CN112255390B - Centrifugal model test device and method for simulating reservoir bank slope instability induced by water level fluctuation - Google Patents
Centrifugal model test device and method for simulating reservoir bank slope instability induced by water level fluctuation Download PDFInfo
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Abstract
The invention discloses a centrifugal model test device and a method for inducing instability of a bank side slope by simulating water level fluctuation.A bank water level simulation area is formed between the waterside side of the side slope and the inner wall of a model box, a water inlet is formed on the top wall of the model box of the bank water level simulation area, an overflow port and a water outlet are sequentially formed on the side wall of the model box of the bank water level simulation area from top to bottom, and an electromagnetic valve A is arranged at the water outlet; a triangular support is arranged between the backwater side of the side slope and the inner wall of the model box, the bottom edge of the triangular support is supported on a support, an underground water level simulation area is formed between the backwater side of the side slope and the inner wall of the model box, a communicating pipe is fixedly connected to the support and is communicated with the reservoir water level simulation area and the underground water level simulation area, and a miniature pressure type water level sensor is arranged inside the side slope. The invention can simulate the reservoir water level elevation, the fluctuation speed and the stable angle of repose, can ensure that the test result can truly reflect the deformation and the stability of the bank slope of the actual reservoir, and has better reference significance for the slope maintenance and reinforcement technology.
Description
Technical Field
The invention relates to the field of geotechnical engineering, in particular to a centrifugal model test device and method for simulating reservoir bank slope instability induced by water level fluctuation.
Background
In order to meet the requirement of flood control and fully develop water conservancy and hydropower resources, a large number of hydropower projects are built in China for decades. The construction of the reservoir dam changes the hydrological characteristics of the original river basin, and the fluctuation of the upstream water level of the reservoir changes the stress characteristics of the bank side slope soil body, so that the instability of the bank side slope is caused. The soil body of the bank slope is saturated with water, the physical mechanical strength is reduced, and the change of the bank topography is finally caused under the action of the periodical back-and-forth seepage, so that the repose angle of a certain angle is formed.
The dynamic development process of the deformation of the soil bank slope induced by the periodic fluctuation of the reservoir water is a process of repeatedly changing and continuously adjusting the dynamic and static water pressure in the slope body, and a common physical model test is difficult to simulate a real stress environment, so most students usually adopt a centrifugal model test method to research the evolution and deformation damage of the bank slope.
However, the existing side slope centrifugal model test device and method have the defects of single model structure, low repeatability, inconsistency between test operation and actual conditions and the like. The application number is 2018106427390, the invention name is Chinese invention patent application of a physical model for simulating underground water to induce soil slope instability, only the influence of underground water level lifting on a bank side slope is considered, the actual reservoir operation condition is ignored, and the influence effect of repeated circulation fluctuation of the bank water level on the side slope cannot be realized. In the centrifugal model device disclosed in the application, the water tank is arranged on one side of the model box, so that the centrifugal machine is easy to wear when running at high speed, and the device is difficult to ensure continuous supply of water flow under the action of centrifugal force generated by high-speed rotation of the centrifugal machine and is difficult to realize conversion from a 1g gravity field to Ng gravity field water flow.
Disclosure of Invention
The invention aims to provide a centrifugal model test device and a centrifugal model test method for simulating water level fluctuation to induce bank side slope instability aiming at the engineering problem of bank side slope instability damage under the condition of bank water fluctuation, which can truly simulate the influence of the bank water level fluctuation on the slope stability, lead the test conclusion to be closer to the actual situation and provide a theoretical basis for slope stability reinforcement and disposal.
In order to achieve the purpose, the invention adopts the technical scheme that:
a centrifugal model test device for simulating water level fluctuation to induce reservoir bank side slope instability comprises a model box, wherein a support is arranged at the bottom of the model box, a side slope model is arranged on the support, the water side of the side slope is an inclined plane, a reservoir water level simulation area is formed between the water side of the side slope and the inner wall of the model box, a water inlet is formed in the top wall of the model box of the reservoir water level simulation area, an overflow port and a water outlet are sequentially formed in the side wall of the model box of the reservoir water level simulation area from top to bottom, and a solenoid valve A is arranged at the water outlet; a triangular support is arranged between the backwater side of the side slope and the inner wall of the model box, the bottom edge of the triangular support is supported on a support, an underground water level simulation area is formed between the backwater side of the side slope and the inner wall of the model box, a communicating pipe is fixedly connected onto the support, an electromagnetic valve B is arranged on the communicating pipe, the communicating pipe communicates the reservoir water level simulation area and the underground water level simulation area, and a miniature pressure type water level sensor is arranged inside the side slope.
The device also comprises a data acquisition system which comprises a data acquisition module on the rotating arm of the centrifuge, an image monitoring system and a ground industrial personal computer and can synchronously acquire strain signals, video signals and voltage signals. The water level and deformation conditions of the side slope can be obtained by installing the miniature pressure type water level sensor in the side slope model, the high-speed high-definition camera installed in the model box can extract video images frame by frame, test details are analyzed, and the ground industrial personal computer can realize real-time control, acquisition and storage of monitoring data. Since the data acquisition system is the prior art, it is not described herein in detail.
The overflow port, the support and the electromagnetic valve jointly form an automatic water level control system.
And after the support is installed, anti-seepage quick-drying glue is coated on the joint of the support, the triangular support and the communicating pipe so as to ensure that water stored in the support structure flows into the side slope model in a one-way manner.
The invention utilizes the space-time amplification effect generated by the centrifuge to ensure that the model and the prototype side slope are in the same stress state, and can simulate the reservoir water level elevation, the fluctuation speed and the stable repose angle, thereby ensuring that the test result can truly reflect the deformation and the stability of the actual reservoir bank side slope and having better reference significance for the side slope maintenance and reinforcement technology.
Furthermore, a stainless steel plate is arranged on the backwater side of the side slope, a stainless steel net is further arranged on the stainless steel plate, and the stainless steel net is fixed on the stainless steel plate through a triangular support.
The stainless steel plate of the backwater side is provided with a plurality of round holes with the diameter of 3mm, so that the water permeating effect is achieved, and the triangular support is made of 304 stainless steel and plays a supporting role. The stainless steel net is preferably 200 meshes, so that fine particles in the slope model can be prevented from reversely sliding into the water storage structure through the opening.
Preferably, one end of the communicating pipe, which is positioned in the reservoir water level simulation area, is provided with a filter screen.
The communicating pipe and the electromagnetic valve B keep the water levels at the two sides of the slope model at a preset height by utilizing the communicating vessel principle, and the pipeline at one side of the water inlet of the communicating pipe is additionally provided with a filter screen to prevent the flushed soil sample from blocking the pipeline.
Preferably, the solenoid valve a is a japanese TACO two-in-one combination solenoid valve. The electromagnetic valve is driven by the built-in PLC control module, the analog quantity output module is connected to a controller of the electromagnetic valve, when a large valve of the electromagnetic valve A is closed and the predicted leakage flow is input, the control module can convert the large valve into a corresponding current or pulse signal, and the controller can control the opening of a small valve according to the received signal so as to meet the requirement on control precision. Usually, the control opening is determined by superposing the input signal by a negative feedback signal, and the whole control process is not influenced by the supergravity field and can quickly respond to the control signal.
The electromagnetic valve A adopts a duplex combination and is composed of a big valve, a small valve and a big valve, the big valve is opened to enable water flow to be discharged in a short time, and the small valve can further control the discharging precision.
Preferably, the support at the bottom of the model box is an impermeable steel plate.
Preferably, the downstream face of the overflow outlet is at an angle, preferably 20 to 30, to the upstream face. The water can be quickly drained to control the maximum water level in the model box.
Preferably, gaps are reserved among the bottom of the reservoir water level simulation area, the support and the side wall of the model box to form a grit chamber. To protect the equipment such as pipes in the mold box from wear and blockage.
A centrifugal model test method for simulating reservoir bank slope instability induced by water level fluctuation comprises the following steps:
(1) determining the similarity ratio N of the centrifugal model and the on-site slope by combining the scale of the prototype slope, the on-site form and the load capacity condition of the centrifugal machine; surveying rock soil samples of the on-site side slope and hydrographic water environment conditions, measuring the density, the grain composition, the water content, the compressibility and the permeability coefficient of rock soil materials, and configuring bedrocks and filling materials which have the physical and mechanical properties similar to those of the on-site side slope;
before making the model, it is necessary to analyze the geological data of the prototype landslide, such as the material properties and the problem of boundary conditions, so as to be as close as possible to the prototype landslide when making the model. Data such as reservoir water level elevation, slope ratio and hydrological data where the prototype side slope is located need to be collected and analyzed so as to be as same as conditions where the prototype side slope is located as possible. Orthogonal compounding tests are usually designed to ultimately determine similar materials and compounding ratios. Most of the slope bedrock is sandstone, and the materials are generally made of barite powder, cement and gypsum. The covered soil body material is roughly divided into sandy cohesive soil and gravelly cohesive soil, the sandy soil can be directly used as the field soil material of the prototype side slope, and the gravelly soil is generally selected from quartz sand, cement, gypsum and borax which are mixed with water. The binder is generally prepared by mixing gypsum, cement and water. The used rock and soil materials need to be sieved before the test so as to ensure that all the particle sizes are uniformly mixed.
(2) According to the determined similarity ratio N, a model box corresponding to the reservoir water flow and size is prepared, and a water inlet pipe, a support and a water storage structure are installed in the model box;
and designing the model box according to the determined similarity ratio N, wherein the shell of the box body is made of an aluminum alloy material, so that the rigidity is extremely high, and deformation is hardly generated. The size of the model box is consistent with that of a water storage tank of a water supply system. Wherein water supply system supplies water simultaneously through setting up 4 storage water tanks at the centrifuge is outdoor, supplies water to incasement storehouse water level simulation district through the water inlet at model roof portion, utilizes to connect water ring and the coaxial rotation of centrifuge pivot, can guarantee continuously supplying of rivers under high-speed rotatory condition, also can guarantee overall structure's safety and stability, can overcome prior art well water tank and establish in model case one side, takes place the technical problem of wearing and tearing easily when centrifuge high-speed operation.
(3) Preparing a model in a model box according to the actual shape of a prototype side slope, embedding monitoring equipment in the side slope model, hoisting and fixing the model box on a centrifuge hanging basket after the model is made, mounting a high-definition camera on the hanging basket and connecting a data acquisition system, and testing whether each monitoring device can work normally;
according to the data model measured on site, the soil slope with rock mass and without rock mass in the deep layer can be divided. For the bank slope with rock mass in the deep layer, firstly, materials such as barite powder, cement and the like are mixed, poured and vibrated at the bottom of the model box, and the mixture is kept still for 24 hours to be solidified and molded. The upper soil body filling is consistent with the deep rock-free soil slope, a layered filling method is adopted, the stacking height of each layer is 4cm, the soil body with certain water content and uniform mixing is uniformly spread by a quality control method, and a planar tamping plate is adopted to tamp to a preset height under the action of a certain tamping force. And (3) performing scraping treatment between every two layers of filling soil, spraying a layer of adhesive on every filling layer, and burying corresponding monitoring equipment when the landslide model is filled to the height of the sensor mark. The sensor should be embedded closely in contact with the model material, and the power line and the sensor lead should be bent to be fixed on the guide rod of the rotating arm or the peripheral wall of the model box in a snake shape so as to prevent the sensor from being broken by force. Two similar sensors are arranged on the same measuring point in parallel as far as possible, so that mutual checking is facilitated. The contact surface between the side wall of the model box and the model is provided with measures, and silicone oil or vaseline can be coated to reduce the friction resistance.
After the model box is hoisted into the hanging basket, linearity test and conversion coefficient calibration are required to be carried out on the sensor so as to test whether the monitoring device can work normally. A high-definition camera is respectively arranged at the top of the model box and right in front of the downstream slope so as to monitor the development process of the slope under the action of water level fluctuation of the reservoir in real time.
(4) After the centrifugal machine is weighted, the centrifugal machine starts to accelerate step by step, so that the model and the prototype side slope are in the same stress state; after the centrifugal acceleration is stabilized to the target acceleration, a water supply system is started, water is injected into the reservoir water level simulation area through a water inlet in the top of the model box, the electromagnetic valve A is closed, and the electromagnetic valve B is opened, so that the two sides of the slope model, the reservoir water level simulation area and the underground water level simulation area are kept at higher water levels;
(5) after the change of the pore water pressure in the side slope model tends to be stable, controlling the flow of the electromagnetic valve A to be increased, wherein the discharge flow of the electromagnetic valve A is larger than the water inlet flow of a water supply system, closing the electromagnetic valve B, reducing the water level of the reservoir water level simulation area at a certain speed, and simulating the rapid falling process of the water level when the reservoir soaks;
the reservoir level and the reservoir fluctuation time have N times of similarity ratio in the centrifuge, so the average fluctuation speed at one side of the reservoir level is consistent with the maximum average fluctuation speed measured on site.
And closing the electromagnetic valve in the support, opening the electromagnetic valve A, adjusting the water discharge flow of the electromagnetic valve A to be larger than the water inlet flow, and keeping the water level to be lowered to the bottom elevation of the electromagnetic valve A at an expected speed. The changes of water level, pore pressure and repose angle in the slope model can be recorded through the internal sensor and the external identification point coordinates. The output signal of the pressure type water level sensor is a voltage signal, and the pressure type water level sensor can be directly connected to a voltage signal acquisition module of a centrifuge data acquisition system for data acquisition. The deformation and damage conditions of the side slope can be observed by adopting an image acquisition and displacement measurement system in the centrifuge.
The specific falling water level and speed can be controlled by the output water flow in the electromagnetic valve, and the calculation formula is as follows:
wherein Q isIntoIs the inflow (fixed flow in the test process) of cm3/min；QGo outFor the discharge flow (adjustable by a solenoid valve during the test), cm3/min；SvThe measured fluctuation speed of the reservoir water level (the rising of the reservoir water level is negative, and the falling of the reservoir water level is positive) is cm/min; b is a modelThe width of the inner diameter of the box is cm; z is the distance between the slope toe and the wall of the model box, namely cm; delta h is the fluctuation range of the water level, cm; alpha is the slope angle of the model slope.
(6) After the change of the pore water pressure in the side slope model tends to be stable, controlling the flow of the electromagnetic valve A to be reduced, wherein the discharge flow of the electromagnetic valve A is smaller than the water inlet flow of a water supply system, so that the water level of the reservoir water level simulation area is lifted at a certain speed, and the rapid rising process of the water level when a reservoir stores water is simulated;
keeping the electromagnetic valve B closed, adjusting the water discharge quantity of the electromagnetic valve A to be smaller than the water inlet flow, calculating the reservoir water level at a certain speed according to the formula (1), rising to the bottom elevation of the overflow port and keeping the water level stable. And (5) the underground water level simulation area generates a back drop after going through the step (5), the electromagnetic valve B is kept closed, and seepage from the reservoir simulation area to the underground water level simulation area is formed by the existence of water level difference on two sides of the model. And recording the changes of the water level, the pore pressure and the repose angle in the slope model through the coordinates of the internal sensor and the external identification point, so that one-time back-and-forth seepage circulation is realized.
(7) And (4) after the pore water pressure is basically kept stable, opening the electromagnetic valve B to lift the water level of the underground water level simulation area to the initial height, and repeating the steps (4) to (7) to simulate the influence of the periodic back-and-forth seepage on the bank side slope.
In the test process, the water supply system is filled with water all the time, and the water supply system is closed after the test is finished.
In order to simulate the influence of multiple cyclic fluctuation of the reservoir water level on the reservoir bank slope, the variation amplitude of the slope repose angle is calculated in the water level fluctuation process, if the variation amplitude of the two fluctuations is less than 10%, the test can be stopped, and test data are recorded.
Compared with the prior art, the invention has the beneficial effects that:
the invention designs a reservoir water level simulation area and an underground water level simulation area, simulates the multiple cyclic fluctuation of the reservoir water level through an overflow port and an electromagnetic valve, simulates the influence of the multiple cyclic fluctuation of the reservoir water level on the instability of the side slope, and better reflects the actual condition of the reservoir.
The automatic water level control system formed by the overflow port, the electromagnetic valve and the like in the model box can accurately adjust the height of the water level inside and outside the slope and the rising and falling speed, the process of driving the electromagnetic valve by the control module is not influenced by a supergravity field, and the automatic water level control system can quickly respond to a control signal so as to meet the requirements of control speed and precision.
According to the invention, the water level change of the side slope model under the action of multiple reservoir water level fluctuation and the water pressure at different moments can be accurately obtained through the miniature pressure type water level sensor, the change condition of the repose angle of the side slope model can be visually described by the aid of a high-definition image, and a basis is provided for engineering such as slope cutting reinforcement.
The water supply system is arranged outside the centrifuge chamber and supplies water into the model box uninterruptedly, so that the abrasion of the centrifuge in the high-speed rotation process is reduced, the actual test operation is safer and more stable, and the water supply speed can be adjusted manually.
The invention has important guidance and practical value for the reinforcing and disposing engineering of the bank side slope.
Drawings
The invention will be further described in detail with reference to the drawings and the detailed description, in which:
FIG. 1 is a flow chart of a centrifugal model test device and method for simulating reservoir bank slope instability induced by water level fluctuation according to the present invention;
FIG. 2 is a perspective view of the mold of the present invention;
FIG. 3 is a front view of a mold box according to the present invention;
FIG. 4 is an automatic reservoir level control system according to the present invention;
FIG. 5 is a structure of a stainless steel plate;
FIG. 6 is a structure of a triangular bracket;
the labels in the figure are: 1. model box, 2, solenoid valves A, 3, solenoid valves B, 4, water inlet, 5, overflow port, 6, water outlet, 7, side slope model, 8, miniature pressure type water level sensor, 9, communicating pipe, 10, stainless steel net, 11, stainless steel plate, 12, filter screen, 13, grit chamber, 14, support, 15, triangular support, 16, high-speed high definition camera.
Detailed Description
The technical scheme of the invention is further explained by combining the attached drawings and specific implementation.
As shown in fig. 2-6, a centrifugal model test device for simulating water level fluctuation to induce bank slope instability comprises a model box 1 made of aluminum alloy, wherein a support 14 is arranged at the bottom of the model box, a slope model 7 is arranged on the support, the side of the slope facing water is an inclined plane, a bank water level simulation area is formed between the side of the slope facing water and the inner wall of the model box, a water inlet 4 is formed in the top wall of the model box of the bank water level simulation area, an overflow port 5 and a water outlet 6 are sequentially formed in the side wall of the model box of the bank water level simulation area from top to bottom, an electromagnetic valve A2 is arranged at the water outlet, and a Japanese TACO duplex combined electromagnetic valve; a triangular support 15 is arranged between the backwater side of the side slope and the inner wall of the model box, the bottom edge of the triangular support is supported on a support, an underground water level simulation area is formed between the backwater side of the side slope and the inner wall of the model box, a communicating pipe 9 is fixedly connected onto the support, an electromagnetic valve B3 is arranged on the communicating pipe, the communicating pipe communicates the reservoir water level simulation area and the underground water level simulation area, and a miniature pressure type water level sensor 8 is arranged inside the side slope. The side slope is provided with stainless steel plate 11 on the lee side, still is provided with stainless steel net 10 on the stainless steel plate, and the stainless steel net passes through A-frame 15 to be fixed on the stainless steel plate. One end of the communicating pipe, which is positioned in the reservoir water level simulation area, is provided with a filter screen 12, and gaps are reserved among the bottom of the reservoir water level simulation area, the support and the side wall of the model box to form a grit chamber 13.
As shown in FIG. 1, a centrifugal model test method for simulating reservoir bank slope instability induced by water level fluctuation comprises the following steps.
Step 1, surveying and measuring material parameters of the on-site side slope, and configuring bedrock and filling materials with physical and mechanical properties similar to those of the on-site side slope. In the present invention, a deep rockless bank slope will be described as an example.
And collecting and analyzing data such as reservoir water level elevation, slope ratio, hydrological data and the like of the prototype side slope to be as same as the conditions of the prototype side slope as possible. And selecting a plurality of different positions along a plurality of exploration lines on the prototype side slope, drilling to obtain undisturbed samples with different depths, and carrying out grading test. Soil body materials are roughly divided into sandy cohesive soil and gravelly cohesive soil, and as the whole grain size of the sandy cohesive soil is smaller, if the grain size is reduced according to a similar scale in a centrifugal model test, the property of a side slope is probably influenced, so that the original side slope soil material is directly adopted, and the gravelly soil is generally prepared by mixing quartz sand, cement, gypsum and borax with a certain proportion of water. And measuring the spatial distribution of the dry density and the water content of the undisturbed slope soil material through an indoor test, and contrasting statistical analysis results to obtain the dry density and the water content of the filling of the model sample. Weighing the test soil sample, proportioning a proper amount of water according to the water content designed according to the scheme, uniformly stirring, and wrapping and standing for 48 hours by using a plastic film for subsequent model manufacturing.
And 2, preparing a model box corresponding to the water quantity and the size of the reservoir according to the determined similarity ratio N, and presetting and installing a water supply system, a water level automatic control system and an underground water level simulation area in the side slope. And determining the similarity ratio N of the centrifugal model and the on-site slope by combining the conditions of the scale of the prototype slope, the on-site form, the load capacity of the centrifugal machine and the like, and taking the ratio of the height of the prototype to the height of the model box, wherein the ratio is usually 1: 100-1: 200. And designing the model box according to the determined similarity ratio N, wherein the shell of the box body is made of an aluminum alloy material, so that the rigidity is extremely high, and deformation is hardly generated. As shown in FIG. 2, the effective size of the inside of the mold box of the centrifugal model test of the present invention is 1200X 600X 800mm, and comprises: the water supply system, the water level automatic control system, the underground water level simulation area in the side slope and the data acquisition system.
The water supply system supplies water simultaneously by arranging 4 water storage tanks outside the centrifugal machine chamber, and the maximum water supply amount of a single test is 10m by utilizing the coaxial rotation of the water receiving ring and the rotating shaft of the centrifugal machine3。
As shown in fig. 3, the automatic water level control system comprises a rectangular thin-walled overflow port 5, a bottom support 14 and an electromagnetic valve. As shown in figure 4, the wall of the overflow port 5 on one side of the water inlet pipe is provided, the width c of the overflow port is 200mm, the height a of the opening on the outer side of the overflow port is 80mm, the height b of the opening on the inner side of the overflow port is 50mm, the distance from the weir crest to the bottom of the model box is 200mm, and the included angle between the downstream surface of the overflow port and the upstream vertical surface is 20-30 degrees, so that the rapid drainage is facilitated. The water outlet 6 is arranged under the overflow port, wherein the electromagnetic valve A adopts a duplex combination and is composed of a big valve and a small valve, the big valve is opened to enable water flow to be discharged in a short time, and the small valve can further control the discharging precision. The main body of the bottom support 14 is an anti-seepage steel plate, the communicating pipe 9 and the electromagnetic valve B are installed inside the bottom support, and the filter screen 12 is additionally arranged on the pipeline on one side of the water inlet to prevent the washed soil sample from blocking the pipeline. The front side of the steel plate is provided with a small grit chamber 13 to protect the facilities such as the pipelines in the mold box from abrasion and blockage.
As shown in FIG. 5, the groundwater level simulation area in the slope is composed of a side supporting water storage structure made of 304 stainless steel, and the length, width and height of the outside are 600X 100X 800 mm. The side contacted with the slope model 7 is composed of the diameter
The round stainless steel plate 11 is used for supporting and permeating water. The two sides of the perforated steel plate are supported and fixed by a triangular bracket 15, and a layer of 200-mesh stainless steel net 10 is clamped between the steel plate and the bracket to prevent fine particles in the side slope model from reversely sliding into the supporting water storage structure through the perforations. After the bottom support and the supporting water storage structure are installed, the anti-seepage quick-drying glue is smeared on the joint so as to ensure that the water stored in the supporting structure flows into the side slope model in a one-way mode.
The data acquisition system comprises a data acquisition module on a rotating arm of the centrifuge, an image monitoring system and a ground industrial personal computer, and can synchronously acquire strain signals, video signals and voltage signals. As shown in fig. 3, the miniature pressure type water level sensor 8 installed in the slope model can obtain the water level and deformation condition of the slope, the high-speed high-definition camera 16 installed in the model box can extract video images frame by frame, and analyze test details, and the ground industrial personal computer can realize real-time control, acquisition and storage of monitoring data according to a PID control algorithm.
And 3, preparing a model in the model box according to the actual shape of the prototype side slope, burying monitoring devices such as a miniature pressure type water level sensor and the like in the model, hoisting and fixing the model box on a centrifuge hanging basket after the model making is finished, installing and connecting a data acquisition system, and testing whether each monitoring device can work normally. Taking a deep soil slope without rock mass as an example, filling a slope soil sample according to a designed dry density by adopting a layered filling method, wherein the stacking height of each layer is 4cm, uniformly spreading a soil body with a certain water content and uniformly mixed by adopting a quality control method, and tamping to a preset height by adopting a planar tamping plate under a certain tamping force. And (3) performing scraping treatment between every two layers of filling soil, spraying a layer of adhesive on every filling layer, and burying corresponding monitoring equipment when the landslide model is filled to the height of the sensor mark. The sensor should be embedded closely in contact with the model material, and the power line and the sensor lead should be bent to be fixed on the guide rod of the rotating arm or the peripheral wall of the model box in a snake shape so as to prevent the sensor from being broken by force. Two similar sensors are arranged on the same measuring point in parallel as far as possible, so that mutual checking is facilitated. The contact surface between the side wall of the model box and the model is provided with measures, and silicone oil or vaseline can be coated to reduce the friction resistance.
After the model box is hoisted into the hanging basket, linearity test and conversion coefficient calibration are required to be carried out on the sensor so as to test whether the monitoring device can work normally. A high-definition camera is respectively arranged at the top of the model box and right in front of the downstream slope so as to monitor the development process of the slope under the action of water level fluctuation of the reservoir in real time.
And 4, after the centrifugal acceleration is stabilized to the target acceleration, starting the water supply system, closing the electromagnetic valve A, and opening the electromagnetic valve B to keep the two sides of the slope model at the same higher water level.
After the centrifugal machine is weighted, in order to avoid sudden damage to a slope body caused by rapid loading, the centrifugal acceleration is gradually accelerated from 1g to Ng, the centrifugal acceleration increased at each stage is 5g, and the next stage is applied after the soil body is deformed and stabilized for a period of time. And carrying out linearity test and conversion coefficient calibration on the sensor so as to improve the data accuracy.
After the water supply system is started, water storage is started in the model box, the opening size of the electromagnetic valve A is controlled at the moment, the water level is flushed with the overflow port, and infiltration can occur inside and outside the slope model at the high water level, so that the water saturation condition of the model material is accelerated. And observing real-time data, and indicating that the infiltration is basically finished when the pressure of the inner hole of the model is stable.
And 5, after the change of the pore water pressure in the slope model tends to be stable, controlling the flow of the electromagnetic valve A to be increased, closing the electromagnetic valve B, reducing the water level on one side of the reservoir at a certain speed, and simulating the rapid falling process of the water level when the reservoir is full of the reservoir.
And closing the electromagnetic valve B, opening the electromagnetic valve A, adjusting the water discharge flow of the electromagnetic valve A to be larger than the water inlet flow, and keeping the water level to be reduced to the bottom elevation of the electromagnetic valve A at an expected speed. The changes of water level, pore pressure and repose angle in the slope model can be recorded through the internal sensor and the external identification point coordinates. The output signal of the pressure type water level sensor is a voltage signal, and the pressure type water level sensor can be directly connected to a voltage signal acquisition module of a centrifuge data acquisition system for data acquisition. The deformation and damage conditions of the side slope can be observed by adopting an image acquisition and displacement measurement system in the centrifuge.
The specific falling water level and speed can be controlled by the output water flow in the electromagnetic valve, and the calculation formula is as follows:
wherein Q isIntoIs the inflow (fixed flow in the test process) of cm3/min；QGo outFor the discharge flow (adjustable by a solenoid valve during the test), cm3/min；SvThe measured fluctuation speed of the reservoir water level (the rising of the reservoir water level is negative, and the falling of the reservoir water level is positive) is cm/min; b is the width of the inner diameter of the model box, cm; z is the distance between the slope toe and the wall of the model box, namely cm; delta h is the fluctuation range of the water level, cm; alpha is the slope angle of the model slope.
When the large valve in the electromagnetic valve A is closed, the calculated leakage flow is input, the control module can convert the leakage flow into a corresponding current or pulse signal, and the controller can control the opening of the small valve according to the received signal so as to meet the requirement of control precision.
And 6, after the change of the pore water pressure in the slope model tends to be stable, controlling the flow of the electromagnetic valve A to be reduced, so that the water level on one side of the reservoir is lifted at a certain speed, and simulating the rapid rising process of the water level when the reservoir stores water.
Keeping the electromagnetic valve B closed, and adjusting the water discharge quantity of the electromagnetic valve A to be smaller than the water inlet flow, so that the reservoir water level rises to the bottom elevation of the overflow port at a certain speed (the specific size of the reservoir water level is calculated according to the formula (1)) and the water level is kept stable. And (5) the underground water level simulation area generates a back drop after going through the step (5), the electromagnetic valve B is kept closed, and seepage from the reservoir simulation area to the underground water level simulation area is formed by the existence of water level difference on two sides of the model. And recording the changes of the water level, the pore pressure and the repose angle in the slope model through the coordinates of the internal sensor and the external identification point, so that one-time back-and-forth seepage circulation is realized.
And 7, after the pore water pressure is basically kept stable, opening the electromagnetic valve B to lift the water level of the underground water level simulation area to the initial height, and repeating the steps (4) to (7) to simulate the influence of multiple circulating fluctuation of the reservoir water level on the bank side slope.
In order to simulate the influence of multiple cyclic fluctuation of the reservoir water level on the reservoir bank slope, the variation amplitude of the slope repose angle is calculated in the water level fluctuation process, if the variation amplitude of the two fluctuations is less than 10%, the test can be stopped, and test data are recorded.
Claims (5)
1. A centrifugal model test method for simulating water level fluctuation to induce bank slope instability is characterized by comprising the following steps:
(1) determining the similarity ratio N of the centrifugal model and the on-site slope by combining the scale of the prototype slope, the on-site form and the load capacity condition of the centrifugal machine; surveying rock soil samples of the on-site side slope and hydrographic water environment conditions, measuring the density, the grain composition, the water content, the compressibility and the permeability coefficient of rock soil materials, and configuring bedrocks and filling materials which have the physical and mechanical properties similar to those of the on-site side slope;
(2) according to the determined similarity ratio N, a model box corresponding to the reservoir water flow and size is prepared, and a water inlet pipe, a support and a water storage structure are installed in the model box;
(3) preparing a model in a model box according to the actual shape of a prototype side slope, embedding monitoring equipment in the side slope model, fixing the model box on a centrifuge hanging basket after the model is made, mounting a high-definition camera on the hanging basket and connecting a data acquisition system, and testing whether each monitoring device can work normally;
(4) after the centrifugal machine is weighted, the centrifugal machine starts to accelerate step by step, so that the model and the prototype side slope are in the same stress state; after the centrifugal acceleration is stabilized to the target acceleration, a water supply system is started, water is injected into the reservoir water level simulation area through a water inlet in the top of the model box, the electromagnetic valve A is closed, and the electromagnetic valve B is opened, so that the two sides of the slope model are kept at a higher water level;
(5) after the change of the pore water pressure in the side slope model tends to be stable, controlling the flow of the electromagnetic valve A to be increased, wherein the discharge flow of the electromagnetic valve A is larger than the water inlet flow of a water supply system, closing the electromagnetic valve B, reducing the water level of the reservoir water level simulation area at a certain speed, and simulating the rapid falling process of the water level when the reservoir soaks;
the calculation of the output water flow in the control solenoid valve a is disclosed as follows:
wherein Q isIntoFor the inflow, QGo outFor the discharge flow, SvIn order to actually measure the fluctuation speed of the reservoir water level, B is the width of the inner diameter of the model box, Z is the distance between the slope toe and the wall of the model box,hthe water level of the reservoir water level simulation area at the beginning of reservoir water level rising or falling and the risinghIs the lowest water level, when the water level is lowered,hthe highest water level; delta h is the water level fluctuation amplitude, the water level is a negative value when rising, the water level is a positive value when falling, and alpha is the model side slope angle;
(6) after the change of the pore water pressure in the side slope model tends to be stable, controlling the flow of the electromagnetic valve A to be reduced, wherein the discharge flow of the electromagnetic valve A is smaller than the water inlet flow of a water supply system, so that the water level of the reservoir water level simulation area is lifted at a certain speed, and the rapid rising process of the water level when a reservoir stores water is simulated;
(7) after the pore water pressure is kept stable, opening the electromagnetic valve B to lift the water level of the underground water level simulation area to the initial height, and repeating the steps (4) to (7), so that the influence of the periodic back-and-forth seepage on the bank side slope can be simulated;
the testing device for the testing method comprises a model box, wherein a support is arranged at the bottom of the model box, the support is an anti-seepage steel plate, a side slope model is arranged on the support, the water side of the side slope is an inclined plane, a reservoir water level simulation area is formed between the water side of the side slope and the inner wall of the model box, a water inlet is formed in the top wall of the model box of the reservoir water level simulation area, an overflow port and a water outlet are sequentially formed in the side wall of the model box of the reservoir water level simulation area from top to bottom, an included angle of 20-30 degrees is formed between the downstream surface and the upstream surface of the overflow port, and an electromagnetic valve A; a triangular support is arranged between the backwater side of the side slope and the inner wall of the model box, the bottom edge of the triangular support is supported on a support, an underground water level simulation area is formed between the backwater side of the side slope and the inner wall of the model box, a stainless steel plate is arranged on the backwater side of the side slope, a stainless steel mesh is further arranged on the stainless steel plate, and the stainless steel mesh is fixed on the stainless steel plate through the triangular support; the support is fixedly connected with a communicating pipe, an electromagnetic valve B is arranged on the communicating pipe, the communicating pipe is communicated with the reservoir water level simulation area and the underground water level simulation area, and a miniature pressure type water level sensor is arranged inside the side slope.
2. The centrifugal model test method for simulating reservoir bank slope instability induced by water level fluctuation according to claim 1, wherein after the centrifugal machine is weighted in step (4), the centrifugal acceleration is gradually accelerated from 1g to Ng, the centrifugal acceleration increased at each stage is 5g, and the next stage is applied after the soil body is deformed and stabilized for a period of time.
3. The method of claim 1, wherein during the water level fluctuation, the variation range of the slope repose angle is calculated, and if the variation range of the two fluctuations is less than 10%, the test can be stopped, and the test data is recorded.
4. The centrifugal model test method for simulating reservoir bank slope instability induced by water level fluctuation according to claim 1, wherein a filter screen is arranged at one end of the communicating pipe located in the reservoir bank water level simulation area.
5. The centrifugal model test method for simulating reservoir bank slope instability induced by water level fluctuation according to claim 1, wherein a clearance is formed between the bottom of the reservoir water level simulation area, the support and the side wall of the model box to form a grit chamber.
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