A method for strengthening the slope of an expansive soil foundation pit

Abstract

The present invention discloses a method for microwave reinforcement of the slope of an expansive soil foundation pit. It includes the following steps: First, determine the treatment area according to the requirements of engineering construction; Second, use a drill or a vibrating pile driver to drill holes in the slope of the expansive soil foundation pit to a predetermined position, and place the grouting pipe into the holes; Third, inject the slurry prepared in the cement slurry preparation system into the soil to be reinforced through the grouting pipe after pressurization by an air compressor; Fourth, while grouting, start the microwave heating system through the microwave control device to accelerate the early hydration of cement, so that the early strength of the slurry is formed relatively quickly; Fifth, after the grouting is completed, continue to irradiate the slurry-soil mixture with microwaves through the microwave transmission device to promote the rapid solidification and condensation of the slurry in the rock and soil body, while reducing the moisture content of the rock and soil body itself, reducing the expansibility of the soil, and increasing the shear strength of the soil. After reaching the design standard, move to the next drill hole and repeat the above steps. The present invention uses microwave technology to shorten the construction period and greatly enhance the stability of the slope of the foundation pit.

Description

Technical Field

[0001] The present invention relates to the field of improving expansive soil foundation pits, and particularly to a method for strengthening the slopes of expansive soil foundation pits based on microwave technology. Background Art

[0002] With the continuous development of urbanization construction, high-rise buildings emerge in an endless stream everywhere. The urban land is becoming increasingly in short supply. The increasing demand for the utilization of underground space makes the foundation pits deeper and deeper, and the subsequent foundation pit safety accidents are becoming more and more frequent. Foundation pit engineering plays a decisive role in the safety and cost of the entire construction project, so its importance cannot be ignored. Expansive soil, as a special type of clay, contains a large amount of hydrophilic minerals and has the characteristics of swelling when absorbing water and shrinking when losing water. It is easy to cause the instability of the foundation pit under artificial excavation, rainfall and other conditions. At the same time, expansive soil is widely distributed in China. For example, it is distributed in different ranges in Guangxi, Yunnan, Henan, Hubei, Sichuan, Shaanxi, Hebei, Anhui, Jiangsu and other places. In engineering, due to the lack of understanding of the properties of expansive soil and the negligence of deep foundation pit support, major engineering problems such as slope collapse, excessive deformation of the support, and settlement of surrounding buildings often occur. Therefore, it is urgent to solve the problem of supporting the slopes of expansive soil foundation pits.

[0003] In traditional slope support technologies, most of them form a certain support effect through external force reinforcement, such as anchor cables, soil nail walls and retaining walls. The high-pressure jet grouting method is a relatively new but technically mature support means and is applied to the support of many deep foundation pit slopes. Using the grouting method for foundation pit support has the advantages of simple operation, high strength of the consolidated body and high reliability. However, due to the high water sensitivity of expansive soil, a water content change of only 1%-2% will cause volume expansion. The water in the unhardened cement slurry will cause a temporary increase in the water content in the soil, affecting the soil stability. At the same time, the chemical reaction time in the expansive soil after grouting is relatively long. Therefore, there is an urgent need for a method to quickly and effectively treat the slopes of expansive soil foundation pits.

[0004] Microwave technology can promote the rapid solidification of the slurry, improve the early strength of concrete, improve the construction efficiency and shorten the construction period. In addition, microwaves can also improve the physical and chemical properties of expansive soil and further improve the stability of the foundation pit. Summary of the Invention

[0005] Therefore, it is necessary to invent a method for improving expansive soil foundation pits based on microwave technology, which can promote the rapid coagulation of the soil and improve the construction efficiency through this method.

[0006] To achieve the above object, using the combined method of grouting and microwave, the present invention provides the following technical solutions. A method for improving expansive soil foundation pits based on microwave technology, comprising the following steps:

[0007] Step 1: Determine the treatment area according to the requirements of engineering construction;

[0008] Step 2: Use a drill rig or vibrating pile driver to drill holes in the slope of the expansive soil foundation pit to a predetermined position, and place the grouting pipe into the holes.

[0009] Step 3: Inject the slurry prepared in the cement slurry preparation system into the soil to be reinforced through the grouting pipe after being pressurized by an air compressor.

[0010] Step 4: While grouting, start the microwave heating system through the microwave control device to accelerate the early hydration of cement, so that the early strength of the slurry is formed relatively quickly.

[0011] Step 5: After the grouting is completed, continue to irradiate the slurry-soil mixture with microwaves through the microwave transmission device to promote the rapid solidification and condensation of the slurry in the rock and soil mass. At the same time, reduce the water content of the rock and soil mass itself, reduce the expansibility of the soil, and improve the shear strength of the soil. After reaching the design standard, move to the next hole and repeat the above steps.

[0012] Further settings are as follows:

[0013] The pile driver can assist the grouting pipe to enter the holes on slopes at different angles.

[0014] The cement slurry preparation system includes a water tank, a cement silo, a mixer, a slurry bucket, and a high-pressure cement pump. Among them, both ends of the mixer are connected to the water tank and the cement silo respectively. Water and cement enter the mixer and are fully stirred and then enter the slurry bucket connected to the mixer. The slurry bucket is used to temporarily store the cement slurry. Finally, when starting to work, the cement slurry in the slurry bucket enters the high-pressure cement pump connected to the other end. The high-pressure cement pump makes the cement slurry enter the grouting pipe through high-intensity pressure to prepare for the subsequent work.

[0015] The grouting pipe is a double grouting pipe, which injects cement slurry and a mixed gas of air and a small amount of quicklime respectively.

[0016] The grouting pipe body is provided with a microwave control device, an air compressor, and a microwave transmission device.

[0017] The microwave control device is installed at the uppermost end of the grouting pipe and is connected to the microwave transmission device at the bottom through a hidden circuit to create conditions for the work of the microwave transmission device. The microwave control device includes a control power supply and a power control system. Among them, the control power supply is used to turn on and off the microwave control system, and the power control system is used to adjust the magnitude of different microwave powers.

[0018] The air compressor is used to compress the mixed gas of quicklime and air, increase the movement speed of air molecules, make its kinetic energy converted into pressure energy, so as to increase the pressure of the compressed gas.

[0019] The described microwave transmission device is installed at the lower part of the grouting pipe and includes a magnetron, a waveguide, and a cooling water circulation device. The magnetron is arranged at the bottom end of the pipe, which converts electrical energy into microwave energy, and the industrial microwave frequency is 2.45 GHz. The waveguide is arranged at the lower part of the grouting pipe, wrapping the lower pipe body. The waveguide transmits the microwave frequency from the magnetron, causing uniform internal energy to be generated in the substances near the waveguide. The cooling water circulation device ensures the normal operation of the microwave transmission device, and the waveguide needs to be perforated. The position of the perforation is consistent with the spray hole of the grouting pipe. The diameter of the nozzle of the grouting pipe is 2 - 3.2 mm, and the outer diameter of the waveguide is not less than 5 cm.

[0020] The working principle of the present invention is as follows:

[0021] a. The cement slurry is sprayed and cut into the soil under high pressure through the nozzle, and is fully mixed with the expanded soil to generate a cementitious substance with relatively high strength. The mixed gas of air and a small amount of quicklime passes through the air compressor, generating a huge pressure, and is sprayed into the soil through the nozzle at the lower part of the pipe body. When the quicklime encounters the water in the expanded soil, it hydrates into calcium ions, generating a new substance calcium hydroxide, and further generating calcium carbonate precipitation, forming a bond with the soil particles, thereby improving the bearing capacity of the expanded soil.

[0022] b. Microwaves have a longer wavelength and better penetrability. When microwaves penetrate into the expanded soil body, the polar molecules in the soil interact with the microwave electromagnetic field. Under the action of the electromagnetic field, the polar molecules in the soil are polarized and change their orientation alternately with the change of the polarity of the external alternating electromagnetic field. Due to the frequent mutual friction loss of so many polar molecules, the electromagnetic energy is converted into heat energy, causing the temperature to rise. Microwave heating is used during the reaction to increase the temperature, which can accelerate the early hydration of cement and improve the early strength; it also accelerates the reaction rate between quicklime and the water in the expanded soil, promoting the formation of calcium carbonate precipitation. Microwave heating is used after the reaction has coagulated. After the soil body has been cemented and solidified, the temperature of the solidified soil can be controlled by controlling the temperature of the microwave tube to evaporate the remaining small amount of water molecules in the soil without decomposing the calcium carbonate precipitate. The consolidation time of the soil body is shortened, and the cement solidification and the precipitate are mixed to form a soil body with greater strength.

[0023] Compared with the related methods for treating expanded soil foundation pits, the advantages of the method for microwave-reinforcing the slope of an expanded soil foundation pit provided by the present invention are as follows:

[0024] (1) In the present invention, the slope of the expanded soil foundation pit, including the foundation, can be treated from different angles.

[0025] (2) The present invention uses microwave irradiation to mix the soil body, accelerating the reaction process, accelerating the consolidation of the soil body, and shortening the construction period.

[0026] (3) The present invention improves the properties of the expanded soil through microwave irradiation, improving the slope stability. Description of the Drawings

[0027] Figure 1 Flow chart of the method of the present invention

[0028] Figure 2 High-pressure jet mechanical device diagram of the present invention

[0029] In the figure: 1 pile driver, 2 grouting pipe, 3 microwave transmission device, 4 air compressor, 5 microwave control device, 6 high-pressure mud pump, 7 slurry bucket, 8 water tank, 9 mixer, 10 cement silo, 11 cement slurry preparation system Specific implementation method

[0030] As Figure 1 shown, a method for microwave-reinforcing the slope of an expansive soil foundation pit of the present invention includes the following steps:

[0031] Step 1: Determine the treatment area, and determine the treatment scope and treatment thickness of the slope of the expansive soil foundation pit according to the Building Technical Code for Expansive Soil Regions (GB50112-2013).

[0032] Step 2: Use a drill or a vibrating pile driver to drill holes in the slope of the expansive soil foundation pit to a predetermined position. The drilling layout form is plum blossom shape, rectangle or rectangle. A multi-directional high-pressure jet grouting device is in place, and the grouting pipe is inserted into the drill hole to a predetermined depth with the assistance of a pile driver.

[0033] Step 3: After preparing the cement slurry, add a small amount of quicklime to the air compressor at the same time. The cement slurry prepared in the cement slurry preparation system and the mixed gas are simultaneously pressurized by the air compressor and then quickly ejected from the spray hole through the grouting pipe. The pile driver is used to slowly and evenly lift and rotate the grouting pipe to cut and mix the expansive soil.

[0034] Step 4: At this time, start the microwave heating system through the microwave control device to control the temperature. Increasing the temperature can accelerate the early hydration of cement, and the early strength is formed relatively quickly; it also accelerates the reaction rate between quicklime and the water in the expansive soil, and promotes the formation of calcium carbonate precipitation.

[0035] Step 5: After forming a mixed consolidated soil body of a cementitious material with higher strength and calcium carbonate precipitate, irradiate it with microwaves through the microwave transmission device to evaporate the remaining small amount of water molecules in the soil, increase the connection between soil particles, reduce the expansion freedom, and improve the shear strength of the soil body. After reaching the design standard, move to the next drill hole and repeat the above steps.

[0036] As Figure 2 shown, a method for treating an expansive soil foundation pit with microwaves, the multi-directional high-pressure jet grouting device described includes three main parts: a pile driver 1, a grouting pipe 2, and a cement slurry preparation system 11.

[0037] The pile driver 1 described can assist the grouting pipe to enter the drill holes on slopes at different angles.

[0038] The described cement slurry preparation system 11 includes a water tank 8, a cement silo 10, a mixer 9, a slurry bucket 7, and a high-pressure cement pump 6. Among them, both ends of the mixer 9 are respectively connected to the water tank 8 and the cement silo 10, and the left side is connected to the slurry bucket 7, and the slurry bucket 7 is connected to the high-pressure mud pump 6. The mixture stirred from the water tank 8 and the cement silo 10 is in the mixer 9 and enters the high-pressure mud pump 6 via the slurry bucket 7.

[0039] The described grouting pipe 2 is a double grouting pipe, which respectively injects cement slurry and a mixed gas of air and a small amount of quicklime.

[0040] The described grouting pipe body 2 is provided with a microwave control device 5, an air compressor 4, and a microwave transmission device 3. The air compressor 4 is above the grouting pipe 2, and its top is connected to the microwave control device 5; the microwave transmission device 3 is installed at the lower part of the grouting pipe 2.

[0041] The present invention provides a method for strengthening the slope of an expansive soil foundation pit by using microwaves. This method combines microwaves with the grouting modification method. Microwaves make the original modification process faster, improve the efficiency, shorten the construction period, greatly increase the strength, and have high economy. The technical means disclosed in the solution of the present invention are not limited to the technical means disclosed in the above embodiments, but also include technical solutions composed of any of the above technical features.

Claims

1. A method for strengthening the slope of an expansive soil foundation pit using microwaves, characterized in that, The method comprises the following steps: Step 1: Determine the treatment area according to the requirements of engineering construction; Step 2: Use a drilling rig or a vibrating pile driver to drill holes in the slope of the expansive soil foundation pit to a predetermined position, and place the grouting pipe into the holes; Step 3: Inject the slurry prepared in the cement slurry preparation system into the soil to be reinforced through the grouting pipe after being pressurized by an air compressor; Step 4: While grouting, start the microwave heating system through the microwave control device to accelerate the early hydration of cement, so that the early strength of the slurry is formed relatively quickly; Step 5: After the grouting is completed, continue to irradiate the slurry-soil mixture with microwaves through the microwave transmission device to promote the rapid solidification and condensation of the slurry in the rock and soil mass, at the same time reduce the moisture content of the rock and soil mass itself, reduce the expansibility of the soil, and improve the shear strength of the soil; after reaching the design standard, move to the next hole and repeat the above steps.

2. The method for strengthening the slope of an expansive soil foundation pit by using microwaves according to claim 1, characterized in that: The pile driver can assist the grouting pipe to enter the holes on slopes at different angles.

3. A method for reinforcing the slope of an expansive soil foundation pit using microwaves according to claim 1, wherein: The cement slurry preparation system includes a water tank, a cement silo, a mixer, a slurry bucket, and a high-pressure cement pump. Among them, the two ends of the mixer are respectively connected to the water tank and the cement silo. Water and cement enter the mixer and are fully stirred and then enter the slurry bucket connected to the mixer. The slurry bucket is used to temporarily store the cement slurry; finally, when starting to work, the cement slurry in the slurry bucket enters the high-pressure cement pump connected to the other end; the high-pressure cement pump makes the cement slurry enter the grouting pipe through high-intensity pressure to prepare for subsequent work.

4. A method for reinforcing the slope of an expansive soil foundation pit using microwaves according to claim 1, wherein: The grouting pipe is a double grouting pipe, which respectively injects cement slurry and a mixed gas of air and a small amount of quicklime, and is provided with a microwave control device, an air compressor, and a microwave transmission device.

5. A method for reinforcing the slope of an expansive soil foundation pit using microwaves according to claim 1, wherein: The microwave control device is installed at the uppermost end of the grouting pipe and is connected to the microwave transmission device at the bottom through a hidden circuit to create conditions for the work of the microwave transmission device. The microwave control device includes a control power supply and a power control system. Among them, the control power supply is used to turn on and off the microwave control system, and the power control system is used to adjust the magnitude of different microwave powers.

6. A method for strengthening the slope of an expansive soil foundation pit using microwaves according to claim 1, characterized in that: The air compressor is used to compress the mixed gas of quicklime and air, increase the movement speed of air molecules, make its kinetic energy be converted into pressure energy, and thus increase the pressure of the compressed gas.

7. A method for reinforcing the slope of an expansive soil foundation pit using microwaves according to claim 1, characterized in that: The microwave transmission device is installed at the lower part of the grouting pipe and includes a magnetron, a waveguide, and a cooling water circulation device; the magnetron is arranged at the bottom end of the pipe, which converts electrical energy into microwave energy, and the industrial microwave frequency is 2.45 GHz; the waveguide is arranged at the lower part of the grouting pipe and wraps the lower pipe body. The waveguide transmits the microwave frequency from the magnetron to make the substances near the waveguide generate uniform internal energy; the cooling water circulation device ensures the normal operation of the microwave transmission device; the waveguide needs to be perforated, and the perforation position is consistent with the nozzle of the grouting pipe. The nozzle diameter of the grouting pipe is 2 - 3.2 mm, and the outer diameter of the waveguide is not less than 5 cm.

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