Method for enhancing bearing capacity of road foundation in deep and thick high-temperature permafrost region

Abstract

The invention relates to a deep and thick high-temperature permafrost region highway foundation bearing capacity enhancing method which comprises the following steps: detecting the bearing capacity of a permafrost foundation through static sounding to obtain the spatial distribution characteristics of the bearing capacity of an original-state foundation; the spatial distribution characteristics of the bearing capacity of the undisturbed foundation at least comprise a bearing capacity mean value, a bearing capacity range and a bearing capacity decline ratio; establishing a mapping model at least based on the spatial distribution characteristics of the original-state foundation bearing capacity and the shallow foundation enhancement mode; based on the mapping model, according to the spatial distribution characteristics, obtained through detection, of the original-state foundation bearing capacity, the shallow foundation strengthening mode is determined, and the shallow foundation strengthening mode comprises a structural strengthening measure, a material strengthening measure and a hydrological regulation and control strengthening measure and is used for improving the overall bearing performance of the foundation and restraining permafrost degradation; the structural reinforcing measure at least comprises the steps that a composite bearing structure system is constructed in a shallow foundation, and the mechanical property of the whole foundation is improved by enhancing the bearing capacity of a local area of the foundation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of permafrost highway engineering construction, in particular to a method for enhancing the bearing capacity of highway foundation in deep high-temperature permafrost regions. BACKGROUND

[0002] Due to the warming trend in recent years, the permafrost region of the Qinghai-Tibet Plateau faces a series of problems such as road surface settlement, road side water accumulation, foundation water enrichment, melting interlayer thickening, and continuous degradation of permafrost. The traditional highway subgrade design mainly follows the principle of protecting permafrost, and through the use of special structure subgrade forms such as raising the subgrade, setting heat rods, stone blocks, ventilation pipes, and thermal insulation layers, it attempts to increase the thermal resistance, reduce the heat input, or actively introduce additional cold to achieve the non-degradation of permafrost. However, these protective measures face real challenges such as complex on-site hydrogeological conditions, harsh construction conditions on the Qinghai-Tibet Plateau, and insufficient maintenance funds, resulting in a long-term reduction in the actual application effect and performance.

[0003] The current permafrost subgrade design method mainly has the following problems: First, the traditional cooling measures such as heat rods, stone blocks, and ventilation pipes have insufficient cooling efficiency, and the permafrost continues to degrade in the face of long-term climate warming; Second, the traditional method does not treat the subgrade itself, ignoring the influence of changes in subsoil properties such as warming and degradation of underlying permafrost, development of melting interlayer, and water enrichment of subsoil on the performance of subgrade during long-term service; Third, the traditional method does not assess the bearing capacity of the foundation, and lacks a clear understanding of the spatial variability of the deformation risk of the foundation; Fourth, the source layer of the settlement continuously expands to the deep part of the foundation, and the existing permafrost protection subgrade technology has poor universality in inhibiting the effect of melting and sinking, and the effect of the same technical measures applied to different road sections is significantly different.

[0004] Therefore, it is urgent to develop a new method for enhancing the bearing capacity of the foundation based on the concept of permafrost foundation treatment to fundamentally solve the technical problem of differential settlement and deformation of highway subgrade in permafrost regions. SUMMARY

[0005] The present application discloses a method for enhancing the bearing capacity of highway foundation in deep high-temperature permafrost regions, which is used to solve the problems in the prior art.

[0006] The present application provides a method for enhancing the bearing capacity of highway foundation in deep high-temperature permafrost regions, which comprises: The bearing capacity of the permafrost foundation is detected by static sounding to obtain the spatial distribution characteristics of the undisturbed foundation bearing capacity, which at least includes the mean value, range, and decay ratio of the bearing capacity; A mapping model is established based on the spatial distribution characteristics of the bearing capacity of the original state foundation and the shallow foundation reinforcement mode; Based on the mapping model, the spatial distribution characteristics of the bearing capacity of the original state foundation are detected to determine the shallow foundation reinforcement mode, which at least includes structural reinforcement measures, material reinforcement measures and hydrological regulation reinforcement measures, for improving the overall bearing performance of the foundation and inhibiting the degradation of permafrost. The structural reinforcement measures at least include constructing a composite bearing structure system in the shallow foundation to improve the mechanical properties of the overall foundation by enhancing the bearing capacity of the local area of the foundation.

[0007] As a preferred technical solution, the construction of the mapping model includes: According to the preset foundation bearing capacity evaluation standard, the limit value method is used to divide the bearing capacity mean value, bearing capacity range and bearing capacity decay ratio into at least two evaluation intervals; According to the combination of the bearing capacity mean value, bearing capacity range and bearing capacity decay ratio in the respective evaluation intervals, the bearing stability grade of the foundation is determined; The mapping relationship between the bearing stability grade and different shallow foundation reinforcement modes is established to form a graded reinforcement decision matrix for guiding the selection of reinforcement measures for foundations with different bearing stability grades.

[0008] As a preferred technical solution, the graded reinforcement decision matrix is configured as: When the bearing stability grade is low, the 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 grade is medium, the material reinforcement measures are applied to improve the material properties of the foundation to enhance the shear strength and stability of the foundation; When the bearing stability grade is high and there is hydrothermal sensitivity, the hydrological regulation reinforcement measures are applied to adjust the hydrothermal state of the foundation to maintain the stability of permafrost.

[0009] As a preferred technical solution, the construction of the mapping model further includes: Obtain multi-source information of foundation temperature, moisture content and soil type; Based on the multi-source information, the graded reinforcement decision matrix is corrected by parameter weight adjustment method to set the corresponding correction factor; According to the correction factor and its weight coefficient, the determination result of the bearing stability grade is adjusted.

[0010] As a preferred technical solution, the structural reinforcement measures include a pile-raft integrated roadbed structure, which includes mixing piles arranged in the lower part and raft plates arranged in the upper part: The stirring pile adopts a hole-free process to form a solidified body by stirring cementitious material with in-situ soil, and the cementitious material includes a temperature-stable cement-based material with low hydration heat; The raft is formed by a lean concrete through a rolling process, and forms an integral stress system with the stirring pile structure.

[0011] As a preferred technical solution, the structural reinforcement measures include a pipe pile composite foundation structure, which includes a prefabricated pipe pile arranged in the lower part and a pile cap bearing platform arranged in the upper part: The prefabricated pipe pile is constructed by a static pressure implantation or a hole implantation method, and the length of the prefabricated pipe pile is not greater than 10 meters; The area between and above the pile cap bearing platform is provided with a geogrid reinforced gravel cushion.

[0012] As a preferred technical solution, when the bearing capacity decay ratio is greater than 80%, the following structural reinforcement measures are applied to the prefabricated pipe pile: The outer surface of the prefabricated pipe pile is provided with a concave-convex texture structure to enhance the shear strength of the pile-soil interface; And / or, the inner cavity of the prefabricated pipe pile is filled with a low-thermal-conductivity phase-change material to achieve passive cold storage temperature adjustment, enhance the freezing strength of the pile-soil interface, and reduce the deep permafrost warming rate.

[0013] As a preferred technical solution, the structural reinforcement measures include a stirring pile composite foundation structure, which includes a stirring pile arranged in the lower part and a gravel cushion pad arranged in the upper part; The stirring pile adopts a hole-free process, and the stirring pile is formed by stirring a temperature-stable low-hydration-heat cement-based cementitious material with in-situ soil; The gravel cushion pad is laid with a geogrid for load dispersion and balanced transmission.

[0014] As a preferred technical solution, the material type reinforcement measures include a block stone dynamic compaction replacement composite foundation structure, in which: The dynamic compaction energy level is determined according to the permafrost upper limit depth to achieve a controlled influence on deep permafrost; The construction window period and the hole implantation process are determined based on the active layer freezing strength and freezing depth parameters; The dynamic compaction termination standard is set as the cumulative settlement deformation reaching the permafrost upper limit depth value.

[0015] As a preferred technical solution, the material type reinforcement measures include shallow replacement of gravel, specifically including: The shallow soft soil layer is excavated and replaced with gravel material meeting the engineering grading requirements, and the treatment thickness is not less than 2m.

[0016] As a preferred technical solution, the material type reinforcement measures include in-situ solidification enhancement, specifically including: The original foundation soil is added with a solidifying agent by plant mixing or road mixing, and is solidified in situ; The technical performance of the solidified soil body should meet the following requirements: the 7-day unconfined compressive strength is greater than or equal to 1.0 MPa, the strength loss rate is less than 10% after 10 freeze-thaw cycles in an environment of-20 DEG C, the mass loss rate is less than 5%, and the water stability coefficient is greater than 80%.

[0017] As a preferred technical solution, the hydrological regulation type reinforcement measure comprises a water-resisting cofferdam, and specifically comprises: A steel sheet pile is arranged at the slope foot of the roadbed, or a water-resisting curtain is formed by using a mixing pile. Compared with the prior art, the technical solution adopted by the present application can achieve the following beneficial effects: The present application provides a deep and high-temperature permafrost area highway foundation bearing capacity enhancement method, which provides a systematic solution to the problems of insufficient foundation treatment, lack of bearing capacity evaluation and inability to effectively respond to the continuous degradation of permafrost caused by long-term climate warming in the traditional technology.

[0018] The method first comprehensively evaluates the bearing capacity of the permafrost foundation by using the static sounding technology, obtains the spatial distribution characteristics including the mean value, range and decay ratio of the bearing capacity, establishes a precise mapping model of the foundation bearing stability and reinforcement measures, and based on the mapping model, systematically classifies three reinforcement measure systems of structure type, material type and hydrological regulation type, so that different foundations with different bearing stability grades can be treated differently.

[0019] In the structure type reinforcement measure, the method innovatively designs a pile-raft integrated roadbed structure, a pipe pile composite foundation structure and a mixing pile composite foundation structure suitable for the permafrost environment; especially in the pipe pile composite foundation structure, the shallow short pile design concept is adopted, and the length of the pile body is not more than 10 m to reduce the dead load, and the temperature stable low hydration heat material selection, the concave-convex texture enhancement of the outer surface and the phase change cold storage in the cavity and other key technologies are integrated into the pile body design, so that the passive cold storage and heat resistance functions are realized, the frozen strength of the pile-soil interface can be effectively enhanced, and the deep permafrost warming rate can be reduced.

[0020] In the aspect of the material type reinforcement measure, the method proposes a block stone dynamic compaction replacement composite foundation, a shallow replacement gravel and an in-situ solidification enhancement technical solution, which improves the shear strength and stability by improving the material properties of the foundation; especially the block stone dynamic compaction replacement technology, the dynamic compaction power level is determined according to the upper limit depth of the permafrost, so that the deep permafrost is controlled and affected, and the thermal stability damage caused by excessive disturbance is avoided.

[0021] Compared with the traditional permafrost foundation treatment method, the technical scheme of the present application not only solves the problem of insufficient bearing capacity of the active layer, but also effectively copes with the challenge of continuous warming degradation of permafrost through the design of the composite foundation structure, realizing the uniformization and overall improvement of the bearing capacity of the shallow foundation. Through the implementation of the method, the long-standing engineering problem of differential settlement deformation of highway subgrade in permafrost regions can be fundamentally solved, and the method has significant technical and economic advantages. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed in the following embodiment description will be briefly introduced, which constitutes a part of the present application. The illustrative embodiments of the present application and their description explain the present application, and do not constitute an improper limitation on the present application. In the drawings: Figure 1 a flow chart of a deep high-temperature permafrost region highway foundation bearing capacity enhancement method disclosed in a preferred embodiment of the present application; Figure 2 a schematic diagram of a pile-raft integrated subgrade structure disclosed in a preferred embodiment of the present application; Figure 3 a schematic diagram of a pipe pile composite foundation structure disclosed in a preferred embodiment of the present application; Figure 4 a schematic diagram of a block stone dynamic compaction replacement composite foundation structure disclosed in a preferred embodiment of the present application; Figure 5 a schematic diagram of a waterproof cofferdam disclosed in a preferred embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the technical scheme of the present application will be described clearly and completely in combination with the specific embodiments of the present application and the corresponding drawings. In the description of the present application, it should be noted that the term “or” is generally used in the sense of including “and / or”, unless the context clearly indicates otherwise.

[0024] In the description of the present application, it should be noted that the terms “mounting”, “connection” and “connection” should be understood in a broad sense, unless otherwise specified and limited. In addition, in the description of the present application, the terms “first”, “second” and the like are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0025] Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] The permafrost in the Qinghai-Tibet Plateau is significantly different from the permafrost in high latitudes due to its high temperature, fragility, sensitivity, and complexity, forming a typical high-altitude permafrost in middle and low latitudes. In recent years, the trend of warming and humidification in the permafrost region along the Qinghai-Tibet Corridor and the Ganzhu-Yushu Corridor has become increasingly evident. From 1961 to 2022, the average annual temperature in the Qinghai-Tibet region increased by 0.35℃ per decade, which is more than twice the global warming rate during the same period. The average annual precipitation showed a significant increasing trend, with an average increase of 9.4mm per decade. The direct impact of climate warming and humidification on highway infrastructure is the exacerbation of uneven subsidence of roadbeds. The surface subsidence of the Sichuan-Tibet Highway and the Qinghai-Tibet Highway has already occurred, which seriously reduces the traffic efficiency and threatens the safety of driving. In addition, new situations such as distortion of subsidence morphology, roadside water accumulation, water-rich foundation, and development of deep melting interlayer have appeared, posing severe challenges to the governance and reconstruction of existing facilities.

[0027] For a long time, the design principles of highway roadbeds and building foundations in permafrost regions can be fundamentally divided into two categories: the protection of permafrost principle and the allowance of thawing principle. Since the 1970s of last century, China has mainly developed and improved the design theory and technical system centered on the principle of protecting permafrost. In order to protect permafrost, a series of special structure roadbed forms and construction technologies such as raising the roadbed, setting heat rods, stone blocks, ventilation pipes, and thermal insulation layers have been proposed. However, under the huge challenge of a 2℃ increase in global average surface temperature in the future, the actual effect of existing various permafrost protection engineering measures is uneven, and permafrost continues to degrade. In particular, the main problem of the current design method based on the principle of protecting permafrost is that it ignores the influence of changes in the properties of the underlying permafrost, such as the warming and degradation of permafrost, the development of melting interlayers, and the weakening of water-rich foundations, on the performance of the roadbed during long-term service. These changes are induced and exacerbated by long-term climate warming and humidification, which can be summarized as temperature changes of soil (warming of permafrost), phase changes of soil (from permafrost to positive melting soil forming melting interlayer), and moisture content changes of soil (water produced by permafrost melting and increased soil moisture caused by increased precipitation), which are new problems that the current design method did not anticipate when evaluating permafrost engineering sites.

[0028] To solve the various problems existing in the prior art, the embodiment of the present application provides a method for enhancing the bearing capacity of a highway foundation in a deep and high-temperature permafrost region. The method enhances the shallow foundation by non-excavation treatment, ultimately eliminating the differential settlement deformation of the roadbed.

[0029] Reference Figure 1 In a preferred embodiment, the above method at least includes steps S110-S130.

[0030] In step S110, the bearing capacity of the permafrost foundation is detected by static sounding to obtain the spatial distribution characteristics of the bearing capacity of the original foundation.

[0031] Step S120, a mapping model is established based on at least the spatial distribution characteristics of the undisturbed foundation bearing capacity and the shallow foundation reinforcement mode.

[0032] Step S130, based on the mapping model, the spatial distribution characteristics of the undisturbed foundation bearing capacity obtained by detection are used to determine the shallow foundation reinforcement mode; the shallow foundation reinforcement mode at least includes structural reinforcement measures, material reinforcement measures and hydrological regulation reinforcement measures, which are used to improve the overall bearing performance of the foundation and inhibit the degradation of permafrost; wherein the structural reinforcement measures at least include constructing a composite bearing structure system in the shallow foundation, and improving the mechanical properties of the overall foundation by enhancing the bearing capacity of the local area of the foundation.

[0033] Compared with the traditional frozen soil foundation treatment method, the technical scheme of the embodiment of the present application can first comprehensively evaluate the bearing capacity of the permafrost foundation, and implement differential treatment for the foundation with different bearing stability grades, which not only solves the problem of insufficient bearing capacity of the active layer, but also effectively copes with the challenge of continuous warming and degradation of permafrost, and realizes the uniformization and overall improvement of the bearing capacity of the shallow foundation.

[0034] In a preferred embodiment, in the step S110, the spatial distribution characteristics of the undisturbed foundation bearing capacity obtained by static sounding at least include the profile bearing capacity characteristic value, the bearing capacity average value, the bearing capacity range and the bearing capacity decay ratio of each point.

[0035] Specifically, static sounding is a non-disturbance or micro-disturbance in-situ testing method, which vertically presses a standardized probe into the foundation soil at a constant rate, measures the probe tip resistance and side friction resistance in real time, and then evaluates the bearing capacity, strength and deformation characteristics of the foundation soil. Since static sounding has the advantages of fast testing speed, good data continuity, accurate identification of stratigraphic layering interface, etc., it is especially suitable for foundation evaluation in the freezing-melting alternating environment of permafrost regions. Compared with traditional drilling sampling laboratory testing, static sounding can maintain the undisturbed stress state of the foundation soil, avoid testing errors caused by sample disturbance, and quickly obtain continuous mechanical parameters of the foundation profile on site, thereby providing a reliable data basis for the spatial variability analysis of the bearing capacity of permafrost foundation.

[0036] Specifically, the undisturbed foundation refers to a natural foundation that has not been artificially treated, and maintains the unique structure of frozen soil layer and active layer in permafrost regions. By arranging static sounding points on the preset route according to the designed interval to form a test grid, the tip resistance value and side friction resistance value of the foundation soil at different depths are obtained. According to these direct measurement values, combined with the temperature-mechanical property relationship of permafrost, the spatial distribution characteristics of the undisturbed foundation bearing capacity are calculated.

[0037] Specifically, the characteristic value of the cross-section bearing capacity of each point is the tip resistance value obtained by static sounding, which is converted by an empirical formula. The characteristic value reflects the change rule of the bearing capacity of the foundation soil at different depths, and can be used to identify soft interlayers and determine the upper limit position of the permafrost.

[0038] Specifically, the average bearing capacity refers to the average bearing capacity value of all test points in the test area within the design depth range. This index reflects the average level of the overall bearing capacity of the foundation in the test area, and is a basic parameter for evaluating whether the foundation needs reinforcement and what kind of reinforcement is needed.

[0039] Specifically, the bearing capacity range refers to the difference between the maximum bearing capacity value and the minimum bearing capacity value in the test area. This index represents the degree of spatial variation of the foundation bearing capacity. A larger bearing capacity range means that the foundation bearing capacity is unevenly distributed, which may lead to differential settlement of the structure. Since the uneven melting of permafrost can cause significant differences in the bearing capacity of the foundation, this index is more important in permafrost regions.

[0040] Specificly, the bearing capacity decay ratio is a key index to measure the change trend of the bearing capacity of permafrost foundation with depth. It is calculated by comparing the relative change between the bearing capacity values at the ground surface and the design depth. This index reflects the degree of degradation of permafrost under the action of heat. A high decay ratio indicates that the permafrost layer may be undergoing significant thermal melting process, and the bearing capacity is rapidly decreasing, requiring stronger foundation reinforcement measures.

[0041] In this embodiment, the above-mentioned indexes are preferentially selected as evaluation parameters, mainly based on the special nature of permafrost foundation: the average bearing capacity reflects the overall bearing level of the foundation, the bearing capacity range reflects the spatial unevenness of the foundation bearing capacity, and the bearing capacity decay ratio is particularly aimed at the strength decay characteristics in the thermal degradation process of permafrost. Through comprehensive analysis of these three parameters, the bearing stability of permafrost foundation can be comprehensively evaluated, providing a basis for subsequent determination of targeted foundation reinforcement measures, so as to accurately grasp the bearing characteristics of permafrost foundation under the action of thermal-mechanical coupling.

[0042] In a preferred embodiment, in the step S120, the construction of the mapping model includes: according to the preset foundation bearing capacity evaluation standard, using the limit value method to divide the average bearing capacity, the bearing capacity range and the bearing capacity decay ratio into at least two evaluation intervals respectively; determining the bearing stability grade of the foundation according to the combination of the average bearing capacity, the bearing capacity range and the bearing capacity decay ratio in their respective evaluation intervals; establishing a mapping relationship between the bearing stability grade 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 grades.

[0043] Specifically, by dividing the bearing capacity mean value, bearing capacity range and bearing capacity degradation ratio into multiple evaluation intervals respectively, the continuous distribution of the bearing capacity parameters can be discretely processed, which is convenient for decision-making in engineering practice. At the same time, the use of limit value method instead of continuous function relationship can simplify the engineering application process, improve the efficiency of on-site decision-making, and ensure the rationality of the treatment scheme. The determination of the limit value fully considers the design load requirements of highway engineering in permafrost regions, the mechanical properties of frozen soil and the engineering safety margin.

[0044] In a preferred embodiment, the bearing capacity mean value is divided into a high value interval (> 150 kPa), a medium value interval (50-150 kPa) and a low value interval (< 50 kPa); the bearing capacity range is divided into a high variation interval (> 50 kPa) and a low variation interval (< 50 kPa or < 20 kPa); the bearing capacity degradation ratio is divided into a high degradation interval (> 50%), a medium degradation interval (20%-50%) and a low degradation interval (< 10% or < 20%). These interval divisions fully consider the mechanical response characteristics of frozen soil foundation in different states, and can effectively distinguish the foundation conditions that require different reinforcement measures.

[0045] In a preferred embodiment, according to the combination of the bearing capacity mean value, bearing capacity range and bearing capacity degradation ratio in their respective evaluation intervals, the foundation bearing stability level can be divided into high level, medium level and low level. In a preferred embodiment, when the bearing capacity mean value is high, the range is small and the degradation ratio is low, it indicates that the overall bearing capacity of the foundation is strong, the uniformity is good and the thermal stability is high, which belongs to the high level; when the bearing capacity mean value is moderate, the range is small and the degradation ratio is moderate, it belongs to the medium level; when the bearing capacity mean value is low, the range is large or the degradation ratio is high, it indicates that the overall bearing capacity of the foundation is weak, the non-uniformity is strong or the thermal degradation is serious, which belongs to the low level.

[0046] Further, the hierarchical reinforcement decision matrix directly links the foundation state with the corresponding reinforcement measures, enabling engineering implementers to quickly determine the appropriate foundation treatment scheme based on test results; the establishment of the decision matrix takes into account the technical characteristics, applicable conditions and economy of different reinforcement measures, ensuring that the most efficient scheme is selected under the premise of ensuring engineering safety.

[0047] In a preferred embodiment, the hierarchical reinforcement decision matrix is configured as follows: when the bearing stability level is low, structural reinforcement measures are applied to build 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 material properties of the foundation to enhance the shear strength and stability of the foundation; when the bearing stability level is high and there is water-thermal sensitivity, hydrological regulation type reinforcement measures are applied to adjust the water-thermal state of the foundation to maintain the stability of permafrost.

[0048] In a preferred embodiment, the specific ground reinforcement measures are configured as follows according to the hierarchical reinforcement decision matrix: When the bearing capacity mean value > 150 kPa, the bearing capacity range < 50 kPa, and the bearing capacity degradation ratio < 10%, it is determined that the ground bearing stability level is high, and the traditional active cooling method is preferably used, such as a heat rod, a ventilation pipe, etc. When the bearing capacity mean value < 50 kPa, the bearing capacity range > 50 kPa, and the bearing capacity degradation ratio > 50%, it is determined that the ground bearing stability level is low, and the pile-raft integrated roadbed structure is preferably used. When the bearing capacity mean value > 50 kPa, the bearing capacity range > 50 kPa, and the bearing capacity degradation ratio > 50%, it is determined that the ground bearing stability level is low, and the pipe pile composite foundation structure is preferably used. When the bearing capacity mean value > 50 kPa, the bearing capacity range > 50 kPa, and the bearing capacity degradation ratio < 50%, it is determined that the ground bearing stability level is low, and the mixing pile composite foundation structure is preferably used. When the bearing capacity mean value > 50 kPa, the bearing capacity range < 50 kPa, and the bearing capacity degradation ratio < 20%, it is determined that the ground bearing stability level is medium, and the block stone dynamic compaction replacement composite foundation structure is preferably used. When the bearing capacity mean value < 50 kPa and the bearing capacity degradation ratio < 20%, it is determined that the ground bearing stability level is medium, and the shallow layer replacement of sand and gravel or in-situ solidification reinforcement measures are preferably used. When the bearing capacity mean value > 50 kPa, the bearing capacity range < 20 kPa, and the bearing capacity degradation ratio < 20%, it is determined that the ground bearing stability level is high, and there is water-heat sensitivity, and the water-blocking cofferdam measure is preferably used.

[0049] In a preferred embodiment, in the step S110, the spatial distribution characteristics of the undisturbed ground bearing capacity obtained by the static sounding further include the profile bearing capacity characteristic value of each point, the bearing capacity mean value, the bearing capacity range, and the bearing capacity degradation ratio, and further include the ground temperature distribution, the water content change, and the soil type distribution characteristics.

[0050] Preferably, the ground temperature distribution is obtained by arranging a temperature sensor array in the static sounding hole, the sensor spacing is not greater than 0.5 m, and the monitoring depth reaches at least 3 m below the upper limit of permafrost. The temperature data collection should last at least 24 hours to eliminate the influence of short-term temperature fluctuations and obtain a stable ground temperature gradient curve. The ground temperature data can directly reflect the thermal state of permafrost, which is a key indicator for evaluating the thermal stability of frozen soil and has important significance for judging the degradation trend of frozen soil and predicting future deformation risks.

[0051] Preferably, the ground water content variation is determined in-situ by resistivity measurement or time domain reflectometry (TDR) while static sounding. In permafrost regions, water content is a key factor affecting the bearing capacity of the ground, especially in the phase transition zone near 0°C, where a small temperature change can cause a significant change in water content, leading to a sharp decrease in ground strength. The water content measurement depth is consistent with the temperature monitoring, focusing on the water content distribution of the active layer and the permafrost transition zone. The water content data should include both the volume water content and the unfrozen water content, the former representing the total water content, and the latter directly related to the strength characteristics of the soil under negative temperature conditions.

[0052] Specifically, the soil type distribution is determined by analyzing the friction ratio during static sounding combined with necessary sampling identification. The friction ratio (i.e. the ratio of side friction to tip resistance) is an effective indicator for identifying soil types, and generally the friction ratio of cohesive soil is higher than that of sandy soil. By establishing the friction ratio-soil type correlation of the survey area, continuous identification of soil layer distribution can be achieved, and for key soil layers, sampling analysis should be conducted to determine physical indicators such as particle size composition, liquid-plastic limit, and organic matter content, providing basic data for subsequent ground enhancement mode selection. Special attention should be paid to ice-rich soil layers with high ice content and thermally sensitive soil layers with high organic matter content, as these special soil layers are often key factors affecting ground instability.

[0053] In a preferred embodiment, the construction of the mapping model in step S120 is not only based on the spatial distribution characteristics of the undisturbed ground bearing capacity, but also considers multiple source information such as ground temperature, water content, and soil type, forming a multi-parameter coupled enhancement measure selection model, which improves the accuracy and adaptability of the ground treatment scheme.

[0054] Specifically, on the established foundation mapping model, a multi-source information correction system is introduced to optimize the enhancement measure selection through parameter weight adjustment method. The correction system uses a two-stage discrimination method: the first stage is based on the mean value of bearing capacity, the range of bearing capacity, and the bearing capacity decay ratio for preliminary classification; the second stage introduces parameters such as ground temperature, water content, and soil type for fine adjustment; the mathematical expression of the correction system is:

[0055] wherein, is the final selected enhancement measure type, is the enhancement measure type preliminarily determined based on the bearing capacity characteristics, is the weight coefficient of the i-th additional parameter, is the correction factor of the i-th additional parameter.

[0056] Specifically, in the above formula, Rather than directly representing specific reinforcement measures, it represents the foundation bearing stability grade value preliminarily determined based on the bearing capacity characteristics, using a quantitative assignment of 1-7, wherein 1 represents the highest grade (high stability), and 7 represents the lowest grade (low stability). For example, when the bearing capacity average is > 150 kPa, the bearing capacity range is < 50 kPa, and the bearing capacity decay ratio is < 10%, the M0 assignment is 1; when the bearing capacity average is < 50 kPa, the bearing capacity range is > 50 kPa, and the bearing capacity decay ratio is > 50%, the M0 assignment is 7. Different M0 values correspond to different types of reinforcement measures, achieving the mapping conversion of numerical values to measures.

[0057] Specifically, represents the weighted sum of each correction factor, wherein i represents the correction factor type (temperature T, water content W, soil type S, etc.), represents the weight coefficient of the i-th correction factor, represents the numerical value of the i-th correction factor. The weight coefficient reflects the influence degree of each factor on the stability of the foundation, which is determined through engineering experience and statistical analysis. Preferably, the weight coefficients of the current foundation temperature, water content, and soil type are set to 0.4, 0.35, and 0.25, respectively, and the weight sum is 1, ensuring the rationality of the correction system. The specific numerical value of the correction factor is determined according to the deviation degree of the engineering measured parameter from the standard reference value. The foundation temperature correction factor is determined according to the degree of deviation of the foundation temperature from the -1.0℃ benchmark, with a value range of 0-0.8; the water content correction factor is determined according to the degree of deviation of the water content from the 20% benchmark, with a value range of 0-0.9; the soil type correction factor is determined according to the degree of deviation of the organic matter content and ice content from the benchmark value, with a value range of 0-0.8. The larger the correction factor value, the farther the parameter deviates from the benchmark value, and the greater the adjustment of the foundation stability rating is required. The term in the formula represents a correction coefficient, whose value range is usually 0.7-1.3, used to adjust the preliminary stability grade value.

[0058] The corrected value is converted to the final foundation bearing stability grade through the rounding operation, and then the corresponding reinforcement measure is determined according to the pre-set grade-measure mapping table. For example, when the calculated value is 4.2, it is rounded to grade 4, and the corresponding reinforcement measure may be a pipe pile composite foundation structure; when the value is 2.7, it is rounded to grade 3, and the corresponding reinforcement measure may be a mixing pile composite foundation structure.

[0059] Preferably, the setting principles of the foundation temperature correction factor are as follows: When the permafrost table temperature T > -0.5℃, = 0.8, to reduce the basic model discriminant level, and consider using enhanced measures with higher structural strength. When -1.0℃≤T≤-0.5℃, = 0.4, to moderately adjust the basic model discriminant result. When T < -1.0℃, = 0, the basic model discriminant result remains unchanged. When the ground temperature gradient is greater than 0.05℃ / m, regardless of the absolute value of the ground temperature, should consider = 0.6 to deal with the risk of rapid thermal degradation.

[0060] Preferably, the water content correction factor is set as follows: When the water content at the bottom of the active layer W > 30% or the unfrozen water content W' > 15%, = 0.9, to significantly reduce the basic model discriminant level. When 20% < W≤30% or 10% < W'≤15%, = 0.5, to moderately adjust the basic model discriminant result. When W≤20% and W'≤10%, = 0, the basic model discriminant result remains unchanged. During seasonal thawing, when the water content is monitored to increase by more than 5% in a short period of time (within 7 days), should temporarily set = 0.7 to deal with the sudden change in bearing capacity caused by melting water.

[0061] Preferably, the soil type correction factor is set as follows: When the soil layer has an organic matter content > 8% or an ice content > 25%, = 0.8, to significantly reduce the basic model discriminant level. When 5% < organic matter content ≤ 8% or 15% < ice content ≤ 25%, = 0.4, to moderately adjust the basic model discriminant result. When organic matter content ≤ 5% and ice content ≤ 15%, = 0, the basic model discriminant result remains unchanged. For special soil layers, such as high-salinity soil (salinity content > 0.5%) or high-sensitivity clay (sensitivity > 8), should set = 0.6 to deal with their special mechanical behavior.

[0062] Under the multi-parameter correction mechanism, the application rules of the hierarchical enhancement decision matrix are adjusted as follows: when When the value drops by more than 30%, the type of reinforcement measure is upgraded to one level, such as from material reinforcement measure to structural reinforcement measure; when 15%< When the value drops by ≤30%, a higher strength option should be selected among similar reinforcement measures, such as changing from shallow gravel filling to in-situ solidification reinforcement; When the value drops by ≤15%, the basic model judgment result remains unchanged, but the technical parameters can be fine-tuned, such as increasing the treatment depth or improving material properties.

[0063] In particular, special decision rules are set for the following typical composite working conditions: When the mean bearing capacity is moderate (50 kPa to 100 kPa), the extreme bearing capacity difference is large (>40 kPa), the bearing capacity decline ratio is moderate (20% to 40%), and the permafrost upper temperature limit is high (>-0.3°C) and the moisture content is high (>25%), pipe pile composite foundation structures are preferred, combined with water-proof cofferdam measures to form a comprehensive treatment plan. When the bearing capacity performance 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 high-level, at least material reinforcement measures should be adopted to prevent possible future thermal degradation risks. In cross-regional projects, when the ground temperature, moisture content, or soil properties of adjacent measuring points show significant differences (temperature difference >1°C, moisture content difference >10%, or completely different soil types), a transition section design should be adopted at the junction of the zones to mitigate differential deformation.

[0064] This multi-parameter coupled reinforcement measure selection model comprehensively considers the complex characteristics of permafrost foundations, ensuring the optimal match between reinforcement measures and actual foundation conditions, thereby improving project quality and long-term stability. This model continuously optimizes correction coefficients and weight parameters based on engineering practice data, forming an adaptive design system that provides a scientific basis for the treatment of highway foundations in permafrost regions.

[0065] like Figure 2 In a preferred embodiment, in step S130, the pile-raft integrated roadbed structure includes mixing piles 210 and raft slab 220. The mixing piles 210 are vertically positioned at the bottom, preferably using a dredging-free process, where a cementitious material is mixed with the in-situ soil to form a solidified body. The cementitious material comprises a temperature-stable, low-heat-of-hydration cement-based material. The raft slab 220 is horizontally positioned at the top, preferably formed using lean concrete through a rolling process, forming an integrated load-bearing system with the mixing piles 210. In this embodiment, the pile-raft-soil synergistic mechanism effectively distributes loads and improves the stress state of the foundation.

[0066] Specifically, the traditional process needs to drill holes and then pour concrete, which is complex and high in cost; the hole-free mixing pile 210 process of the embodiment of the application directly uses special mixing equipment to mix and solidify the temperature-stable low-hydraulic heat cement-based binding material and in-situ soil, to form a composite soil pile body with certain strength. The diameter of the mixing pile 210 is preferably 400 mm to 800 mm, the single pile length is not more than 10 m, and the pile body strength should reach more than 1.5 MPa.

[0067] Preferably, the temperature-stable low-hydraulic heat cement-based binding material used in the mixing pile 210 includes special low-heat Portland cement, fly ash, slag powder, water reducing agent and retarder, and the peak temperature of the hydraulic heat is 35℃ to 55℃ lower than that of ordinary Portland cement, the heat released in the hydraulic process is significantly reduced, and the thermal disturbance of a large amount of heat generated in the solidification process of traditional cement to the surrounding frozen soil is avoided. At the same time, the binding material can still maintain normal hydration reaction in a negative temperature environment, and the pile body formed after solidification has good freeze-thaw cycle resistance and durability.

[0068] In a preferred embodiment, the raft 220 structure in the embodiment is essentially different from the traditional cast-in-place concrete vibration and compaction process. Lean concrete refers to concrete with less cement and more aggregate, and the water-cement ratio is usually controlled between 0.35 and 0.40, and the cement content is about 220 kg / m³ to 280 kg / m³, which is significantly lower than the traditional 350 kg / m³ to 450 kg / m³. The thickness of the lean concrete raft 220 is generally 20 cm to 40 cm, which has the advantages of low hydration heat, small shrinkage deformation and simple construction.

[0069] Specifically, the rolling process refers to using a vibrating road roller or other equipment to compact the laid lean concrete, replacing the traditional vibration and compaction process with mechanical compaction. This process is fast in construction speed and can be operated continuously on a large area, significantly improving engineering efficiency. The rolling process is usually divided into 3 passes of rolling, and the compaction degree of each pass of rolling should reach more than 95% of the design requirement, to finally form a uniform and compact raft 220 structure.

[0070] In a preferred embodiment, the pile foundation arrangement of the pile-raft integrated roadbed structure should be optimized and designed according to the highway load characteristics and the foundation bearing capacity distribution. The raft 220 and the mixing pile 210 form an integrated stress system through structural connection, can effectively bear the highway traffic load, and uniformly disperse and transmit the load to the lower rigid pile, reduce the pressure on the permafrost layer, and prevent differential settlement of the roadbed.

[0071] Specifically, compared with the traditional structure, the pile-raft integrated roadbed structure provided by the embodiment of the present application realizes significant improvement in economy and applicability while maintaining the basic configuration through innovative material selection and construction process. The traditional method adopts hole guide pile pouring and cast-in-situ concrete, and the raft 220 also adopts ordinary concrete vibration compaction. Not only is the process complex and the construction period long, but also because the hydration heat of ordinary concrete is large, it will cause significant thermal disturbance to the surrounding permafrost and accelerate the degradation of permafrost. The process of the mixing pile 210 and the roller compacted lean concrete raft 220 provided by the embodiment of the present application effectively solves the above problems, and the engineering cost is reduced by more than 80%, and at the same time, it is more suitable for the special environmental conditions of permafrost regions.

[0072] As Figure 3 In a preferred embodiment, in step S130, the pipe pile composite foundation structure includes prefabricated pipe piles 310 arranged in the lower part and pile cap bearing platforms 320 arranged in the upper part, which optimizes the traditional pile foundation design, especially considering the thermal sensitivity and freeze-thaw cycle characteristics of permafrost, and forms a composite bearing system through shallow pile foundation support and soil cooperation.

[0073] In a preferred embodiment, the prefabricated pipe pile 310 is made of high-strength and 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 needs, but not more than 10 meters. The design concept of limiting pile length in this embodiment is different from the principle of deepening long piles into stable layers in traditional pile foundation engineering. The purpose is to reduce the dead load and avoid excessive pressure on deep permafrost, while reducing construction difficulty and engineering cost.

[0074] Specifically, the embedded spacing of the prefabricated pipe pile 310 is usually 1.5m-2.5m, forming a uniform support network. The prefabricated pipe pile 310 can be constructed by two main methods: one is static pressure implantation method, which directly presses the prefabricated pipe pile 310 into the foundation using a static pressure pile driver, which has small disturbance to the foundation and is suitable for relatively soft active layers; the other is hole guide implantation method, which first drills a guide hole in the permafrost with a diameter slightly smaller than the pipe pile, and then implants and hammers the pipe pile to the designed depth, which is suitable for relatively hard permafrost layers.

[0075] Preferably, when the bearing capacity degradation ratio of the foundation exceeds 80%, it indicates that the permafrost is seriously degraded, and additional structural reinforcement measures need to be taken.

[0076] In a preferred embodiment, when the bearing capacity degradation ratio of the foundation exceeds 80%, a concave-convex texture structure such as a spiral rib, an annular protrusion or a grid-shaped convex texture is further arranged on the outer surface of the prefabricated pipe pile 310. These concave-convex texture structures can significantly increase the contact area between the pile body and the surrounding soil, improve the interfacial shear strength, and effectively prevent the settlement and displacement of the pile body under the action of freeze-thaw cycles.

[0077] In a preferred embodiment, when the ground base shear strength C < 15 kPa and the internal friction angle φ < 10°, a sawtooth texture structure is adopted, the sawtooth height is set to 10-15 mm, the sawtooth angle is 45°, and the texture interval is 80-100 mm. Such a texture structure can provide the maximum uplift resistance in low-strength soil bodies, and the enhancement factor can reach 1.4-1.6.

[0078] In a preferred embodiment, when 15 kPa ≤ C < 25 kPa and 10° ≤ φ < 15°, a ring texture structure is adopted, the ring protrusion height is 8-12 mm, the ring interval is 120-150 mm, and the ring cross section is trapezoidal with a top width of 5 mm and a bottom width of 10 mm. Such a texture structure has the best performance in medium-strength soil bodies, and the enhancement factor is 1.3-1.5.

[0079] In a preferred embodiment, when C ≥ 25 kPa and φ ≥ 15°, a spiral texture structure is adopted, the spiral height is 6-10 mm, the spiral pitch is 180-220 mm, and the spiral angle is 30°. Such a texture structure provides stable shear resistance in high-strength soil bodies, and the enhancement factor is 1.2-1.4.

[0080] Specifically, the material of the texture structure should be consistent with the main body of the prefabricated pipe pile 310, and high-strength C40 or above concrete is usually used, and the texture surface roughness Ra is controlled within the range of 0.8-1.2 mm to increase the friction coefficient. The optimized configuration of the concave-convex texture structure can increase the pile-soil interface strength by 20%-35% in heat-sensitive areas, significantly prolonging the service life of the project.

[0081] In a preferred embodiment, when the bearing capacity degradation ratio of the foundation exceeds 80%, the inner cavity of the prefabricated pipe pile 310 can be selectively filled with a phase change cold storage material with low thermal conductivity. The selection of the phase change material should meet the following conditions: the phase change temperature is between -5℃ and 0℃, the thermal conductivity is less than 0.3 W / (m·K), and the phase change latent heat is greater than 180 kJ / kg. This material absorbs heat and changes phase when the temperature rises, and releases heat and restores the original phase when the temperature drops, thereby achieving a passive cold storage temperature regulation function, effectively slowing down the conduction of external heat to permafrost, and delaying the permafrost degradation process. Preferably, the phase change cold storage material can be selected from a water-glycol mixture, an alkane material, or a salt solution.

[0082] In a preferred embodiment, when the permafrost upper limit temperature T > -0.5℃, a material with a phase change temperature of -1℃ to -0.5℃ is selected, such as a 12%-15% glycol water solution; the filling thickness is preferably not less than 70% of the inner diameter of the pipe pile, ensuring sufficient heat buffering capacity. Such a configuration is suitable for high-temperature permafrost areas close to the phase change point, and can provide the maximum phase change cooling effect.

[0083] In a preferred embodiment, when -1.0℃≤T≤-0.5℃, a material with a phase transition temperature of -2℃ to -1.5℃ is selected, such as a 18%-22% mass fraction of ethylene glycol aqueous solution or n-tetradecane; the filling thickness is preferably not less than 60% of the inner diameter of the pipe pile, providing moderate thermal stability. Such configuration is suitable for medium temperature permafrost regions, balancing thermal stability and cost effectiveness.

[0084] In a preferred embodiment, when T<-1.0℃, a material with a phase transition temperature of -3℃ to -2.5℃ is selected, such as a 25%-28% mass fraction of ethylene glycol aqueous solution or n-dodecane; the filling thickness is preferably not less than 50% of the inner diameter of the pipe pile, providing basic thermal stability support. Such configuration is suitable for low temperature stable permafrost regions, as a preventive measure to delay thermal degradation.

[0085] In a preferred embodiment, to improve the performance stability of the phase change material, 3%-5% of nano-sized graphite or carbon fiber can be added to enhance thermal conductivity, 0.5%-1% of nucleating agent can be added to reduce the supercooling phenomenon of phase change, and 0.1%-0.3% of antioxidant can be added to extend the service life. The phase change material should be filled in a sealed manner, with 5%-8% expansion space reserved, and the inner wall coated with an epoxy resin anticorrosive layer with a thickness of 0.8-1.2mm.

[0086] Through the optimization of the above concave-convex texture structure and phase change cold storage material, the adaptability and stability of the prefabricated pipe pile 310 in permafrost regions can be significantly improved, and long-term stable support can be achieved for high thermal sensitivity foundation, so as to effectively cope with the engineering risks caused by climate change.

[0087] Preferably, a pile cap bearing platform 320 is provided at the top of the pipe pile, and the pile cap is preferably installed by site pouring or prefabrication. A gravel cushion layer with a thickness of 30cm~50cm is provided between and on the pile caps, and the gravel material should be selected with a frost heaving rate less than 1%, good gradation, and a gravel content of not less than 60% with a particle size greater than 5mm, to ensure good drainage and stability.

[0088] Preferably, a plurality of geogrids 330 are embedded in the gravel cushion layer for reinforcement, and the tensile strength of the geogrid 330 is not less than 20kN / m, and the grid size is 25mm×25mm. The geogrid 330 functions to limit the lateral displacement of the gravel material, increase the overall stiffness and bearing capacity of the cushion layer, and improve the distribution state of the load, reducing local stress concentration.

[0089] Specifically, the overall working mechanism of the tubular pile composite foundation is to bear the upper load through the pile-soil interaction. When the roadbed bears the traffic load, the load is reasonably distributed to the prefabricated tubular pile 310 and the surrounding soil through the sand gravel cushion enhanced by the pile cap bearing platform 320 and the geogrid 330. The prefabricated tubular pile 310 bears 70% to 80% of the load, and the rest is borne by the soil. This load sharing mechanism avoids the unreasonable state that the pile body bears all the load in the traditional pile foundation structure, and is especially suitable for the special geological conditions in the permafrost region.

[0090] Compared with the traditional pile foundation structure, the tubular pile composite foundation structure of the present application has the following significant advantages: first, the pile length is controlled within 10 meters, reducing the disturbance to deep permafrost; second, the concave-convex texture structure is arranged on the outer surface of the pile and the inner cavity is filled with phase change material, realizing the dual functions of structure bearing and thermal stability; third, a composite bearing system is formed through the sand gravel cushion enhanced by the pile cap and the geogrid 330, improving the overall bearing performance and uniformity. These innovations work together to effectively solve the problem of differential settlement caused by permafrost degradation in the permafrost region, significantly improving the long-term stability and durability of the project.

[0091] In a preferred embodiment, in step S130, the agitated pile composite foundation structure includes an agitated pile placed in the lower part and a sand gravel cushion pad arranged in the upper part. This structure effectively improves the bearing characteristics of the foundation by constructing a composite bearing system in the shallow foundation, while minimizing the thermal disturbance to the permafrost layer.

[0092] Preferably, the agitated pile adopts a hole-free drilling process, and the agitated pile is formed by agitating the temperature-stable low-hydraulic heat cement-based binder material with the in-situ soil to form a solidified body; preferably, the temperature-stable low-hydraulic heat cement-based binder material includes special low-heat Portland cement, active admixture, water reducing agent, retarder and other additives, and the water-cement ratio is controlled between 0.45 and 0.55. The maximum temperature rise in the hydration process of this binder material does not exceed 25℃, which is significantly lower than the 60℃ to 80℃ of ordinary Portland cement, effectively reducing the thermal disturbance to the surrounding permafrost during construction.

[0093] Preferably, the sand gravel cushion pad arranged on the upper part of the agitated pile is an important component of the agitated pile composite foundation structure. The thickness of the sand gravel cushion pad is usually 30cm to 50cm, and sand gravel materials with good gradation and frost heaving rate less than 1% should be selected, among which the content of gravel with particle size greater than 2mm should account for 60% to 80%, and the fine particle content should not exceed 5%, to ensure good drainage and stability.

[0094] Preferably, the sand-gravel cushion layer is laid with geogrids for load dispersion and uniform transmission. The geogrids are made of biaxial tensile plastic or glass fiber, with tensile strength not less than 20 kN / m and ultimate elongation not more than 3%, and the grid size is 25 mm x 25 mm. The geogrids are usually arranged in 1 to 3 layers in the sand-gravel cushion layer, with the first layer located at the bottom of the cushion layer, 10 cm away from the top surface of the mixing pile; if there are multiple layers, the distance between layers is not less than 20 cm.

[0095] In this embodiment, the working mechanism of the mixing pile composite foundation is to bear the upper load through the pile-soil-cushion system. When the subgrade bears the traffic load, the load is first transmitted to the sand-gravel cushion layer, and the presence of the geogrids makes the load more evenly distributed, then part of the load is transmitted to the deeper soil layer through the mixing pile, and part of the load is borne by the soil between the piles.

[0096] Compared with traditional foundation treatment methods, the mixing pile composite foundation structure has the following significant advantages: first, the construction process has little disturbance to the original foundation, reducing the thermal impact on permafrost; second, low-water-heat cementitious materials are used, further reducing the heat input during construction; third, through the pile-soil collaborative working mechanism, the load is reasonably shared, avoiding local stress concentration; fourth, the sand-gravel cushion layer reinforced by geogrids has good drainage performance, reducing the impact of water on permafrost; fifth, the overall system design fully considers the particularity of permafrost, achieving the dual goals of improving the bearing capacity of the foundation and protecting permafrost.

[0097] In a preferred embodiment, to further improve the applicability of the mixing pile composite foundation structure in permafrost regions, the configuration of the mixing pile can be optimized according to specific engineering conditions. When the subgrade bearing capacity is poor and the bearing capacity deterioration ratio is large, the number of mixing piles in areas with smaller pile spacing can be appropriately increased; when the bearing capacity deterioration ratio is close to 50%, an expansion agent of 0.5% to 1.5% can be added to the cementitious material to compensate for the possible settlement caused by the thawing of frozen soil; when there is a significant seasonal thawing layer in the subgrade, the top of the mixing pile can be extended 10 cm to 15 cm above the layer to cut off the heat conduction path.

[0098] As Figure 4 In a preferred embodiment, in step S130, the block stone dynamic compaction replacement composite foundation structure comprehensively uses the principles of block stone replacement and dynamic compaction for foundation treatment, significantly improving the bearing characteristics of the shallow foundation through the triple action of replacement, compaction, and impact consolidation.

[0099] In a preferred embodiment, the ramming energy level of the block stone dynamic compaction composite foundation structure is designed according to the depth of the permafrost table. When the depth of the permafrost table is 1.5m-2.5m, the ramming energy level is preferably 800kN·m-1200kN·m; when the depth of the permafrost table is 2.5m-4.0m, the ramming energy level is preferably 1200kN·m-2000kN·m. The reasonable selection of the ramming energy level ensures that the ramming energy can be effectively transmitted to the bottom of the active layer, while only producing a controlled impact on the permafrost layer, avoiding excessive impact that can damage the structure of the permafrost.

[0100] In a preferred embodiment, the construction window period and the hole drilling process are determined based on the freezing strength and freezing depth of the active layer, and are preferably performed when the freezing strength of the active layer reaches 0.8MPa-1.2MPa and the freezing depth reaches 60%-80% of the thickness of the active layer. This time window usually occurs from November to February of the following year in winter, when the active layer has formed a certain strength of frozen body and can withstand the impact load of dynamic compaction, while the temperature of the frozen soil layer has not reached the minimum value, leaving a certain deformation capacity, which is beneficial to the exertion of the compaction effect.

[0101] In a preferred embodiment, the hole drilling process is a key process of the block stone dynamic compaction composite foundation structure. The hole diameter is usually 0.8m-1.2m, and the depth is at least 80% of the thickness of the active layer. The hole can be drilled by mechanical drilling or hot melting method, and mechanical drilling method is preferred in permafrost regions to reduce thermal disturbance. After the hole is completed, the block stone material should be backfilled immediately to form a dynamic compaction block stone pier 410 to prevent the collapse of the hole wall or the infiltration of underground water. Preferably, a crushed stone leveling layer 420 is also provided above the dynamic compaction block stone pier.

[0102] In a preferred embodiment, the termination criterion of dynamic compaction is set as the cumulative settlement deformation reaching the value of the depth of the permafrost table. This criterion fully considers the particularity of the foundation in the permafrost region. When the cumulative settlement approaches or reaches the value of the depth of the permafrost table, it indicates that the active layer soil has been fully compacted, while the permafrost layer has not been significantly disturbed. At this time, dynamic compaction should be stopped to avoid excessive impact on the deep permafrost layer.

[0103] Specifically, the bearing capacity of the foundation treated by the block stone dynamic compaction composite foundation structure can be improved by 50%-80%, and the compression modulus can be improved by 60%-90%, significantly improving the engineering properties of the shallow foundation in the permafrost region. At the same time, since this technology mainly targets the active layer, the disturbance to the permafrost layer is relatively small, maintaining the stability of the permafrost, and is a foundation treatment method that takes into account both engineering benefits and ecological protection.

[0104] In a preferred embodiment, in step S130, the shallow replacement of sand and gravel directly improves the bearing capacity and stability of the foundation by replacing the original low-bearing-capacity, high-frost-heaving soft soil layer with sand and gravel materials with good engineering performance. The construction includes: excavating the shallow soft soil layer and replacing it with sand and gravel materials that meet the engineering grading requirements, and the treatment thickness is not less than 2m, preferably 2.5m~3.5m; the replacement width should exceed the roadbed edge by 1.5m~2.5m.

[0105] In a preferred embodiment, in step S130, in-situ solidification and reinforcement is particularly suitable for areas with fine soil and difficult sand and gravel acquisition; this method improves the strength and stability of the original foundation soil by adding a specific solidification agent without changing the soil structure.

[0106] Preferably, the solidification agent used for in-situ solidification and reinforcement mainly includes: inorganic cementitious materials such as cement, lime, fly ash, and silicates, and organic stabilizers such as polymers and resins. In permafrost regions, low-heat cement and fly ash composite solidification agent is preferred, and the solidification agent content is usually 5%~10% of the soil weight, and the specific ratio should be determined through laboratory tests. The selection of solidification agent should consider its activity, hydration heat and compatibility with the original soil in low temperature environment.

[0107] In a preferred embodiment, the construction of in-situ solidification and reinforcement can adopt factory mixing or road mixing. Among them, the factory mixing method is to transport the excavated original soil to the mixing station, mix it with the solidification agent, and then transport it back to the site for backfilling; the road mixing method is to directly mix the solidification agent with the original soil on site through special equipment. Considering the particularity of permafrost, the factory mixing method is preferred to more accurately control the mixing quality and solidification agent content.

[0108] 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%.

[0109] As Figure 5 In a preferred embodiment, in step S130, the main purpose of the water-blocking cofferdam is to block the erosion and thermal disturbance of surface water and groundwater to the roadbed. Preferably, its construction measures specifically include: directly placing steel sheet piles 510 at the roadbed toe, or using mixing piles to form a water-blocking curtain.

[0110] When using the steel sheet pile 510 scheme, the length of the steel sheet pile 510 is preferably 4m~6m, the thickness of the sheet pile is 8mm~12mm, the material is selected from low-temperature resistant steel, and the surface should be treated for corrosion prevention; the steel sheet pile 510 is placed underground by vibration pile sinking machine or static pressure pile sinking equipment, the pile top is 20cm~30cm above ground, and the inter-pile connection or lap joint method is used to ensure the waterproof effect.

[0111] When the mixing pile is used to form the waterproof curtain, the diameter of the mixing pile is 500mm-800mm, the pile spacing is not greater than 40cm, and the mixing pile is arranged in a single row or a double row; the permeability coefficient of the mixing pile curtain should be less than 1x10 -7 cm / s, to ensure good waterproof effect; the top of the curtain is usually flush with the ground or slightly higher, and the bottom should enter the permafrost layer by more than 1.5m to form a complete impermeable barrier, effectively blocking the seepage of water to the roadbed and protecting the thermal stability of the permafrost.

[0112] Compared with the prior art, the deep high-temperature permafrost area highway foundation bearing capacity enhancement method provided by the above embodiment considers the frozen soil-roadbed as a unified engineering system as a whole, and effectively enhances the bearing capacity and stability of the highway foundation in the permafrost area through the technical route of accurate identification-directional design-comprehensive treatment.

[0113] Firstly, the embodiment of the present application breaks through the limitation of insufficient consideration of the characteristics of permafrost in traditional foundation treatment, and establishes an accurate identification system based on three-dimensional parameters of bearing capacity mean value, bearing capacity range and bearing capacity decay ratio, realizing scientific evaluation of the engineering characteristics of frozen soil foundation; secondly, the embodiment of the present application selects the most suitable enhancement measures according to different frozen soil foundation characteristics, including pipe pile composite foundation, mixing pile composite foundation, block stone dynamic compaction replacement, shallow replacement with sand and gravel, in-situ solidification enhancement and water retaining cofferdam, avoiding the one-size-fits-all drawbacks of traditional treatment methods; thirdly, the present application fully considers the thermal sensitivity and dynamic change characteristics of permafrost, and each treatment scheme emphasizes the protection of the thermal stability of permafrost, such as using low-heat materials, controlling the treatment depth, optimizing the construction time window, etc., which fundamentally solves the problem of frozen soil degradation caused by thermal disturbance in traditional technology; finally, the method of the present application is economical and applicable, fully considering the construction conditions and material availability in extremely cold regions, reducing the engineering cost and improving the construction efficiency, providing systematic technical support and solutions for highway construction in deep high-temperature permafrost areas.

[0114] Those skilled in the art will understand that, except for mutual exclusivity between features, all features disclosed in this specification (including the claims, abstract and drawings accompanying it) and all processes or units of any method or apparatus disclosed thus can be combined in any combination. Unless explicitly stated otherwise, each feature disclosed in this specification (including the claims, abstract and drawings accompanying it) can be replaced by an alternative feature providing the same, equivalent or similar purpose.

Claims

1. A method for enhancing the bearing capacity of highway foundation in deep high-temperature permafrost areas, characterized in that: include: Testing the bearing capacity of permafrost foundations by static penetration testing to obtain spatial distribution characteristics of the original foundation bearing capacity, wherein the spatial distribution characteristics of the original foundation bearing capacity include at least the bearing capacity mean, the bearing capacity range, and the bearing capacity decay ratio; Establishing 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, and according to the spatial distribution characteristics of the original foundation bearing capacity obtained through detection, a shallow foundation reinforcement method is determined, wherein 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 at least include constructing a composite load-bearing structure system in the shallow foundation, thereby improving the mechanical properties of the entire foundation by enhancing the load-bearing capacity of a local area of ​​the foundation.

2. The method according to claim 1, characterized in that The construction of the mapping model includes: According to a preset foundation bearing capacity evaluation standard, the bearing capacity mean, the bearing capacity range, and the bearing capacity decay ratio are divided into at least two evaluation intervals using a limit value method; determining a bearing stability grade of the foundation according to a combination of the bearing capacity mean, the bearing capacity range, and the bearing capacity decay ratio in respective evaluation intervals; A mapping relationship between the bearing stability grade and different shallow foundation reinforcement methods is established to form a graded reinforcement decision matrix to guide the selection of reinforcement measures for foundations with different bearing stability grades.

3. The method according to claim 2, characterized in that The hierarchical enhancement decision matrix is ​​configured as follows: When the bearing stability level is low, the 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, the material reinforcement measures are applied to improve the foundation material properties to enhance the foundation shear strength and stability; When the bearing stability level is high and hydrothermal sensitivity exists, the hydrological regulation enhancement measures are applied to adjust the hydrothermal state of the foundation to maintain the stability of permafrost.

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

5. The method according to claim 3, characterized in that The structural reinforcement measures include a pile-raft integrated roadbed structure, which includes mixing piles arranged at the bottom and a raft plate arranged at the top: The mixing pile adopts a hole-free process to form a solidified body by mixing a cementitious material with an in-situ soil body. The cementitious material includes a temperature-stable cement-based material with low hydration heat. The raft slab is formed by using lean concrete through a rolling process, and forms an integral force-bearing system with the mixing pile structure.

6. The method according to claim 3, characterized in that The structural reinforcement measures include a pipe pile composite foundation structure, which includes prefabricated pipe piles arranged at the bottom and a pile cap bearing platform arranged at the top: The prefabricated pipe piles are constructed by static pressure implantation or hole implantation, and the length of the prefabricated pipe piles is not more than 10 meters; A geogrid-reinforced gravel cushion is provided between and above the pile cap bearing platforms.

7. The method according to claim 6, characterized in that When the bearing capacity decay ratio is greater than 80%, the prefabricated pipe piles shall be strengthened with the following structural measures: The outer surface of the prefabricated pipe pile is provided with a concave-convex texture structure to enhance the shear strength of the pile-soil interface; And / or, the inner cavity of the prefabricated pipe pile is filled with a phase-changing 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 heating rate of deep permafrost.

8. The method according to claim 3, 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 hole-free process, and the mixing pile adopts a temperature-stable low-hydration hot cement-based gelling material and is mixed with the in-situ soil to form a solidified body; The gravel cushion layer is covered with geogrids for load dispersion and balanced transfer.

9. The method according to claim 3, characterized in that The material-based reinforcement measures include a stone compaction replacement composite foundation structure, wherein: The dynamic compaction energy level is determined based on the upper limit of permafrost burial depth to achieve a controlled impact on deep permafrost; The construction window period and drilling technology are determined based on the freezing intensity and freezing depth parameters of the active layer; The termination criterion for dynamic compaction is set when the accumulated settlement deformation reaches the upper limit of the burial depth of permafrost.

10. The method according to claim 3, characterized in that The material reinforcement measures include shallow gravel replacement, specifically including: Excavate the shallow soft soil layer and replace it with sand and gravel materials that meet the engineering grading requirements, and the treatment thickness shall not be less than 2m.

11. The method according to claim 3, characterized in that The material type reinforcement measures include in-situ curing reinforcement, specifically including: Add curing agent to the original foundation soil by factory mixing or road mixing, and 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 after 10 freeze-thaw cycles at -20°C <10%, mass loss rate <5%, and water stability coefficient >80%.

12. The method according to claim 3, characterized in that The hydrological regulation enhancement measures include water-blocking cofferdams, specifically: Steel sheet piles are placed at the foot of the roadbed slope, or mixing piles are used to form a water-blocking curtain.

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