WO2023040492A1

WO2023040492A1 - Device for indoor test of clogging characteristics of gravel pile drainage anti-liquefaction channel

Info

Publication number: WO2023040492A1
Application number: PCT/CN2022/109720
Authority: WO
Inventors: 陈平山; 梁小丛; 邱青长; 周红星; 王婧; 王德咏; 张璟泓
Original assignee: 中交第四航务工程局有限公司
Priority date: 2021-09-15
Filing date: 2022-08-02
Publication date: 2023-03-23
Also published as: CN113884423A

Abstract

A device for an indoor test of clogging characteristics of a gravel pile drainage anti-liquefaction channel. The device comprises: a soil sample chamber (1), which has a transparent cylinder structure with a closed bottom, wherein scales are provided on a side wall of the soil sample chamber to facilitate observation of movement and clogging states of a soil sample in the soil sample chamber (1); a vertical loading system, which comprises a reaction frame (2) and a pressure-applying mechanism (3), wherein the soil sample chamber (1) is arranged in the reaction frame (2), and the pressure-applying mechanism (3) is arranged on the reaction frame (2) and is used for applying a vertical pressure to the soil sample in the soil sample chamber (1); a pore pressure loading system, which is in communication with a water outlet (12) formed at the top of the soil sample chamber (1) and a water inlet (11) formed at the bottom of the soil sample chamber (1), and which is used for providing different pore pressures when the soil sample chamber (1) is subjected to permeability and clogging tests; and a power system, which provides a power source for the vertical loading system and the pore pressure loading system. The device has a simple structure and is convenient to operate, can observe the clogging morphology of a gravel pile drainage anti-liquefaction channel under the action of different confining pressures and pore pressure ratios, and can test a permeability coefficient after clogging is stabilized.

Description

A device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channel

technical field

The invention belongs to the field of foundation treatment drainage anti-liquefaction technology, and in particular relates to a device for indoor testing the clogging characteristics of drainage anti-liquefaction channels of gravel piles.

Background technique

For foundation treatment projects located in strong earthquake areas, gravel pile composite foundation drainage and anti-liquefaction foundation treatment is often used. The drainage and liquefaction resistance of gravel piles mainly provides vertical drainage channels in the foundation to quickly dissipate the excess pore water pressure generated by earthquakes. When a fixed replacement rate is selected, the permeability coefficient of the gravel pile is the key factor affecting the rapid dissipation of pore pressure, but the permeability coefficient of the drainage channel of the gravel pile is easily silted by the movement of surrounding soil particles, resulting in a decrease in the permeability coefficient of the pile body, which in turn affects the crushing capacity. Long-term service performance of stone pile drainage channels. In the design process of anti-liquefaction foundation treatment of gravel piles, a suitable drainage channel permeability coefficient is usually selected according to the gravel gradation. It has deviated from the original design value, so it is necessary to have a reasonable evaluation of the drainage performance after the drainage channel is blocked in the design stage.

At present, the common method to obtain the clogging characteristics of drainage channels is based on on-site core sampling, and carries out gradation analysis and permeability coefficient measurement indoors to evaluate the performance of drainage channels after clogging. However, the shape distribution of sand particle clogging cannot be observed due to disturbance samples , and the core sample gradation is also easily disturbed, and if the undisturbed sampling method is used, the cost is expensive. In addition, on-site sampling cannot obtain the clogging characteristics of the drainage channel under different confining pressure and pore pressure ratio.

Therefore, it is necessary to develop a convenient device for detecting the silting characteristics of drainage channels, which can accurately obtain the silting shape and permeability coefficient changes of piles by soil particles around drainage channels, and reasonably evaluate the drainage function of gravel piles after silting.

Contents of the invention

In view of this, the present invention provides a device for indoor testing the clogging characteristics of the drainage anti-liquefaction channel of the gravel pile, which can be used to observe the clogging of the anti-liquefaction channel of the gravel pile under different confining pressure and pore pressure ratio form, and can test the permeability coefficient after the clogging is stabilized.

The present invention is realized by the following technical solutions:

A device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channel, which includes:

The soil sample chamber is a transparent cylindrical structure with a closed bottom, with scales on the side walls, a permeable floor and a permeable partition inside, and the permeable partition is vertically arranged at the bottom of the soil sample chamber; the permeable bottom is located at The upper part of the permeable partition is used for filling soil samples; the top of the soil sample chamber is provided with a water outlet, and the bottom is provided with a water inlet;

The vertical loading system includes a reaction frame and a pressurization mechanism, the soil sample chamber is placed in the reaction frame, the pressurization mechanism is arranged on the top of the reaction frame, and penetrates the reaction frame and the soil The soil sample in the sample chamber contacts to apply vertical pressure to the soil sample;

A pore pressure loading system communicated with the water outlet and the water inlet for providing different pore pressures when the soil sample chamber is used for seepage clogging tests;

The power system is electrically connected to the vertical loading system and the pore pressure loading system respectively, and provides power sources for the vertical loading system and the pore pressure loading system.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention uses a transparent cylinder as the experimental device, which has good stability and is not easily disturbed by the external environment. It can facilitate the observation of the shape distribution of sand particles and the movement and convergence of soil samples under different pressures. Obtain the relationship between silting thickness and time, effectively reducing experimental errors.

2. The present invention uses a soil sample chamber combined with a vertical loading system and a pore pressure loading system, which can apply confining pressure and pore pressure to soil samples at the same time, and can be used to simulate environmental conditions at different depths and different pore pressures, and test soil samples The permeability coefficient of the combination under different confining pressure and pore pressure.

Further, the reaction force frame includes a bottom plate, a top plate and several reaction force rods, the two ends of the reaction force rods are respectively fixedly connected to the top plate and the bottom plate, and there is also a hole on the top plate that allows the pressurization mechanism to pass through through holes. The function of the reaction force frame is to provide support reaction force for the pressurization mechanism and support the pressurization mechanism. The top plate and the bottom plate are spirally connected by a plurality of reaction force rods to form a reaction force frame. The soil sample chamber is put into it from the top of the reaction force frame, and the pneumatic cylinder in the pressurizing mechanism is set on the top of the reaction force frame. Apply vertical pressure.

Further, the pressurizing mechanism includes a pneumatic cylinder, a dowel rod and a water-permeable loading plate; the pneumatic cylinder is arranged on the top plate, and its bottom is fixedly connected to the top plate and covers the through hole; the water-permeable The loading plate is arranged in the soil sample chamber; one end of the dowel rod is arranged in the air cylinder, and the other end enters the soil sample chamber through a through hole, and is fixedly connected with the permeable loading plate arranged above the soil sample. The pneumatic cylinder is set on the top of the reaction frame, and the pressure value is applied by the power system. The vertical pressure on the soil sample is realized through the dowel rod and the permeable loading plate, and the confining pressure of the soil sample at different depths can be simulated.

Further, the pore pressure loading system includes a water tank, a gas-liquid converter, and a measuring cylinder; the water tank is communicated with the gas-liquid converter through a three-way switch to realize air pressure conversion to water pressure, and the other port of the three-way switch is connected to to the water inlet at the bottom of the soil sample chamber; the measuring cylinder is used to receive the water discharged from the water outlet at the top of the soil sample chamber. The water tank and gas-liquid converter are connected to the soil sample chamber through a three-way switch to realize the interconnection and closure of the water tank, gas-liquid converter and soil sample chamber; during the test, the operator first rotates the three-way switch Connect the soil sample chamber and the water tank. The water in the water tank enters the soil sample chamber from the water inlet at the bottom of the soil sample chamber. When the water overflows the soil sample and overflows from the water outlet, turn the three-way switch to connect the gas-liquid converter and the soil sample chamber. , the power system provides test air pressure to the gas-liquid converter. At the same time, the water in the gas-liquid converter flows into the soil sample chamber under the action of air pressure, and flows out from the water outlet to the measuring cylinder. During this process, the soil sample is observed in the hole Mobile silting under pressure and record relevant data.

Further, the power system adopts a double-outlet air compressor, one of which is connected to a pneumatic cylinder, and the other is connected to a gas-liquid converter.

Further, between the double outlet air compressor and the pneumatic cylinder, between the double outlet air compressor and the gas-liquid converter, there are pneumatic regulators and air pressure gauges connected in series. The function of the pneumatic regulator is to stabilize the pressure and cooperate with the barometer to precisely control the pressure value applied to the pneumatic cylinder and the gas-liquid converter.

Further, the permeable base plate is welded and fixed to the permeable partition, and a permeable stone layer is laid on the permeable base plate. The permeable bottom plate and the permeable partition are welded to form an assembly with a certain cavity. The permeable bottom plate and the permeable partition can be moved out of the soil sample chamber freely, which is convenient for cleaning the residual sand particles at the bottom of the barrel after the test. The assembly is placed at the bottom of the soil sample chamber, and the water inlet of the soil sample chamber is opened in the formed cavity. The water enters the soil sample chamber from the bottom, flows through the assembly, the permeable stone, the soil sample, the permeable loading plate in turn, and finally flows from the exit The spout overflows into the graduated cylinder. The cavity formed by the permeable bottom plate and the permeable partition can ensure that the water pressure is evenly applied to the bottom of the soil sample, and can transmit the pressure loaded on the upper part. The permeable stone layer placed on the bottom plate can transmit the pore pressure and prevent the sand from scattering.

Further, the pressurizing mechanism further includes a pressure sensor, and the pressure sensor is fixed on the dowel rod to measure the pressure of the dowel rod. The pressure sensor is arranged on the dowel rod, and the load is applied in feedback.

Further, a limiting groove with the same diameter as the soil sample chamber is opened on the bottom plate for centering and positioning of the soil sample chamber. The soil sample chamber is placed in the limit groove to prevent left and right movement and reduce test errors.

Further, one end of the reaction rod is provided with an external thread, and the edge of the bottom plate is provided with an internal thread matching the reaction rod, and the reaction rod and the bottom plate are screwed and fixedly connected by an external thread; the top plate A round hole corresponding to the reaction pull rod is opened on the top, and the other end of the reaction pull rod passes through the round hole and is fixedly connected with the top plate through a nut.

Description of drawings

Fig. 1 is the structural representation of test device of the present invention;

Fig. 2 is the top view of the water-permeable bottom plate in the test device of the present invention;

Fig. 3 is the side view of the water-permeable partition in the test device of the present invention;

Fig. 4 is the structural representation of reaction force frame in the test device of the present invention;

Fig. 5 is a side view of the reaction force frame in the test device of the present invention.

Among them, the description of the drawings, 1-soil sample chamber; 2-reaction frame; 3-pressurization mechanism; 4-air-liquid converter; 5-water tank; Press machine; 9-pneumatic regulator; 10-barometer; 11-water inlet; 12-water outlet; 13-permeable floor; 14-permeable partition; 15-permeable stone; -Reaction rod; 24-Nut; 25-Limiting card slot; 31-Pneumatic cylinder; 32-Drop rod; 33-Permeable loading plate; 34-Pressure sensor; Tank outlet.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings, but the described embodiments are only part of the embodiments of the present invention, not all embodiments, and the scope of protection of the present invention is not limited to this.

Please refer to Fig. 1, the present invention provides a kind of device that is used for indoor testing anti-silting characteristics of gravel pile drainage and liquefaction channel, which is composed of four parts: soil sample chamber 1, vertical loading system, pore pressure loading system and power system;

The soil sample chamber 1 is a transparent cylindrical structure with a closed bottom, with a scale on the wall, a water outlet 12 on the top side wall, a water inlet 11 on the bottom side wall, and a permeable floor 13 and a permeable partition inside. 14. The permeable bottom plate 13 and the top of the permeable partition 14 are welded into an assembly and placed at the bottom of the soil sample chamber 1. The permeable partition 14 separates the permeable bottom plate 13 from the bottom of the soil sample chamber 1 to form a certain cavity, as shown in the figure 2 and FIG. 3; the water inlet 11 of the bottom side wall of the soil sample chamber 1 is opened in the formed cavity, and water enters the soil sample chamber 1 from the bottom, and gradually overflows the soil sample and overflows from the water outlet 12. In addition, the cavity formed by the permeable partition 14 can ensure that the water pressure is evenly applied to the bottom of the soil sample 1, and can transmit the pressure loaded on the upper part. The permeable stone 15 is placed on the permeable bottom plate 13. While transmitting the pore pressure, It can prevent sand and soil from scattering.

The soil sample chamber 1 of this embodiment adopts a transparent plexiglass cylinder with a closed bottom, with an inner diameter of 300 mm, an inner height of 400 mm, and a wall thickness of 10 mm. Referring to the "Standards for Geotechnical Test Methods" (GBT50123-2019), the penetration test cylinder The ratio of the inner diameter to the maximum particle diameter should not be less than 5:1, so the cylinder of this embodiment can be used to test crushed stones with a maximum particle diameter of 60 mm.

The vertical loading system includes a reaction force frame 2 and a pressurizing mechanism 3, and the reaction force frame 2 has a circular top plate 22, a bottom plate 21 and eight reaction force pull rods 23, as shown in Fig. 1, Fig. 4 and Fig. 5 As shown, the top plate 22 is evenly provided with a circular hole matching the reaction force rod 23 along the circumference, and one end of the reaction force rod 23 is fixedly connected to the nut 24 on the top plate 22 through the circular hole, thereby being connected and fixed to the top plate 22, The other end is provided with an external thread, and the corresponding position of the bottom plate 21 is provided with an internal thread matching the external thread. The other end of the reaction force rod 23 is screwed and fixed with the bottom plate 21 to form a reaction force frame 2 as a whole, which is a pressurization mechanism. 3. Provide support reaction force; the pressurizing mechanism 3 includes a pneumatic cylinder 31, a dowel bar 32 and a permeable loading plate 33. The pneumatic cylinder 31 is fixed at the middle position of the top plate 22 of the reaction force frame, and the top plate 22 is provided with an allowable force transmission The through hole through which the rod 32 passes is set at the center of the top plate 22, one end of the dowel rod 32 is set in the pneumatic cylinder 31, and the other end passes through the through hole and is fixedly connected to the permeable loading plate 33 placed above the soil sample; The frame 2 provides the support reaction force for the pneumatic cylinder 31, and the dowel rod 32 and the permeable loading plate 33 exert vertical pressure on the soil sample, simulating the confining pressure of the soil sample at different depths.

In this embodiment, the top plate 22 adopts a circular steel plate with a diameter of 480 mm and a thickness of 20 mm, and 8 circular holes with a diameter of 20 mm are evenly distributed on its circumference; the bottom plate 21 adopts a steel plate with a thickness of 50 mm, and there are 20mm in diameter and 30mm in depth internal thread; the reaction pull rod 23 is a high-strength pull rod with a diameter of 20mm.

In this embodiment, the permeable loading plate 33, the permeable bottom plate 13 and the permeable partition 14 are all made of perforated steel plates with a thickness of 10 mm, a perforation rate of 40%-60%, and a perforation diameter of 2 mm to ensure that the soil samples The water in chamber 1 flowed over all soil samples without hindrance.

In one embodiment, the bottom plate 21 of the reaction force frame 2 is provided with a limiting slot 25 with a depth of 2 mm, the diameter of which is consistent with the diameter of the soil sample chamber 1, and the center point of the limiting slot 25 is located at the center of the bottom plate 21. , when in use, the soil sample chamber 1 is placed in the limit card slot 25, which is not easy to move, so as to avoid external influences during the test process and cause test deviations.

In one embodiment, a pressure sensor 34 is also provided on the dowel bar 32, and the pressure sensor 34 can monitor the pressure of the dowel bar 32 at any time and collect data for subsequent data processing.

The pore pressure loading system includes a water tank 5, a gas-liquid converter 4 and a measuring cylinder 7; as shown in Figure 1, the water tank 5, the gas-liquid converter 4 and the water inlet 11 of the soil sample chamber 1 are connected through a three-way switch 6 , realize the interconnection and closure among the water tank 5, the gas-liquid converter 4, and the soil sample chamber 1; water.

Preferably, the outlet 51 of the water tank is at the same height as the top of the gas-liquid converter 4 .

Described power system adopts double outlet air compressor 8, and its outlet is connected to pneumatic cylinder 31, provides pressure for pneumatic cylinder 31, and the other outlet is connected to gas-liquid converter 4, provides air pressure for gas-liquid converter 4, and Between the double-export air compressor 8, the pneumatic cylinder 31 and the gas-liquid converter 4, there are also a pneumatic regulator 9 and a barometer 10 in series, and the pneumatic cylinder 31 is connected in series with the double-export air compressor 8 through the pneumatic regulator 9, The pressure value applied to the soil can be precisely controlled. The gas-liquid converter 4 is connected in series with the double-exit air compressor 8 through the pneumatic regulator 9 to realize the gas-liquid conversion, and convert the air pressure into water pressure, and cooperate with the barometer 10 to precisely apply Pore pressure.

Based on such scheme, the test process of the present invention is as follows:

1) Take out the soil sample chamber 1, place the permeable bottom plate 13, the permeable partition plate 14 assembly, and the permeable stone 15 in order, and lay sand and gravel layers in layers, and place the soil sample chamber 1 on the bottom plate of the reaction force frame In the limiting groove 25 of 21, adjust the dowel bar 32 and the permeable loading plate 33 to make it contact with the top surface of the gravel soil; 12 overflow for 1-2 minutes to fully saturate the soil, then rotate the three-way switch 6 to connect the water tank 5 and the gas-liquid converter 4, open the gas-liquid converter vent hole 41, wait until the water level of the gas-liquid converter 4 is in line with the water tank 5 When the water level is equal, close the tee and open 6.

2) Start the double outlet air compressor 8, open the switch connected with the vertical loading system, apply a fixed pressure value through the pneumatic constant value device 9, provide the test confining pressure value, and turn on the double outlet air compressor 8 after the compressed soil is stable Connect the switch with the pore pressure loading system, apply a fixed pressure value through the pneumatic regulator 9, and provide the pore pressure for the test, and at the same time rotate the three-way switch 6 to connect the gas-liquid converter 4 and the soil sample chamber 1. At this time, the gas-liquid converter 4 The water in the soil flows into the soil sample chamber 1 under the action of excess pore pressure. According to the sequence from bottom to top, the water flows through the permeable bottom plate 13, the permeable stone 15 and the permeable loading plate 33 respectively, overflows from the water outlet 13, and flows into the measuring cylinder 7.

3) When the overflow of the water outlet 13 is stable, the slow movement of sand particles under the action of excess pore pressure can be observed and the clogging process can be observed. The thickness of the clogging layer H ₂ can be recorded at a certain interval during the observation. When the clogging height no longer changes , start to use a stopwatch to record the flow received by the measuring cylinder 7 per unit time, repeat the measurement three times, and calculate the permeability coefficient K at this time.

Before the start of the test, the permeability coefficient K ₁ of sandy soil and the permeability coefficient of gravel soil K ₃ were respectively obtained, and according to the principle of water flow continuity of vertical seepage, the soil layer was regarded as sand layer, silting layer and gravel layer respectively, and the height could be measured Obtained as H ₁ and H ₃ , the flow rate through each soil layer is the same as the flow rate through the equivalent soil layer, and the permeability coefficient K ₂ of the silting layer can be calculated. According to the thickness H ₂ of the clogging layer and the permeability coefficient K ₂ obtained, the anti-liquefaction characteristics of the drainage channel after clogging can be evaluated.

As can be seen from the above, the test device provided by the present invention is equipped with a vertical loading system and a pore pressure loading system at the same time, which can realize simultaneous application of confining pressure and pore pressure to soil samples, and facilitate testing of gravel drainage channels under different confining pressures and pore pressures The thickness of the silting and the permeability coefficient after the silting is stable can be used to reasonably evaluate the drainage function of the gravel pile after silting.

The test device provided by the invention is easy to operate, has good stability, can carry out gradation analysis and permeability coefficient measurement indoors to evaluate the performance of the drainage channel after clogging, is not affected by the environment of the construction site, and can be popularized and used.

The above descriptions are only part of the embodiments of the present invention, and are not intended to limit the implementation and protection scope of the present invention. For those skilled in the art, they should be able to realize that all equivalent replacements made by using the content of the description of the present invention are obvious and obvious The scheme obtained by the change should be included in the protection scope of the present invention.

Claims

A device for indoor testing the anti-clogging characteristics of drainage channels of crushed stone piles, characterized in that it includes:

The soil sample chamber is a transparent cylindrical structure with a closed bottom, with scales on the side walls, a permeable floor and a permeable partition inside, and the permeable partition is vertically arranged at the bottom of the soil sample chamber; the permeable bottom is located at The upper part of the permeable partition is used for filling soil samples; the top of the soil sample chamber is provided with a water outlet, and the bottom is provided with a water inlet;

The vertical loading system includes a reaction frame and a pressurization mechanism, the soil sample chamber is placed in the reaction frame, the pressurization mechanism is arranged on the top of the reaction frame, and penetrates the reaction frame and the soil The soil sample in the sample chamber contacts to apply vertical pressure to the soil sample;

A pore pressure loading system communicated with the water outlet and the water inlet for providing different pore pressures when the soil sample chamber is used for seepage clogging tests;

The power system is electrically connected to the vertical loading system and the pore pressure loading system respectively, and provides power sources for the vertical loading system and the pore pressure loading system.
According to claim 1, a device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channel, characterized in that, the reaction force frame includes a bottom plate, a top plate and several reaction force rods, and the reaction force Both ends of the pull rod are respectively fixedly connected to the top plate and the bottom plate, and a through hole is opened on the top plate to allow the pressurizing mechanism to pass through.
According to claim 2, a device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channel, characterized in that, the pressurization mechanism includes a pneumatic cylinder, a dowel rod and a water-permeable loading plate; the air pressure The cylinder is set on the top plate, the bottom of which is fixedly connected to the top plate, and covers the through hole; the permeable loading plate is set in the soil sample chamber; one end of the dowel rod is set in the pneumatic cylinder , and the other end enters the soil sample chamber through the through hole, and is fixedly connected with the permeable loading plate arranged above the soil sample.
According to claim 1, a device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channels, characterized in that, the pore pressure loading system includes a water tank, a gas-liquid converter and a measuring cylinder; the water tank and The gas-liquid converter is connected through a three-way switch to realize air pressure conversion to water pressure. The other port of the three-way switch is connected to the water inlet at the bottom of the soil sample chamber; the measuring cylinder is used to receive water from the top water outlet of the soil sample chamber. drained water.
According to claim 3 or 4, a device for indoor testing the anti-clogging characteristics of drainage and liquefaction channels of gravel piles is characterized in that the power system adopts a double-outlet air compressor, one of which is connected to a pneumatic cylinder, The other outlet is connected to the gas-liquid converter.
According to claim 5, a device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channel, characterized in that, between the double-outlet air compressor and the pneumatic cylinder, the double-outlet air Between the compressor and the gas-liquid converter, a pneumatic regulator and a barometer are connected in series.
According to claim 1, a device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channels, characterized in that the permeable bottom plate and the permeable partition are welded and fixed, and the permeable bottom plate is laid with Permeable stone layer.
The device for indoor testing the anti-clogging characteristics of gravel pile drainage and liquefaction channel according to claim 3, characterized in that, the pressurizing mechanism also includes a pressure sensor, and the pressure sensor is fixed on the force transmission rod to measure dowel rod pressure.
According to claim 2, a device for indoor testing the anti-clogging characteristics of drainage and liquefaction channels of gravel piles, characterized in that, the bottom plate is provided with a limit groove with the same diameter as the soil sample chamber, It is used for the centering and positioning of the soil sample chamber.
According to claim 2, a device for indoor testing the anti-silting characteristics of gravel pile drainage and liquefaction channel, characterized in that, one end of the reaction force rod is provided with an external thread, and the edge of the bottom plate is provided with a The internal thread matched with the reaction force rod, the reaction force rod and the bottom plate are fixedly connected by the external thread screw; the top plate is provided with a round hole corresponding to the reaction force rod, and the other end of the reaction force rod passes through the circle The hole is fixedly connected with the top plate by a nut.