A method for evaluating the plasticity state of shield tunnel excavated soil in sandy and gravelly strata

Abstract

This application provides a method for evaluating the plasticity of tunnel boring machine (TBM) excavated soil in gravelly strata, relating to the field of earth pressure balance (EPB) tunnel construction technology. The method includes: conducting slump tests on multiple groups of excavated soil samples with particle sizes smaller than a set threshold to obtain a first slump value; conducting landslide tests on all groups of excavated soil samples at different preset inclination angles to obtain a first particle ratio and a second particle ratio, and calculating a first flowability coefficient for the excavated soil samples; determining a slump function based on the first slump value and the first flowability coefficient; placing the gravelly excavated soil in a chute device for a landslide test and calculating a second flowability coefficient for the gravelly excavated soil; calculating a second slump value for the gravelly excavated soil based on the second flowability coefficient and the slump function, and determining the plasticity state of the gravelly excavated soil. This method achieves accurate evaluation of the plasticity of gravelly excavated soil, providing reliable technical support for timely understanding the plasticity state of excavated soil during EPB TBM construction in gravelly strata.

Description

Technical Field

[0001] This application generally relates to the field of earth pressure balance tunnel construction technology, and specifically to a method for evaluating the plasticity state of shield tunnel excavated soil in sandy and gravelly strata. Background Technology

[0002] Earth pressure balance (EPB) shield tunneling machines have become one of the main construction methods for tunnel engineering due to their advantages such as safety, efficiency, and economy. More than 90% of urban land tunnels worldwide are constructed using EPB shield tunneling. During the shield tunneling process, the soil cut by the cutterhead enters the soil chamber and acts as a support medium to maintain the stability of the shield face.

[0003] To achieve the above objectives, the excavated soil needs to possess suitable plasticity. Excessive fluidity may lead to over-discharge of excavated soil, potentially causing surface collapse; conversely, insufficient fluidity may result in stagnation of excavated soil, easily leading to surface heave. Accurately assessing the plasticity of the excavated soil is crucial for the safe and efficient tunneling of shield tunnels. Existing assessment methods primarily rely on slump tests. However, due to limitations imposed by the size of the slump test cylinder, slump tests are not applicable to excavated soil with a maximum particle size of 40mm. Furthermore, the particle size of sandy and gravelly strata generally exceeds 40mm, making it impossible to ascertain the plasticity state of the sandy and gravelly excavated soil when tunneling in such strata. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a method for evaluating the plasticity state of shield tunneling slag in sandy and gravelly strata, so as to know the plasticity state of sandy and gravelly slag.

[0005] This application provides a method for evaluating the plasticity state of shield tunnel excavated soil in sandy and gravelly strata, including the following steps:

[0006] Slump tests were conducted on multiple groups of slag soil samples with particle sizes smaller than a set threshold to obtain the first slump value of each group of slag soil samples.

[0007] All groups of slag samples were placed in an adjustable-angle chute device and landslide tests were conducted at different preset angles to obtain the first particle size ratio and the second particle size ratio of the slag samples at different preset angles; and the first flowability coefficient of the slag samples was calculated based on the first particle size ratio and the second particle size ratio; the particle size corresponding to the first particle size ratio is smaller than the particle size corresponding to the second particle size ratio.

[0008] The slump function is determined based on the first slump value and the first fluidity coefficient;

[0009] The sandy gravelly soil is placed in the chute device and landslide tests are carried out at different preset angles to obtain corresponding third particle proportions and fourth particle proportions of the sandy gravelly soil at different preset angles; and according to the third particle proportions and the fourth particle proportions, a second flowability coefficient of the sandy gravelly soil is calculated;

[0010] According to the second flowability coefficient and the slump function, a second slump value of the sandy gravelly soil is calculated;

[0011] According to the second slump value of the sandy gravelly soil, a plastic flow state of the sandy gravelly soil is determined.

[0012] According to the technical scheme provided in the present application, a plurality of groups of slag soil samples with a particle size less than a set threshold value are subjected to slump tests to obtain a first slump value of each group of slag soil samples, which specifically includes the following steps:

[0013] S11, a plurality of groups of slag soil samples prepared with different improvement parameters are obtained, the improvement parameters including a foam injection ratio and a water content;

[0014] S12, one group of the slag soil samples is loaded into a slump cylinder and uniformly inserted and tamped for a preset number of times;

[0015] S13, after tamping, the cylinder opening of the slump cylinder is scraped flat, the slump cylinder is vertically lifted and collapsed, and the height difference after collapsing is taken as the first slump value of the group of slag soil samples;

[0016] S14, for the next group of slag soil samples, steps S12 and S13 are repeatedly executed until the first slump values of all groups of slag soil samples are obtained.

[0017] According to the technical scheme provided in the present application, all groups of slag soil samples are placed in a chute device with adjustable inclination and subjected to landslide tests at different preset angles to obtain corresponding first particle proportions and second particle proportions of the slag soil samples at different preset angles, which specifically includes the following steps:

[0018] The slag soil sample is poured into the upper end of the chute device with adjustable inclination, and the chute device is controlled to be in a horizontal state;

[0019] The chute device is uniformly rotated to a preset inclination angle with the horizontal plane, at the preset inclination angle, the baffle at the upper end of the chute device is lifted, and after the slag soil sample slides down and stops, all slag soil samples in the collection box at the lower end of the chute device are collected; the preset inclination angle at least includes 10°, 20°, 30° and 40°;

[0020] The collected slag samples are divided into first particles and second particles based on a preset particle size. The proportion of the mass of the first particle at each preset inclination angle to the total mass of the first particles corresponding to all preset inclination angles is taken as the proportion of the first particles in the slag sample at that preset inclination angle. The proportion of the mass of the second particle at each preset inclination angle to the total mass of the second particles corresponding to all preset inclination angles is taken as the proportion of the second particles in the slag sample at that preset inclination angle.

[0021] According to the technical solution provided in this application, the method further includes the following steps:

[0022] After collecting all the slag samples from the collection box at the lower end of the chute device, the collected slag samples are dried.

[0023] According to the technical solution provided in this application, the preset particle size is 20mm, the first particle is a particle with a particle size less than or equal to 20mm, and the second particle is a particle with a particle size greater than 20mm.

[0024] According to the technical solution provided in this application, the slump function is determined based on the first slump value and the first fluidity coefficient, specifically including the following steps:

[0025] A scatter dataset is constructed with the first slump value of the slag sample as the ordinate and the first fluidity coefficient of the slag sample as the abscissa.

[0026] Linear regression analysis was performed on the scatter dataset to obtain the collapse function.

[0027] According to the technical solution provided in this application, the plastic flow state of the sand and gravel slag is determined based on the second slump value of the sand and gravel slag, specifically including the following steps:

[0028] If the second slump value is greater than or equal to the plasticity threshold, the sand and gravel slag is determined to have plasticity; if the second slump value is less than the plasticity threshold, the sand and gravel slag is determined to have poor plasticity.

[0029] According to the technical solution provided in this application, the chute device includes:

[0030] A base, wherein a sliding groove is provided on the base, and the lower end of the sliding groove is hinged to the surface of the base; when the upper end of the sliding groove is lifted, the sliding groove rotates around the hinge position.

[0031] A baffle, which is slidably disposed at the upper end of the slide groove;

[0032] A collection box is provided adjacent to the base, and the inlet of the collection box is provided corresponding to the lower end of the chute.

[0033] According to the technical solution provided in this application, the angular velocity range of the tilt adjustment of the slide device is 0.5~1° / s, the width of the lower end of the slide is 2~3 times the width of the upper end of the slide, and the edge depth of the slide is 5~10cm.

[0034] According to the technical solution provided in this application, the particle size of the slag sample is less than 40 mm, and the particle size of the sand and gravel slag includes particles larger than 40 mm; the foam injection ratio varies from 0% to 60%, and the moisture content varies from 0% to 40%.

[0035] As can be seen from the above technical solution, this application has at least the following beneficial effects:

[0036] This application provides a method for evaluating the plasticity of shield tunnel excavated soil in gravel strata, comprising: conducting slump tests on multiple groups of excavated soil samples with particle sizes smaller than a set threshold to obtain a first slump value for each group of excavated soil samples; placing all groups of excavated soil samples in an adjustable-angle chute device and conducting landslide tests at different preset inclination angles to obtain a first particle size ratio and a second particle size ratio corresponding to the excavated soil samples at different preset inclination angles; and calculating a first flowability coefficient of the excavated soil samples based on the first particle size ratio and the second particle size ratio; wherein the particle size corresponding to the first particle size ratio is smaller than the second particle size ratio. The particle size corresponding to the particle size ratio is determined; the slump function is determined based on the first slump value and the first flowability coefficient; the sand and gravel slag is placed in a chute device and landslide tests are conducted at different preset angles to obtain the third and fourth particle sizes corresponding to the sand and gravel slag at different preset inclination angles; the second flowability coefficient of the sand and gravel slag is calculated based on the third and fourth particle sizes; the second slump value of the sand and gravel slag is calculated based on the second flowability coefficient and the slump function; and the plastic flow state of the sand and gravel slag is determined based on the second slump value of the sand and gravel slag.

[0037] This application first conducts slump tests on multiple groups of slag soil samples with particle sizes smaller than a set threshold to obtain the first slump value. Then, it uses an adjustable-angle chute device to conduct landslide tests on these slag soil samples at different preset angles to obtain the first particle ratio, the second particle ratio, and calculate the first flowability coefficient. Based on the first slump value and the first flowability coefficient, the slump function is determined. Finally, following the same landslide test procedure, the third particle ratio, the fourth particle ratio, and the second flowability coefficient of the sand and gravel slag soil are obtained. Substituting the second flowability coefficient into the slump function yields the second slump value. This second slump value can be used to determine the plastic flow state of the sand and gravel slag soil. Compared to the conventional slump test, which is limited by particle size and cannot evaluate the plasticity of sand and gravel slag, this scheme utilizes the correlation between particle size and flowability coefficient and function fitting to make the slump data of slag with different particle sizes universally applicable. This achieves accurate evaluation of the plasticity of sand and gravel slag with a particle size generally exceeding 40mm, providing reliable technical support for timely understanding of the plasticity of slag during earth pressure balance shield tunneling in sand and gravel strata. It effectively avoids the problems of surface collapse due to excessive slag flowability or surface heave due to insufficient flowability, ensuring the safety and efficiency of shield tunneling. Attached Figure Description

[0038] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0039] Figure 1 A flowchart for evaluating the plasticity state of shield tunnel excavated soil applicable to sandy and gravelly strata.

[0040] Figure 2 Example diagram of a slump test for a soil sample.

[0041] Figure 3 This is a fitted curve between the first fluidity coefficient and the first slump value.

[0042] Figure 4 This is a structural diagram of the chute device.

[0043] Figure 5 This is a top view of the chute.

[0044] The following are labeled in the diagram: 1. Slump cone; 2. Slag sample; 3. Chute; 4. Baffle; 5. Collection box; 6. Hinge; 7. Base. Detailed Implementation

[0045] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0047] like Figure 1 As shown, this application provides a method for evaluating the plasticity state of shield tunnel excavated soil in sandy and gravelly strata, comprising the following steps:

[0048] S100. Slump test is conducted on multiple groups of slag soil samples with particle size smaller than the set threshold to obtain the first slump value of each group of slag soil samples.

[0049] Here, the threshold is set to, for example, 40 mm, and the particle size of soil sample 2 is less than 40 mm.

[0050] Slump tests were conducted on multiple groups of slag soil samples with particle sizes smaller than a set threshold to obtain the first slump value for each group of slag soil samples. The specific steps included:

[0051] S11. Obtain multiple sets of improved parameters to prepare different slag samples. The improved parameters include foam injection ratio and moisture content.

[0052] Among them, the foam injection ratio varies from 0% to 60%, and the foam is used to improve the lubricity and fluidity of the slag; the moisture content varies from 0% to 40%, and the moisture content directly affects the cohesiveness and flow characteristics of the slag; through various combinations of foam injection ratio and moisture content, no less than 50 sets of slag samples under test conditions are prepared to ensure that the data cover slag conditions with different plastic flow states.

[0053] S12. Load one set of slag samples into the slump cone and tamp it evenly a preset number of times.

[0054] The preset number of times is, for example, 25. The soil sample 2 is slowly poured into the slump cone 1, and then a special tamping rod is used to evenly tamp it a preset number of times. The tamping process should be carried out in a spiral motion from the wall of the slump cone 1 towards its center to ensure consistent compaction throughout the soil sample 2, avoiding localized looseness or clumping. Here, the specifications of the slump cone 1 are, for example, a frustum-shaped cylinder with an upper diameter of 100mm, a lower diameter of 200mm, and a height of 300mm.

[0055] S13. After tamping, scrape the opening of the slump cone to level it, lift the slump cone vertically and let it collapse. Take the height difference after collapse as the first slump value of the slag sample.

[0056] After tamping, the excess soil sample 2 at the opening of the slump cone 1 is scraped level with a scraper, ensuring that the soil sample 2 inside the slump cone 1 is flush with the opening, guaranteeing a uniform initial volume and height; then, as... Figure 2As shown, the slump cone 1 is quickly and vertically lifted to avoid uneven stress on the slag and affect the slump shape caused by tilting. During the lifting process, the slag sample 2 collapses naturally under its own weight. The difference between the height of the slag sample inside the cone before collapse and the height of the slag sample after collapse is calculated. This difference is the first slump value of the slag sample 2. Figure 2 In this context, T represents the first slump value.

[0057] S14. For the next set of slag samples, repeat steps S12 and S13 until the first slump value of all sets of slag samples is obtained.

[0058] In this process, for each group of slag samples 2 prepared in step S11, the operations of steps S12 and S13 are repeated to obtain the first slump value of all groups of slag samples 2.

[0059] S200. Place all groups of slag samples in an adjustable chute device and conduct landslide tests at different preset inclination angles to obtain the first particle ratio and the second particle ratio of the slag samples at different preset inclination angles; and calculate the first flowability coefficient of the slag samples based on the first particle ratio and the second particle ratio; the particle size corresponding to the first particle ratio is smaller than the particle size corresponding to the second particle ratio.

[0060] The process involves placing all soil samples 2 in an adjustable-angle chute device and conducting landslide tests at different preset angles to obtain the first particle size ratio and the second particle size ratio of soil samples 2 at different preset angles. The specific steps include:

[0061] Pour the soil sample onto the upper end of the adjustable-angle chute device and control the chute device to be in a horizontal state.

[0062] Rotate the chute device at a constant speed to a preset angle with the horizontal plane. At the preset angle, lift the baffle at the top of the chute device. After the soil sample slides down and comes to a stop, collect all the soil samples in the collection box at the bottom of the chute device. The preset angle includes at least 10°, 20°, 30° and 40°.

[0063] The collected slag samples are divided into first particles and second particles based on a preset particle size. The proportion of the mass of the first particle at each preset inclination angle to the total mass of the first particles at all preset inclination angles is taken as the proportion of the first particles in the slag sample at that preset inclination angle. The proportion of the mass of the second particle at each preset inclination angle to the total mass of the second particles at all preset inclination angles is taken as the proportion of the second particles in the slag sample at that preset inclination angle.

[0064] It should be noted that a set of prepared soil samples 2 are evenly poured onto the upper end of the adjustable chute device. At this time, the chute device is kept horizontal. This allows the soil samples 2 to be evenly spread in the chute 3 of the chute device, ensuring that the force is even during subsequent landslides and avoiding test errors caused by premature flow or uneven distribution of soil due to the initial tilt angle.

[0065] Rotate the chute 3 at a constant speed to the preset inclination angle. Once the chute 3 is stable at the corresponding preset inclination angle, remove the sliding baffle 4 at the upper end of the chute 3, allowing the soil sample 2 to slide down the chute 3 naturally under gravity. After the soil sample 2 has completely slid down and stopped, use the collection box 5 at the lower end of the chute 3 to collect all the soil sample 2, ensuring the integrity of subsequent particle size distribution measurements. Here, the preset inclination angle can be, for example, 10°, 20°, 30°, and 40°. Different inclination angles can also be added according to actual needs. By conducting experiments at multiple different inclination angles, the flow differences of the soil sample 2 under different forces can be more comprehensively reflected.

[0066] In addition, this method also includes the following steps:

[0067] After collecting all the soil samples from the collection box at the bottom of the chute device, the collected soil samples are dried.

[0068] Among them, the presence of moisture in soil sample 2 will increase its apparent mass. Furthermore, the adsorption state of moisture varies between different particles. Direct weighing would lead to inaccurate particle mass data, thus requiring a drying operation. After drying, regardless of the initial moisture content of soil sample 2, the proportion can be calculated under the same mass measurement standard, ensuring the comparability of test data from different groups of soil samples 2 at different inclination angles.

[0069] The preset particle size is, for example, 20 mm. The dried slag sample 2 is separated using 20 mm as the preset particle size boundary. Particles with a diameter less than or equal to 20 mm are designated as the first particle, and particles with a diameter greater than 20 mm are designated as the second particle. Then, the mass of the first particle and the mass of the second particle in each group of slag sample 2 at different preset inclination angles are weighed. The sum of the masses of the first particles in each group of slag sample 2 at all preset inclination angles is taken as the total mass of the first particles, and the sum of the masses of the first particles in each group of slag sample 2 at all preset inclination angles is taken as the total mass of the second particles. Finally, the mass of the first particles at each preset inclination angle and the total mass of the first particles are taken as the proportion of the first particles in slag sample 2 at that preset inclination angle, and the mass of the second particles at each preset inclination angle and the total mass of the second particles are taken as the proportion of the second particles in slag sample 2 at that preset inclination angle.

[0070] The overall fluidity of the slag sample 2 is indirectly reflected by the difference in the flow ratio of particles of different sizes at different inclination angles. The better the fluidity, the higher the proportion of particles that can flow at a smaller inclination angle.

[0071] Calculate the first fluidity coefficient of soil sample 2 using the following formula:

[0072] ;

[0073] in, The first liquidity coefficient, The first particle size distribution of soil sample 2 corresponding to the i-th preset inclination angle. The proportion of the first particle size of soil sample 2 corresponding to the (i-1)th preset inclination angle. The second particle size distribution of the slag sample 2 corresponding to the i-th preset inclination angle. The second particle ratio of soil sample 2 corresponding to the (i-1)th preset inclination angle.

[0074] Furthermore, such as Figure 4 As shown, the chute device includes:

[0075] The base 7 has a sliding groove 3, the lower end of which is hinged to the surface of the base 7; when the upper end of the sliding groove 3 is lifted, the sliding groove 3 rotates around the hinge position.

[0076] Baffle 4 is slidably disposed on the upper end of the slide groove 3;

[0077] Collection box 5 is arranged adjacent to base 7, and the inlet of collection box 5 is arranged corresponding to the lower end of slide 3.

[0078] It should be noted that the base 7 serves as the basic supporting component of the sliding groove device. The sliding groove 3 is mounted on the base 7, and its lower end is connected to the surface of the base 7 via a hinge 6. This hinge 6 is, for example, a pin. Specifically, through holes are made on the surface of the base 7 and at the lower end of the sliding groove 3. A pin is used to pass through each through hole sequentially, thus achieving the hinged connection between the lower end of the sliding groove 3 and the surface of the base 7. Here, the upper end of the sliding groove 3 refers to the movable end that can rotate relative to the base 7, and the lower end refers to the hinged connection end with the base 7. When adjusting the tilt angle of the sliding groove 3, lifting the upper end of the sliding groove 3 allows it to rotate flexibly around the hinged position, switching from a horizontal state to preset tilt angles such as 10°, 20°, 30°, and 40°. The rotational angular velocity can be controlled between 0.5 and 1° / s, ensuring uniform and stable tilt angle adjustment. A special tool, such as an electric hoist, can be used to apply the force to lift the sliding groove 3.

[0079] The chute 3, serving as a channel for the flow of excavated soil, can simulate the sliding scenario of tunnel excavated soil under natural forces. For example... Figure 5As shown, the chute 3 has a trapezoidal structure. The width of the lower end of the chute 3 is 2 to 3 times that of the upper end, and the edge depth is, for example, 5 to 10 cm. This trapezoidal design guides the slag to flow towards the lower end of the chute 3, preventing particles from scattering. The width ratio and edge depth design of the upper and lower ends ensure that the slag has sufficient flow space and prevents the slag from overflowing from both sides of the chute during the flow process. In addition, a sliding baffle 4 is provided at the upper end of the chute 3. Before the test, the baffle 4 is in a closed state, which can temporarily intercept the slag sample 2 at the upper end of the chute 3, ensuring that the slag starts to flow after the chute 3 is adjusted to the preset inclination angle, ensuring uniform initial test conditions. When a landslide test is required, the baffle 4 is pulled out, allowing the slag sample 2 to slide down the chute 3.

[0080] The collection box 5 is arranged adjacent to the base 7, and the inlet of the collection box 5 corresponds to the lower end of the chute 3, which is used to collect all the slag samples 2 that slide down in the chute 3.

[0081] During the test, the chute 3 was first adjusted to a horizontal state (i.e., the bottom of the chute 3 was parallel to the base 7), the baffle 4 was closed and the soil sample 2 was poured in; then the chute 3 was rotated at a constant speed to the preset inclination angle, and after stabilization, the baffle 4 was pulled out. The soil slid down naturally along the trapezoidal channel of the chute 3 and finally flowed into the collection box 5, thus completing the flow and collection of one landslide test.

[0082] Here, the angular velocity range during the tilt adjustment of the chute device is, for example, 0.5~1° / s, to ensure a smooth tilt adjustment process and avoid affecting the initial state of the slag due to excessively fast or slow angular velocities. Furthermore, the angular velocities for all test conditions are kept consistent.

[0083] S300. Determine the slump function based on the first slump value and the first fluidity coefficient.

[0084] The determination of the slump function based on the first slump value and the first fluidity coefficient includes the following steps:

[0085] A scatter dataset is constructed with the first slump value of the waste soil sample as the ordinate and the first fluidity coefficient of the waste soil sample as the abscissa.

[0086] Linear regression analysis was performed on the scatter dataset to obtain the collapse function.

[0087] It should be noted that, as Figure 3 As shown, a data coordinate system is constructed with the first fluidity coefficient of each group of slag soil sample 2 as the abscissa and the corresponding first slump value as the ordinate. Then, the first fluidity coefficient and the corresponding first slump value are marked in the data coordinate system to obtain a scatter dataset containing multiple data pairs.

[0088] Then, using linear regression analysis, we can see that... It indicates that there is a very strong linear correlation between the first slump value and the first fluidity coefficient, and the linear model can accurately describe this relationship.

[0089] By using statistical analysis tools (such as Excel, Origin, etc.) to perform linear fitting on the scatter dataset, the linear equation T=aF+b is obtained, where T is the first slump value, F is the first fluidity coefficient, a is the slope, and b is the intercept. The slope and intercept are calculated using this equation, and then the slump function is obtained.

[0090] The universally applicable slump function formula is:

[0091] ;

[0092] in, This is the slump value. This is the liquidity coefficient.

[0093] S400. Place the sand and gravel slag in the chute device and conduct landslide tests at different preset angles to obtain the third and fourth particle proportions of the sand and gravel slag at different preset inclination angles; and calculate the second fluidity coefficient of the sand and gravel slag based on the third and fourth particle proportions.

[0094] In step S200, following the experimental setup and procedure, sand and gravel (with particle sizes generally exceeding 40mm) are placed into a chute device, and a landslide test is conducted at the same preset inclination angle. The landslide debris is then collected. Using the preset particle size as a dividing line, the third and fourth particles are distinguished. After drying and weighing, the proportions of the third and fourth particles at different inclination angles are obtained. The second fluidity coefficient is then calculated using the same formula as in step S200.

[0095] S500. Calculate the second slump value of sand and gravel slag based on the second fluidity coefficient and slump function.

[0096] Substitute the second fluidity coefficient obtained in step S400 into the slump function established in step S300 to obtain the second slump value corresponding to sand and gravel slag, which is equivalent to the directly measured slump result.

[0097] S600. Determine the plastic flow state of the sand and gravel slag based on the second slump value.

[0098] The determination of the plastic flow state of sand and gravel slag based on the second slump value includes the following steps:

[0099] If the second slump value is greater than or equal to the plasticity threshold, the sand and gravel soil is determined to have plasticity; if the second slump value is less than the plasticity threshold, the sand and gravel soil is determined to have poor plasticity.

[0100] It should be noted that plasticity is a key property for maintaining the stability of the tunnel face of the tunnel excavated soil, and it needs to be within a suitable range that does not flow or stagnate.

[0101] When the second slump value is greater than or equal to the plasticity threshold, the sand and gravel slag exhibits moderate fluidity, with a balance between cohesion and fluidity, and good plasticity. In this state, the sand and gravel slag can form stable support within the soil chamber, preventing surface collapse due to excessive flow or surface heave due to stagnation, thus meeting the requirements for safe and efficient tunneling. When the second slump value is less than the plasticity threshold, the slag lacks plasticity. At this point, the slag has insufficient fluidity and excessive cohesion, easily causing clumping and blockage within the soil chamber, leading to poor soil removal and consequently increased tunneling resistance and surface heave. In such cases, timely adjustments to construction parameters (such as increasing the foam injection ratio and optimizing the moisture content) are necessary to improve the slag's properties. The plasticity threshold can be set according to actual construction needs.

[0102] This application first conducts slump tests on multiple groups of slag soil samples 2 with particle sizes smaller than a set threshold to obtain the first slump value. Then, it uses an adjustable-angle chute device to conduct landslide tests on these slag soil samples 2 at different preset angles to obtain the first particle ratio, the second particle ratio, and calculate the first flowability coefficient. Based on the first slump value and the first flowability coefficient, the slump function is determined. Finally, following the same landslide test procedure, the third particle ratio, the fourth particle ratio, and the second flowability coefficient of the sand and gravel slag soil are obtained. Substituting the second flowability coefficient into the slump function yields the second slump value. This second slump value can be used to determine the plastic flowability state of the sand and gravel slag soil. Compared to the conventional slump test, which is limited by particle size and cannot evaluate the plasticity of sand and gravel slag, this scheme utilizes the correlation between particle size and flowability coefficient and function fitting to make the slump data of slag with different particle sizes universally applicable. This achieves accurate evaluation of the plasticity of sand and gravel slag with a particle size generally exceeding 40mm, providing reliable technical support for timely understanding of the plasticity of slag during earth pressure balance shield tunneling in sand and gravel strata. It effectively avoids the problems of surface collapse due to excessive slag flowability or surface heave due to insufficient flowability, ensuring the safety and efficiency of shield tunneling.

[0103] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for evaluating the plastic flow state of muck in a shield tunneling operation in a sandy cobble stratum, characterized by, The method comprises the following steps: a slump test is performed on a plurality of groups of slag samples with a particle size less than a set threshold value to obtain a first slump value of each group of slag samples; all groups of slag samples are placed in a chute device with adjustable inclination and landslide tests are performed at different preset inclinations to obtain corresponding first and second particle proportions of the slag samples at different preset inclinations; the first and second particles are divided according to a preset particle size as a boundary line for the collected slag samples; the first particle proportion of the slag samples at each preset inclination is the proportion of the mass of the first particles at each preset inclination in the total mass of the first particles corresponding to all preset inclinations, and the second particle proportion of the slag samples at each preset inclination is the proportion of the mass of the second particles at each preset inclination in the total mass of the second particles corresponding to all preset inclinations; and a first flowability coefficient of the slag samples is calculated according to the first and second particle proportions; the particle size corresponding to the first particle proportion is smaller than the particle size corresponding to the second particle proportion; a slump function is determined according to the first slump value and the first flowability coefficient; a landslide test is performed on the sandy pebble slag in the chute device at different preset angles to obtain corresponding third and fourth particle proportions of the sandy pebble slag at different preset inclinations; and a second flowability coefficient of the sandy pebble slag is calculated according to the third and fourth particle proportions; a second slump value of the sandy pebble slag is calculated according to the second flowability coefficient and the slump function; a plastic flow state of the sandy pebble slag is determined according to the second slump value of the sandy pebble slag; The first flowability coefficient of the slag sample (2) is calculated according to the following formula: ； wherein, is the first flowability coefficient, is the first particle proportion of the slag sample (2) corresponding to the i-th preset inclination angle, is the first particle proportion of the slag sample (2) corresponding to the i-1-th preset inclination angle, is the second particle proportion of the slag sample (2) corresponding to the i-th preset inclination angle, is the second particle proportion of the slag sample (2) corresponding to the i-1-th preset inclination angle.

2. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 1, characterized in that, a slump test is performed on a plurality of groups of slag samples with a particle size less than a set threshold value to obtain a first slump value of each group of slag samples, specifically comprising the following steps: S11, a plurality of groups of slag samples prepared with different improvement parameters are obtained, the improvement parameters including a foam injection ratio and a water content; S12, one group of the slag samples is loaded into a slump cylinder and uniformly inserted and tamped for a preset number of times; S13, after tamping, the cylinder opening of the slump cylinder is scraped flat, the slump cylinder is vertically lifted and collapsed, and the height difference after collapsing is taken as the first slump value of the group of slag samples; S14, for the next group of slag samples, steps S12 and S13 are repeatedly executed until the first slump values of all groups of slag samples are obtained.

3. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 1, characterized in that, all groups of slag samples are placed in a chute device with adjustable inclination and landslide tests are performed at different preset inclinations to obtain corresponding first and second particle proportions of the slag samples at different preset inclinations, specifically comprising the following steps: the slag samples are poured into the upper end of the chute device with adjustable inclination, and the chute device is controlled to be in a horizontal state; The chute device is rotated at a constant speed to a preset inclination angle with the horizontal plane, at the preset inclination angle, a baffle at the upper end of the chute device is lifted, and after the slag sample slides down and stops, all the slag samples in the collection box at the lower end of the chute device are collected; the preset inclination angle at least includes 10°, 20°, 30° and 40°; The collected slag sample is divided into first particles and second particles according to a preset particle size, and the proportion of the first particle mass at each preset inclination angle to the total mass of the first particles corresponding to all preset inclination angles is taken as the first particle proportion of the slag sample corresponding to the preset inclination angle, and the proportion of the second particle mass at each preset inclination angle to the total mass of the second particles corresponding to all preset inclination angles is taken as the second particle proportion of the slag sample corresponding to the preset inclination angle.

4. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 3, characterized in that, The method further comprises the following steps: After collecting all the slag samples in the collection box at the lower end of the chute device, the collected slag samples are subjected to drying treatment.

5. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 3, characterized in that, The preset particle size is 20 mm, the first particles are particles with a particle size less than or equal to 20 mm, and the second particles are particles with a particle size greater than 20 mm.

6. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 1, characterized in that, According to the first slump value and the first fluidity coefficient, a slump function is determined, specifically comprising the following steps: A scatter point data set is constructed with the first slump value of the slag sample as the ordinate and the first fluidity coefficient of the slag sample as the abscissa; Linear regression analysis is performed on the scatter point data set to obtain a slump function.

7. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 1, characterized in that, According to the second slump value of the sandy pebble slag, the plastic flow state of the sandy pebble slag is determined, specifically comprising the following steps: If the second slump value is greater than or equal to a plastic flow threshold value, it is determined that the sandy pebble slag has plastic flow; if the second slump value is less than the plastic flow threshold value, it is determined that the sandy pebble slag is under plastic flow.

8. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 1, characterized in that, The chute device comprises: a base, the base is provided with a chute, the lower end of the chute is hingedly connected to the surface of the base; when the upper end of the chute is lifted, the chute rotates around the hinge position; a baffle, the baffle is slidably arranged at the upper end of the chute; a collection box, the collection box is arranged adjacent to the base, and the inlet of the collection box is correspondingly arranged with the lower end of the chute.

9. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 8, characterized in that, The angular velocity range of the inclination angle adjustment of the chute device is 0.5-1° / s, the width of the lower end of the chute is 2-3 times the width of the upper end of the chute, and the edge depth of the chute is 5-10 cm.

10. The method for evaluating the plastic flow state of muck suitable for sandy cobble stratum according to claim 2, characterized in that, The particle size of the slag sample is less than 40 mm, the particle size of the sandy pebble slag includes particles greater than 40 mm; the variation range of the foam injection ratio is 0%-60%, and the variation range of the water content is 0%-40%.

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