CN111877417A - Method for measuring instability critical water content of rainfall parameter weakening type foundation pit slope - Google Patents

Method for measuring instability critical water content of rainfall parameter weakening type foundation pit slope Download PDF

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CN111877417A
CN111877417A CN202010841498.XA CN202010841498A CN111877417A CN 111877417 A CN111877417 A CN 111877417A CN 202010841498 A CN202010841498 A CN 202010841498A CN 111877417 A CN111877417 A CN 111877417A
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foundation pit
water content
slope
displacement
determining
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张兰阁
苏群山
董新红
吴远超
张岚
贾向军
都宏全
祝孝成
王渊
曾良
王龙飞
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Henan DR Construction Group Co Ltd
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    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
    • E02D33/00—Testing foundations or foundation structures
    • E—FIXED CONSTRUCTIONS
    • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
    • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
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Abstract

The invention relates to the technical field of foundation pit slope instability early warning, in particular to a method for determining rainfall parameter weakening type foundation pit slope instability critical water content, which adopts a uniform deformation control value to judge whether the foundation pit slope is unstable or not is unreasonable, and a method for determining rainfall parameter weakening type foundation pit slope instability critical water content comprises the steps of determining basic physical mechanical parameters of the foundation pit slope, determining foundation pit slope cohesive force and internal friction angle weakening rules under different water content conditions, determining foundation pit displacement and slope water content monitoring equipment arrangement and installation under a rainfall condition, determining water content dynamic unloading parameters under different water content conditions, determining foundation pit slope water content dynamic unloading and displacement coupling evaluation parameters, determining foundation pit slope instability critical water content criterion in step six, and judging foundation pit slope state by adopting a plurality of variables, the early warning method has the advantages of achieving the purpose of timely and effective early warning, and having good development prospect in the technical field of early warning of foundation pit slope instability.

Description

Method for measuring instability critical water content of rainfall parameter weakening type foundation pit slope
Technical Field
The invention relates to the technical field of early warning of foundation pit slope instability, in particular to a method for measuring rainfall parameter weakening type critical water content of foundation pit slope instability.
Background
The foundation pit engineering has the characteristics of large deformation, strong paroxysmal property, serious harmfulness, multiple instability factors and the like, occupies a considerable proportion in engineering construction accidents, and in the construction process of the deep foundation pit engineering, even if a permanent foundation pit is excavated, the accident of the foundation pit slope instability is frequently caused under the action of rainfall because the construction environment is very complicated.
Therefore, after the foundation pit is excavated, the water content of the slope body and the weakening of related physical parameters and the stability of the foundation pit slope in the rainfall process need to be monitored in real time, so that necessary measures are taken to ensure the safety of the foundation pit.
At present, a method for predicting and evaluating a foundation pit side slope in a rainfall process is mainly based on the observation of displacement, atmospheric rainfall and underground water level, the corresponding relation of rainfall capacity and rainfall intensity to the foundation pit side slope displacement and instability of the foundation pit side slope is researched, and a time sequence statistical prediction model of the foundation pit side slope displacement and rainfall is established, so that the purpose of prediction and forecast is achieved. However, the evaluated parameters are only the change rule of displacement or displacement rate in the evolution process of the foundation pit slope, only the deformation change rule of the slope can be reflected and described, the formation mechanism and the mechanical cause of slope deformation and instability cannot be disclosed, and the prediction evaluation result is easily influenced and has strong uncertainty due to more assumed conditions and limiting conditions of modeling. And because the foundation pit type, the safety level, the working condition, the surrounding environment, the engineering geological condition and the like of each foundation pit project are different, and the adoption of a uniform deformation control value is obviously unreasonable, even if corresponding control standards are formulated according to the engineering conditions or project characteristics, the phenomena that the foundation pit slope deformation is overlarge, the foundation pit slope is not unstable or the foundation pit slope deformation does not exceed the deformation control value and the foundation pit slope is unstable often occur. Therefore, the prediction and evaluation model established by using the single displacement information parameter is often influenced and limited in accuracy of prediction and evaluation due to the single information quantity. Therefore, a method for improving the prediction accuracy of the foundation pit slope safety is urgently needed.
Disclosure of Invention
Aiming at the situation, in order to overcome the defects of the prior art, the invention provides a method for measuring the critical water content of the rainfall parameter weakening type foundation pit side slope instability, and solves the problems that the existing foundation pit side slope prediction and evaluation method does not disclose the formation mechanism and the mechanical factor causing the foundation pit side slope deformation and instability, and a unified deformation control value is adopted to judge whether the foundation pit side slope is unstable or not and is unreasonable.
The technical scheme is that the method for measuring the instability critical water content of the rainfall parameter weakening type foundation pit slope,
step one, measuring basic physical and mechanical parameters of a foundation pit slope: carrying out systematic geophysical prospecting, testing, investigation and surveying and mapping on the foundation pit slope to be measured;
determining the weakening rule of the cohesive force and the internal friction angle of the foundation pit slope body under the condition of different water contents: according to the process that the water content in the slope body is gradually increased when rainfall infiltrates, the cohesive force c and the internal friction angle of the slope body of the foundation pit under the condition of different water content are determined
Figure BDA0002641590480000021
The weakening rule of (2);
thirdly, arranging and installing foundation pit displacement and slope water content monitoring equipment under the rainfall condition;
determining the dynamic unloading parameters of the water content under the conditions of different water contents: setting n displacement monitoring points, and determining the skid resistance of the ith soil strip under the rainfall condition, wherein the average skid resistance of the n soil strips corresponding to the t monitoring time is a water content power unloading parameter;
fifthly, determining parameters for power unloading and displacement coupling evaluation of the water content of the foundation pit slope;
and step six, determining the criterion of the instability critical water content of the foundation pit slope.
Furthermore, in the first step, the vertical depth of the foundation pit side slope body and the change rule of the inclination angle are determined, the equal-width vertical striping is carried out on the foundation pit side slope body according to the inclination rule, and the inclination angle of the foundation pit is recorded as thetaiThe average height of the ith soil strip divided by the equal-width vertical strips is recorded as liComprehensively measuring the heavy gamma of the foundation pit slope soil layer and the cohesive force c internal friction angle of the soil under the conditions of different water contents w
Figure BDA0002641590480000022
Furthermore, the cohesive force c and the internal friction angle of the foundation pit slope body under the condition of different water contents in the second step
Figure BDA0002641590480000023
The weakening rule is as follows:
Figure BDA0002641590480000024
Figure BDA0002641590480000025
in the formula: b ═ eB，a＝am；d＝eD，e＝em；
Taking logarithm of both sides of formula (1):
Figure BDA0002641590480000026
let lnc be y; lnb ═ B;
Figure BDA0002641590480000027
namely: y ═ B + ax (4)
Let the experimental data of equation (4) be n, which can be obtained from the basic principle of least squares:
the value of B, a can be obtained by substituting the above formula into equation (5):
Figure BDA0002641590480000031
similarly, the determinations D and e can be obtained from the above stepsmThe value of (c):
Figure BDA0002641590480000032
furthermore, in the third step, a monitoring time interval unit of the foundation pit is set, the wireless GPS displacement monitoring device and the DltaT type moisture meter are adopted to monitor the displacement of the foundation pit and the moisture content of the slope body in real time according to a unit time interval, and the displacement time sequence S of the side slope of the foundation pit is respectively determinedtTime series omega of water content of Hepo slope bodyti；
(1) The method for monitoring the displacement of the foundation pit side slope body comprises the following steps: the displacement value of the ith displacement monitoring point at the time t is recorded as StiSetting no less than three deformation monitoring datum points in an area without deformation outside a monitored foundation pit slope body, setting a plurality of monitoring points, setting a foundation pit slope site automatic total station at each monitoring point to transmit monitoring data to a remote monitoring terminal for classification pretreatment, communicating the remote monitoring terminal, and then pretreating to obtain an average value of displacement changes of n displacement monitoring points
Figure BDA0002641590480000033
Figure BDA0002641590480000034
(2) The method for monitoring the water content of the foundation pit side slope body comprises the following steps: firstly, laying a water content sensor at the top of a foundation pit slope and the surface layer, the middle layer and the bottom layer of each soil strip in the slope, then laying a water content sensor at the position which is less than or equal to 1m from the surface layer of each soil strip at the toe of the foundation pit slope, and recording the total number of the water content sensors laid by each soil strip at the toe of the foundation pit slope as n;
determining the average water content of each soil strip at the top and in the slope of the foundation pit:
Figure BDA0002641590480000035
determining the average water content of each soil strip of the slope toe of the foundation pit slope:
Figure BDA0002641590480000036
in the formula: omegatiThe water content of the ith soil strip at the time t.
Further, the specific method for determining the water content power unloading parameters under the conditions of different water content in the fourth step is as follows:
the skid resistance of the ith soil strip under rainfall conditions is determined according to the formula (10):
Figure BDA0002641590480000041
the average skid resistance of n soil strips under rainfall conditions is determined according to the formula (11):
Figure BDA0002641590480000042
in the formula: xiIs the width of the soil body, /)iIs the average height of the soil strips;
wherein the average skid resistance of n soil strips corresponding to the t monitoring time is a water content power unloading parameter, and the average value of displacement changes of n displacement monitoring points corresponding to the t monitoring time
Figure BDA0002641590480000043
Is the displacement response.
Furthermore, the concrete method for determining the power unloading and displacement coupling evaluation parameters of the water content of the foundation pit slope in the fifth step is as follows:
initial monitoring time t of foundation pit1Dynamic unloading capacity of water content of corresponding foundation pit slope
Figure BDA0002641590480000044
Initial displacement response value corresponding thereto
Figure BDA0002641590480000045
The ratio is defined as the response rate lambda of the displacement of the initial water content of the foundation pit slope during dynamic unloading0：
Figure BDA0002641590480000046
The dynamic capacity of unloading the water content at any time t
Figure BDA0002641590480000047
Dynamic displacement response corresponding thereto
Figure BDA0002641590480000048
The ratio of the water content to the displacement response rate is defined as the response rate lambda of the water content power unloading displacement at any time tt：
Figure BDA0002641590480000049
The water content power unloading displacement response rate lambda of any time ttAnd its initial time water content power unloading displacement response rate lambda0The ratio is defined as the water cut power unloading displacement response ratio etat：
Figure BDA00026415904800000410
When etatWhen the foundation pit is 1 or fluctuates near 1, judging that the foundation pit slope is in a stable stage;
when etat>1 and continuously increasing, and judging that the foundation pit side slope is in an unstable development stage.
Further, for the foundation pit slope in the unstable development stage, the ratio of the variation of the average surface water content to the variation of the power unloading response ratio of the water content is determined as the variation rate sigma of the power unloading response ratio of the water contentt：
Figure BDA0002641590480000051
Rate of change of response to power-off ratio sigmatWhen the slope of the foundation pit is infinitely close to a constant, judging that the slope of the foundation pit is in an accelerated deformation stage, and performing prevention and treatment measures on the foundation pit at the moment; rate of change of response to power-off ratio sigmatAnd when the slope gradually or suddenly increases, judging that the foundation pit slope is in the integral sliding stage.
Further, in the second step, rock-soil in-situ test or indoor soil test is adopted to comprehensively measure the heavy gamma of the foundation pit side slope soil layer and the cohesive force c internal friction angle of the soil under the conditions of different water contents w
Figure BDA0002641590480000052
The invention has the beneficial effects that: a method for measuring rainfall parameter weakening type foundation pit slope instability critical water content determines a relation between slope instability and parameter weakening under rainfall conditions, considers the influence of reduction of anti-slip force on slope stability caused in the foundation pit soil parameter weakening process due to rainfall infiltration under the rainfall conditions, takes the average anti-slip force of n soil strips as a power unloading parameter, and takes foundation pit slope displacement in a corresponding time period as a power unloading displacement response parameter; the method comprises the steps of measuring the change and the evolution trend of a dynamic slope stability coefficient under the condition of continuous rainfall, determining a coupling prediction parameter and an evaluation model of a power unloading displacement response ratio of the foundation pit slope according to the relation between the power unloading parameter and the displacement response parameter, primarily judging the stability of the foundation pit slope by taking the power unloading displacement response ratio as a parameter, judging the slope at the unstable development stage by utilizing the change rate of the power unloading response ratio of the water content, predicting and forecasting, wherein the slope is at the domestic advanced level.
Drawings
FIG. 1 is a flow chart of the present invention.
Fig. 2 is a schematic diagram of arrangement of monitoring points and datum points of a foundation pit slope.
FIG. 3 is a schematic view of the foundation pit slope strip soil-splitting structure of the present invention.
FIG. 4 is a schematic diagram showing the infiltration characteristics of the water content in the slope body at the early stage of rainfall.
FIG. 5 is a schematic diagram showing the infiltration characteristics of the water content in the slope body in the middle stage of rainfall.
FIG. 6 is a schematic diagram showing the infiltration characteristics of the water content in the slope body in the late rainfall period.
FIG. 7 is a schematic view showing the infiltration characteristics of the water content in the interior of the slope body after rain-stop according to the present invention.
In the figure: 10-foundation pit side slope body; 20-displacement monitoring points; 30-displacement monitoring reference point; 40-an observation station; 50-an automatic total station; 60-remote monitoring center.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by a person of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the protection scope of the present invention.
It should be noted that in the description of the present invention, the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. indicating the directions or positional relationships are based on the directions or positional relationships shown in the drawings, which are only for convenience of description, and do not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
Furthermore, it should be noted that, in the description of the present invention, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
Taking the foundation pit depth as 14 meters, the length as 150 meters and the width as 100 meters as an example, the method is adopted to measure the rainfall parameter weakening type foundation pit slope instability critical water content.
The first embodiment is as follows: as given by fig. 1 to 3;
step 1, measuring basic physical and mechanical parameters of a foundation pit slope:
according to the engineering rock mass test method standard and the geotechnical test regulation, systematic geophysical prospecting, testing, investigation and surveying and mapping are carried out on the foundation pit slope to be measured, the change rule of the vertical depth of the foundation pit slope body by the inclination angle is determined, according to the inclination rule, the equal-width vertical strip division is carried out on the foundation pit slope body, and the inclination angle of the foundation pit is recorded as thetaiThe average height of the ith soil strip is recorded as liSee table 1.
Table 1 list of basic physical and mechanical parameters of foundation pit slope
Parameters of soil strips 1 2 3 4
Xi 4 4 4 4
li 12.5 10.4 8.6 4.1
θ i 60° 60° 60° 60°
Comprehensively measuring the soil gravity of a foundation pit side slope soil layer to be 13 by using a rock-soil in-situ test or an indoor soil test and comprehensively measuring the cohesive force c internal friction angle of the soil under the conditions of different water contents (w)
Figure BDA0002641590480000071
The results are shown in Table 2.
TABLE 2 summary of the results of the experiment
Figure BDA0002641590480000072
Step two, determining weakening rules of cohesive force and internal friction angle of foundation pit slope body under different water content conditions
Determining the cohesive force c and the internal friction angle of the foundation pit slope body under the conditions of different water contents according to the steps, the principle 1 and the formulas (1) and (2)
Figure BDA0002641590480000073
The weakening rule of (2):
Figure BDA0002641590480000074
Figure BDA0002641590480000075
in the formula: b ═ eB，a＝am；d＝eD，e＝em
Taking logarithm of both sides of formula (1):
Figure BDA0002641590480000076
let lnc be y; lnb ═ B;
Figure BDA0002641590480000077
namely: y ═ B + ax (4)
Let the experimental data of equation (4) be n, which can be obtained from the basic principle of least squares:
the value of B, a can be obtained by substituting the above formula into equation (5):
Figure BDA0002641590480000081
similarly, the determinations D and e can be obtained from the above stepsmThe value of (c):
Figure BDA0002641590480000082
the calculation results are shown in Table 3
TABLE 3 summary of the results of the calculations
B b a＝am D d e＝em
5.03 153 -0.46 4.5 90 -0.56
Step three, arrangement and installation of foundation pit displacement and slope water content monitoring equipment under rainfall condition
According to the duration of a rainfall event and the displacement and stability conditions of the side slope of the foundation pit, one hour is taken as a monitoring time interval of the foundation pit, a wireless GPS displacement monitoring device and a DltaT type moisture meter are adopted (shown in figure 3) to monitor the displacement of the foundation pit and the moisture content of the slope body in real time at a certain time interval, and S is determined according to the displacement time sequence of the side slope of the foundation pit and the displacement and stability conditions of the side slope of the foundation pittTime series omega of water content of Hehe slopeti。
The specific monitoring steps are as follows:
(1) monitoring of foundation pit displacement
Setting n displacement monitoring points on key points of internal force and deformation of the foundation pit side slope, setting more than 3 deformation monitoring reference points in the area without deformation except the monitored foundation pit side slope, and transmitting the monitoring data to a remote monitoring terminal for classification and pre-classification through an automatic total station of the foundation pit side slope siteProcessing and then preprocessing the obtained average value of the displacement change of the n displacement monitoring points
Figure BDA0002641590480000083
Figure BDA0002641590480000084
In the formula: stiThe displacement value of the ith displacement monitoring point is t time.
The monitoring data are shown in Table 4
Table 4 summary of monitoring data
Figure BDA0002641590480000091
(2) Monitoring of water content of foundation pit slope body
According to the principle 1, the water content sensors are distributed on each soil strip of the foundation pit slope top, the slope middle and the slope foot, firstly, one water content sensor is distributed on the surface layer, the middle layer and the bottom layer of each soil strip of the foundation pit slope top and the slope middle and then, 4 water content sensors are distributed at the position which is less than or equal to 1m from the surface layer of each soil strip of the foundation pit slope foot.
Determining the average water content of each soil strip at the top and in the slope of the foundation pit slope according to a formula (8):
Figure BDA0002641590480000092
determining the average water content of each soil strip of the slope toe of the foundation pit slope according to a formula (9):
Figure BDA0002641590480000093
in the formula: omegatiThe water content of the ith soil strip at the time t.
The water content monitoring results are shown in Table 5.
TABLE 5 moisture content monitoring results List
Figure BDA0002641590480000094
Step four, determining the dynamic unloading parameters of the water content under the conditions of different water contents
Determining the skid resistance of the ith soil strip under the rainfall condition according to the formula (10):
Figure BDA0002641590480000095
determining the average skid resistance of n soil strips under the rainfall condition according to a formula (11):
Figure BDA0002641590480000101
in the formula: xiIs the width of the soil body, /)iIs the average height of the soil strips.
Wherein the average skid resistance of n soil strips corresponding to the t monitoring time is a water content power unloading parameter, and the average value of displacement changes of n displacement monitoring points corresponding to the t monitoring time
Figure BDA0002641590480000102
Is the displacement response.
The calculation results are shown in Table 6
TABLE 6 summary of the calculated results
Figure BDA0002641590480000103
Step five, determining power unloading and displacement coupling evaluation parameters of foundation pit slope water content
Initial monitoring time t of foundation pit1Dynamic unloading capacity of water content of corresponding foundation pit slope
Figure BDA0002641590480000104
Initial displacement response value corresponding thereto
Figure BDA0002641590480000105
The ratio is defined as the pitSlope initial water content power unloading displacement response rate lambda0。
Figure BDA0002641590480000106
The dynamic capacity of unloading the water content at any time t
Figure BDA0002641590480000107
Dynamic displacement response corresponding thereto
Figure BDA0002641590480000108
The ratio of the water content to the displacement response rate is defined as the response rate lambda of the water content power unloading displacement at any time tt。
Figure BDA0002641590480000109
The water content power unloading displacement response rate lambda of any time ttAnd its initial time water content power unloading displacement response rate lambda0The ratio is defined as the water cut power unloading displacement response ratio etatNamely:
Figure BDA0002641590480000111
when etatWhen the foundation pit is 1 or fluctuates near 1, judging that the foundation pit slope is in a stable stage; when etatAnd (5) the slope is less than 1 and is continuously increased, and the foundation pit slope is judged to be in an unstable development stage.
The calculation results are shown in Table 7
TABLE 7 summary of the calculated results
Figure BDA0002641590480000112
Step six, determining critical water content criterion for foundation pit slope instability
Determining the ratio of the variation of the average surface water content to the variation of the power unloading response ratio of the water content as the power of the water content for the foundation pit slope in the unstable development stageUnload response ratio rate of change σt:
Figure BDA0002641590480000113
The calculation results are shown in Table 8
TABLE 8 summary of the calculated results
Figure BDA0002641590480000114
Rate of change of response to power-off ratio sigmatWhen the slope of the foundation pit is infinitely close to a constant, judging that the slope of the foundation pit is in an accelerated deformation stage, and performing prevention and treatment measures on the foundation pit at the moment; rate of change of response to power-off ratio sigmatWhen the slope of the foundation pit gradually or suddenly increases, the slope of the foundation pit is judged to be in the integral slip stage, and sigma is obtained when the monitoring time is 3h, 4h and 5h according to the analysis of the table 7tInfinitely approaching 11.3, so that the foundation pit is judged to be in an accelerated deformation stage; monitoring time 6h time sigmatGradually increasing, wherein the foundation pit begins to be in an integral slip stage at the moment, and sigma is measured after monitoring time is 6htAnd (5) suddenly increasing, wherein the foundation pit is in an integral sliding stage.
Example two: given by fig. 4 to 7:
rainfall infiltration is the process that the internal moisture content of slope increases gradually (namely from unsaturated to saturated motion process), and the infiltration characteristics of the internal moisture content of slope are different at different rainfall stages: at the early stage of rainfall, along with the duration of rainfall time, the water content and the gravity of a slope body are gradually increased, and a plastic zone is formed on the surface layer of the side slope at first and gradually extends towards the slope toe; in the middle stage of rainfall, the surface layer of the slope toe is saturated at first, and simultaneously, the plastic area of the surface rock-soil body is further accelerated to extend upwards and inwards along the slope surface under the softening action of rainwater; in the later stage of rainfall, the surface rock and soil body tend to be saturated, the rainfall infiltration depth is further enlarged, the substrate suction is reduced, the plastic zone formed at the toe of the slope is maximized, and the plastic zone with certain connectivity is formed in the slope body; after the rain stops, the saturated area on the surface layer of the slope body has a gradual dissipation process, one part of rainwater is converted into surface runoff, one part of rainwater is continuously infiltrated into the soil body, and the area of the deep plastic area in the slope body is also continuously increased due to the continuous infiltration of the rainwater, so that a plastic area distribution belt with connectivity is formed, and favorable conditions are provided for the formation of a potential slip surface of the side slope.
Under the rainfall condition, the degree of water weakening of rock and soil body parameters at the toe, the top and the interior of a slope body is greatly different; the seepage diagram in the whole process of rainfall infiltration shows that: in the early stage of rainfall, the surface layer of the slope body is most sensitive to the influence of rainfall, so that the soil parameters of the rock and the soil body of the surface layer of the slope body are weakened firstly; with the progress of rainfall, the slope toe is saturated firstly, and the saturation area of the slope toe is gradually increased along with the continuation of the rainfall time, so that the degree of the water weakening of the slope toe is obviously higher than that of other parts of the slope body.
Parameters such as shear strength, elastic modulus and the like are main characteristic indexes of rock and soil mass, and the size of the parameters directly influences the capacity of liquid or solid for resisting external interference; the mineral composition, the original density, the soil structure, the water content and other factors of the soil particles all influence the cohesive force and the size of the internal friction angle; for the soil with the same property, the shear strength parameter of the soil is mainly influenced by rainfall, the rainfall infiltration increases the water content in the slope body so as to cause the weak bonding water and the free water content among soil particles to rise, the particle gaps are filled with water molecules, and the frictional resistance and the cohesive force among the particles are reduced; the influence of the water content on the shear strength of the rock-soil mass has attracted the attention of scholars at home and abroad very early; due to the difference of regions and rainfall, the soil quality is mainly unsaturated soil, and when the natural density is constant, the shear strength of the cohesive soil is obviously reduced along with the increase of the water content; when the water content is constant, the larger the natural density is, the larger the shear strength is; the larger the natural density is, the more obvious the cohesive force of the cohesive soil is weakened along with the increase of the water content; according to the existing research results of scholars at home and abroad, the method comprises the following steps: along with the increase of the water content, the process of reducing the rock-soil body parameters is roughly divided into three sections: a rapid descending stage, a descending speed slowing stage and a stage without obvious change, and the water content and the rock-soil body parameters are never in a simple linear relation or a relationship of the water content and the rock-soil body parameters; according to a great amount of research data of the predecessors, the weakening rule of the cohesive force and the internal friction angle is found to be gradually weakened as the functional relation of the formulas (1) and (2).
Figure BDA0002641590480000131
Figure BDA0002641590480000132
In the formula: b ═ eB，a＝am；d＝eD，e＝em；
Taking logarithm of both sides of formula (1):
Figure BDA0002641590480000133
let lnc be y; lnb ═ B;
Figure BDA0002641590480000134
namely: y ═ B + ax (4)
Figure BDA0002641590480000135
Figure BDA0002641590480000136
Let the experimental data of equation (4) be n, which can be obtained from the basic principle of least squares:
Figure BDA0002641590480000137
Figure BDA0002641590480000138
Figure BDA0002641590480000139
Figure BDA00026415904800001310
Figure BDA00026415904800001311
the value of B, a can be obtained by substituting the above formula into equation (12):
Figure BDA00026415904800001312
the solving steps of the formula (2) and the formula (1) are the same; determining D and e according to equation (13)mThe value of (c):
Figure BDA00026415904800001313
the invention has the beneficial effects that: a method for measuring rainfall parameter weakening type foundation pit slope instability critical water content determines a relation between slope instability and parameter weakening under rainfall conditions, considers the influence of reduction of anti-slip force on slope stability caused in the foundation pit soil parameter weakening process due to rainfall infiltration under the rainfall conditions, takes the average anti-slip force of n soil strips as a power unloading parameter, and takes foundation pit slope displacement in a corresponding time period as a power unloading displacement response parameter; the method comprises the steps of measuring the change and the evolution trend of a dynamic slope stability coefficient under the condition of continuous rainfall, determining a coupling prediction parameter and an evaluation model of a power unloading displacement response ratio of the foundation pit slope according to the relation between the power unloading parameter and the displacement response parameter, primarily judging the stability of the foundation pit slope by taking the power unloading displacement response ratio as a parameter, judging the slope at the unstable development stage by utilizing the change rate of the power unloading response ratio of the water content, predicting and forecasting, wherein the slope is at the domestic advanced level.
The present invention has been described in detail with reference to the specific embodiments and examples, but these are not intended to limit the present invention. Many variations and modifications may be made by one of ordinary skill in the art without departing from the principles of the present invention, which should also be considered as within the scope of the present invention.

Claims (9)

1. A method for measuring the instability critical water content of a rainfall parameter weakening type foundation pit slope is characterized in that,
the method comprises the following steps of firstly, measuring basic physical and mechanical parameters of the foundation pit side slope (10): carrying out systematic geophysical prospecting, testing, investigation and surveying and mapping on the foundation pit slope to be measured;
determining the weakening rule of the cohesive force and the internal friction angle of the foundation pit slope body under the condition of different water contents: according to the process that the water content in the slope body is gradually increased when rainfall infiltrates, the cohesive force c and the internal friction angle of the slope body of the foundation pit under the condition of different water content are determined
Figure FDA0002641590470000017
The weakening rule of (2);
thirdly, arranging and installing foundation pit displacement and slope water content monitoring equipment under the rainfall condition;
determining the dynamic unloading parameters of the water content under the conditions of different water contents: setting n displacement monitoring points (20) and determining the skid resistance of the ith soil strip under the rainfall condition, wherein the average skid resistance of the n soil strips corresponding to the t monitoring time is a water content power unloading parameter;
fifthly, determining parameters for power unloading and displacement coupling evaluation of the water content of the foundation pit slope;
and step six, determining the criterion of the instability critical water content of the foundation pit slope.
2. The method for determining the critical water content of the rainfall parameter weakening type foundation pit slope instability according to claim 1, wherein in the step one, the change rule of the vertical depth and the inclination angle of the foundation pit slope body is determined, the equal-width vertical striping is carried out on the foundation pit slope body according to the inclination rule, and the inclination angle of the foundation pit is recorded as thetaiThe average height of the ith soil strip divided by the equal-width vertical strips is recorded as liComprehensively measuring the heavy gamma of the foundation pit slope soil layer and the cohesive force c internal friction angle of the soil under the conditions of different water contents w
Figure FDA0002641590470000015
3. The method for determining the critical moisture content of the rainfall parameter weakening type foundation pit slope instability according to claim 2, wherein in the second step, the cohesive force c and the internal friction angle of the foundation pit slope body under the condition of different moisture contents
Figure FDA0002641590470000016
The weakening rule is as follows:
Figure FDA0002641590470000011
Figure FDA0002641590470000012
in the formula: b ═ eB，a＝am；d＝eD，e＝em；
Taking logarithm of both sides of formula (1):
Figure FDA0002641590470000013
let lnc be y; lnb ═ B;
Figure FDA0002641590470000014
namely: y ═ B + ax (4)
Let the experimental data of equation (4) be n, which can be obtained from the basic principle of least squares:
the value of B, a can be obtained by substituting the above formula into equation (5):
Figure FDA0002641590470000021
similarly, the determinations D and e can be obtained from the above stepsmThe value of (c):
Figure FDA0002641590470000022
4. the method for determining the critical water content of the rainfall parameter weakening type foundation pit slope instability according to claim 1, wherein in the third step, a monitoring time interval unit of the foundation pit is set, a wireless GPS displacement monitoring device and a DltaT type moisture meter are adopted to monitor the displacement of the foundation pit and the water content of the slope body in real time according to a unit time interval, and a foundation pit slope displacement time sequence S is respectively determinedtTime series omega of water content of Hepo slope bodyti；
(1) The method for monitoring the displacement of the foundation pit side slope body comprises the following steps: the displacement value of the ith displacement monitoring point at the time t is recorded as StiSetting no less than three deformation monitoring datum points (30) in areas without deformation outside the monitored foundation pit slope body, setting a plurality of monitoring points (40), setting a foundation pit slope site automatic total station (50) at each monitoring point to transmit monitoring data to a remote monitoring terminal for classification pretreatment, communicating the remote monitoring terminal (60), and then pretreating to obtain the average value of displacement change of n displacement monitoring points
Figure FDA0002641590470000023
Figure FDA0002641590470000024
(2) The method for monitoring the water content of the foundation pit side slope body comprises the following steps: firstly, laying a water content sensor at the top of a foundation pit slope and the surface layer, the middle layer and the bottom layer of each soil strip in the slope, then laying a water content sensor at the position which is less than or equal to 1m from the surface layer of each soil strip at the toe of the foundation pit slope, and recording the total number of the water content sensors laid by each soil strip at the toe of the foundation pit slope as n;
determining the average water content of each soil strip at the top and in the slope of the foundation pit:
Figure FDA0002641590470000025
determining the average water content of each soil strip of the slope toe of the foundation pit slope:
Figure FDA0002641590470000026
in the formula: omegatiThe water content of the ith soil strip at the time t.
5. The method for determining the critical water content of the rainfall parameter weakening type foundation pit slope instability according to claim 4, wherein the specific method for determining the dynamic unloading parameters of the water content under the conditions of different water contents in the fourth step is as follows:
the skid resistance of the ith soil strip under rainfall conditions is determined according to the formula (10):
Figure FDA0002641590470000031
the average skid resistance of n soil strips under rainfall conditions is determined according to the formula (11):
Figure FDA0002641590470000032
in the formula: xiIs the width of the soil body, /)iIs the average height of the soil strips;
wherein the average skid resistance of n soil strips corresponding to the t monitoring time is a water content power unloading parameter, and the average value of displacement changes of n displacement monitoring points corresponding to the t monitoring time
Figure FDA0002641590470000039
Is the displacement response.
6. The method for determining the critical moisture content of the foundation pit slope instability of the rainfall parameter weakening type according to claim 1, wherein the concrete method for determining the dynamic unloading and displacement coupling evaluation parameters of the moisture content of the foundation pit slope in the fifth step is as follows:
initial monitoring time t of foundation pit1Dynamic unloading capacity of water content of corresponding foundation pit slope
Figure FDA0002641590470000033
Initial displacement response value corresponding thereto
Figure FDA0002641590470000034
The ratio is defined as the response rate lambda of the displacement of the initial water content of the foundation pit slope during dynamic unloading0：
Figure FDA0002641590470000035
The dynamic capacity of unloading the water content at any time t
Figure FDA0002641590470000036
Dynamic displacement response corresponding thereto
Figure FDA0002641590470000037
The ratio of the water content to the displacement response rate is defined as the response rate lambda of the water content power unloading displacement at any time tt：
Figure FDA0002641590470000038
The water content power unloading displacement response rate lambda of any time ttAnd its initial time water content power unloading displacement response rate lambda0The ratio is defined as the water cut power unloading displacement response ratio etat：
Figure FDA0002641590470000041
When etatWhen the foundation pit is 1 or fluctuates near 1, judging that the foundation pit slope is in a stable stage;
when etat>1 and continuously increasing, and judging that the foundation pit side slope is in an unstable development stage.
7. The method for determining the unstable critical water content of the foundation pit slope with the weakened rainfall parameters according to claim 6, wherein the ratio of the variation of the average surface water content to the variation of the dynamic unloading response ratio of the water content is determined as the variation of the dynamic unloading response ratio of the water content to the foundation pit slope in the unstable development staget：
Figure FDA0002641590470000042
Rate of change of response to power-off ratio sigmatWhen the slope of the foundation pit is infinitely close to a constant, judging that the slope of the foundation pit is in an accelerated deformation stage, and performing prevention and treatment measures on the foundation pit at the moment; rate of change of response to power-off ratio sigmatAnd when the slope gradually or suddenly increases, judging that the foundation pit slope is in the integral sliding stage.
8. The method for determining the unstable critical water content of the foundation pit slope with the weakened rainfall parameters according to claim 2, wherein a rock-soil in-situ test is adopted to determine the heavy gamma of the soil layer of the foundation pit slope and the internal friction angle of the cohesive force c of the soil under the conditions of different water contents w
Figure FDA0002641590470000043
9. The method for determining the critical moisture content of the rainfall parameter weakening type foundation pit slope instability according to claim 2, characterized in that an indoor geotechnical test is adopted to comprehensively determine the heavy gamma of a foundation pit slope soil layer and the cohesive force c internal friction angle of soil under the conditions of different moisture contents w
Figure FDA0002641590470000044
CN202010841498.XA 2020-08-20 2020-08-20 Method for measuring instability critical water content of rainfall parameter weakening type foundation pit slope Pending CN111877417A (en)

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