A method for solving differential settlement of roadbed based on overconsolidation ratio

Abstract

This invention discloses a method for solving differential settlement of roadbeds based on overconsolidation ratio, comprising the following steps: sampling the roadbed soil layer of soft soil sections through drilling to obtain test soil samples; conducting indoor rheological tests on the obtained test soil samples to obtain the lower limit of the initial rheological stress; calculating the self-weight stress value within a certain depth range of the foundation and recording it as the total additional stress value; comparing the total additional stress value with the initial rheological stress value; if the total additional stress value is less than the lower limit of the initial rheological stress, it indicates that the soft soil section is in a safe state; if the total additional stress value is greater than the lower limit of the initial rheological stress, it indicates that the soft soil section is in a potential danger state, and then proceeding to material selection; after selecting a lightweight replacement material, replacement construction is carried out. This invention can effectively solve the problem of differential settlement of soft soil roadbeds and has good prospects for engineering practice and promotion.

Description

Technical Field

[0001] The invention relates to the technical field of roadbed settlement, and in particular to a method for solving roadbed differential settlement based on an overconsolidation ratio. Background Art

[0002] There is often a certain thickness of soft soil in coastal areas. Due to the characteristics of soft soil, the post-construction settlement of transportation infrastructure built on soft soil foundation is large, and the existence of elevated facilities and ground transportation makes this settlement present different forms. In addition to the characteristics of the foundation itself, the unevenness of artificial foundation treatment and reinforcement also makes the roadbed settlement more uneven. The uneven settlement of the roadbed will have a certain impact on driving comfort and road life. Especially for large-scale urban high-speed elevated roads, ground roads, underground transportation and other three-dimensional transportation, once the roadbed settles, serious traffic accidents will occur.

[0003] The core issue of uneven settlement of soft soil roadbed is the overall coordination of the stress and deformation state between soft soil and structures. Engineering technicians have studied the differential settlement between soft soil foundations and different structures by using powder injection piles, slurry injection piles, vacuum combined preloading, plastic drainage board overload preloading, sand pile overload preloading, etc., and found that the insufficient stability of the stress and deformation state of the soft soil roadbed and the bottom stress of the soft soil roadbed greater than the lower rheological threshold of the soft soil are two key factors that affect and solve the uneven settlement of highway soft soil roadbeds. This is also the reason why many engineering measures to control uneven settlement can only improve, but rarely have a radical effect. Based on the artificial over-consolidation stress state and from the perspective of reducing the consolidation settlement and compression deformation of the foundation, this application proposes an optimization method for differential settlement of roadbeds in coastal areas based on over-consolidation stress ratio. Summary of the invention

[0004] In order to solve the deficiencies in the above-mentioned prior art, the present invention provides a method for solving differential settlement of roadbed based on super consolidation ratio, which can better solve the problem of differential settlement of soft soil roadbed and has good prospects for promotion in engineering practice.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a method for solving differential settlement of roadbed based on super consolidation ratio, comprising the following steps:

[0006] S1: Sampling the subgrade soil layer of the soft soil section by drilling to obtain test soil samples;

[0007] S2: Perform an indoor rheological test on the test soil sample obtained in step S1 to obtain the lower limit value of the initial rheological stress σ 1 ;

[0008] S3: Calculate the material self-weight stress value at the sampling depth, and record the sum of the vehicle load and the self-weight stress value of the foundation material at this depth as the total additional stress value σ caused by the self-weight at this depth 2 ;

[0009] S4: Compare the total additional stress value with the initial flow stress value. If the total additional stress value σ 2 Less than the initial flow stress value σ 1 , indicating that the soft soil section is in a safe state. If the total additional stress value σ 2 Greater than the lower limit of initial flow stress σ 1 , indicating that the soft soil section is in a hidden danger state, then proceed to step S5;

[0010] S5: According to Among them, σ 1 It represents the initial rheological lower limit value of a soil sample at a certain layer obtained through experiments, H represents the thickness of the roadbed soil layer to be replaced, g represents the gravity acceleration, and ρ represents the density value of the lightweight replacement material of the roadbed soil layer;

[0011] S6: Select density as ρ 1 Prefabricated lightweight blocks, where ρ 1 is less than ρ,

[0012] S7: excavate the roadbed soil layer at a depth of H;

[0013] S8: compacting and leveling the base;

[0014] S9: laying a lower bearing plate on the base for load transfer and dispersion;

[0015] S10: Installing the prefabricated assembled lightweight block in step S6 on the lower bearing plate;

[0016] S11: Laying an upper bearing plate for load transfer and dispersion on the prefabricated assembled lightweight blocks;

[0017] S12: pouring a continuous reinforced cement concrete load-bearing slab on the upper bearing plate;

[0018] S13: Maintain the continuously reinforced cement concrete load-bearing slab to the specified age;

[0019] S14: Spread and apply cement-stabilized crushed stone leveling layer on the continuously reinforced cement concrete load-bearing slab;

[0020] S15: Rolling the cement stabilized crushed stone leveling layer to the specified compaction degree;

[0021] S16: Spread the asphalt surface layer and compact it, and finally open it to traffic.

[0022] Preferably, in step S1, the initial flow stress value σ is obtained.1 The steps are as follows,

[0023] S101: trim the test soil samples into multiple groups of test pieces with the same specifications;

[0024] S102: multiple groups of specimens were placed under loading stresses of 25 KPa, 50 KPa, 100 KPa and 200 KPa respectively, with the shortest loading time of each specimen being 144 hours and the longest loading time being 172 hours;

[0025] S103: Record data once every 1 hour at the beginning of the test, record data once every 4 hours in the middle and late stages of the test, and draw a rheological deformation curve of the soft soil, wherein the abscissa of the rheological curve of the soft soil represents the loading time, and the ordinate of the rheological curve of the soft soil represents the settlement of the sample;

[0026] S104: By observing the rheological curve of soft soil, the lower limit of initial rheological stress that allows the sample to remain stable is obtained. That is, when the stress level of the additional load is lower than the lower limit of initial rheological stress, the influence of the additional external load on the rheology of the sample can be ignored; when the stress level is higher than the lower limit of initial rheological stress, the influence of the additional external load on the rheology of the sample cannot be ignored, and roadbed replacement is required.

[0027] Preferably, in step S3, σ 2 It is obtained by the following calculation formula: Among them, ρ i It represents the reduced average density of the excavated roadbed soil layer, h i is the thickness of the excavated roadbed soil layer, G D The vehicle dynamic load is equivalent to the static load of 0.5 meters of fill evenly distributed on the soft soil foundation according to the highway engineering technical standard JTGB01-2014, and the additional load caused by the soil bulk density is 8.5KPa.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] (1) Through experimental calculation, the replacement thickness of lightweight materials with appropriate density is selected to form an artificial over-consolidation stress state at the bottom of the roadbed, which can put the soft soil foundation under the action of vehicle load in an elastic deformation state;

[0030] (2) One year after the test road construction, the settlement of the lightweight replacement pavement structure remained at about 1 mm, the differential settlement had been resolved and tended to be stable, and it had been significantly reduced compared with conventional pavement. The settlement curve was gentle and tended to be stable, there was no sudden change in settlement, and the longitudinal slope was extremely small, which could well ensure driving safety and comfort. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the pavement structure diagram of a section of Jintangli Xiaoxian Road in Zhoushan City, Zhejiang Province;

[0032] Figure 2 It is a deformation curve diagram of the soft soil rheological test in the present invention;

[0033] Figure 3 This is a comparison chart of the settlement of replacement pavement and conventional pavement. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0035] Embodiment 1: A method for optimizing differential settlement of roadbed in coastal areas based on overconsolidation stress ratio comprises the following steps:

[0036] S1: Sampling the subgrade soil layer of the soft soil section by drilling to obtain test soil samples;

[0037] S2: Perform an indoor rheological test on the test soil sample obtained in step S1 to obtain the initial rheological stress value σ 1 ;

[0038] S3: Calculate the material self-weight stress value at the sampling depth, and record the sum of the vehicle load and the self-weight stress value of the foundation material at this depth as the total additional stress value σ caused by the self-weight at this depth 2 ;

[0039] S4: Compare the total additional stress value with the lower limit of the initial flow stress. If the total additional stress value σ 2 Less than the initial flow stress value σ 1 , indicating that the soft soil section is in a safe state. If the total additional stress value σ 2 Greater than the initial flow stress value σ 1 , indicating that the soft soil section is in a hidden danger state, then proceed to step S5;

[0040] S5: According to Among them, σ 1 It represents the initial rheological lower limit value obtained through experiments of a soil sample at a certain layer, H represents the thickness of the roadbed soil layer to be replaced (according to the calculation and analysis of the depth of influence of automobile load transfer, 2>H>1.5 meters), g represents the acceleration of gravity, and ρ represents the density value of the lightweight replacement material of the roadbed soil layer;

[0041] S6: Select density as ρ 1 Prefabricated lightweight blocks, where ρ 1 Less than ρ;

[0042] S7: excavate the roadbed soil layer at a depth of H;

[0043] S8: compacting and leveling the base;

[0044] S9: Laying a lower bearing plate on the base for load distribution;

[0045] S10: Installing the prefabricated assembled lightweight block in step S6 on the lower bearing plate;

[0046] S11: Laying an upper bearing plate for load distribution on the prefabricated lightweight blocks;

[0047] S12: pouring a continuous reinforced cement concrete load-bearing slab on the upper bearing plate;

[0048] S13: Maintain the continuously reinforced cement concrete load-bearing slab to the specified age;

[0049] S14: Spread cement stabilized crushed stone leveling layer on the continuously reinforced cement concrete load-bearing slab;

[0050] S15: Rolling the cement stabilized crushed stone leveling layer to the specified compaction degree;

[0051] S16: Spread the asphalt surface layer and compact it, and finally open it to traffic.

[0052] Preferably, in step S1, the initial flow stress value σ is obtained. 1 The steps are as follows,

[0053] S11: Trim the test soil samples into multiple groups of specimens with the same specifications;

[0054] S12: Multiple groups of specimens were placed under loading stresses of 25KPa, 50KPa, 100KPa and 200KPa respectively. The shortest loading time for each specimen was 144 hours and the longest loading time was 172 hours.

[0055] S13: record data once every 1 hour at the beginning of the test, record data once every 4 hours in the middle and late stages of the test, and draw a rheological deformation curve of the soft soil, where the abscissa of the rheological curve of the soft soil represents the loading time, and the ordinate of the rheological curve of the soft soil represents the settlement of the sample;

[0056] S14: By observing the rheological curve of soft soil, the lower limit of initial rheological stress that allows the sample to remain stable is obtained. That is, when the stress level of the additional load is lower than the lower limit of the initial rheological stress, the influence of the additional external load on the rheology of the sample can be ignored; when the stress level is higher than the lower limit of the initial rheological stress, the influence of the additional external load on the rheology of the sample cannot be ignored, and a lightweight replacement technology solution needs to be adopted.

[0057] Preferably, in step S3, σ 2 It is obtained by the following calculation formula: Among them, ρ i It represents the reduced average density of the excavated roadbed soil layer, h i is the thickness of the excavated roadbed soil layer, GD The vehicle dynamic load is equivalent to the static load of 0.5 meters of fill evenly distributed on the soft soil foundation according to the highway engineering technical standard JTGB01-2014, and the additional load caused by the soil bulk density is 8.5KPa.

[0058] Example 2: A section of Jintangli Xiaoxian Road in Zhoushan City, Zhejiang Province may have a potential for subsidence. By analyzing the structural section, as shown in the attached manual, Figure 1 As shown, the road section is mainly composed of a roadbed soil layer 1, a cushion layer 2, a cement-stabilized granular layer 3 and an asphalt pavement layer 4. The roadbed soil layer of the soft soil section is sampled by drilling to obtain test soil samples.

[0059] The obtained test soil samples were subjected to indoor rheological tests. Specifically, the following method was used:

[0060] S101: trim the test soil samples into multiple groups of test pieces with the same specifications;

[0061] S102: multiple groups of specimens are placed under loading stresses of 25 KPa, 50 KPa, 100 KPa and 200 KPa respectively, and the loading time of each specimen is 144 hours;

[0062] S103: Record data once every 1 hour at the beginning of the test, record data once every 4 hours in the middle and late stages of the test, and draw a rheological deformation curve of the soft soil, wherein the abscissa of the rheological curve of the soft soil represents the loading time, and the ordinate of the rheological curve of the soft soil represents the settlement of the sample;

[0063] S104: By observing the rheological curve of soft soil, the lower limit of initial rheological stress that allows the sample to remain stable is obtained. That is, when the stress level of the additional load is lower than the lower limit of initial rheological stress, the influence of the additional external load on the rheology of the sample can be ignored; when the stress level is higher than the lower limit of initial rheological stress, the influence of the additional external load on the rheology of the sample cannot be ignored, and roadbed replacement is required.

[0064] The test results are as attached in the instruction manual. Figure 2 As shown in the figure, the subgrade soil layer rapidly increases with time at the initial stage of settlement, then the increasing trend gradually decreases and tends to a stable state. By comparing the rheological data at stress levels of 25, 50, 100, and 200 KPa, it can be found that when the stress level is 25 KPa or less than 25 KPa, the influence of rheology on the settlement of the subgrade soil layer can be basically ignored; and when the stress is 50, 100, and 200 KPa, the influence of rheology on the settlement of the subgrade soil layer is extremely large. Based on the above results, its initial rheological stress value σ 1It is set to 25KPa, that is, when the additional load stress level is lower than the lower limit of the initial rheological stress, the influence of the additional external load on the sample rheology can be ignored; when the stress level is higher than the lower limit of the initial rheological stress, the influence of the additional external load on the sample rheology cannot be ignored, and a lightweight replacement technology solution needs to be adopted.

[0065] According to the calculation theory of elastic layered system of pavement structure, the stress level of traffic load on soft soil foundation is generally low, and the main action range is within 2m below the pavement. Therefore, the thickness of the excavated roadbed soil layer is also controlled within 2m.

[0066] σ 2 It is obtained by the following calculation formula: Among them, ρ i It represents the reduced average density of the excavated roadbed soil layer, h i is the thickness of the excavated roadbed soil layer, G D The vehicle dynamic load is equivalent to the static load of 0.5 meters of fill soil evenly distributed on the soft soil foundation according to the highway engineering technical standard (JTGB01-2014). The additional load caused by the soil bulk density is 8.5KPa. The calculation results are shown in the following table.

[0067] Conventional pavement structure stress value table

[0068]

[0069]

[0070] Next, according to Among them, σ 1 It represents the initial rheological lower limit value obtained through experiments of a soil sample at a certain layer, H represents the thickness of the roadbed soil layer to be replaced (according to the calculation and analysis of the depth of influence of automobile load transfer, 2>H>1.5 meters), g represents the acceleration of gravity, and ρ represents the density value of the lightweight replacement material of the roadbed soil layer;

[0071] Right now That is, the upper limit of the safe density value is 475kg / m 3 Generally speaking, the density of the lightweight replacement material recommended by the design is 1 Controlled at 30kg-80kg / m3, the density of the lightweight replacement material actually used in this test section is ρ 1 45kg / m 3 , using polymer prefabricated blocks. The pavement structure stress value table is obtained by calculating the replacement, which is theoretically feasible. The specific results are shown in the following table:

[0072] Stress value table of pavement structure after replacement:

[0073]

[0074]

[0075] The lightweight replacement pavement structure must first meet the physical and mechanical properties required for the long-term performance of the roadbed. Samples were selected to conduct indoor testing on the lightweight replacement roadbed materials. The test results are shown in the table:

[0076] The measured mechanical properties parameter table of the replacement lightweight material is as follows:

[0077]

[0078] From the measured mechanical properties data, it can be seen that the lightweight material of the replacement roadbed meets the parameter requirements in the "Technical Specifications for Highway Roadbed Construction" (JTG / T3610-2019) and the "Highway Roadbed Design Specifications" (JTGD30-2015).

[0079] The lightweight replacement pavement structure uses lightweight roadbed fillers, which greatly reduces the additional stress of the foundation and improves the deformation stability of the embankment. For normal newly built or expanded coastal soft soil roads, the construction process is as follows:

[0080] 1. Excavate the roadbed soil layer at depth H; compact and fill the base;

[0081] 2. Lay a lower bearing plate on the base for load distribution;

[0082] 3. Install the prefabricated lightweight blocks on the lower bearing plate;

[0083] 4. Lay an upper bearing plate for load distribution on the prefabricated lightweight blocks;

[0084] 5. Cast a continuously reinforced cement concrete load-bearing slab on the upper load-bearing slab;

[0085] 6. Maintain the continuously reinforced cement concrete load-bearing slab to the specified age;

[0086] 7. Spread cement-stabilized crushed stone leveling layer on the continuously reinforced cement concrete load-bearing slab;

[0087] 8. Roll the cement stabilized gravel leveling layer to the specified compaction degree;

[0088] 9. Spread the asphalt surface and compact it, then open it to traffic.

[0089] In order to understand the post-construction settlement degree of the replacement pavement structure and provide a reliable design basis for the subsequent improvement of the treatment plan for differential settlement of soft soil roadbeds in coastal highways, the site was first measured. A total of 40 observation points were set up, including 20 observation points in the replacement pavement structure test section and 20 observation points in the conventional pavement structure section. After a year of settlement data collection, the settlement comparison between the lightweight replacement pavement and the conventional pavement is shown in the attached manual. Figure 3 As shown in the figure, the horizontal axis represents the observation time, and the vertical axis represents the observed settlement. Figure 3 From the data comparison and analysis, it can be seen that: after one year of use, the settlement value of the lightweight replacement pavement structure has always remained at about 1mm, while the settlement of the conventional pavement structure has developed to about 15mm. The research results show that when the uneven settlement difference is within 15mm, it has almost no effect on the driving of the vehicle, but when the uneven settlement difference reaches 15-35mm, the vehicle will feel very uncomfortable and bumpy when driving. In addition, the comparative analysis shows that on the same longitudinal line shape, the differential settlement of the lightweight replacement pavement structure has been significantly reduced compared with the conventional pavement, the settlement curve is gentle and has tended to be stable, there is no sudden change in settlement, and the longitudinal slope is extremely small, which can well ensure the safety and comfort of driving, while the differential settlement of the conventional pavement structure cannot be stable.

[0090] It is worth noting that the above is only a preferred embodiment of the present invention, and does not limit the scope of patent protection of the present invention. The present invention can also improve the materials and structures of the above-mentioned various parts, or replace them with technical equivalents. Therefore, all equivalent structural changes made by using the description and illustrations of the present invention, or directly or indirectly applied to other related technical fields are also included in the scope of the present invention.

Claims

1. A method for solving differential settlement of roadbed based on overconsolidation ratio, characterized by: The following steps are included: S1: Sampling the subgrade soil layer of the soft soil section by drilling to obtain test soil samples; S2: Performing an indoor rheological test on the test soil sample obtained in step S1 to obtain the lower limit value of the initial rheological stress σ1; S3: Calculate the material self-weight stress value at the sampling depth, and record the sum of the vehicle load and the self-weight stress value of the foundation material at the depth as the total additional stress value σ2 caused by the self-weight at the depth; S4: Compare the total additional stress value with the initial rheological stress value. If the total additional stress value σ2 is less than the initial rheological stress value σ1, it indicates that the soft soil section is in a safe state. If the total additional stress value σ2 is greater than the initial rheological stress lower limit value σ1, it indicates that the soft soil section is in a hidden danger state, then enter step S5; S5: According to Among them, σ1 represents the initial rheological lower limit value obtained by experiment for a soil sample at a certain layer, H represents the thickness of the roadbed soil layer to be replaced, g represents the gravity acceleration, and ρ represents the density value of the lightweight replacement material for the roadbed soil layer; S6: Select prefabricated lightweight blocks with a density of ρ1, where ρ1 is less than ρ, S7: excavate the roadbed soil layer at a depth of H; S8: compacting and leveling the base; S9: laying a lower bearing plate on the base for load transfer and dispersion; S10: Installing the prefabricated assembled lightweight block in step S6 on the lower bearing plate; S11: Laying an upper bearing plate for load transfer and dispersion on the prefabricated assembled lightweight blocks; S12: pouring a continuous reinforced cement concrete load-bearing slab on the upper bearing plate; S13: Maintain the continuously reinforced cement concrete load-bearing slab to the specified age; S14: Spread and apply cement-stabilized crushed stone leveling layer on the continuously reinforced cement concrete load-bearing slab; S15: Rolling the cement stabilized crushed stone leveling layer to the specified compaction degree; S16: Spread asphalt surface and compact it, and finally open to traffic; Among them, in step S1, the steps for obtaining the initial flow stress value σ1 are as follows: S101: trim the test soil samples into multiple groups of test pieces with the same specifications; S102: multiple groups of specimens were placed under loading stresses of 25 KPa, 50 KPa, 100 KPa and 200 KPa respectively, with the shortest loading time of each specimen being 144 hours and the longest loading time being 172 hours; S103: Record data once every 1 hour at the beginning of the test, record data once every 4 hours in the middle and late stages of the test, and draw a rheological deformation curve of the soft soil, wherein the abscissa of the rheological curve of the soft soil represents the loading time, and the ordinate of the rheological curve of the soft soil represents the settlement of the sample; S104: By observing the rheological curve of soft soil, the lower limit of initial rheological stress that allows the sample to remain stable is obtained. That is, when the stress level of the additional load is lower than the lower limit of initial rheological stress, the influence of the additional external load on the rheology of the sample can be ignored; when the stress level is higher than the lower limit of initial rheological stress, the influence of the additional external load on the rheology of the sample cannot be ignored, and roadbed replacement is required.

2. The method for solving differential settlement of roadbed based on overconsolidation ratio according to claim 1 is characterized in that: In step S3, σ2 is obtained by the following calculation formula, Among them, ρ i It represents the reduced average density of the excavated roadbed soil layer, h i is the thickness of the excavated roadbed soil layer, G D The vehicle dynamic load is equivalent to the static load of 0.5 meters of fill evenly distributed on the soft soil foundation according to the highway engineering technical standard JTG B01-2014, and the additional load caused by the soil bulk density is 8.5 KPa.

Images