岩土工程技术

2024, 38(3)

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2024, 38(3): 1-3.

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Bearing Capacity of Frozen Soil Pile Foundations in Cold Regions: A State-of-the-Art Review

Tang Liyun, Ding Bing, Zheng Jianguo, Xu Peizhi, Qiu Peiyong

2024, 38(3): 253-262. doi: 10.3969/j.issn.1007-2993.2024.03.001

[Abstract](168) [FullText HTML] (35)

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In cold regions, seasonal temperature variations, atmospheric warming, and intensified human engineering activities often lead to disasters such as frost heaving, thaw settlement, tilting, and concrete cracking in pile foundations. These incidents often result in the decrease of the bearing capacity of pile foundations, posing new and greater challenges to pile foundations in cold regions. The current research status of the bearing capacity of frozen soil pile foundations was summarized. Based on the unique properties of frozen soil, the main force types and characteristics of frozen soil pile foundation systems were described; the changing mechanisms of mechanical properties at the pile-frozen soil interface were detailed in terms of experimental testing and the load transfer mechanism; the variations in the bearing capacity of frozen soil pile foundations and the methods for analysis and prediction were illustrated from the perspectives of experimental tests, theoretical analyses and numerical simulations; main monitoring techniques for temperature, moisture, stress and strain in the pile-frozen soil system were also described. Finally, prospects for future research on the bearing characteristics of frozen soil pile foundations in cold regions were presented.

Elastic-plastic Constitutive Model Considering Structural Effects of Deep-sea Energy Soil

Jiang Kaisong, Qi Chengzhi, Lu Chunsheng, Wang Zefan, Zhang Yujia

2024, 38(3): 263-272. doi: 10.3969/j.issn.1007-2993.2024.03.002

[Abstract](82) [FullText HTML] (32) [PDF 1850KB](19)

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Deep-sea energy soil refers to deep-sea sediments where gas hydrates are filled in various modes within the pores. The filling effect of gas hydrates significantly impacts the density and porosity ratio of deep-sea energy soil. Additionally, the cementation effect of gas hydrates generates increasing bonding force with increasing saturation, jointly affecting the complex mechanical properties of deep-sea energy soil. Furthermore, deep-sea energy soil is a distinctive structural soil, wherein the particle framework, pore characteristics, and arrangement influence its strength, strain softening, and characteristics such as shear dilation and contraction. Within the framework of the CSUH model, this research reflected the compressibility characteristics of gas hydrates on energy soil by establishing pressure-hardening parameters related to gas hydrate saturation. Furthermore, considering the influence of gas hydrate filling effects, the actual initial porosity calculation formula for energy soil was derived and incorporated into the state parameters to reflect its shear dilation characteristics. Finally, utilizing structural parameters describing soil damage effects and cementation parameters related to gas hydrate saturation as hardening rules, an elastoplastic constitutive model for structural deep-sea energy soil considering gas hydrate filling effects was established. Comparative analysis with indoor experimental results validates the model's efficacy in effectively reflecting the complex mechanical properties of energy soil under various gas hydrate saturations and confining pressure conditions, including strain hardening and softening, as well as volume shear dilation and contraction.

Research on Micro-motion Detection Method and Blasting Technology for Isolated Rocks in Shield Construction in Prosperous Urban Areas

Liu Haoming, Song Qingshan, Su Dong, Zeng Decheng, Ping Yang, Zhang Xiao

2024, 38(3): 273-278. doi: 10.3969/j.issn.1007-2993.2024.03.003

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Micro-motion detection technology is widely used in shallow geological structure detection due to its fast, economical, and adaptation to site conditions. Isolated rocks are common in the granite area of southern China. To solve the problem of large-diameter isolated rocks encountered during shield tunneling in the second bid of Zhuhai Xingye Express Line (south section), the following approaches were adopted. First, the micro-motion detection technology was used. The micro-motion array detection geophysical detection method, and the quasi-spatial autocorrelation method-SPAC method were used to extract the Rayleigh wave dispersion curve from the micro-motion array records. Data analysis can directly reflect the change of formation lithology and explain the geological conditions. Secondly, the size and location of the isolated rocks can be accurately obtained by combining it with the method of borehole detection. Finally, the controlled deep-hole blasting technology was used to blast the isolated rocks within the scope of the shield tunnel, with optimized hole layout parameters and charge quantity. According to the coring results from the construction site, the blast can ensure a good crushing effect with the size of single body being within 30 cm. This fully meets the requirements of the shield tunneling construction. The research results can provide a reference for shield construction projects in similar strata.

Design and Calculation of Plane Stability of Concrete Support for Foundation Pit

Hu Jisong

2024, 38(3): 279-286. doi: 10.3969/j.issn.1007-2993.2024.03.004

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Regulations concerning foundation pits often lack specific provisions regarding the calculation length factor within the plane of pit supports, commonly assuming a value of 1.0. Through an analysis of the planar stability of foundation pit concrete supports it is evident that the stability within the support plane, arranged as a framework, cannot be overlooked and constitutes a primary controlling factor for support-bearing capacity, implying a calculation length factor greater than 1. Drawing from the theory of stable buckling, a simple and applicable length calculation coefficient formula is proposed, along with key measures to improve support stability.

Analysis and Prediction of Settlement Characteristics of Double-layer Soft Soil Foundation Treated by Vacuum Preloading Method

Sun Chong, Liu Yinpeng, Chen Shaoqing, Cheng Lin

2024, 38(3): 287-293. doi: 10.3969/j.issn.1007-2993.2024.03.005

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The double-layer soft soil foundation composed of artificial fill layer and original marine sedimentary soil layer is different from the conventional foundation form, and its settlement prediction results have large discreteness. The foundation of a certain project in the coastal area of Tianjin is a double-layer soft soil foundation. The vacuum preloading method was used for foundation treatment. Based on this engineering example, the settlement characteristics of the double-layer soft soil foundation were revealed through on-site monitoring. In terms of settlement prediction, a double-layer soft soil foundation settlement prediction model was established using convolutional neural networks, and compared with hyperbolic fitting method. The research results showed that this method can also accurately predict foundation settlement deformation, meeting the needs of engineering construction.

Lithology Recognition of Rock Image Based on Convolutional Neural ResNet50 Residual Network

Wang Xiaobing, Liu Lin, Wang Junqing, Hu Shilei, Wen Lei

2024, 38(3): 294-302. doi: 10.3969/j.issn.1007-2993.2024.03.006

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Deep learning convolutional neural network algorithm is widely used in the lithology identification of rock images. A rock image lithology recognition model was constructed by combining the convolutional neural residual ResNet50 network, and the parameters of the network model were optimized and verified according to the defined loss function. At the same time, the lithology of the rock image was predicted by the constructed recognition model, and the error causes were analyzed according to the prediction results. The research showed that based on the deep convolutional neural ResNet50 residual network, the lithology prediction model can be constructed and the parameters can be optimized according to the ratio of the training set, test set, and verification set 8: 1: 1, to realize the lithology prediction of rock image. Combined with the project example, the rock image lithology identification model of four kinds of lithology, such as biotite granodiorite, metamorphic sandstone, quartzite, and biotite granite, is constructed. The recognition accuracy of the model is generally up to 75%~90%, except for the fractured rock mass with structural joints. The accuracy of rock image prediction results is greatly affected by the development of rock mass structural fissures and the quality of rock images. The accuracy of prediction results can be improved by increasing the number of training samples.

Mechanism of Deep Shaft Surrounding Rock Failure and Shaft Wall Structure Design

Jia Chenggang, Li Chen, Guo Yulong, Chen Tuantuan

2024, 38(3): 303-308. doi: 10.3969/j.issn.1007-2993.2024.03.007

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To provide effective guidance for shaft construction, theoretical analysis and numerical simulation were used to study the damage and deformation of the surrounding rock and the structure of the shaft wall. The results show that the horizontal confining pressure coefficient for shaft crossing geological formations is 1.75 to 1.86, leading to a butterfly-shaped distribution of the plastic zone in the weak strata. The RPP characteristics of the relationship between plastic zone size and bidirectional principal stress have a significant impact on the strength of the surrounding rock. The size differences of the damage forms of the wellbore surrounding rock before and after freezing and timely pouring are significant at a burial depth of 500~600 meters. The freezing method was selected for construction before and after freezing based on the vector displacement of the surrounding rock. Based on this, the theoretical calculation and design of the shaft wall structure parameters were verified, and on-site construction monitoring shows that the design parameters can meet the safety and stability requirements of the project construction. The research results have practical significance for the construction of similar shafts under similar conditions.

Numerical Simulation on Sealing Performance of Pipe Jacking Hole Sealing Device

Du Kun, Lyu Feihua, Ji Xinyu, Han Jiajia, Jiang Donglai

2024, 38(3): 309-316. doi: 10.3969/j.issn.1007-2993.2024.03.008

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A simplified two-dimensional plane model was established by using ABAQUS software based on the curtain rubber plate + folding plate combined waterproof device commonly used in the pipe jacking construction site. By changing the parameters of the rubber plate, folding plate, and material hardness, the sealing law of the waterproof device was studied, and the sealing evaluation standard and optimal combination form were proposed. The research shows that the sealing device with the combination of curtain rubber plate and folding plate can effectively avoid the phenomenon of water and sand leakage at the hole. However, if the rubber plate is too long or the folding plate is too short, the effective contact stress of the end will be reduced. Too short a rubber plate or too long a folding plate will cause stress concentration at the end of the rubber plate, and the effective contact length is small. At the same time, too high hardness will also cause stress concentration at the end position and reduce the effective contact length. In these cases, the sealing performance will decrease.

Flow State of Single Rough Fracture Based on Lattice Boltzmann Method

Duan Zhichao, Wang Jingjing, Li Yuhong, Guan Yanli, Hu Xuanyi

2024, 38(3): 317-321. doi: 10.3969/j.issn.1007-2993.2024.03.009

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Based on the lattice Boltzmann method and D2G9 discrete model, a single fracture seepage model was established considering different roughness, with the advantages of the easy setting of boundary conditions, high computational efficiency, and visualization of calculation results. The upper and lower boundaries of the model were set as full rebound boundaries without slip. The distribution function boundary of the left and right edges was used in the non-equilibrium extrapolation format, and the model is verified with the Poiseuille flow problem of classical fluid mechanics. Finally, the influence of the surface roughness of rock fracture on the seepage state was analyzed. The calculation results showed that with the increase of the roughness of the wall surface, the flow velocity, size, and direction of the fluid will change to different degrees. In the parts where the gap width changes sharply due to the change of roughness, the formation of local fluid vortices will lead to the increase of internal friction resistance of the fluid, resulting in greater local energy loss.

Underground Pipe Network and Road Disease Monitoring Technology Based on DVS

Cui Xiao

2024, 38(3): 322-329. doi: 10.3969/j.issn.1007-2993.2024.03.010

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Because of the problems of low accuracy, insufficient application effect and inability to realize automation in the monitoring of underground pipeline leakage and road voids by conventional detection methods, distributed optical fiber vibration sensing technology is proposed to monitor underground pipe networks and road diseases. A technology method for real-time intelligent monitoring of underground pipe network operation and maintenance status and changes of road subgrade and surrounding soil diseases is developed. Through the test verification, the signal and background noise automatically collected by the front-end optical fiber equipment were analyzed, and the monitoring efficiency and accuracy of the underground pipe network and road disease were improved. The results show that the overall recognition rate of this method for underground pipeline leakage and road diseases is over 90%, meeting the needs of underground pipeline networks and road maintenance and accident prevention.

Underpinning Methods of Diaphragm Wall of Subway Station Constructed by Cut and Cover Reverse Method under Foundation Pit Cover Plate

Luo Peng, Liu Yingjing, Lu Jingke, Lin Tingsong, Zhu Hanhua

2024, 38(3): 330-336. doi: 10.3969/j.issn.1007-2993.2024.03.011

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The connection between the auxiliary structure and the subway station usually requires breaking the diaphragm wall, which is more difficult and risky when a temporary cover plate is installed on the diaphragm wall. Based on the demolition construction of the diaphragm wall of a subway station constructed by cover and top-down construction method, a construction method of underpinning demolition using a local demolition body as temporary vertical support was proposed, and the problem was solved. First of all, the influence of different underpinning distances on the structural system of the cover plate was calculated numerically, and considering the construction progress and workspace, the temporary underpinning columns with a width of 1 m and a breaking distance of no more than 12 m were determined as the control indicators, which can meet the load-bearing performance requirements of each stressed structural system under temporary underpinning construction. Secondly, the demolition of the diaphragm wall under the cover plate and the transfer construction of the cut blocks were detailed, and the control indicators and practices of key construction links such as block size, cutting block hoisting, and reserved column nodes were given. The implementation results showed that using the existing diaphragm wall as a temporary underpinning structure for the construction of the diaphragm wall is safe, reliable, fast in construction, and economical in cost.

Stability Analysis of High Fill Slope Based on in-situ Borehole Shear Test

Qiu Zhihua

2024, 38(3): 337-343. doi: 10.3969/j.issn.1007-2993.2024.03.012

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The soil strength parameters of the slope have an important impact on the stability of the slope, and the accuracy of the slope stability analysis results restricts the construction of the project. To more accurately analyze the soil strength parameters of the slope and provide a reliable foundation for the subsequent reinforcement of the slope, an in-situ borehole shear test was conducted to obtain the shear strength index of the slope fill, and the stability of the slope was analyzed. The results show that the soil strength index can be effectively obtained through in-situ borehole shear tests, which can reflect the soil characteristics. It is of great significance for improving the accuracy of slope stability analysis and evaluation.

Experimental Study on Improvement of Heavy-haul Railway Subgrade Filler

Wu Weigang, Li Yan

2024, 38(3): 344-350. doi: 10.3969/j.issn.1007-2993.2024.03.013

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Based on static and dynamic triaxial tests, the effects of three reinforcement methods, including fiber improvement, curing agent improvement, and fiber - curing agent improvement, on the performance of heavy-haul railway subgrade filler were studied, and the best improvement scheme was proposed. The results show that when the curing agent content in the curing soil is 5%, the strength reaches the peak, and the longer the curing time, the higher the strength. With fiber improvement, when the fiber content is 0.2%, the soil static dynamic performance of fiber reaches the best; When the fiber length is 0~12 mm, the strength increases with the increase of fiber length, and when the length is 12~18 mm, the strength decreases with the increase of fiber length. The fiber-curing agent combined improvement scheme is the best reinforcement effect. It is recommended that the fiber-curing agent combined improvement scheme be used to enhance the mechanical properties of the subgrade filler, and the optimal curing agent content is 5%, fiber content is 0.2%, and fiber length is 12 mm.

Sandstone Damage and Creep Acoustic Emission under Salt Water Dry-wet Cycle

Ma Xingchen, Song Haibo, An Xuelei, Wang Chenbo, Wang Xinjian

2024, 38(3): 351-357. doi: 10.3969/j.issn.1007-2993.2024.03.014

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To study the damage and deterioration mechanism of red sandstone under the action of aqueous chemical solution, a dry-wet cycle test and creep acoustic emission test were carried out in Na₂SO₄solution and NaOH solution. The results showed that the damage of red sandstone gradually accumulates with the increase of dry-wet cycle times, and the damage deterioration degree of sandstone in acid Na₂SO₄ solution is greater than that in NaOH solution. With the increase of dry-wet cycles, the softening damage of sandstone is becoming increasingly severe, the creep acoustic emission signal gradually changes from "high frequency and high amplitude" to "low frequency and low amplitude", and the cumulative number of acoustic emission events gradually decreases. Under the same dry-wet cycle times, the cumulative number of acoustic emission events of sandstone in Na₂SO₄solution is lower than that in NaOH solution. The acoustic emission b value shows four stages of "decrease - dynamic stability - sudden drop - increase". The sudden drop occurs before and after the accelerated creep stage, which can be used as a precursor of creep instability failure of sandstone. The b value of acoustic emission gradually increases with the increase of dry-wet cycles. The more serious the hydrochemical damage softening phenomenon is, the greater the proportion of small-scale damage in the creep process.

Impact of Ultrasound-assisted Complex Leaching on Engineering Properties of Contaminated Clay

Shao Li, Ni Yifei, Wang Shuai, Wu Fangjin, Chi Lin

2024, 38(3): 358-364. doi: 10.3969/j.issn.1007-2993.2024.03.015

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The ultrasonic-assisted complex leaching agents (tartaric acid and ethylenediaminetetraacetic acid disodium salt (Na₂EDTA)) were employed to carry out experiments on contaminated clay containing heavy metals Cu²⁺, Ni²⁺, and Pb²⁺. The variation laws of engineering properties such as soil pH, liquid plastic limit, strength characteristics, and compression characteristics before and after ultrasonic-assisted complex leaching were scrutinized under different heavy metal ion concentrations. The results revealed: (1) Post ultrasonic-assisted complex leaching remediation, the pH value of the contaminated clay reduces significantly, with the acidic leaching agent inducing severe soil acidification. (2) Upon remediation, the soil's liquidity index increases while the plasticity index decreases. (3) After ultrasonic leaching remediation, the shear strength of the soil body reduces, with the overall internal friction angle decreasing by 2°~3°. (4) The porosity ratio decreases as consolidation pressure increases, with the reduction being more substantial the higher the heavy metal concentration. (5) Post-remediation, the compressibility of the soil body increases, as does the compression coefficient, while the modulus of compressibility diminishes.

PFC3D Particle Flow Simulation of Nano-Clay Modified Loess Triaxial Test

Zhang Zixuan, Cao Baohua, Han Zemin, Xu Jiangbo, Cheng Fanghui, Chen Shaohua, Hou Xinmin, Zhan Haochen

2024, 38(3): 365-373. doi: 10.3969/j.issn.1007-2993.2024.03.016

[Abstract](70) [FullText HTML] (13) [PDF 2679KB](9)

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PFC3D software was used to study the influence of different nanomaterials, dosage, confining pressure, and dry density on the mechanical properties of improved loess, and determine the parameter relationship between macro and meso of improved loess. Through a numerical model of improved loess and a three-axis experiment, the stress-strain curve of improved loess was obtained. The results of the numerical simulation were compared with the results of indoor experiments, and the shear strength index of improved loess was consistent. The experimental results showed that: (1) When the confining pressure is constant, the deviatoric stress of the improved loess sample increases with the increase of nano-clay content. The stress and strain of the improved loess are positively correlated. When the confining pressure is different, it shows a softening type and a strong hardening type. (2) When the content of attapulgite is less than 2%, the shear strength obtained by numerical simulation is generally lower than that derived from laboratory tests; conversely, when the content exceeds 2%, the situation is reversed. (3) When the content of nano-montmorillonite modified loess in numerical test samples is less than or equal to 4%, the shear strength obtained through numerical simulation is higher than that measured in laboratory tests; conversely, when the content exceeds 4%, the situation is reversed.

Experimental Study on Physical and Mechanical Indexes of Modified Silt

Yao Miaoxian

2024, 38(3): 374-378. doi: 10.3969/j.issn.1007-2993.2024.03.017

[Abstract](116) [FullText HTML] (31) [PDF 954KB](27)

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To solve the engineering problems existing in the filling of silt in the airport pavement subgrade effectively, the silt was modified with lime, mixed lime (strength grade 42.5 cement and lime), and cement (strength grade 42.5 and 52.5), the dosage to mass ratio of which was 4%, 6%, 8%, 10% and 12% respectively. Unconfined compressive strength tests, compression tests, compaction tests, and reaction modulus tests on different modified materials were conducted. The results show that the unconfined compressive strength and compression modulus of each sample increase with the increase of curing time and dosage ratio. The modified silt can effectively improve the compaction degree and subgrade reaction modulus of the original silt. The optimal content to mass ratio of silt was silt combined with 8% cement (strength grade 52.5). The modified silt can be used as a filler in the airfield subgrade directly.

2024 Vol. 38, No. 3