A method for enhancing the bearing capacity of highway foundation in deep high-temperature permafrost regions

Abstract

The present application relates to a kind of deep high temperature permafrost area highway foundation bearing capacity enhancement method, comprising: the bearing capacity of permafrost foundation is detected by static sounding, to obtain the spatial distribution characteristics of original ground bearing capacity, the spatial distribution characteristics of original ground bearing capacity at least include bearing capacity mean, bearing capacity range and bearing capacity recession ratio;Establish at least based on the mapping model of the spatial distribution characteristics of original ground bearing capacity and shallow ground foundation enhancement mode;Based on mapping model, according to the spatial distribution characteristics of original ground bearing capacity detected, determine shallow ground foundation enhancement mode, shallow ground foundation enhancement mode includes: structural type enhancement measure, material type enhancement measure and hydrology control type enhancement measure, for improving the overall bearing performance of foundation and inhibiting permafrost degradation;Structural type enhancement measure at least includes building composite bearing structure system in shallow ground foundation, the bearing capacity of local area of foundation is enhanced to improve the mechanical properties of overall foundation.

Description

Technical Field

[0001] This invention relates to the field of frozen soil highway engineering construction technology, specifically a method for enhancing the bearing capacity of highway foundations in deep, high-temperature permafrost regions. Background Technology

[0002] Due to the recent warming and humidification trend, highways in service in the permafrost region of the Qinghai-Tibet Plateau face a series of problems, including road surface subsidence, roadside water accumulation, water-rich foundations, thickening of thawed interlayers, and continuous permafrost degradation. Traditional highway subgrade design mainly follows the principle of permafrost protection, attempting to increase thermal resistance, reduce heat input, or actively introduce additional cooling to prevent permafrost degradation through special subgrade structures such as raising the subgrade, installing heat pipes, riprap, ventilation pipes, and insulation layers. However, these protective measures face practical challenges in application, including complex on-site hydrogeological conditions, harsh construction conditions on the Qinghai-Tibet Plateau, and insufficient maintenance funds, resulting in significantly reduced practical application effectiveness and long-term performance maintenance.

[0003] Current roadbed design methods in permafrost regions mainly suffer from the following problems:

[0004] First, the traditional cooling measures such as heat pipes, rock blocks, and ventilation pipes are not effective enough, and the permafrost continues to degrade in the face of long-term warming.

[0005] Second, traditional methods do not address the underlying soil structure and neglect the impact of changes in soil properties, such as the warming and degradation of the underlying permafrost, the development of thawing interlayers, and the weakening of the foundation due to water enrichment, on the performance of the roadbed during long-term service.

[0006] Third, traditional methods do not assess the bearing capacity of the foundation and lack a clear understanding of the spatial variability of foundation deformation risk;

[0007] Fourth, the source layers of subsidence are constantly expanding into the deeper parts of the foundation. Existing roadbed technologies for protecting permafrost have insufficient universality in suppressing thaw settlement, and the same technical measures have significantly different effects when applied to different road sections.

[0008] Therefore, it is urgent to develop new methods for enhancing the bearing capacity of foundations based on the concept of permafrost foundation treatment, so as to fundamentally solve the technical problem of differential settlement and deformation of roadbeds in permafrost areas. Summary of the Invention

[0009] This invention discloses a method for enhancing the bearing capacity of highway foundations in deep, high-temperature permafrost regions, which addresses the problems existing in the prior art.

[0010] This invention provides a method for enhancing the bearing capacity of highway foundations in deep, high-temperature permafrost regions, comprising:

[0011] The bearing capacity of permafrost foundations is tested by static cone penetration testing to obtain the spatial distribution characteristics of the bearing capacity of undisturbed foundations. The spatial distribution characteristics of the bearing capacity of undisturbed foundations include at least the mean bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio.

[0012] Establish a mapping model based at least on the spatial distribution characteristics of the original foundation bearing capacity and the shallow foundation reinforcement method;

[0013] Based on the mapping model, the shallow foundation reinforcement method is determined according to the spatial distribution characteristics of the original foundation bearing capacity obtained by detection. The shallow foundation reinforcement method includes at least: structural reinforcement measures, material reinforcement measures and hydrological regulation reinforcement measures, which are used to improve the overall bearing capacity of the foundation and inhibit permafrost degradation.

[0014] Among them, structural reinforcement measures include at least constructing a composite load-bearing structure system in the shallow foundation to improve the overall mechanical properties of the foundation by enhancing the load-bearing capacity of local areas of the foundation.

[0015] As a preferred technical solution, the construction of the mapping model includes:

[0016] Based on the preset foundation bearing capacity evaluation standard, the limit value method is used to divide the mean bearing capacity, the range of bearing capacity, and the bearing capacity degradation ratio into at least two evaluation intervals.

[0017] The bearing stability level of the foundation is determined based on the combination of the mean bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio within their respective evaluation intervals.

[0018] A mapping relationship between bearing stability level and different shallow foundation reinforcement methods is established to form a graded reinforcement decision matrix, which is used to guide the selection of reinforcement measures for foundations with different bearing stability levels.

[0019] As a preferred technical solution, the hierarchical enhanced decision matrix is ​​configured as follows:

[0020] When the load-bearing stability level is low, structural reinforcement measures are applied to construct a composite load-bearing structural system to improve the overall load-bearing performance of the foundation.

[0021] When the bearing stability level is medium, material reinforcement measures are applied to improve the properties of the foundation materials in order to enhance the shear strength and stability of the foundation.

[0022] When the bearing stability level is high and there is hydrothermal sensitivity, hydrological regulation enhancement measures should be applied to adjust the hydrothermal state of the foundation in order to maintain the stability of permafrost.

[0023] As a preferred technical solution, the construction of the mapping model also includes:

[0024] Acquire multi-source information on foundation temperature, moisture content, and soil type;

[0025] Based on multi-source information, the hierarchical enhanced decision matrix is ​​modified by setting corresponding modification factors through parameter weight adjustment method;

[0026] The determination result of the load-bearing stability level is adjusted according to the correction factor and its weight coefficient.

[0027] As a preferred technical solution, structural reinforcement measures include a pile-raft integrated roadbed structure, which comprises mixing piles at the bottom and a raft slab at the top.

[0028] The mixing pile adopts a pre-drilling process, which uses cementitious materials to mix with in-situ soil to form a solidified body. The cementitious materials include temperature-stable cement-based materials with low heat of hydration.

[0029] The raft foundation is made of lean concrete and formed by compaction, forming an integral load-bearing system with the mixing pile structure.

[0030] As a preferred technical solution, the structural reinforcement measures include a pipe pile composite foundation structure, which includes precast pipe piles at the bottom and a pile cap bearing platform at the top.

[0031] Precast pipe piles are constructed using static pressure implantation or pre-drilling implantation methods, and the length of the precast pipe piles shall not exceed 10 meters.

[0032] A geogrid-reinforced gravel cushion layer is installed in the area between and above the pile cap bearing platform.

[0033] As a preferred technical solution, when the bearing capacity degradation ratio is greater than 80%, the following structural reinforcement measures should be applied to precast pipe piles:

[0034] The outer surface of the precast pipe pile is textured to enhance the shear strength of the pile-soil interface.

[0035] And / or, the inner cavity of the precast pipe pile is filled with a phase change material with low thermal conductivity to achieve passive cold storage and temperature regulation, enhance the freezing strength of the pile-soil interface, and reduce the warming rate of deep permafrost.

[0036] As a preferred technical solution, the structural reinforcement measures include a mixing pile composite foundation structure, which includes mixing piles placed at the bottom and a gravel cushion layer placed at the top.

[0037] The mixing pile adopts a pre-drilling process, and the mixing pile uses a temperature-stable, low-hydration-heat cementitious material to mix with the in-situ soil to form a solidified body.

[0038] Geogrids are laid on the gravel cushion layer to distribute and balance the load.

[0039] As a preferred technical solution, material-based reinforcement measures include a riprap dynamic compaction replacement composite foundation structure, wherein:

[0040] The dynamic compaction energy level is determined based on the upper limit of the burial depth of permafrost, so as to achieve controlled influence on deep permafrost.

[0041] The construction window period and pilot hole technique are determined based on the parameters of the freezing strength and freezing depth of the active layer.

[0042] The termination standard for dynamic compaction is set at the point where the cumulative settlement deformation reaches the upper limit of the burial depth of permafrost.

[0043] As a preferred technical solution, material-based reinforcement measures include shallow replacement with gravel, specifically including:

[0044] The shallow, weak soil layer is excavated and replaced with gravel material that meets the engineering gradation requirements, and the treatment thickness is not less than 2m.

[0045] As a preferred technical solution, material-based reinforcement measures include in-situ curing reinforcement, specifically including:

[0046] For the original foundation soil, add the curing agent using plant mixing or road mixing methods, and then perform in-situ curing;

[0047] The technical performance of the solidified soil should meet the following requirements: unconfined compressive strength ≥1.0MPa after 7 days, strength loss rate <10% after 10 freeze-thaw cycles at -20℃, mass loss rate <5%, and water stability coefficient >80%.

[0048] As a preferred technical solution, hydrological regulation enhancement measures include water-blocking cofferdams, specifically including:

[0049] Steel sheet piles can be placed at the toe of the roadbed slope, or water-mixing piles can be used to form a water-resistant curtain.

[0050] Compared with the prior art, the technical solution adopted in this invention can achieve the following beneficial effects:

[0051] This invention provides a method for enhancing the bearing capacity of highway foundations in deep, high-temperature permafrost regions. It offers a systematic solution to problems such as insufficient foundation treatment, lack of bearing capacity assessment, and inability to effectively address the continuous degradation of permafrost caused by long-term climate warming in traditional technologies.

[0052] This method first comprehensively evaluates the bearing capacity of permafrost foundations using static cone penetration testing (CPPT) technology, obtaining spatial distribution characteristics including the mean, range, and degradation ratio of bearing capacity. It then establishes a precise mapping model between foundation bearing stability and reinforcement measures. Based on this mapping model, it systematically classifies three major reinforcement measure systems: structural, material, and hydrological control types, enabling differentiated treatment for foundations with different bearing stability levels.

[0053] In structural reinforcement measures, this method innovatively designs pile-raft integrated roadbed structures, pipe pile composite foundation structures, and mixing pile composite foundation structures adapted to permafrost environments. In particular, in the pipe pile composite foundation structure, a shallow short pile design concept is adopted, with the pile length not exceeding 10m to reduce dead load. At the same time, key technologies such as the selection of temperature-stable low heat of hydration materials, external surface texture enhancement, and internal phase change cold storage are incorporated into the pile design, realizing passive cold storage and heat insulation functions, which can effectively enhance the freezing strength of the pile-soil interface and reduce the warming rate of deep permafrost.

[0054] Regarding material-based reinforcement measures, this method proposes technical solutions such as boulders dynamic compaction replacement composite foundation, shallow gravel replacement, and in-situ solidification reinforcement. These solutions improve shear strength and stability by enhancing the properties of foundation materials. In particular, the boulders dynamic compaction replacement technology determines the dynamic compaction energy level based on the upper limit of the permafrost depth, achieving controlled influence on deep permafrost and avoiding thermal stability damage caused by excessive disturbance.

[0055] Compared to traditional permafrost foundation treatment methods, the technical solution of this invention not only solves the problem of insufficient bearing capacity of the active layer, but also effectively addresses the challenge of continuous warming and degradation of permafrost through composite foundation structure design, achieving uniformity and overall improvement of the bearing capacity of the shallow foundation. By implementing this method, the long-standing engineering problem of differential settlement and deformation of highway subgrades in permafrost regions can be fundamentally solved, demonstrating significant technical and economic advantages. Attached Figure Description

[0056] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, forming part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0057] Figure 1 This is a flowchart of a method for enhancing the bearing capacity of highway foundations in deep, high-temperature permafrost regions, as disclosed in a preferred embodiment of the present invention.

[0058] Figure 2 This is a schematic diagram of a pile-raft integrated roadbed structure disclosed in a preferred embodiment of the present invention;

[0059] Figure 3 This is a schematic diagram of a pipe pile composite foundation structure disclosed in a preferred embodiment of the present invention;

[0060] Figure 4 This is a schematic diagram of a boulders dynamic compaction replacement composite foundation structure disclosed in a preferred embodiment of the present invention;

[0061] Figure 5 This is a schematic diagram of a water-resistant cofferdam disclosed in a preferred embodiment of the present invention. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. In the description of this invention, it should be noted that the term "or" is generally used to include the meaning of "and / or," unless otherwise expressly indicated.

[0063] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0064] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0065] The permafrost of the Qinghai-Tibet Plateau, characterized by its high temperature, fragility, sensitivity, and complexity, is significantly different from that of high-latitude permafrost, forming a typical high-altitude permafrost region in mid-to-low latitudes. In recent years, the warming and humidification trend of permafrost areas along the Qinghai-Tibet Corridor and the Gongyu Corridor has become increasingly pronounced. From 1961 to 2022, the average annual temperature in the Qinghai-Tibet region rose by 0.35℃ every 10 years, more than twice the global warming rate during the same period. Average annual precipitation also showed a significant increasing trend, increasing by an average of 9.4 mm every 10 years. The direct impact of climate warming and humidification on highway infrastructure is reflected in the exacerbation of uneven subgrade settlement. Surface subsidence has already occurred on the Sichuan-Tibet Highway and the Qinghai-Tibet Highway, severely reducing traffic efficiency and threatening driving safety. Furthermore, new situations such as distorted subsidence morphology, roadside water accumulation, water-rich foundations, and the development of deep thawed interlayers have emerged in large numbers, posing serious challenges to the treatment and renovation of existing facilities.

[0066] For a long time, the design principles for highway subgrades and building foundations in permafrost regions, both domestically and internationally, have been fundamentally divided into two categories: the principle of permafrost protection and the principle of allowing thawing. Since the 1970s, China has mainly developed and improved a design theory and technical system centered on the principle of permafrost protection. For permafrost protection, a series of special subgrade structures and construction technologies have been proposed, such as raising the subgrade, installing heat pipes, riprap, ventilation pipes, and insulation layers. However, under the enormous challenge of a future global average annual surface temperature rise of 2°C, the actual effects of existing permafrost protection engineering measures have varied, and permafrost continues to degrade. In particular, the main problem with the current design method based on the principle of permafrost protection is that it ignores the impact of changes in the properties of the underlying permafrost during long-term service, such as warming and degradation, development of thaw interlayers, and weakening of the foundation due to water enrichment. These changes are induced and aggravated by long-term warming and humidification of the climate, and can be summarized as changes in soil temperature (warming of permafrost), changes in soil phase (from permafrost to thawed soil forming thaw interlayers), and changes in soil moisture content (increased soil moisture content due to water generated by permafrost thawing and increased precipitation). This is a new problem that the current design method has not anticipated when evaluating permafrost engineering sites.

[0067] To address the various problems existing in the prior art, this invention provides a method for enhancing the bearing capacity of highway foundations in deep, high-temperature permafrost regions. By strengthening the shallow foundation through excavation-free treatment, differential settlement deformation of the roadbed is ultimately eliminated.

[0068] refer to Figure 1 In a preferred embodiment, the above method includes at least steps S110 to S130.

[0069] Step S110: The bearing capacity of the permafrost foundation is tested by static cone penetration test to obtain the spatial distribution characteristics of the bearing capacity of the original foundation.

[0070] Step S120: Establish a mapping model based at least on the spatial distribution characteristics of the original foundation bearing capacity and the shallow foundation reinforcement method.

[0071] Step S130: Based on the mapping model, determine the shallow foundation reinforcement method according to the spatial distribution characteristics of the original foundation bearing capacity obtained by detection; the shallow foundation reinforcement method includes at least: structural reinforcement measures, material reinforcement measures and hydrological regulation reinforcement measures, which are used to improve the overall bearing capacity of the foundation and inhibit permafrost degradation; among them, the structural reinforcement measures include at least constructing a composite bearing structure system in the shallow foundation to improve the overall mechanical properties of the foundation by enhancing the bearing capacity of local areas of the foundation.

[0072] Compared with traditional permafrost foundation treatment methods, the technical solution of this invention can first comprehensively evaluate the bearing capacity of permafrost foundations and implement differentiated treatment for foundations with different bearing stability levels. This not only solves the problem of insufficient bearing capacity of the active layer, but also effectively addresses the challenge of continuous warming and degradation of permafrost, achieving uniformity and overall improvement of the bearing capacity of shallow foundations.

[0073] In a preferred embodiment, in step S110 above, the spatial distribution characteristics of the original foundation bearing capacity obtained by static penetration testing include at least: the profile bearing capacity characteristic value, the average bearing capacity, the bearing capacity range, and the bearing capacity decay ratio at each point.

[0074] Specifically, static cone penetration testing (CPPT) is an in-situ testing method that involves undisturbed or minimally undisturbed penetration of a standardized probe vertically into the foundation soil at a constant rate. It measures the tip resistance and side friction of the probe in real time, thereby assessing the bearing capacity, strength, and deformation characteristics of the foundation soil. Due to its advantages such as fast testing speed, good data continuity, and accurate identification of strata interfaces, static cone penetration testing is particularly suitable for foundation evaluation in permafrost regions under alternating freeze-thaw environments. Compared with traditional drilling and sampling laboratory testing, static cone penetration testing can maintain the original stress state of the foundation soil, avoiding testing errors caused by sample disturbance. Simultaneously, it can quickly obtain continuous mechanical parameters of the foundation profile in the field, providing a reliable data foundation for the spatial variability analysis of the bearing capacity of permafrost foundations.

[0075] Specifically, undisturbed foundation refers to natural foundation that has not been artificially treated, maintaining the unique structure of the permafrost layer and active layer in permafrost regions. By setting up static contact test points at designed intervals along a predetermined route to form a test grid, the tip resistance and side friction values ​​of the foundation soil at different depths are obtained. Based on these direct measurements and combined with the temperature-mechanical properties of permafrost, the spatial distribution characteristics of the bearing capacity of the undisturbed foundation are calculated.

[0076] Specifically, the characteristic value of the profile bearing capacity at each point is obtained by converting the tip resistance value obtained from the static cone penetration test through an empirical formula. This characteristic value reflects the variation law of the bearing capacity of the foundation soil at different depths and can be used to identify weak interlayers and determine the upper limit of permafrost.

[0077] Specifically, the average bearing capacity refers to the average bearing capacity value of all measuring points within the test area within the design depth range. This indicator reflects the average level of the overall bearing capacity of the foundation within the test area and is a basic parameter for assessing whether the foundation needs reinforcement and what kind of reinforcement treatment should be carried out.

[0078] Specifically, the bearing capacity range refers to the difference between the maximum and minimum bearing capacity values ​​within the test area. This indicator characterizes the spatial variability of foundation bearing capacity. A large bearing capacity range means that the foundation bearing capacity is unevenly distributed, which may lead to differential settlement of the structure. Because uneven thawing of permafrost can cause significant differences in foundation bearing capacity, this indicator is even more important in permafrost regions.

[0079] Specifically, the bearing capacity degradation ratio is a key indicator for measuring the trend of bearing capacity change with depth in permafrost foundations. It is calculated by comparing the relative change in bearing capacity between the surface and the design depth. This indicator reflects the degree of degradation of permafrost under thermal action. A high degradation ratio indicates that the permafrost layer may be undergoing a significant thermal thawing process, resulting in a sharp decline in bearing capacity, and requiring stronger foundation reinforcement measures.

[0080] In this embodiment, the aforementioned indicators are preferentially selected as evaluation parameters, primarily based on the unique characteristics of permafrost foundations: the mean bearing capacity reflects the overall bearing capacity level of the foundation, the bearing capacity range reflects the spatial non-uniformity of the bearing capacity, and the bearing capacity degradation ratio specifically addresses the strength attenuation characteristics during the thermal degradation process of permafrost. Through comprehensive analysis of these three parameters, the bearing stability of permafrost foundations can be fully assessed, providing a basis for subsequently determining targeted foundation reinforcement measures, thereby achieving a precise understanding of the bearing characteristics of permafrost foundations under thermo-mechanical coupling.

[0081] In a preferred embodiment, the construction of the mapping model in step S120 includes: dividing the mean bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio into at least two evaluation intervals according to the preset foundation bearing capacity evaluation standard using the limit value method; determining the bearing stability level of the foundation based on the combination of the mean bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio in their respective evaluation intervals; establishing a mapping relationship between the bearing stability level and different shallow foundation reinforcement methods to form a graded reinforcement decision matrix, which is used to guide the selection of reinforcement measures for foundations with different bearing stability levels.

[0082] Specifically, by dividing the mean bearing capacity, the range of bearing capacity, and the bearing capacity degradation ratio into multiple evaluation intervals, the continuously distributed bearing capacity parameters can be discretized, facilitating decision-making in engineering practice. Simultaneously, using the boundary value method instead of a continuous function relationship simplifies the engineering application process, improving on-site decision-making efficiency while ensuring the rationality of the treatment plan. The determination of the boundary values ​​fully considers the design load requirements of highway engineering in permafrost regions, the mechanical properties of permafrost, and the engineering safety margin.

[0083] In a preferred embodiment, the mean bearing capacity is divided into a high-value range (>150 kPa), a medium-value range (50-150 kPa), and a low-value range (<50 kPa); the bearing capacity range is divided into a high-variability range (>50 kPa) and a low-variability range (<50 kPa or <20 kPa); and the bearing capacity degradation ratio is divided into a high-degradation range (>50%), a medium-degradation range (20%-50%), and a low-degradation range (<10% or <20%). These range divisions fully consider the mechanical response characteristics of frozen soil foundations under different conditions and can effectively distinguish foundation conditions requiring different reinforcement measures.

[0084] In a preferred embodiment, the foundation bearing stability level can be classified into high, medium, and low levels based on the combination of the mean bearing capacity, the range of bearing capacity, and the degradation ratio within their respective evaluation intervals. In another preferred embodiment, when the mean bearing capacity is high, the range is small, and the degradation ratio is low, it indicates that the foundation has strong overall bearing capacity, good uniformity, and high thermal stability, classifying it as a high-level foundation. When the mean bearing capacity is moderate, the range is small, and the degradation ratio is moderate, it classifies it as a medium-level foundation. When the mean bearing capacity is low, the range is large, or the degradation ratio is high, it indicates that the foundation has weak overall bearing capacity, strong non-uniformity, or severe thermal degradation, classifying it as a low-level foundation.

[0085] Furthermore, the hierarchical enhancement decision matrix establishes a direct link between the foundation condition and the corresponding enhancement measures, enabling engineering personnel to quickly determine the appropriate foundation treatment scheme based on the test results. The establishment of the decision matrix takes into account the technical characteristics, applicable conditions, and economic efficiency of different enhancement measures, ensuring that the most efficient scheme is selected while guaranteeing the safety of the project.

[0086] In a preferred embodiment, the graded reinforcement decision matrix is ​​configured as follows: when the bearing stability level is low, structural reinforcement measures are applied to construct a composite bearing structure system to improve the overall bearing performance of the foundation; when the bearing stability level is medium, material reinforcement measures are applied to improve the properties of foundation materials to enhance the shear strength and stability of the foundation; when the bearing stability level is high and there is hydrothermal sensitivity, hydrological regulation reinforcement measures are applied to regulate the hydrothermal state of the foundation to maintain the stability of permafrost.

[0087] In a preferred embodiment, based on the hierarchical enhancement decision matrix, the specific foundation enhancement measures are configured as follows:

[0088] When the average bearing capacity is >150kPa, the bearing capacity range is <50kPa, and the bearing capacity decay ratio is <10%, the foundation bearing stability level is determined to be high, and traditional active cooling methods, such as heat pipes and ventilation pipes, are preferred.

[0089] When the average bearing capacity is <50kPa, the bearing capacity range is >50kPa, and the bearing capacity decay ratio is >50%, the foundation bearing stability level is determined to be low, and the pile-raft integrated roadbed structure is preferred.

[0090] When the average bearing capacity is >50kPa, the bearing capacity range is >50kPa, and the bearing capacity decay ratio is >50%, the foundation bearing stability level is determined to be low, and the pipe pile composite foundation structure is preferred.

[0091] When the average bearing capacity is >50kPa, the bearing capacity range is >50kPa, and the bearing capacity decay ratio is <50%, the foundation bearing stability level is determined to be low, and the mixing pile composite foundation structure is preferred.

[0092] When the average bearing capacity is >50kPa, the bearing capacity range is <50kPa, and the bearing capacity decay ratio is <20%, the foundation bearing stability level is determined to be medium level, and the composite foundation structure of rubble dynamic compaction replacement is preferred.

[0093] When the average bearing capacity is <50kPa and the bearing capacity decay ratio is <20%, the foundation bearing stability level is determined to be medium level, and shallow replacement with gravel or in-situ solidification reinforcement measures are preferred.

[0094] When the average bearing capacity is >50kPa, the bearing capacity range is <20kPa, and the bearing capacity decay ratio is <20%, the foundation bearing stability level is determined to be high, and there is hydrothermal sensitivity. Therefore, the water-proof cofferdam measure is preferred.

[0095] In a preferred embodiment, in step S110 above, the spatial distribution characteristics of the original foundation bearing capacity obtained by static cone penetration testing include not only the profile bearing capacity characteristic value, bearing capacity mean, bearing capacity range and bearing capacity decay ratio of each point, but also the foundation temperature distribution, water content variation and soil type distribution characteristics.

[0096] Preferably, the ground temperature distribution is obtained by deploying an array of temperature sensors in static penetration test boreholes, with a sensor spacing of no more than 0.5 m and a monitoring depth of at least 3 m below the upper limit of permafrost. Temperature data acquisition should continue for at least 24 hours to eliminate the influence of short-term temperature fluctuations and obtain a stable ground temperature gradient curve. Ground temperature data directly reflects the thermal state of permafrost and is a key indicator for assessing permafrost thermal stability, which is of great significance for judging permafrost degradation trends and predicting future deformation risks.

[0097] Preferably, changes in soil moisture content are determined by resistivity measurement during static cone penetration testing or by in-situ measurement using time domain reflectometry (TDR). In permafrost regions, moisture content is a key factor affecting the bearing capacity of the foundation, especially in the phase transition zone near 0°C, where even small temperature changes can lead to significant changes in moisture content, resulting in a sharp decrease in foundation strength. The depth of moisture content measurement is consistent with temperature monitoring, with a focus on the moisture content distribution in the transition zone between the active layer and permafrost. Moisture content data should include both volumetric water content and unfrozen water content; the former characterizes the total water content, while the latter directly relates to the soil strength characteristics under sub-zero temperatures.

[0098] Specifically, soil type distribution is determined through friction ratio analysis during static cone penetration testing, combined with necessary sampling and identification. The friction ratio (the ratio of lateral friction to tip resistance) is an effective indicator for identifying soil types; generally, cohesive soils have a higher friction ratio than sandy soils. By establishing a friction ratio-soil type correlation for the test area, continuous identification of soil layer distribution can be achieved. For key soil layers, sampling and analysis should be conducted to determine their particle size distribution, liquid and plastic limits, organic matter content, and other physical indicators, providing fundamental data for subsequent foundation reinforcement method selection. Special attention should be paid to ice-rich soil layers with high ice content and heat-sensitive soil layers with high organic matter content, as these special soil layers are often key factors influencing foundation instability.

[0099] In a preferred embodiment, in step S120 above, the construction of the mapping model is not only based on the spatial distribution characteristics of the original foundation bearing capacity, but also comprehensively considers multi-source information such as foundation temperature, water content and soil type, forming a multi-parameter coupled enhancement measure selection model, which improves the accuracy and adaptability of the foundation treatment scheme.

[0100] Specifically, based on the established basic mapping model, a multi-source information correction system is introduced, and the selection of enhancement measures is optimized through parameter weight adjustment. This correction system employs a two-stage discrimination method: the first stage performs preliminary classification based on the mean bearing capacity, the bearing capacity range, and the bearing capacity degradation ratio; the second stage introduces parameters such as foundation temperature, water content, and soil type for fine-tuning. The mathematical expression of the correction system is as follows:

[0101]

[0102] in, For the final selected type of enhancement, The type of reinforcement measures initially determined based on bearing capacity characteristics, The weighting coefficient for the i-th additional parameter. It is the correction factor for the i-th additional parameter.

[0103] Specifically, in the above formula, This does not directly represent specific reinforcement measures, but rather a preliminary determination of the foundation bearing capacity stability level based on bearing capacity characteristics. A quantitative value of 1-7 is used, where 1 represents the highest level (high stability) and 7 represents the lowest level (low stability). For example, when the average bearing capacity > 150 kPa, the bearing capacity range < 50 kPa, and the bearing capacity degradation ratio < 10%, M0 is assigned a value of 1; when the average bearing capacity < 50 kPa, the bearing capacity range > 50 kPa, and the bearing capacity degradation ratio > 50%, M0 is assigned a value of 7. Different M0 values ​​correspond to different reinforcement measure types, achieving a mapping conversion from numerical values ​​to specific measures.

[0104] Specifically, This represents the weighted sum of all correction factors, where i represents the type of correction factor (temperature T, water content W, soil type S, etc.). This represents the weight coefficient of the i-th type of correction factor. This represents the numerical value of the i-th type of correction factor. The weighting coefficients reflect the degree of influence of each factor on foundation stability and are determined through engineering experience and statistical analysis. Preferably, the weighting coefficients for foundation temperature, moisture content, and soil type are currently set to 0.4, 0.35, and 0.25, respectively, with a weight sum of 1, ensuring the rationality of the correction system. Correction Factor The specific value is determined based on the degree of deviation between the measured parameters of the project and the standard reference value. Foundation temperature correction factor. The value is determined based on the degree to which the foundation temperature deviates from the -1.0℃ benchmark, and ranges from 0 to 0.8; the water content correction factor... The soil type correction factor is determined based on the degree to which the moisture content deviates from the 20% benchmark, and its value ranges from 0 to 0.9. The correction factor is determined based on the degree to which the organic matter content and ice content deviate from the benchmark values, with a range of 0 to 0.8. A larger correction factor indicates a greater deviation from the benchmark values, requiring a more significant adjustment to the foundation stability rating. (In the formula...) The term represents a correction factor, which typically ranges from 0.7 to 1.3 and is used to adjust the initial stability rating.

[0105] Revised The value is converted into the final foundation bearing capacity stability level through a rounding operation, and then the corresponding reinforcement measures are determined according to a preset level-measure mapping table. For example, when the calculated value is... When the value is 4.2, rounded to level 4, the corresponding reinforcement measure may be a composite foundation structure of pipe piles; when When the value is 2.7, it is rounded down to level 3, and the corresponding reinforcement measure may be a soil mixing pile composite foundation structure.

[0106] Preferably, the foundation temperature correction factor The setting principles are as follows:

[0107] When the upper limit temperature of permafrost T > -0.5℃, =0.8, reduce the discrimination level of the basic model, and consider adopting reinforcement measures with higher structural strength;

[0108] When -1.0℃≤T≤-0.5℃, =0.4, and make appropriate adjustments to the basic model's discrimination results;

[0109] When T < -1.0℃, =0, the basic model's discrimination result remains unchanged;

[0110] When the geothermal gradient is greater than 0.05℃ / m, regardless of the absolute value of the geothermal temperature, it should be considered =0.6, to address the risk of rapid thermal degradation.

[0111] Preferably, the moisture content correction factor The setting principles are as follows:

[0112] When the moisture content W at the bottom of the active layer is greater than 30% or the non-freezing water content W' is greater than 15%, =0.9, significantly reducing the discrimination level of the basic model;

[0113] When 20% < W ≤ 30% or 10% < W' ≤ 15% =0.5, a moderate adjustment is made to the basic model's discrimination results;

[0114] When W≤20% and W'≤10% =0, the basic model's discrimination result remains unchanged;

[0115] During seasonal thawing, if an increase in moisture content exceeding 5% is detected within a short period (7 days), temporary measures should be implemented. =0.7, to cope with sudden changes in bearing capacity caused by meltwater.

[0116] Preferably, soil type correction factor The setting principles are as follows:

[0117] When the soil organic matter content is >8% or the ice content is >25%, =0.8, significantly reducing the discrimination level of the basic model;

[0118] When 5% < organic matter content ≤ 8% or 15% < ice content ≤ 25%, =0.4, and make appropriate adjustments to the basic model's discrimination results;

[0119] When the organic matter content is ≤5% and the ice content is ≤15%, =0, the basic model's discrimination result remains unchanged;

[0120] For special soil layers, such as high-salt soil (salt content > 0.5%) or highly sensitive clay (sensitivity > 8), [further details should be provided]. =0.6, to cope with its special mechanical behavior.

[0121] Under the multi-parameter correction mechanism, the application rules for the hierarchical enhanced decision matrix are adjusted as follows:

[0122] when When the value decreases by more than 30%, the reinforcement type is upgraded by one level, such as from material-based reinforcement to structural reinforcement; when 15% < When the value decreases by ≤30%, select a stronger option among similar reinforcement measures, such as changing from shallow gravel replacement to in-situ solidification reinforcement; when When the value decreases by ≤15%, the basic model's discrimination result remains unchanged, but the technical parameters can be fine-tuned, such as increasing the treatment depth or improving material properties.

[0123] Specifically, special decision-making rules are set for the following typical combined operating conditions:

[0124] When the average bearing capacity is at a medium level (50kPa to 100kPa), the bearing capacity range is large (>40kPa), the bearing capacity degradation ratio is moderate (20% to 40%), and the upper limit temperature of permafrost is high (>-0.3℃) and the water content is high (>25%), pipe pile composite foundation structure should be given priority, and combined with water-proof cofferdam measures to form a comprehensive treatment plan; when the bearing capacity is good but the soil type is ice-rich fine-grained soil (ice content >20%, fine particle content >60%), even if the foundation model is judged to be of high grade, at least material reinforcement measures should be adopted to prevent the risk of possible thermal degradation in the future; in cross-regional projects, when the ground temperature, water content or soil characteristics of adjacent measuring points show significant differences (temperature difference >1℃, water content difference >10%, or completely different soil types), a transition section design should be adopted at the boundary of the zone to mitigate differential deformation.

[0125] The multi-parameter coupled reinforcement selection model described above comprehensively considers the complex characteristics of permafrost foundations, ensuring optimal matching between reinforcement measures and actual foundation conditions, thus improving project quality and long-term stability. This model can be continuously optimized using engineering practice data to correct coefficients and weight parameters, forming an adaptive design system and providing a scientific basis for highway foundation treatment in permafrost regions.

[0126] like Figure 2In a preferred embodiment, in step S130, the integrated pile-raft subgrade structure includes mixing piles 210 and a raft slab 220. The mixing piles 210 are vertically arranged at the bottom, preferably using a pre-drilling process, where a cementitious material is mixed with the in-situ soil to form a solidified body. The cementitious material includes a temperature-stable cement-based material with low heat of hydration. The raft slab 220 is horizontally arranged at the top, preferably formed using lean concrete through a compaction process, forming an integrated load-bearing system with the mixing piles 210. In this embodiment, the pile-raft-soil collaborative working mechanism effectively disperses the load and improves the stress state of the foundation.

[0127] Specifically, traditional processes require drilling before concrete pouring, which is complex and costly. In contrast, the pre-drilling-free mixing pile 210 process of this invention directly utilizes specialized mixing equipment to mix and solidify a temperature-stable, low-heat-of-hydration cementitious material with the in-situ soil, forming a composite soil pile with a certain strength. The diameter of the mixing pile 210 is preferably 400mm to 800mm, the length of a single pile does not exceed 10m, and the pile strength should reach at least 1.5MPa.

[0128] Preferably, the temperature-stable, low-heat-of-hydration cementitious material used in the mixing pile 210 includes special low-heat silicate cement, fly ash, slag powder, water-reducing agent, and retarder. Its peak hydration heat temperature is 35℃~55℃ lower than that of ordinary silicate cement, significantly reducing the heat released during hydration and avoiding the thermal disturbance to the surrounding frozen soil caused by the large amount of heat generated during the curing process of traditional cement. Simultaneously, this cementitious material can maintain normal hydration reaction even in sub-zero temperatures, resulting in a pile body with excellent freeze-thaw cycle resistance and durability after curing.

[0129] In a preferred embodiment, the raft foundation 220 structure differs fundamentally from the traditional vibratory compaction process for cast-in-place concrete. Lean concrete refers to concrete with a lower cement content and a higher aggregate content, typically with a water-cement ratio controlled between 0.35 and 0.40. The cement content is approximately 220 kg / m³ to 280 kg / m³, significantly lower than the 350 kg / m³ to 450 kg / m³ of traditional concrete. The lean concrete raft foundation 220 is generally 20 cm to 40 cm thick and offers advantages such as low heat of hydration, minimal shrinkage deformation, and ease of construction.

[0130] Specifically, the compaction process refers to using equipment such as vibratory rollers to compact lean concrete, replacing the traditional vibratory compaction process with mechanical compaction. This process offers fast construction speed, allows for large-scale continuous operation, and significantly improves project efficiency. The compaction process typically involves three passes, with each pass achieving a compaction degree of at least 95% of the design requirements, ultimately forming a uniform and dense raft foundation structure.

[0131] In a preferred embodiment, the pile layout of the integrated pile-raft subgrade structure should be optimized according to the highway load characteristics and the distribution of foundation bearing capacity. The raft slab 220 and the mixing piles 210 are structurally connected to form an integrated load-bearing system, which can effectively bear the highway traffic load and evenly distribute the load to the lower rigid piles, reducing the pressure on the permafrost layer and preventing differential settlement of the subgrade.

[0132] Specifically, compared to traditional structures, the integrated pile-raft subgrade structure provided in this embodiment of the invention, while maintaining the basic configuration, achieves significant improvements in economy and applicability through innovative material selection and construction technology. Traditional methods involve drilling piles and then pouring cast-in-place concrete, with the raft slab 220 also using ordinary concrete compacted by vibration. This not only involves complex procedures and a long construction period, but also causes significant thermal disturbance to the surrounding permafrost due to the high heat of hydration of ordinary concrete, accelerating permafrost degradation. The mixing pile 210 and roller-compacted lean concrete raft slab 220 technology provided in this embodiment of the invention effectively solve the above problems, reducing project costs by more than 80%, and is more suitable for the special environmental conditions of permafrost regions.

[0133] like Figure 3 In a preferred embodiment, in step S130, the pipe pile composite foundation structure includes a precast pipe pile 310 disposed at the bottom and a pile cap bearing platform 320 disposed at the top. This structure optimizes the traditional pile foundation design, especially taking into account the thermal sensitivity and freeze-thaw cycle characteristics of permafrost. Through shallow pile foundation support and the soil working together, a composite bearing system is formed.

[0134] In a preferred embodiment, the precast pipe pile 310 is made of a high-strength, low-thermal-conductivity material, with a typical diameter of 300mm~500mm, a wall thickness of 8mm~12mm, and a length determined according to actual engineering requirements, but not exceeding 10 meters. This design concept of limiting pile length differs from the traditional principle of long piles penetrating deep into stable layers in pile foundation engineering. Its purpose is to reduce dead load, avoid excessive pressure on deep permafrost, and simultaneously reduce construction difficulty and project cost.

[0135] Specifically, the precast pipe piles 310 are typically installed at intervals of 1.5m to 2.5m, forming a uniform support network. Two main construction methods can be used for the precast pipe piles 310: one is the static pressure implantation method, which uses a static pile driver to directly press the precast pipe piles 310 into the foundation. This method causes minimal disturbance to the foundation and is suitable for relatively soft, active layers. The other is the pilot hole implantation method, which involves first pre-drilling a pilot hole in the frozen soil with a diameter slightly smaller than that of the pipe pile, then implanting the pipe pile and hammering it to the designed depth. This method is suitable for harder frozen soil layers.

[0136] Preferably, when the bearing capacity of the foundation declines by more than 80%, it indicates that the permafrost is severely thermally degraded and additional structural reinforcement measures are required.

[0137] In a preferred embodiment, when the bearing capacity of the foundation declines by more than 80%, a textured structure, such as spiral ribs, annular protrusions, or grid-like textures, is further provided on the outer surface of the precast pipe pile 310. These textured structures can significantly increase the contact area between the pile and the surrounding soil, improve the shear strength of the interface, and effectively prevent the settlement and displacement of the pile under freeze-thaw cycles.

[0138] In a preferred embodiment, when the foundation shear strength C < 15 kPa and the internal friction angle φ < 10°, a serrated texture structure is adopted, with a serration height of 10-15 mm, a serration angle of 45°, and a texture spacing of 80-100 mm. This type of texture structure can provide the maximum pull-out resistance in low-strength soils, with an enhancement factor of 1.4-1.6.

[0139] In a preferred embodiment, when 15 kPa ≤ C < 25 kPa and 10° ≤ φ < 15°, a ring-shaped texture structure is adopted. The height of the ring protrusions is 8-12 mm, the ring spacing is 120-150 mm, and the ring cross-section is trapezoidal, with an upper width of 5 mm and a lower width of 10 mm. This type of texture structure performs optimally in medium-strength soils, with an enhancement factor of 1.3-1.5.

[0140] In a preferred embodiment, when C≥25kPa and φ≥15°, a spiral texture structure is adopted, with a spiral height of 6-10mm, a pitch of 180-220mm, and a spiral angle of 30°. This type of texture structure provides stable shear resistance in high-strength soils, with an enhancement factor of 1.2-1.4.

[0141] Specifically, the material of the textured structure should be consistent with the main body of the precast pipe pile 310, typically using high-strength C40 or higher concrete. The surface roughness Ra of the texture should be controlled within the range of 0.8-1.2mm to improve the friction coefficient. The optimized configuration of the concave-convex textured structure can increase the pile-soil interface strength by 20%-35% in heat-sensitive areas, significantly extending the service life of the project.

[0142] In a preferred embodiment, when the bearing capacity degradation ratio of the foundation exceeds 80%, the inner cavity of the precast pipe pile 310 can be selectively filled with a low thermal conductivity phase change material. The phase change material should meet the following conditions: phase change temperature between -5℃ and 0℃, thermal conductivity less than 0.3 W / (m·K), and latent heat of phase change greater than 180 kJ / kg. This material absorbs heat and undergoes a phase change when the temperature rises, and releases heat to restore its original phase when the temperature drops, thereby achieving passive cold storage and temperature regulation, effectively slowing down the conduction of external heat to permafrost and delaying the permafrost degradation process. Preferably, the phase change material can be a water-ethylene glycol mixture, an alkane material, or a salt solution.

[0143] In a preferred embodiment, when the upper limit temperature of permafrost T > -0.5℃, a material with a phase change temperature of -1℃ to -0.5℃ is selected, such as an ethylene glycol aqueous solution with a mass fraction of 12%-15%; the filling thickness is preferably not less than 70% of the inner diameter of the pipe pile to ensure sufficient thermal buffering capacity. This configuration is suitable for high-temperature permafrost areas close to the phase change point and can provide the maximum phase change cooling effect.

[0144] In a preferred embodiment, when -1.0℃ ≤ T ≤ -0.5℃, a material with a phase change temperature of -2℃ to -1.5℃ is selected, such as an ethylene glycol aqueous solution or n-tetradecane with a mass fraction of 18%-22%; the filling thickness is preferably not less than 60% of the inner diameter of the pipe pile, providing moderate thermal stability. This configuration is suitable for areas with moderately cold permafrost, balancing thermal stability and cost-effectiveness.

[0145] In a preferred embodiment, when T < -1.0℃, a material with a phase change temperature of -3℃ to -2.5℃ is selected, such as an aqueous solution of ethylene glycol or n-dodecane with a mass fraction of 25%-28%; the filling thickness is preferably not less than 50% of the inner diameter of the pipe pile to provide thermal stability support for the foundation. This configuration is suitable for low-temperature stable permafrost regions as a preventative measure to delay thermal degradation.

[0146] In a preferred embodiment, to improve the performance stability of the phase change material, 3%-5% of nano-scale graphite or carbon fiber can be added to enhance thermal conductivity, 0.5%-1% of nucleating agent can be added to reduce phase change undercooling, and 0.1%-0.3% of antioxidant can be added to extend service life. The phase change material should be sealed and filled, with a 5%-8% expansion space reserved, and the inner wall should be coated with an epoxy resin anti-corrosion layer with a thickness of 0.8-1.2 mm.

[0147] Through the optimized configuration of the above-mentioned textured structure and phase change cold storage material, the adaptability and stability of precast pipe piles 310 in permafrost areas can be significantly improved, providing long-term stable support for foundations with high thermal sensitivity, so as to effectively cope with engineering risks caused by climate change.

[0148] Preferably, a pile cap bearing platform 320 is provided at the top of the pipe pile, and the pile cap is preferably installed by on-site casting or prefabrication. A gravel cushion layer with a thickness of 30cm to 50cm is provided between and above the pile caps. The gravel material should be selected with a frost heave rate of less than 1% and good gradation, of which the content of gravel with a particle size greater than 5mm is not less than 60% to ensure good drainage and stability.

[0149] Preferably, multiple layers of geogrid 330 are embedded in the gravel cushion layer for reinforcement. The tensile strength of the geogrid 330 is not less than 20kN / m, and the mesh size is 25mm×25mm. The function of the geogrid 330 is to restrict the lateral displacement of the gravel material, increase the overall stiffness and bearing capacity of the cushion layer, improve the load distribution, and reduce local stress concentration.

[0150] Specifically, the overall working mechanism of the pipe pile composite foundation is that the pile and soil work together to bear the superstructure load. When the roadbed is subjected to traffic loads, the load is rationally distributed to the precast pipe piles 310 and the surrounding soil through the pile cap bearing platform 320 and the gravel cushion layer reinforced by the geogrid 330. The precast pipe piles 310 bear 70% to 80% of the load, and the rest is borne by the soil. This load-sharing mechanism avoids the unreasonable state in traditional pile foundation structures where the pile body bears all the load, and is especially suitable for the special geological conditions of permafrost areas.

[0151] Compared with traditional pile foundation structures, the pipe-pile composite foundation structure of this invention has the following significant advantages: First, the pile length is controlled within 10 meters, reducing disturbance to deep permafrost; second, the textured surface of the pile and the phase change material filling the inner cavity achieve the dual functions of structural load-bearing and thermal stability; third, the composite load-bearing system formed by the pile cap and the 330 geogrid-reinforced gravel cushion layer improves the overall load-bearing capacity and uniformity. These innovations work together to effectively solve the problem of differential settlement caused by permafrost degradation in highways in permafrost regions, significantly improving the long-term stability and durability of the project.

[0152] In a preferred embodiment, in step S130, the mixing pile composite foundation structure includes mixing piles placed at the bottom and a gravel cushion layer placed at the top. This structure effectively improves the bearing characteristics of the foundation by constructing a composite bearing system in the shallow foundation, while minimizing thermal disturbance to the permafrost layer.

[0153] Preferably, the mixing pile adopts a pre-drilling process, and the mixing pile uses a temperature-stable, low-heat-of-hydration cementitious material to mix with the in-situ soil to form a solidified body; preferably, the temperature-stable, low-heat-of-hydration cementitious material includes special low-heat silicate cement, active admixtures, water-reducing agents, retarders and other additives, with a water-cement ratio controlled between 0.45 and 0.55. The maximum temperature rise of this cementitious material during the hydration process does not exceed 25°C, which is significantly lower than the 60°C to 80°C of ordinary silicate cement, effectively reducing the thermal disturbance to the surrounding frozen soil during construction.

[0154] Preferably, the gravel cushion layer set on top of the mixing piles is an important component of the mixing pile composite foundation structure. The thickness of the gravel cushion layer is usually 30cm to 50cm. It should be made of well-graded gravel with a frost heave rate of less than 1%, of which gravel with a particle size greater than 2mm should account for 60% to 80% and fine particles should not exceed 5% to ensure good drainage and stability.

[0155] Preferably, a geogrid is laid in the gravel cushion layer for load distribution and balanced transfer. The geogrid is a biaxially oriented plastic geogrid or a fiberglass geogrid with a tensile strength of not less than 20 kN / m, an ultimate elongation of not more than 3%, and a mesh size of 25 mm × 25 mm. The geogrid is typically arranged in 1 to 3 layers in the gravel cushion layer, with the first layer located at the bottom of the cushion layer, 10 cm from the top surface of the mixing pile; if there are multiple layers, the distance between layers should not be less than 20 cm.

[0156] In this embodiment, the working mechanism of the mixing pile composite foundation is to bear the superstructure load through the synergistic action of the pile-soil-cushion system. When the roadbed is subjected to traffic load, the load is first transferred to the gravel cushion layer. The presence of the geogrid makes the load more evenly distributed. Then, part of the load is transferred to the deeper soil layer through the mixing piles, and part of the load is borne by the soil between the piles.

[0157] Compared with traditional foundation treatment methods, the soil mixing pile composite foundation structure has the following significant advantages: First, the construction process causes less disturbance to the original foundation, reducing the thermal impact on permafrost; second, the use of low-hydration-heat cementitious materials further reduces heat input during construction; third, the pile-soil collaborative working mechanism achieves reasonable load sharing and avoids local stress concentration; fourth, the geogrid-reinforced gravel cushion layer has good drainage performance, reducing the impact of moisture on permafrost; and fifth, the overall system design fully considers the special characteristics of permafrost, achieving the dual goals of improving foundation bearing capacity and protecting permafrost.

[0158] In a preferred embodiment, to further improve the applicability of the mixing pile composite foundation structure in permafrost regions, the configuration of the mixing piles can be optimized according to specific engineering conditions. When the bearing capacity difference of the foundation is large, the number of mixing piles in areas with smaller pile spacing can be appropriately increased; when the bearing capacity degradation ratio is close to 50%, 0.5% to 1.5% of an expansion agent can be added to the cementitious material to compensate for the settlement that may be caused by the thawing of the permafrost; when there is an obvious seasonal thawing layer in the foundation, the top of the mixing piles can be extended 10cm to 15cm above this layer to cut off the heat conduction channel.

[0159] like Figure 4In a preferred embodiment, in step S130, the boulders dynamic compaction replacement composite foundation structure comprehensively utilizes the foundation treatment principles of boulders replacement and dynamic compaction. Through the triple action of replacement, compaction and impact consolidation, it significantly improves the bearing characteristics of shallow foundations.

[0160] In a preferred embodiment, the dynamic compaction energy level of the riprap-replacement composite foundation structure is optimized based on the upper limit of the permafrost depth. When the upper limit of the permafrost depth is 1.5m to 2.5m, the dynamic compaction energy level is preferably 800kN·m to 1200kN·m; when the upper limit of the permafrost depth is 2.5m to 4.0m, the dynamic compaction energy level is preferably 1200kN·m to 2000kN·m. The appropriate selection of the dynamic compaction energy level ensures that the compaction energy can be effectively transferred to the bottom of the active layer, while only having a controlled impact on the permafrost layer, avoiding excessive impact that could damage the permafrost structure.

[0161] In a preferred embodiment, the construction window and pre-drilling process are determined based on the freezing strength and freezing depth parameters of the active layer. Preferably, construction is carried out when the freezing strength of the active layer reaches 0.8 MPa to 1.2 MPa and the freezing depth reaches 60% to 80% of the active layer thickness. This time window typically occurs from November to February of the following year, when the active layer has formed a frozen body of a certain strength, capable of withstanding the impact load of dynamic compaction. Simultaneously, the temperature of the frozen soil layer has not yet reached its minimum value, retaining a certain degree of deformation capacity, which is beneficial for achieving the desired compaction effect.

[0162] In a preferred embodiment, the pre-drilling process is a key step in the construction of a riprap dynamic compaction replacement composite foundation. The diameter of the pre-drilling hole is typically 0.8m to 1.2m, and the depth is at least 80% of the active layer thickness. Pre-drilling can be performed using mechanical drilling or thermal fusion methods; mechanical drilling is preferred in permafrost regions to reduce thermal disturbance. After the pre-drilling is completed, riprap material should be backfilled immediately to form a dynamic compaction riprap pier 410 to prevent the pre-drilling hole wall from collapsing or groundwater from seeping in. Preferably, a crushed stone leveling layer 420 is also provided above the dynamic compaction riprap pier.

[0163] In a preferred embodiment, the termination criterion for dynamic compaction is set at the point where the cumulative settlement deformation reaches the upper limit of the permafrost depth. This criterion fully considers the special characteristics of foundations in permafrost regions. When the cumulative settlement approaches or reaches the upper limit of the permafrost depth, it indicates that the active soil layer has been sufficiently compacted, while the permafrost layer has not been significantly disturbed. At this point, dynamic compaction should be stopped to avoid excessive impact on the deep permafrost.

[0164] Specifically, the bearing capacity of the foundation treated with a riprap dynamic compaction replacement composite foundation structure can be increased by 50% to 80%, and the compression modulus can be increased by 60% to 90%, significantly improving the engineering characteristics of shallow foundations in permafrost regions. At the same time, because this technology mainly targets the active layer, it causes relatively little disturbance to the permafrost layer, maintaining the stability of the permafrost. It is a foundation treatment method that balances engineering benefits and ecological protection.

[0165] In a preferred embodiment, in step S130, the shallow gravel replacement directly improves the bearing capacity and stability of the foundation by replacing the original weak soil layer with low bearing capacity and high frost heave with gravel material with good engineering performance. The specific construction includes: excavating the shallow weak soil layer and replacing it with gravel material that meets the engineering gradation requirements, with a treatment thickness of not less than 2m, preferably 2.5m to 3.5m; the replacement width should extend 1.5m to 2.5m beyond the edge of the roadbed.

[0166] In a preferred embodiment, in step S130, in-situ solidification reinforcement is particularly suitable for areas with fine soil and where gravel is difficult to obtain; the method improves the strength and stability of the soil without changing its structure by adding a specific solidifying agent to the original foundation soil.

[0167] Preferably, the curing agents used for in-situ solidification reinforcement mainly include inorganic cementitious materials such as cement, lime, fly ash, and silicates, as well as organic stabilizers such as polymers and resins. In permafrost regions, low-heat cement and fly ash composite curing agents are preferred, with the curing agent dosage typically being 5% to 10% of the soil weight. The specific ratio should be determined through laboratory tests. The selection of the curing agent should consider its activity under low-temperature conditions, heat of hydration, and compatibility with the original soil.

[0168] In a preferred embodiment, in-situ solidification reinforcement can be carried out using either plant mixing or road mixing. Plant mixing involves transporting the excavated soil to a mixing plant, thoroughly mixing it with the curing agent, and then transporting it back to the site for backfilling. Road mixing involves directly mixing the curing agent with the original soil on-site using specialized equipment. Considering the special characteristics of permafrost, plant mixing is preferred to allow for more precise control of mixing quality and curing agent dosage.

[0169] Preferably, the technical performance of the solidified soil should meet the following requirements: 7-day unconfined compressive strength ≥1.0MPa, strength loss rate <10% after 10 freeze-thaw cycles at -20℃, mass loss rate <5%, and water stability coefficient >80%.

[0170] like Figure 5In a preferred embodiment, in step S130, the main purpose of the water-resistant cofferdam is to block the erosion and thermal disturbance of the roadbed by surface water and groundwater. Preferably, its construction measures specifically include: directly inserting steel sheet piles 510 at the toe of the roadbed slope, or using mixing piles to form a water-resistant curtain.

[0171] When using the steel sheet pile 510 scheme, the preferred length of the steel sheet pile 510 is 4m to 6m, the thickness of the sheet pile is 8mm to 12mm, the material is low-temperature resistant steel, and the surface should be treated with anti-corrosion. The steel sheet pile 510 is placed into the ground by a vibratory pile driving machine or static pressure pile driving equipment, with the top of the pile 20cm to 30cm above the ground. The piles are connected by grooves or overlaps to ensure waterproofing.

[0172] When using mixing piles to form a water-tight curtain, the diameter of the mixing piles should be 500mm~800mm, the spacing between piles should not exceed 40cm, and they should be arranged in single or double rows; the permeability coefficient of the mixing pile curtain should be less than 1×10⁻⁶. -7 cm / s ensures good water-proofing effect; the top of the curtain is usually level with or slightly higher than the ground, and the bottom should penetrate more than 1.5m into the permafrost layer to form a complete seepage barrier, effectively blocking the seepage of water into the roadbed and protecting the thermal stability of the permafrost.

[0173] Compared with existing technologies, the method for enhancing the bearing capacity of highway foundations in deep, high-temperature permafrost regions provided in the above embodiments considers the permafrost-roadbed as a unified engineering system. Through the technical route of precise identification, directional design, and comprehensive treatment, it effectively enhances the bearing capacity and stability of highway foundations in permafrost regions.

[0174] First, this invention overcomes the limitations of traditional foundation treatment methods that fail to adequately consider the characteristics of permafrost. It establishes a precise identification system based on three-dimensional parameters: mean bearing capacity, bearing capacity range, and bearing capacity degradation ratio, enabling a scientific assessment of the engineering characteristics of permafrost foundations. Second, this invention selects the most suitable reinforcement measures according to different permafrost foundation characteristics, including various technical solutions such as pipe pile composite foundations, mixing pile composite foundations, riprap dynamic compaction replacement, shallow gravel replacement, in-situ solidification reinforcement, and water-resistant cofferdams, avoiding the one-size-fits-all drawbacks of traditional treatment methods. Third, this invention fully considers the thermal sensitivity and dynamic change characteristics of permafrost. Each treatment scheme emphasizes the protection of the thermal stability of permafrost, such as using low-heat materials, controlling the treatment depth, and optimizing the construction time window, fundamentally solving the problem of permafrost degradation caused by thermal disturbance in traditional technologies. Finally, this invention is economical and applicable, fully considering the construction conditions and material availability in extremely cold regions, reducing project costs, improving construction efficiency, and providing systematic technical support and solutions for highway construction in deep, high-temperature permafrost areas.

[0175] Those skilled in the art will understand that, apart from the mutual exclusion of features, all features disclosed in this specification (including the accompanying claims, abstract, and drawings) and all processes or units of any method or apparatus so disclosed can be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including the accompanying claims, abstract, and drawings) may be replaced by an alternative feature serving the same, equivalent, or similar purpose.

Claims

1. A method for enhancing the bearing capacity of highway subgrade in deep, high-temperature permafrost regions, characterized in that, include: The bearing capacity of permafrost foundations is tested by static cone penetration testing to obtain the spatial distribution characteristics of the bearing capacity of the undisturbed foundation. The spatial distribution characteristics of the bearing capacity of the undisturbed foundation include at least the mean bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio. Establish a mapping model based at least on the spatial distribution characteristics of the original foundation bearing capacity and the shallow foundation reinforcement method; Based on the mapping model, the shallow foundation reinforcement method is determined according to the spatial distribution characteristics of the original foundation bearing capacity obtained by detection. The shallow foundation reinforcement method includes at least: structural reinforcement measures, material reinforcement measures and hydrological regulation reinforcement measures, which are used to improve the overall bearing capacity of the foundation and inhibit permafrost degradation. The structural reinforcement measures include at least constructing a composite load-bearing structure system in the shallow foundation to improve the overall mechanical properties of the foundation by enhancing the load-bearing capacity of local areas of the foundation. The construction of the mapping model includes: Based on the preset foundation bearing capacity evaluation standard, the limit value method is used to divide the mean bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio into at least two evaluation intervals respectively. The bearing stability level of the foundation is determined based on the combination of the mean bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio within their respective evaluation intervals. A mapping relationship is established between the bearing stability level and different shallow foundation reinforcement methods to form a graded reinforcement decision matrix, which is used to guide the selection of reinforcement measures for foundations with different bearing stability levels.

2. The method according to claim 1, characterized in that, The hierarchical enhanced decision matrix is ​​configured as follows: When the load-bearing stability level is low, the aforementioned structural reinforcement measures are applied to construct a composite load-bearing structural system to improve the overall load-bearing performance of the foundation. When the bearing stability level is medium, the aforementioned material reinforcement measures are applied to improve the properties of the foundation materials in order to enhance the shear strength and stability of the foundation. When the bearing stability level is high and there is hydrothermal sensitivity, the aforementioned hydrological regulation enhancement measures are applied to adjust the foundation hydrothermal state in order to maintain the stability of permafrost.

3. The method according to claim 2, characterized in that, The construction of the mapping model also includes: Acquire multi-source information on foundation temperature, moisture content, and soil type; Based on the multi-source information, the hierarchical enhancement decision matrix is ​​modified by setting corresponding modification factors through parameter weight adjustment method; The determination result of the bearing stability level is adjusted according to the correction factor and its weight coefficient.

4. The method according to claim 2, characterized in that, The structural reinforcement measures include a pile-raft integrated roadbed structure, which comprises mixing piles at the bottom and a raft slab at the top. The mixing pile adopts a pre-drilling process, in which cementitious materials are mixed with in-situ soil to form a solidified body. The cementitious materials include temperature-stable cement-based materials with low heat of hydration. The raft slab is formed by compaction of lean concrete and forms an integral load-bearing system with the mixing pile structure.

5. The method according to claim 2, characterized in that, The structural reinforcement measures include a pipe pile composite foundation structure, which comprises precast pipe piles at the bottom and a pile cap bearing platform at the top. The precast pipe piles are constructed using static pressure implantation or pre-drilling implantation methods, and the length of the precast pipe piles is no more than 10 meters. A geogrid-reinforced gravel cushion layer is provided in the area between and above the pile cap bearing platform.

6. The method according to claim 5, characterized in that, When the bearing capacity degradation ratio is greater than 80%, the precast pipe piles shall be reinforced with the following structural measures: The outer surface of the precast pipe pile is provided with a textured structure to enhance the shear strength of the pile-soil interface. And / or, the inner cavity of the precast pipe pile is filled with a phase change material with low thermal conductivity to achieve passive cold storage and temperature regulation, enhance the freezing strength of the pile-soil interface, and reduce the warming rate of deep permafrost.

7. The method according to claim 2, characterized in that, The structural reinforcement measures include a mixing pile composite foundation structure, which includes mixing piles placed at the bottom and a gravel cushion layer placed at the top. The mixing pile adopts a pre-drilling process, and the mixing pile uses a temperature-stable, low-hydration-heat cementitious material to mix with the in-situ soil to form a solidified body. The gravel cushion layer is covered with geogrid for load distribution and balanced transfer.

8. The method according to claim 2, characterized in that, The material-based reinforcement measures include a riprap dynamic compaction replacement composite foundation structure, wherein: The dynamic compaction energy level is determined based on the upper limit of the burial depth of permafrost, so as to achieve controlled influence on deep permafrost. The construction window period and pilot hole technique are determined based on the parameters of the freezing strength and freezing depth of the active layer. The termination standard for dynamic compaction is set at the point where the cumulative settlement deformation reaches the upper limit of the burial depth of permafrost.

9. The method according to claim 2, characterized in that, The material-based reinforcement measures include shallow replacement with gravel, specifically including: The shallow, weak soil layer is excavated and replaced with gravel material that meets the engineering gradation requirements, and the treatment thickness is not less than 2m.

10. The method according to claim 2, characterized in that, The material-based reinforcement measures include in-situ curing reinforcement, specifically including: For the original foundation soil, add the curing agent using plant mixing or road mixing methods, and then perform in-situ curing; The technical performance of the solidified soil should meet the following requirements: 7-day unconfined compressive strength ≥1.0MPa, strength loss rate <10% after 10 freeze-thaw cycles at -20℃, mass loss rate <5%, and water stability coefficient >80%.

11. The method according to claim 2, characterized in that, The hydrological regulation enhancement measures include water-blocking cofferdams, specifically including: Steel sheet piles can be placed at the toe of the roadbed slope, or water-mixing piles can be used to form a water-resistant curtain.

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