Risk assessment method for hydraulic construction under soft ground and variable water level conditions

Abstract

A kind of hydraulic construction risk assessment method for soft foundation and variable water level condition, the method comprises the following steps: obtaining the permeability of each soil layer of foundation structure and pore water pressure, combined with water level change during construction, the initial state representation of layered foundation and water level change is constructed.Based on the initial state representation, the non-synchronous dissipation characteristics of the pore water pressure of the soil layer whose water level drop speed exceeds the set threshold value are extracted with time variation.The effective stress variation between adjacent soil layers is compared and analyzed according to the non-synchronous dissipation characteristics, to identify the effective stress sudden increase interval.Based on the effective stress sudden increase interval, the transient instability risk in different time periods during construction is determined to output the foundation transient risk assessment result.The present application locks the risk assessment target on the most dangerous interface and time period to identify the effective stress sudden increase interval, which can effectively serve the early capture of transient failure window under the condition of rapid drawdown, and improve the risk assessment accuracy and stability of hydraulic construction.

Description

Technical Field

[0001] This invention belongs to the field of river management technology, and more specifically, relates to a method for risk assessment of hydraulic engineering construction under conditions of weak foundation and variable water level. Background Technology

[0002] Common construction contents in river management projects include river dredging, bank and dike reinforcement, sluice gate and culvert reconstruction, energy dissipation and erosion control, and riverbed regulation. These projects are generally carried out linearly along the river channel, with the construction area adjacent to the main channel and floodplains. They are significantly affected by water inflow processes, upstream scheduling, flood season fluctuations, and sudden flood discharges, resulting in frequent changes in water level boundaries during the construction period. Simultaneously, the riverbanks and riverbed cover layers are mostly alluvial and diluvial deposits, with alternating layers of soft clay, silt, silt, and sand. Weak foundations and permeable interlayers coexist, exhibiting significant spatial variations. Construction activities (e.g., cofferdams, diversion, foundation pit excavation, surcharge loading, and machinery movement) superimposed on water level fluctuations cause continuous changes in the seepage field and effective stress state, further triggering risks such as settlement, slippage, and seepage damage. Therefore, in river management scenarios, there is an urgent need for construction risk assessments addressing weak foundations and variable water level conditions to support the safety control of construction organization, diversion, and temporary structures.

[0003] Currently, existing risk assessments for river management construction primarily rely on phased stability calculations. These typically treat the foundation as approximately homogeneous or describe it using parameters from a few representative layers. Safety reserves are calculated based on a given water level condition, and then controlled using monitoring thresholds. While this approach is applicable when water levels change slowly or soil permeability characteristics are not significantly different, it struggles to accurately reflect the transient response of layered foundations in common river management scenarios such as rapid water level drops, diversion switching, and abrupt changes in head difference between the inside and outside of cofferdams. The key challenges are twofold: firstly, in river alluvial strata, high-permeability sand layers or permeable interlayers coexist with overlying soft clay layers, resulting in significant differences in pore water pressure dissipation rates between layers. Rapid water level changes can lead to intense remodeling of seepage boundaries within a short period. Secondly, construction risks are not solely determined by water level amplitude but are coupled with factors such as the rate of water level change, interlayer drainage conditions, interlayer location, and connectivity, potentially leading to nonlinear and asynchronous abrupt changes in effective stress. The aforementioned coupling process is characterized by its short duration, locality, and mechanistic sensitivity, making it difficult to cover using traditional "continuous evolution assumptions" or single steady-state conditions. Furthermore, river management projects often involve tight schedules and densely overlapping procedures, with frequent adjustments to diversion and excavation rhythms during construction. This results in shorter risk trigger windows and greater difficulty in early detection, leading to inherent limitations in the current technology for identifying transient instability.

[0004] Therefore, during river management construction, if a sudden flood discharge or water release causes a rapid drop in water level, and if there is a high-permeability interlayer in the foundation, and the overlying soft clay and the interlayer pore pressure dissipate asynchronously, the local effective stress will suddenly increase in a short period of time and induce transient instability. Existing assessment methods based on the evolution of continuous effective stress are difficult to lock in this transient failure window in advance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to overcome the aforementioned deficiencies and propose a risk assessment method for hydraulic engineering construction under conditions of weak foundations and variable water levels.

[0006] The present invention adopts the following technical solution.

[0007] The first aspect of this invention discloses a method for risk assessment in hydraulic engineering construction under conditions of weak foundation and variable water level, the method comprising:

[0008] The permeability characteristics and pore water pressure of each soil layer of the foundation structure are obtained, and combined with the water level changes during construction, the initial state characterization of the layered foundation and water level changes is constructed.

[0009] Based on the initial state characterization, the asynchronous dissipation characteristics of soil pore water pressure over time when the water level drop rate exceeds a set threshold are extracted.

[0010] Based on the asynchronous dissipation characteristics, the effective stress changes between adjacent soil layers are compared and analyzed to identify the effective stress surge intervals.

[0011] Based on the effective stress surge range, the transient instability risk at different time periods during construction is determined to output the transient risk assessment results of the foundation.

[0012] Furthermore, the process of obtaining the permeability characteristics and pore water pressure of each soil layer in the foundation structure of the construction area, combined with water level changes during construction, constructs an initial state characterization of the layered foundation and water level changes, including:

[0013] The foundation structure is longitudinally divided into multiple soil layers, and the top and bottom elevations of each soil layer are solidified to calculate the thickness of each soil layer based on the top and bottom elevations.

[0014] The permeability coefficients of each soil layer in different directions are solidified, and the equivalent permeability coefficients of each soil layer and the permeability comparison index of adjacent soil layers are determined based on the solidified permeability coefficients. The equivalent permeability coefficients are used to characterize the drainage rate of the corresponding soil layer, and the permeability comparison indexes are used to determine whether there is a sudden change in permeability between adjacent soil layers.

[0015] Furthermore, the acquisition of the permeability characteristics and pore water pressure of each soil layer in the foundation structure of the construction area, combined with the water level changes during construction, to construct an initial state characterization of the layered foundation and water level changes, also includes:

[0016] The external water level is obtained at multiple discrete moments according to the set sampling period, and the water level change rate of adjacent sampling period time is calculated based on the external water level at each discrete moment, so as to determine the precipitation intensity based on the water level change rate.

[0017] The initial external water level and the midpoint elevation of any soil layer are obtained at the initial moment before the water level change. Based on the initial external water level and midpoint elevation, the initial pore water pressure and initial effective stress are approximately determined by hydrostatic pressure.

[0018] When the permeability comparison index exceeds a set threshold, an interlayer permeability abrupt change zone is identified, and adjacent soil layers with the permeability abrupt change zone are marked with abrupt changes. The initial state characterization is generated by combining the initial pore water pressure and the initial effective stress.

[0019] Furthermore, the extraction of asynchronous dissipation characteristics of soil pore water pressure over time when the water level drop rate exceeds a set threshold, based on the initial state characterization, includes:

[0020] The time period during which the precipitation intensity continuously meets the set precipitation conditions is defined as the precipitation time window, and the start and end times of each precipitation time window are fixed to quantify the average precipitation intensity of each precipitation time window.

[0021] Based on the equivalent permeability coefficient and soil thickness of each soil layer, a pore pressure dissipation time constant is constructed for each soil layer. Then, taking the initial pore water pressure as the starting point, the pore water pressure of each soil layer at each time is determined in combination with the pore pressure dissipation time constant.

[0022] Furthermore, the step of extracting the asynchronous dissipation characteristics of soil pore water pressure over time when the water level drop rate exceeds a set threshold, based on the initial state characterization, also includes:

[0023] The pore pressure difference between adjacent soil layers is calculated hour by hour within the time window of the water level, and the pore pressure difference at all times within the time window of the water level is accumulated to obtain the interlayer differential energy.

[0024] The interlayer differential energy is normalized by the initial pore water pressure, and the abrupt change marker of the permeability abrupt change zone is introduced as a weight to calculate the asynchronous index.

[0025] The asynchronous index is sorted among all soil interfaces to screen out key interlayer interfaces with an asynchronous index not lower than a set threshold, and the critical moment when the absolute value of the pore pressure difference of the key interlayer interface is located within the water level time window is determined.

[0026] The asynchronous dissipation feature is composed of the key interlayer interface and the key time period constructed at key moments.

[0027] Furthermore, the step of comparing and analyzing the effective stress changes between adjacent soil layers based on the asynchronous dissipation characteristics to identify effective stress surge intervals includes:

[0028] The adjacent interlayer interfaces are extracted from the asynchronous dissipation features, and the effective interlayer stress of the adjacent interlayer interfaces at each discrete time and the effective stress difference at different times are calculated, so as to identify stress surge candidates based on the effective interlayer stress and the effective stress difference.

[0029] The effective stress difference is subjected to adjacent difference to obtain the effective stress surge increment and the effective stress surge growth rate. Based on the effective stress surge increment and the effective stress surge growth rate, the surge candidate interval that meets the preset stress short-term surge rule is selected from the stress surge candidate objects.

[0030] The transient surge interval is determined based on the start and end times of the candidate surge interval, and the stress surge intensity and stress surge duration are quantified within the transient surge interval.

[0031] Furthermore, based on the effective stress surge range, the transient instability risk during different time periods of construction is determined to output the foundation transient risk assessment result, including:

[0032] Based on the stress change intensity and stress change duration in the transient increase interval, the equivalent stress margin and time reduction factor are calculated, and the equivalent stress margin and time reduction factor are combined into a transient instability determination quantity.

[0033] Obtain the range of values ​​for the transient instability judgment quantity corresponding to each inter-layer interface in the asynchronous dissipation feature, and classify the range of values ​​for the judgment quantity according to the set risk judgment threshold to obtain the transient risk level and window time period corresponding to each inter-layer interface.

[0034] Furthermore, the method of determining the transient instability risk at different time periods during construction based on the effective stress surge interval, and outputting the foundation transient risk assessment result, also includes:

[0035] The principle of maximum risk is introduced, and the overall transient risk level, as well as the inter-layer interface position and window time period corresponding to the overall transient risk level, are determined based on the principle of maximum risk.

[0036] The transient risk levels and window time periods of all inter-layer interfaces in the asynchronous dissipation characteristics are summarized. Combined with the overall transient risk level and the inter-layer interface locations and window time periods corresponding to the overall transient risk level, the foundation transient risk assessment results are output.

[0037] The second aspect of this invention discloses a hydraulic construction risk assessment device for soft foundations and variable water level conditions, used to implement the hydraulic construction risk assessment method for soft foundations and variable water level conditions as described in any one of the first aspects, the device comprising:

[0038] The initial state characterization module is used to obtain the permeability characteristics and pore water pressure of each soil layer of the foundation structure, and to construct the initial state characterization of the layered foundation and water level changes in combination with the water level changes during construction.

[0039] The feature extraction module is used to extract the asynchronous dissipation features of soil pore water pressure over time when the water level drop rate exceeds a set threshold, based on the initial state characterization.

[0040] The stress surge identification module is used to compare and analyze the effective stress changes between adjacent soil layers based on the asynchronous dissipation characteristics, so as to identify the effective stress surge interval.

[0041] The risk assessment module is used to determine the transient instability risk at different time periods during construction based on the effective stress surge range, and output the transient risk assessment results of the foundation.

[0042] A third aspect of the present invention discloses a terminal, including a processor and a storage medium;

[0043] The storage medium is used to store instructions;

[0044] The processor is configured to operate according to the instructions to perform the steps of the method described in the first aspect.

[0045] A fourth aspect of the present invention discloses a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0046] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention has the following advantages:

[0047] (1) This invention characterizes the permeability and initial pore water pressure of each soil layer according to the foundation layer structure within the hydraulic construction area, and simultaneously acquires the water level change process during construction, forming a layered initial state set to reflect the initial hydraulic and mechanical state of different soil layers before water level changes. Subsequently, the change process of pore water pressure of each soil layer over time under rapid water level drop is characterized in layers, forming a set of asynchronous pore pressure dissipation characteristics that reflects the difference in pore pressure dissipation rate between high-permeability interlayers and overlying soft clay layers. By locking the risk assessment target at the most dangerous interface and time period to identify the effective stress surge interval, it can effectively serve the early capture of transient failure windows under rapid water level drop.

[0048] (2) This invention identifies effective stress surge intervals caused by differences in pore pressure dissipation rates by comparing and analyzing the effective stress changes between adjacent soil layers. It constructs a set of transient stress characteristics reflecting the intensity and duration of interlayer stress mutations, providing actionable input for the final risk assessment. This serves as a basis for determining transient instability under conditions of rapid water level drop and high-permeability interlayers. Finally, it assesses the transient instability risk at different times during construction, outputting the corresponding transient risk assessment results for the foundation under rapid water level drop conditions. This clarifies whether a transient failure window induced by a high-permeability interlayer exists, thus completing the construction risk assessment for soft foundations and variable water level conditions. By pre-identifying the transient failure window caused by interlayer response differences, the accuracy and stability of risk assessment in hydraulic engineering construction are improved. Attached Figure Description

[0049] Figure 1 This is a flowchart illustrating the risk assessment method for hydraulic construction under conditions of weak foundation and variable water level provided by the present invention.

[0050] Figure 2 This is a schematic diagram of the structure of the hydraulic construction risk assessment device for soft foundations and variable water level conditions provided by the present invention. Detailed Implementation

[0051] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.

[0052] like Figure 1 As shown in one embodiment, a method for risk assessment of hydraulic engineering construction under conditions of weak foundation and variable water level includes the following steps:

[0053] Step S110: Obtain the permeability characteristics and pore water pressure of each soil layer of the foundation structure, and combine them with the water level changes during construction to construct an initial state characterization of the layered foundation and water level changes.

[0054] In some embodiments, the hydraulic construction risk assessment method for soft foundations and variable water level conditions provided by the present invention includes the following steps in step S110:

[0055] Step S111: Divide the foundation structure longitudinally into multiple soil layers, and solidify the top and bottom elevations of each soil layer so as to calculate the thickness of each soil layer based on the top and bottom elevations.

[0056] Step S112: Solidify the permeability coefficients of each soil layer in different directions, and determine the equivalent permeability coefficient and permeability comparison index of each soil layer based on the solidified permeability coefficients. The equivalent permeability coefficient is used to characterize the drainage rate of the corresponding soil layer, and the permeability comparison index is used to determine whether there is a sudden change in permeability between adjacent soil layers.

[0057] In some embodiments, the hydraulic construction risk assessment method for soft foundations and variable water level conditions provided by the present invention further includes the following steps in step S110:

[0058] Step S113: Obtain the external water level at multiple discrete moments according to the set sampling period, and calculate the water level change rate for adjacent sampling period time based on the external water level at each discrete moment, so as to determine the precipitation intensity based on the water level change rate.

[0059] Step S114: Obtain the initial external water level and the midpoint elevation of any soil layer at the initial moment before the water level change, and based on the initial external water level and midpoint elevation, approximately determine the initial pore water pressure and initial effective stress through hydrostatic pressure.

[0060] Step S115: When the permeability comparison index exceeds a set threshold, the interlayer permeability abrupt change zone is identified, and the adjacent soil layers with permeability abrupt change zones are marked with abrupt change markers. Combined with the initial pore water pressure and initial effective stress, an initial state characterization is generated. In some embodiments, the initial state characterization refers to a unified, frozen engineering description of the actual hydraulic and mechanical states of each soil layer in the foundation before the water level begins to change, serving as the starting point for subsequent evolution calculations. For example, before the dam releases water, the pore pressure of the sand layer is recorded as 120 kPa, and the pore pressure of the overlying soft clay is recorded as 115 kPa. Simultaneously, the thickness and permeability coefficient of both layers are solidified; this set of data constitutes the initial state characterization. Similarly, before river regulation construction, the external water level of 8.5 m, the midpoint elevation of each layer, and the corresponding effective stress are determined at once, serving as the initial reference benchmark for subsequent rapid water level reduction analysis.

[0061] Under the superimposed conditions of "rapid water level drop + high permeability interlayer," the risk evolution exhibits structural distortion. During river regulation or dam construction, sudden upstream flood discharge or water release causes a rapid drop in water level within a short period. Meanwhile, the foundation contains high permeability sand layers or permeable interlayers, whose pore pressure dissipates significantly faster than the overlying soft clay layer. Existing technical solutions typically base risk assessments on the logic of continuous effective stress evolution, which makes it difficult to consider the following: severely inconsistent pore pressure dissipation rates among different soil layers; sudden increases in effective stress in local soil layers within a short time; and this abrupt change is not a gradual evolution but rather a transient instability triggered by interlayer differences. Therefore, the risk assessment results constructed based on overall evolutionary characteristics in existing technical solutions are difficult to capture in advance the transient failure window caused by interlayer response differences. To solve this technical problem, this invention provides a risk assessment method for hydraulic construction under conditions of weak foundations and changing water levels, comprising steps 1 to 4:

[0062] Step 1: Construct an initial state characterization of the layered foundation-water level change.

[0063] Within the hydraulic construction area, the permeability characteristics and initial pore water pressure state of each soil layer are characterized according to the layered structure of the foundation. Simultaneously, the water level change process during construction is acquired, forming a layered initial state set reflecting the initial hydraulic and mechanical states of different soil layers before water level changes. This includes the following sub-steps:

[0064] Sub-step 1.1: Determining the layered structure and solidifying the layer thickness parameters.

[0065] Specifically, the foundation is divided vertically into multiple soil layers (usually 2-12 layers, with the "layering at key soil property changes" as the standard in engineering). The top and bottom elevations of each layer are fixed, and the thickness of each layer is determined based on the top and bottom elevations, i.e., the difference between the top and bottom elevations, in meters.

[0066] Sub-step 1.2: Characterization of the permeability characteristics and equivalent permeability coefficient of each layer.

[0067] Specifically, for the first The vertical and horizontal permeability coefficients of the layer are solidified, and then an equivalent permeability coefficient is defined to uniformly characterize the "drainage speed" of the layer. The equivalent permeability coefficient is equal to the average of the vertical and horizontal permeability coefficients, and the unit is meters per second.

[0068] For common hydraulic foundations, the empirical range for vertical and horizontal permeability coefficients is 1×10⁻¹⁰ - 1×10⁻³ m / s, for sand layers it is usually 1×10⁻⁶ - 1×10⁻³ m / s, and for soft clay layers it is usually 1×10⁻¹⁰ - 1×10⁻⁸ m / s.

[0069] Subsequently, to highlight the difference between the "high-permeability interlayer" and the overlying layer, a permeability comparison index between adjacent layers was defined, which is numerically equal to the ratio of the equivalent permeability coefficients of adjacent soil layers. This index represents the amplification factor of the permeability capacity of a soil layer relative to its adjacent layers. When the permeability comparison index between adjacent layers is greater than or equal to 10, it is determined that there is a significant permeability abrupt change zone at that location, which serves as the key interlayer interface to focus on during subsequent transient failure.

[0070] Sub-step 1.3: Discretization of the water level change process and characterization of the precipitation intensity.

[0071] Specifically, a sampling period is selected to collect discrete water levels, with the sampling period ranging from 1 to 60 minutes, preferably 5 to 15 minutes, to cover "rapid water level drops caused by sudden flood discharge". The external water level is recorded at a discrete moment, and the rate of water level change and the intensity of water level drops in adjacent time periods are calculated. The rate of water level change in adjacent time periods is equal to the difference between the external water levels at adjacent moments, used as the numerator ratio to the sampling period. The intensity of water level drops is the maximum value of the inverse of the rate of water level change, measured in meters per second, and is only positive when the water level is falling. In engineering practice, a threshold intensity of water level drops greater than or equal to 5 × 10⁻⁵ – 5 × 10⁻³ meters per second can be used to characterize the range of "rapid water level drops," with the specific threshold determined based on the river cross-section and the scheduling method.

[0072] Sub-step 1.4: Construction of the stratified state of initial pore water pressure and effective stress.

[0073] Specifically, the starting time before the water level change and the corresponding external water level are selected. For any soil layer, its representative depth is chosen (the elevation of the midpoint of the layer is taken). The initial pore water pressure is approximately constructed based on hydrostatic pressure, and the initial effective stress is obtained from the total stress and pore pressure. The expression is as follows:

[0074]

[0075] In the formula, For the first Initial pore water pressure of the soil layer, in Pascals; The density of water is 980-1025 kg per cubic meter. The acceleration due to gravity is 9.78-9.83 meters per second squared. The external water level at the starting time, in meters; For the first The representative elevation of each soil layer is in meters. So, the... The initial effective stress of a soil layer is the difference between the initial total stress (in Pascals, obtained by integrating the unit weight of the overlying soil layer) at the elevation represented by that layer and the initial pore water pressure.

[0076] Subsequently, to identify potential asynchronous interfaces caused by high-permeability interlayers, interlayer abrupt change markers were constructed by combining the aforementioned permeability comparison indicators. The expression is as follows:

[0077]

[0078] In the formula, This serves as a marker for interlayer mutations, with values ​​ranging from 0 to 1. This serves as a permeability comparison indicator between adjacent layers. It is an exponential function. When the permeability comparison index between adjacent layers is much greater than 10, the interlayer abrupt change marker is close to 1, indicating that the interlayer interface is a key interface at risk of transient instability.

[0079] Step S120: Based on the initial state characterization, extract the asynchronous dissipation characteristics of soil pore water pressure over time when the water level drop rate exceeds a set threshold.

[0080] In some embodiments, the hydraulic construction risk assessment method for soft foundations and variable water level conditions provided by the present invention includes the following steps in step S120:

[0081] Step S121: Define the time period during which the precipitation intensity continuously meets the set precipitation conditions as a precipitation time window, and fix the start and end times of each precipitation time window to quantify the average precipitation intensity of each precipitation time window.

[0082] Step S122: Based on the equivalent permeability coefficient and soil thickness of each soil layer, construct the pore pressure dissipation time constant for each soil layer, and determine the pore water pressure of each soil layer at each time point by taking the initial pore water pressure as the starting point and combining the pore pressure dissipation time constant.

[0083] In some embodiments, the hydraulic construction risk assessment method for soft foundations and variable water level conditions provided by the present invention further includes the following steps in step S120:

[0084] Step S123: Calculate the pore pressure difference between adjacent soil layers at each time within the precipitation time window, and accumulate the pore pressure difference at all times within the precipitation time window to obtain the interlayer differential energy.

[0085] Step S124: Normalize the interlayer differential energy using the initial pore water pressure, and introduce the abrupt change marker of the permeability abrupt change zone as a weight to calculate the asynchronous index.

[0086] Step S125: Sort the asynchronous index among all soil interfaces to screen out the key interlayer interfaces whose asynchronous index is not lower than the set threshold, and determine the key moment when the absolute value of the pore pressure difference of the key interlayer interface is at its peak within the water level time window.

[0087] The asynchronous dissipation characteristic refers to the set of engineering phenomena in which different soil layers experience inconsistent rates of pore water pressure decline during rapid water level drops due to differences in permeability, resulting in quantifiable differences between layers. This phenomenon is jointly constituted by key interlayer interfaces and key time periods formed by key moments. For example, when the external water level drops sharply, the pore pressure of the sand layer decreases by 30 kPa within 10 minutes, while the overlying soft clay only decreases by 5 kPa. The difference between the two continues to amplify over time, constituting a typical asynchronous dissipation characteristic. Additionally, within the same water level time window, the pore pressure of the interlayer rapidly approaches the external water level, while the upper layer maintains a high pore pressure state, forming a significant peak value of interlayer pore pressure difference, which is also a asynchronous dissipation characteristic.

[0088] In a specific embodiment, the hydraulic construction risk assessment method provided by the invention for soft foundations and variable water level conditions includes step 2, which characterizes the asynchronous dissipation characteristics of pore water pressure in different soil layers. Based on the stratified initial state set obtained in step 1, the change process of pore water pressure in each soil layer over time under rapid water level drop conditions is characterized in layers, forming a set of asynchronous pore pressure dissipation characteristics that reflects the difference in pore pressure dissipation rates between high-permeability interlayers and overlying soft clay layers. This includes the following sub-steps:

[0089] Sub-step 2.1: Rapid water level interval identification and pore pressure calculation time axis solidification.

[0090] Specifically, in the discrete water level sequence, the precipitation intensity sequence is used as the criterion to filter out discrete time intervals that meet the rapid precipitation condition. Each consecutive time interval that meets the condition is defined as a rapid precipitation time window. The start and end times of each time window are then fixed, and the set of discrete times within that window is defined. The criterion for identifying rapid precipitation is that the precipitation intensity at any discrete time within the time window is greater than or equal to a set threshold (valued at 5 × 10⁻⁵ - 5 × 10⁻³ m / s). To quantify the average precipitation intensity of each time window, the average precipitation intensity of the window is defined as the mean of the precipitation intensity at all discrete times within that time window, i.e., the ratio of the sum of all precipitation intensities within the time window to its quantity.

[0091] Sub-step 2.2: Construct the pore pressure dissipation time constant for each soil layer and establish the pore pressure update formula over time.

[0092] Specifically, for the first For each soil layer, a pore pressure dissipation time constant is constructed based on the aforementioned solidified equivalent permeability coefficient and soil layer thickness to reflect the rate of pore pressure dissipation in that layer. To ensure project feasibility, the unit weight of water intake (valued at 9.6 × 10³ - 10.1 × 10³ N / m³) and the soil's equivalent water storage coefficient (valued at 1 × 10⁻⁶ - 1 × 10⁻³ Pa, obtained from consolidation tests or empirical values) are used in the construction of the time constant, expressed as follows:

[0093]

[0094] In the formula, For the first The dissipation time constant between soil layers and pore layers, in seconds; For the first The equivalent water storage coefficient of the soil layers; The unit weight of water; For the first The thickness of each soil layer; For the first The equivalent permeability coefficient of the soil layer.

[0095] Subsequently, within each rapid precipitation time window, the discrete moments are recursively updated according to time. The pore water pressure of the soil layers is established using the initial pore water pressure mentioned above as a starting point and the boundary pore water pressure caused by changes in the external water level as a time-varying boundary, and an expression for the update of pore water pressure over time is established:

[0096]

[0097] In the formula, For the first Soil layers at discrete time The boundary pore water pressure at time, in Pascals; , The first Soil layers at discrete time and Pore ​​water pressure at that time; The sampling period is in seconds. The above formula can be used to generate a sequence of pore pressure variations over time for each layer.

[0098] Sub-step 2.3 calculates the difference in asynchronous pore pressure dissipation and forms interlayer difference characteristics.

[0099] Specifically, for two adjacent soil layers, the interlayer pore pressure difference is calculated hourly within a rapid precipitation time window. This difference represents the difference in pore water pressure between the adjacent soil layers at the same discrete moment, directly characterizing the transient degree of "asynchronous pore pressure between the interlayer and the overlying layer." Furthermore, to avoid focusing solely on single-point differences and ignoring persistence, the pore pressure differences within the time window are accumulated. The accumulated pore pressure difference energy is then obtained, which is the sum of the squares of all pore pressure differences within the window and the sampling period.

[0100] Subsequently, to facilitate comparisons between different projects and at different initial water levels, an asynchronous index was defined. The differential energy was normalized using the initial pore pressure level, and an interlayer abrupt change marker was introduced as a weight to preferentially amplify high-permeability abrupt change interfaces. The expression is as follows:

[0101]

[0102] In the formula, The non-synchronous index of interlayer pore pressure is dimensionless. , These are the initial pore water pressures of the two adjacent solidified layers, respectively, in Pascals. For the first Layer and First The energy difference between layers, expressed in Pascals squared times per second.

[0103] Sub-step 2.4: Extract the asynchronous key interlayer dominated by the high-permeability interlayer and output the final pore pressure asynchronous dissipation feature set.

[0104] Specifically, among all interlayer interfaces, they are sorted from largest to smallest by their asynchronous index, and those interfaces whose asynchronous index is greater than or equal to a set threshold (ranging from 0.05 to 0.50 or the upper quartile of all asynchronous indices) are selected as the key interlayer set. Then, for each key interlayer, the moment when the absolute value of the orifice pressure difference reaches its peak is located within a time window, and a key time period is constructed near this moment to characterize the time segment with the "strongest asynchronousity." The key time period is taken as two to ten times the sampling period, preferably five times the sampling period. The final output is a set of orifice pressure asynchronous dissipation characteristics containing key interlayers, key time periods, and the asynchronous index of key interlayers.

[0105] Step S130: Based on the asynchronous dissipation characteristics, a comparative analysis of the effective stress changes between adjacent soil layers is performed to identify the effective stress surge interval.

[0106] The effective stress surge interval refers to a short period of time during which the effective stress at a certain interlayer interface increases rapidly and concentratedly due to asynchronous dissipation of pore pressure, rather than a long-term, slow evolution process. For example, if the effective stress of the overlying soft soil suddenly increases by 25 kPa within 15 minutes, while the total stress remains almost unchanged, this period is identified as the effective stress surge interval.

[0107] In some embodiments, the hydraulic construction risk assessment method for soft foundations and variable water level conditions provided by the present invention includes the following steps in step S130:

[0108] Step S131: Extract the interlayer interface from the asynchronous dissipation features, and calculate the effective stress of the interlayer interface at each discrete time and the effective stress difference at different times, so as to identify the candidate objects of stress surge based on the effective stress and the effective stress difference.

[0109] Step S132: Perform adjacent difference on the effective stress difference to obtain the effective stress surge increment and the effective stress surge growth rate, and select the surge candidate interval that meets the preset stress short-term surge rule from the stress surge candidate objects according to the effective stress surge increment and the effective stress surge growth rate.

[0110] Step S133: Determine the transient surge interval based on the start and end times of the surge candidate interval, and quantify the stress surge intensity and stress surge duration in the transient surge interval.

[0111] In a specific embodiment, the hydraulic construction risk assessment method provided by the invention for soft foundations and variable water level conditions includes step 3, identifying the transient surge intervals of effective stress between layers. Based on the asynchronous dissipation feature set of pore pressure output in step 2, a comparative analysis of the effective stress changes between adjacent soil layers is performed to identify the effective stress surge intervals formed in a short period of time due to differences in pore pressure dissipation rates, and to construct a transient stress feature set reflecting the intensity and duration of interlayer stress abrupt changes. This includes the following sub-steps:

[0112] Sub-step 3.1: Construct an effective stress time series between layers based on the asynchronous characteristics of pore pressure.

[0113] Specifically, for each interlayer interface in the key interlayer set determined in step 2, the effective stress of the adjacent two layers is calculated at discrete moments within the key time period set corresponding to that interlayer interface, and the difference in effective stress between the layers is calculated to form a basic time series for identifying "transient surges". The effective stress is determined using the engineering definition of "total stress minus pore pressure", where the total stress is considered not to change abruptly with a sudden drop in water level within a short time window, but only to change slowly with self-weight and additional construction loads. Therefore, it can be approximately regarded as a constant or linearly slowly varying term within the same key time period.

[0114] The total stress is numerically equal to the sum of the total stress corresponding to each soil layer and the equivalent vertical stress of the construction load converted to the representative depth. Therefore, the effective stress of a soil layer at a certain discrete moment is the difference between the total stress and the pore water pressure of the corresponding layer at that moment. The difference in effective stress between adjacent layers at the same discrete moment is selected as the candidate for sudden increase.

[0115] Sub-step 3.2: Calculate the effective stress transient surge increment and surge rate, and screen for surge candidate segments.

[0116] Specifically, for each key interface, the effective stress difference between layers is differentially analyzed within its key time period to obtain the sudden increase and rate of increase of effective stress. Based on this, candidate segments that meet the "significant increase in a short period" criterion are selected. First, the sudden increase needs to be defined as the increment of the effective stress difference between layers at adjacent times, and the sudden rate of increase is the ratio of the sudden increase to the time interval. Then, threshold values ​​for sudden increase criteria are set for selecting candidate segments (including a sudden increase threshold and a sudden rate of increase threshold; the sudden increase threshold is set to 5×10³-5×10⁴ Pa, and the sudden rate of increase threshold is set to 10-500 Pa per second, which can be adjusted according to engineering scale and allowable deformation level). Consecutive times that satisfy both the sudden increase and the sudden rate of increase thresholds are merged into candidate segment intervals, and the maximum sudden increase and maximum sudden rate of increase within each segment are recorded.

[0117] Sub-step 3.3: Determine the boundaries of the transient burst interval and quantify the intensity and duration of the mutation.

[0118] Specifically, for each candidate interval in the candidate burst fragment, the transient burst interval is further defined within that interval using the "burst start point and fall end point" as boundaries, and its burst intensity and duration are quantified. The interval boundary is determined using the engineering criterion of "burst increment regression baseline": the effective interlayer stress difference at the moment preceding the candidate interval start point is used as the baseline value. When the corresponding effective interlayer stress difference continuously rises from the baseline and falls back to no higher than the baseline plus a set tolerance (valued at 1×10³-5×10³ Pa to avoid misjudgment caused by noise), the interval is considered to have ended. Burst enhancement is defined by the peak increment of the effective interlayer stress difference within the interval, i.e., the effective interlayer stress difference minus the peak value of the baseline. The duration is calculated by the interval length and sampling period, i.e., the product of the difference between the two ends of the interval plus the value of 1 and the sampling period.

[0119] Step S140: Based on the effective stress surge range, determine the transient instability risk at different time periods during construction to output the foundation transient risk assessment results.

[0120] Understandably, the result of a foundation transient risk assessment refers to an engineering judgment output that clearly indicates whether the foundation has a transient instability risk within a specific time window after comprehensively considering the intensity and duration of the effective stress surge.

[0121] In some embodiments, the hydraulic construction risk assessment method for soft foundations and variable water level conditions provided by the present invention includes the following steps in step S140:

[0122] Step S141: Based on the stress change intensity and stress change duration in the transient increase interval, calculate the equivalent stress margin and time conversion factor, and combine the equivalent stress margin and time conversion factor into a transient instability judgment quantity.

[0123] Step S142: Obtain the range of transient instability judgment values ​​for each inter-layer interface in the asynchronous dissipation feature, and classify the range of judgment values ​​according to the set risk judgment threshold to obtain the transient risk level and window time period corresponding to each inter-layer interface.

[0124] In some embodiments, the hydraulic construction risk assessment method for soft foundations and variable water level conditions provided by the present invention further includes the following steps in step S140:

[0125] Step S143 introduces the maximum risk principle, and determines the overall transient risk level and the inter-layer interface position and window time period corresponding to the overall transient risk level based on the maximum risk principle.

[0126] Step S144: Summarize the transient risk level and window time period of all inter-layer interfaces in the asynchronous dissipation characteristics, and output the foundation transient risk assessment result by combining the overall transient risk level and the inter-layer interface location and window time period corresponding to the overall transient risk level.

[0127] In a specific embodiment, the hydraulic construction risk assessment method provided by the invention for soft foundations and variable water level conditions includes step 4, which generates transient risk assessment results for rapid water level drop conditions. Based on the transient stress surge characteristics obtained in step 3, the transient instability risk during different time periods of construction is determined, and the corresponding transient risk assessment results for the foundation under rapid water level drop conditions are output. This is used to clarify whether there is a transient failure window induced by high-permeability interlayers, thereby completing the construction risk assessment for soft foundations and variable water level conditions. This includes the following sub-steps:

[0128] Sub-step 4.1: Construct transient instability judgment criteria and generate risk judgment input quantities.

[0129] Specifically, for each critical interlayer interface and its transient surge range, along with its abrupt change intensity and duration, the initial effective stress corresponding to that interface is first introduced to characterize the bearing capacity benchmark before the water level change. Then, based on the abrupt change intensity of the interface, an equivalent stress margin is defined, i.e., the difference between the initial effective stress and the abrupt change intensity, to characterize the degree of encroachment of the transient surge relative to the original bearing capacity level. Subsequently, the influence of duration on the transient surge is introduced, constructing a time reduction factor to reflect the engineering fact that "the longer the surge lasts, the higher the risk of instability." The time reduction factor is numerically equal to 1 plus the ratio of the surge duration to a reference time constant (ranging from 300-1800 seconds, determined according to the foundation consolidation and seepage characteristics). Finally, the equivalent stress margin is calculated as the numerator, and the ratio to the time reduction factor is used as the transient instability risk assessment metric.

[0130] Sub-step 4.2: Identification of transient destruction windows and classification of risk levels.

[0131] Specifically, for each key inter-layer interface, the transient instability risk is classified into levels based on its transient instability risk assessment value. During this classification process, risk assessment thresholds need to be predefined, including a first threshold and a second threshold. The first threshold ranges from 0 to 20 × 10³ Pa, and the second threshold ranges from 20 × 10³ to 80 × 10³ Pa. Then, the risk level is determined by comparing the transient instability risk assessment value with the risk assessment threshold.

[0132] When the transient instability risk assessment value is less than or equal to 0, the risk level is assessed as Level 3, which indicates extremely high risk and that the interface has entered or is close to a transient instability state.

[0133] When the transient instability risk assessment value is greater than 0 and less than or equal to the first threshold, the risk level is assessed as Level 2 risk, indicating high risk and the existence of a clear transient failure window.

[0134] When the transient instability risk assessment value is greater than the first threshold and less than or equal to the second threshold, the risk level is assessed as Level 1 risk, which indicates a medium risk and requires close attention.

[0135] When the transient instability risk assessment value is greater than the second threshold, the risk level is assessed as level zero, indicating low risk.

[0136] Finally, the risk levels obtained are conveniently associated with the sudden increase interval time identified in step 3, so that the risk level can be bound to the specific occurrence time and a "transient damage window" can be generated.

[0137] Sub-step 4.3 generates transient risk assessment results under rapid precipitation conditions.

[0138] Specifically, the risk levels of all key inter-layer interfaces are summarized to generate an overall transient risk assessment result for rapid rainfall conditions. To reflect the superimposed risks of multiple interfaces acting simultaneously, the maximum risk principle is introduced to define the overall transient risk level of the construction area under the current rapid rainfall conditions. Furthermore, the interface number and failure window time period of the overall transient risk level are recorded simultaneously and used as the dominant risk source. The final transient risk assessment result includes the overall transient risk level, the dominant risk interface, the corresponding transient failure window time period, and the classification results of each key interface.

[0139] The following describes the hydraulic construction risk assessment device for soft foundations and variable water level conditions provided by the present invention. The hydraulic construction risk assessment device for soft foundations and variable water level conditions described below can be referred to in correspondence with the hydraulic construction risk assessment method for soft foundations and variable water level conditions described above.

[0140] like Figure 2 As shown in one embodiment, a hydraulic construction risk assessment device for soft foundations and variable water level conditions includes an initial state characterization module, a feature extraction module, a stress surge identification module, and a risk assessment module.

[0141] The initial state characterization module is used to obtain the permeability characteristics and pore water pressure of each soil layer of the foundation structure, and combined with the water level changes during construction, to construct the initial state characterization of the layered foundation and water level changes.

[0142] The feature extraction module is used to extract asynchronous dissipation features of soil pore water pressure over time when the water level drop rate exceeds a set threshold, based on the initial state characterization.

[0143] The stress surge identification module is used to compare and analyze the effective stress changes between adjacent soil layers based on asynchronous dissipation characteristics, so as to identify the effective stress surge interval.

[0144] The risk assessment module is used to determine the transient instability risk at different time periods during construction based on the effective stress surge range, and output the transient risk assessment results of the foundation.

[0145] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A method for risk assessment in hydraulic engineering construction under conditions of weak foundation and variable water level, characterized in that, The method includes: The permeability characteristics and pore water pressure of each soil layer of the foundation structure are obtained, and combined with the water level changes during construction, the initial state characterization of the layered foundation and water level changes is constructed. Based on the initial state characterization, the asynchronous dissipation characteristics of soil pore water pressure over time when the water level drop rate exceeds a set threshold are extracted. Based on the asynchronous dissipation characteristics, the effective stress changes between adjacent soil layers are compared and analyzed to identify the effective stress surge intervals. Based on the effective stress surge range, the transient instability risk at different time periods during construction is determined to output the transient risk assessment results of the foundation.

2. The method for risk assessment of hydraulic engineering construction under soft foundation and variable water level conditions according to claim 1, characterized in that, The process involves acquiring the permeability characteristics and pore water pressure of each soil layer in the foundation structure of the construction area, and combining this with water level changes during construction to construct an initial state characterization of the layered foundation and water level changes, including: The foundation structure is longitudinally divided into multiple soil layers, and the top and bottom elevations of each soil layer are solidified to calculate the thickness of each soil layer based on the top and bottom elevations. The permeability coefficients of each soil layer in different directions are solidified, and the equivalent permeability coefficients of each soil layer and the permeability comparison index of adjacent soil layers are determined based on the solidified permeability coefficients. The equivalent permeability coefficients are used to characterize the drainage rate of the corresponding soil layer, and the permeability comparison indexes are used to determine whether there is a sudden change in permeability between adjacent soil layers.

3. The method for risk assessment of hydraulic construction under soft foundation and variable water level conditions according to claim 2, characterized in that, The process of obtaining the permeability characteristics and pore water pressure of each soil layer in the foundation structure of the construction area, and constructing an initial state characterization of the layered foundation and water level changes in conjunction with water level changes during construction, also includes: The external water level is obtained at multiple discrete moments according to the set sampling period, and the water level change rate of adjacent sampling period time is calculated based on the external water level at each discrete moment, so as to determine the precipitation intensity based on the water level change rate. The initial external water level and the midpoint elevation of any soil layer are obtained at the initial moment before the water level change. Based on the initial external water level and the midpoint elevation, the initial pore water pressure and the initial effective stress are approximately determined by hydrostatic pressure. When the permeability comparison index exceeds a set threshold, the interlayer permeability abrupt change zone is determined, and the adjacent soil layers with the permeability abrupt change zone are marked with abrupt changes. The initial state characterization is generated by combining the initial pore water pressure and the initial effective stress.

4. The method for risk assessment of hydraulic construction under soft foundation and variable water level conditions according to claim 3, characterized in that, The extraction of asynchronous dissipation characteristics of soil pore water pressure over time when the water level drop rate exceeds a set threshold, based on the initial state characterization, includes: The time period during which the precipitation intensity continuously meets the set precipitation conditions is defined as the precipitation time window, and the start and end times of each precipitation time window are fixed to quantify the average precipitation intensity of each precipitation time window. Based on the equivalent permeability coefficient and soil thickness of each soil layer, a pore pressure dissipation time constant for each soil layer is constructed. Then, taking the initial pore water pressure as the starting point, the pore water pressure of each soil layer at each time is determined in combination with the pore pressure dissipation time constant.

5. The method for risk assessment of hydraulic construction under soft foundation and variable water level conditions according to claim 4, characterized in that, The method of extracting the asynchronous dissipation characteristics of soil pore water pressure over time when the water level drop rate exceeds a set threshold, based on the initial state characterization, further includes: The pore pressure difference between adjacent soil layers is calculated hour by hour within the time window of the water level, and the pore pressure difference at all times within the time window of the water level is accumulated to obtain the interlayer differential energy. The interlayer differential energy is normalized by the initial pore water pressure, and the abrupt change marker of the permeability abrupt change zone is introduced as a weight to calculate the asynchronous index. The asynchronous index is sorted among all soil interfaces to screen out key interlayer interfaces whose asynchronous index is not lower than a set threshold, and the critical moment when the peak value of the absolute value of the pore pressure difference of the key interlayer interface is determined within the water level time window. The asynchronous dissipation feature is composed of the key interlayer interface and the key time period constructed at key moments.

6. The method for risk assessment of hydraulic engineering construction under soft foundation and variable water level conditions according to claim 1, characterized in that, The step of comparing and analyzing the effective stress changes between adjacent soil layers based on the asynchronous dissipation characteristics to identify intervals of sudden increases in effective stress includes: The adjacent interlayer interfaces are extracted from the asynchronous dissipation features, and the effective interlayer stress of the adjacent interlayer interfaces at each discrete time and the effective stress difference at different times are calculated, so as to identify stress surge candidates based on the effective interlayer stress and the effective stress difference. The effective stress difference is subjected to adjacent difference to obtain the effective stress surge increment and the effective stress surge growth rate. Based on the effective stress surge increment and the effective stress surge growth rate, the surge candidate interval that meets the preset stress short-term surge rule is selected from the stress surge candidate objects. The transient surge interval is determined based on the start and end times of the candidate surge interval, and the stress surge intensity and stress surge duration are quantified within the transient surge interval.

7. The method for risk assessment of hydraulic construction under soft foundation and variable water level conditions according to claim 6, characterized in that, Based on the effective stress surge interval, the transient instability risk during different time periods of construction is determined to output the foundation transient risk assessment result, including: Based on the stress change intensity and stress change duration in the transient increase interval, the equivalent stress margin and time reduction factor are calculated, and the equivalent stress margin and time reduction factor are combined into a transient instability determination quantity. The range of values ​​for the transient instability judgment quantity corresponding to each inter-layer interface in the asynchronous dissipation feature is obtained, and the range of values ​​for the judgment quantity is classified into levels according to the set risk judgment threshold to obtain the transient risk level and window time period corresponding to each inter-layer interface.

8. The method for risk assessment of hydraulic construction under soft foundation and variable water level conditions according to claim 7, characterized in that, The method of determining the transient instability risk at different time periods during construction based on the effective stress surge interval, and outputting the foundation transient risk assessment result, also includes: The principle of maximum risk is introduced, and the overall transient risk level, as well as the inter-layer interface position and window time period corresponding to the overall transient risk level, are determined based on the principle of maximum risk. The transient risk levels and window time periods of all inter-layer interfaces in the asynchronous dissipation characteristics are summarized. Combined with the overall transient risk level and the inter-layer interface locations and window time periods corresponding to the overall transient risk level, the foundation transient risk assessment results are output.

9. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-8.

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