Cement-soil indoor curing and permeability coefficient testing device and method considering groundwater seepage

Abstract

The application discloses a cement soil indoor maintenance and permeability coefficient testing device and method considering groundwater seepage action, and the device comprises a cement soil maintenance and permeability coefficient testing mechanism. The device provides a pressure source for the pressure tank through an air compressor, adjusts the size of the osmotic pressure through a data control acquisition system in combination with the groundwater conditions of a construction site, provides a suitable hydraulic gradient for the flow of water in the cement soil sample, collects the exudate through an exudate metering pipe, and records the exudate through the data control acquisition system. According to the Darcy permeation law, the permeability coefficient of the cement soil sample is tested, and the change rule of the cement soil permeability coefficient under the seepage action is intuitively reflected. After the cement soil sample reaches a predetermined maintenance age, the unconfined compressive strength test is carried out to evaluate the strength characteristics.

Description

Technical Field

[0001] This invention belongs to the technical field of performance evaluation of foundation pit water-stop curtain in cement mixing pile construction and geotechnical engineering testing, and in particular, it is a device and method for indoor curing of cement soil and permeability coefficient testing considering the effect of groundwater seepage. Background Technology

[0002] With the rapid pace of urbanization, foundation pit construction has experienced explosive growth. As a crucial component of foundation pits, the water-stop curtain plays a vital role in preventing leakage. Cement mixing piles are widely used due to their ease of construction, low cost, and short construction period. However, in highly permeable strata such as silty soil, groundwater seepage can cause cement mixing piles to be eroded before they have fully developed their strength. In particular, the unhardened colloidal molecules in the cement hydration products are easily carried away by flowing groundwater, preventing the cement from fulfilling its intended purpose.

[0003] On the other hand, in the indoor tests for evaluating the performance of cement-soil mixing piles, cement-soil samples are often prepared for strength and permeability tests. These cement-soil samples are all placed under standard curing conditions to ensure the full hydration of cement. However, because the sample preparation method and curing conditions are relatively idealized, the premise of cement-soil mixing piles forming under groundwater seepage conditions is ignored. This leads to the final test results being far better than the actual field results, and the field performance of cement-soil mixing piles being overestimated.

[0004] Due to the dynamic forming environment of cement mixing piles and the differences in seepage conditions in different projects, the cement-soil curing conditions under groundwater seepage conditions should be considered in relevant studies of cement mixing piles in order to evaluate the actual achievable strength and permeability coefficient. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for indoor curing and permeability testing of cement-soil samples that takes into account groundwater seepage. This allows for simultaneous testing of the permeability coefficient variation during the curing process. The test results are more consistent with the on-site hydrogeological conditions, avoiding the overestimation of the strength and permeability of cement-soil mixing piles caused by traditional indoor curing methods. The device is highly efficient and convenient to operate, providing continuous and accurate data readings.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] An indoor curing and permeability coefficient testing device for cement-soil considering groundwater seepage includes:

[0008] The pressure chamber body has an air inlet at the top and a water outlet at the bottom, and the pressure chamber body contains test water.

[0009] An air source channel switch is provided with an air inlet, a first air outlet and a second air outlet. The first air outlet is connected to the air inlet through a first air pipe, the second air outlet is connected to the atmosphere through a second air pipe, and the air inlet is connected to the outlet of a pressure gauge through a third air pipe. The air inlet of the pressure gauge is connected to an air compressor and a data control and acquisition module through pipes.

[0010] The hydraulic switch has a first inlet, a second inlet, and an outlet. The first inlet is connected to the outlet on the pressure chamber body via a first liquid pipe. The second inlet is connected to the outlet of a supply pipe via a second liquid pipe. The outlet is connected to the water inlet switch on the curing permeation mold via a third liquid pipe. The outlet of the curing permeation mold is connected to the permeate metering pipe via a fourth liquid pipe.

[0011] The main body of the pressure chamber is made of a transparent material.

[0012] The permeable mold for curing consists of a first permeable stone, a first filter paper, a cement-soil sample, a second permeable stone, and a second filter paper arranged sequentially according to the direction of water flow.

[0013] The curing and penetration mold includes a cylindrical mold body with openings at the top and bottom, and a mold thread plug connected to the two opening ends of the cylindrical mold body. The cylindrical mold body is made of a transparent material.

[0014] This invention further discloses a testing method based on the aforementioned indoor curing and permeability coefficient testing device for cement-soil considering groundwater seepage.

[0015] S1. Set the osmotic pressure to 0 through the data control and acquisition system, then turn on the air compressor, adjust the air source channel switch to connect the air compressor with the air inlet on the main body of the pressure chamber, and adjust the hydraulic switch to connect the water outlet on the main body of the pressure chamber with the maintenance osmotic system.

[0016] S2. Set the permeation pressure to the system value using the data control and acquisition system and start the test. The data control and acquisition system simultaneously reads the volume of permeate in the permeate metering tube and calculates the permeability coefficient of the cement-soil sample.

[0017]

[0018]

[0019] In the formula, k The value is the permeability coefficient of the cement-soil sample, in cm / s.

[0020] t The time interval between two readings, in seconds;

[0021] Q for t The volume of exudate inside, i.e. t Internal data control acquisition system reading changes, unit: cm 3 ;

[0022] H represents the height of the cement-soil sample, in cm;

[0023] A represents the cross-sectional area of ​​the cement-soil sample, in cm². 2 ;

[0024] Δh The total water head difference between the two sides of the cement-soil sample is expressed in cm.

[0025] P Osmotic pressure, unit: Pa;

[0026] ρ The density of the exudate is expressed in g / cm³. 3 ;

[0027] S3. After the cement-soil sample has been cured to the specified age, take out the cement-soil sample and conduct an unconfined compressive strength test to evaluate the strength characteristics of the cement-soil.

[0028] When the liquid in the main body of the pressure chamber is insufficient, adjust the air source channel switch to connect the pressure chamber to the atmosphere, and adjust the hydraulic switch to connect the water outlet on the main body of the pressure chamber to the liquid supply pipe side, so as to replenish the liquid in the pressure chamber through the liquid supply pipe.

[0029] Beneficial effects:

[0030] This invention simulates the seepage conditions of a cement-soil mixing pile waterstop during its forming process by applying osmotic pressure to cement-soil samples. This allows for a systematic evaluation of the strength of cement-soil subjected to groundwater seepage. During the curing process, the permeability coefficient of the cement-soil samples is calculated by real-time monitoring of the seepage flow rate. The change in the permeability coefficient of the cement-soil mixing pile waterstop during the sample forming process is studied, providing a direct reflection of the variation law of the permeability coefficient of cement-soil under seepage. After the cement-soil samples reach the predetermined curing age, they are taken out for unconfined compressive strength tests to evaluate their strength characteristics. Attached Figure Description

[0031] Figure 1 A schematic diagram of the overall structure of the cement-soil sample curing and permeability coefficient testing system provided by the present invention;

[0032] Figure 2 This is a schematic diagram of the pressure chamber in the device of the present invention;

[0033] Figure 3 This is a schematic diagram of the plexiglass mold in the device of the present invention;

[0034] Figure 4 This is a disassembled diagram of the plexiglass mold in the device of the present invention;

[0035] Figure 5 This is a top view of the acrylic mold base in the device of the present invention;

[0036] Figure 6 This is a top view of the threaded plug on the upper part of the plexiglass mold in the device of the present invention;

[0037] In the diagram, 1. Air compressor; 2. Data control and acquisition system; 3. Pressure gauge; 4. Air source channel switch; 5. Air inlet; 6. Bolt; 7. Upper flange of pressure chamber body; 8. Threaded rod; 9. Acrylic glass column; 10. Water; 11. Lower flange of pressure chamber body; 12. Water outlet; 13. Hydraulic switch; 14. Liquid supply pipe; 15. Mold water inlet switch; 16. Mold base; 17. First rubber ring; 18. First permeable stone; 19. First filter paper; 20. Cement soil sample; 21. Mold body; 22. Second filter paper; 23. Second permeable stone; 24. Second rubber ring; 25. Upper threaded plug of mold; 26. Mold water outlet; 27. Leakage metering pipe. Detailed Implementation Plan

[0038] To make the technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, and not all embodiments. Based on the embodiments described in the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Reference Figure 1-6 As shown, this invention provides a system for indoor curing and permeability coefficient testing of cement-soil samples considering groundwater seepage. The system includes an air compressor 1, a data control and acquisition system 2, and a curing and permeation system. The data control and acquisition system 2 is used to control the seepage pressure and read the seepage flow rate. The curing and permeation system is used for curing and permeation testing of cement-soil samples. The curing and permeation system includes a liquid supply pipe 6, a pressure gauge 3, an air source channel switch 4, a pressure chamber, a hydraulic switch 13, a curing and permeation mold, and an exudate metering pipe 27.

[0040] The pressure gauge 3 is connected to the data control and acquisition system 2 and the air compressor 1 respectively, and controls the input pressure to the system set value through the data control and acquisition system 2. The pressure chamber consists of a pressure chamber air inlet 5, bolts 6, upper flange 7, threaded rod 8, plexiglass column 9, water 10, lower flange 11, and pressure chamber water outlet 12. The use of plexiglass as the main body of the pressure chamber facilitates observation of the liquid conditions inside the pressure chamber.

[0041] The gas source channel switch 4 is connected to the air inlet 5 of the pressure chamber and the atmosphere through a thin tube. When performing maintenance and permeability testing, the gas source channel switch 4 is adjusted to connect the air inlet 5 of the pressure chamber and the pressure gauge 3. When replenishing the liquid in the pressure chamber, the gas source channel switch 4 is adjusted to connect the air inlet 5 of the pressure chamber to the atmosphere, which facilitates the exhaust of the chamber.

[0042] The hydraulic switch 13 is connected to the liquid supply pipe 14, the pressure chamber outlet 12, and the curing permeation mold water inlet switch 15 via a thin tube. When performing curing and permeability coefficient testing, the hydraulic switch 13 is adjusted to connect the pressure chamber outlet 12 with the curing permeation mold water inlet switch 15, and the water inlet switch 15 corresponding to the mold containing the cement soil sample is opened. When replenishing the pressure chamber liquid, the hydraulic switch 13 is adjusted to connect the pressure chamber outlet 12 with the liquid supply pipe 14.

[0043] The cement-soil sample is placed in a custom-made acrylic curing permeation mold. The mold water inlet switch 15 is located on the lower half of the mold base 16 to control the start and end of the cement-soil sample test of a single mold. The upper half of the mold base 16 is threaded on the side, which matches the internal thread of the mold body 21. A first rubber ring 17 is set between the mold base 16 and the mold body 21 to ensure the mold is sealed.

[0044] The interior of the mold, from bottom to top, consists of a first permeable stone 18, a first filter paper 19, a cement-soil sample 20, a second filter paper 22, and a second permeable stone 23. The mold body is sealed by a threaded plug 25 at the top of the mold, and a second rubber ring 24 is installed between the mold body 21 and the threaded plug 25 at the top of the mold for sealing. The mold outlet 26 is located on the threaded plug 25 at the top and is connected to the exudate metering pipe 27 through a thin tube.

[0045] This invention provides a method for curing and testing the permeability coefficient of cement-soil samples using the aforementioned system for indoor testing and curing of cement-soil that considers groundwater seepage, comprising the following steps:

[0046] Step 1, determine the seepage pressure: The selection of seepage pressure is based on the groundwater seepage conditions in the representative strata of the on-site construction to ensure its authenticity and representativeness;

[0047] Step 2, Instrument Assembly: Assemble the components of the instrument, excluding the mold, according to the above device diagram;

[0048] Step 3, Cement-Soil Sample Loading: Install the first rubber ring on the plexiglass mold base, and place the first permeable stone and the first filter paper in sequence. Tighten the mold base knob and the mold body to ensure the lower part is sealed. Pour the prepared cement-soil into the mold and vibrate to compact it. After the cement-soil sample reaches the designated height of the mold, place the second filter paper and the second permeable stone in sequence on the top of the cement-soil sample. Install the second rubber ring on the threaded plug at the top of the mold and tighten it to ensure the upper part of the mold is sealed. Connect the mold water inlet switch and the pressure chamber outlet, and connect the outlet to the leachate metering pipe. The height of the cement-soil sample is H, and the cross-sectional area is A.

[0049] Step 4: Curing and Permeability Measurement of Cement-Soil Samples: Set the osmotic pressure to 0 using the data control and acquisition system. Then, turn on the air compressor and adjust the air source channel switches to connect the air compressor to the air inlet of the pressure chamber. Adjust the hydraulic switch to connect the water outlet of the pressure chamber to the curing and permeability system. Set the permeability pressure to the system value using the data control and acquisition system and start the test. The data control and acquisition system simultaneously reads the volume of permeate in the permeate metering tube. Calculate the permeability coefficient of the cement-soil sample.

[0050]

[0051]

[0052] In the formula, k The value is the permeability coefficient of the cement-soil sample, in cm / s. t The time interval between two readings, in seconds; Q for t The volume of exudate inside, i.e. t Internal data control acquisition system reading changes, unit: cm 3 H is the height of the cement-soil sample, in cm; A is the cross-sectional area of ​​the cement-soil sample, in cm². 2 ; Δh The total water head difference between the two sides of the cement-soil sample is expressed in cm. P Osmotic pressure, unit: Pa; ρ The density of the exudate is expressed in g / cm³. 3 .

[0053] The above description is merely a specific embodiment of the present invention, and while the description is quite specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that the scope of protection of the present invention is not limited thereto. For those skilled in the art, any equivalent substitutions or modifications made without departing from the concept of the present invention are all within the scope of protection of the present invention.

Claims

1. A method for curing and testing cement-soil indoors, taking into account groundwater seepage, using a permeability coefficient testing device, the testing device comprising: The pressure chamber body has an air inlet at the top and a water outlet at the bottom, and the pressure chamber body contains test water. An air source channel switch is provided with an air inlet, a first air outlet and a second air outlet. The first air outlet is connected to the air inlet through a first air pipe, the second air outlet is connected to the atmosphere through a second air pipe, and the air inlet is connected to the outlet of a pressure gauge through a third air pipe. The air inlet of the pressure gauge is connected to an air compressor and a data control and acquisition module through pipes. A hydraulic switch, comprising a first inlet, a second inlet, and an outlet, wherein the first inlet is connected to the outlet on the pressure chamber body via a first liquid pipe; the second inlet is connected to the outlet of a supply pipe via a second liquid pipe; the outlet is connected to a water inlet switch on a curing permeation mold via a third liquid pipe; and the outlet of the curing permeation mold is connected to an exudate metering pipe via a fourth liquid pipe; characterized by comprising the following steps: S1. Set the osmotic pressure to 0 through the data control and acquisition system, then turn on the air compressor, adjust the air source channel switch to connect the air compressor with the air inlet on the main body of the pressure chamber, and adjust the hydraulic switch to connect the water outlet on the main body of the pressure chamber with the maintenance osmotic system. S2. Set the permeation pressure to the system value using the data control and acquisition system and start the test. The data control and acquisition system simultaneously reads the volume of permeate in the permeate metering tube and calculates the permeability coefficient of the cement-soil sample. ， ， In the formula, k is the permeability coefficient of the cement-soil sample, in cm / s; t is the time interval between the two readings, in seconds; Q represents the volume of exudate within time t, i.e., the change in readings of the data control acquisition system within time t, in cm. 3 ; H represents the height of the cement-soil sample, in cm; A represents the cross-sectional area of ​​the cement-soil sample, in cm². 2 ; Δh represents the total water head difference between the two sides of the cement-soil sample, in cm; P is osmotic pressure, in Pa; ρ is the density of the exudate, in g / cm³. 3 ; S3. After the cement-soil sample has been cured to the specified age, the cement-soil sample is taken out and an unconfined compressive strength test is conducted to evaluate the strength characteristics of the cement-soil. When the liquid in the main body of the pressure chamber is insufficient, adjust the air source channel switch to connect the pressure chamber to the atmosphere, and adjust the hydraulic switch to connect the water outlet on the main body of the pressure chamber to the liquid supply pipe side, so as to replenish the liquid in the pressure chamber through the liquid supply pipe.

2. The method for curing and testing cement-soil using the indoor curing and permeability coefficient testing device considering groundwater seepage as described in claim 1, characterized in that, The main body of the pressure chamber is made of a transparent material.

3. The method for curing and testing cement-soil using the indoor curing and permeability coefficient testing device considering groundwater seepage as described in claim 1, characterized in that... The permeable mold for curing consists of a first permeable stone, a first filter paper, a cement-soil sample, a second permeable stone, and a second filter paper arranged sequentially according to the direction of water flow.

4. The method for curing and testing cement-soil indoor curing and permeability coefficient testing using the device for considering groundwater seepage as described in claim 1, characterized in that, The curing and penetration mold includes a cylindrical mold body with openings at the top and bottom, and a mold thread plug connected to the two opening ends of the cylindrical mold body. The cylindrical mold body is made of a transparent material.

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