CN111310392B - Method for evaluating unstable area amplification effect of foundation pit excavation slope - Google Patents

Method for evaluating unstable area amplification effect of foundation pit excavation slope Download PDF

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CN111310392B
CN111310392B CN202010144792.5A CN202010144792A CN111310392B CN 111310392 B CN111310392 B CN 111310392B CN 202010144792 A CN202010144792 A CN 202010144792A CN 111310392 B CN111310392 B CN 111310392B
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李亮
褚雪松
路世豹
袁长丰
凌贤长
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Qingdao University of Technology
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Abstract

The invention belongs to the field of geotechnical engineering safety evaluation and instability risk quantification, and particularly relates to a method for evaluating an amplification effect of an instability area of a foundation pit excavation slopeiLess than 1; adjusting the horizontal earthquake acceleration value to ensure that the safety coefficient of the side slope under the original soil layer mechanical parameters is Fi(ii) a Simulating the displacement field in the last two steps by using a smooth particle fluid dynamics method; setting a critical value, and respectively counting the sliding areas of the side slopes under the two conditions; calculating an amplitude xi between the intensity reduction effect and the seismic effecti(ii) a Updating the reduction factor and the previous seismic acceleration value to reduce FiRepeating the above operations; and fitting all the horizontal seismic acceleration values and the amplification values to obtain a change curve of the instability area of the foundation pit excavation slope under the action of the earthquake, thereby obtaining an amplification effect. The method can reasonably, effectively and quickly provide the amplification effect of the instability area of the foundation pit excavation slope under the action of the earthquake load.

Description

Method for evaluating unstable area amplification effect of foundation pit excavation slope
Technical Field
The invention belongs to the field of geotechnical engineering safety evaluation and instability risk quantification, and particularly relates to a method for evaluating an amplification effect of an instability area of a foundation pit excavation slope.
Background
The instability of the foundation pit side slope is one of the dangerous factors influencing the construction of the building engineering in China, and once the instability of the foundation pit side slope occurs, the instability affects the construction progress of the building, disturbs the progress of a project and increases the construction cost; the life danger of the construction workers is seriously threatened. Many foundation pit collapse accidents occur in China every year, and the economic loss of China is caused to different degrees. According to statistics, the accident of foundation pit slope instability under the action of earthquake also happens occasionally. Therefore, how to evaluate the instability risk of the foundation pit side slope under the action of the earthquake is very important to avoid foundation pit collapse.
In the field of foundation pit slope instability risk evaluation, a limit balance method, a finite element strength reduction method and a limit analysis method are generally adopted to quantify the instability area of the foundation pit slope, the instability area corresponding to the minimum safety factor is determined through different search mechanisms, and the instability area index is utilized to evaluate the foundation pit slope instability risk. However, for the excavation slope of the foundation pit, which must consider the action of the earthquake load, the excavation slope is generally performed by a dynamic time course method, and the calculation is time-consuming and quite huge. Therefore, an evaluation method for foundation pit excavation slope instability area amplification effect capable of reasonably and effectively considering earthquake load effect is needed at present.
Disclosure of Invention
According to the defects of the prior art, the invention provides the method for evaluating the amplification effect of the instability area of the foundation pit excavation slope, and the amplification effect of the instability area of the foundation pit excavation slope under the action of the earthquake load can be reasonably and effectively given.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method for evaluating the unstable area amplification effect of a foundation pit excavation slope comprises the following steps:
step 1, simulating an intensity reduction effect: let i be more than or equal to 1, i be a positive integer, and when the horizontal seismic acceleration value is zero, the minimum safety coefficient of the foundation pit excavation slope is reduced to a certain value less than 1 by reducing the original soil layer mechanical parameters, and the value is recorded as Fi；
Step 2, simulating earthquake action effect: by adjusting the horizontal seismic acceleration value alphahiCalculating the safety coefficient of the foundation pit excavation slope under the original soil layer mechanical parameters by utilizing a simplified Pickup method in a limit balance method, so that the minimum safety coefficient reaches Fi；
Step 3, simulating the minimum safety factor F of the foundation pit excavation side slope in the step 1 and the step 2 respectively by using a smooth particle fluid dynamics methodiA displacement field of time;
step 4, giving a critical value epsilon, and counting the excavation edge of the foundation pit in the step 1 based on the two displacement fields in the step 3Area of slope sliding, marked A1iCounting the sliding area of the foundation pit excavation slope in the step 2, and recording the area as A2i；
Step 5, calculating an amplification value xi between the intensity reduction effect and the earthquake action effectiWherein
Figure GDA0002945191410000021
Step 6, selecting M as the number of times of calculation, wherein M is set as a positive integer according to the requirement;
if i<M, let i equal to i +1, update the reduction coefficient λ in step 1iAnd the horizontal seismic acceleration value in step 2 is alphahiWherein λ isi>λi-1Recalculating the minimum factor of safety FiTo a minimum safety factor Fi<Fi-1(ii) a Repeating the steps 3-6;
if i is equal to M, entering the next step;
step 7, fitting all horizontal seismic acceleration values
Figure GDA0002945191410000022
And the amplification value
Figure GDA0002945191410000023
Obtaining a variation curve of the instability area of the foundation pit excavation side slope under the action of the earthquake, wherein the variation curve shows the variation rule of the instability area of the foundation pit excavation side slope under the action of the earthquake;
step 8, obtaining a horizontal seismic acceleration value alpha by inquiring a foundation pit design filehAnd inquiring a corresponding amplification value xi on the change curve, wherein the amplification effect is 1+ xi.
Further, the specific implementation process of step 1 is as follows:
step 1.1, establishing a geometric model of a foundation pit excavation side slope, and acquiring mechanical parameters of an original soil layer according to a geological survey report: volume weight gamma, cohesion c and internal friction angle
Figure GDA0002945191410000024
Step 1.2, when the horizontal earthquake acceleration value is zero, utilizing a simplified Pickup method in a limit balance method to calculate a safety coefficient F of the foundation pit excavation slopes；
Step 1.3, selecting a reduction coefficient lambdai，λi>0, reducing the mechanical parameters of cohesive force c and internal friction angle of the original soil layer
Figure GDA0002945191410000031
Obtaining new soil layer mechanical parameter cohesive force c'iAnd angle of internal friction
Figure GDA0002945191410000032
Wherein the content of the first and second substances,
Figure GDA0002945191410000033
δi＝Fs+λi；
step 1.4, based on new soil layer mechanical parameters, when the horizontal earthquake acceleration value is zero, the minimum safety coefficient of the foundation pit excavation side slope is calculated by utilizing the simplified Pico-Purpt method in the extreme balance method again to enable the minimum safety coefficient to reach a value smaller than 1, and the value is recorded as Fi。
Further, the geometric model of the foundation pit excavation slope is established to comprise the excavation depth H of the foundation pit slope and a slope angle beta of the slope.
Further, the specific implementation process of step 2 is as follows:
setting mechanical parameters of an original soil layer of a foundation pit excavation side slope and a horizontal seismic acceleration value alphahiAnd calculating the safety coefficient F of the foundation pit excavation slope by utilizing a simplified Pico-Purpur method in a limit balance methodsIf the calculated safety factor F is obtaineds>FiThen, α is increased stepwisehiMake the safety factor Fs＝Fi(ii) a If calculated Fs<FiThen α is decreased stepwisehiMake Fs＝Fi(ii) a Recording the factor of safety Fs＝FiAlpha of timehi。
The invention has the following beneficial effects: when the foundation pit excavation side slope has the same safety coefficient, a mapping relation between a foundation pit excavation side slope soil layer mechanical parameter reduction effect and a seismic action effect is established, the area of the foundation pit side slope instability under the reduction effect and the seismic action effect is further determined through a smooth particle fluid dynamic method, the change rule of the area of the foundation pit excavation side slope instability under the seismic action is established through comparative analysis, the foundation pit excavation side slope instability area amplification effect is finally evaluated, the calculation process is reasonable, and the efficiency is far higher than that of foundation pit excavation side slope risk evaluation under the seismic loading action through a power time-course method in the prior art.
Drawings
FIG. 1 is a schematic flow diagram of a method provided by the present invention;
FIG. 2 is a schematic view of a side slope of a foundation pit excavation according to an embodiment of the present invention;
FIG. 3 is a cloud view of a displacement field of a foundation pit excavation slope corresponding to the strength reduction effect under a certain minimum safety factor in the embodiment of the present invention;
FIG. 4 is a cloud view of a displacement field of a side slope of a foundation pit excavation corresponding to an earthquake action effect under a certain minimum safety factor in an embodiment of the invention;
FIG. 5 is a graph showing the variation of the unstable area of the excavation slope of the foundation pit under the effect of earthquake.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
The first embodiment is as follows:
as shown in fig. 1, the method for evaluating the effect of amplifying the unstable area of the excavation slope of the foundation pit provided by the invention comprises the following steps:
step 1, simulating an intensity reduction effect:
let i be more than or equal to 1, i be a positive integer, and when the horizontal seismic acceleration value is zero, the minimum safety coefficient of the foundation pit excavation slope is reduced to a certain value less than 1 by reducing the original soil layer mechanical parameters, and the value is recorded as Fi；
The method specifically comprises the following steps:
step 1.1, aiming at the researched foundation pit excavation side slope, establishing a geometric model of the foundation pit excavation side slope, which can comprise foundation pit side slope excavationDepth H, slope angle beta, and obtaining mechanical parameters of an original soil layer according to a geological survey report: comprising a volume weight gammajC, cohesion forcejAnd angle of internal friction
Figure GDA0002945191410000041
j is 1,2, n, n is the number of soil layers;
step 1.2, based on the geometric models H and beta of the foundation pit excavation side slope, considering the mechanical parameter unit weight gamma of the original soil layerjC, cohesion forcejAnd angle of internal friction
Figure GDA0002945191410000042
The safety factor F of the foundation pit excavation slope is calculated by utilizing a simplified Pico-Puff method in a limit balance method without considering the earthquake load, namely the horizontal earthquake acceleration is zeros；
Step 1.3, selecting a reduction coefficient lambdai，λi>0，λiGenerally a small positive number, and carrying out reduction operation on mechanical parameters of an original soil layer to obtain a new soil layer mechanical parameter of cohesive force c'jiAnd angle of internal friction
Figure GDA0002945191410000043
Wherein the content of the first and second substances,
Figure GDA0002945191410000044
δi＝Fs+λi；
step 1.4, when the horizontal earthquake acceleration value is zero, based on new soil layer mechanical parameters, calculating the minimum safety coefficient of the foundation pit excavation side slope by utilizing a simplified Pico-Purpur method in the extreme balance method again to enable the minimum safety coefficient to reach a value less than 1, and recording as Fi。
Step 2, simulating earthquake action effect:
based on geometric models H and beta of foundation pit excavation side slope, mechanical parameter volume weight gamma of original soil layer is consideredjC, cohesion forcejAnd angle of internal friction
Figure GDA0002945191410000051
By adjusting the horizontal seismic acceleration value alphahiCalculating the safety coefficient F of the foundation pit excavation slope under the original soil layer mechanical parameters by utilizing a simplified Pickup method in a limit balance methodsIf the calculated safety factor F is obtaineds>FiThen, α is increased stepwisehiMake the safety factor Fs＝Fi(ii) a If calculated Fs<FiThen α is decreased stepwisehiMake Fs＝Fi(ii) a Recording the factor of safety Fs＝FiAlpha of timehi。
Step 3, simulating the minimum safety factor F of the foundation pit excavation side slope in the step 1 and the step 2 respectively by using a smooth particle fluid dynamics methodiA displacement field of time;
the method specifically comprises the following steps:
dispersing a foundation pit excavation slope geometric model into G circular particles with the radius of R;
simulating foundation pit excavation slope safety coefficient F in steps 1 and 2 by using smooth particle fluid dynamics method respectivelyiA displacement field of time;
recording and storing displacement value of each particle
Figure GDA0002945191410000052
G is 1,2, …, G is a positive integer, superscripts s and e respectively represent foundation pit excavation slope displacement fields in the step 1 and the step 2, and G is the total number of the round particles;
step 4, giving a critical value epsilon, counting the sliding area of the foundation pit excavation slope in the step 1 based on the two displacement fields in the step 3, and recording the area as A1iCounting the sliding area of the foundation pit excavation slope in the step 2, and recording the area as A2i；
The method specifically comprises the following steps:
calculating a sliding identification value theta which is H multiplied by epsilon, wherein H is the excavation depth of the foundation pit, and if the sliding identification value theta is H multiplied by epsilon, H is the excavation depth of the foundation pit
Figure GDA0002945191410000053
G is 1,2, …, G, the area of the G-th particle is added to a1i(ii) a If it is
Figure GDA0002945191410000054
G is 1,2, …, G, the area of the G-th particle is added to a2i。
Step 5, calculating an amplification value xi between the intensity reduction effect and the earthquake action effectiWherein
Figure GDA0002945191410000055
Step 6, selecting M as the number of times of calculation, namely the number of groups of data to be finally obtained, wherein M is set as a positive integer according to the requirement;
if i<M, let i equal to i +1, update the reduction coefficient λ in step 1iAnd the horizontal seismic acceleration value in step 2 is alphahiWherein λ isi>λi-1Recalculating the minimum safety factors F of step 1 and step 2iTo a minimum safety factor Fi<Fi-1(ii) a Repeating the steps 3-6;
if i is equal to M, entering the next step;
step 7, obtaining M horizontal seismic acceleration values and M amplitude values, and fitting the obtained horizontal seismic acceleration values
Figure GDA0002945191410000061
And the amplification value
Figure GDA0002945191410000062
Obtaining a variation curve of the instability area of the excavation slope of the foundation pit under the action of the earthquake; the change curve shows the change rule of the instability area of the foundation pit excavation slope under the earthquake action effect.
Step 8, obtaining a horizontal seismic acceleration value alpha by inquiring a foundation pit design filehAnd inquiring a corresponding amplification value xi on the change curve, wherein the amplification effect is 1+ xi.
According to the method provided by the invention, when the foundation pit excavation side slope has the same safety coefficient, a mapping relation between the foundation pit excavation side slope soil layer mechanical parameter reduction effect and the earthquake action effect is established, the area of the foundation pit side slope instability under the reduction effect and the earthquake action effect is further determined by a smooth particle fluid dynamic method, the change rule of the area of the foundation pit excavation side slope instability under the earthquake action is established through contrast analysis, the foundation pit excavation side slope instability area amplification effect is finally evaluated, the calculation process is reasonable, and the efficiency is far higher than the foundation pit excavation side slope risk evaluation under the earthquake load action through a power time course method in the prior art.
The following example is described with reference to fig. 2.
As shown in fig. 2, the slope height of a certain excavation slope of a foundation pit, that is, the excavation depth of the foundation pit is H5 m, the slope angle β of the slope is 45 °, and a uniform soil layer is formed within the excavation depth, that is, n is 1. The mechanical parameters of the original soil layer of the foundation pit excavation side slope are as follows: the gravity gamma of the soil is 20kN/m3Angle of internal friction
Figure GDA0002945191410000063
The cohesive force c of the soil is 9.0 kPa;
not considering the action of seismic load, namely taking gamma as 20kN/m when the horizontal seismic acceleration is zero3，
Figure GDA0002945191410000064
c is 9.0kPa, and the safety factor F is calculated according to the simplified method of the extreme balance methods＝1.10；
Taking a reduction coefficient lambda1＝0.05，δ1＝Fs+λ1＝1.15，γ＝20kN/m3Reducing the original parameters of the soil layer of the excavation side slope of the foundation pit,
Figure GDA0002945191410000065
obtaining new soil layer mechanical parameters: wherein c'1＝7.83kPa，
Figure GDA0002945191410000066
Recalculating its safety factor F according to a simplified method of the extreme balance1＝0.96；
The mechanical parameters of the original soil layer of the side slope of foundation pit excavation are considered, wherein gamma is 20kN/m3，
Figure GDA0002945191410000067
c is 9.0kPa, and a horizontal seismic acceleration value alpha is found by trial calculationh1When the weight is 0.1g, the safety factor F of the foundation pit excavation slope under the action of earthquake load is considered1＝0.96；
Dispersing the side slope shown in figure 2 into 4080 circular particles with the diameter of 0.2m, and respectively excavating the foundation pit with the side slope soil layer mechanical parameters (gamma)1’＝20kN/m3，
Figure GDA0002945191410000071
c1’＝7.83kPa，αh0.0 and (gamma-20 kN/m)3，
Figure GDA0002945191410000072
c＝9.0kPa，αh0.1g) is input into a fluid dynamics method program of the smooth particles, displacement fields of the excavation side slopes of the foundation pit are obtained and are shown in figures 3 and 4, and the displacement values of the side slope particles under two conditions are recorded and stored respectively and are recorded as
Figure GDA0002945191410000073
The critical value epsilon is given to be 0.05, the sliding recognition value theta is calculated to be H multiplied by epsilon to be 5 multiplied by 0.05 to be 0.25m,
Figure GDA0002945191410000074
when g is 1,2, …,4080, the area of the g-th particle is added to a11(ii) a If it is
Figure GDA0002945191410000075
When g is 1,2, …,4080, the area of the g-th particle is added to a21(ii) a Finally adding to obtain A11＝10.68m2，A21＝15.68m2。
Calculating the instability sliding area increase value
Figure GDA0002945191410000076
Continuously increasing the reduction coefficient, and taking lambda2＝0.23，λ3Obtaining new foundation pit excavation side slope as 0.32%Factor of safety F20.90 and F3New horizontal seismic acceleration value α of 0.84h20.15g and αh30.2g, corresponding new value xi20.35 and xi30.66, i.e. M is selected to be 3;
fitting the above to obtain a series
Figure GDA0002945191410000077
Value sum
Figure GDA0002945191410000078
The obtained value is shown in figure 5, and the variation curve of the instability area of the foundation pit excavation slope under the earthquake action effect is obtained.
Obtaining a horizontal seismic acceleration value alpha by inquiring a foundation pit design filehThe gain value xi is inquired to be 0.42 on the fitting curve, and the amplification effect is 1+ xi to be 1.42.
In order to prove the effectiveness of the method, comparative analysis is carried out, the earthquake load action is not considered in the instability area of the traditional foundation pit excavation slope, and if the earthquake load action needs to be considered, a long calculation time is needed (according to the current calculation speed, the instability area can be obtained within 1 month generally, and the instability risk evaluation of the foundation pit excavation slope by geotechnical engineering personnel is extremely not facilitated); the method establishes the correlation between the earthquake action effect and the intensity reduction effect by using the same safety factor condition, and determines the instability sliding area by using a smooth particle fluid dynamics method, so that the amplitude value of the earthquake load action effect is 0.42. And (4) comprehensive judgment: after 0.12g of seismic load is considered, the instability area of the excavation side slope of the foundation pit is amplified by 1.42 times, so that the comparison shows that: the traditional method cannot effectively consider the effect of seismic load action on the amplification of the instability area of the foundation pit excavation slope, underestimates the instability area and the instability risk of the foundation pit excavation slope, and is not beneficial to the prevention and treatment of the instability risk of the foundation pit excavation slope. The effectiveness of the invention was verified by comparative example analysis.
The above description is an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications, equivalents, and flow changes made by using the contents of the present specification and drawings, or applied directly or indirectly to other related technical fields are included in the scope of the present invention.

Claims (3)

1. A method for evaluating the unstable area amplification effect of a foundation pit excavation slope is characterized by comprising the following steps:
step 1, simulating an intensity reduction effect:
let i be more than or equal to 1, i be a positive integer, and when the horizontal seismic acceleration value is zero, the minimum safety coefficient of the foundation pit excavation slope is reduced to a certain value less than 1 by reducing the original soil layer mechanical parameters, and the value is recorded as Fi；
Step 2, simulating earthquake action effect:
by adjusting the horizontal seismic acceleration value alphahiCalculating the safety coefficient of the foundation pit excavation slope under the original soil layer mechanical parameters by utilizing a simplified Pickup method in a limit balance method, so that the minimum safety coefficient reaches Fi；
Step 3, simulating the minimum safety factor F of the foundation pit excavation side slope in the step 1 and the step 2 respectively by using a smooth particle fluid dynamics methodiA displacement field of time;
step 4, giving a critical value epsilon, counting the sliding area of the foundation pit excavation slope in the step 1 based on the two displacement fields in the step 3, and recording the area as A1iCounting the sliding area of the foundation pit excavation slope in the step 2, and recording the area as A2i；
Step 5, calculating an amplification value xi between the intensity reduction effect and the earthquake action effectiWherein
Figure FDA0002992018540000011
Step 6, selecting M as the number of times of calculation, wherein M is set as a positive integer according to the requirement;
if i < M, let i equal i +1, update the reduction coefficient λ in step 1iAnd the horizontal seismic acceleration value in step 2 is alphahiWherein λ isi＞λi-1Recalculating the minimum factor of safety FiTo minimize the safetyCoefficient Fi＜Fi-1(ii) a Repeating the steps 3-6;
if i is equal to M, entering the next step;
step 7, fitting all horizontal seismic acceleration values
Figure FDA0002992018540000012
And the amplification value
Figure FDA0002992018540000013
Obtaining a variation curve of the instability area of the excavation slope of the foundation pit under the action of the earthquake;
step 8, obtaining a horizontal seismic acceleration value alpha by inquiring a foundation pit design filehInquiring a corresponding amplification value xi on the change curve, wherein the amplification effect is 1+ xi;
the specific implementation process of the step 1 is as follows:
step 1.1, establishing a geometric model of a foundation pit excavation side slope, and acquiring mechanical parameters of an original soil layer according to a geological survey report: volume weight gamma, cohesion c and internal friction angle
Figure FDA0002992018540000024
Step 1.2, when the horizontal earthquake acceleration value is zero, utilizing a simplified Pickup method in a limit balance method to calculate a safety coefficient F of the foundation pit excavation slopes；
Step 1.3, selecting a reduction coefficient lambdai，λiMore than 0, reducing the mechanical parameters of cohesive force c and internal friction angle of original soil layer
Figure FDA0002992018540000021
Obtaining new soil layer mechanical parameter cohesive force c'iAnd angle of internal friction
Figure FDA0002992018540000022
Wherein the content of the first and second substances,
Figure FDA0002992018540000023
δi＝Fs+λi；
step 1.4, based on new soil layer mechanical parameters, when the horizontal earthquake acceleration value is zero, the minimum safety coefficient of the foundation pit excavation side slope is calculated by utilizing the simplified Pico-Purpt method in the extreme balance method again to enable the minimum safety coefficient to reach a value smaller than 1, and the value is recorded as Fi。
2. The method for evaluating the effect of amplifying the unstable area of the excavation slope of the foundation pit according to claim 1, wherein: and establishing a geometric model of the foundation pit excavation slope, wherein the geometric model comprises a foundation pit slope excavation depth H and a slope angle beta.
3. The method for evaluating the unstable area amplification effect of the foundation pit excavation slope according to claim 1 or 2, wherein the concrete implementation process of the step 2 is as follows:
setting mechanical parameters of an original soil layer of a foundation pit excavation side slope and a horizontal seismic acceleration value alphahiAnd calculating the safety coefficient F of the foundation pit excavation slope by utilizing a simplified Pico-Purpur method in a limit balance methodsIf the calculated safety factor F is obtaineds＞FiThen, α is increased stepwisehiMake the safety factor Fs＝Fi(ii) a If calculated Fs＜FiThen α is decreased stepwisehiMake Fs＝Fi；
Recording the factor of safety Fs＝FiAlpha of timehi。
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