A frozen soil pile foundation hydration heat simulation test device and test method

Abstract

The present invention discloses a frozen soil pile foundation hydration heat simulation test device and test method. The test device includes an aluminum tube for simulating the pile foundation and a temperature controller for adjusting the temperature. The aluminum tube is provided with an electric heating rod. The outer surface of the aluminum tube is provided with a quartz sand particle layer and a temperature sensor for detecting the surface temperature of the aluminum tube. The output end of the temperature controller is connected to a solid-state relay, and the electric heating rod is connected to the solid-state relay. The device of the present invention has a simple structure, a reasonable design, is easy to implement and has low cost. In combination with the test method, it can be effectively applied in frozen soil pile foundation hydration heat simulation tests to simulate the exothermic temperature rise process and the refreezing process of concrete hydration heat. The entire hydration heat process is more closely aligned with actual working conditions, shortening the test cycle, achieving good results, and facilitating widespread use.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and in particular relates to a frozen soil pile foundation hydration heat simulation test device and a test method. Background Art

[0002] Pile foundations are widely used in permafrost regions. The hydration heat of bored cast-in-place pile concrete significantly perturbs the ground temperature field. This hydration heat-induced change in ground temperature directly affects the physical and mechanical properties of frozen ground. Studies have shown that as the temperature of frozen ground increases, its bearing capacity and freezing strength decrease. Therefore, studying the effect of pile foundation hydration heat on the temperature of the surrounding soil, as well as analyzing the changes in ground temperature during the refreezing of frozen ground, provides important guidance and reference value for optimizing the construction schedule and construction technology of bored cast-in-place piles in permafrost regions.

[0003] At present, the commonly used methods for studying the influence of pile foundation hydration heat on frozen soil are field test, software simulation test, and laboratory cast-in-place model test. Although the three existing methods are relatively complete, they still have certain shortcomings, as follows:

[0004] Field test method: Although field tests can actually reflect the impact of pile foundation hydration heat on the soil around the pile in the project, the cost is too high and the observation period is long. Field tests have limitations. They can only study the impact of pile foundation hydration heat on the soil around the pile and the relationship between the freezing time around the pile, and cannot measure the bearing capacity of the pile foundation at each freezing stage. Field tests require the arrangement of multiple instruments and observation components, which affects normal construction and is not conducive to multi-faceted actual measurements.

[0005] Software simulation test method; the software mainly uses the principles of heat transfer and cement hydration heat formula for calculation and simulation. Although it can quickly derive the impact of frozen soil pile foundation hydration heat on frozen soil and bearing capacity at different stages, the theoretical calculation is too idealized according to the adiabatic temperature rise of the pile foundation hydration heat process, which deviates from the actual heat release process; the frozen soil around the piles is relatively complex, and the software simulation cannot more realistically reflect the actual hydration heat situation in the soil.

[0006] Indoor test cast-in-place model test; this method requires casting according to the scale of the project size. When exploring the bearing capacity of the pile foundation, the concrete needs to be cured for a certain number of days so that it has a certain strength before the experiment can be carried out, resulting in a long test cycle; after loading to the pile body is damaged, the concrete pile needs to be re-cast for testing, which increases the test cost and the test cycle; when the size of the pile required for the test is too large, the test conditions cannot be met indoors. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a frozen soil pile foundation hydration heat simulation test device in response to the deficiencies in the above-mentioned prior art. The device has a simple structure, reasonable design, easy implementation and low cost. Combined with the test method, it can be effectively applied to the frozen soil pile foundation hydration heat simulation test to simulate the concrete hydration heat exothermic temperature rise process and the refreezing process, making the entire hydration heat process more in line with the actual working conditions, shortening the test cycle, having good use effect, and being easy to promote and use.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a frozen soil pile foundation hydration heat simulation test device, including an aluminum tube for simulating the pile foundation and a temperature controller for adjusting the temperature, an electric heating rod is arranged inside the aluminum tube, a quartz sand particle layer and a temperature sensor for detecting the surface temperature of the aluminum tube are arranged on the outer surface of the aluminum tube, the output end of the temperature controller is connected to a solid-state relay, and the electric heating rod is connected to the solid-state relay.

[0009] In the above-mentioned frozen soil pile foundation hydration heat simulation test device, one end of the aluminum tube is closed and the other end of the aluminum tube is open. The open end is used to insert an electric heating rod, and the electric heating rod is arranged close to the inner wall of the aluminum tube.

[0010] In the above-mentioned frozen soil pile foundation hydration heat simulation test device, the quartz sand particle layer is adhered to the outer surface of the aluminum tube using epoxy resin glue to simulate the pile side roughness.

[0011] The present invention also discloses a frozen soil pile foundation hydration heat simulation test method, using the above-mentioned test device, the test method comprises the following steps:

[0012] Step 1: Establishing a thermal conductivity model of the test device;

[0013] Step 2: Determine the boundary conditions of the thermal conductivity model and establish the temperature distribution model of the heating rod;

[0014] Step 3: Establish a correlation model between the temperature change of the electric heating rod and the temperature change of the simulated pile surface;

[0015] Step 4: Establish a correlation model between the heat generation rate of the electric heating rod and the heat generation rate of concrete;

[0016] Step 5: Calculate the heat release of concrete of the simulated pile size according to the concrete hydration heat release formula;

[0017] Step 6: Select the power and power-on time of the heating rod according to the correlation model between the heat generation rate of the heating rod and the heat generation rate of concrete;

[0018] Step 7: Set the temperature section of the temperature controller, and set the temperature rise and fall limits and maintenance time of each temperature section;

[0019] Step 8: The temperature controller adjusts the temperature according to the real-time feedback from the temperature sensor to simulate the heat release process of concrete hydration;

[0020] Step 9: After the heat release is completed, disconnect the power supply and allow the temperature of the soil around the simulated pile to drop naturally through the ambient temperature to simulate the pile foundation refreezing process.

[0021] In the above-mentioned frozen soil pile foundation hydration heat simulation test method, the thermal conductivity model of the test device in step 1 is:

[0022]

[0023] Among them, r is the distance from the center of the aluminum tube, T is the surface temperature of the aluminum tube, is the heat generation rate of the electric heating rod, and k is the thermal conductivity of the aluminum tube.

[0024] In the above-mentioned frozen soil pile foundation hydration heat simulation test method, the temperature distribution model of the test device in step 2 is:

[0025]

[0026] Where T(r) is the temperature at different distances from the center of the simulated pile, T s (t) is the temperature of frozen soil beside the pile at time t, and r0 is the radius of the pile, T0 is the frozen soil temperature on the pile side at the initial moment, and h is the heat transfer coefficient.

[0027] In the above-mentioned frozen soil pile foundation hydration heat simulation test method, the correlation model between the temperature change of the electric heating rod and the temperature change of the simulated pile surface in step 3 is:

[0028]

[0029] Where T(r,t) is the temperature at the center of the pile at time t, T ∞ is the temperature at the center of the pile at time t, T i is the pile temperature at the initial moment, C1,ξ1 are both one-dimensional transient thermal conductivity, α is the thermal diffusion coefficient and t is the time.

[0030] In the above-mentioned frozen soil pile foundation hydration heat simulation test method, the correlation model between the heat generation rate of the electric heating rod and the heat generation rate of concrete in step 4 is:

[0031]

[0032] Where a is the correlation coefficient between the heating rate of the electric heating rod and the heating rate of concrete, C c is the volumetric heat capacity of concrete, θ is the maximum adiabatic temperature rise of concrete, k tis the concrete hydration chemical reaction rate at the initial temperature t0.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The device of the present invention has a simple structure, reasonable design, easy implementation and low cost.

[0035] 2. The present invention uses a temperature controller to regulate the heat release of the electric heating rod to simulate hydration heat release, which provides convenience for the experimental research on the hydration heat of different frozen soil piles, solves the problem of needing cast-in-place concrete piles when studying the hydration heat of concrete pile foundations, reduces the amount of materials such as concrete, reduces the test cost, and shortens the test cycle.

[0036] 3. The present invention can replace the power of the electric heating rod according to the needs of the test heat release and heat release time, meet the test requirements of pile foundations of different sizes, and explore the influence of heat.

[0037] 4. The present invention establishes a correlation model between the temperature change of the electric heating rod and the temperature change of the simulated pile surface, effectively simulating the relationship between the hydration heat of the pile foundation concrete and the temperature change of the pile surface, and converting the influence of the concrete hydration heat on the frozen soil around the pile into the influence of the temperature change on the pile side on the frozen soil.

[0038] 5. The present invention can be effectively applied in the hydration heat simulation test of frozen soil pile foundation, and can simulate the exothermic temperature rise process and refreezing process of concrete hydration heat, making the entire hydration heat process more close to the actual working conditions, with good use effect and easy promotion and use.

[0039] In summary, the device of the present invention has a simple structure, reasonable design, easy implementation and low cost. Combined with the test method, it can be effectively applied to the hydration heat simulation test of frozen soil pile foundation, to simulate the exothermic temperature rise process and refreezing process of concrete hydration heat, make the entire hydration heat process more in line with the actual working conditions, shorten the test cycle, have good use effect, and be easy to promote and use.

[0040] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the device structure of the present invention;

[0042] Figure 2 Flow chart of the method of the present invention.

[0043] Description of the accompanying drawings:

[0044] 1—aluminum tube; 2—temperature controller; 3—electric heating rod;

[0045] 4—Quartz sand granular layer; 5—Temperature sensor; 6—Solid-state relay. DETAILED DESCRIPTION

[0046] like Figure 1 As shown, the frozen soil pile foundation hydration heat simulation test device of the present invention includes an aluminum tube 1 for simulating the pile foundation and a temperature controller 2 for adjusting the temperature, an electric heating rod 3 is provided in the aluminum tube 1, a quartz sand particle layer 4 and a temperature sensor 5 for detecting the surface temperature of the aluminum tube 1 are provided on the outer surface of the aluminum tube 1, the output end of the temperature controller 2 is connected to a solid-state relay 6, and the electric heating rod 3 is connected to the solid-state relay 6.

[0047] In practice, the outer diameter, inner diameter, and height of the aluminum tube 1 can be adjusted to the desired test dimensions, simulating pile foundations of varying sizes and better matching actual operating conditions. The electric heating rod 3 can be configured with different power levels to simulate different operating conditions. A temperature controller 2 regulates the heat release of the electric heating rod 3 to simulate the hydration heat release of frozen soil pile foundations, facilitating hydration heat testing of frozen soil pile foundations. A temperature sensor 5 monitors the surface temperature of the aluminum tube 1 to simulate the temperature of the frozen soil surrounding the pile.

[0048] In this embodiment, one end of the aluminum tube 1 is closed, and the other end of the aluminum tube 1 is open. The open end is used to insert the electric heating rod 3, and the electric heating rod 3 is arranged closely against the inner wall of the aluminum tube 1.

[0049] During specific implementation, the electric heating rod 3 is placed close to the inner wall of the aluminum tube 1 so that the aluminum tube 1 is heated evenly.

[0050] In this embodiment, the quartz sand granular layer 4 is adhered to the outer surface of the aluminum tube 1 using epoxy resin glue to simulate the pile side roughness.

[0051] like Figure 2 As shown, the frozen soil pile foundation hydration heat simulation test method of the present invention comprises the following steps:

[0052] Step 1: Establishing a thermal conductivity model of the test device;

[0053] The thermal conductivity model of the test device is:

[0054]

[0055] Where r is the distance from the center of the aluminum tube 1, T is the surface temperature of the aluminum tube 1, is the heat generation rate of the electric heating rod 3, and k is the thermal conductivity of the aluminum tube 1.

[0056] Step 2: Determine the boundary conditions of the thermal conductivity model and establish the temperature distribution model of the heating rod;

[0057] The temperature distribution model of the test device is:

[0058]

[0059] Where T(r) is the temperature at different distances from the center of the simulated pile, T s (t) is the temperature of frozen soil beside the pile at time t, and r0 is the radius of the pile, T0 is the frozen soil temperature on the pile side at the initial moment, and h is the heat transfer coefficient.

[0060] Step 3: Establish a correlation model between the temperature change of the electric heating rod and the temperature change of the simulated pile surface;

[0061] The correlation model between the temperature change of the electric heating rod and the temperature change of the simulated pile surface is:

[0062]

[0063] Where T(r,t) is the temperature at the center of the pile at time t, T ∞ is the temperature at the center of the pile at time t, T i is the pile temperature at the initial moment, C1,ξ1 are both one-dimensional transient thermal conductivity, α is the thermal diffusion coefficient and t is the time.

[0064] During specific implementation, based on the transient heat transfer equation of the heat transfer principle, a relationship equation is established that conforms to the test device's simulated pile surface temperature changes and the temperature changes of the electric heating rod. The influence of hydration heat on frozen soil is converted into the influence of simulated pile surface temperature changes on frozen soil, which can more directly and effectively study the direct relationship between hydration heat and frozen soil.

[0065] Step 4: Establish a correlation model between the heat generation rate of the electric heating rod and the heat generation rate of concrete;

[0066] The correlation model between the heat generation rate of the electric heating rod and the heat generation rate of concrete is:

[0067]

[0068] Where a is the correlation coefficient between the heating rate of the electric heating rod and the heating rate of concrete, C c is the volumetric heat capacity of concrete, θ is the maximum adiabatic temperature rise of concrete, k t is the concrete hydration chemical reaction rate at the initial temperature t0.

[0069] During specific implementation, the heat generation rate and temperature change of the electric heating rod in the test device are related to the heat generation rate of concrete. In order to be closer to the concrete hydration heat release process of actual engineering and to make the electric heating rod simulation more realistic, the correlation coefficient a is introduced. a is related to the power of the electric heating rod and the type of cement, and its value ranges from 0 to 1.

[0070] Step 5: Calculate the heat release of concrete of the simulated pile size according to the concrete hydration heat release formula;

[0071] Step 6: Select the power and power-on time of the heating rod according to the correlation model between the heat generation rate of the heating rod and the heat generation rate of concrete;

[0072] Step 7: Set the temperature section of the temperature controller, and set the temperature rise and fall limits and maintenance time of each temperature section;

[0073] Step 8: The temperature controller adjusts the temperature according to the real-time feedback from the temperature sensor to simulate the heat release process of concrete hydration;

[0074] Step 9: After the heat release is completed, disconnect the power supply and allow the temperature of the soil around the simulated pile to drop naturally through the ambient temperature to simulate the pile foundation refreezing process.

[0075] During specific implementation, the test device and test method of the present invention can simulate both the concrete hydration and heating process and the pile foundation refreezing process. They can simulate the change in pile foundation bearing capacity under different total pile foundation heat releases, explore the optimal bearing capacity under different pile foundation heat releases, and the variation pattern of the optimal pile foundation hydration heat and pile foundation size. At the same time, by adjusting the power-on time and power of the electric heating rod, the pile foundation refreezing time under different heat releases and the change in bearing capacity during the refreezing process are explored, solving the problem that existing cast-in-place piles cannot be reloaded when exploring the effect of hydration heat on the pile foundation refreezing bearing capacity.

[0076] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A frozen soil pile foundation hydration heat simulation test method, wherein the device used comprises an aluminum tube (1) for simulating a pile foundation and a temperature controller (2) for adjusting the temperature, wherein an electric heating rod (3) is provided in the aluminum tube (1), a quartz sand particle layer (4) and a temperature sensor (5) for detecting the surface temperature of the aluminum tube (1) are provided on the outer surface of the aluminum tube (1), an output end of the temperature controller (2) is connected to a solid-state relay (6), and the electric heating rod (3) is connected to the solid-state relay (6); wherein the device comprises: The test method comprises the following steps: Step 1: Establishing a thermal conductivity model of the test device; Step 2: Determine the boundary conditions of the thermal conductivity model and establish the temperature distribution model of the heating rod; Step 3: Establish a correlation model between the temperature change of the electric heating rod and the temperature change of the simulated pile surface; Step 4: Establish a correlation model between the heat generation rate of the electric heating rod and the heat generation rate of concrete; The correlation model between the heat generation rate of the electric heating rod and the heat generation rate of concrete in step 4 is: Where a is the correlation coefficient between the heating rate of the electric heating rod and the heating rate of concrete, C c is the volumetric heat capacity of concrete, θ is the maximum adiabatic temperature rise of concrete, k t is the concrete hydration chemical reaction rate at the initial temperature t0; Step 5: Calculate the heat release of concrete of the simulated pile size according to the concrete hydration heat release formula; Step 6: Select the power and power-on time of the heating rod according to the correlation model between the heat generation rate of the heating rod and the heat generation rate of concrete; Step 7: Set the temperature section of the temperature controller, and set the temperature rise and fall limits and maintenance time of each temperature section; Step 8: The temperature controller adjusts the temperature according to the real-time feedback from the temperature sensor to simulate the heat release process of concrete hydration; Step 9: After the heat release is completed, disconnect the power supply and allow the temperature of the soil around the simulated pile to drop naturally through the ambient temperature to simulate the pile foundation refreezing process.

2. A frozen soil pile foundation hydration heat simulation test method according to claim 1, characterized in that: One end of the aluminum tube (1) is closed, and the other end of the aluminum tube (1) is open. The open end is used to insert the electric heating rod (3), and the electric heating rod (3) is arranged closely against the inner wall of the aluminum tube (1).

3. A frozen soil pile foundation hydration heat simulation test method according to claim 1, characterized in that: The quartz sand particle layer (4) is adhered to the outer surface of the aluminum tube (1) using epoxy resin glue to simulate the pile side roughness.

4. A frozen soil pile foundation hydration heat simulation test method according to claim 1, characterized in that: The thermal conductivity model of the test device in step 1 is: Where r is the distance from the center of the aluminum tube (1), T is the surface temperature of the aluminum tube (1), is the heat generation rate of the electric heating rod (3), and k is the thermal conductivity of the aluminum tube (1).

5. A frozen soil pile foundation hydration heat simulation test method according to claim 4, characterized in that: The temperature distribution model of the test device in step 2 is: Where T(r) is the temperature at different distances from the center of the simulated pile, T s (t) is the temperature of frozen soil beside the pile at time t, and r0 is the radius of the pile, T0 is the frozen soil temperature on the pile side at the initial moment, and h is the heat transfer coefficient.

6. A frozen soil pile foundation hydration heat simulation test method according to claim 5, characterized in that: The correlation model between the temperature change of the electric heating rod and the temperature change of the simulated pile surface in step 3 is: Where T(r,t) is the temperature at the center of the pile at time t, T ∞ is the temperature at the center of the pile at time t, T i is the pile temperature at the initial moment, C1,ξ1 are both one-dimensional transient thermal conductivity, α is the thermal diffusion coefficient and t is the time.

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