Calculation method of layered laying thickness of single-point compacted fill soil

Abstract

The present invention belongs to the technical field of soil filling engineering in foundation, and discloses a method for calculating the layered laying thickness of single-point dynamic compaction filling soil. The calculation method includes the following steps: calculating and determining the corresponding plastic body strain threshold when the filling soil reaches the required dry density requirement; using a numerical simulation method to calculate and determine the distribution of plastic body strain in the filling soil under dynamic compaction; taking the maximum depth from the tamping surface corresponding to the plastic body strain threshold in the distribution diagram of the plastic body strain as the layered laying thickness of the dynamic compaction filling soil. The present invention can achieve a dense connection between the upper and lower tamping layers of soil in the process of layered dynamic compaction filling of multiple layers of soil, ensuring that the compaction degree of the entire multi-layer filling body meets the control requirements, and the calculation process is simple to operate, and can conveniently realize the design analysis and calculation of the layered laying thickness problem of single-point dynamic compaction filling soil, and has good technical rationality and practical operability.

Description

Technical Field

[0001] The invention relates to the technical field of soil filling engineering in foundation, and in particular to a method for calculating the layered laying thickness of strongly compacted filling soil. Background Art

[0002] Dynamic compaction is an available engineering technology method for backfill reinforcement. This method uses lifting equipment to lift a heavy hammer to a certain height, and then allows it to fall freely, generating a large impact energy in the backfill, thereby compacting the backfill and improving the strength and deformation modulus of the backfill. For high backfill, a layered filling construction method is generally adopted. After each layer of dynamic compaction is completed, the filled soil should meet the specified compaction index requirements. Among them, the reasonable determination of the thickness of the layered soil becomes one of the key factors in the design of dynamic compaction engineering, which directly determines the quality of the rammed and reinforced soil and the economy of the dynamic compaction engineering.

[0003] For the strong compaction reinforcement of fill soil, there are two traditional methods to determine the thickness of the layered soil: one is to determine it based on the properties of the filler by using the engineering analogy method based on past experience; the other is to conduct a tamping test on site and determine it through the test results of the tamping action under several different fill soil thicknesses. However, both methods of determining the thickness of the layered soil by strong compaction have defects. The former relies too much on engineering experience and cannot reflect the differential effects of different fillers, and the estimated fill soil thickness is blind; the latter relies entirely on on-site tamping tests, but the types of layered soil thickness in on-site tests are often very limited, making it difficult to accurately determine the appropriate layered soil thickness, and the test operation is time-consuming and labor-intensive, and there is also the problem of additional engineering costs. Summary of the invention

[0004] The purpose of the present invention is to overcome the technical problems existing in the prior art in determining the layered laying thickness of strongly compacted fill soil by the engineering analogy method and the on-site tamping test method, and to provide a method for calculating the layered laying thickness of a single-point strongly compacted fill soil.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The method for calculating the layered laying thickness of single-point compaction fill soil includes the following steps:

[0007] Calculate and determine the corresponding plastic volume strain threshold when the fill soil reaches the required dry density requirement;

[0008] The distribution of plastic volume strain in fill soil under dynamic compaction is determined by numerical simulation method.

[0009] The maximum depth from the tamping surface corresponding to the plastic volume strain threshold in the distribution diagram of the plastic volume strain is taken as the layered laying thickness of the strongly compacted fill soil.

[0010] The technical concept of the method for calculating the layered laying thickness of single-point compaction fill soil of the present invention is: using the plastic volume strain threshold of the compacted soil as the basic judgment indicator, based on the relationship between it and the compaction degree of the soil, that is: the higher the compaction degree requirement, the greater the plastic volume strain, and the corresponding effective action depth produced by the compaction is shallow, so the required compaction thickness of each layer is small. Therefore, after determining the plastic body strain distribution in the compacted soil by calculation, the actual layered laying thickness of the compacted soil is the depth corresponding to the plastic body strain threshold, and the layered laying thickness of the compacted soil can be calculated and determined.

[0011] The essence of the technical solution of the method for calculating the layered laying thickness of the single-point strongly compacted fill soil body of the present invention is: first, the present invention adopts the quantitative correspondence between the plastic volume strain limit threshold value of the soil body and the compaction degree, and calculates and determines the plastic volume strain threshold value of the soil body by controlling the compaction degree; then, a three-dimensional numerical simulation method is used to calculate and determine the plastic volume strain distribution range diagram of the strongly compacted soil body, and the maximum depth corresponding to the plastic volume strain threshold value in the diagram is determined accordingly, so as to obtain the layered laying thickness of the single-point strongly compacted fill soil body.

[0012] It can be seen that the method for calculating the layered laying thickness of single-point compaction fill soil of the present invention has the advantages of reasonably reflecting the control requirements for the compaction degree of fill soil, and can achieve the dense connection between the upper and lower ramming layers of soil in the process of layered compaction filling of multi-layer soil, ensuring that the compaction degree of the entire multi-layer filling body meets the control requirements, and the calculation process is simple to operate, and can conveniently realize the design analysis and calculation of the layered laying thickness problem of single-point compaction fill soil, has good technical rationality and practical operability, and provides an effective method and scientific basis for the simple, efficient and rational engineering design of compaction fill soil, which has important technical significance and engineering application value.

[0013] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Additional aspects and advantages of the present invention will be partially given in the following description, partially become apparent from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings constituting a part of the present invention are used to assist the understanding of the present invention. The contents provided in the drawings and their related descriptions in the present invention can be used to explain the present invention, but do not constitute improper limitations on the present invention.

[0015] Figure 1 It is a schematic structural diagram of the single-point dynamic compaction fill soil body of the test example of the present invention.

[0016] Figure 2 It is a geometric dimension diagram of the three-dimensional numerical model of the single-point dynamic compaction fill soil of the test example of the present invention.

[0017] Figure 3 This is a cloud diagram of the plastic volume strain distribution in the single-point compaction fill soil of the test example of the present invention.

[0018] Figure 4 This is a diagram of the effective reinforcement range of strong compaction corresponding to different plastic volume strain thresholds in the single-point strong compaction fill soil of the test example of the present invention.

[0019] Figure 5 It is a comparison chart of the measured compaction value and the required compaction value of the test example of the present invention.

[0020] The markings in the above-mentioned figures are: 100 - fill soil; 200 - foundation; 300 - rammer. DETAILED DESCRIPTION

[0021] The present invention is described clearly and completely below in conjunction with the accompanying drawings. A person skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that:

[0022] The technical solutions and technical features provided in each part of the present invention, including the following description, may be combined with each other if there is no conflict.

[0023] In addition, the embodiments of the present invention involved in the following description are generally only a part of the embodiments of the present invention, rather than all the embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0024] About the terms and units in the present invention: The terms "include", "have" and any variations thereof in the description and claims of the present invention and related parts are intended to cover non-exclusive inclusions.

[0025] The specific implementation method of the layered laying thickness calculation method of the single-point dynamic compaction fill soil body of the present invention comprises the following steps:

[0026] Step 100, calculating and determining the corresponding plastic volume strain threshold when the fill soil mass reaches the required dry density requirement;

[0027] Step 200, using a numerical simulation method to calculate and determine the distribution of plastic volume strain in the fill soil under the action of strong compaction;

[0028] Step 300, taking the maximum depth from the tamping surface corresponding to the plastic volume strain equal to the plastic volume strain threshold in the distribution diagram of the plastic volume strain as the layered laying thickness of the strongly compacted fill soil.

[0029] Wherein, step 100 specifically includes steps 110-160, which are as follows:

[0030] Step 110: According to the Geotechnical Test Method Standard (GB / T 50123-2019), the maximum dry density of the fill soil is measured by test. r dmax , minimum dry density r dmin , Dry density in loose filling state r d0 and the dry soil particle density in the fill soil r s .

[0031] Step 120: Calculate and determine the minimum void ratio, maximum void ratio, and void ratio of the fill soil in a loose filling state.

[0032] According to the dry soil density in the fill soil r s and the maximum dry density of fill soil r dmax , calculate the minimum void ratio of fill soil e min , its calculation expression is:

[0033] ;

[0034] According to the dry soil density in the fill soil r s and the minimum dry density of fill soil r dmin , calculate the maximum void ratio of fill soil e max , its calculation expression is:

[0035] ;

[0036] According to the dry soil density in the fill soil r s and the dry density of the loose filling state of the fill soil r d0 , calculate the void ratio of the loose filling state of the fill soil e 0, its calculation expression is:

[0037] ;

[0038] Step 130: Calculate the relative density of the loose filling state of the fill soil according to the void ratio of the fill soil in different states. D r0 , whose expression is:

[0039] ;

[0040] Step 140: Determine the volume strain value of the fill soil under the minimum porosity state.

[0041] According to the recommendations of the Highway Geotechnical Test Code (JTG3430-2020), the volume strain value of fill soil under the minimum porosity state is e max It is usually taken as 0.105-0.117. In actual operation, the upper boundary value of 0.117 is taken for the case where the fine particles in the fill soil are relatively high, and the lower boundary value of 0.105 is taken for the case where the coarse particles in the fill soil are relatively high. For the case where the coarse and fine particles in the fill soil are similar or the coarse and fine particles are uncertain, the value can be taken as the middle value of 0.111 between the upper and lower boundaries.

[0042] Step 150: Calculate and determine the dry density that the fill soil needs to achieve based on the compaction requirement.

[0043] According to the required compaction degree of fill soil K , calculate its corresponding dry density r d , which is the required dry density value, and its calculation expression is:

[0044] ;

[0045] Step 160: Calculate and determine the corresponding plastic volume strain threshold when the fill soil mass reaches the required dry density requirement.

[0046] According to the soil mechanics method, the required dry density of the fill soil is derived. r d The corresponding plastic volume strain threshold e v , its calculation expression is:

[0047] ;

[0048] Step 200 specifically includes: adopting a three-dimensional numerical simulation method, which may be implemented by using a finite element method or a finite difference method to establish a three-dimensional numerical model of sufficient size.

[0049] The boundary of the three-dimensional numerical model adopts a standard constraint boundary, that is, only normal constraints are set on all four sides of the three-dimensional numerical model, and three-way fixed constraints are set at the bottom of the three-dimensional numerical model at the same time.

[0050] The classical ideal elastic-plastic stress-strain relationship, Mohr-Coulomb yield criterion and non-associated flow law are used for the constitutive relationship of soil.

[0051] For both the compacted soil and the rammer, the first-order eight-node three-dimensional solid reduced integration unit is used to mesh the three-dimensional numerical model. Considering the calculation accuracy and efficiency, the minimum width of the grid is taken as 1 / 10~1 / 12 of the wavelength of the site vibration shear wave, and the wavelength of the site vibration shear wave is equal to the wave velocity of the site vibration shear wave divided by the main frequency of the ramming vibration.

[0052] The wave velocity of the site vibration shear wave and the main frequency of the impact vibration are all parameters determined through field tests. At the same time, the parameters required for calculation such as the soil weight, elastic modulus, Poisson's ratio, internal friction angle, shear dilation angle, cohesion, tensile strength, damping ratio, etc. are all parameters determined through tests.

[0053] The step size of the calculation time of the three-dimensional numerical simulation is 0.01s, and the calculation time of the rammer tamping process is 0.5s.

[0054] In the three-dimensional numerical simulation, the tamping hammer is placed on the soil surface and an initial velocity is applied. v 0 simulates the tamping load. The initial velocity is calculated according to the classic free fall motion formula related to the vertical drop distance of the tamping hammer. The calculation expression is: ;

[0055] In the formula, g is the acceleration due to gravity, usually 10m / s 2 ; H It is the vertical drop distance of the rammer.

[0056] The plastic volume strain ε in the fill soil is obtained by calculating the effect of single-point compaction on the fill soil through three-dimensional numerical simulation. p The distribution cloud diagram and its corresponding numerical size.

[0057] Step 300 specifically includes: calculating and measuring the plastic volume strain value in the cloud diagram of the distribution of plastic volume strain in the fill soil obtained by three-dimensional numerical simulation e p Equal to the plastic volume strain threshold e v The corresponding maximum depth from the ramming surface h , then this depth is the corresponding soil layer laying thickness when the fill soil is compacted layer by layer from bottom to top.

[0058] The beneficial effects of the present invention are described below through specific test examples.

[0059] Figure 1Schematic diagram of the structure of the single-point compaction filling soil body of the test example of the present invention. Figure 1 As shown in FIG. 1 , the fill soil 100 on a foundation 200 is reinforced by a single-point tamping method, and a circular tamping hammer 300 weighing 14000 kg is used for tamping, the diameter of the tamping hammer 300 is 2.5 m, and the tamping energy is 2002 kJ (= tamping hammer weight (14000 kg) × gravity acceleration (10 N / kg) × tamping hammer vertical drop distance (14.3 m)). The coarse and fine particle contents in the fill soil 100 are similar. The main parameters of the fill soil 100 are shown in Table 1.

[0060] Table 1 Main parameters of fill soil 100

[0061]

[0062] The compaction degree of the fill soil 100 is taken as 0.92, 0.93, 0.94, etc., and the corresponding layered paving soil thickness needs to be determined. The specific calculation process is as follows:

[0063] Step 110: According to the geotechnical test method standard (GB / T 50123-2019), the relevant parameters of the fill soil are measured through the test:

[0064] Maximum dry density r max =2220 kg / m 3 ;

[0065] Minimum dry density r min =1700 kg / m 3 ;

[0066] Dry density of loose filling state r 0=1850 kg / m 3 ;

[0067] Density of dry soil particles in fill soil r s =2650 kg / m 3 .

[0068] Step 120: Substitute the relevant parameters into equations (1), (2), and (3) to obtain:

[0069]

[0070] Step 130: Substituting the relevant parameters into equation (4) yields:

[0071]

[0072] Step 140: Since the coarse and fine particle contents in the fill soil are similar, the volume strain of the fill soil in the minimum porosity state is e max =0.111.

[0073] Step 150: Compactness K =0.92, 0.93, 0.94, substituting the relevant parameters into formula (5) yields:

[0074]

[0075] Step 160: Substitute the relevant parameters into equation (6) to obtain:

[0076]

[0077] Step 200: Figure 2 As shown in the figure, the geometric dimensions of the fill soil of the three-dimensional numerical model established by using the three-dimensional numerical simulation software ABAQUS are length × width × height = 30m × 30m × 20m. Considering the main factors such as the boundary conditions, mesh division, soil constitutive relationship, and soil physical and mechanical parameters of the three-dimensional numerical model, the boundary of the three-dimensional numerical model of the single-point dynamic compaction fill soil adopts the standard constraint boundary; according to formula (7), the initial velocity applied by the tamping hammer on the soil surface is v 0=16.91m / s; Calculate the effect of single-point dynamic compaction on the fill soil and obtain the plastic volume strain in the single-point dynamic compaction on the fill soil e p The distribution cloud diagram and its corresponding numerical value are as follows Figure 3 shown.

[0078] Step 300: Figure 3 The distribution cloud diagram of plastic volume strain in the fill soil obtained by three-dimensional numerical simulation can be further drawn Figure 4 The corresponding plastic body strain threshold is shown e v =6%, 7%, 8% of the effective reinforcement range of strong compaction, it can be seen that the plastic volume strain e p Equal to the plastic volume strain threshold e v =6%, 7%, 8%, the corresponding maximum depth from the tamping surface h The depths are 5.02m, 4.88m and 4.76m respectively. Therefore, the depths are the layered paving thicknesses of the soil corresponding to compaction degrees of 0.92, 0.93 and 0.94 respectively when the soil is filled by single-point compaction from bottom to top.

[0079] Results test:

[0080] The required compaction values ​​of 0.92, 0.93 and 0.94 calculated by the method of the present invention correspond to soil layered paving thicknesses of 5.02m, 4.88m and 4.76m, respectively. Then, the compaction is tested on site by the sand injection method after single-point tamping according to these thicknesses. The test is conducted twice at each paving thickness, and the corresponding measured compaction values ​​are 0.916 and 0.921, 0.925 and 0.929, and 0.944 and 0.945, respectively.

[0081] Figure 5 This is a comparison chart between the measured compaction value and the required compaction value. Figure 5 As shown, the two are generally consistent, and the absolute values ​​of the relative errors between the average values ​​of the measured values ​​and the required values ​​are 0.2%, 0.3% and 0.5% respectively. These comprehensive results show that the method of the present invention has a certain degree of rationality.

[0082] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Although the present invention has been described in detail with reference to the above embodiments, the present invention is not limited to the above specific implementation methods. Therefore, any modification or equivalent replacement of the present invention; and all technical solutions and improvements thereof that do not depart from the spirit and scope of the invention should be included in the scope of the claims of the present invention.

[0083] The above is a description of the relevant contents of the present invention. A person skilled in the art will be able to implement the present invention based on these descriptions. Based on the above contents of the present invention, all other embodiments obtained by a person skilled in the art without creative work shall fall within the scope of protection of the present invention.

Claims

1. A method for calculating the layered laying thickness of single-point compacted fill soil, characterized in that: The following steps are involved: Calculate and determine the corresponding plastic volume strain threshold when the fill soil reaches the required dry density requirement; The distribution of plastic volume strain in fill soil under dynamic compaction is determined by numerical simulation method. The maximum depth from the tamping surface corresponding to the plastic volume strain threshold value in the distribution diagram of the plastic volume strain is taken as the layered laying thickness of the strongly compacted fill soil; Among them, the plastic volume strain threshold ε v The calculation expression is: ； In the formula, ρ d It is the dry density of the fill soil when it reaches the required compaction degree; ρ dmax is the maximum dry density of fill soil; ρ dmin is the minimum dry density of fill soil; D r0 It is the relative density of the fill soil in the loose filling state; ε max is the volume strain value of fill soil under the minimum porosity state.

2. The method for calculating the layered laying thickness of the single-point compaction fill soil body according to claim 1, characterized in that: Relative density D of the loose filling state of the fill soil r0 The calculation expression is: ； Dry density at the required compaction ρ d The calculation expression is: ； In the formula, e min is the minimum void ratio of fill soil; e max is the maximum void ratio of the fill soil; e 0 is the void ratio of the fill soil in the loose filling state; K The required compaction.

3. The method for calculating the layered laying thickness of the single-point dynamic compaction fill soil body according to claim 2, characterized in that: Minimum void ratio of fill soil e min The calculation expression is: ； Maximum void ratio of fill soil e max The calculation expression is: ； The void ratio of the loose filling state of the fill soil e The calculation expression of 0 is: ； In the formula, ρ s is the dry soil particle density in the fill soil; ρ d0 It is the dry density of the fill soil in a loose filling state.

4. The method for calculating the layered laying thickness of the single-point dynamic compaction fill soil body according to claim 3, characterized in that: According to the geotechnical test method standard GB / T 50123-2019, the maximum dry density of fill soil was measured by test ρ dmax , minimum dry density ρ dmin , Dry density in loose filling state ρ d0 and the dry soil particle density in the fill soil ρ s .

5. The method for calculating the layered laying thickness of the single-point dynamic compaction fill soil body according to claim 1, characterized in that: Determine the volume strain value of fill soil under the minimum porosity state according to the highway geotechnical test specification JTG3430-2020 ε max .

6. The method for calculating the layered laying thickness of the single-point dynamic compaction fill soil body according to claim 1, characterized in that: The numerical simulation method is a finite element method or a finite difference method.

7. The method for calculating the layered laying thickness of the single-point dynamic compaction fill soil body according to claim 6, characterized in that: Normal constraints are set around the three-dimensional numerical model, and three-way fixed constraints are set at the bottom of the three-dimensional numerical model at the same time; the classical ideal elastic-plastic stress-strain relationship, Mohr-Coulomb yield criterion and non-associated flow law are used for the constitutive relationship of the soil; for the strongly compacted soil and rammer, the first-order eight-node three-dimensional solid reduced integration unit is used to mesh the three-dimensional numerical model; the minimum width of the grid is taken as 1 / 10~1 / 12 of the wavelength of the site vibration shear wave, and the wavelength of the site vibration shear wave is equal to the wave velocity of the site vibration shear wave divided by the main frequency of the ramming vibration; in the three-dimensional numerical simulation, the ramming load is simulated by placing the rammer on the surface of the soil and applying the initial velocity; the effect of single-point strongly compacted fill soil is calculated by three-dimensional numerical simulation, and the plastic volume strain ε in the fill soil is obtained. p The distribution cloud diagram and its corresponding numerical size.

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