岩土工程技术

2024, 38(4): 1-1.

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2024, 38(4): 1-3.

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Analysis on Characteristics and Optimization of Common Drilling Technology in Engineering Investigation

Dong Jiaoshe, Qu Weijia, Zhang Wenzhuo, Liu Gaomin

2024, 38(4): 379-383. doi: 10.3969/j.issn.1007-2993.2024.04.001

[Abstract](268) [FullText HTML] (55) [PDF 719KB](130)

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Combined with the actual situation of engineering investigation, the characteristics of core pipe drilling, threaded drilling, three-wing drilling and impact drilling, such as adapted strata, the drilling process, disturbance and destruction to soil, operation procedure, were analyzed. The advantages and disadvantages of these four kinds of drilling techniques were summarized in detail. According to engineering investigation experience and the analysis and research on the mechanism of each drilling process, threaded drilling has absolute advantages in terms of the accuracy of stratification discrimination, the quality of samples and the reliability of standard penetration test data for clay and interlayered or mixed soil dominated by clay. There is no major breakthrough in four kinds of drilling technology widely used in the field of engineering investigation, and all kinds of related drilling equipment are aging. This analysis further described the progress of improvement and optimization on drilling technology, and the research direction and expectation of drilling technology in engineering survey were put forward.

Design Technology Innovation of “Two Walls Integration” Diaphragm Walls in Deep Foundation Pits

Li Wei, Li Yongdong

2024, 38(4): 384-390. doi: 10.3969/j.issn.1007-2993.2024.04.002

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A project in Beijing CBD has a foundation pit depth of 36 meters. Due to space limitations, a “two walls integration”+internal support system was adopted to achieve the functions of retaining soil and water in the foundation pit, while completing the construction of the exterior wall of the underground structure. To improve the quality and construction efficiency of the project, technological innovations have been made in the connection between the ground connecting wall and the main structure, the treatment method of groove section joints, and the combination of limited space guide walls and pre-bracing of adjacent buildings. Good engineering results have been achieved, which can be used as a reference for similar projects.

Influence of Shield Close-spaced Construction on Settlement of Bridge Pile and Protective Measures

Lin Xiang, Chen Xiangyu, Wei Jincheng

2024, 38(4): 391-397. doi: 10.3969/j.issn.1007-2993.2024.04.003

[Abstract](138) [FullText HTML] (52) [PDF 6535KB](34)

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During close-spaced tunnel construction passing through existing bridge piles, and based on the field measured data, the change rules of bridge pile settlement, the settlement proportion of each stage, the distribution of soft strata in the tunnel body, and the impact of sleeve valve pipe driving method on the bridge pile settlement were analyzed. The conclusion shows that when shield tunneling side through bridge piles in soft strata, the vertical displacement of the bridge pile shows the change rule of “first rising slightly, then sinking”; the settlement of bridge piles mainly occurs during and one week after the shield passes, accounting for 80%～90% of the total settlement; when the plane clear distance between the tunnel and the bridge pile is less than 2D, the bridge pile adjacent to the tunnel shall be pre-grouted with sleeve valve pipe around the pile for reinforcement, which can effectively reduce the impact of shield construction on the settlement of the bridge pile; the higher the distribution proportion of soft soil layer in the tunnel body, the greater the settlement of bridge piles; the sleeve valve pipe grouting hole around the pile shall be set vertically to avoid the blind area of grouting, so as to ensure the effect of soil reinforcement and bridge pile settlement control.

Kalman Filter in Automatic Monitoring Data Noise Processing

Zhang Zizhen, Zhou Honglei, Zhang Jiankun, Jia Hui

2024, 38(4): 398-401. doi: 10.3969/j.issn.1007-2993.2024.04.004

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The application of Kalman filtering in denoising static leveling and fixed inclinometer raw data was investigated. The results indicated that under slow deformation conditions, Kalman filtering can effectively filter out noise in the original data, provide reliable results, and reveal the true deformation situation of the monitored object. But in case of sudden deformation, Kalman filtering reflects lag. Therefore, in practical applications, the data before and after filtering should be comprehensively used to more accurately analyze deformation trends and patterns. It provided new ideas and methods for noise processing in automatic monitoring data. The application of Kalman filtering can further improve the accuracy and reliability of monitoring data, providing support for engineering safety monitoring and geological disaster warning.

Characteristics and Prediction Method of Ground Settlement Caused by River Crossing Construction of Shield Tunneling in Soft Soil Area

Lian Tian, Chen Youwen

2024, 38(4): 402-407. doi: 10.3969/j.issn.1007-2993.2024.04.005

[Abstract](127) [FullText HTML] (49) [PDF 1357KB](38)

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River crossing construction of shield tunneling causes loss of soil mass and settlement of surface and upper bridges. Based on a shield construction project with river crossing construction in a muddy soft soil area, the ground and bridge pier settlement characteristics caused by river crossing construction under shallow overburden conditions were measured and analyzed. A method for predicting the settlement caused by the river crossing construction of shield tunneling considering construction sequences and process parameters was proposed using the long-short-term memory network model. The settlement control measures of construction were also discussed. The research shows that the settlement change of monitoring points in front of the river caused by river crossing construction can be divided into four stages. The surface settlement of the measuring points near the river is greater than that of other measuring points of the shield section. The settlement of pile foundations mainly occurs during the process of shield tunneling crossing the river. The analysis based on the measured data shows that the long-short-term memory network model can better characterize the construction impact parameters and corresponding settlement of each ring and can be used for the settlement prediction analysis caused by the river crossing construction of shield tunneling.

Structural Characteristics of Large-angle Cable-stayed Pile

Wang Zhen, Gou Jiaman, Zhang Xiangheng, Zhang Hao, He Jianyong

2024, 38(4): 408-414. doi: 10.3969/j.issn.1007-2993.2024.04.006

[Abstract](116) [FullText HTML] (42) [PDF 2547KB](34)

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The large-angle cable-stayed pile support structure can save space outside the pit, has advantages such as convenient construction and low cost, and is suitable for scenarios where the anchoring space outside the pit is limited. To further study its deformation and stress mechanism, typical medium-dense sandy soil was selected for numerical modeling of a single soil layer, and the stress and deformation characteristics of the structure were analyzed by changing the angle of the anchor cable and the excavation depth. The results show that the change of the angle of the anchor cable has a great impact on the stress and deformation of the structure, and simplifying the anchor cable into a horizontal elastic support will produce a large calculation deviation. It is necessary to consider the effect of axial force on the flexural and shear bearing capacity of pile and the vertical bearing capacity of single pile. On this basis, the constraint effect of anchor cable on soil retaining pile is considered as inclined elastic support, and a mechanical calculation model which is more in line with the actual stress state and the plane rod system finite element method were established. It is applied to a practical project and compared with the monitoring data. The results show that: large angle cable-stayed pile has good supporting performance, and the mechanical calculation model proposed can reflect the stress and deformation characteristics of this new structure.

Remedial Reinforcement Methods for Seepage Damage in Foundation Pits Near Rivers and Streams

Gu Weibin, Guo Bailiang, Cai Qiang, Cai Minghui

2024, 38(4): 415-419. doi: 10.3969/j.issn.1007-2993.2024.04.007

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A riverbank foundation pit utilized a triaxial cement-soil mixed wall for water seepage prevention. During excavation, water gushing, sand effusion, and seepage destruction occurred. After several unsuccessful attempts at sealing and remediation, a combined technique of dual-liquid grouting with jet grouting piles was proposed. The issues of water and sand gushing were solved, and the remediation and reinforcement of the seepage control were accomplished, without adversely affecting the pit or its surrounding environment, thereby ensuring the continuation of subsequent excavation works. Taking this project as a case study, the process of remediation and reinforcement undertaken for the seepage damage of this foundation pit is outlined, and the technical key points of the dual-liquid jet grouting piles technique are summarized.

The Phased Construction Settlement Analysis of Beijing Fengtai Station Reconsruction and Expansion Project

Wang Yuan, Li Weiqiang, Tang Hu

2024, 38(4): 420-426. doi: 10.3969/j.issn.1007-2993.2024.04.008

[Abstract](116) [FullText HTML] (53) [PDF 17545KB](35)

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During the construction period, it is necessary to ensure that the existing railway transportation line that originally passed through here was not affected. The project of Fengtai station reconstruction was divided into three phases of construction, and construction was carried out in two phases in sequence and post-cast strips were set up at the junction of the phased construction. Due to the station's main structure consisting mainly of cast-in-place concrete frame structures, the presence of post-cast strips has a significant impact on the progress of subsequent construction. Based on the deformation calculation analysis of the superstructure-foundation-soil, a refined modeling of the strata, structure, and construction steps was carried out. The results show that the differential settlement caused by the later construction on both sides of the settlement post pouring belt meets the specifications and design requirements. The settlement post-cast strips were cancelled and created conditions to ensure the construction period. Verified by settlement measurement data, the numerical calculation prediction results are reliable, and this method can be used as a reference for similar projects.

Analysis and Research on Early Closure of Settlement Post-cast Strip for a Type II Residential Land Project

Zhao Can, Zhang Jingyi, Wang Yuan, Li Weiqiang

2024, 38(4): 427-430. doi: 10.3969/j.issn.1007-2993.2024.04.009

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A Class II residential land project in Daxing District, Beijing is surrounded by multiple high-rise residential buildings and an underground parking garage. To eliminate the adverse effects of differential settlement, multiple post-cast strips were installed. The existence of post-cast strips seriously restricts the project schedule. Therefore, based on the geological conditions of the site, the foundation scheme, and the distribution of loads on the upper structure, PLAXIS3D was used for settlement analysis, and the early closure of settlement post-cast strips was feasibility according to practical engineering experience. The project implemented an early closure of the post-cast strips, thereby accomplishing the intended objectives.

Impact Analysis of Deep Foundation Pit Construction on Deformation of Adjacent Buildings

Guan Yanli, Li Yuhong, Li Jiayan, Duan Zhichao, Xu Yongbing

2024, 38(4): 431-435. doi: 10.3969/j.issn.1007-2993.2024.04.010

[Abstract](156) [FullText HTML] (55) [PDF 2313KB](64)

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Combined with a foundation pit project in Kunming, numerical modeling was established using finite element software MIDAS GTS. Three numerical simulations were carried out on the surface settlement of the foundation pit and deformation of the neighboring buildings, including no buildings in the surrounding, the longitudinal wall of the building parallelling to the foundation pit, and the longitudinal wall of the building being perpendicular to the foundation pit. The results show that: (1) the settlement of the floor plate of the neighboring building near the pit is larger, the building as a whole is tilted to the pit, and the two ends of the floor plate in the width direction are synchronously sinking and symmetrically concave, compared to the settlement of the building when the longitudinal wall is perpendicular to the pit, and (2) in the case of the no building or building with longitudinal wall parallel to the pit, the maximum settlement of the surface of the pit occurs in the range of 5~7.5 m from the edge of the pit, which is approximately (0.5~0.75)H (H is the depth of the pit); for the case where the longitudinal wall of the building is perpendicular to the pit, the maximum settlement of the surface of the pit occurs at a distance of about 9~12 m from the edge of the pit, which is about (0.9~1.2)H.

Discussion on Causes of Abnormal Bearing Capacity of Post Grouting at Pile End

Li Yucan

2024, 38(4): 436-439. doi: 10.3969/j.issn.1007-2993.2024.04.011

[Abstract](156) [FullText HTML] (45) [PDF 1086KB](75)

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The bearing capacity of post grouting piles in deep soft soil layers is influenced by multiple factors. Taking three sets of post grouting piles at the pile end of a certain project in Shanghai as the research object, the influencing factors on the bearing capacity of post grouting piles were investigated, with the ninth layer of silt layer as the bearing layer of the pile foundation. The results indicated that the bearing capacity of post grouting piles was greatly influenced by the drilling process, grouting process, and sediment thickness. To avoid the influence of the above factors, the reverse circulation drilling and circulation mud sand removal construction technology were adopted, and the structure of the grouting hole was improved. The use of alternating high and low pressure grouting significantly increased the grouting amount, effectively cemented the sediment at the bottom of the hole, and solved the problem of insufficient bearing capacity of grouting pile in the area.

Safety Influence of Percussion Drilling Construction on Existing Railway Bridge Piers

Zhu Zhaobin

2024, 38(4): 440-446. doi: 10.3969/j.issn.1007-2993.2024.04.012

[Abstract](112) [FullText HTML] (43) [PDF 1601KB](32)

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To study the dynamic and static responses of existing railway bridge piers under the influence of percussion drilling, the theoretical analysis, numerical simulation, and field test of the influence of percussion drilling on railway bridge piers were carried out. The theoretical analyses show that the maximum vibration velocity of the railway track under the condition of percussion drilling and the vibration velocity of the existing bridge pier under the coupling of percussion drilling construction and train vibration meet the requirements of the code. The numerical simulation results show that the total displacement, horizontal displacement, and vertical displacement of the existing pier top are all within the scope of the code. Field tests show that the displacement and vibration velocity of the affected piers meet the requirements of the code. However, data comparisons show that the theoretical analysis and numerical simulation do not consider the adverse effects of uneven foundation and construction disturbance, and the calculation results tend to be dangerous.

Stability Analysis of High Fill Retaining Wall Slope in Nujiang Airport

Deng Yiming, Zhang Dongming, Li Yuanbiao, Yang Zhongguo, Peng Haiyan

2024, 38(4): 447-452. doi: 10.3969/j.issn.1007-2993.2024.04.013

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Nujiang airport is located in the high intensity seismic mountainous area in the southwest of China.The stability of the slope under the high fill load and seismic load is the key factor restricting the airport construction. The methods of theoretical analysis and numerical simulation were used to analyze the stability of the high filling slope. The results show that under the high filling load of the retaining wall, most of the base of the retaining wall does not meet the bearing capacity requirements, and the differential settlement of the retaining wall is large. The comprehensive shear strength parameters of the filling interface should meet c≥50 kPa and φ≥25° to ensure the stability of the backfill soil. The seismic action has a great impact on the stress and deformation of backfill soil, and the deformation of retaining wall increases by 0.6～1.1 mm, which may cause the cracking of retaining wall. It is suggested to strengthen the basement rock mass and carry out seismic design for the retaining wall.

Narrow and Deep Foundition Pit Engineering Practice under Conditions of High Permeable Layers in Sensitive Environments

Fang Qing, Chen Sheng, Pan Chen, Liu Xuezhu

2024, 38(4): 453-458. doi: 10.3969/j.issn.1007-2993.2024.04.014

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A deep foundation pit is situated in the flood plain of Nanjing. The geological condition is that the flowing plastic mucky silty clay is distributed in the upper part, and a deep gravel layer with high permeability and strong bearing ability is distributed in the lower part. The foundation pit is a narrow cuboid with 250 m in east-west length, 50 m in north-south width, and 11~14 m in depth. Some adjacent sensitive buildings are existed in the south side of the foundation pit while some important municipal pipelines including natural gas pipeline and water supply pipe are close to the north side of the foundation pit. Based on the scheme comparison and pile testing, the combined supporting system composed of retaining pile and concrete inner support was adopted. To effectively control the underground water level, the triaxial cement-soil mixing column was taken as the waterproof curtain and the drainage was carried out through the dewatering well inside the foundation pit. Considering the mechanical property of narrow foundation pit and deformation control of the surrounding environment, the supporting structure and waterproof curtain in the south of the foundation pit were enhanced. A specific scheme of subarea and time-sharing construction was conducted to avoid the shape effect induced by pit excavation. The rational construction parameters for ultra-long waterproof curtain crossing different stratums were determined using pile testing. The detection and monitoring results show that the waterproof curtain is continuous and integral. Both the strength and deformation of structure and surrounding environment fit the requirement of design and specification. These situations can be a reference for the similar foundation pit engineering.

Stability Analysis and Treatment Measures of Landslidein Quping Village, Tianshui

Zhang Xiongwei, Lai Guoquan, Zhang Qianyi

2024, 38(4): 459-464. doi: 10.3969/j.issn.1007-2993.2024.04.015

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The landslide disasters in the north and south mountain areas of Tianshui are extremely developed, and it is extremely challenging to build roads in this area. Taking the analysis and remediation of a large tractive deposit landslide in Quping village, Tianshui as an example, engineering geological mapping, drilling, deep displacement monitoring, and indoor mechanical tests were conducted to analyze the form, deformation, and development characteristics of the landslide. The disaster mechanism of the landslide was studied and its stability was evaluated, and remediation measures were provided. The results show that the Quping landslide could be divided into two stages in plane morphology, the sliding direction is broken line, the sliding body is mainly composed of silty clay, and the sliding bed is Neogene mudstone, which is a typical accumulation landslide. The buried depth of the sliding surface is 6.0~13.0 m, and the deformation mode is traction type, which is induced by the geological environment of the slope, earthquake, heavy rainfall, and other natural factors. In view of the landslide, a set of treatment plans such as drainage interception, retaining, and monitoring was put forward, which can provide a reference for the control of similar landslide disasters.

Hydrofracturing Ground Stress Testing in Tunnel Survey in Mountainous Area

Tang Hui, Zhang Ruisong, Sun Kai

2024, 38(4): 465-470. doi: 10.3969/j.issn.1007-2993.2024.04.016

[Abstract](129) [FullText HTML] (56) [PDF 1388KB](29)

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The layout of deep buried tunnels and the stability of surrounding rocks are closely related to ground stress conditions. The hydraulic fracturing method is a widely used and mature in-situ stress testing method for deep-buried tunnels. The hydraulic fracturing method was used to test the in-situ ground stress of a tunnel in East China mountainous area, and the maximum and minimum horizontal principal stress and other mechanical parameters were obtained, the characteristics of ground stress were analyzed, which can provide a scientific basis for the layout of tunnel lines and the prediction of rock burst in the surrounding rock. The research showed that the horizontal principal stress of the tunnel increases linearly with the buried depth, and two stress types of thrust stress and strike-slip stress were developed from shallow to deep, respectively. The dominant direction of the maximum horizontal principal stress in the buried depth of the tunnel is consistent with the direction of regional geological tectonic stress, and the angle between the maximum horizontal principal stress and the tunnel strike is less than the optimal angle, which has a certain impact on the stability of surrounding rock. The rock burst risk of surrounding rock increases with the increase of depth, there may be slight rock burst in the surrounding rock at the depth of the tunnel, and relevant measures should be taken to release the ground stress of surrounding rock in time to ensure the construction safety. The research results provide a certain technical reference for the survey, planning, and design of oil and gas pipelines, transportation, and other engineering construction in mountainous areas in the future.

Effective Estimation of Karst Development Intensity in Engineering Projects

Peng Gongxun, Song Jian, Xu Tao, Zhao Xuguang, Liu Xiaoting, Ai Qun

2024, 38(4): 471-476. doi: 10.3969/j.issn.1007-2993.2024.04.017

[Abstract](128) [FullText HTML] (44) [PDF 1678KB](50)

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Based on the spatial distribution characteristics of karst, the horizontal uneven distribution and vertical zonation characteristics of karst were summarized, and their impact on karst rate statistics was analyzed. Based on the investigation data of a buried sewage plant, the vertical zonation of voids and line karstification rates were analyzed. Furthermore, the probability relationship between the statistical data of borehole porosity rate and liner karst rate was analyzed according to the principle of sampling error. It is considered that the horizontal heterogeneity and vertical zonation of karst development, as while as the actual number of limestone holes and the depth of rock drilled, should be taken into account in each exploration stage. Therefore, the karstification rate is effectively estimated using interval estimation.

Geological Risk Analysis of Cable Tunnel Construction

Hao Bing, Liu Yingguang, Li Congyun, Liu Shiyan

2024, 38(4): 477-481. doi: 10.3969/j.issn.1007-2993.2024.04.018

[Abstract](102) [FullText HTML] (49) [PDF 656KB](29)

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The engineering risks that may arise from geological conditions mainly include safety risks, quality risks, construction period risks, environmental risks, and investment risks. Geotechnical engineering survey documents should focus on safety and quality risks. The construction methods and procedures of cable tunnels were studied, and various risks during the excavation of shaft support, underground water control in the shaft, and construction of the main body of the tunnel were analyzed. Geological risk identification was carried out based on the engineering geological conditions. It is recommended to establish geological risk lists and develop risk control measures based on the experience of risk control in rail transit.

Stability Analysis and Optimal Design of a Railway Tunnel Slope During Route Selection

Yuan Xiaobo, Man Jun, Sun Dongze, Li Huiqiang, Xie Meng

2024, 38(4): 482-488. doi: 10.3969/j.issn.1007-2993.2024.04.019

[Abstract](108) [FullText HTML] (28) [PDF 1794KB](50)

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Taking a railway tunnel entrance slope construction site as an example, the slope safety factor at different tunnel entrance elevation, different conditions (slope not excavated, excavation not loaded, loading after excavation), different conditions (natural conditions, rainstorm conditions, earthquake conditions), and different failure modes (internal sliding, multiple sliding, sliding along the contact surface) was studied. The combination of tunnel excavation and slope unloading effectively reduces the slope sliding load, optimizes the design scheme of the treatment project, ensures the safety of the project, and can provide reference for the same type of projects in route selection and slope design.

Application Research of Elastic Wave CT Method in Karst Exploration

Jia Haipeng

2024, 38(4): 489-493. doi: 10.3969/j.issn.1007-2993.2024.04.020

[Abstract](146) [FullText HTML] (47) [PDF 1667KB](45)

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The underground hidden karst developed in the limestone area has brought great safety hazards to urban engineering construction. Conventional geophysical prospecting methods are difficult to meet the high-precision detection requirements of urban engineering for karst diseases. This research introduced a cross-hole elastic wave CT technology, which can perform high-precision imaging of the underground structure of the engineering site. In combination with other geological data of the site, the shape and scale of the karst in the site area can be accurately predicted. The technology was applied in project practice, and the results show that the elastic wave CT method has achieved accurate identification of underground hidden karst, which is consistent with the geological drilling data.

Mechanical Properties and Deformation Characteristics of Single Graded Rockfill Materials

Li Cunzhu, Cao Suqian

2024, 38(4): 494-498. doi: 10.3969/j.issn.1007-2993.2024.04.021

[Abstract](88) [FullText HTML] (39) [PDF 1202KB](30)

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Particle gradation is one of the main factors that affect the mechanical properties of rock-fill materials. To study the mechanical properties and deformation characteristics of the rock-fill materials with single particle size, the large-scale triaxial test and numerical simulation of particle flow were conducted. The main results are as follows: in the case of dense state, the shear contraction of the sample occurs, and the specimen presents the strain hardening model, which shows the opposite rule of the conventional coarse aggregate or sand materials. When the confining pressure is same, and axial strain is identical, the shear contraction of grain with small particle size is more obvious than that of large particle size. When the condition is the same, the deviatoric stress of large particle is larger than small particle's. At the same time, it is found that the particle size of the single graded rockfill materials will have an important influence on its mechanical properties and deformation characteristics.

Experimental Research on Long Spiral Drilling Pressure Grouting Pile of a Project in Xi’an

Dang Zhirong, Li Youjian, Dang Jingmao, Liu Ping, Fan Mingming

2024, 38(4): 499-504. doi: 10.3969/j.issn.1007-2993.2024.04.022

[Abstract](169) [FullText HTML] (66) [PDF 1212KB](53)

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The commonly used technology of bored piles in sand and pebble fields is mud protection wall rotary excavation or reverse circulation drilling technology. This type of drilling technology requires a large amount of mud and high-quality control, which is prone to quality problems such as collapse and excessive sludge, resulting in single pile bearing capacity not meeting the design requirements. The long spiral drilling and pressure grouting pile technology have no slurry cake and sediment, greatly improving the quality of the pile and the bearing capacity of a single pile. However, for ultra-long piles, the full-length steel cage cannot be used in this progress, which to some extent limits the use of this technology. Based on the experimental research of the Xi'an Olympic Sports Center project, the reinforcement of the entire length was changed to 2/3 of the pile length and not exceeding 25 meters, guaranteeing the use of this method in the project.

2024 Vol. 38, No. 4