岩土工程技术

2023, 37(5): 1-1.

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2023, 37(5): 1-3.

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Discussion on the Development of Drilling Techniques for Engineering Investigation

Wen Jiwei, Liu Xinghong, Bai Kunxiao, Zhang Yingxu, Xiang Tian, Hu Ping

2023, 37(5): 505-517. doi: 10.3969/j.issn.1007-2993.2023.05.001

[Abstract](587) [FullText HTML] (78) [PDF 4803KB](144)

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The drilling techniques involved in engineering investigation were systematically summarized, including soil sampler and coring drill, in-situ testing techniques, high-efficient drilling coring (sampling) techniques and joint investigation techniques, and their characteristics were combed, compared and analyzed. Suggestions were put forward to solve the existing problems. It is recommended to further optimize the drilling process and upgrade the modular and intelligent research and development of the matching drilling tools, promote the cross integration of different types of drilling technologies, as well as the joint application of drilling technology with multidisciplinary technologies such as geophysical exploration and remote sensing. It can lay a foundation for the high-efficient development of subsequent engineering investigation.

Analysis of Slope Stability and Treatment Measures for a Highway in Southern Shaanxi

Shi Jing, Zhang Hao, Zhao Xin, Fan Hongying

2023, 37(5): 518-523. doi: 10.3969/j.issn.1007-2993.2023.05.002

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A typical third level slope in the southern Shaanxi region experienced large-scale collapse during treatment construction. Failure to timely protect after excavation was the direct cause of slope instability, while continuous heavy rainfall in autumn was the indirect cause of slope collapse. The strength reduction method and numerical software were used for calculation and analysis. The results show that the slope unloading and the use of single anchor point prestressed anchor cable anti-slip pile reinforcement at the first level platform has the best treatment effect. The comprehensive analysis adopts a treatment plan of graded slope unloading, single anchor point prestressed anchor cable anti-skid pile, comprehensive drainage system, and greening measures. Real time monitoring of surface displacement, deep displacement, groundwater level, video monitoring, and other aspects of the slope can effectively monitor slope stability and ensure highway operation safety. The research results have a certain reference value for similar slope treatment.

Short-term Undrained Analysis of Passive Instability of Shield Tunnel Excavation Face

Wang Haifeng, Kang Bo, Li Pengfei, Liu Zenghui, Di Qiguang, Chen Keyi

2023, 37(5): 524-531. doi: 10.3969/j.issn.1007-2993.2023.05.003

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The construction environment of shield tunnel becomes more and more complex. However, there are few researches on passive instability failure modes of shield tunnel excavation face in water-rich clay stratum. A theoretical model of passive instability failure of shield excavation face under undrained effect was proposed. The unknown quantity of ultimate support force function was analyzed for homogeneous soil and layered soil respectively. After fitting the results, a theoretical calculation formula for rapid estimation of ultimate support force was given. Finally, the applicability of the model is further discussed by comparing the numerical results with the theoretical results. The results show that under the condition of shallow burial (C/D≤1.0), the boundary of the upper failure zone of the vault is approximately vertical, which is consistent with the proposed failure mode assumption. With the increase of buried depth ratio, the influence of the damaged area on the surface becomes less and less, and even the damaged area does not extend to the surface when buried deeply.

Research on Axial Force Prediction of Bolt in TBM Headrace Tunnel Based on ACO-SVM

Wang Jian, Wang Liming, Zhou Zhenliang, Lu Wenjia, Mao Peiliang

2023, 37(5): 532-537. doi: 10.3969/j.issn.1007-2993.2023.05.004

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Based on the monitoring data of anchor axial force in Ka-Shuang tunnel of Xinjiang YEGS water conveyance project, the change trend of anchor axial force were forecasted and analyzed through ant colony algorithm (ACO) and particle swarm optimization (PSO) to optimize the support vector machine (SVM) model. The research shows that ACO-SVM prediction model fully considers the tunnel buried depth compared with PSO-SVM and traditional SVM prediction model. After a number of nonlinear influencing factors such as temperature and action time, the predicted value is closer to the measured value, the relative error is basically within 15%, and the average absolute percentage error is only 5.92. The model has better robustness, stability and generalization ability, and is more suitable for the prediction and analysis of the variation trend of bolt axial force in TBM tunnel. It has certain engineering application and popularization value.

Research on Pile Settlement Caused by Large-area Disorderly Soil Stacking

Zhang Nan, Wu Yue, Liu Yongchao, Zhang Zongjun, Han Yutao, Lu Hongyu

2023, 37(5): 538-544. doi: 10.3969/j.issn.1007-2993.2023.05.005

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A large-scale construction project needs to mound soil over a large area on the constructed foundation pile due to the change of excavation conditions. Large-area mounded soil will cause the settlement of group foundation piles. After the excavation of foundation trench, the settlement of foundation piles is discrete, and the maximum settlement of foundation piles is as high as 670 mm, the maximum extreme value of settlement between foundation piles in single buildings is as high as 510 mm, which far exceeds the standard calculation value, thus the settlement attribution is controversial. Using the finite element software PLAXIS3D, a three-dimensional numerical model was set up and comprehensive analysis of pile settlement was carried out. The results show that large area soil mounded above the completed pile foundation can cause large settlement of the foundation pile. Maximum settlement of ground surface and pile top are located at the center of the mounded soil, negative friction of two piles with maximum and minimum settlement is doubled; According to regional analysis, the overall settlement trend of pile caused by large area disorderly mounded soil conforms to the settlement law in soft soil area; The main factors of large dispersion of each foundation pile include: the height, area and time of the mounded soil, drainage conditions, soil layer conditions of pile crossing, soil layer conditions of underlying layer at pile end, etc. This research has accumulated experience for similar projects.

Study on Comprehensive Treatment of Geotechnical Engineering in a Site Area

Zhang Liqian, Tian Yibin, Yan Jing, Li Bing, Meng Liang

2023, 37(5): 545-552. doi: 10.3969/j.issn.1007-2993.2023.05.006

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A site is located in the deep V-shaped valley between the north-south ridges on both sides. It faces stability of high slopes on both sides of the south and north and flood control in the east valley. The geotechnical problems on the three sides are coupled and progressive in time and space, and there are considerable difficulties in treatment. Based on the systematic description of the engineering geological characteristics of the geotechnical problems on the three sides, the protection and treatment countermeasures are formulated. The research and practice show that the accurate engineering geological data is the foundation and premise of geotechnical treatment, and the overall conceptual control of the treatment project is the key to guiding the investigation and design. The close combination of treatment design and treatment investigation is the core element of the success or failure of geotechnical treatment engineering. Flood control of the project located in the valley is a key issue and it is necessary to establish a smooth flood discharge channel, scientifically and reasonably formulate flood control standards according to the importance level of the site, and determine the frequent flow. For the treatment of small-scale landslide, it is more reasonable to give priority to the treatment measures of clearing the earth. For the high slope after clearing the earth, it is still necessary to carry out stability analysis and evaluation, determine reasonable protection measures, and ensure the safety of the whole slope. The contents can provide guidance and reference for similar projects.

An Example of Foundation Pile Design under Settlement Control

Zhang Wu, Yao Xiaoxu, Zhang Bo, Guo Zhe

2023, 37(5): 553-558. doi: 10.3969/j.issn.1007-2993.2023.05.007

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Through an engineering example of optimal design of track pile foundation of a container terminal in West Africa, the displacement of pile top under load was estimated by comparing the current Chinese code method with the vertical compressive stiffness method of single pile. The engineering example shows that the vertical compressive stiffness method of single pile can simply evaluate the settlement of pile top under working load, the maximum settlement under specified test load, and the residual settlement of pile top after unloading after the maximum load, which meets the technical requirements of pile foundation settlement control in international professional standards.

Risk Assessment Method of Internal Support Structure and Feasibility Study of Dismantling the Support

Yin Aiyue, Lu Zhuo, Wang Xubo, Wei Huanwei, Wang Jiekun, Zheng Xiao

2023, 37(5): 559-566. doi: 10.3969/j.issn.1007-2993.2023.05.008

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The study of risk assessment methods of internal support structures, which are widely used in the construction of deep foundation pit projects, can timely discover the risks existing in the construction process and effectively reduce the probability of engineering accidents. Starting from the actual needs of the project, the typical deformation and internal force monitoring data of the internal support structure were summarized as safety evaluation indexes. The monitoring alarm values were used as evaluation scales to quantify each index. According to the Analytic Hierarchy Process (AHP) theory, a risk analysis method based on on-site measured data was established, and the rationality of the risk assessment method was verified through practical engineering. Finally, a finite element three-dimensional simulation model was established using PLAXIS3D software to analyze the feasibility of the support demolition stage. The study shows that the problem of taking the corresponding weights of each evaluation index is the key to influence the risk level of the foundation pit, and the pile body measurement inclination, as the main safety evaluation index, should play a controlling role in the process of risk analysis. It is suggested that the risk degree should be strictly controlled below 0.6 in the actual project to ensure that the foundation pit is in a safe state.

Monitoring and Analysis of Structural Deformation During Subway Station Construction Interval under Soft Soil-bedrock Conditions

Ke Lei, Li Hong, Liu Kun, Chen Mingyin

2023, 37(5): 567-573. doi: 10.3969/j.issn.1007-2993.2023.05.009

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There are insufficient researches on the structural deformation monitoring and evaluation of subway stations during construction intervals under the condition of soft soil-bedrock. The fiber Bragg grating sensing technology was applied in the structural deformation monitoring research during the construction interval of the station. Taking a subway station in Shenzhen as a research case, the optical fiber sensor was installed on the main structure of the station, and the deformation information of the structure during the construction interval was obtained automatically and remotely. The results show that the main structure of the soft soil-bedrock foundation has a certain degree of deformation during the construction interval. During the monitoring period, the maximum strain of the station floor is 62 μɛ, and the maximum deformation of the wall column structure of the second underground floor of the station is 249 μɛ. Wall-column structures located near the soft soil-bedrock interface are affected by both shear and compressive stresses. Therefore, the flexural and shear strength design of the base plate and the bottom wall column should be respectively considered in the subsequent station construction of the soft soil-bedrock foundation.

Study on Selection of Road Soft Foundation Treatment Scheme

He Changming, Li Jun

2023, 37(5): 574-580. doi: 10.3969/j.issn.1007-2993.2023.05.010

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The quality of road soft foundation treatment directly affects the driving safety and comfort. To determine an economic, reasonable and environmental friendly soft foundation treatment scheme is the key to the success or failure of road soft foundation treatment. The technical feasibility analysis is carried out from the aspects of geological condition adaptability, subgrade stability, construction period requirements, foundation bearing capacity requirements, post construction settlement value requirements, etc; The economic rationality should be analyzed from the aspects of soft foundation treatment engineering cost and operation and maintenance cost; Environmental impact analysis shall be carried out from the aspects of environmental impact from surrounding area, during construction, and during operation, as well as resource consumption. According to the analysis results of technical feasibility, economic rationality and environmental impact, the analytic hierarchy process is introduced to establish the analytic hierarchy process model of soft foundation treatment scheme selection. Combined with expert decision system and fuzzy theory, the influencing factors are quantitatively evaluated, so as to simplify the complex non quantitative factor problem. An example is given to verify the adaptability of analytic hierarchy process model in the selection of soft foundation treatment scheme.

Matter Element Evaluation of Foundation Pit Safety Based on Game Theory Combination Weighting

Su Zhengkai, Zhang Kunyong, Li Fudong, Jian Yongzhou

2023, 37(5): 581-589. doi: 10.3969/j.issn.1007-2993.2023.05.011

[Abstract](65) [FullText HTML] (25) [PDF 1965KB](20)

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The scale of excavation projects is progressively increasing, accompanied by a growing number of factors influencing their safety status. To accurately assess the safety status of excavation projects using commonly available monitoring data, the matter-element extension model, typically used for evaluating the level of things, is introduced into excavation safety assessment to address the issue of incompatibility among different indicators. For enhancing the authenticity of weight values, a game theory-based combination weighting approach was employed, which overcomes the limitations of single-weighting methods and considers both subjective and objective factors. The asymmetric fuzzy preference theory was used as a substitute for the maximum membership degree criterion, resulting in improved evaluation accuracy. Taking a foundation pit project in the Yangtze River floodplain as a case study, this research assessed safety conditions using common monitoring indicators, yielding highly accurate results closely aligned with actual observations. Sensitivity analysis of these assessment indicators identified pivotal factors significantly impacting the evaluation outcomes. This method shows promise for widespread application in similar foundation pit projects.

Analysis of Structural Internal Force and Settlement on Nonlinear Elastic Foundation Based on Compression Curve

Gao Xinghe, Zhang Feng, Lv Ben, Li Can

2023, 37(5): 590-594. doi: 10.3969/j.issn.1007-2993.2023.05.012

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Foundation settlement is not only harmful to buildings, but also one of the main factors affecting the stress and deformation of superstructure. The layerwise summation method used in engineering settlement calculation takes the compression curve (e-p curve or e-lgp curve) as the input, which better reflects the nonlinearity of soil deformation and has good accuracy. A numerical calculation method of elastic foundation was developed in this research. Based on the compression curve, the tangent elastic modulus was obtained through the derivation of elastic theory, and the nonlinear finite element method was used for calculation. The example shows that this method is essentially the same as the layerwise summation method in the calculation of foundation settlement, and obtains rich results without the cumbersome manual calculation process. The stress and deformation analysis of superstructure can also better reflect the influence of elastic foundation. The calculation method of nonlinear elastic foundation based on compression curve does not need complex geotechnical test, and avoids the disadvantage of simple linear elastic constitutive model, so it has strong practical value.

Field Experimental Study on Compaction Performance of Impervious Soil Material in High Altitude Borrow of an Ultra-high Earth-rockfill Dam

Zheng Xing, Ao Dahua, Zhang Sheng, Wei Weiqiong, Yang Wenchao, Xu Yongwang

2023, 37(5): 595-601. doi: 10.3969/j.issn.1007-2993.2023.05.013

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An impervious soil material borrow of an ultra-high earth rock dam is located at an altitude of 3500 m. In-site compaction test of soil was carried out at this elevation. The tests include the selection of compaction parameters, the influence of variable moisture content on soil compaction characteristics, and the comparative study of compaction effects of different compaction methods. The experimental research shows that when the paving thickness of soil is 35 cm, the greatest degree of compaction is acquired. Considering the design index of soil compaction and cost, the paving thickness is determined as 30～35 cm and rolling times is 10. It is found that when the thickness of soil material is thin, the more rolling times, the greater the disturbance and the worse the compaction degree. Combined with the climatic conditions of the soil borrow, it is found that the loss of soil moisture content is 1.2% in the whole process from soil loading to compaction. By changing the moisture content of soil, the influence of moisture content on the compaction effect is explored, and the range of compactable moisture content of soil in the project is determined. The comparative experimental study of different compaction methods shows that the compaction degree obtained by vibratory flat roller is higher than that by vibratory bump roller under different paving thickness and rolling times.

Experimental Study on Freeze-thaw Cycle of Collapsible Loess Red Sandstone Integrated Cement Soil Filling Material

Jin Shenglian, Yang Zuoqing, Zhang Xin, Zeng Haizhen, Zhu Yanpeng

2023, 37(5): 602-608. doi: 10.3969/j.issn.1007-2993.2023.05.014

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In the collapsible loess area, the backfill area of the foundation trough often produces a large area of settlement due to the self-subsidence and collapsibility of backfill, which has a severe impact on the regular use of buildings and the everyday life of residents. According to the regional engineering practice, the collapsible loess-red sandstone integrated cement-soil filling material is put forward. The orthogonal test was carried out by setting different proportions of collapsible loess, red sandstone, cement, and water. The best mixture ratio of developing new foundation trench backfill material using loess and red sandstone was obtained. Through freeze-thaw cycling tests on integrated cement-soil specimens and plain cement-soil specimens, it was found that the freeze-thaw resistance of integrated cement-soil specimens is significantly better than that of plain cement-soil specimens, with better mechanical properties and durability. This study provides some reference for the engineering application of fill materials in collapsible loess areas.

Deterioration Characteristics of High-fill Loess Shear Strength under Freeze-thaw

Sun Jielong, Wang Hongqi, Li Shengbin, Li Dawei, Qiu Mingming

2023, 37(5): 609-613. doi: 10.3969/j.issn.1007-2993.2023.05.015

[Abstract](68) [FullText HTML] (13) [PDF 1524KB](17)

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Taking the high-fill loess in Yan'an New Area as an example, the experimental study on the shear strength of high-fill loess under freeze-thaw action was carried out, and the influence of freeze-thaw action on shear strength index of high-fill loess and its deterioration characteristics were analyzed. The results show that the cohesive force of high-fill loess decreases gradually with the increase of freeze-thaw cycles under the action of freeze-thaw, after the fourth freeze-thaw cycle the cohesive force damage increases to the maximum, and then decreases gradually with the continuation of freeze-thaw. When the dry density is the same, the smaller the water content, the greater the cohesion, and the smaller the moisture content under freeze-thaw, the greater the amplitude and rate of cohesion deterioration. The internal friction angle has no obvious regular change under the action of freeze-thaw. The cohesive damage degradation model of high-fill loess under freeze-thaw action is given and verified by independent test data. The results show that the model can effectively describe the cohesive force degradation characteristics of high-fill loess under freeze-thaw.

Study on the Effect of Drying and Wetting Cycles on the Crack Evolution and Strength of Expansive Mudstone

Song Lei, Zhang Rongkuan, Tang Yong

2023, 37(5): 614-617. doi: 10.3969/j.issn.1007-2993.2023.05.016

[Abstract](106) [FullText HTML] (39) [PDF 1004KB](15)

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Based on the indoor drying and wetting cycles test of the undisturbed expansive mudstone in a water conservancy project in Hefei area, the crack images of expansive mudstone under different times of drying and wetting cycles were analyzed, and the direct shear test was carried out. The results show that the cohesion and internal friction angle of expansive mudstone decrease with the increasing number of drying and wetting cycles time, and the fracture length and total fracture area increase with the increasing number of drying and wetting cycles under the condition of limited water swelling deformation. The research results have guiding significance for engineering construction in this kind of expansive mudstone area.

Experimental Study on Micro-macro Shear Properties of Sand Considering Particle Size

Wang Bo, Lv Guo, Li Jiang

2023, 37(5): 618-622. doi: 10.3969/j.issn.1007-2993.2023.05.017

[Abstract](57) [FullText HTML] (16) [PDF 2554KB](15)

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In order to explore the influence of sand particle size on its shear resistance, strain controlled direct shear apparatus and discrete element software were used to conduct shear tests on three kinds of sand with different average particle sizes, and the shear characteristics of sand were analyzed from both macro and micro perspectives. The results show that the shear strength increases with the increase of normal stress and average particle size, and the internal friction angle increases with the increase of average particle size. A multivariate linear prediction model of sand shear strength is established, and the model prediction is accurate. The thickness of shear band increases with the increase of average particle size. The relationship between shear band thickness and normal stress can be expressed by a quadratic function. Therefore, in the actual project construction, reasonable use of sand with larger particle size is conducive to improving the shear capacity.

Solutions to Problems Encountered in Deep Foundation Pit Affected by Multi-layer Groundwater

Liu Xuanpeng, Qin Guodong, Ma Shimin, Su Tiezhi, Guo Yongsheng, Yan Qiming

2023, 37(5): 623-630. doi: 10.3969/j.issn.1007-2993.2023.05.018

[Abstract](76) [FullText HTML] (23) [PDF 5802KB](28)

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The groundwater level in Beijing has generally risen under the influence of ecological water replenishment in recent years, which poses a great threat to the safety of foundation pit. A series of problems encountered in the construction of a foundation pit supporting project affected by multi-layer groundwater in Dongxiaokou area, Changping, Beijing, as follows: water stop curtain leaking; surface collapse; sand flowing between pile. Through the analysis of the reasons and combined with field tests, the effective technical treatment measures were adopted such as decompression of drainage holes, "double liquid" sealing of L-shaped grouting pipes, "formwork support" between piles, etc. The disease problems in the process of foundation pit excavation were solved, which ensured the safety of the foundation pit.

2023 Vol. 37, No. 5