟不同温度下桩-土界面法向应力、侧摩擦力、法向及切向变形等参数的变化，为研究冷、热循环作用下桩-土界面力学特性的变化机理提供理论基础。
 技术解决方案
为实现上述发明目的，本发明采用如下技术方案：
一种能源桩桩-土界面力学行为特性试验设备，包括框架、桩-土界面模拟系统、竖向压力加载系统、循环控温系统、数据采集系统。
所述框架用于支撑试验设备其它系统。
所述桩-土界面模拟系统包括底座、环形土样、混凝土空心圆柱、压板、空心圆环和伺服步进电机。所述底座上部的位置用于放置混凝土空心圆柱和环形土样。。预制的混凝土空心圆柱安装于空心圆环 内。在混凝土空心圆柱和空心圆环之间装入试验土体，形成环形土样。利用混凝土空心圆柱与环形土样的接触面模拟桩-土界面。所述伺服步进电机安装在底座上，用于推动混凝土空心圆柱，也可以采用其它方式推进，伺服步进电机不是本发明的试验设备必须的。当伺服步进电机推动混凝土空心圆柱时，环形土样保持不动，使混凝土空心圆柱与环形土样的接触面发生相对剪切错动，模拟桩-土界面的变形。混凝土空心圆柱外壁设有安装孔，用于放置土压力计及第一温度传感器，测量桩-土界面的法向应力和温度，空心部分用于引出传感器信号线。在混凝土空心圆柱内预埋换热管，利用循环液对混凝土空心圆柱升温或降温。土样上部盖有压板，通过压板对土样进行竖向加载，模拟桩周土体的天然地应力状态。空心圆环安装于框架的底座上部空间之中，空心圆环底板下部设有传压腔。此外，传压腔与底座咬合能起到固定空心圆环的作用。混凝土空心圆柱能真实模拟桩土之间的相互作用，且利于进行剪切试验，便于放置传感器，避免传感器对土样的扰动。所述混凝土空心圆柱的上部和底部均安装有钢筒。
所述竖向压力加载系统用于向环形土样施加竖向载荷。
所述循环控温系统用于模拟桩体的温度变化过程，包括夏季桩体的升温过程和冬季桩体的降温过程。所述数据采集系统包括土压力计和第一温度传感器，土压力计和第一温度传感器布置在混凝土空心圆柱外壁的安装孔内，采集桩-土界面的法向应力及温度数据。
所述空心圆环为铟钢环，铟钢在常温下具有很低的热膨胀系数，导热系数低，能很好地满足试验要求。也可以采用有机玻璃制作。
进一步的，所述数据采集系统还包括分布式光纤传感器，在混凝土空心圆柱外壁环向粘贴分布式光纤应变传感器，用于测量变温条件下桩体的径向变形。
进一步的，数据采集系统还包括荷载传感器及位移传感器，所述荷载传感器及位移传感器安装在竖向压力加载系统和混凝土空心圆柱之间，用于获得伺服步进电动机工作时厚壁混凝土空心圆柱的位移、速度及桩-土界面的摩擦力。
进一步的，所述能源桩桩-土界面力学行为特性试验设备还包括注水排水系统。所述注水排水系统包括通水孔、注排水阀 、排气阀。所述通水孔开设在底座底部，所述压板通过橡皮圈与空心圆柱上端上部的钢筒和空心圆环紧密接触，空心圆环与下部传压腔通过橡皮圈紧密接触，底座与混凝土空心圆柱下部的钢筒通过橡皮圈紧密接触，防止环状土样在试验过程中发生渗漏，达到密封的目的。所述注排水阀安装在通水孔外部，可以通过通水孔、注水排水控制土样饱和状态。在所述通水孔外部安装孔隙水压力计，实时测量试验过程中孔隙水压力的变化。所述压板上开设有排气孔，排气阀门在压板上，与压板排气孔相连。在温度升高过程中，混凝土空心圆柱会向外膨胀挤压土体；在温度降低过程中，厚壁混凝土空心圆柱又会向内收缩，造成桩土之间的应力状态发生变化，真实模拟能源桩由于冷、热循环而造成的桩土之间的相互作用。
进一步的，所述循环控温系统包括低温恒温槽、循环水泵、换热管、节流阀、流速计；数据采集系统还包括第二温度传感器，用于监控循环液的温度。所述低温恒温槽包括加温器及降温器，具有温度调节功能。恒温槽周围用绝热材料（比如聚苯乙烯泡沫塑料）包裹，防止热量散失。循环水泵将恒温槽内循环液经由导水管泵入模拟桩体（混凝土空心圆柱）中的换热管，为循环液流动提供动力。在所述导水管上设置节流阀，用于调节换热管中液体的流速，使管内液体呈紊流状态。在所述换热管进口及出口处布置第二温度传感器，用于测量换热管进出口循环液的温度。另布置流速计，用于测量和控制循环液的流速。通过进出口温度及循环液流速控制模拟桩体的升温及降温过程。试验中采用乙二醇的水基型防冻液作为循环液，乙二醇的水基型防冻液具有沸点高、挥发性小、粘度适中并随温度变化小、热稳定性好等优点，工作温度在-45~155℃，符合试验要求。
进一步的，所述竖向压力加载系统采用杠杆加载系统，杠杆加载系统包括杠杆、砝码、螺纹杆、传力杆。所述竖向压力加载系统装有若干个杠杆，呈辐射状分布，中间有螺纹杆，螺纹杆四周装有钢轴，杠杆一端通过钢轴连接在螺纹杆上，另一端施加砝码，通过杠杆原理对环状土样施加竖向荷载。所述螺纹杆一端带有螺纹，通过螺帽连接在杠杆上，螺纹杆可上下移动。传力杆下端为内凹形，与压板承载点接触，传递竖向荷载。
进一步的， 数据采集系统还包括传力杆轴力传感器，用于测量竖向施加在环状土样上的压力。
另一种改进，一种能源桩桩-土界面力学行为特性试验设备，包括支架、竖向压力加载系统、桩-土界面模拟系统、循环控温系统、数据采集系统；
所述支架包括支柱、上连接梁和下连接梁；
所述桩-土界面模拟系统包括底座、混凝土空心圆柱、压板和空心圆环；所述底座上部的位置用于放置混凝土空心圆柱和环形土样；预制的所述混凝土空心圆柱安装于空心圆环内；在所述混凝土空心圆柱和空心圆环之间装入试验土体，形成环形土样；所述混凝土空心圆柱外壁设有安装孔，用于放置土压力计及第一温度传感器；环形土样上部盖有压板；所述空心圆环具有沿口，底座和沿口均采用硬聚氯乙烯板制作，空心圆环安装于底座上；支柱穿过底座边沿位置；底座底部具有透水孔；所述混凝土空心圆柱的上部和底部均安装有钢筒；
竖向压力加载系统包括气缸和传压块；所述气缸安装在上连接梁下方，传压块放置于压板上；传压块成“凸”字形，凸起部分为空心结构，顶部有螺纹孔，气缸与传压块通过气缸轴头部与螺纹孔配合连接；两个所述钢筒分别安装在所述底座的内孔和传压块凸起部分内部，所述底座的内孔和传压块凸起部分的内壁均设置环形滚珠凹槽，在所述滚珠内放置滚珠；所述底座的内孔和传压块凸起部分的内壁均设置环形密封凹槽，在所述密封凹槽内放置密封圈。
由于在使用本发明的试验设备及方法进行试验的过程中，可能需要竖向压力加载系统向环形土样加载数万牛的力，实施例一中采用砝码施加力显然不能满足这样的试验要求。故将砝码加载竖向力的方式替换为气缸加载方式。
一种采用上述试验设备进行变温条件下桩-土界面力学特性试验的方法，包括以下步骤：
1）对环形土样施加竖向压力，读取此时桩-土界面法向应力值，作为桩-土界面初始法向应力值，并采集此时桩-土界面的温度值；
2）对土样进行饱和；
3）按试验设计调控混凝土空心圆柱的温度；
4）根据桩-土界面中的第一温度传感器及换热管出入口第二温度传感器值判断土样温度是否达到平衡状态，采集温度变化过程中桩-土界面法向应力值及温度、土的孔隙水压力等数据；
5）根据试验设计，当桩体和桩周土体温度达到试验要求，推动厚壁混凝土空心圆柱按一定方式运动，使桩-土界面产生相对剪切，模拟实际桩-土界面在变温条件下的力学行为，采集桩土界面的摩擦力。
步骤4）和5）根据试验需要进行，不分先后顺序。
 有益效果
本发明提出的一种能源桩桩-土界面力学行为特性试验设备及方法，优点在于采用杠杆加载系统，对土样施加竖向压力，依据土的静止侧压力原理对桩-土界面施压，与桩体的实际受力条件是相同的。利用循环液通过循环控温系统调控厚壁混凝土空心圆柱的温度，真实模拟能源桩热交换过程中的升温和降温过程。采用注水排水系统，对环形土样进行饱和、排水，模拟饱和土样在不同温度条件下桩周土和桩-土界面法向应力孔隙水压力的变化过程。在厚壁混凝土空心圆柱外壁布置相关传感器，采集桩-土界面法向压力及温度数据。通过传力杆轴力传感器和位移传感器，采集桩-土界面的摩擦力和相对剪切变形。通过数据的采集和分析，为冷、热循环作用下桩-土界面的力学行为特征及其演化过程的研究提供试验数据。本发明的试验设备和方法对于掌握能源桩桩-土界面力学性能随温度的变化规律，揭示能源桩承载能力的特征，推动能源桩技术的推广和应用，具有重要的理论研究和工程应用价值。
 附图说明
图1是本发明的试验设备一个实施例结构示意图；
图2是混凝土空心圆柱内换热管布置图；
图3是光纤传感器、土压力计和温度传感器安装示意图；
图4是桩-土界面局部图；
图5是底座剖面图；
图6是底座俯视图；
图7是底座三维图
图8是空心圆环主视图；
图9是空心圆环底部示意图；
图10是空心圆环顶部示意图；
图11是竖向加载系统俯视图；
图12是本发明的试验设备另一个实施例的主视图；
图13是图12显示的试验设备的俯视图（只显示了部分零部件）。
 本发明的最佳实施方式
下面结合附图，对本发明提出的一种能源桩桩-土界面力学行为特性试验设备及方法进行详细说明。在本发明的描述中，需要理解的是，术语“左侧”、“右侧”、“上部”、“下部”、“底部”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，“第一”、“第二”等并不表示零部件的重要程度，因此不能理解为对本发明的限制。本实施例中采用的具体尺寸只是为了举例说明技术方案，并不限制本发明的保护范围。
实施例一：
如图1所示，一种能源桩桩-土界面力学行为特性试验设备，包括框架、竖向压力加载系统、桩-土界面模拟系统、循环控温系统、数据采集系统。
框架1优选钢架装置，作用是为本装置其它系统提供支撑点，钢架结构由槽钢和钢板无缝焊接而成，底板作了加宽处理，沿主梁和次梁长度方向作加强处理，钢架式框架提供了模拟试验的足够空间。其它能够支撑试验设备的材料亦可。
桩-土界面模拟系统包括底座6、混凝土空心圆柱7、透水石8、压板9、空心圆环10、绝热材料11、橡皮圈12。混凝土空心圆柱7采用厚壁，厚壁混凝土空心圆柱7能真实模拟实际工程中的桩，空心结构主要便于引出传感器的信号线。如图5至7所示，底座6上半部分中间为圆柱形空间，用于安装厚壁混凝土空心圆柱7，厚壁混凝土空心圆柱7安装在中间位置；底座6的右侧下部设有通水孔13，底座下部分空心且右侧开口，用于放置伺服步进电动机14。中间有一可上下移动的连接杆，伺服步进电动机14通过连接杆，以一定速率推动厚壁混凝土空心圆柱7，具有使桩-土界面发生剪切变形的作用。为了更好的防水效果，混凝土空心圆柱71的上部和底部均安装有钢筒，钢筒可以在预制混凝土空心圆柱71时，放置在混凝土空心圆柱模的上下两端。
如图3所示，厚壁混凝土空心圆柱7为空心结构，且外壁设有若干安装孔，用于安装土压力计16和第一温度传感器17，安装孔数量可根据需要布设的传感器数量决定。安装孔内径与传感器外径相匹配，采用环氧树脂将土压力计和温度传感器固定于安装孔内，信号线则通过厚壁混凝土空心圆柱空心结构导出，与外部解调仪28相连，然后连接到计算机，用于采集桩-土界面法向应力及温度数据。如图2所示，在厚壁混凝土空心圆柱内预埋换热管15，与外部换热管相连。
如图4所示，预制的混凝土空心圆柱安装于空心圆环内，二者圆心重合，在混凝土空心圆柱和空心圆环之间装入试验土体，分层压实，形成环形土样。利用混凝土空心圆柱与环形土样的接触面模拟桩-土界面。底板下部设有传压腔，与底座通水孔通过橡皮圈紧密连接，底板中间为空心结构，空心内径与厚壁混凝土空心圆柱外径相匹配，且通过橡皮圈到达密封目的，底板上部有一圆环凹槽，注水时能充分饱和土样排除孔隙内的空气。空心圆环10外围包裹绝热材料11，防止热量散失，底部绝热材料11开有五个圆孔，下部凸出钢柱穿过绝热材料11支撑上部荷载，既具有绝热作用，又能支撑上部荷载。
如图8、9和10所示，空心圆环10采用铟钢环，铟钢环热膨胀系数低，在变温条件下不产生形变，能约束土样的膨胀变形，且导热系数低，具有一定的绝热作用。
厚壁混凝土空心圆柱7能真实模拟实际工程中桩，其空心结构便于引出传感器的信号线。为防止注水排水过程中水体渗漏，在相关位置安装橡皮圈12，达到密封的目的。在温度升高过程中，厚壁混凝土空心圆柱7会向外膨胀压缩土体，在温度降低过程中，厚壁混凝土空心圆柱又会向内收缩，造成桩土之间的应力状态发生变化，真实模拟能源桩由于冷热循环而造成的桩土之间的相互作用。
循环控温系统包括换热管15、低温恒温槽18，循环水泵19、节流阀20、流速计21、第二温度传感器22，用于模拟夏季、冬季地热交换中桩体的降温及升温过程。低温恒温槽18包括加温器及降温器，循环液采用乙二醇的水基型防冻液，具有沸点高，挥发性小，粘度适中并且随温度变化小，热稳定性好等特点。低温恒温槽18周围可以用绝热材料聚苯乙烯泡沫塑料包裹，防止热量散失。循环水泵19将循环液泵入模拟桩体中，为循环液在导水管15及换热管中循环流动提供动力。在导水管15上，靠近水泵出水口处设置节流阀20用于调节导水管中循环液的流速，使管内水流为紊流状态，节流阀20也可以安装在导水管15上其他部位。在导水管进水及出水处布置第二温度传感器22。另布置流速计21，根据流速计21调整节流阀20达到控制流速的目的，通过进出口温度及循环液流速来控制模拟桩体的升温及降温过程。
数据采集系统包括桩-土界面微型土压力计16、温度传感器17、传力杆4上的轴力传感器23、底座孔隙水压力计24、分布式光纤传感器25、荷载传感器26及位移传感器27。在厚壁混凝土空心圆柱7外壁四周布置土压力计16及温度传感器17，采集桩-土界面的法向应力及温度数据，通过传力杆4上的轴力传感器23，测量竖向施加的荷载。底座孔隙水压力计24采集饱和土样孔隙水压力数据。在厚壁混凝土空心圆柱7外壁环向粘贴分布式光纤应变传感器25，与外部解调仪28相连，监测厚壁混凝土空心圆柱的径向变形。在厚壁混凝土空心圆柱7与衔接装置5之间及伺服步进电动机14与上部连接杆之间安装荷载传感器26及位移传感器27，用于监测剪切过程中桩-土界面的摩擦力与剪切位移。
注水排水系统包括通水孔13、注排水阀29、排气阀30 ；通水孔13通过底座6，与铟钢环10下部传压腔相接，注排水阀29安装在通水孔13外部。可以通过通水孔13、注排水阀29、排气阀30对土样进行饱和，在通水孔13外部安装孔隙水压力计24监测孔隙水压力的变化。
竖向压力加载系统可以采用直接加载竖向力的方式，也可以采用间接加载竖向力的方式。为了达到较好的效果，本实施例中，采用杠杆加载系统，包括杠杆2、砝码3、螺纹杆4、传力杆5，如图11所示，加载系统中有四个杠杆加载装置，呈辐射状分布，杠杆2一端通过钢轴连接在框架上，另一端施加砝码3，通过杠杆原理施加竖向荷载，螺纹杆4一端带有螺纹，通过螺帽连接在框架上，可上下移动。传力杆5上通过钢轴与杠杆2相连，下端与钢板接触，传递竖向荷载。在杠杆一端放置相应重量的砝码，精确地控制竖向压力，稳定性好，且通过传力杆及衔接装置过滤由于土样压缩、杠杆偏转而造成的横向荷载。当环形土样截面积较大时，辐射式加载系统能够提供较高的竖向荷载，且加载均匀，操作简单。
具体试验方法：
试验土样选择砂土，假设室内温度20℃。
准备工作：安装底座6，固定底座6螺栓，检查水阀29及通水孔13，运行伺服电动机14，检查是否能正常运作，后在相关位置安装位移传感27及荷载传感器22。放置土样之前在四周及底部放置绝热材料11，在厚壁混凝土空心圆柱内布置土压力计16、温度传感器17及分布式光纤传感器25，之后放入铟钢环10及透水石8并将装好传感器的厚壁混凝土空心圆柱安装在底座，在四周分层填入土样并压实，土样填好后放入透水石8及压板9并在压板上部放置绝缘材料11。在螺纹杆4与厚壁混凝土空心圆柱之间安装位移传感器27及荷载传感器26，将传力杆5安装在预定位置上，调整螺纹杆4并在其下部放入压力传感器23。
在底座6外侧安装孔隙水压力计24及水阀29，检查控温系统。
试验步骤：
首先利用杠杆加载系统，通过放置砝码对环状土样施加竖向荷载，利用静止侧压力原理使桩-土界面的法向应力达到一定值。该法向应力设定值根据实验需要具体设定，如50kPa，100kPa，200kPa等。
之后根据设计的试验条件，启用注水排水系统对环形土样进行饱和与排水。饱和：确定排气阀门24打开后通过通水孔13向环形土样缓慢注水，排除土样空隙中的空气并使土样饱和，之后关闭排气阀门24及注排水阀23（也可以在加载之前使土样达到饱和状态并进行加载）；排水：试验过程中始终开启注排水阀23；
利用循环水泵19将低温恒温槽18中的循环液泵入厚壁混凝土空心圆柱中，通过循环控温系统调控厚壁混凝土空心圆柱7的温度，记录流速计21数值，根据出入口水温调节节流阀20控制流速。
根据试验设计，当桩体和桩周土体温度达到试验要求，启动伺服电动机14，推动混凝土空心圆柱按设计速率运动，如0.02mm/min，使桩-土界面产生相对剪切，模拟实际桩-土界面在变温条件下的力学行为，得到桩土界面的摩擦力。除了速率之外，还可以控制混凝土空心圆柱的运动方式的其它方面，比如往返剪切或一次性的直线剪切、比如螺旋式剪切等等。
在试验全程过程中利用数据采集系统采集不同温度下桩-土界面法向应力、温度、孔隙水压力，厚壁混凝土空心圆柱的位移、径向变形、与环形土样的摩擦力等相关数据。
实施例二：
由于在使用本发明的试验设备及方法进行试验的过程中，可能需要竖向压力加载系统向环形土样加载数万牛的力，实施例一中采用砝码施加力显然不能满足这样的试验要求。故将砝码加载竖向力的方式替换为气缸加载方式。具体结构如下：
如图12和3所示，一种能源桩桩-土界面力学行为特性试验设备，包括支架、竖向压力加载系统、桩-土界面模拟系统、循环控温系统、数据采集系统。
支架包括支柱31、上连接梁32和下连接梁33。在本实施例中，支柱31有三根，在同一个圆周上等距离放置。
桩-土界面模拟系统包括底座66、混凝土空心圆柱71、压板91和空心圆环101；底座66上部的位置用于放置混凝土空心圆柱71和环形土样。预制的混凝土空心圆柱71安装于空心圆环101内；在混凝土空心圆柱71和空心圆环101之间装入试验土体，形成环形土样；混凝土空心圆柱71外壁设有安装孔，用于放置土压力计161及第一温度传感器171。环形土样上部盖有压板91；空心圆环101具有沿口，底座66和沿口均采用硬聚氯乙烯板制作，空心圆环101安装于底座66上。支柱31穿过底座66边沿位置。底座66底部具有透水孔。为了更好的防水效果，混凝土空心圆柱71的上部和底部均安装有钢筒，钢筒可以在预制混凝土空心圆柱71时，放置在混凝土空心圆柱模的上部和底部。
竖向压力加载系统包括气缸34和传压块35；气缸34安装在上连接梁32下方，传压块35放置于压板上；传压块35成“凸”字形，凸起部分为空心结构，顶部有螺纹孔，气缸35与传压块35通过气缸轴头部与螺纹孔配合连接。采用气缸35加载的竖向力通过传压块35和压板传递到环形土样。两个钢筒分别安装在底座66的内孔和传压块凸起部分内部，底座66的内孔和传压块凸起部分的内壁均设置环形滚珠凹槽36，在环形滚珠凹槽36内放置滚珠，便于安装带有钢筒的混凝土空心圆柱71，并减小钢筒上下运动时的摩擦力。底座66的内孔和传压块凸起部分的内壁均设置环形密封凹槽，在密封内放置密封圈，避免环形土样中的水发生渗漏。
本实施的能源桩桩-土界面力学行为特性试验设备还包括注水排水系统，循环控温系统、注水排水系统和数据采集系统与实施例一相同，一个位移传感器271安装支柱31上，位移传感器271探头放置在传压块35顶部位置，一个位移传感器271安装在传压块35和钢筒之间，另一个位移传感器271安装在下方的钢筒上，另一个荷载传感器231安装在下方的钢筒底部，其它零部件的安装也按照实施例一的安装方式安装。
基于对本发明优选实施方式的描述，应该清楚，由所附的权利要求书所限定的本发明并不仅仅局限于上面说明书中所阐述的特定细节，未脱离本发明宗旨或范围的对本发明的许多显而易见的改变同样可能达到本发明的目的。 

Claims (10)

  1. 一种能源桩桩-土界面力学行为特性试验设备，其特征在于，包括框架、竖向压力加载系统、桩-土界面模拟系统、循环控温系统、数据采集系统；
    所述框架用于支撑试验设备其它系统；
    所述桩-土界面模拟系统包括底座、环形土样、混凝土空心圆柱、压板和空心圆环；所述底座上部的位置用于放置混凝土空心圆柱和环形土样；预制的混凝土空心圆柱安装于空心圆环内；在混凝土空心圆柱和空心圆环之间装入试验土体，形成环形土样；所述混凝土空心圆柱外壁设有安装孔，用于放置土压力计及第一温度传感器；所述环形土样上部盖有压板；所述空心圆环安装于底座上部空间之中，空心圆环底板下部设有传压腔；所述混凝土空心圆柱的上部和底部均安装有钢筒；
    所述竖向压力加载系统用于向环形土样施加竖向载荷；
    所述循环控温系统用于模拟桩体的温度变化过程；
    所述数据采集系统包括土压力计和第一温度传感器，土压力计和第一温度传感器布置在混凝土空心圆柱外壁的安装孔内。
  2. 根据权利要求1所述的能源桩桩-土界面力学行为特性试验设备，其特征在于，所述空心圆环为铟钢环或采用有机玻璃制作。
  3. 根据权利要求1所述的能源桩桩-土界面力学行为特性试验设备，其特征在于，所述数据采集系统还包括分布式光纤传感器，在混凝土空心圆柱外壁环向粘贴分布式光纤应变传感器。
  4. 根据权利要求1所述的能源桩桩-土界面力学行为特性试验设备，其特征在于，所述数据采集系统还包括荷载传感器及位移传感器，所述荷载传感器及位移传感器安装在竖向压力加载系统和混凝土空心圆柱之间。
  5. 根据权利要求1所述的能源桩桩-土界面力学行为特性试验设备，其特征在于，还包括注水排水系统；所述注水排水系统包括通水孔、注排水阀、排气阀；所述通水孔开设在底座底部，所述压板通过橡皮圈与混凝土空心圆柱上部的钢筒和空心圆环紧密接触，空心圆环与下部传压腔通过橡皮圈紧密接触，底座与混凝土空心圆柱下部的钢筒通过橡皮圈紧密接触；所述注排水阀安装在通水孔外部；在所述通水孔外部安装孔隙水压力计；所述压板上开设有排气孔，排气阀门在压板上，与压板排气孔相连。
  6. 根据权利要求1所述的能源桩桩-土界面力学行为特性试验设备，其特征在于，所述循环控温系统包括低温恒温槽、循环水泵、换热管、节流阀、流速计；数据采集系统还包括第二温度传感器；所述低温恒温槽包括加温器及降温器；所述换热管预埋在所述混凝土空心圆柱内；所述循环水泵用于将恒温槽内循环液经由导水管泵入所述换热管；在所述导水管上设置节流阀；在所述换热管进口及出口处布置第二温度传感器；另布置流速计。
  7. 根据权利要求1所述的能源桩桩-土界面力学行为特性试验设备，其特征在于，所述竖向压力加载系统采用杠杆加载系统，杠杆加载系统包括杠杆、砝码、螺纹杆、传力杆；加载系统装有若干个杠杆，呈辐射状分布，中间有螺纹杆，螺纹杆四周装有钢轴，杠杆一端通过钢轴连接在螺纹杆上，另一端施加砝码；螺纹杆一端带有螺纹，通过螺帽连接在杠杆上，螺纹杆可上下移动；传力杆下端为内凹形，与压板承载点接触。
  8. 根据权利要求1所述的能源桩桩-土界面力学行为特性试验设备，其特征在于，所述数据采集系统还包括传力杆轴力传感器，用于测量竖向施加在环状土样上的压力。
  9. 一种能源桩桩-土界面力学行为特性试验设备，其特征在于，包括支架、竖向压力加载系统、桩-土界面模拟系统、循环控温系统、数据采集系统；
    所述支架包括支柱、上连接梁和下连接梁；
    所述桩-土界面模拟系统包括底座、混凝土空心圆柱、压板和空心圆环；所述底座上部的位置用于放置混凝土空心圆柱和环形土样；预制的所述混凝土空心圆柱安装于空心圆环内；在所述混凝土空心圆柱和空心圆环之间装入试验土体，形成环形土样；所述混凝土空心圆柱外壁设有安装孔，用于放置土压力计及第一温度传感器；环形土样上部盖有压板；所述空心圆环具有沿口，底座和沿口均采用硬聚氯乙烯板制作，空心圆环安装于底座上；支柱穿过底座边沿位置；底座底部具有透水孔；所述混凝土空心圆柱的上部和底部均安装有钢筒；
    所述竖向压力加载系统包括气缸和传压块；所述气缸安装在上连接梁下方，传压块放置于压板上；传压块成“凸”字形，凸起部分为空心结构，顶部有螺纹孔，气缸与传压块通过气缸轴头部与螺纹孔配合连接；两个所述钢筒分别安装在所述底座的内孔和传压块凸起部分内部，所述底座的内孔和传压块凸起部分的内壁均设置环形滚珠凹槽，在所述环形滚珠凹槽内放置滚珠；所述底座的内孔和传压块凸起部分的内壁均设置环形密封凹槽，在所述密封凹槽内放置密封圈。
  10. 一种采用权利要求1至9任一项所述的试验设备进行变温条件下桩-土界面力学特性试验的方法，其特征在于，包括以下步骤：
    1）对环形土样施加竖向压力，读取此时桩-土界面法向应力值，作为桩-土界面初始法向应力值，并采集此时桩-土界面的温度值；
    2）对土样进行饱和；
    3）按试验设计调控混凝土空心圆柱的温度；
    4）根据桩-土界面中的第一温度传感器及换热管出入口第二温度传感器值判断土样温度是否达到平衡状态，采集温度变化过程中桩-土界面法向应力值及温度、土的孔隙水压力等数据；
    5）根据试验设计，当桩体和桩周土体温度达到试验要求，推动厚壁混凝土空心圆柱按一定方式运动，使桩-土界面产生相对剪切，模拟实际桩-土界面在变温条件下的力学行为，采集桩土界面的摩擦力。
     
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