A test apparatus and method for determining seepage-settlement of an aquifer under unstable water level conditions.
By integrating an unstable water level control system and a settlement monitoring system, and combining total stress correction and parametric nonlinear models, the accuracy problem of traditional seepage and settlement analysis under dynamic water level changes has been solved. This has enabled accurate simulation and monitoring of seepage and settlement under unstable water level conditions, thereby improving the ability to predict and prevent geological disasters.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG HUADONG CONSTR ENG
- Filing Date
- 2026-04-16
- Publication Date
- 2026-06-30
Smart Images
Figure CN122306655A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a test apparatus and method for determining the seepage-settlement of an aquifer under unstable water level conditions, belonging to the field of seepage-settlement experimental and calculation technology under unstable water level conditions. Background Technology
[0002] With the accelerating pace of urbanization, the exploitation and regulation of groundwater resources are becoming increasingly frequent, leading to unstable fluctuations in aquifer water levels. This, in turn, triggers geological hazards such as ground fissures and surface subsidence, seriously threatening the safety and stability of infrastructure. Traditional groundwater seepage and subsidence analyses are mostly based on steady-state water level assumptions, making it difficult to accurately reflect the impact of dynamic water level changes caused by precipitation, water injection, or tidal effects on soil deformation in actual engineering projects. Therefore, developing experimental devices and computational methods capable of simulating aquifer seepage and subsidence processes under unstable water level conditions is of great significance for revealing the intrinsic mechanism between dynamic water level changes and stratum subsidence, and for improving the ability to predict and prevent geological hazards.
[0003] Based on this, this invention proposes a seepage-settlement test device and calculation method for determining aquifers under unstable water level conditions. By integrating an unstable water level control system, a soil column device, a settlement monitoring system, and a water level measurement system, it achieves accurate simulation and monitoring of soil settlement processes under different water level change patterns (such as periodic, linear, or exponential changes). The device can dynamically adjust the amplitude and frequency of water level fluctuations, and combined with a multi-level settlement and water level data acquisition system, it can effectively obtain the deformation response law of soil under different water level change conditions. Simultaneously, the accompanying calculation method introduces total stress correction, parametric nonlinear evolution, and a layered settlement accumulation model, realizing refined simulation and quantitative analysis of the settlement process under unstable seepage conditions. This invention not only provides an efficient and reliable platform for indoor experiments but also provides theoretical basis and technical support for predicting ground settlement caused by water level fluctuations in actual engineering areas, possessing broad application prospects and practical value. Summary of the Invention
[0004] This invention provides an economical, practical, and easy-to-operate apparatus and calculation method for determining the seepage-settlement test of an aquifer under unstable water level conditions.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A seepage-settlement test device for determining an aquifer under unstable water level conditions includes: an unstable water level control system, a communicating vessel, a soil column device, a settlement monitoring system, and a water level measurement system. The unsteady water level control system includes a water storage tank, a rotating plate, a motor, an overflow tank, and a peristaltic pump; The water tank has an inlet at the top of its side wall; An adjustment through hole is provided on the right side wall of the water storage tank. A rotating plate covers the adjustment through hole and seals it. The center of the outer side plate of the rotating plate is connected to the motor rod and can rotate under the drive of the motor. An overflow port is provided on the rotating plate to determine the amplitude of the change of the unstable water level function. The phase of the unstable water level function can be determined by the position of the overflow port when the motor rotates. The overflow tank is attached to the bottom side of the water storage tank where the rotating plate is located, and the water overflowing from the overflow outlet enters the overflow tank; the bottom side wall of the overflow tank is equipped with a tank drain outlet; The peristaltic pump is installed on the side wall of the water storage tank and located outside the overflow tank. The inlet of the peristaltic pump is connected to the bottom of the overflow tank through a pipeline, and the inlet of the peristaltic pump is connected to the water storage tank through a pipeline. One side of the soil column device is connected to the left side wall of the water storage tank via a connector; the bottom of the soil column device is equipped with a column drainage outlet; a settlement monitoring system is used to measure the settlement in the soil column device. On the other side of the soil column device, there are more than 10 pressure measuring holes arranged along the height direction. Each pressure measuring hole is equipped with a water pressure sensor to form a water level measurement system.
[0006] The aforementioned water inlet is located at the top of the side wall of the water storage tank, so that the water storage tank can reach a full state when it is filled with water.
[0007] The aforementioned overflow outlet, located at any point on the rotatable plate, is used to determine the amplitude of the change in the unsteady water level function.
[0008] The aforementioned connecting device (the connection point with the soil column device) and pressure measuring hole are located on both sides of the soil column device.
[0009] To improve accuracy, a preferred implementation of the soil column device includes a soil column cylinder, a base, and a drainage pipe; The soil column is vertically installed on the base; the soil column is filled with a first medium sand layer, a silty sand layer and a second medium sand layer from top to bottom; The communicating vessel is a tubular structure. One end of the communicating vessel is connected to the side wall of the soil column at the top of the second medium sand layer, and the other end is connected to the left side wall of the water storage tank. That is, the communicating vessel and the rotating plate are located on the two sides of the water storage tank, and the two ends of the communicating vessel are connected to the inside of the soil column and the inside of the water storage tank, respectively. One end of the drainage pipe is connected to the bottom of the soil column, and the other end extends out from the side wall of the base as the column drainage outlet; a water-stop clamp is provided on the drainage pipe extending out of the base; Piezometer holes are arranged at equal intervals along the height direction on the side wall of the soil column to form a water level measurement system. The water level measurement system covers the entire height of the first medium sand layer, the entire height of the silty sand layer, and more than half the height of the second medium sand layer from the top. Each piezometer hole is equipped with a filter screen inside, that is, there is a filter screen layer between each piezometer hole and the first medium sand layer, silty sand layer and second medium sand layer directly opposite, to avoid the normal water level of the piezometer hole being affected by sand clogging the hole during the test.
[0010] The aforementioned settlement monitoring system includes a dial gauge, settlement bar, data acquisition hub, and computer; There are three dial gauges and three settlement rods, each corresponding to a specific one. The bottom of each settlement rod extends to the top surface of the first medium sand layer, the top surface of the silty sand layer, and the top surface of the second medium sand layer, respectively. Each settlement rod is located outside the soil column and connected to the corresponding dial gauge. Each dial gauge transmits the collected data to the computer through a data acquisition hub.
[0011] When measuring settlement data, the bottom plane of each settlement rod should be extended to the top surface of the first medium sand layer, the top surface of the silty sand layer, and the top surface of the second medium sand layer, respectively, to determine the total settlement below the corresponding layer.
[0012] The measured values of data 1, 2, and 3 in the above data acquisition hub correspond to the total settlement of the first medium sand layer and below, the total settlement of the silty sand layer and below, and the total settlement of the second medium sand layer and below in the soil column device, respectively.
[0013] The aforementioned rotating plate is circular, and there are two or more overflow ports with different center distances on the rotating plate to adjust the amplitude of the fluctuating water level. Each overflow port is equipped with a sealing cap, and only one overflow port can be opened at any given time.
[0014] For ease of control, the motor's shaft is connected to a large gear, and the central shaft of the large gear is connected to the center of the outer plate of the rotating plate. In other words, the central shaft of the large gear, which is linked to the motor's shaft, is located at the center of the rotating plate. Rotation of the motor's shaft drives the large gear to rotate, which in turn drives the rotating plate to rotate. This employs a speed reducer or a gearbox principle.
[0015] The radius of the aforementioned rotating plate should be as large as possible, or the overflow outlet should be as small as possible while still meeting the drainage rate requirements, in order to reduce the impact of the lowest point of the overflow outlet on errors in calculations based on circular motion. Preferably, the diameter of the rotating plate is at least 60 times the diameter of the overflow outlet.
[0016] To save space and facilitate installation, use, and control, the peristaltic pump is installed on the side wall of the water storage tank above the overflow tank.
[0017] If the overflow outlet moves periodically on the rotating plate, and the center of the rotating plate is taken as the water level reference point, then there is a water head. H ( t )= A sin(ω t ); where A is the distance from the center of the overflow outlet to the center of the rotating plate, and ω is affected by the motor speed determined by the conditions; If the water head in the soil column of the device is to change linearly, with the center of the rotating plate as the water level reference point, then the water head... H ( t )=A sin(ω t ); where A is the distance from the center of the overflow outlet to the center of the rotating plate, and ω is affected by the motor speed determined by the conditions, i.e. The coded rotational speed, where t is time (s); If the water head in the soil column of the device changes exponentially, with the center of the rotating plate as the water level reference point, then there is a water head... H ( t )= A sin(ω t ); where A is the distance from the center of the overflow outlet to the center of the rotating plate, and ω is affected by the motor speed determined by the conditions, i.e. The coded rotational speed, where b is an undetermined coefficient (without actual physical meaning).
[0018] A method for calculating seepage-settlement of an aquifer under unstable water level conditions, using the aforementioned test apparatus for determining seepage-settlement of an aquifer under unstable water level conditions, includes the following steps: 1) Before the test begins, check the test apparatus for leaks. If any leaks are found, seal them with glue. Also check if the settlement monitoring system is functioning properly. 2) Open the inlet to fill the entire device with water. Wait for the water to slowly submerge the entire soil column device and record the initial water head value of the pressure measuring hole. 3) Turn on the water pressure sensor and record the water level change process in the pressure measuring hole. This information will be used to read the water level value in the pressure measuring hole later and obtain the water pressure change curve. 4) In an unstable water level control system, the fixed speed of the electric motor drives the rotating plate to rotate regularly, thereby causing the overflow outlet to move in a regular manner. 5) Excess water in the storage tank will flow to the overflow tank through the overflow outlet. When the water level in the overflow tank exceeds the maximum water level, the peristaltic pump will be turned on to send the water in the overflow tank back to the storage tank to prevent the water in the overflow tank from overflowing. 6) Using the rotational speed of the rotating plate in the unstable water level control system as an influencing factor, the water head in the soil column device is controlled, and the water level change process is monitored and recorded through the pressure measuring hole; 7) The changing unstable water level conditions will affect the settlement and deformation process of the aquifer. Settlement data is obtained under the monitoring of dial gauge and settlement bar. The data is transmitted through the data acquisition hub and finally presented on the computer as settlement-time curves under different conditions. 8) Continue observation. When the collected dial gauge data tends to stabilize, the experiment can be considered to be in a stable state, and the next experiment can be carried out or the experiment can be ended.
[0019] In step 1) above, when checking for leaks in the device, close the tank drain outlet and use a water-stop clamp to close the column drain outlet. In step 1), it is also necessary to check if the filter screen inside the pressure testing hole is damaged. Before the formal test begins, check the overall airtightness of the device, especially the pressure testing hole connections, to prevent leaks during subsequent tests.
[0020] In step 4) above, the speed of commercial electric motors is generally faster and does not match the actual fluctuation frequency. Therefore, it is necessary to use a small gear to drive a large gear to adjust the speed (that is, to use a speed reducer) in order to achieve control of various unstable water level changes.
[0021] The above seepage-settlement calculation method is as follows: (1) Model specification and discretization: In the discretized model, the first medium sand layer, the silty sand layer, and the second medium sand layer are each divided into two or more thin layers along the height direction, with each thin layer having a thickness of ≤1cm. The depth of each thin layer is determined based on its initial midpoint depth. Compared with the current water level Determine if the relationship is saturated; if If the sublayer is below the water level, it is in a saturated state; otherwise, it is above the water level, is in an unsaturated state, and no more settlement occurs. The precipitation process is discretized into several small steps, and the settlement increment is calculated layer by layer. (2) Total stress correction: When precipitation causes the thickness of the uppermost layer (layer 1) to change from saturated to unsaturated, the overlying load decreases, and the total stress changes; let the saturated unit weight of layer 1 be... (dimension After dewatering, the water holding capacity is (dimension ), the density of water The buoyancy density of the first layer (dimension (Water level drop) Subsequently, the overlying load of the entire aquifer system changes, and its effects are transmitted to all points below the water level. For any point in the system located below the post-rainwater level (i.e., within the saturation zone), the reduction in total stress depends only on the drainage characteristics of the uppermost layer and is independent of the point's depth.
[0022] In the formula: The total stress change (kPa); The saturated unit weight of the first layer (kN / m³) 3 ); The water holding capacity after dewatering (kN / m³) 3 ); This represents the change in water level. The pore water pressure at all points within the saturation zone decreases by the same amount:
[0023] In the formula: The change in pore water stress (kPa); The specific weight of water (kN / m³) 3 Other parameters are the same as above; According to the effective stress principle The effective stress increment at any point within the saturation region can be obtained:
[0024] In the formula: Effective stress increment (kPa); The buoyancy unit weight of the first layer (kN / m) 3 Other parameters are the same as above; (3) Parameter nonlinearity correction: Volume compressibility Porosity and permeability coefficient These parameters change dynamically with stress state, and the parameters of each sublayer evolve independently. Their relationship is determined by the soil compression and permeability characteristics. Under one-dimensional compression conditions, the first The volume compressibility of a sublayer can be expressed as the current effective stress. and porosity Functions:
[0025] In the formula: For the first Sublayer volume compressibility coefficient; For the first Compression index of individual soil layers; For the first Effective stress of each sublayer; For the first Porosity of each sublayer; The relationship between void ratio and settlement is given by geometric conditions:
[0026] In the formula: For the first The cumulative settlement of each sub-layer ( ); For the first The initial porosity of each sublayer; For the first The initial formation thickness of each sublayer; other parameters are the same as above; The evolution of the permeability coefficient has a significant impact on the consolidation process; according to the Kozeny–Carman theory, the permeability coefficient… It can be expressed as a function of void ratio; for sandy soils, the specific surface area during compression is... and particle density It can be considered as a constant, thus yielding a dimensionless relation:
[0027] In the formula: For the first Initial formation permeability coefficient of each sublayer; For the first The permeability coefficient of each sublayer; other parameters are the same as above; For cohesive soils, due to the presence of immovable water, the concept of effective void ratio needs to be introduced; the immovable void ratio is defined. Ratio to total porosity The relationship is ,in For soil-related indices (sand) silt clay Based on this, a corrected expression for the permeability coefficient of cohesive soil can be derived:
[0028] (4) Calculation of settlement increment: The coupled model simultaneously introduces total stress correction and parameter dynamic evolution; the effective stress increment adopts a correction form. The parameter update is based on the current state; the first Step 1 The expression for the settlement increment of a saturated sublayer is:
[0029] In the formula: For the first Step 1 The settlement increment of a saturated sublayer; For the first Step 1 Effective stress of each sublayer; For the first Step 1 Porosity of each sublayer; For the first Step head change value; For the first Step 1 One saturated sublayer thickness; other parameters are the same as above; (5) State variable update: After each calculation step is completed, update the thickness, porosity, and effective stress of that sublayer:
[0030] In the formula: For the first Step 1 Porosity of each sublayer; For the first Step 1 One saturated sublayer thickness; For the first Step 1 Effective stress of each sublayer; other parameters are the same as above; (6) Total settlement:
[0031] In the formula: The total settlement is obtained by summing the settlement increments of all sublayers at each step.
[0032] Based on the above experimental measurements of the soil column under unstable water level conditions, the settlement law and experimental parameters under the experimental conditions were obtained, and the total settlement was finally obtained.
[0033] Unless otherwise specified in this invention, all techniques are based on existing technologies.
[0034] This invention provides an apparatus and method for determining seepage-settlement of aquifers under unstable water level conditions. It has good compatibility and can conduct simulation tests on actual geological conditions where the effects of varying water head are different under different permeability coefficients and patterns. By using small-scale soil sample simulation, it can analyze and predict the settlement caused by precipitation in actual engineering areas. It is simple to operate, highly accurate, and highly practical. Attached Figure Description
[0035] Figure 1 A schematic diagram of the seepage-settlement test device for an aquifer under unstable water level conditions, as shown in this invention. Figure 2 This is a schematic diagram of the speed reduction gear of the electric motor of the present invention; Figure 3 This is a schematic diagram of the overflow outlet at different center distances in the rotating plate of the present invention; Figure 4 Schematic diagram of aquifer system and drawdown; Figure 5 Time-stress curve during water level drop; Figure 6Figures showing the evolution of parameters in the bottom sublayers of each layer; (a) porosity-time, (b) compressibility-time, (c) volume compressibility-time, (d) permeability-time; Figure 7 Comparison of settlement of various aquifers under different model calculations; In the diagram, 1 represents the unstable water level control system, 11 is the inlet, 12 is the water storage tank, 13 is the overflow outlet, 14 is the rotating plate, 15 is the motor, 16 is the overflow tank, 17 is the peristaltic pump, and 18 is the tank drain outlet; 2 represents the soil column device, 21 is the first medium sand layer, 22 is the silty sand layer, 23 is the second medium sand layer, 24 is the base, 25 is the column drain outlet, and 26 is the stop clamp; 3 represents the settlement monitoring system, 31 is the dial gauge, 32 is the settlement rod, 33 is the data acquisition hub, and 34 is the computer; 4 represents the water level measurement system, and 41 is the pressure measuring hole. Detailed Implementation
[0036] To better predict ground subsidence caused by dewatering before foundation pit construction, this invention provides an economical, practical, and easy-to-operate test device and method for monitoring the subsidence of aquifers under periodic water level fluctuations. In this application, directional terms such as "upper," "lower," "left," and "right" are based on the relative orientations or positional relationships shown in the accompanying drawings and should not be construed as limiting the scope of this application. However, the content of this invention is not limited to the following embodiments.
[0037] Example 1
[0038] like Figure 1 As shown, a seepage-settlement test device for determining an aquifer under unstable water level conditions includes an unstable water level control system, a communicating vessel, a soil column device, a settlement monitoring system, and a water level measurement system. The unsteady water level control system includes a water storage tank, a rotating plate, a motor, an overflow tank, and a peristaltic pump; The water tank has an inlet at the top of its side wall to ensure it is fully filled. An adjustment hole is located on the right side wall of the tank, covered and sealed by a rotating plate. The center of the outer side plate of the rotating plate is connected to the motor rod, allowing it to rotate under the motor's drive. Overflow outlets with different center distances are located on the rotating plate to determine the amplitude of the unstable water level function. The phase of the unstable water level function can be determined by rotating the overflow outlets. The overflow tank is located close to the bottom of the side of the water tank with the rotating plate, and water overflowing from the overflow outlets enters the overflow tank. A drain outlet is located at the bottom of the overflow tank's side wall. A peristaltic pump is installed on the side wall of the water tank above the overflow tank. The pump's inlet is connected to the bottom of the overflow tank via a pipe, and the pump's inlet is connected to the water tank via a pipe. The soil column device includes a soil column cylinder, a base, and a drainage pipe; The soil column is vertically installed on the base; the soil column is filled with a first medium sand layer, a silty sand layer and a second medium sand layer from top to bottom. Sixteen pressure measuring holes are arranged on one side of the outer wall of the device to connect to the pressure measuring pipe, and the center of adjacent pressure measuring holes is 0.03m apart. The communicating vessel is a tubular structure. One end of the communicating vessel is connected to the side wall of the soil column at the top of the second medium sand layer, and the other end is connected to the left side wall of the water storage tank. That is, the communicating vessel and the rotating plate are located on the two sides of the water storage tank, and the two ends of the communicating vessel are connected to the inside of the soil column and the inside of the water storage tank, respectively. One end of the drainage pipe is connected to the bottom of the soil column, and the other end extends out from the side wall of the base as the column drainage outlet; a water-stop clamp is provided on the drainage pipe extending out of the base; Pressure measuring holes are arranged at equal intervals along the height direction on the side wall of the soil column. The connection between the communicating vessel and the soil column and the pressure measuring holes are located on both sides of the soil column. Each pressure measuring hole is equipped with a water pressure sensor to form a water level measurement system. The water level measurement system covers the entire height of the medium sand layer, the entire height of the silty sand layer, and more than half the height of the medium sand layer from the top. Each pressure measuring hole is equipped with a filter screen inside, that is, there is a filter screen layer between each pressure measuring hole and the first medium sand layer, silty sand layer and second medium sand layer directly opposite, to avoid the normal water level of the pressure measuring hole being affected by sand clogging the hole during the test.
[0039] The settlement monitoring system includes a dial gauge, settlement bar, data acquisition hub, and computer; There are three dial gauges and three settlement rods, each corresponding to a specific one. The bottom of each settlement rod extends to the top surface of the first medium sand layer, the top surface of the silty sand layer, and the top surface of the second medium sand layer, respectively. The top of each settlement rod is located outside the soil column and is connected to the corresponding dial gauge. Each dial gauge transmits the data collected from the first medium sand layer, the silty sand layer, and the second medium sand layer to the computer through a data acquisition hub.
[0040] When measuring settlement data, the bottom plane of each settlement rod should be extended to the top surface of the first medium sand layer, the top surface of the silty sand layer, and the top surface of the second medium sand layer, respectively, to determine the total settlement below the corresponding layer.
[0041] The measured values of data 1, 2, and 3 in the above data acquisition hub correspond to the total settlement of the first medium sand layer and below, the total settlement of the silty sand layer and below, and the total settlement of the second medium sand layer and below in the soil column device, respectively.
[0042] Example 2
[0043] Based on Example 1, the following improvements were made: the rotating plate is circular, the motor's shaft is connected to the large gear, and the center rod of the large gear is connected to the center of the outer plate of the rotating plate. That is, the center rod of the large gear, which is linked to the motor's shaft, is located at the center of the rotating plate. Rotation of the motor's shaft drives the large gear to rotate, which in turn drives the rotating plate to rotate.
[0044] Example 3
[0045] Based on Example 2, the following improvements were made: In the unsteady water level control system, the radius of the rotating plate should be as large as possible, or the overflow outlet should be as small as possible while meeting the drainage rate requirements, in order to reduce the influence of the lowest point of the overflow outlet on the error calculation based on circular motion. In this example, the diameter of the rotating plate is 60 times the diameter of the overflow outlet; the rotating plate is provided with 15 overflow outlets with the same center distance to adjust the amplitude of fluctuating water levels, and each overflow outlet is provided with a sealing cap, so that only one overflow outlet is open at any given time.
[0046] If the overflow outlet moves periodically on the rotating plate, and the center of the rotating plate is taken as the water level reference point, then there is a water head. H ( t )= A sin(ω t ); where A is the distance from the center of the overflow outlet to the center of the rotating plate, and ω is affected by the motor speed determined by the conditions; if the water head in the soil column of the device is to change linearly, with the center of the rotating plate as the water level reference point, then the water head is H ( t )= A sin(ω t ); where A is the distance from the center of the overflow outlet to the center of the rotating plate, and ω is affected by the motor speed determined by the conditions, i.e. The coded rotational speed; if the water head in the soil column of the device changes exponentially, with the center of the rotating plate as the water level reference point, then the water head... H ( t )= A sin(ω t ); where A is the distance from the center of the overflow outlet to the center of the rotating plate, and ω is affected by the motor speed determined by the conditions, i.e. The coded rotational speed; where t is time (s) and b is an undetermined coefficient (without actual physical meaning). A method for calculating seepage-settlement of an aquifer under unstable water level conditions, using the aforementioned test apparatus for determining seepage-settlement of an aquifer under unstable water level conditions, includes the following steps: 1) Before the test begins, check the test apparatus, close the drain outlet of the chamber and close the drain outlet of the column with a water-stop clamp; check for leaks in the apparatus, and if there are any leaks, seal them with glue; check if the filter screen wrapped around the pressure measuring hole is damaged; test if the dial gauge is working properly. 2) Open the inlet to fill the entire device with water. Wait for the water to slowly submerge the entire soil column assembly, and record the initial water head value of the pressure test hole. 3) Turn on the water pressure sensor and record the water level change process during pressure measurement. This information will be used to read the water level value of the pressure measuring hole later and obtain the water pressure change curve. 4) In an unstable water level control system, the fixed speed of the electric motor drives the rotating plate to rotate regularly, thereby causing the overflow outlet to move in a regular manner. 5) Excess water in the storage tank will flow to the overflow tank through the overflow outlet. When the water level in the overflow tank is high, the peristaltic pump will be turned on to send the water in the overflow tank back to the storage tank. When the water level in the overflow tank exceeds the maximum water level of the overflow tank, the peristaltic pump will be turned on to send the water in the overflow tank back to the storage tank to prevent the water in the overflow tank from overflowing. 6) Using an unstable water level control system as an influencing factor, control the water head in the soil column device, and monitor and record the water level change process through pressure measuring holes; 7) Changing unstable water level conditions will affect the settlement and deformation process of the aquifer. Settlement data are obtained under the monitoring of dial gauge and settlement bar. 8) The data transmission through the data acquisition hub is finally presented on the computer as settlement-time curves under different conditions; 9) Continue observation. When the collected dial gauge data tends to stabilize, the experiment can be considered to be in a stable state, and the next experiment can be carried out or the experiment can be ended.
[0047] In step 1), a filter screen covering the cross-section of the pressure measuring hole is attached to the inside of the hole to prevent sand from clogging the hole and affecting the normal water level during the test. After attaching the filter screen, it is necessary to check whether it is secure. Before the formal test begins, the airtightness of the entire device should be checked, especially the connection between the pressure measuring hole and the water pressure sensor, to prevent water leakage during subsequent tests.
[0048] In step 4), commercial electric motors generally have a high speed, which does not match the actual fluctuation frequency. Therefore, it is necessary to use a small gear to drive a large gear to adjust the speed in order to achieve control of various unstable water level changes.
[0049] The following is a method for calculating the seepage-settlement test of an aquifer under unstable water level conditions: (1) Model specification and discretization: In the discretized model, each principal layer is subdivided into several thin layers (e.g., 1 cm thick), and each thin layer is determined based on its initial midpoint depth. Compared with the current water level Determine if the relationship is saturated; if If the sublayer is below the water level, it is in a saturated state; otherwise, it is above the water level, is in an unsaturated state, and no more settlement occurs. The precipitation process is discretized into several small steps, and the settlement increment is calculated layer by layer. (2) Total stress correction: When precipitation causes the thickness of the uppermost layer (layer 1) to change from saturated to unsaturated, the overlying load decreases, and the total stress changes; let the saturated unit weight of layer 1 be... (dimension After dewatering, the water holding capacity is (dimension ), the density of water The buoyancy density of the first layer (dimension (Water level drop) Subsequently, the overlying load of the entire aquifer system changes, and its effects are transmitted to all points below the water level. For any point in the system located below the post-rainwater level (i.e., within the saturation zone), the reduction in total stress depends only on the drainage characteristics of the uppermost layer and is independent of the point's depth.
[0050] In the formula: The total stress change (kPa); The saturated unit weight of the first layer (kN / m³) 3 ); The water holding capacity after dewatering (kN / m³) 3 ); This represents the change in water level. The pore water pressure at all points within the saturation zone decreases by the same amount:
[0051] In the formula: The change in pore water stress (kPa); The specific weight of water (kN / m³) 3 Other parameters are the same as above; According to the effective stress principle The effective stress increment at any point within the saturation region can be obtained:
[0052] In the formula: Effective stress increment (kPa); The buoyancy unit weight of the first layer (kN / m) 3 Other parameters are the same as above; (3) Parameter nonlinearity correction: Volume compressibility Porosity and permeability coefficient These parameters change dynamically with stress state. The parameters of each sublayer evolve independently, and their relationship is determined by the soil's compression and permeability characteristics.
[0053] Under one-dimensional compression conditions, the first The volume compressibility of a sublayer can be expressed as the current effective stress. and porosity Functions:
[0054] In the formula: For the first Sublayer volume compressibility coefficient; For the first Compression index of individual soil layers; For the first Effective stress of each sublayer; For the first Porosity of each sublayer; The relationship between void ratio and settlement is given by geometric conditions:
[0055] In the formula: For the first The cumulative settlement of each sub-layer ( ); For the first The initial porosity of each sublayer; For the first The initial formation thickness of each sublayer; other parameters are the same as above; The evolution of the permeability coefficient has a significant impact on the consolidation process; according to the Kozeny–Carman theory, the permeability coefficient… It can be expressed as a function of void ratio; for sandy soils, the specific surface area during compression is... and particle density It can be considered as a constant, thus yielding a dimensionless relation:
[0056] In the formula: For the first Initial formation permeability coefficient of each sublayer; For the first The permeability coefficient of each sublayer; other parameters are the same as above; For cohesive soils, due to the presence of immovable water, the concept of effective void ratio needs to be introduced; the immovable void ratio is defined. Ratio to total porosity The relationship is ,in For soil-related indices (sand) silt clay Based on this, a corrected expression for the permeability coefficient of cohesive soil can be derived:
[0057] (4) Calculation of settlement increment: The coupled model simultaneously introduces total stress correction and parameter dynamic evolution; the effective stress increment adopts a correction form. The parameter update is based on the current state; the first Step 1 The expression for the settlement increment of a saturated sublayer is:
[0058] In the formula: For the first Step 1 The settlement increment of a saturated sublayer; For the first Step 1 Effective stress of each sublayer; For the first Step 1 Porosity of each sublayer; For the first Step head change value; For the first Step 1 One saturated sublayer thickness; other parameters are the same as above; (5) State variable update: After each calculation step is completed, update the thickness, porosity, and effective stress of that sublayer:
[0059] In the formula: For the first Step 1 Porosity of each sublayer; For the first Step 1 One saturated sublayer thickness; For the first Step 1 Effective stress of each sublayer; other parameters are the same as above; (6) Total settlement:
[0060] In the formula: The total settlement is obtained by summing the settlement increments of all sub-layers at each step; Based on the experimental measurements of the soil column under unstable water level conditions, the settlement pattern and experimental parameters under the experimental conditions were obtained, and the total settlement was finally calculated.
[0061] To quantitatively reveal the evolution of stress, parameters, and settlement during precipitation in layered heterogeneous aquifers, and to compare the calculation results with those of proposed theoretical models (classical Terzaghi model and coupled model considering the nonlinearity of total stress and parameters), a one-dimensional numerical model of a layered heterogeneous soil column was constructed. The water tank has dimensions of 1m × 0.6m × 1m (length × width × height); the rotating plate is circular with a diameter of 0.6m; the distance from the center of the outermost overflow outlet (the overflow outlet farthest from the center of the rotating plate) to the center of the rotating plate is 0.293m, and the center-to-center distance between overflow outlets is 0.012m; overflow outlets with different center-to-center distances are used to meet the needs of different water level peaks. During the rotation of the plate, only one overflow outlet is opened (the outermost overflow outlet is opened in this experiment), and the other overflow outlets are closed; the distance from the center of the rotating plate to the bottom of the water tank is 0.6m. The soil apparatus consisted of an acrylic cylinder, 1.10m high, with an outer diameter of 0.40m and an inner diameter of 0.38m. The main body of the apparatus was transparent, allowing clear observation of the thickness of different soil layers within. Sixteen piezometer holes were arranged on one side of the outer wall of the apparatus to connect to piezometer tubes, with the centers of adjacent piezometer holes 0.03m apart. The model consisted of three layers: a first medium sand layer (0.10m), a silty sand layer (0.20m), and a second medium sand layer (0.15m), for a total thickness of 0.45m. During the precipitation process, the water level dropped approximately exponentially, with a total drawdown of 0.05m over a period of 20 minutes. The geological structure was as follows: Figure 4 As shown, the initial physical and mechanical parameters of each stratum are detailed in Table 1.
[0062]
[0063] In the calculation, each layer is further discretized into sublayers with a thickness of 1 mm. The initial effective stress of each sublayer is calculated based on its midpoint depth, and the water level drop process is discretized into 400 time steps. Iterative calculations for two models are implemented using Python programming. In each step, the saturation state of each sublayer is determined based on the current water level, and only saturated sublayers participate in the settlement calculation. For the coupled model, the porosity, thickness, effective stress, and permeability coefficient of the sublayers are updated after each step; for the traditional model and the model with only total stress change, the volume compressibility coefficient remains unchanged. The iterations are repeated until the target drawdown depth is reached.
[0064] Taking the calculation results of the coupled model as an example, we analyze the stress evolution of each layer during precipitation. Figure 5 Curves showing the changes in total stress, pore water pressure, and effective stress over time in different formations are presented.
[0065] Depend on Figure 5It is evident that as the water level drops, both the total stress and pore water pressure in each layer decrease, while the effective stress increases accordingly. In the initial stage of precipitation (0–5 min), the rate of stress change is relatively rapid; it gradually slows down in the later stages, stabilizing around 20 min. The decrease in total stress stems from the presence of unsaturated zones in the overlying soil, leading to a reduction in unit weight, while the decrease in pore water pressure is directly caused by the drop in water level. Since the decrease in total stress is less than the decrease in pore water pressure, the effective stress exhibits a net increase. This result indicates that ignoring the change in total stress will overestimate the increase in effective stress, thus exaggerating settlement predictions.
[0066] During settlement, parameters such as void ratio, soil volumetric compressibility coefficient, compressibility coefficient, and permeability coefficient will change. The changes of these parameters over time are as follows: Figure 6 As shown.
[0067] Depend on Figure 6 It can be seen that in engineering projects where the water level drops, the overall variation patterns of the void ratio, soil volumetric compressibility coefficient, soil compressibility coefficient, and permeability coefficient of the target aquifer are consistent: they all decrease rapidly at first, and then the rate of decrease gradually slows down. Among them, the change in void ratio is relatively small and basically consistent, with the ratio of the maximum to minimum void ratio being 1.0013; the changes in volumetric compressibility coefficient and compressibility coefficient are basically consistent, with the ratio of the maximum to minimum value of both being 1.35; and the ratio of the maximum to minimum value of permeability coefficient is 1.005.
[0068] The two models described above are programmed using Python. During calculation, initial parameter values (natural unit weight of soil, saturated unit weight of soil, water-holding unit weight of soil after precipitation, unit weight of water, porosity, permeability coefficient, and soil compressibility index) are input first, and the calculation step size M is determined. The program then obtains the change of the initial water level over time. Different models are then selected for calculation to obtain settlement values. This calculation process is repeated until the simulated water level reaches the target level. This achieves automatic calculation and storage of stress, parameter, and settlement changes at each moment. In each iteration, the calculation results of the previous iteration are used as the initial values for the current iteration, realizing the dynamic changes of parameters during settlement and accurate calculation of the final settlement.
[0069] Total settlement values of multi-layered heterogeneous aquifers under different models are as follows: Figure 7As shown in the figure, quantitative calculations reveal that a drop in aquifer water level leads to changes in the total stress of the aquifer and related physical parameters of the soil. Therefore, the classical Terzaghi model's neglect of total stress and nonlinear parameter changes results in significant deviations in settlement calculations. Using a total settlement value of 0.180 m measured in laboratory tests as a benchmark, the traditional Terzaghi model calculated a total settlement of 0.259 m, with a relative error of 43.9%; while the coupled model calculated a total settlement of 0.179 m, with a relative error of 0.6%, demonstrating a significant improvement in accuracy compared to the traditional model. This demonstrates that the coupled model, which considers changes in total stress and nonlinear parameters, more accurately reflects the actual settlement behavior of the soil layer, significantly improving calculation accuracy and verifying the effectiveness and superiority of the patented method.
Claims
1. A test apparatus for determining the seepage-settlement of an aquifer under unstable water level conditions, characterized in that: include: Unstable water level control system (1), communicating vessel, soil column device (2), settlement monitoring system (3) and water level measurement system (4); The unsteady water level control system includes a water storage tank (12), a rotating plate (14), an electric motor (15), an overflow tank (16), and a peristaltic pump (17). The water tank (12) has an inlet (11) on the top of its side wall; The right side wall of the water tank (12) is provided with an adjustment through hole. The rotating plate (14) covers the adjustment through hole and seals it. The center of the outer side plate of the rotating plate (14) is connected to the motor rod of the motor (15) and can rotate under the drive of the motor (15). The rotating plate (14) is provided with an overflow port (13) to determine the change amplitude of the unstable water level function. The phase of the unstable water level function is determined by the rotation of the overflow port (13) by the motor (15). The overflow tank (16) is attached to the bottom of the side of the water storage tank (12) where the rotating plate (14) is located. Water overflowing from the overflow port (13) enters the overflow tank (16); the bottom of the side wall of the overflow tank (16) is provided with a tank drain port (18). The peristaltic pump (17) is installed on the side wall of the water storage tank (12) and located outside the overflow tank (16). The inlet of the peristaltic pump (17) is connected to the bottom of the overflow tank (16) through a pipeline, and the inlet of the peristaltic pump (17) is connected to the water storage tank (12) through a pipeline. One side of the soil column device (2) is connected to the left side wall of the water storage tank (12) through a connector; the bottom of the soil column device (2) is provided with a column drainage outlet (25); the settlement monitoring system (3) is used to measure the settlement in the soil column device (2); The soil column device (2) has more than 10 pressure measuring holes (41) arranged along the height direction on the other side. Each pressure measuring hole (41) is equipped with a water pressure sensor to form a water level measurement system (4).
2. The test apparatus for determining the seepage-settlement of an aquifer under unstable water level conditions according to claim 1, characterized in that: The soil column device (2) includes a soil column cylinder, a base (24), and a drainage pipe; The soil column is vertically installed on the base (24); the soil column is filled with a first medium sand layer (21), a silty sand layer (22), and a second medium sand layer (23) from top to bottom. The communicating vessel is a tubular structure. One end of the communicating vessel is connected to the side wall of the soil column at the top of the second medium sand layer (23), and the other end is connected to the left side wall of the water storage tank (12). One end of the drainage pipe is connected to the bottom of the soil column, and the other end passes through the side wall of the base (24) as the column drainage outlet (25); a water-stop clamp (26) is provided on the drainage pipe that passes through the base (24). Pressure measuring holes (41) are arranged at equal intervals along the height direction on the side wall of the soil column to form a water level measuring system (4). The water level measuring system (4) covers the entire height of the first medium sand layer (21), the entire height of the silty sand layer (22), and more than half the height of the second medium sand layer (23) from the top. Each pressure measuring hole (41) is equipped with a filter screen inside.
3. The seepage-settlement test apparatus for determining aquifers under unstable water level conditions according to claim 2, characterized in that: The settlement monitoring system (3) includes a dial gauge (31), a settlement bar (32), a data acquisition hub (33), and a computer (34). There are three dial gauges (31) and three settlement rods (32), and they correspond one-to-one. The bottom of each settlement rod (32) extends to the top surface of the first medium sand layer (21), the top surface of the silty sand layer (22), and the top surface of the second medium sand layer (23), respectively. The top of each settlement rod (32) is located outside the soil column and is connected to the corresponding dial gauge (31). Each dial gauge (31) transmits the collected data to the computer (34) through the data acquisition hub (33).
4. The seepage-settlement test apparatus for determining an aquifer under unstable water level conditions according to any one of claims 1-3, characterized in that: The rotating plate (14) is circular, and there are two or more overflow ports (14) with different center distances on the rotating plate (14) to adjust the amplitude of the fluctuating water level; the motor rod (15) is connected to the large gear, and the center rod of the large gear is connected to the center position of the outer plate of the rotating plate (14).
5. The seepage-settlement test apparatus for determining an aquifer under unstable water level conditions according to any one of claims 1-3, characterized in that: The diameter of the rotating plate (14) is more than 60 times the diameter of the overflow outlet (13); the peristaltic pump (17) is installed on the side wall of the water storage tank (12) above the overflow tank (16).
6. The test apparatus for determining the seepage-settlement of an aquifer under unstable water level conditions according to any one of claims 1-3, characterized in that: The overflow outlet (13) moves periodically on the rotating plate (14). Taking the center of the rotating plate (14) as the water level reference point, there is a water head. H ( t )= A sin(ω t ); where A is the distance from the center of the overflow outlet (13) to the center of the rotating plate (14); if the water head in the soil column (2) of the device changes linearly, The coded rotation speed; if the water head in the soil column (2) of the device changes exponentially, The coded rotational speed; where t is time (s) and b is an undetermined coefficient.
7. A method for determining the seepage-settlement of an aquifer under unstable water level conditions, characterized in that: Using the seepage-settlement test apparatus for determining an aquifer under unstable water level conditions as described in any one of claims 1 to 6, the method includes the following steps: 1) Check if the device is leaking. If there is a leak, seal it with glue. Check if the settlement monitoring system (3) is working properly. 2) Open the inlet (11) to fill the whole device with water, and wait for the water to slowly submerge the whole soil column device (2), and record the initial water head value of the pressure measuring hole (41); 3) Open the water pressure sensor and record the water level change process in the pressure measuring hole (41) for later reading of the water level value in the pressure measuring hole (41) to obtain the water pressure change curve; 4) In the unstable water level control system (1), the rotating plate (14) is driven to rotate regularly by the fixed speed of the motor (15), thereby making the overflow outlet (13) move regularly. 5) The excess water in the storage tank (12) will flow to the overflow tank (16) through the overflow outlet (13). When the water level in the overflow tank (16) exceeds the highest water level in the overflow tank (16), the peristaltic pump will be turned on to send the water in the overflow tank (16) back to the storage tank (12). 6) Using the rotation speed of the rotating plate (14) in the unstable water level control system (1) as an influencing factor, control the water head in the soil column device (2), and monitor and record the water level change process through the pressure measuring hole (41); 7) The changing unstable water level conditions will affect the settlement and deformation process of the aquifer. Settlement data is obtained under the monitoring of dial gauge (31) and settlement rod (32). The data is transmitted through data acquisition hub (33) and finally presented on computer (34) as settlement-time curves under different conditions. 8) Continue to observe until the collected dial gauge (31) data tends to be stable. It can be considered that the experiment has reached a stable state and the next experiment can be carried out or the experiment can be ended.
8. The method for determining the seepage-settlement of an aquifer under unstable water level conditions according to claim 7, characterized in that: In step 1), when checking whether the device is leaking, close the drain outlet (18) of the box and close the drain outlet (25) of the column with the water stop clamp (26); in step 1), it is also necessary to check whether the filter screen in the pressure test hole (41) is damaged.
9. The method for determining the seepage-settlement of an aquifer under unstable water level conditions according to claim 7 or 8, characterized in that: In step 4), the rotation speed is adjusted by using a small gear to drive a large gear, so as to achieve control of various unstable water level changes.
10. The method for determining the seepage-settlement of an aquifer under unstable water level conditions according to claim 7 or 8, characterized in that: The seepage-settlement calculation method is as follows: (1) Model specification and discretization: In the discretized model, the first medium sand layer (21), the silty sand layer (22), and the second medium sand layer (23) are each divided into two or more thin layers along the height direction, with each thin layer having a thickness ≤1cm. The thickness of each thin layer is determined according to its initial midpoint depth. Compared with the current water level Determine if the relationship is saturated; if If the sublayer is below the water level, it is in a saturated state; otherwise, it is above the water level, is in an unsaturated state, and no more settlement occurs. The precipitation process is discretized into two or more small steps, and the settlement increment is calculated layer by layer. (2) Total stress correction: When precipitation causes the thickness of the uppermost layer to change from saturated to unsaturated, the overlying load decreases, and the total stress changes; let the saturated unit weight of the first layer be... After drying, the water holding capacity is The density of water The buoyancy density of the first layer Water level drops Subsequently, the overlying load of the entire aquifer system changes, and its effects are transmitted to all points below the water level. For any point in the system located below the post-rainwater level, the reduction in total stress depends only on the drainage characteristics of the uppermost layer and is independent of the point's depth: In the formula: The total stress change (kPa); The saturated unit weight of the first layer (kN / m³) 3 ); The water holding capacity after dewatering (kN / m³) 3 ); This represents the change in water level. The pore water pressure at all points within the saturation zone decreases by the same amount: In the formula: The change in pore water stress (kPa); The specific weight of water (kN / m³) 3 Other parameters are the same as above; According to the effective stress principle The effective stress increment at any point within the saturation region can be obtained: In the formula: Effective stress increment (kPa); The buoyancy unit weight of the first layer (kN / m) 3 ); (3) Parameter nonlinearity correction: Volume compressibility Porosity and permeability coefficient The parameters change dynamically with the stress state, and the parameters of each sublayer evolve independently. Their relationship is determined by the soil compression and permeability characteristics. Under one-dimensional compression conditions, the first The volume compressibility of a sublayer can be expressed as the current effective stress. and porosity Functions: In the formula: For the first Sublayer volume compressibility coefficient; For the first Compression index of individual soil layers; For the first Effective stress of each sublayer; For the first Porosity of each sublayer; The relationship between void ratio and settlement is given by geometric conditions: In the formula: For the first The cumulative settlement of each sub-layer ( ); For the first The initial porosity of each sublayer; For the first The initial stratigraphic thickness of each sublayer; According to the Kozeny–Carman theory, the permeability coefficient It is expressed as a function of void ratio; for sandy soils, it is the specific surface area during compression. and particle density It can be considered as a constant, thus yielding a dimensionless relation: In the formula: For the first Initial formation permeability coefficient of each sublayer; For the first The permeability coefficient of each sublayer; For cohesive soils, due to the presence of immovable water, the concept of effective void ratio needs to be introduced; the immovable void ratio is defined. Ratio to total porosity The relationship is ,in For soil-related indices (sand) silt clay Based on this, a corrected expression for the permeability coefficient of cohesive soil can be derived: (4) Calculation of settlement increment: The coupled model simultaneously introduces total stress correction and parameter dynamic evolution; the effective stress increment adopts a correction form. The parameter update is based on the current state; the first Step 1 The expression for the settlement increment of a saturated sublayer is: In the formula: For the first Step 1 The settlement increment of a saturated sublayer; For the first Step 1 Effective stress of each sublayer; For the first Step 1 Porosity of each sublayer; For the first Step head change value; For the first Step 1 One saturated sublayer thickness; (5) State variable update: After each calculation step is completed, update the thickness, porosity, and effective stress of that sublayer: In the formula: For the first Step 1 Porosity of each sublayer; For the first Step 1 One saturated sublayer thickness; For the first Step 1 Effective stress of each sublayer; (6) Total settlement: In the formula: The total settlement is obtained by summing the settlement increments of all sublayers at each step.