Method for determining the depth of deep fill reinforcement based on the amount of tamping

Abstract

This invention discloses a method for determining the depth of dynamic compaction reinforcement in deep fill soil based on compaction settlement. In a deep fill soil site, a suitable test area is selected and a finite element model is established. Initial data of soil parameters are determined through field tests, obtaining the relationship curves between compaction settlement and the number of compaction blows at different energy levels. Furthermore, based on measured data and using the elastic modulus of the soil as the basic field variable, the elastic modulus of the reinforced soil layer after each compaction blow is back-calculated to establish the correlation between the elastic modulus and the number of compaction blows. The cumulative vertical deformation along the depth direction under different compaction energies is plotted, and the reinforcement depth under different compaction energies is statistically analyzed to obtain the relationship curve between reinforcement depth and compaction energy. This allows for accurate prediction of reinforcement depth based on dynamic compaction energy. This invention provides important reference for determining and selecting parameters for dynamic compaction reinforcement of deep fill soil foundations, and provides theoretical basis and technical standards for the design of similar dynamic compaction projects for deep soft rock backfill foundations in the future.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering foundation treatment technology, specifically to a method for determining the depth of deep fill reinforcement by dynamic compaction based on the amount of compaction settlement. Background Technology

[0002] With the rapid development of urban construction, the domestic construction land is being consumed at an alarming rate, and land use conflicts are becoming increasingly frequent. In order to solve the problem of tight urban land, developers are gradually turning their attention to undeveloped areas such as urban suburbs or counties and townships. This has led to an increase in projects such as "opening up mountains and filling valleys" and "reclaiming land from the sea". However, due to problems such as uneven backfill thickness, loose backfill, and high compressibility, these projects are difficult to meet the requirements for strength, deformation, and stability in engineering. Appropriate measures need to be taken to eliminate or reduce the risks brought about by poor backfill foundations and ensure the safety of the superstructure.

[0003] Dynamic compaction is an economical and efficient method for treating backfilled soil foundations. A crane lifts a ram to a certain height and then drops it freely. The ram carries enormous energy and impacts the soil surface, giving the foundation a powerful shock. The backfilled soil becomes denser due to its own vibration, reducing the compressibility of the foundation soil. Ultimately, the backfilled soil is compacted and consolidated, improving the bearing capacity and performance of the foundation, thereby achieving the purpose of strengthening the foundation.

[0004] In dynamic compaction, the effective reinforcement depth is an important factor in evaluating the reinforcement effect and a crucial basis for selecting the dynamic compaction treatment scheme. However, there is currently no unified concept regarding the effective reinforcement depth. Relevant specifications indicate that the effective reinforcement depth needs to be determined through field test compaction or regional experience. They also provide a reference range for the correction coefficient of the Mena formula, but in application, there are still problems such as difficulty in parameter selection and large deviations between the results and reality. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a method for determining the depth of dynamic compaction reinforcement of deep fill soil based on the settlement amount. This method provides an important reference for determining and selecting parameters for dynamic compaction reinforcement of deep fill soil foundations, and further determines the effective reinforcement depth of dynamic compaction. It can provide a theoretical basis and technical standards for the design of similar dynamic compaction projects for deep soft rock backfill foundations in the future, and has broad application prospects.

[0006] The technical solution provided by this invention: a method for determining the depth of deep fill reinforcement by dynamic compaction based on the settlement amount, comprising the following steps:

[0007] S1. In a deep fill site, select an area where the fill thickness is greater than the estimated or empirical value of the reinforcement depth as the test area. Based on the geological profile of the test area, establish the calculation model required for dynamic compaction numerical simulation in numerical simulation software to prepare for dynamic compaction numerical calculation. The calculation model includes the hammer element, the surrounding soil element of dynamic compaction, and the model boundary soil element.

[0008] S2. Conduct large-scale direct shear tests on undisturbed fill in the test area to obtain the internal friction angle φ and cohesion c of the soil, and take the average value of the results as the initial data of the soil parameters;

[0009] S3. Conduct dynamic compaction construction at a certain energy level in the test area. During the construction process, monitor the number of compaction blows and settlement at a single compaction point to obtain the relationship curve between compaction settlement and number of compaction blows at that energy level.

[0010] S4. Using the elastic modulus of the soil as the basic field variable, and through initial data of soil parameters, simulate and calculate the calculated value Y of the pit settlement under different compaction cycles at this energy level, so that the calculated value Y of the pit settlement and the measured value y of the dynamic compaction test in the test area satisfy the following relationship. The elastic modulus of the reinforced soil layer after each compaction was calculated.

[0011] S5. Using the elastic modulus of the reinforced soil layer obtained in step S4 after each compaction, substitute it into the calculation model established in step S1 to calculate the vertical deformation of the ground surface under different compaction times at the compaction energy. When the vertical deformation s of the ground surface after the i-th compaction is... i Satisfying relation s i+1 -s i ≈s i -s i-1 Where i = 1, 2, 3K n, it indicates that a stable state is reached after the i-th tamping, and the optimal number of tamping blows is determined to be i.

[0012] S6. Using the optimal number of compaction blows obtained in step S5, plot the curve of the vertical deformation of the soil along the depth direction after the i-th compaction blow at this compaction energy, and use the vertical deformation reduction rate. To analyze and determine the optimal reinforcement depth H1 and maximum reinforcement depth H2 of dynamic compaction, where s hi It is the vertical deformation at depth h after the i-th impact, s i It is the vertical deformation of the ground surface after the i-th impact;

[0013] S7. Dynamic compaction energy levels include low energy level, medium energy level, high energy level and ultra-high energy level. By repeating steps S3-S6, the optimal number of compaction blows, the optimal reinforcement depth H1 and the maximum reinforcement depth H2 can be obtained for different energy levels during dynamic compaction construction.

[0014] S8. Statistically analyze the reinforcement depth under different tamping energies to obtain the relationship curve between reinforcement depth and tamping energy. Fit the curve to obtain the relationship between reinforcement depth and tamping energy. The reinforcement depth H and tamping energy W are basically linearly related. After fitting, the formula for the optimal reinforcement depth H1 is H1=a1W+b1, and the formula for the maximum reinforcement depth H2 is H2=a2W+b2.

[0015] Furthermore, in step S1, the tamping hammer element and the surrounding soil element in the calculation model are simulated using linear elements. Since the dynamic analysis of geotechnical systems in semi-infinite spaces often involves the dynamic analysis of the infinite boundary, and the biggest problem with artificially truncated boundaries is that waves will reflect off the boundary interface, thus transferring energy back to the analysis grid, while in reality the waves will propagate to infinity. To reduce the impact of this reflection phenomenon on the analysis area, the soil element at the model boundary is simulated using infinite element elements.

[0016] The process of a tamping hammer impacting soil is achieved through contact between the hammer surface and the soil surface, including both normal and tangential forces between the hammer and the soil. The normal contact condition is the condition that must be observed to determine whether objects have entered contact and when they have entered contact; the relationship between their normal directions satisfies the following: when the separation distance U between the contact pairs... open When the distance between the hammer and the soil is 0, a contact relationship is established, and any force between them along the normal direction will be transmitted; when the separation distance U between the contact pairs is 0... open When τ > 0, the contact relationship between the hammer and the soil is broken, and the normal contact force between them is zero. The tangential interaction satisfies the modified Coulomb friction model, that is, the friction coefficient is used to represent the frictional characteristics between the contact surfaces. eq <τ crit At this time, the contact surface is in an adhesive state; when τ eq =τ crit At that time, the contact surface is in a sliding state, where t crit =mp,τ eq For the critical sliding force, τ crit Let μ be the critical shear stress, μ be the friction coefficient, p be the normal contact force, and τ be the normal shear stress. i Let i be the sliding force in the i-direction.

[0017] Furthermore, in step S2, the large-scale direct shear test in the field involves applying different vertical loads to each group of samples by stacking different counterweights, placing the jack horizontally, and applying horizontal shear force until the sample is sheared and fails. This yields the relationship curve between normal stress and shear stress. After linear fitting, the slope angle is the internal friction angle φ, and the intercept with the vertical axis is the cohesion c. After multiple sets of tests are completed, the average value is taken as the test result, which is the initial data for numerical simulation calculation of soil parameters.

[0018] Furthermore, during the monitoring process in step S3, the original elevation of the point needs to be measured and stored first. A complete set of data is measured after each tamping blow until the entire single-point tamping is completed. Based on the relationship curve between the settlement and the number of tamping blows, an exponential function relationship is obtained: S = ae^(- ... -bN In the formula, S is the initial settlement of the single-blow compaction, in cm; N is the number of blows; a and b are fitting coefficients, which are parameters of the initial settlement of the dynamic compaction. a is positively correlated with the initial settlement, and b is negatively correlated with the initial settlement, both of which are affected by the dynamic compaction energy level.

[0019] Furthermore, in step S4, the relationship curve between the back-calculated elastic modulus of the reinforced soil and the number of blows is fitted to obtain the elastic modulus of the reinforced soil layer under each blow, which exhibits a power function distribution law. The fitting formula is E′=EN. a In the formula, E′ is the elastic modulus of the soil in the reinforced area after N tampings, E is the initial elastic modulus of the foundation, N is the number of tampings, and α is the fitting parameter.

[0020] Furthermore, in step S6, when δ = 5% of a certain depth, the reinforcement depth is the optimal reinforcement depth H1; when δ = 2% of a certain depth, the reinforcement depth is the maximum reinforcement depth H2; when 0 ≤ δ < 2%, considering the deviation of the simulation calculation method, the reinforcement depth is ignored. When extracting the vertical displacement at different depths, the reinforcement depth is calculated by linear interpolation at the nodes of vertical deformation reduction rate δ.

[0021] Furthermore, the classification criteria for the dynamic compaction energy level E are as follows: low energy level: E≤4000kN·m; medium energy level: 4000kN·m<E≤6000kN·m; high energy level: 6000kN·m<E≤8000kN·m; ultra-high energy level: E>8000kN·m.

[0022] The beneficial effects of this invention are as follows: This invention establishes a computational model for dynamic compaction numerical simulation in numerical simulation software using geological profile maps of the test area, preparing for the numerical calculation of dynamic compaction. Dynamic compaction tests were conducted in the test area at four energy levels (low, medium, high, and ultra-high energy). The results monitored after actual dynamic compaction in the test area yielded the relationship curves between compaction settlement and the number of blows at the corresponding energy levels. These curves were compared with the calculated settlement values ​​of the compaction pit and the number of blows obtained from the computational model, demonstrating the reliability of the numerical model and ensuring the reliability of the reinforcement depth results obtained in subsequent steps. The optimal number of blows and the optimal reinforcement depth H1 and maximum reinforcement depth H2 obtained by this invention at different energy levels can be selected according to the appropriate dynamic compaction energy level and number of blows. Fitting the relationship between reinforcement depth and compaction energy can accurately predict the reinforcement depth after selecting a certain energy level. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the numerical simulation sample model of the present invention;

[0024] Figure 2 This is a flowchart of the dynamic compaction simulation calculation program;

[0025] Figure 3-a , Figure 3-b , Figure 3-c , Figure 3-d and Figure 3-e The comparison shows the calculated and measured values ​​of cumulative settlement of the ramming pit under different ramming energies (3000 kN·m, 6000 kN·m, 8000 kN·m, 12000 kN·m, 15000 kN·m).

[0026] Figure 4 This is a graph showing the relationship between the reinforcement depth and the impact energy of the present invention. Detailed Implementation

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments. Figures 1 to 4 All accompanying drawings are simplified versions of embodiments and are intended only to clearly and concisely illustrate the embodiments of the present invention. The technical solutions shown in the drawings below are specific solutions of embodiments of the present invention and are not intended to limit the scope of the claimed invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0028] The embodiment provides a method for determining the depth of dynamic compaction reinforcement for deep fill based on the settlement amount. An experimental analysis was conducted on a specific deep fill site, and the specific steps are as follows:

[0029] (1) In the deep fill site, select an area where the fill thickness is greater than the estimated or empirical value of the reinforcement depth as the test area. Based on the geological profile of the test area, establish the calculation model required for dynamic compaction numerical simulation in the numerical simulation software to prepare for dynamic compaction numerical calculation. The calculation model includes the hammer unit, the surrounding soil unit of dynamic compaction and the model boundary soil unit.

[0030] (2) Conduct large-scale direct shear tests on undisturbed fill in the test area to obtain the internal friction angle φ and cohesion c of the soil, and take the average value of the results as the initial data of the soil parameters;

[0031] The large-scale direct shear test in the field consists of four specimens per group, with three groups of tests conducted in each test area, and no less than 12 valid data points in each test area. Specifically, the large-scale direct shear test in the field involves applying different vertical loads to each group of specimens by stacking different counterweights, placing the jacks horizontally, and applying horizontal shear force until the specimens are sheared and fail. The relationship curve between normal stress and shear stress is obtained, and the slope angle after linear fitting is the internal friction angle φ, and the intercept with the vertical axis is the cohesion c. After several groups of tests are completed, the average value is taken as the test result, which is the initial data for numerical simulation calculation of soil parameters.

[0032] (3) Dynamic compaction construction of different energy levels such as 3000kN·m, 6000kN·m, 8000kN·m, 12000kN·m and 15000kN·m was carried out in the test area. During the dynamic compaction construction, the number of compaction blows and settlement of a single compaction point were monitored to obtain the relationship curves between compaction settlement and number of compaction blows at different energy levels.

[0033] Table 1. Zoning of Dynamic Compaction Tests

[0034]

[0035] During the monitoring process, the original elevation of the point needs to be measured and stored first. A complete set of data is measured after each compaction blow until the entire single-point compaction is completed. Based on the relationship curve between settlement and the number of compaction blows, an exponential function relationship is obtained: S = ae^(- ... -bN In the formula, S is the single-click settlement amount in cm; N is the number of tamping blows; and a and b are the fitting coefficients, as shown in Table 2.

[0036] Table 2 Fitting parameters for the dynamic compaction and single-impact settlement evolution model

[0037]

[0038] (4) Based on the measured data of the dynamic compaction test in the test area, and taking the elastic modulus of the soil as the basic field variable, the settlement value Y of the ramming pit under different ramming times at this energy level is simulated and calculated, so that the calculated settlement value Y of the ramming pit and the measured value y of the dynamic compaction test in the test area satisfy the relationship. The elastic modulus of the reinforced soil layer after each compaction is calculated. The change in the elastic modulus affects the deformation. By comparing the monitoring results and the calculated results, if the difference does not meet the requirement of η, the software will recalculate.

[0039] By fitting the curves of the relationship between the back-calculated elastic modulus of the reinforced soil and the number of blows at each blow, it was found that the elastic modulus of the reinforced soil layer at each blow follows a power function distribution law, and the fitting formula is E′=EN. a In the formula, E′ is the elastic modulus of the soil in the reinforced area after N tampings, E is the initial elastic modulus of the foundation, N is the number of tampings, and the fitting parameter a = 0.4971 to 0.5395.

[0040] (5) Substitute the elastic modulus of the reinforced soil layer obtained after each compaction into the calculation model established in step (1) to calculate the vertical deformation of the ground surface under different compaction times at the compaction energy. When the vertical deformation s of the ground surface after the i-th compaction is... i Satisfying relation s i+1 -s i ≈s i -s i-1 Where i = 1, 2, 3Kn, this indicates that a stable state is reached after the i-th compaction, and the optimal number of compaction blows under this compaction energy is determined to be i. Using the obtained optimal number of compaction blows under this compaction energy, a curve showing the change in vertical deformation of the soil along the depth direction after the i-th compaction under this compaction energy is plotted, with the vertical deformation reduction rate as the criterion. To analyze and determine the optimal reinforcement depth H1 and maximum reinforcement depth H2 of dynamic compaction, where s hi It is the vertical deformation at depth h after the i-th impact, s i It is the vertical deformation of the ground surface after the i-th impact. The center point of the ground surface at the impact location is selected. Nodes along the depth direction can be selected on the model established in step (1). After each impact, the deformation at the center point of the ground surface and the vertical deformation of each node along the depth direction can be obtained.

[0041] When δ ≥ 5%, the soil under the compaction pit undergoes significant settlement under dynamic compaction. The settlement decreases rapidly with increasing depth, and most of the settlement under dynamic compaction is completed within this depth range. This reflects that the reinforcement effect of dynamic compaction weakens with increasing depth. The reinforcement depth at this point is the optimal reinforcement depth H1, which is the actual reinforcement depth used in the project. When 2% ≤ δ < 5%, the soil basically does not deform. The reinforcement depth at this point is the maximum reinforcement depth H2, which can be used as a safety reserve or for further utilization in the project. When 0 ≤ δ < 2%, considering the deviations in simulation calculations, the reinforcement depth at this point can be ignored. When extracting vertical displacements at different depths, linear interpolation is not used at the vertical deformation reduction rate δ node to calculate the reinforcement depth. Since the model elements have thickness, as can be seen from the modeling diagram, there will be cases where δ = 5.8% at a depth of 7m and δ = 4.3% at a depth of 8m. In these cases, interpolation can be used for calculation. Using the methods described above, the optimal and maximum reinforcement depths for each dynamic compaction level were determined, as shown in Table 3.

[0042] Table 3. Statistics on Reinforcement Depth

[0043]

[0044] (6) Statistical analysis of reinforcement depth under different tamping energies was conducted to obtain the relationship curve between reinforcement depth and tamping energy. The relationship between reinforcement depth and tamping energy was obtained by fitting the curve. Based on this, the reinforcement depth can be accurately predicted based on the dynamic tamping energy.

[0045] The reinforcement depth H and the impact energy W are basically linearly correlated. After fitting, the optimal reinforcement depth H1 is calculated as y = 0.00055x + 4.4687, and the maximum reinforcement depth H2 is calculated as y = 0.00065x + 6.2328. It can be seen that the numerical simulation results are very close to the measured results at low impact energies. However, at high impact energies, because material is added to the crater after each impact, the calculated reinforcement depth is significantly lower than the measured value.

[0046] This invention provides an important reference for determining and selecting parameters for dynamic compaction reinforcement of deep fill foundations, and further determines the effective reinforcement depth of dynamic compaction. The reinforcement depth value determined by this method is close to the measured value, which has certain advantages.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for determining the depth of deep fill reinforcement by dynamic compaction based on the settlement, characterized in that, Includes the following steps: S1. In a deep fill site, select an area where the fill thickness is greater than the estimated or empirical value of the reinforcement depth as the test area. Based on the geological profile of the test area, establish the calculation model required for dynamic compaction numerical simulation in numerical simulation software to prepare for dynamic compaction numerical calculation. The calculation model includes the hammer element, the surrounding soil element of dynamic compaction, and the model boundary soil element. S2. Conduct large-scale direct shear tests on undisturbed fill in the test area to obtain the internal friction angle φ and cohesion c of the soil, and take the average value of the results as the initial data of the soil parameters; S3. Conduct dynamic compaction construction at a certain energy level in the test area. During the construction process, monitor the number of compaction blows and settlement at a single compaction point to obtain the relationship curve between compaction settlement and number of compaction blows at that energy level. S4. Using the elastic modulus of the soil as the basic field variable, and through initial data of soil parameters, simulate and calculate the calculated value Y of the pit settlement under different compaction cycles at this energy level, so that the calculated value Y of the pit settlement and the measured value y of the dynamic compaction test in the test area satisfy the following relationship. The elastic modulus of the reinforced soil layer after each compaction is calculated. S5. Using the elastic modulus of the reinforced soil layer obtained in step S4 after each compaction, substitute it into the calculation model established in step S1 to calculate the vertical deformation of the ground surface under different compaction times at the compaction energy. The vertical deformation of the ground surface after the i-th compaction is then calculated. Satisfying the relation This indicates that a stable state is reached after the i-th impact, and the optimal number of impacts under this impact energy is determined to be i. S6. Using the optimal number of compaction blows obtained in step S5, plot the curve of the vertical deformation of the soil along the depth direction after the i-th compaction blow at this compaction energy, and use the vertical deformation reduction rate. To analyze and determine the optimal reinforcement depth of dynamic compaction. H 1 and maximum reinforcement depth H 2, of which It is the vertical deformation at depth h after the i-th impact. It is the vertical deformation of the ground surface after the i-th impact; S7. Dynamic compaction energy levels include low energy, medium energy, high energy, and ultra-high energy. By repeating steps S3-S6 during dynamic compaction at different energy levels, the optimal number of compaction blows and the optimal reinforcement depth can be obtained for each energy level. H 1 and maximum reinforcement depth H 2; S8. Statistically analyze the reinforcement depth under different tamping energies to obtain the relationship curve between reinforcement depth and tamping energy. Fit the curve to obtain the relationship between reinforcement depth and tamping energy. The reinforcement depth H and tamping energy W are basically linearly correlated. After fitting, the optimal reinforcement depth H1 formula is H1=a1W+b1, and the maximum reinforcement depth H2 formula is H2=a2W+b2.

2. The method for determining the depth of deep fill reinforcement based on the settlement volume according to claim 1, characterized in that: In step S1, the tamping hammer element and the surrounding soil element of the dynamic compaction in the calculation model are simulated using linear elements, while the soil element at the model boundary is simulated using infinite element elements.

3. The method for determining the depth of deep fill reinforcement based on the settlement volume according to claim 1, characterized in that: In step S2, the large-scale direct shear test in the field involves applying different vertical loads to each group of samples by stacking different counterweights. The jacks are placed horizontally, and horizontal shear force is applied by pushing until the samples are sheared and broken. The relationship curve between normal stress and shear stress is obtained. After linear fitting, the slope angle is the internal friction angle φ, and the intercept with the vertical axis is the cohesion c. After multiple sets of tests are completed, the average value is taken as the test result, which is the initial data for numerical simulation calculation of soil parameters.

4. The method for determining the depth of deep fill reinforcement based on the settlement volume according to claim 1, characterized in that: During the monitoring process in step S3, the original elevation of the point needs to be measured and stored first. A complete set of data is measured after each tamping blow until the entire single-point tamping is completed. Based on the relationship curve between the settlement and the number of tamping blows, an exponential function relationship is obtained: In the formula, S is the initial settlement of the single-blow compaction, in cm; N is the number of blows; a and b are fitting coefficients, which are parameters of the initial settlement of the dynamic compaction. a is positively correlated with the initial settlement, and b is negatively correlated with the initial settlement, both of which are affected by the dynamic compaction energy level.

5. The method for determining the depth of deep fill reinforcement based on the settlement volume according to claim 1, characterized in that: In step S4, the relationship curves between the back-calculated elastic modulus of the reinforced soil at each number of blows and the number of blows are fitted to obtain a power function distribution of the elastic modulus of the reinforced soil layer at each number of blows. The fitting formula is as follows: In the formula, E´ is the elastic modulus of the soil in the reinforced area after N tampings, E is the initial elastic modulus of the foundation, N is the number of tampings, and α is the fitting parameter.

6. The method for determining the depth of deep fill reinforcement based on the settlement volume according to claim 1, characterized in that: In step S6, when δ = 5% of a certain depth, the reinforcement depth at this point is the optimal reinforcement depth. H 1. When δ = 2% at a certain depth, the reinforcement depth at this point is the maximum reinforcement depth. H 2, when 0≤ δ When the vertical displacement is less than 2%, considering the deviation of the simulation calculation method, the reinforcement depth is ignored. When extracting the vertical displacement at different depths, the reinforcement depth is calculated by linear interpolation at the node of vertical deformation reduction rate δ.

7. The method for determining the depth of deep fill reinforcement based on the settlement volume according to claim 1, characterized in that: The dynamic compaction energy level E The classification criteria are as follows: Low energy level: E ≤4000 kN·m; Intermediate energy level: 4000 kN·m < E ≤6000 kN·m, high energy level: 6000 kN·m < E ≤8000 kN·m, ultra-high energy level: E >8000 kN·m.

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