岩土工程技术

2022, 36(3): 1-1.

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2022, 36(3): 1-3.

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Formation Mechanisms of High Rock-slope Deformation Under Heavy Rainfall

Liu Min, Zhou Kui, Zhang Chao, Yao Chenhui, Huang Lei, Liu Zhenghong

2022, 36(3): 173-178. doi: 10.3969/j.issn.1007-2993.2022.03.001

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A series of deformation and failure occurred at different elevations during the excavation process on the right bank slope of a dam site of a hydropower station under construction in Southeast Asia, which were mainly manifested as cracks, partial collapses, and landslides, and the slope was in a critical state of instability. Based on the actual engineering geological conditions, field geological survey and monitoring data after the excavation of the slope, the deformation characteristics of the slope were summarized and the cause mechanism of the deformation and failure was analyzed. The results show that the free surface is formed and the stress field is redistributed after slope excavation, and the rock mass rebound to the free surface, which intensifies the opening and penetration of the rock mass fissures, and provides a good channel for rainwater infiltration. The material in the F11 fault absorbs water and softens, resulting in uneven deformation, which lead to the cracks and partial landslides. The fracture accelerated its development to the deep and the rock (soil) softens rapidly as well as accumulates a large amount of compression creep due to the twice of heavy rains, the creep slip-pull crack type landslide is formed after the slip surface penetrates. This research could provide a certain degree of excavation and support for the later period.

Application of Pipe Pile Combined with Double Semicircular Support System in Foundation Pit Engineering

Xu Guan, Zeng Jie, Cheng Yichong, Wang Jiedong, Wu Caide

2022, 36(3): 179-184. doi: 10.3969/j.issn.1007-2993.2022.03.002

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Combined with the foundation pit of a project, the engineering application of prestressed pipe pile was carried out, and the advantages and disadvantages of different supporting systems were compared. The design and construction points, process parameters, structural section and deformation characteristics of double-ring internal support system of prestressed pipe pile were introduced. The regional deformation of prestressed pipe pile exceeds the alarm value, but there is no crack in the pile body, which verifies the safety and reliability of prestressed pipe pile as a supporting pile.

Application of Data Warehouse and Data Mining on Landslide Prediction

Qin Wentao, Guo Xiaokun, Guo Junfeng, Hao Lu, Hong Biwu

2022, 36(3): 185-189. doi: 10.3969/j.issn.1007-2993.2022.03.003

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In order to obtain effective prediction from the historical landslide data, the data mining technology based on data warehouse were used. Combined with the existing landslide multi-dimensional data set, taking the landslide disaster distribution in the new urban area of Badong County as the research object, the landslide disaster sensitivity and disaster zoning model are established. The result shows that the prediction accuracy of the model for the spatial distribution of landslide can reach about 87.5%, and the prediction accuracy on the time scale of landslide is low, about 65%. Its accuracy can meet the engineering requirements. The data warehouse and data mining technology in the field of geological disaster forecast has wide application prospect, which is more convenient and rapid than traditional prediction methods.

Study on Settlement Calculation Method of Composite Foundation in View of Interaction Between Ground and Foundation

Wang Haoran, Zheng Haoqin, Li Jie

2022, 36(3): 190-195. doi: 10.3969/j.issn.1007-2993.2022.03.004

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For the settlement calculation method of the composite foundation based on the assumption of flexible foundation, the calculated value is often larger than the measured value due to the non-uniformity of base reaction distribution under the influence of foundation interaction and the non coincidence between the maximum base reaction and the maximum settlement position. Two composite ground settlement calculation methods considering foundation interaction were studied, including the SFIA method and elastic theory method used in the foundation design module of YJK building software. Foudation settlement calculation was conducted based on the above two methods as well as flexible foudation method. Compared with the flexible foundation method, the calculated values of the maximum settlement and differential settlement of the foundation are smaller and closer to the measured values due to the consideration of the interaction effect of the foundation. The research results can provide reference for the settlement calculation of composite foundation.

Research on Construction Technology and Stress of Retaining Structure System with Recoverable Soil Nail Wall

Zhang Qinxi, Zhang Zhenshuang, Zhai Yuxin, Wei Meng, Wang Yu

2022, 36(3): 196-202. doi: 10.3969/j.issn.1007-2993.2022.03.005

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Based on the concept of green environmental protection and carbon neutrality, a recyclable soil nail wall supporting structure system was proposed, and the composition and construction process of the supporting structure system were introduced. The new supporting structure system was applied to practical engineering, and its mechanical performance was discussed. The variation laws of soil nailing axial force and active earth pressure under 1∶0.30, 1∶0.50 and 1∶0.70 supporting slopes were discussed, and the influences of different supporting slopes on soil nailing axial force and active earth pressure were analyzed, which were compared with the theoretical values calculated by modified formula in the code. The test results show that the axial force of soil nailing and active earth pressure increase with the increase of slope in the same depth. For the earth pressure at the same slope, the axial force of soil nailing increases with the increase of depth. According to the change of depth, comparing the actual value with the theoretical value, it can be concluded that the theoretical value and the actual value of active earth pressure have the same trend with the change of depth, and the theoretical value is slightly larger than the actual value. The theoretical value and actual value of axial tensile force of soil nailing show the same trend with the increase of depth. There is a big difference between the calculated axial force and the actual monitored axial force, and the theoretical calculation is relatively conservative.

Control Effect of Two Types of Retaining Walls Combined with Anti-slide Tie

Ta Guoshan, Liu Changqing, Kang Kai, Zhang Yuxiang

2022, 36(3): 203-207. doi: 10.3969/j.issn.1007-2993.2022.03.006

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Based on the landslide control project of a cableway base in Yanqing District of Beijing, the prevention and treatment effects of vertical retaining walls and inclined retaining walls combined with anti-slide tie were analyzed through modeling. The results show that for self-balancing retaining wall treatment plan, in the condition of certain length of the anti-slide tie and certain height of the retaining wall, when the top of the slope is a natural side slope and the external load is relatively small, the prevention effect of the inclined retaining wall combined with the anti-slide tie is better; when there is a large external load on the top of the slope,the prevention effect of vertical retaining wall + anti-slide tie balanced retaining wall is better. Through the comparative analysis of two self-balancing retaining walls, the treatment measure of vertical retaining wall + anti-slide tie was finally adopted. The supporting structure is currently operating well and the slope is stable, which has certain reference value for similar slope projects.

Stability Analysis of a Landslide in Yalong River

Li Hongying, Pu Shikun, Tan Yuehu

2022, 36(3): 208-213. doi: 10.3969/j.issn.1007-2993.2022.03.007

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In order to provide a reliable basis for landslide risk assessment, the stability of a typical landslide body was calculated and analyzed. Two different methods were used, compared and analyzed, including reliability method and strength reduction method. With the help of GEO-SLOPE software and the method of limit equilibrium theory, the stability of the landslide body was analyzed. The probability of instability of the landslide occurs under two conditions: water storage and heavy rain, water storage and earthquake. The finite element strength reduction method was used to analyze each working condition, and the relationship between seismic intensity and safety coefficient was obtained through software calculation and analysis. With the increase of seismic intensity, the safety coefficient decreases rapidly. It is convenient to calculate through limit equilibrium method but has great limitation. The finite element strength reduction method is based on the elastic-plastic theory, which can directly reflect the deformation, displacement and failure process of the landslide. This method is closer to the actual engineering situation.

Research on Application of Accurate Positioning and Detecting Technology for Deep-buried Foundation Piles

Wu Fengshou, Cui Ran

2022, 36(3): 214-218. doi: 10.3969/j.issn.1007-2993.2022.03.008

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In order to accurately detect the deep underground foundation piles left over from the urban renewal process, physical characteristics of foundation piles and the characteristics of engineering projects were analyzed. The comprehensive method combining high density electric method and magnetic gradient method was used to detect deep buried foundation pile. A variety of drilling methods were used, and the inclinometer was used to correct the change of deep hole channel inclination, so as to achieve the precise positioning of deep foundation pile. Through engineering application, it is proved that the method combining comprehensive geophysical exploration and scientific exploration can locate and detect the deep buried foundation pile accurately and effectively.

Application of Unloading and Pressure-foot Method in Treatment of Unstable Slope

Li Shigui, Xu Qian

2022, 36(3): 219-223. doi: 10.3969/j.issn.1007-2993.2022.03.009

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There are many approaches for the treatment of slope, among which the combined treatment method of unloading and pressure-foot is simple, convenient and effective. Reasonable unloading and pressure-foot treatment scheme can not only greatly save project cost and shorten project period, but also achieve permanent treatment effect. Taking an unstable slope in Shennongjia Forestry District of Hubei Province as an example, the method of unloading and pressure-foot was applied based on stability analysis calculation software. The influence of different bar numbers on the stability coefficient of slope was summarized, and the boundary between the main sliding and the resistant section was calculated. Four kinds of unloading and pressure-foot treatment schemes were designed. According to the stability coefficient and the remaining sliding force, the scheme that meets the standards requirements is selected. The optimal scheme is obtained by comparing the cost-performance ratio. This method could provide reference for similar slope and landslide treatment engineering.

Restoration Process and Measures of a Slope Damaged by Severe Disaster

Wang Wei, Mao Huiyong, Fan Jianpeng, Zhang Jiqiang

2022, 36(3): 224-229. doi: 10.3969/j.issn.1007-2993.2022.03.010

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Disaster assessment and supplementary geological survey were carried out, and monitoring data was analyzed in a damaged slope of a power plant in Nepal. Internationally stability analysis software was used for stability calculations. The deformation characteristics and causes were studied comprehensively, and the treatment schemes of integral restoration and local restoration were put forward. The slope restoration has been completed, and the slope is in good condition after the monsoon flood. It provides experience and reference for the treatment of artificial slopes after flood and earthquake disasters.

Analysis and Countermeasures of Key and Difficult Points in the Investigation of a Super Large Diameter Shield Project

Sun Changqing

2022, 36(3): 230-237. doi: 10.3969/j.issn.1007-2993.2022.03.011

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With the continuous development of urban municipal construction to ultra deep underground space, super large diameter tunnel construction technology is gradually adopted. At present, the technology of super large diameter shield tunnel is developing in the direction of large depth, large section and long distance. Due to the large cross-section size, large fluctuation of buried depth, complex engineering geological and hydrogeological conditions, complex geotechnical engineering problems will be encountered. Based on the reconstruction tunnel project of Beijing East Sixth Ring Road, the characteristics of the large-diameter shield project, such as high survey level, complex engineering geology and hydrogeology, and great difficulty in ultra deep foundation pit support and groundwater control were summarized. Standard penetration in situ test and indoor physical and mechanical tests such as particle analysis, static lateral pressure coefficient and subgrade bed coefficient have been carried out. A special hydrogeological survey such as layered observation of groundwater level, pore water pressure test of cohesive soil layer, pumping test and water injection test was carried out to provide hydrogeological parameters. All these provided a basis for the selection of super large diameter shield machine, cutter head and cutter configuration, the matching of various construction parameters in the process of super large shield tunneling, the support design of shield shaft and the design of groundwater control scheme. It also provides reference for similar projects.

Analysis of Ground Settlement Caused by Shield Passing Through the Area of Long-term Precipitation

Wang Yong, Sheng Zhizhan, Gao Sufang, Hu Gaowei

2022, 36(3): 238-242. doi: 10.3969/j.issn.1007-2993.2022.03.012

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The main stratum of Chengdu rail transit construction is sandy pebble stratum, which is mixed with a large number of fine particles. Some EPB tunnels need to cross the existing cut and cover stations with long-term precipitation. The vertical displacement of soil mass during construction is significantly different from that in the area without precipitation. Soil structure, settlement mechanism, settlement control mode and engineering examples in long-term precipitation area were analyzed, and conclusions are as following: (1) long-term precipitation of foundation pit will lead to the loss of fine particles in the sandy pebble stratum, forming a skeleton pore structure; (2) the properties of grouting and improved grouting materials have a significant control effect on the vertical displacement of soil caused by area of fine particle loss due to long-term precipitation; (3) the largest proportion of settlement is caused by the shield tail out stage when the precipitation area is not entered, the proportion of soil consolidation settlement and cutter arrival stage increases after entering the precipitation area. The conclusions have been verified by the shield engineering of Ming-Jiu section of Chengdu rail transit Line 17, and the research results can provide theoretical basis and reference value for similar projects.

Effects of Freeze-thaw Cycles on the Strength of Straw Fiber-reinforced Soil

Liu Lu

2022, 36(3): 243-247. doi: 10.3969/j.issn.1007-2993.2022.03.013

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Straw fiber-reinforcement is a newly developed soil improvement technology. The variation in soil strength caused by seasonal temperature changes damages the safety and stability of geotechnical engineering projects. To investigate the effects of freeze-thaw cycles on the strength of fiber-reinforced soil, the unconfined compressive tests and the direct shear tests of reinforced samples are carried out after different freeze-thaw cycles. The test results indicates that unconfined compressive strength and the cohesion of the soil samples decreases exponentially with the increasing number of freeze-thaw cycles. However, the decrease ratio of the reinforced soil is smaller than that of the unreinforced soil. The internal friction angle of the soil samples increases exponentially with the increasing number of freeze-thaw cycles. Moreover, SEM indicates that a very distinct increase in the amount of pores and microfissures is found in the unreinforced soil after the cycles. This leads to the decrease of soil strength. The soil surrounding the fiber becomes less dense after freeze-thaw cycles, which indicates the decrease in the interfacial strength of the fiber/soil. However, the complex spatial stress network established by fibers still plays an role in the reinforcement of the fibers, which can improve the stability of frozen soil.

Non-in Situ Test Analysis of Reinforcement Construction Near Subway Tunnel

Zhang Cheng

2022, 36(3): 248-251. doi: 10.3969/j.issn.1007-2993.2022.03.014

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Triaxial mixing pile was used to reinforce the soil around the subway tunnel of Shanghai Metro Line 2. In order to test the influence of construction method on subway tunnel structure and optimize the design of construction parameters, non-in situ test research was carried out before construction. During the construction of triaxial mixing pile, the lateral displacement of deep soil in the range of 1.5~3.0 m from the center of pile wall was tested. The test results show that when triaxial mixing sinks to the design depth, the deformation of surrounding soil reaches the peak value. The deformation value begins to fall 3 hours after pile completion, and the deformation was basically stable at 1~2 mm at 64 hours after pile completion. The deformation depth was mainly in the shallow part, and the superposition influence of construction would lead to the downward movement of the deformation influence depth. This research could provide reference for similar projects.

Experimental Study on Static Characteristics of Calcareous Sand Solidified by Nano-SiO₂Superfine Cement

Jiao Huihui, Chen Hao, He Qingkun, Gao Meng

2022, 36(3): 252-258. doi: 10.3969/j.issn.1007-2993.2022.03.015

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To study the incorporation of nano-SiO₂ for calcareous sand-super fine cement plus solid static characteristics, nano-SiO₂ and ultra-fine cement were used to replace ordinary portland cement to reinforce calcareous sand. Unconfined compressive strength test and triaxial shear test were designed under different conditions, and the microstructure of samples was observed by SEM to analyze the mechanism of action. The test results show that superfine cement has better reinforcement effect on calcareous sand than ordinary portland cement; there is a critical value for the effect of nano-SiO₂ incorporation on the strength of ultrafine cement, and the strength decreases after the amount exceeds the critical value. In terms of peak strength, peak strain and cohesion, nano-SiO₂ can improve the static characteristics of superfine cement calcareous sand. From a microscopic point of view, it is found that ultra-fine cement produces more ettringite crystals than ordinary cement, forming a certain grid-like structure, thereby enhancing its macro strength.

2022 Vol. 36, No. 3