岩土工程技术

2024, 38(5): 1-1.

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2024, 38(5): 1-3.

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Development Progress and Prospects of Foundation Pit and Slope Engineering Under Carbon Peaking and Carbon Neutrality Policy

Li Jianguang, Liu Rongyi, Liu Qingqing, Yan Liming

2024, 38(5): 505-511. doi: 10.3969/j.issn.1007-2993.2024.05.001

[Abstract](123) [FullText HTML] (21) [PDF 491KB](34)

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With the implementation of the carbon peaking and carbon neutrality policy, low-carbon strategies and sustainable development in the field of construction engineering have become particularly important. With the continuous development and application of the Internet of Things, artificial intelligence, BIM technology, and green materials, new sustainable development directions such as digitization, intelligence, and low-carbon have emerged in foundation pit and slope engineering. Typical cases of foundation pit and slope engineering in China in recent years were introduced, and new technologies, new processes, new equipment for green and low-carbon support and monitoring were summarized, as well as new progress in carbon emission calculation. Prospects for the new trends in the future development of foundation pit and slope engineering under the caron peaking and cabon neutrality policy were proposed.

Analysis Conversion Method of Self-balanced Test Pile and Engineering Application

Yang Di, Bai Lu, Sang Runhui, Jiang Jie

2024, 38(5): 512-518. doi: 10.3969/j.issn.1007-2993.2024.05.002

[Abstract](46) [FullText HTML] (8) [PDF 1192KB](10)

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An analytical conversion method for self-balanced test of foundation pile was proposed. The finite difference method was used to establish the control equations for each micro-section of the upper and lower piles, and the internal forces and displacements at each micro-section of the upper and lower piles can be obtained by programmed solution, which can be substituted into the exact conversion formula to convert the self-balanced test pile results into the form of the load (Q) - displacement (s) curves similar to those of the traditional static test and to solve the ultimate bearing capacity. This analytical conversion method was applied to convert the test results in conjunction with the test project of self-balanced method for three drilled piles in Yuda Wutong Court, Laibin, Guangxi. The internal forces of the three test piles all show that the soil layer closer to the loading end bears a larger load, the axial force gradually decreases from the loading end to both ends, and the change characteristics of the lateral resistances show a hyperbolic distribution. In terms of single pile bearing capacity, the simplified conversion method is conservative, while the analytical conversion method takes into account the differences in the characteristics of the soil layers on the pile side, and the accuracy can be improved by about 12% compared to the simplified conversion method. The analytical conversion method can accurately reflect the distribution law of internal force of upper and lower pile body and the bearing characteristics of soil layer on the pile side, and can efficiently and accurately realize the conversion of bearing capacity, which is widely used in the field of self-balanced test engineering of pile foundation bearing capacity.

Stability Analysis of a New Prefabricated Block Gravity Retaining Wall

Lin Zhiguo, Li Wei

2024, 38(5): 519-526. doi: 10.3969/j.issn.1007-2993.2024.05.003

[Abstract](52) [FullText HTML] (13) [PDF 2251KB](13)

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A new type of prefabricated block gravity retaining wall was proposed, which was mainly composed of cast-in-place concrete base, precast block unit, reserved grouting hole, post-insertion steel bar and cast-in-place pressure top beam, etc., and was designed from the aspects of wall precast block, interblock connection, foundation form, etc. The local stability of the new prefabricated block gravity retaining wall under earth pressure was analyzed by the finite element method, and the force failure mode, displacement characteristics and stress distribution characteristics of retaining walls with different sizes were obtained. It was concluded that the weak points of the failure of the retaining wall were located between the base and the first layer assembly. According to the finite element numerical simulation results, combined with the classical retaining wall stability calculation theory, the calculation method and process of prefabricated block gravity retaining wall stability analysis were proposed, and the rationality of the calculation method and process was verified by engineering examples.

Road Automation Monitoring System Based on Deep Learning: an Application Research

Liu Shiwei, Wang Rong, Zhang Tonghu, Wu Huiguo

2024, 38(5): 527-532. doi: 10.3969/j.issn.1007-2993.2024.05.004

[Abstract](38) [FullText HTML] (10) [PDF 1078KB](6)

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Traditional monitoring methods are inefficient and cannot predict soil deformation in real-time and continuously with accuracy in road construction. A road automation monitoring system integrated with artificial intelligence technology was proposed. The system consists of a real-time Internet of Things (IoT) system and a data processing system. The real-time IoT system includes embedded settlement instruments with dual pressure sensors, a data acquisition system, and a network transmission system. The data processing system utilizes deep learning algorithms to train the measured data to predict soil deformation. The composition and working principles of the monitoring system was introduced. The system was validated through on-site experiments. By comparing the data from the dual pressure sensors in the embedded settlement instruments with the data from settlement plates, the results show that the error between the two is only 6.7%. This indicated that the automated monitoring instrument has high precision in road construction monitoring. On-site experimental results also prove that the deformation prediction method based on deep learning algorithms can accurately predict soil deformation during the road construction process, with a maximum prediction error of only 5.3%.

Function Assessment Method for Underground Pipe Trench of Ancient Architectural Drainage System in the Forbidden City

Zhao Shuqiang, Cao Pulin, Hu Xinrui, Jia Ziheng

2024, 38(5): 533-538. doi: 10.3969/j.issn.1007-2993.2024.05.005

[Abstract](36) [FullText HTML] (12) [PDF 1193KB](5)

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The underground pipe trench of ancient architectural drainage system is an important component of ancient buildings, and its function degradation is common after a long historical process. Before taking protective measures, it is necessary to conduct a functional assessment of the pipe trench. Taking the underground pipe trench of the drainage system of the Forbidden City as an example, a unit scoring method and a section method for the assessment of the pipe trench were proposed, and the specific implementation of the methods was given. The characteristics of the two methods in terms of data collection, analysis and assessment, and adaptability were compared. This provides a reference for the practice and research of the assessment of the underground pipe trench of ancient architectural drainage system.

Instability Evolution of Single Fracture with Different Dip Angles on Heterogeneous Rock

Wang Tingjing

2024, 38(5): 539-547. doi: 10.3969/j.issn.1007-2993.2024.05.006

[Abstract](41) [FullText HTML] (13) [PDF 4269KB](9)

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Fractures in rock mass have a significant influence on the mechanical behavior, energy evolution and instability failure of rock. To clarify the rock energy evolution and instability failure mechanism of single fracture with different dip angles, based on the particle flow PFC2D method, a numerical model of sandy mudstone with single fracture with different dip angles was established, and the uniaxial compression test of sandy mudstone with single fracture with different dip angles was simulated. The results show that with the increase of single fracture dip angle, the strength and elastic modulus of sandy mudstone decrease first and then increase, and the prefabricated crack will affect the crack initiation position of the fracture surface and accelerate the formation of the fracture surface. The acoustic emission event has a small range of quiet period before the rock sample is destroyed, which can be used as a precursory criterion for rock failure. With the increase of fracture dip angle, the total energy continues to increase, and the elastic energy and dissipation energy show a trend of increasing first and then decreasing. When the dip angle is 30°, the rock sample has the weakest impact tendency, which is beneficial to reduce the risk of rock burst. When the dip angle is 90°, the rock sample has the strongest impact tendency, which is not conducive to the prevention and control of rock burst.

Numerical Analysis on Group Pile Effect of Pressure Grouted Helical Pile Group

Fan Yimin, Zong Zhongling, Huang Yunhan, Zhuang Xiaoxuan

2024, 38(5): 548-553. doi: 10.3969/j.issn.1007-2993.2024.05.007

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Helix Stiffened Cement Mixing Pile (HSCMP) is a new type of composite pile, and its group pile effect and bearing capacity variation law is still unclear. Based on the finite element numerical simulation method, the ratio of HSCMP pile spacing to helix diameter (S_g/D_H) and the ratio of cement soil strength to soil strength around the pile (C_ref/S_u) were parametrically analyzed and the results were compared with the theoretical calculation of the group pile effect coefficient. The results show that the group pile bearing capacity is positively correlated with soil strength and pile spacing when the helix diameter and soil properties are kept constant; when S_g/D_H≤2, the existing theoretical calculation results are similar to the numerical simulation results, and the numerical simulation results are more consistent with the stress superposition method as S_g/D_H increases; when S_g/D_H≤2, the stress superposition effect of soil between piles is significant, which is easy to lead to the damage of the interface of helical pile core-cement soil column, but when C_ref/S_u≥40, the damage mode will not be changed again, and it is shown as the damage of the interface of cement soil column-soil.

Shear Strength Index Reduction Method Based on Water Content Change in Design and Calculation of Foundation Supporting in Expansive Soil

Li Lingfeng, Wang Qinyuan, Wang Junyang

2024, 38(5): 554-559. doi: 10.3969/j.issn.1007-2993.2024.05.008

[Abstract](39) [FullText HTML] (10) [PDF 2469KB](11)

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Based on the laboratory test of expansive soil, the quantitative relationship between water content and shear strength index was statistically analyzed. Research shows that the shear strength index gradually decreases with the increase of water content. Compared with the internal friction angle φ, the cohesive force c is more sensitive to changes in water content. For each 5% increase in water content, cohesion c decreases by 7.5 kPa and internal friction angle φ 3° lower. On this basis, a shear strength index reduction method based on changes in water content was proposed for the design and calculation of expansive soil foundation pit support. The applicability of this method in the design of expansive soil foundation pit support was verified through engineering case calculations and on-site monitoring.

Influence of Double Track Shield Tunnel Overpassing Construction on Existing Subways Based on HSS Model

Li Wenqian, Huang Gaoliang, Zhu Xiaoang, Liu Minghong, Chen Yuchao, Hu Anfeng

2024, 38(5): 560-565. doi: 10.3969/j.issn.1007-2993.2024.05.009

[Abstract](32) [FullText HTML] (12) [PDF 1713KB](7)

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A three-dimensional finite element model was established based on the HSS constitutive model for a newly constructed shield tunnel adjacent to an existing subway project. The correctness of the numerical calculation was verified by comparing it with measured data. On this basis, further analysis was conducted on the vertical deformation characteristics of existing tunnels caused by the construction of new tunnels, as well as the influence of the two parameters of tunnel horizontal clearance and overlap angle on the deformation of existing tunnels. The results show that the calculated results of HSS model are in good agreement with the measured values, and can effectively predict the deformation of existing subway tunnel. Under the influence of the new tunnel overpassing, the existing subway tunnel has vertical uplift deformation, and the deformation mainly occurs in the range of 1.5 times the diameter of the new tunnel before the shield tunneling under-crossing to 2 times the diameter of the new tunnel after the crossing. The uplift peak point of the existing subway tunnel will shift with the second crossing of the shield, and its vertical deformation curve shows a "double peak" trend. Increasing the horizontal clearance of double track tunnels and the overlapping angle of new and old tunnels can reduce the deformation of existing tunnels.

Bearing Capacity and Deformation Characteristics of Dense Medium Sand Layer of Weihe First-order Terrace

Wang Fuhui, Xu Zhangjian, Wang Yonggang, Sun Wei, Zhao Zhihai, Yan Jianlong

2024, 38(5): 566-571. doi: 10.3969/j.issn.1007-2993.2024.05.010

[Abstract](48) [FullText HTML] (12) [PDF 1165KB](9)

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Based on a project in the Weihe first-order terrace in Xi'an, the bearing capacity and deformation characteristics of the dense sand layer foundation were studied through field tests and numerical simulations to determine whether natural foundations for high-rise buildings of nearly 100 meters can be built in similar sites. The results show that: the P-s curve of the load test of the dense sand layer in the Weihe first-order terrace is gently variable, the characteristic value of the bearing capacity of the foundation can be 600 kPa, and the deformation modulus can be 40 MPa. The empirical coefficient Ψ_S can be taken as 0.2 for the calculation of foundation settlement by the sum-of-layers method for similar projects in the Weihe first-order terrace. When the geological conditions are similar, it is feasible to use natural foundations for the construction of high-rise buildings of nearly 100 meters. The results can provide a reference for the adoption of natural foundations for high-rise buildings on the Weihe first-order terrace, and also provide empirical parameters for deformation calculations on similar sites.

Field Measurement Study of Hydraulic Gradient in Flood Control Area of Wuhan Area

Quan Wei, Chen Lyu, Xiong Zonghai, Zhu Pudong

2024, 38(5): 572-576. doi: 10.3969/j.issn.1007-2993.2024.05.011

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According to “Technical Code for Building Foundation” （DB 42/242—2014）, the recommended slope of confined water head in the flood control area of Wuhan is 0.5%～0.8%, from which the anti-floating water level in the flood control area and the confined water head of foundation pit dewatering can be approximately deduced. However, since 2003, due to the substantial shortening of the supply time on both sides of the Yangtze River and the large-scale foundation pit dewatering in urban construction, the corresponding hydraulic gradient in the flood control area has also changed greatly. Combined with the water level observation and statistical data of 40 projects in the flood control area, there is a large deviation between the measured hydraulic gradient in the control area and the recommended value of the code, and there is a non-linear attenuation relationship with the water level of the Yangtze River and the distance of the project. Through data analysis, the curve equations of peak hydraulic gradient in high water period, average hydraulic gradient in high water period and average hydraulic gradient in low water period were derived and verified by the project. The conclusion can provide reference for the revision of the code, and provide support for the selection of anti-floating water level in flood control area and dewatering of foundation pit engineering.

Cause Analysis and Comprehensive Treatment of Back Mountain Landslide Slope of Bailian Temple in Ningde

Huang Chaoyang

2024, 38(5): 577-583. doi: 10.3969/j.issn.1007-2993.2024.05.012

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The back mountain landslide of Bailian Temple in Ningde is a medium-sized traction type soil landslide, which is a typical landslide caused by unreasonable excavation at the foot of the slope and heavy rainfall. According to the survey results, the arc method and finite element method were used to analyze the stability of the landslide. The analysis results show that the landslide is basically stable under general conditions, and unstable - understable under rainstorm conditions. The landslide treatment adopts comprehensive measures such as slope cutting and unloading, anchor frame beams, vegetation protection, anti-slip piles, retaining walls, and setting up interception and drainage ditches. The treatment effect is good and can provide reference for similar landslide projects.

Numerical Simulation and Laboratory Tests of Unloading Stress Path of Fly Ash Stratum Tunnel Excavation

Li Lin, Xie Jinhong, Yang Shangchuan

2024, 38(5): 584-591. doi: 10.3969/j.issn.1007-2993.2024.05.013

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The stress path of soil is closely tied to deformation during dynamic tunnel excavation. A three-dimensional model of tunnel construction was created using the FLAC3D finite difference software. The double-side wall guide pit method was used to simulate the excavation process of a large-section tunnel and measure the resulting soil stress state. The changing laws of the stress state were then investigated based on the numerical simulation results. Indoor triaxial tests were conducted on soil reinforced with fly ash cement under different stress paths to replicate the stress and deformation of soil units during tunnel excavation and unloading. Unreinforced soil specimens were used as a control group. The numerical simulations and laboratory test results reveal that the stress paths of the surrounding rock unit soil at monitoring points are complex, and can be roughly divided into two categories: the process of constant confining pressure unloading axial pressure and constant confining pressure rising axial pressure. The cement-reinforced specimens showed less deformation and no signs of failure, while the unreinforced specimens were damaged during the stress path tests of different soil positions within the simulated surrounding rock unit.

Influence of Loading Conditions and Particle Size on Stick-Slip Characteristics of Granular Materials

Ou Fanyi, Fei Jianbo, Ma Weibin, Chen Xiangsheng

2024, 38(5): 592-597. doi: 10.3969/j.issn.1007-2993.2024.05.014

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Combining the common bonding slip phenomena in natural faults with the characteristics of granular materials, indoor direct shear tests and discrete element numerical analysis using glass bead particles were conducted. By changing the normal stress, shear rate, and particle size, the influence of loading conditions and particle size on the stick-slip characteristics of granular materials were investigated. Model experiments and numerical simulations indicate that glass bead particles exhibit periodic stick-slip under shear conditions, and the frictional healing and stick-slip period are key parameters characterizing the stick-slip characteristics of particles. The frictional healing decreases with increasing shear rate and increases with increasing particle diameter, while the normal stress has a smaller impact on the frictional healing. Stick-slip period and frictional healing show a positive correlation, with the stick-slip period significantly decreasing with increasing shear rate. The frictional interlocking between particles is an important factor influencing stick-slip behavior.

Permeability Characteristics of Improved Granite Residual Soils

Yang Xueqiang, Zhong Huabin, Tao Jiaqi, Zhou Baogui, Cai Chifeng

2024, 38(5): 598-604. doi: 10.3969/j.issn.1007-2993.2024.05.015

[Abstract](34) [FullText HTML] (12) [PDF 1586KB](8)

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In response to the mechanical characteristics of the residual soil of granite in Youxi, Fujian, which is prone to softening and disintegration when encountering water, the external additives mixing method was used to improve its properties by adding additives to reduce its permeability coefficient. Adding ratios of lime, fly ash, and residual soil were set to 1∶1∶8, 1∶2∶7, and 1∶3∶6, respectively. Basic physical property index tests, compaction tests, and particle grading analysis tests were conducted on the granite residual soil from Youxi in Fujian. Variable water head permeability tests were conducted on the granite residual soil and improved granite residual soils separately. The test results showed that: (1) The saturated permeability coefficients of the improved granite residual soils by adding lime and fly ash into soil were decreased remarkably compared with that of the remolded residual soil, and its impermeability has been improved. (2) When the ratio of lime, ash, and soil is 1∶2∶7, the decrease in saturated permeability coefficient is the greatest, and the improvement effect in permeability is the best. (3) Whether remolded soil or improved soil, its saturated permeability coefficient increases with the increasing of its pore ratio, and decreases with the increasing of its dry density.

Suitability of NB01 Curing Agent to Solidify Construction Waste Soil as Roadbed Filler

Xu Dapeng, Zhu Jianfeng, Wang Zhengqing

2024, 38(5): 605-610. doi: 10.3969/j.issn.1007-2993.2024.05.016

[Abstract](30) [FullText HTML] (7) [PDF 1166KB](8)

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The accumulation of construction waste soil has occupied a large amount of land resources and result in environmental pollution. A new curing agent, NB01, was adopted to solidify typical construction waste soil in Ningbo. Through conducting a series of macro-micro laboratory tests such as unconfined compressive strength test, road performance test, X-ray diffraction test, and electron microscopy scanning test, the solidification effect of NB01 solidified construction waste soil roadbed filler was investigated, and the mechanism of NB01 solidified construction waste soil was further revealed. The test results show that the unconfined compression strength, q_u, of solidified muck increases with the increase of curing age and content. After 28-day curing, q_u of the solidified muck can reach 1396 kPa, the water stability coefficient of the solidified soil approaches to 0.96, and the CBR value is larger than 25.80%, which meets the performance requirements of subgrade filler. The hydration reaction of NB01 can produce C-A-H and C-S-H gel, which enhance the cementation between soil particles and fill the pores and further promote the mechanical properties of solidified construction waste soil. The study could provide guidance for the recycling and utilization of construction waste resources.

Experimental Study on Engineering Characteristics of Fluidized Solidified Soil Containing Collapsible Loess and Gravel

Zhang Xin, Ji Haifeng, Yang Zuoqing, Zhu Yanpeng, Liu Dongrui

2024, 38(5): 611-617. doi: 10.3969/j.issn.1007-2993.2024.05.017

[Abstract](40) [FullText HTML] (7) [PDF 2695KB](8)

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To eliminate the defects of traditional backfilling methods and materials, combined with the characteristics of collapsible loess area, the premixed fluidized solidified soil with collapsible loess and gravel as aggregate was prepared. The influence of different loess-to-gravel (L/G), water-to-solid (W/S) and binder-to-aggregate (B/A) ratios on the workability and mechanical properties of the premixed fluid solidified soil was analyzed by carrying out flowability and unconfined compressive strength tests. The permeability test and collapsibility test were conducted to discuss the performance change of the proposed material after solidification and water exposure. The main conclusions are as follows: (1) For certain fixed cementitious material content, with the increase of collapsible loess content, the amount of water required to meet the flowability requirements of the mixture also increases, but the strength of the sample decreases as a whole. (2) The increase of the content of cementitious materials improves the strength of the sample, but reduces the flowability of the mixture, especially for the mixture with large L/G ratio and relatively low W/S ratio. (3) Premixed fluidized solidified soil made with collapsible loess and gravel which meets the requirements of flowability and minimum strength also meets the requirements of impermeability and collapsibility in the relevant specifications. (4) According to the test results, after W/S ratio is adjusted to meet the flowability requirement, the fluidized premixed solidified soil with L/G ratio between 1.50 and 1.86 and B/A ratio not less than 0.06 has good workability and mechanical properties.

Small Strain Stiffness Property of Structured Loess

Liu Shuguang

2024, 38(5): 618-623. doi: 10.3969/j.issn.1007-2993.2024.05.018

[Abstract](32) [FullText HTML] (11) [PDF 1344KB](9)

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Because of the soil skeleton containing dominant silt as well as interparticle cementation, the natural loess behaves in a structured way. To study the influence of structural properties on the small-strain stiffness of loess, resonant column tests were performed on typical natural and remolded loess under different confining pressures. The results showed that both the original and remolded loess exhibit a nonlinear stiffness characteristic within the small strain range and their shear modulus-shear strain (G-γ) relationships can be fitted by the Hardin-Drnevich hyperbolic model. Structural properties were found to significantly control the small-strain stiffness properties of loess, as exemplified by a higher shear modulus and a lower sensitivity of the maximum shear modulus to confining pressure of natural loess compared to the case of remolded soil. In addition, this study quantified the effect of structure on the small strain stiffness of loess and makes comparisons with some well-studied sands and clays (including London clay and Ottawa sand). This research enhanced the understanding of the mechanical behavior of structured loess and can provide technical reference for related engineering design.

Mechanical Characteristics of Slight-Expansive Soil in Hefei and its Effect by Saturation Disturbance

Luo Guangcai, Zhou Ziwei, Wang Zhichao, Ha Jizhang, Wu Jiaxin

2024, 38(5): 624-630. doi: 10.3969/j.issn.1007-2993.2024.05.019

[Abstract](45) [FullText HTML] (8) [PDF 2668KB](8)

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To study the influence of water and disturbance on the strength and deformation of weak-expansive soil in the Hefei area, the undisturbed samples and saturated disturbed samples of weak-expansive soil in the deep foundation pit of Huifu Road Station of Hefei Metro Line 7 were subjected to conventional saturated triaxial compression (CTC) and triaxial tension (CTE) under three confining pressures of 50 kPa, 100 kPa and 200 kPa, and the undisturbed non-immersed samples were subjected to a triaxial compression test. By comparing the differences of stress-strain, strength index, and deformation modulus between undisturbed and saturated disturbed samples, the influence of saturated disturbance on the mechanical properties of expansive soil was discussed, and the mineral composition and content of expansive soil were tested by XRD diffraction. The test results show that: (1) The soil of the foundation pit of Hefei Metro Line 7 is cohesive weak expansive soil, and the montmorillonite content in clay minerals accounts for 46%. (2) The decrease of cohesion mainly manifests the decrease of strength of Hefei weak-expansive soil. The cohesion of the undisturbed sample is 56% lower than that of the disturbed saturated remolded sample, while the friction angle change is insignificant. (3) The weak-expansive soil in the foundation pit of Hefei Metro Line 7 has the phenomenon of over-consolidation, characterized by the dilatancy softening of the undisturbed sample. (4) The initial modulus of Hefei weak-expansive soil decreased by about 20% after water disturbance, and water infiltration significantly reduced the deformation resistance of expansive soil.

Current Issue 2024, Volume 38, Issue 5

Current Issue
2024, Volume 38, Issue 5