2023 Vol. 37, No. 1

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2023, 37(1): .
Abstract:
2023, 37(1): 1-3.
Abstract:
Technology Development and Exploration
Deformation Analyses of Large Section Rectangular Pipe Jacking Crossing Underneath Combined Sewage Culvert
Ding Chuansong
2023, 37(1): 1-6. doi: 10.3969/j.issn.1007-2993.2023.01.001
Abstract:
Surrounding influence caused by the construction for large section pipe jacking has obvious size effect. When pipe jacking crossing underneath sewage culvert, it is of vital importance to analyze the deformation of sewage culvert and surrounding soil, and provide the guiding suggestion for construction. In the process of large section pipe jacking crossing underneath the combined sewage box culvert, the basic law of vertical and triaxial displacement of sewage culvert, vertical displacement and pore pressure of soil in deep stratum were analyzed. Based on data information, construction measures were adopted to overcome the difficulties of difficult construction controlling procedures, small crossing space, high risks etc. The conclusion provide valuable regional experience for future.
Study on Seismic Stability of West Slope of Tianwan Nuclear Power Station
Zhang Shuxuan, Chen Liwei, Liu Xiangyu, Zheng Xuan
2023, 37(1): 7-12. doi: 10.3969/j.issn.1007-2993.2023.01.002
Abstract:
The west slope of Tianwan nuclear power station is a slope related to nuclear safety. When evaluating the stability of the slope, the seismic action should be determined according to the ultimate safe ground motion (once in ten thousand years) of the nuclear power station, and the slope stability coefficient should meet the requirements of the code for seismic design of nuclear power station. Based on the depth study of the engineering geological conditions of the west slope of the nuclear power station, considering various calculation conditions, the stability of the slope is comprehensively evaluated by using the limit equilibrium method and the finite difference method. The results show that the original west slope of Tianwan nuclear power station is stable as a whole, but it still has the risk of local sliding under rare seismic. The west slope of Tianwan nuclear power station formed after excavation process after is stable in both natural and rare seismic conditions, and it will not bring the threat to buildings which related to nuclear safety.
Application of Double Point Linear-angular Intersection in Foundition Pit Monitoring
Yan Boduo, Wang Yuping, Ma Lianzhong, Sun Huichao
2023, 37(1): 13-18. doi: 10.3969/j.issn.1007-2993.2023.01.003
Abstract:
According to the characteristics of foundation pit engineering, the datum point (network) for monitoring the horizontal displacement of foundation pit was established based on double point liner-angular intersection method, and the working datum point (line) could be detected and calculated. The practical application shows that the method is simple, convenient and accurate, and can meet the requirements of foundation pit monitoring. Some practical suggestions are presented for reference.
Road Performance Analysis of Different Solidified Silt Base Based on DCP
Sun Zhaoyun, Wang Lin, Zhang Lei, Fu Guanghui, Gao Han
2023, 37(1): 19-23. doi: 10.3969/j.issn.1007-2993.2023.01.004
Abstract:
In order to analyze the road performance of asphalt emulsion, asphalt powder and inorganic compound type solidified silt base course, field dynamic cone penetrometer (DCP) tests of different structural layers were conducted based on the Yellow River alluvial plain rural highway project, and compared with 8% cement solidified silt base simultaneously. The results show that the penetration of asphalt emulsion, asphalt powder and inorganic composite solidified silt base is between 1.33 mm/blow and 1.74 mm/blow, less than 2.09 mm/blow of the penetration of cement stabilized silt structural layer, and the overall curing effect is better. There is a good correlation between DCP converted unconfined compressive strength and measured unconfined compressive strength of coring, DCP cumulative average penetration and FWD deflection of the three different solidified silts, layered calculation and cumulative calculation can be used for rapid evaluation of single-layer strength and overall bearing capacity respectively. The DCP test results can also provide data reference and engineering reference for the evaluation of improved and solidified road performance of silt in the alluvial plain of the Yellow River.
Application of Accurate Location and Comprehensive Detection of Urban Subsurface Obstacles
Wu Fengshou, Cui Ran
2023, 37(1): 24-28. doi: 10.3969/j.issn.1007-2993.2023.01.005
Abstract:
In the process of urban development, a large number of obstacles have been left underground, such as building structure foundation and concrete pipeline, which has brought new challenges to urban modernization. According to the characteristics of unique urban spatial structure and rich interference sources, the advantages and disadvantages of geophysical exploration techniques in the detection of urban underground obstacles were analyzed, such as geological radar, high-density electrical method and seismic imaging. By using a variety of geophysical methods combined with penetration and trenching, the regular and irregular obstacles were located and delimited accurately, which provided a basic guarantee for construction design and effectively solves the problems encountered in the project.
Study on Displacement Prediction of Completely Weathered Slope Based on Set Pair Analysis and Combination Theory
Liu Wenjie, Huang Yongjun, Pan Shiqiang, Tan Peng
2023, 37(1): 29-34. doi: 10.3969/j.issn.1007-2993.2023.01.006
Abstract:
The displacement of weathered granite slope is affected by many uncertain factors, resulting in complicated uncertain problem for its prediction. A weathered granite slope in Ping-Yi Expressway was taken as the study object. Based on a small number of monitoring data, five single prediction models were established. Then, the set pair relationship between each single model predicted value and the measured value was quantitatively analyzed based on the set pair relation criterion, and the combination weight coefficient was determined by the relation number.Finally,the combined prediction model of slope displacement was established, and the predicted value was compared with the measured value. The study shows that the optimal combination of prediction information is realized by using the set pair analysis and combination theory. Compared with the single model, the maximum relative error of the combined model is less than 20%, and the absolute error square SSE, standard error SSE as well as other indicators are small, which can provide a more reliable basis for dynamic slope construction management. The application scope of the set pair analysis and combination theory is expanded, and ideas for solving displacement prediction problems of other similar projects are provided.
Determination of Rock-socketed Pile Interface in Granite Area of Shenzhen, China
Zhao Jie, Jia Shaojie, Jia Haipeng
2023, 37(1): 35-41. doi: 10.3969/j.issn.1007-2993.2023.01.007
Abstract:
Affected by the development of fissures and uneven weathering, the surface of the medium- or micro- weathered bedrock has significant undulations, companying with weak interlayers and spherical boulders. The correct determination of the rock-socketed pile interface is the key, but there are no unified judgment standards and methods at present. Accordingly, with the background of the characteristics of granite strata in Shenzhen, relying on the engineering example of a high-rise building embedded rock pile, the engineering experience of the rock-socketed pile interface determination from the perspective of investigation and construction were summarized. Combining the low-strain integrity test and the field load test, the bearing capacity effect of a single pile with higher bearing capacity requirements was evaluated. According to the test results, the integrity of the pile body was evaluated as class Ⅰ. The measured values of vertical compressive bearing capacity of single pile meet the maximum load required by the load test and meet the design requirements.
Contrastive Study on Permeability Characteristics of Angolan Red Sand and Chinese Malan Loess
Li Shuo, Xu Qingqing, Qiao Jianwei, Liu Min
2023, 37(1): 42-46. doi: 10.3969/j.issn.1007-2993.2023.01.008
Abstract:
The permeability coefficients of Luanda red sand in Angola is measured by laboratory variable head permeability test and double-ring water infiltration test. Based on the test data and references, the permeability characteristics of Angola red sand and Chinese Malan loess were compared and analyzed. The results show that the permeability coefficient of natural red sand in laboratory test is 1/8 of that in field test, and the permeability coefficient of compacted red sand in laboratory test is close to that in field test. The logarithm of the permeability coefficient of red sand is positively correlated with the void ratio, and increases linearly with the increase of void ratio. The permeability coefficient of red sand can be estimated according to the void ratio in engineering construction. The permeability coefficient of red sand in natural state is about 10 times that of Malan loess, and the field test results are greater than the laboratory test results. Both red sand and Malan loess have horizontal infiltration and vertical infiltration, but the infiltration distance of red sand is larger than Malan loess. The infiltration process of red sand is mainly unsaturated, while that of Malan loess is mainly saturated. The research results can provide reference for engineering construction in red sand area.
Numerical Simulation on Optimization of Support System for a Tunnel through Debris Flow Deposits
Zan Wenbo, Zhong Yujian, Wang Enbo, Qian Ruolin
2023, 37(1): 47-52. doi: 10.3969/j.issn.1007-2993.2023.01.009
Abstract:
Based on Nianggai village tunnel in Nyingchi-Lhasa section of national highway 318, three optimized measures proposed were aimed at deficiencies of steel frame and shotcrete net support for a tunnel through debris flow deposits. The numerical models with complete consistence were established to analyze the effects of each optimized measure comparatively. The results show that three optimized measures are of effective benefit for controlling vault settlement and peripheral convergence, and the effect of grouting behind initial support, optimized bolt and double-layer densifying reinforcement mesh are in descending order. The backfilling grouting is prone to cause the uplift of inverts, therefore, the grouting amount and pressure must be strictly controlled. The axial force of feet-lock bolt is increased to 110.3% compared to the original one after removing the systematic bolts. The distribution of positive and negative bending moment for the initial support is more uniform, and then it is more advantageous to the structure stress. The bending moment of the support is increased to 1.63 times of the original one when double-layer densifying reinforcement mesh is adopted. A larger range of surrounding rock around the cavern is mobilized to participate in bearing capacity together. Furthermore, the bending moment of supporting structures and axial force of the bolts are reduced to 67.6% and 79% compared to the original one. It is indicated that the proposed optimized measures are significantly effective to control tunnel deformation and reduce the stress of supporting structure. The research conclusions are supposed to provide reference for the selection of tunnel support method in debris flow accumulation.
Research on Formation Mechanism and Optimization Control of Segment Crack Damage under Combined Thrust
Yao Xufei, Niu Xiaokai, Sun Xiaoyu, Li Mingxing
2023, 37(1): 53-59. doi: 10.3969/j.issn.1007-2993.2023.01.010
Abstract:
The damage of segment under the thrust of jacks during construction was studied. Based on the actual situation of a subway line in Suzhou, a multi-ring three-dimensional finite element model was established to analyze the formation, evolution and distribution of shield segment fracture under the combined action of excessive and uneven thrust of jacks, and the corresponding engineering control measures were put forward. The results show that the segment damage is mainly distributed uniformly along the bolt hole under different thrust, and the damage on the inner cambered surface is larger than that on the outer cambered surface. The maximum damage factor of the segment increases approximately linearly, and the damage area increases nonlinearly. When thrust is evenly distributed, segment damage is mainly concentrated in the first ring segment, while when thrust is not uniform, segment damage will transfer to the side with larger thrust, and gradually develop to the second and third ring segment. The uneven thrust forces advance the loading of segment cracks by about 11% under the same thrust. The formation of segment crack damage during shield construction can be reduced by adopting engineering control measures such as strictly controlling uneven thrust of jacks, optimizing segment design and implementing segment control.
Stability Evaluation and Treatment Measures of High Slope
Liu Haiting, Zhu Youlu, Yang Peng, Nie Shouzhi
2023, 37(1): 60-65. doi: 10.3969/j.issn.1007-2993.2023.01.011
Abstract:
Taking a high slope as example, the cause of local slump was analyzed according to the basic characteristics of the high slope. The potential slip surface of high slope was determined by comprehensive analysis, and its stability was qualitatively and quantitatively evaluated. After the demonstration of various landslide control schemes, the comprehensive control scheme of graded brush slope unloading + pile-plate anti-slide retaining wall + anchor cable frame beam + drainage + afforestation was finally adopted. The synergistic relationship between pile and anchor cable was fully considered in the treatment. The change of potential sliding surface and the comprehensive determination of residual sliding force after slope brushing were designed and analyzed, and the pile section size and pile distance were optimized. The research results can be used in the treatment of similar high and steep slopes.
Stability Analysis and Reinforcement Design of Bedding Rock Slope
Yang Yifei, Sun Shaorui, Min Wang, Yu Yongxiang, Song Jinglei
2023, 37(1): 66-71. doi: 10.3969/j.issn.1007-2993.2023.01.012
Abstract:
Taking the bedding rock slope of Qixia Ancient Town in Nanjing as an example, the stability of the slope after excavation was studied by using the limit equilibrium method and the strength reduction method, and the causes of slope instability and deformation characteristics were analyzed. The reinforcement scheme was designed for the potential landslide problem of the slope, and the reinforcement effect of the bolt under different combinations of length and inclination angle was simulated. According to the slope stability coefficient and the displacement and stress distribution of the slope after anchoring, the bolt length of 7 m and inclination angle of 20° are determined as the best schemes. Combined with other reinforcement measures, the stability of the slope is improved. The analysis results show that the slope stability coefficient after reinforcement meets the specification requirements, and the slope displacement is controlled within the safe range. The reinforcement design scheme is reasonable and feasible.
Influence Analysis of Injection-production Operation of Salt Cavern Gas Storage on the Safety of Adjacent Railways
Zhang Xing, Li Wenbin, Xie Nan, Ben Jianhua, Wang Chenglin, Huang Shenglong, Ye Liangliang
2023, 37(1): 72-76. doi: 10.3969/j.issn.1007-2993.2023.01.013
Abstract:
Salt cavern gas storage is a main method of underground natural gas storage. With the construction and development of salt cavern gas storage in China, its position in the oil and gas storage and transportation industry has become very prominent. At the same time, due to the rheological characteristics of salt rock, the volume of the salt cavern will gradually decrease with the operating time during the operation of the gas storage, which may cause a series of environmental problems such as surface subsidence. For the construction project of salt cavern gas storage in Pingdingshan, the surface subsidence caused by salt cavern in the operation of gas storage was simulated by using the power exponential model suitable for salt rock creep deformation, and the possible influence on the operation of adjacent railways was analyzed. It shows that after 30 years of operation, the subsidence of the gas storage area is uniform as a whole, with no obvious surface tilt. The maximum subsidence in the area is 196 mm, and the maximum vertical and horizontal tilt rates do not exceed 0.1 mm/m. The regional ground subsidence caused by the operation of gas storage group has no obvious influence on the operation of the adjacent railway.
Application of Precise Design Concept in Prevention and Treatment of Slope
Zhang Lizhan, Wang Duli, Wang Xiaobo, Li Shu
2023, 37(1): 77-82. doi: 10.3969/j.issn.1007-2993.2023.01.014
Abstract:
Based on an unstable slope in Fangshan district of Beijing, three hidden dangers were pointed out by precise investigation and analysis of requirements of protected object and engineering geological conditions. The hidden dangers were the unstable slope behind the house, the collapse of the roadbed and the collapse of the retaining wall in front of the yard. On the basis of taking the geological and topographical conditions and householders’ requirements into consideration, precise design concept was applied. Gravity retaining wall and intercepting drain were used to control the slope behind the house. Two-stage gravity retaining walls were used to treat the collapse of the roadbed. Sheet pile wall was applied to prevent the collapse of the retaining wall in front of the yard. Precise design concept in prevention and treatment of slope was discussed and summarized. The principles of ‘project safety, convenient construction, economical cost, people-oriented and environment-friendly’ were put forward.
Experimental Research
Analysis of Bearing Characteristic of Drilling Expanded Bottom Cast-in-situ Piles
Zheng Jinhuo
2023, 37(1): 83-88. doi: 10.3969/j.issn.1007-2993.2023.01.015
Abstract:
To study the bearing characteristic of drilling expanded bottom cast-in-situ pile, static load tests of two expanded bottom bored piles of different shape and one equal diameter pile were conducted, as well as pile stress tests of the expanded bottom bored piles. Test and data analysis results show that the influence of sediment and soil softening on the bearing capacity of expanded bottom pile is relatively sensitive. In addition to directly affecting the pile end resistance, it will also produce the weakening effect of pile side friction resistance. The shape of the enlarged head affects the slag removal effect at the bottom of the hole, and the high pressure grouting at the bottom of the pile can eliminate or partially eliminate the influence of the sediment. The development value of the pile side friction resistance of the same soil layer of different test piles is not fixed. Affected by the diameter change of the expanded bottom pile, the pile side friction resistance of the same soil layer of the same test pile within the range of 3 m above the diameter change is 15%~40%, lower than the value of the pile side friction within the range of 3 m above the diameter change. The test results can provide reference for the design and construction of expanded bottom piles.
In-situ Test Study on Pressured Anchor through Soft Soil in Coastal Foundation Pit
Li Peng, Qu Liqing, Wang Yu, Wang Dianbin, Nie Ning
2023, 37(1): 89-94. doi: 10.3969/j.issn.1007-2993.2023.01.016
Abstract:
Thick marine marshy soft clay are widely distributed in the north shore of Qingdao Jiaozhou Bay. To study the applicability of pressured anchor through the thick soft soil, in-situ comparative tests about pressure-dispersive anchor, tensioned anchor and capsule type pressured expanding anchor were carried out. The test results show that the ultimate bearing capacity of pressure-dispersive anchor and capsule type pressured expanding anchor is less than acceptance standard value. Relative to the ultimate bonding strength and the local bearing capacity, the overall instability of anchorage body caused by the bending of anchor during hole formation may be the main reason for the insufficient ultimate bearing capacity of pressured anchor through soft soil. It is suggested that tensioned anchor should be used first for the prestressed anchor crossing soft soil in coastal foundation pit engineering.
Experimental Study on Water Infiltration Law of Loess Foundation
Chen Mohan, Luo Yunhai, Wang Xiaoyan, Zhang Xuan
2023, 37(1): 95-99. doi: 10.3969/j.issn.1007-2993.2023.01.017
Abstract:
The soaking of soil by water is the decisive condition for the collapse deformation of collapsible loess, so it is of great significance to study the water infiltration law of loess foundation to solve the engineering problems of collapsible loess. The study on the law of water infiltration of loess foundation has certain reference value for collapsible deformation mechanism, foundation treatment, waterproof measures and protection distance. Taking natural loess and compacted loess from Luochuan loess plateau of Shaanxi province as research objects, the microstructure of the loess was studied by scanning electron microscopy, and the permeability coefficient was determined by single-ring water injection test. Meanwhile, food grade brilliant blue aqueous solution was used as tracer of soil water transport, and the spatial distribution pattern of water infiltration was intuitively studied by excavation profile. The results show that the water begins to converge in the horizontal direction at a certain infiltration angle to a certain depth, and finally forms a falling funnel like precipitation. The overall infiltration profile is diamond shaped, and the infiltration angle increases with the decrease of the permeability coefficient.
Application of High Power Vibroflotation Gravel Pile in the Treatment of Liquefied Foundation
Zhang Kai, Song Keying, Feng Keming, Dong Anxin, Han Shoucheng
2023, 37(1): 100-104. doi: 10.3969/j.issn.1007-2993.2023.01.018
Abstract:
A subway depot in Beijing covers an area of about 20 hectares. The ②5 layers of saturated silty fine sand within 20 m depth of the site will produce liquefaction. The liquefaction grade is slight to medium (locally serious), and the thickness of liquefiable layer is 5 m. In the rail transit project, the high-power 100 kW vibroflotation gravel pile is used to treat the liquefied foundation for the first time. The test results show that the vibroflotation gravel pile with large pile spacing not only meets the design requirements of foundation liquefaction treatment, but also creates conditions for the in-situ construction of cast-in-place pile in the later stage. At the same time, the combination of high-power vibroflotation gravel pile and CFG pile foundation treatment is applied to the site, which solves the problems of foundation liquefaction and post construction settlement of track subgrade.
Deep Foundation Pit Technology
Application of Chained Wall in Deep Foundation Pit Engineering in Soft Soil Area
Yao Huang, Cheng Yichong, Wang Jiedong, Wu Caide, Gong Dikuai
2023, 37(1): 105-110. doi: 10.3969/j.issn.1007-2993.2023.01.019
Abstract:
Chained wall of precast concrete piles is an innovative foundation pit retaining structure with both earth retaining and water stopping functions. Based on a deep foundation pit project in soft soil area of Ningbo, the difficulties and key technologies in design and construction of the chained wall were summarized, and the chained wall was compared with traditional bored pile in terms of construction convenience and environmental protection. The results show that the chained wall has the advantages of safety, efficiency and environmental protection, and it is suitable for foundation pit engineering in soft soil area.
Calculation Analysis and Application of Ring Brace Stiffness of Circular Deep Foundation Pit
Song Dexin, Tao Jun, Wu Ren
2023, 37(1): 111-117. doi: 10.3969/j.issn.1007-2993.2023.01.020
Abstract:
Through an example of a circular foundation pit, the horizontal stiffness coefficient of single annular support was deduced, and a simple calculation formula of stiffness coefficient of annular support was proposed. Its analytical solution was used as the initial data for calculating the stiffness of supporting structure element. Through the displacement and internal force calculated by BSC and Midas GTS-NX, combining with the measured displacement and internal force after foundation pit excavation, the horizontal stiffness of the ring brace was deduced and compared with the analytical solution. The results show that the horizontal stiffness coefficient calculated by the analytical solution is larger than that calculated by the inverse calculation. According to the comparative analysis, the calculation formula of the horizontal stiffness coefficient of the ring brace was modified. The modified results can basically coincide with the inverse calculation, which can provide guidance for the design and construction of similar circular deep foundation pit.
Analysis on Deformation Characteristics of Super Large Diameter Ring Bracing Deep Foundation Pit in Soft Soil near Subway
Qiao Liping, Li Yundi, Yang Chao
2023, 37(1): 118-126. doi: 10.3969/j.issn.1007-2993.2023.01.021
Abstract:
Taking the foundation pit of Minghui Garden (phase II) in Shenzhen reclamation area as the engineering background, the monitoring data of lateral deformation, slope top displacement and support axial force caused by foundation pit construction were analyzed. The temporal and spatial distribution characteristics of deep foundation pit deformation in soft soil were discussed, and the relationship between foundation pit deformation and excavation depth as well as soft soil thickness was discussed. The conclusions were as followed: (1) The maximum deformation of the supporting structure gradually increases with the increase of the excavation depth of the foundation pit. After the foundation pit was excavated to the bottom of the pit, the maximum overall deformation was located at the middle of the long side on both sides of the foundation pit, which was supported by a ring. (2) The application of bite pile + super large diameter ring reinforced concrete support structure with large stiffness in soft soil deep foundation pit was very effective in deformation control and reducing the influence of foundation pit engineering on surrounding deformation. (3) With the continuous excavation of the foundation pit downward, the maximum horizontal displacement of the support structure reflected by the three methods gradually increases, but the variation range was different.