Determination and stability determination method for excavation dangerous slip plane of gravel pile composite foundation

Abstract

The invention belongs to the technical field of excavation of dangerous slip planes, and particularly relates to a gravel pile composite foundation excavation dangerous slip plane determination and stability determination method, which can effectively overcome the limitation of standard regulation and a traditional limit equilibrium method, and is wide in application range, high in accuracy and high in reliability. Meanwhile, the adopted criterion can accurately determine the slope crest and slope body stability states of the foundation slope in different stages in the excavation process, and an effective basis is provided for prediction, forecast and treatment of the foundation slope.

Description

Technical Field

[0001] The present application belongs to the technical field of excavation of dangerous sliding surfaces, and in particular relates to a method for determining the dangerous sliding surface of gravel pile composite foundation excavation and measuring its stability. Background Art

[0002] Gravel piles are composite foundation reinforcement piles made of crushed stone or pebbles as the main material. They are suitable for compacting loose sand, silt, plain fill and miscellaneous fill foundations. They are mainly used in geotechnical engineering fields such as soft foundations, dam slope reinforcement and strengthening the bearing capacity of foundation soil. Gravel piles have a displacement and compaction effect on sand, silt and crushed stone soil, and a displacement effect on clay and fill. With the expansion of coastal cities, the demand for land is increasing. The development and utilization of coastal soft soil has become a new topic in engineering construction. In addition, with the rapid development of high-rise buildings, highways and railways, the requirements for foundation bearing capacity are also getting higher and higher. Due to the special physical properties and engineering characteristics of soft soil, it is very easy to have a large settlement, and even the overall instability of the foundation, resulting in construction delays and even huge losses of life and property. Therefore, how to effectively monitor and warn the stability of the composite foundation slope excavation and unloading process and minimize the losses caused is an urgent task in the field of disaster prevention and mitigation of foundation pit slopes in coastal cities.

[0003] In the traditional construction process, the stability of the foundation pit is evaluated according to the specifications based on the displacement of the foundation slope or wall monitored on site, and an alarm is issued when the displacement value exceeds the specified warning value. However, since the slope type, safety level, working condition, surrounding environment, engineering geological conditions, etc. of each slope project are different, it is obviously unreasonable to use a unified deformation control value. It often happens that the foundation slope deformation is too large but the foundation is not unstable, or the foundation slope deformation does not exceed the deformation control value but the foundation is unstable. In addition, the limit equilibrium method is also a commonly used method for slope stability analysis. The solution to the problem is obtained by analyzing the force balance of the soil at the moment of destruction. Typical methods include the Swedish method and the Bishop simplification method. However, when calculating the slope stability safety factor, the limit equilibrium method simplifies many conditions, and the results obtained may deviate greatly from the actual working conditions. When the friction angle of the soil is large or the arc angle of the sliding surface is large, the results are not accurate enough. In addition, the use of gravel piles changes the sliding surface of the original soil, so it cannot be used in the stability evaluation of the soil slope excavation with a weak layer in the gravel pile composite foundation. Summary of the invention

[0004] In order to overcome the shortcomings and limitations of the above-mentioned foundation slope stability determination method, the present invention aims at the action mechanism and displacement dynamic action law of the gravel pile composite foundation slope, corrects the shear strength parameters of the composite foundation, and proposes a dynamic load-displacement response ratio prediction parameter and method that uses the foundation slope excavation depth as the dynamic load increase and the displacement caused by excavation as the dynamic response. This method can overcome the shortcomings and limitations of the above-mentioned traditional foundation slope stability evaluation method to some extent, and has important application value in the field of gravel pile composite foundation slope stability monitoring and determination.

[0005] A method for determining a dangerous sliding surface for excavation of a gravel pile composite foundation comprises the following steps:

[0006] Step 1: Use geotechnical in-situ tests or indoor geotechnical tests to comprehensively determine the cohesion C of the composite soil of the gravel pile composite foundation slope c 、Internal friction angle of composite soil and determine the cohesion C of the crushed stone g 、Internal friction angle of crushed stone

[0007] Step 2: Formulas (1) and (2), as well as the measured shear strength parameters of the gravel pile composite foundation slope soil layer and gravel pile, are used to calculate the cohesion and internal friction angle of the composite soil. The gravel pile composite foundation slope is regarded as a homogeneous rock and soil mass, and the most dangerous slip surface is calculated using the classical arc method.

[0008]

[0009]

[0010] Where: C c is the cohesion of the composite soil, C g is the cohesion of the gravel, C sc For the cohesion of the foundation, is the internal friction angle of the composite soil, is the internal friction angle of crushed stone, is the internal friction angle of the foundation, and m is the area replacement rate.

[0011] A method for determining the stability of a dangerous sliding surface in excavation of a gravel pile composite foundation, wherein the sliding surface is determined by the method of the present application, and deformation monitoring includes measuring the horizontal displacement of the slope top and the horizontal displacement of the slope body to reflect the stability of the slope; the method comprises the following steps:

[0012] Step 3: Selection of slope excavation displacement monitoring points and installation and arrangement of monitoring equipment;

[0013] Step 4: Real-time monitoring and data processing of slope excavation depth and slope displacement;

[0014] Step 5: Determination of displacement response rate of dynamic loading of composite foundation slope excavation;

[0015] Step 6: Determination of evaluation parameters of dynamic load-increase displacement response ratio of composite foundation slope;

[0016] Step 7: Determination of the instability criterion of slope dynamic load-increase displacement response ratio evaluation parameters;

[0017] Step 8: Determination and evaluation of composite foundation slope stability using dynamic load-increase displacement response comparison.

[0018] Preferably, in step three, a high-performance vibrating-string displacement sensor is used to monitor the horizontal displacement of the slope. The number of monitoring points is one for every L meters of the total excavation depth. At the same depth, the sensor is moved horizontally into the slope and the same number of displacement monitoring points are continuously deployed. A distributed GPRS node wireless data acquisition system is used to collect monitoring data.

[0019] Preferably, the depth of each excavation of the composite foundation slope and the resulting horizontal displacement response are monitored in real time; the horizontal displacement is transmitted to the host computer through the radio acquisition device of the monitoring equipment, and the excavation depth is directly obtained from the construction plan, and then the monitoring data is pre-processed and entered into an Excel table; the slope excavation depth is recorded as H i , the horizontal displacement caused by excavation is recorded as S ni , where i is the excavation stage and n is the monitoring point number.

[0020] Preferably, in step 5, during the excavation of the gravel pile composite foundation slope, excavation is the main dynamic factor affecting and controlling the slope displacement and stability. There is a one-to-one correspondence between the excavation depth and the slope displacement. The initial excavation depth H1 of the slope is taken as the initial load increase, and the horizontal displacement S caused by the initial excavation is n1 As the initial displacement response, the initial dynamic load displacement response rate of the slope top can be calculated according to formula (3):

[0021]

[0022] The excavation depth of any subsequent excavation step of the slope is taken as the slope dynamic load increase H of the excavation step. i , horizontal displacement S caused by slope excavation ni As the displacement response of this excavation step, the dynamic load increase displacement response rate of any subsequent excavation step of the slope can be calculated according to formula (4):

[0023]

[0024] Preferably, in step 6, the dynamic load displacement response rate λ under any subsequent excavation step of the slope is niThe initial dynamic load displacement response rate of the slope λ n0 The ratio is defined as the slope dynamic load displacement response ratio of the excavation step, and the slope dynamic load displacement response ratio evaluation model is established, namely:

[0025]

[0026] Where: ΔS n1 , ΔS ni are the horizontal displacement values ​​under the initial excavation step and the subsequent excavation step; H1, H i is the dynamic load increase value under the initial excavation step and the subsequent excavation step. Therefore, the dynamic load displacement response ratio of the slope is used as the stability evaluation parameter of the slope to predict and evaluate its stability.

[0027] Preferably, the safety factor K is defined as the ratio of the limit damage to the maximum allowable damage, that is:

[0028]

[0029] Where: D cr The maximum allowable damage, limit damage D im Take 1; in the whole damage process, the damage variable D i Gradually approaching D cr , so the maximum safety factor K cr It can be expressed as:

[0030]

[0031] The above formula shows that there is a one-to-one correspondence between the dynamic load-increase displacement response ratio and the slope safety factor, that is, the dynamic load-increase displacement response ratio parameter can be used to quantitatively evaluate the slope stability;

[0032]

[0033] When the dynamic load displacement response ratio parameter η ni Less than or equal to η cr When the dynamic load displacement response ratio parameter η ni Greater than η cr , indicating that the slope is in an unstable state and there is a possibility of landslide.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The method is simple to calculate and can analyze the action mechanism and displacement dynamic law of the gravel pile composite foundation slope with high accuracy, providing a new method for determining the excavation stability of the gravel pile composite foundation slope. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The following is a process flow chart of the invention.

[0037] Figure 2 Schematic diagram of slope monitoring points and instrument layout.

[0038] Figure 3 This is the force analysis diagram of slope excavation strips.

[0039] Figure 4 This is the most dangerous sliding surface diagram of the slope. DETAILED DESCRIPTION

[0040] The principles and features of the present invention are described below. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0041] A method for determining the excavation stability of a gravel pile composite foundation slope comprises the following steps:

[0042] Step 1: Exploration and determination of foundation slope shear strength parameters;

[0043] The cohesion C of composite soil of slope with gravel pile composite foundation is comprehensively determined by geotechnical in-situ test or indoor geotechnical test. c 、Internal friction angle of composite soil and determine the cohesion C of the crushed stone g 、Internal friction angle of crushed stone

[0044] Step 2: Determine the most dangerous potential sliding surface of the gravel pile composite foundation slope;

[0045] According to Principle 1, Formulas (1) and (2), as well as the measured shear strength parameters of the soil layer and the gravel piles of the gravel pile composite foundation slope, the cohesion and internal friction angle of the composite soil are calculated. The gravel pile composite foundation slope is regarded as a homogeneous rock and soil mass, and the most dangerous slip surface is calculated by the classical arc method. The characteristics of the slope such as size and distribution range are analyzed to determine the main slip zone of the slope.

[0046]

[0047]

[0048] Where: C c is the cohesion of the composite soil, C g is the cohesion of the gravel, C sc For the cohesion of the foundation, is the internal friction angle of the composite soil, is the internal friction angle of crushed stone, is the internal friction angle of the foundation, and m is the area replacement rate.

[0049] Principle 1 is as follows:

[0050] The area replacement rate method is the method of multiplying the tested strength of the gravel pile and the surrounding coastal soft soil under the same conditions by the proportion of the area they bear. Its disadvantage is that it does not take into account the interaction effect between the pile and the soil.

[0051] Composite soil cohesion:

[0052] C c =mC g +(1-m)C sc (7)

[0053] Internal friction angle of composite soil:

[0054]

[0055] Due to the shear dilatancy of the crushed stone material, the radial stress on the pile-soil contact surface is higher than the confining pressure, which means that the stress of the composite soil is not a simple combination of the stresses of the respective materials under the same test conditions according to the area replacement rate. Factors such as the increase in the pile confining pressure after the lateral interaction between the pile and the soil should be considered. The pile confining pressure in the composite soil is corrected, and the pile-soil interaction coefficient (ζ conforms to the power function law) is supplemented.

[0056] Cohesion of composite soil using action coefficient method:

[0057]

[0058] Internal friction angle of composite soil using action coefficient method:

[0059]

[0060] ξ=m -0.41 (11)

[0061]

[0062] Where: C c is the cohesion of the composite soil, C g is the cohesion of the gravel, C sc For the cohesion of the foundation, is the internal friction angle of the composite soil, is the internal friction angle of crushed stone, is the internal friction angle of the foundation, m is the area replacement rate, and ζ is the pile-soil interaction coefficient.

[0063] In actual engineering, formula (9) and formula (12) can be used to calculate the cohesion and internal friction angle of the composite soil respectively. The gravel pile composite foundation slope can be regarded as a homogeneous rock and soil mass, and the potential slip surface can be calculated.

[0064] Step 3: Selection of slope excavation displacement monitoring points and installation and arrangement of monitoring equipment;

[0065] The deformation monitoring of the present invention mainly measures the horizontal displacement of the top of the slope and the horizontal displacement of the slope body, which directly reflects the stability of the slope. Within the main sliding area, the number of monitoring points is one for every 3m according to the total excavation depth. At the same depth, the same number of displacement monitoring points are laid out by moving horizontally toward the inside of the slope. The monitoring equipment of the present invention uses a high-performance vibrating-string displacement sensor to monitor the horizontal displacement of the slope body. Professional advance drilling equipment is used to place the displacement meter column in the hole, and then the sensor is fixed on the column. The length can be changed due to the range; each sensor is connected, and a distributed GPRS node wireless data acquisition system is used to collect monitoring data, realize multiple interface protocol conversions, automatically perform wireless data transmission management, and integrate internal measurement circuits, which are expanded to multiple outputs through switches. A high-precision laser rangefinder is installed on the top of the slope to monitor the horizontal displacement of the top of the slope.

[0066] Step 4: Real-time monitoring and data processing of slope excavation depth and slope displacement;

[0067] According to the construction plan, the depth of each excavation of the composite foundation slope and the displacement response caused are monitored in real time. The displacement monitoring data of each monitoring point is transmitted to the host through the radio acquisition device of the monitoring equipment. The excavation depth is directly obtained from the construction plan. After that, the monitoring data is pre-processed and entered into an Excel table. The slope excavation depth is recorded as H i , the horizontal displacement caused by excavation is recorded as S ni , where i is the excavation stage and n is the monitoring point number.

[0068] Step 5: Determination of displacement response rate of dynamic loading of composite foundation slope excavation;

[0069] In the process of excavation of gravel pile composite foundation slope, excavation is the main dynamic factor affecting and controlling the displacement and stability of the slope. There is a one-to-one correspondence between the excavation depth and the slope displacement. According to Principle 2, this patent uses the initial excavation depth H1 of the slope as the initial load increase, and the corresponding slope top and slope displacement response S caused by the initial excavation n1 As the initial displacement response. According to formula (3), the initial dynamic load displacement response rate of the slope top can be calculated:

[0070]

[0071] The excavation depth of any subsequent excavation step of the slope is taken as the slope dynamic load increase H of the excavation step. i , the horizontal displacement response S caused by slope excavation ni As the displacement response of this excavation step, the dynamic load increase displacement response rate of any subsequent excavation step of the slope can be calculated according to formula (4):

[0072]

[0073] Principle 2 is as follows:

[0074] Assuming that the slope is a homogeneous rock and soil mass and isotropic, the thickness of the slope changes uniformly, and deformation and instability occur during the slope excavation process, the soil skeleton strips in the potential sliding soil mass of the slope are selected as the research object. The slope model and the stress conditions of the strips during the excavation process are shown in Figure 2. Figure 3 shown.

[0075] Depend on Figure 3 It can be seen that the sliding force and anti-sliding force are the weight components of the slider. The sliding force is represented by T and the anti-sliding force is represented by R. The sliding force and anti-sliding force before and after excavation are respectively expressed by the following formulas:

[0076] Sliding force before excavation T1:

[0077] T1=G1sinθ=(γH1)sinθ (13)

[0078] Sliding force after excavation T2:

[0079] T2=G2sinθ=(γH2)sinθ (14)

[0080] Anti-slip force R1 before excavation:

[0081]

[0082] Anti-sliding force R2 after excavation:

[0083]

[0084] Where: c is the sliding surface cohesion; is the internal friction angle of the sliding surface; l is the bottom width of the strip; γ is the natural weight of the soil, H is the excavation depth, G is the gravity, and θ is the slope inclination. Therefore, the slope sliding force increment ΔP caused by excavation is:

[0085]

[0086] It can be seen from formula (17) that for a specific slope, is a constant value, and H2-H1 is the increase in the height of the sliding block caused by excavation. Only when the slope is excavated downward will the volume of the potential sliding soil of the slope increase, thereby increasing the height of the sliding block after strip division. Therefore, it can be considered that there is a one-to-one correspondence between each excavation depth of the slope and the corresponding residual sliding power increment caused.

[0087] Step 6: Determination of evaluation parameters of dynamic load-increase displacement response ratio of composite foundation slope;

[0088] According to the calculation results of step 5, the dynamic load displacement response rate λ of the slope under any subsequent excavation step is ni The initial dynamic load displacement response rate of the slope λ n0 The ratio is defined as the slope dynamic load displacement response ratio of the excavation step, and the slope dynamic load displacement response ratio evaluation model is established, namely:

[0089]

[0090] Where: ΔS n1 , ΔS ni are the horizontal displacement values ​​under the initial excavation step and the subsequent excavation step; H1, H i is the dynamic load increase value under the initial excavation step and the subsequent excavation step. Therefore, the slope dynamic load displacement response ratio is used as the slope stability evaluation parameter to predict and evaluate its stability.

[0091] Step 7: Determination of the instability criterion of slope dynamic load-increase displacement response ratio evaluation parameters;

[0092] By referring to relevant technical specifications such as "Technical Specifications for Design and Construction of Landslide Prevention Engineering" (DZ / T0219-2006) and "Specifications for Geotechnical Engineering Investigation" (GB50021-2009), according to the safety factor K of the slope and Principle 3, the stability criterion of the slope dynamic load displacement response ratio based on the safety factor is determined:

[0093] Principle 3 is as follows:

[0094] The elastic modulus E of the slope rock and soil is an important parameter to characterize the damage and failure mechanism of the slope. According to the definition of the elastic modulus, that is, the stress required to produce unit elastic deformation, it can be expressed by the formula:

[0095]

[0096] Assume that the inverse of the dynamic load displacement response ratio η is ξ, which can be expressed as:

[0097]

[0098] Where: σ is stress, ε is deformation, Δσ i is the stress increment, Δε i is the deformation increment, and ξ is the deformation modulus increment ratio.

[0099] It can be seen from the above formula that when the slope is not damaged, the elastic modulus does not change and its ξ value is 1; when the slope is completely damaged, the ξ value is 0; when the slope is partially damaged, the ξ value varies between 0 and 1.

[0100] According to the basic principle of damage mechanics, the instability process of the slope is actually the damage process of the sliding zone rock and soil. The damage process and damage degree can be expressed by the damage variable D. i express:

[0101]

[0102] However, for special geological slopes, the overlying rock layer has been nurtured and evolved for many years, so the initial elastic modulus of the slope rock and soil cannot be measured, and only the deformation modulus of the rock and soil after damage can be obtained. In view of this situation, the definition of the comprehensive damage variable (Formula (20)) and the deformation modulus E i The dynamic load displacement response ratio η i The damage amount can be expressed as:

[0103]

[0104] Where: ξ0 is the deformation modulus increment ratio of the slope in a completely elastic stable state, and its value is 1; i is the incremental ratio of deformation modulus under a certain excavation step.

[0105] From the analysis of equations (20) and (21), it can be seen that when the slope material is in an elastically stable state, E i =E0,ξ i =ξ0=1,D i =0; when the slope material is completely damaged, E i =0,ξ i =0,D i =1. Therefore, the damage deformation law of the slope described by equations (20) and (21) is equivalent, so it is feasible to analyze and evaluate the stability of the foundation slope at each excavation stage by using the inverse of the dynamic loading displacement response ratio ξ. According to equations (19) and (21), the relationship between the dynamic loading displacement response ratio and the damage variable can be determined:

[0106]

[0107] From formula (22), we can see that when D i =0, η i =1, the slope is not damaged, the dynamic load displacement response ratio is 1, and the slope is in a stable state; when the slope is completely damaged, that is, D i When it approaches 1, the dynamic load-displacement response ratio tends to infinity, and the slope is in an unstable state.

[0108] The essence of the failure of the composite foundation slope is that under the external excavation disturbance, the shear force of the complex soil on the sliding belt is greater than the shear strength, resulting in the destruction of the sliding belt soil structure. Therefore, from the perspective of soil strength failure, the damage variable parameter D can be definedi It is the probability of failure when the shear stress of the soil on the potential sliding surface of the slope is greater than the shear strength. In slope engineering, the currently recognized slope stability criterion is the slope stability coefficient, which is used to judge the stability of the slope based on the relationship between the actual slope stability coefficient and the safety factor. Zhang Daobing et al. defined the safety factor as the ratio of the limit damage to the maximum allowable damage, that is:

[0109]

[0110] Where: D cr The maximum allowable damage, limit damage D im Take 1. In the whole process of damage and destruction, the damage variable D i Gradually approaching D cr , so the maximum safety factor can be expressed as:

[0111]

[0112] The above formula shows that there is a one-to-one correspondence between the dynamic load-increase displacement response ratio of the slope and the slope safety factor, that is, the dynamic load-increase displacement response ratio parameter can be used to quantitatively evaluate the slope stability.

[0113]

[0114] When the dynamic load displacement response ratio parameter η ni Less than or equal to η cr When the dynamic load displacement response ratio parameter η ni Greater than η cr , indicating that the slope is in an unstable state and there is a possibility of landslide.

[0115] Step 8: Determination and evaluation of composite foundation slope stability using dynamic load-increase displacement response comparison.

[0116] Taking the excavation depth of the composite foundation slope each time as the dynamic load increase, and the displacement or displacement rate caused by the excavation depth as the corresponding response, the slope dynamic load displacement response ratio parameter and evaluation model are determined, and used as the evaluation parameter for slope stability prediction during the composite foundation slope excavation process. At the same time, according to the basic principles of damage mechanics, the quantitative relationship between the dynamic load displacement response ratio and the foundation slope stability coefficient is established through the damage variable parameter D, and the foundation slope dynamic load displacement response ratio stability early warning criterion is determined based on this quantitative relationship.

[0117] In order to explain the content of the present invention in more detail, the excavation stability of a foundation slope in Qingdao is measured and evaluated. The designed excavation depth of the foundation is 10m, which is divided into 8 excavation steps, with the first excavation of 1.5m and layered excavation. The support structure used in the early design of the foundation is a gravel pile with a total length of 17m, a diameter of 1000mm and a spacing of 1.4m.

[0118] Step 1: Exploration and determination of shear strength parameters of foundation slope

[0119] The cohesion c of the slope soil layer of the gravel pile composite foundation slope is 7.7 kPa and the internal friction angle is 7.7 kPa. is 5.8°; and the cohesion c of the gravel column is determined to be 0 kPa, the internal friction angle is 36°; the replacement rate is the ratio of the unit area, that is

[0120] Step 2: Determine the most dangerous potential sliding surface of the gravel pile composite foundation slope

[0121] According to Principle 1, Formulas (1) and (2), and the measured shear strength parameters of the soil layer and the gravel piles of the gravel pile composite foundation slope, the cohesion and internal friction angle of the composite soil were calculated under the condition of a replacement rate of 40%. The gravel pile composite foundation slope was regarded as a homogeneous rock and soil mass. The calculated composite soil cohesion c was 5.11 kPa and the internal friction angle was 2.34 kPa. The most dangerous sliding surface is calculated by the classical arc method, and the main sliding area of ​​the slope is determined by analyzing the characteristics of the slope size and distribution range. Figure 4 .

[0122]

[0123]

[0124] Step 3: Selection of slope excavation displacement monitoring points and installation and arrangement of monitoring equipment

[0125] In order to directly reflect the stability of the slope, it is necessary to monitor the horizontal displacement of the slope top and the slope body. Three monitoring points can be set for an excavation depth of 10m. Then, move 3m further into the slope and continue to set the same number of displacement monitoring points. Figure 2As shown. High-performance vibrating-wire displacement sensors are used to monitor the horizontal displacement of the slope. Professional advance drilling equipment is used to place the displacement meter column in the hole, and then the sensor is fixed on the column. The length can be changed due to the range. The sensors are connected and the distributed GPRS node wireless data acquisition system is used to collect monitoring data, realize multiple interface protocol conversion, automatically perform wireless data transmission management, and integrate internal measurement circuits. It is expanded to multiple outputs through switches. A high-precision laser rangefinder is installed on the top of the slope to monitor the horizontal displacement of the top of the slope.

[0126] Step 4: Real-time monitoring and data processing of slope excavation depth and slope displacement

[0127] According to the construction plan, the depth of each excavation of the composite foundation slope and the displacement response caused are monitored in real time. The displacement monitoring data of each monitoring point is transmitted to the host through the radio acquisition device of the monitoring equipment. The excavation depth is directly obtained from the construction plan. After that, the monitoring data is pre-processed and entered into an Excel table. The slope excavation depth is recorded as H i , the horizontal displacement of the slope is recorded as S ni , where i is the excavation stage and n is the monitoring point number, as shown in Table 1.

[0128] Table 1 Slope excavation monitoring data

[0129]

[0130] Step 5: Determination of displacement response rate of composite foundation slope excavation dynamic loading

[0131] In the process of excavation of gravel pile composite foundation slope, excavation is the main dynamic factor affecting and controlling the slope displacement and stability. There is a one-to-one correspondence between excavation depth and slope displacement. According to Principle 2, the initial excavation depth of the slope is taken as the initial load increase H1, and the horizontal displacement response S caused by the initial excavation is 11 , S 21 As the initial displacement response. According to formula (3), the initial dynamic load displacement response rate of the slope top can be calculated:

[0132]

[0133] The excavation depth of any subsequent excavation step of the slope is taken as the slope dynamic load increase H of the excavation step. i , the horizontal displacement response S caused by slope excavation ni As the displacement response of this excavation step, the dynamic load increase displacement response rate of any subsequent excavation step of the slope can be calculated according to formula (4). The calculation results are shown in Table 2.

[0134]

[0135] Table 2 Dynamic load displacement response rate

[0136]

[0137]

[0138] Step 6: Determination of the evaluation model for dynamic load-increase displacement response ratio of composite foundation slope

[0139] According to the calculation results of step 3, the dynamic load displacement response rate λ of the slope under any subsequent excavation step is i The initial dynamic load displacement response rate of the slope λ n0 The ratio is defined as the slope dynamic load displacement response ratio of the excavation step, and the slope dynamic load displacement response ratio evaluation model is established, namely:

[0140]

[0141] Where: ΔS n1 , ΔS ni are the displacement values ​​under the initial excavation step and the subsequent excavation step; H1, H i It is the power increase value under the initial excavation step and the subsequent excavation step.

[0142] Therefore, the slope dynamic load displacement response ratio is used as the slope stability evaluation parameter to predict and evaluate its stability. The calculation results are shown in Table 3.

[0143] Table 3 Dynamic load displacement response ratio

[0144]

[0145] Step 7: Determination of the instability criterion of slope dynamic load-increase displacement response ratio evaluation parameters

[0146] By referring to relevant technical specifications such as "Technical Specifications for Design and Construction of Landslide Prevention Engineering" (DZ / T0219-2006) and "Specifications for Geotechnical Engineering Investigation" (GB50021-2009), the maximum safety factor K of the slope is determined. cr =1.3 is a stable state that satisfies the safety margin of the specification. According to Principle 3, K cr Substituting into formula (25), the stability criterion of slope dynamic load displacement response ratio based on the maximum safety factor is determined, and η cr is 4.33.

[0147]

[0148] When the dynamic load displacement response ratio parameter η ni Less than or equal to η cr When the dynamic load displacement response ratio parameter ηni Greater than η cr , indicating that the slope is in an unstable state and there is a possibility of landslide.

[0149] Step 8: Determination and evaluation of composite foundation slope stability using dynamic load-increase displacement response comparison.

[0150] The slope dynamic load displacement response ratio is used as the monitoring and early warning dynamic evaluation parameter of slope stability to monitor and evaluate the slope stability. ni and the instability criterion value η cr By comparison, it is obvious that the dynamic load displacement response ratio under any excavation step is η ni Both are greater than the instability criterion value η cr Small, indicating that the slope is in a stable state.

[0151] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining dangerous sliding surfaces in excavation of gravel pile composite foundation, characterized in that: The following steps are involved: Step 1: Use geotechnical in-situ tests or indoor geotechnical tests to comprehensively determine the cohesion C of the composite soil of the gravel pile composite foundation slope c 、Internal friction angle of composite soil and determine the cohesion C of the crushed stone g 、Internal friction angle of crushed stone Step 2: Formulas (1) and (2), as well as the measured shear strength parameters of the gravel pile composite foundation slope soil layer and gravel pile, are used to calculate the cohesion and internal friction angle of the composite soil. The gravel pile composite foundation slope is regarded as a homogeneous rock and soil mass, and the most dangerous slip surface is calculated using the classical arc method. Where: C c is the cohesion of the composite soil, C g is the cohesion of the gravel, C sc For the cohesion of the foundation, is the internal friction angle of the composite soil, is the internal friction angle of crushed stone, is the internal friction angle of the foundation, and m is the area replacement rate.

2. A method for determining the stability of a dangerous sliding surface in a gravel pile composite foundation excavation, wherein the sliding surface is determined by the method of claim 1, and deformation monitoring includes measuring the horizontal displacement of the slope top and the horizontal displacement of the slope body to reflect the stability of the slope; characterized in that: The following steps are involved: Step 3: Selection of slope excavation displacement monitoring points and installation and arrangement of monitoring equipment; Step 4: Real-time monitoring and data processing of slope excavation depth and slope displacement; Step 5: Determination of displacement response rate of dynamic loading of composite foundation slope excavation; Step 6: Determination of evaluation parameters of dynamic load-increase displacement response ratio of composite foundation slope; Step 7: Determination of the instability criterion of slope dynamic load-increase displacement response ratio evaluation parameters; Step 8: Determination and evaluation of composite foundation slope stability using dynamic load-increase displacement response comparison.

3. The method for determining stability of dangerous sliding surface in excavation of gravel pile composite foundation according to claim 2, characterized in that: In the step three, a high-performance vibrating-string displacement sensor is used to monitor the horizontal displacement of the slope. The number of monitoring points is one for every L meters of the total excavation depth. At the same depth, the sensor moves horizontally into the slope and continues to deploy the same number of displacement monitoring points. A distributed GPRS node wireless data acquisition system is used to collect monitoring data.

4. The method for determining stability of dangerous sliding surface in excavation of gravel pile composite foundation according to claim 2, characterized in that: The depth of each excavation of the composite foundation slope and the resulting horizontal displacement response are monitored in real time. The horizontal displacement is transmitted to the host computer through the radio acquisition device of the monitoring equipment. The excavation depth is directly obtained from the construction plan. After that, the monitoring data is preprocessed and entered into an Excel table. The slope excavation depth is recorded as H. i , the horizontal displacement caused by excavation is recorded as S ni , where i is the excavation stage and n is the monitoring point number.

5. The method for determining stability of dangerous sliding surface in excavation of gravel pile composite foundation according to claim 2, characterized in that: In step 5, during the excavation of the gravel pile composite foundation slope, excavation is the main dynamic factor that affects and controls the slope displacement and stability. There is a one-to-one correspondence between the excavation depth and the slope displacement. The initial excavation depth H1 of the slope is taken as the initial load increase, and the horizontal displacement S caused by the initial excavation is n1 As the initial displacement response, the initial dynamic load displacement response rate of the slope top can be calculated according to formula (3): The excavation depth of any subsequent excavation step of the slope is taken as the slope dynamic load increase H of the excavation step. i , horizontal displacement S caused by slope excavation ni As the displacement response of this excavation step, the dynamic load increase displacement response rate of any subsequent excavation step of the slope can be calculated according to formula (4):

6. The method for determining stability of dangerous sliding surface in excavation of gravel pile composite foundation according to claim 5, characterized in that: In step 6, the dynamic load displacement response rate λ under any subsequent excavation step of the slope is ni The initial dynamic load displacement response rate of the slope λ n0 The ratio is defined as the slope dynamic load displacement response ratio of the excavation step, and the slope dynamic load displacement response ratio evaluation model is established, namely: Where: ΔS n1 , ΔS ni are the horizontal displacement values ​​under the initial excavation step and the subsequent excavation step; H1, H i is the dynamic load increase value under the initial excavation step and the subsequent excavation step. Therefore, the dynamic load displacement response ratio of the slope is used as the stability evaluation parameter of the slope to predict and evaluate its stability.

7. The method for determining stability of dangerous sliding surface in excavation of gravel pile composite foundation according to claim 5, characterized in that: The safety factor K is defined as the ratio of the limit damage to the maximum allowable damage, that is: Where: D cr The maximum allowable damage, limit damage D im Take 1; in the whole damage process, the damage variable D i Gradually approaching D cr , so the maximum safety factor K cr It can be expressed as: The above formula shows that there is a one-to-one correspondence between the dynamic load-increase displacement response ratio and the slope safety factor, that is, the dynamic load-increase displacement response ratio parameter can be used to quantitatively evaluate the slope stability; When the dynamic load displacement response ratio parameter η ni Less than or equal to η cr When the dynamic load displacement response ratio parameter η ni Greater than η cr , indicating that the slope is in an unstable state and there is a possibility of landslide.

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