阅读说明：本技术 一种氧化镁固化土碳化过程膨胀性及碳化土抗剪强度测试方法 (Method for testing expansibility and shear strength of carbonized soil in carbonization process of magnesium oxide solidified soil ) 是由 蔡光华 王中 赵志峰 邵光辉 刘成 张欣雅 于 2019-10-21 设计创作，主要内容包括：本发明公开了一种氧化镁固化土碳化过程膨胀性及碳化土抗剪强度测试方法,属于土木工程固化材料的参数测试。该方法包括氧化镁混合土样在碳化固化过程中温度、电阻率和体积膨胀的测试以及碳化试样的抗剪强度测试,具体包括装置组装与连接、试样制备、传感器调试、碳化养护与物理参数测试、直剪试验准备及直剪试验等步骤。本发明实时监测氧化镁固化土试样在碳化过程中温度和电阻率变化以及不同位置处的体积膨胀,以评价材料在不同条件下的碳化进程和膨胀特性；碳化养护后,对碳化试样进行加载,实现其全自动直剪试验和电阻率测试。该方法避免试样在装样过程的扰动、操作步骤简单、参数测试准确,对碳化固化土材料的工程应用和评价具有重要意义。(The invention discloses a method for testing the expansibility of magnesium oxide solidified soil in the carbonization process and the shear strength of carbonized soil, belonging to the parameter test of civil engineering solidified materials. The method comprises the steps of testing the temperature, the resistivity and the volume expansion of a magnesium oxide mixed soil sample in the carbonization and solidification process and testing the shear strength of a carbonized sample, and specifically comprises the steps of assembling and connecting devices, preparing the sample, debugging a sensor, carbonizing and curing, testing physical parameters, preparing a direct shear test, performing the direct shear test and the like. The method monitors the temperature and resistivity change and the volume expansion of different positions of the magnesia solidified soil sample in real time in the carbonization process so as to evaluate the carbonization process and the expansion characteristic of the material under different conditions; and after carbonization and maintenance, loading the carbonized sample to realize a full-automatic direct shear test and a resistivity test of the sample. The method avoids disturbance of the sample in the sample loading process, has simple operation steps and accurate parameter test, and has important significance for engineering application and evaluation of the carbonized solidified soil material.)

1. The method for testing the expansibility and the shear strength of the carbonized soil in the carbonization process of the magnesia curing soil is characterized by comprising the following steps of:

a. assembling and connecting the device: sequentially placing a lower porous plate, filter paper, a lower electrode plate and a temperature sensor in a lower shearing box, placing an upper shearing box on the lower shearing box, adjusting all spring bolts in the shearing box to tightly close two petals of an inner shell of the upper shearing box and two petals of an inner shell of the lower shearing box, coating vaseline on the inner walls of the inner shell of the upper shearing box and the inner shell of the lower shearing box, adjusting an upper scroll and a lower scroll and butting the upper scroll and the lower scroll into a whole, so that the lower shearing box and the upper shearing box are stabilized into a whole;

b. sample preparation: preparing magnesium oxide mixed soil samples under different compactedness by using a cutting ring, extruding the samples into a shearing box from the cutting ring by using a stripper, enabling the bottom of the samples to be in close contact with a temperature sensor and a lower electrode plate, and then sequentially placing an upper electrode plate, the temperature sensor, filter paper and an upper permeable plate on the top of the samples, so that the preformed holes of the upper electrode plate and the upper permeable plate correspond to each other;

c. sensor debugging: adjusting all spring bolts to enlarge the inner diameters of an inner shell of an upper shearing box and an inner shell of a lower shearing box, then rotating an upper scroll and a lower scroll to enable strain gauges to extend out of reserved holes of the inner shells of the upper shearing box and the lower shearing box and to be in contact with the side face of a sample, opening an air compressor and a control valve and adjusting a hydraulic rod to enable the strain gauges on a balance plate to penetrate through the reserved holes in an upper water permeable plate and an upper electrode plate and to be in contact with the upper top face of the sample, and finally opening a data acquisition device in a controller to record initial readings of all the strain gauges, a temperature sensor and resistivity;

d. sample carbonization maintenance and physical parameter testing: installing a sealing box, closing a drain valve and an exhaust valve, opening a constant heater, adjusting a pressure regulating valve to a preset pressure, ventilating and carbonizing, closing the pressure regulating valve, opening the drain valve and the exhaust valve after finishing a specified ventilating time, and performing standard maintenance; deformation, temperature and resistivity are monitored in real time through a strain gauge, a temperature sensor, a lower electrode plate and an upper electrode plate in the processes of ventilation, carbonization and maintenance;

e. preparation of direct shear test: after sample carbonization and maintenance are finished, manually adjusting the push rod to enable the push rod to be in contact with the lower shear box shell and enable the upper shear box shell to be in contact with the dowel bar; rotating the upper scroll to make the strain gauge contract to the back of the inner shell of the upper shearing box and the inner shell of the lower shearing box, separating the upper scroll from the lower scroll, and adjusting and screwing out all the spring bolts to make the front of the inner shell of the upper shearing box and the front of the inner shell of the lower shearing box tightly contact with the surface of the carbonized sample; adjusting the control valve and rotating the hydraulic rod to enable the strain gauge to contract into the balance plate from the preformed hole, adjusting the hydraulic rod to enable the upper permeable plate to be in close contact with the filter paper on the upper electrode plate, adjusting the hydraulic cylinder and the hydraulic rod to enable the pressure sensor to be stabilized to a preset pressure value, and recording initial readings of the displacement sensor and the pressure sensor;

f. direct shear test: starting a motor in the propelling device, adjusting a speed regulator to enable the lower shearing box and the upper shearing box to shear and move, recording a displacement sensor, a stress sensor and a resistivity value in the shearing process, and calculating the shearing parameters of the carbonized sample.

2. The method for testing the expansibility during the carbonization process of magnesia curing soil and the shear strength of carbonized soil according to claim 1, wherein the inner diameter of the cutting ring has the same size as the minimum inner diameter of the inner shell of the upper shear box and the inner shell of the lower shear box.

3. The method for testing the expansibility during the carbonization process of magnesia curing soil and the shear strength of carbonized soil according to claim 1, wherein the adjustment of the spring bolt, the upper reel and the lower reel is realized by a controller.

4. The method for testing the expansibility during carbonization of magnesia curing soil and the shear strength of carbonized soil according to claim 1, wherein the sealing box is a hollow cylinder without a bottom cover and the size of the hollow cylinder is larger than that of the shear box.

Background

With the development of economy and urbanization in China, the foundation construction of urban construction, traffic and water conservancy and the like often meets soft soil layers with different thicknesses, and the soft soil has the characteristics of high water content, large porosity, low strength, high compressibility and the like, so that great challenges are brought to engineering construction and foundation treatment. In the common foundation treatment methods, the construction of a dynamic compaction method and a vibroflotation method is difficult to implement due to large noise, and the traditional replacement and filling method is rarely recommended due to large engineering quantity, high cost and uneven distribution of bearing capacity. The pile foundation reinforcing method of cement/lime soil pile, grouting method, high pressure jet grouting pile and the like is the most used technology at present, the method has long treatment and maintenance period, the used curing materials mainly comprise cement and lime, the energy resource consumption in the cement production process is large, the environmental pollution is serious, and a plurality of negative effects are brought to the sustainable development of economy and environment, so that geotechnical engineering researchers begin to seek new alternative materials and methods. In recent years, the subject group adopts active magnesium oxide and carbon dioxide as curing agents to replace the traditional cement to carry out the curing treatment of weak soil, and discloses a series of invention patents: such as "a method for carbonizing and solidifying soil (201210097042.2)", "a method for carbonizing and solidifying soil and a device thereof (201010604013.1)", "a treatment system and a method for thermally consolidating soft soil foundation using industrial waste gas (201310122135.0)", "a treatment system and a method for forming carbonized pile (2014102039788)" for consolidating foundation "," a method for carbonizing and consolidating replacement mat layer of soft soil foundation (2014102729571) "," a treatment method for in situ carbonizing and solidifying shallow soft foundation (201510348797.9) ", and" a carbonized-stirred pile-air-permeable pile composite foundation and a construction method thereof (201710225231.6) ", etc. The invention patents are soft soil treatment construction technologies disclosed based on a magnesium oxide-carbon dioxide solidification mechanism. However, after the soft soil is carbonized, the physical characteristics and the mechanical characteristics of the soil body are changed greatly, which has important influence on geotechnical engineering construction. Aiming at the particularity of soft soil carbonization and solidification treatment, in the engineering design process of the carbonization treatment foundation, the method tests the expansibility and the shearing resistance of the carbonization and solidification soil and is particularly important for reasonably determining the physical characteristics, the bearing capacity of the foundation soil and the strength parameters (cohesive force and internal friction angle).

As is known, the carbonization reaction of the magnesium oxide mixed soil is a chemical strengthening process with heat release and expansion, the strength is increased quickly, the temperature is increased, and the sample expansion is obvious, because the existing indoor direct shear test is carried out based on a cutting ring sample, the carbonized soil sample is difficult to carry out cutting ring sampling; if the magnesium oxide mixed soil sample is pressed in a cutting ring and then carbonized, the real carbonization process of the sample is difficult to reflect. The expansibility evaluation of the magnesium oxide cured sample mainly comprises the steps of testing the sizes of an indoor cylindrical sample before and after carbonization and averaging, and no accurate testing method is available for evaluating the expansibility of the sample in the carbonization and curing process. The existing expansibility testing device and method mostly concentrate on the geotechnical engineering field, mostly adopt the equilibrium pressurization method, the counter-pressure method and the decompression method to carry out, easily cause the sample to destroy; and the expansibility testing device is few and the cost is high. Although the document discloses a device and a method (201710399344.8) for testing the expansibility of an expansive grouting material in a curing process, the device and the method disclose the expansibility of the grouting material by adopting an elastic constraint part to control the curing expansion deformation of the material and measuring the corresponding expansion force and the change characteristics of the expansion force along with time under different constraint conditions.

At present, the soil layer is subjected to direct shear test by adopting traditional direct shear apparatus mostly at home and abroad, and the shear apparatus mainly comprises a shear box, a vertical loading device, a horizontal loading device and the like. In the traditional direct shear test, a cutting ring is often used for cutting a soil sample to be tested into a specific shape and moving the soil sample into a shear box, and the soil sample is easily disturbed and damaged in the moving and cutting processes, so that the experimental data is inaccurate. The existing direct shear apparatus is mainly reconstructed based on special environment, for example, a chemical corrosion apparatus is added to simulate the field soil pollutant corrosion by a file 'determination method of chemical polluted soil shear strength and a special full-automatic direct shear apparatus (2016100447885)', so as to solve the problem that the conventional direct shear tester can not test the shear strength parameters of the chemical polluted soil; the temperature control type direct shear apparatus (201110079021.3) is characterized in that a sample is placed in a constant temperature water tank, the temperature is controlled by a water temperature detection unit and a measurement mechanism, and the shear strength test of the sample at constant temperature is completed; the large multifunctional frozen soil-structure contact surface circulating direct shear apparatus and the test operation method (201210265653.3) cool a soil sample through refrigerating fluid of a refrigerating device, simultaneously record the temperature of the soil sample in real time through a high-precision temperature sensor, and can replace steel plates with different roughness to simulate contact surfaces with different roughness, thereby completing the shear strength test of frozen soil; the frozen soil-structure direct shear apparatus and the using method (201110186321.1) thereof are characterized in that a semiconductor refrigerating block is arranged at the bottom of a shearing box, a cooling liquid conveying pipe in a low-temperature constant-temperature groove is connected with the semiconductor refrigerating block, different freezing conditions are simulated, and a relation curve of shear stress and shear displacement of a frozen soil-structure contact surface is measured; an unsaturated soil-structure material contact surface shear apparatus (2019100476218) for controlling relative humidity is provided with a closed pressure chamber and a humidity environment control module to simulate different humidity and pressure environments so as to reproduce the humidity state of an actual engineering site and obtain controllable unsaturated soil-structure material contact surface mechanical characteristics which have wide suction range and are suitable for different soil types and different structure materials; the combined indoor consolidation shearing instrument (2018115645426) is provided with a vertical loading device and a horizontal loading device, and directly carries out a shearing test on a sample after consolidation is completed, so that the consolidation coefficients and the shear strengths of different types of soil bodies are continuously determined. Although the direct shear apparatus is greatly improved compared with the traditional direct shear apparatus, soil body direct shear tests under different environments are simulated, but the expansibility of a soil body in the carbonization process and the shear strength test of the carbonized soil body cannot be met, and the detection of the temperature and the resistivity of a soil sample in the carbonization process cannot be completed.

Based on the current situation of rapid development of engineering construction and the advantages of a novel carbonization strengthening method in China, and combining the current situations of difficult parameter test, inaccurate mechanical parameter test of the carbonized soil and the like in the current carbonization strengthening process, the method for testing the expansibility and the shear strength of the carbonized soil in the carbonization process of the magnesia curing soil needs to be researched and developed urgently, and has important significance in the aspects of effectively utilizing carbon dioxide, reasonably designing engineering, applying and the like.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for testing the expansibility and the shear strength of the carbonized soil in the carbonization process of the magnesia curing soil, which comprises the steps of testing the temperature, the resistivity and the volume expansion of a magnesia mixed soil sample in the carbonization and curing process and testing the shear strength of a carbonized sample, and specifically comprises the steps of device assembly and connection, sample preparation, sensor debugging, carbonization maintenance and physical parameter testing, direct shear test preparation, direct shear test and the like. The method monitors the temperature and resistivity change and the volume expansion of different positions of the magnesia solidified soil sample in real time in the carbonization process so as to evaluate the carbonization process and the expansion characteristic of the material under different conditions; and after carbonization and maintenance, loading the carbonized sample to realize a full-automatic direct shear test and a resistivity test of the sample. The method avoids disturbance of the sample in the sample loading process, has simple operation steps and accurate parameter test, and has important significance for engineering application and evaluation of the carbonized solidified soil material.

In order to achieve the aim, the invention discloses a method for testing the expansibility and the shear strength of carbonized soil in the carbonization process of magnesia solidified soil, which is characterized by comprising the following steps:

a. assembling and connecting the device: sequentially placing a lower porous plate, filter paper, a lower electrode plate and a temperature sensor in a lower shearing box, placing an upper shearing box on the lower shearing box, adjusting all spring bolts in the shearing box to tightly close two petals of an inner shell of the upper shearing box and two petals of an inner shell of the lower shearing box, coating vaseline on the inner walls of the inner shell of the upper shearing box and the inner shell of the lower shearing box, adjusting an upper scroll and a lower scroll and butting the upper scroll and the lower scroll into a whole, so that the lower shearing box and the upper shearing box are stabilized into a whole;

b. sample preparation: preparing magnesium oxide mixed soil samples under different compactedness by using a cutting ring, extruding the samples into a shearing box from the cutting ring by using a stripper, enabling the bottom of the samples to be in close contact with a temperature sensor and a lower electrode plate, and then sequentially placing an upper electrode plate, the temperature sensor, filter paper and an upper permeable plate on the top of the samples, so that the preformed holes of the upper electrode plate and the upper permeable plate correspond to each other;

c. sensor debugging: adjusting all spring bolts to enlarge the inner diameters of an inner shell of an upper shearing box and an inner shell of a lower shearing box, then rotating an upper scroll and a lower scroll to enable strain gauges to extend out of reserved holes of the inner shells of the upper shearing box and the lower shearing box and to be in contact with the side face of a sample, opening an air compressor and a control valve and adjusting a hydraulic rod to enable the strain gauges on a balance plate to penetrate through the reserved holes of an upper water permeable plate and an upper electrode plate and to be in contact with the upper top face of the sample, and finally opening a data acquisition device in a controller to record initial readings of all the strain gauges, a temperature sensor and resistivity;

d. sample carbonization maintenance and physical parameter testing: installing a sealing box, closing a drain valve and an exhaust valve, opening a constant heater, adjusting a pressure regulating valve to a preset pressure, ventilating and carbonizing, closing the pressure regulating valve, opening the drain valve and the exhaust valve after finishing a specified ventilating time, and performing standard maintenance; deformation, temperature and resistivity are monitored in real time through a strain gauge, a temperature sensor, a lower electrode plate and an upper electrode plate in the processes of ventilation, carbonization and maintenance;

e. preparation of direct shear test: after sample carbonization and maintenance are finished, manually adjusting the push rod to enable the push rod to be in contact with the lower shear box shell and enable the upper shear box shell to be in contact with the dowel bar; rotating the upper scroll to make the strain gauge contract to the back of the inner shell of the upper shearing box and the inner shell of the lower shearing box, separating the upper scroll from the lower scroll, and adjusting and screwing out all the spring bolts to make the front of the inner shell of the upper shearing box and the front of the inner shell of the lower shearing box tightly contact with the surface of the carbonized sample; adjusting the control valve and rotating the hydraulic rod to enable the strain gauge to contract into the balance plate from the preformed hole, adjusting the hydraulic rod to enable the upper permeable plate to be in close contact with the filter paper on the upper electrode plate, adjusting the hydraulic cylinder and the hydraulic rod to enable the pressure sensor to be stabilized to a preset pressure value, and recording initial readings of the displacement sensor and the pressure sensor;

f. direct shear test: starting a motor in the propelling device, adjusting a speed regulator to enable the lower shearing box and the upper shearing box to shear and move, recording a displacement sensor, a stress sensor and a resistivity value in the shearing process, and calculating the shearing parameters of the carbonized sample.

Preferably, the inner diameter of the cutting ring is the same as the minimum inner diameter of the inner shell of the upper shearing box and the inner shell of the lower shearing box.

Preferably, the adjustment of the spring bolt, the upper reel and the lower reel is realized by a controller.

As another preferred mode, the sealing box is a hollow cylinder without a bottom cover, and the size of the hollow cylinder is larger than that of the shearing box.

Compared with the prior art, the invention has the beneficial effects that:

1) the method realizes the synchronous test of the temperature and the resistivity of the magnesia solidified soil sample, and is convenient for predicting and evaluating the carbonization process of the solidified sample;

2) the strain gauge can be adjusted through the hydraulic rod and the reel, so that the protection and free working test of the strain gauge in the cavity of the balance plate and the shear box are realized, and the volume expansion of a sample in the carbonization process under an unconstrained condition is accurately tested;

3) through the synergistic effect of the spring bolt and the flexible connecting sheet in the double-layer shell of the shearing box, the free change of the inner diameter of the shell in the shearing box is realized, and the test of the shearing strength of a sample is better met;

4) the sample can be subjected to shear test without moving after carbonization, so that the sample damage and stress release in the sample loading process of the carbonized sample are avoided, the influence of the external environment on physical and mechanical parameters is reduced, and the test result has important significance on the application of the carbonization and solidification technology and the design of the carbonized soil foundation

5) All the sensors, the scroll and the spring bolt are connected with the integrated controller, so that the operation is simple and convenient, and the test operation time is reduced;

6) a thermostat is specially arranged on the vent pipe, and a drain pipe is arranged at the bottom of the lower shearing box, so that the condensation of an air pipe and the accumulation of water vapor at the bottom of the shearing box caused by low-temperature compressed gas are avoided;

7) the method realizes the reinforcement of the environment-friendly magnesium oxide to the soil body and the reutilization of the carbon dioxide gas, and has the advantages of low carbon, environmental protection and sustainable development.

Drawings

FIG. 1 is a schematic structural diagram of a device for testing expansibility and shear strength of carbonized soil during carbonization of magnesia-cured soil;

FIG. 2 is a cross-sectional view of the upper and lower shear boxes;

FIG. 3 is a plan view of the upper shear box;

FIG. 4 is a plan view of the balance plate;

FIG. 5 is a plan view of the upper permeable stone;

FIG. 6 is a plan view of an upper electrode plate;

in the figure: 1. an operation table, 2, a fixed seat, 3, a sliding chute, 4, a ball, 5, a lower shearing box, 6, a lower water permeable plate, 7, a lower electrode plate, 8, a temperature sensor, 9, a sample, 10, a vent pipe, 11, a constant heater, 12, a pressure regulating valve, 13, a high-pressure gas tank, 14, a drain pipe, 15, a drain valve, 16, a support column, 17, a seal box, 18, an exhaust valve, 19, a cross beam, 20, an upper shearing box, 21, an upper electrode plate, 22, an upper water permeable plate, 23, a balance plate, 24, a hydraulic rod, 25, a hydraulic cylinder, 26, a propulsion device, 27, a speed regulator, 28, a motor, 29, a displacement sensor, 30, a propulsion rod, 31, a force transmission rod, 32, a stress sensor, 33, a controller, 34, a pressure sensor, 35, a strain gauge, 36, an upper scroll, 37, a control valve, 38, an air compressor, 39, a connecting sheet, 40, a, 42. an upper cutting box inner shell, 43, a lower scroll, 44, a lower cutting box outer shell, 45, a lower cutting box inner shell, 46 and a reserved hole.

Detailed Description

The invention is further described with reference to the following figures and detailed description: