岩土工程技术

Study of Coupling Effect Between the Elastic Deformation of Geogrid and Soil Creep

Zhang Junxian, Gan Jianqiang, Wang Qingbiao

2021, 35(2): 71-76,92. doi: 10.3969/j.issn.1007-2993.2021.02.001

[Abstract](80) [PDF 4702KB](13)

Abstract:
Geogrid is applied widely in soil reinforcement engineering. There is a complex coupling effect between the elastic deformation of geogrid and soil creep. Through theoretical analysis and field test, the coupling effect model of geogrid elastic deformation and soil creep is established, and the constitutive equation as well as the creep equation are deduced. Through field test and theoretical calculation, it is concluded that the stress level of soil has little effect on the strain stability time, but has a great influence on the strain rate and strain stability value. The viscosity coefficient of soil has a great influence on the strain rate and strain stability time, but has little influence on the strain stability value.

Analysis on the Ground Settlement in the Construction of Diaphragm Wall of Subway Excavated Stations

Zhu Yaqian, Xue Hongsong, Liu Xisheng, Du Changlong, Zhao Xu, Zhang Zhihong

2021, 35(2): 77-83,98. doi: 10.3969/j.issn.1007-2993.2021.02.002

[Abstract](62) [PDF 13335KB](16)

Abstract:
The protection of groundwater resources has always been a focus in engineering construction. This analysis is based on an underground diaphragm wall water stop project, which is the first construction in the side pilot tunnel of PBA underground excavation station of urban subway in China. MIDAS/GTS NX software is used to simulate the ground settlement changes of the diaphragm wall construction in the pilot tunnel, including before construction, during construction and after construction, and the results are compared with the actual field monitoring data. The results show that: (1) before the construction of the diaphragm wall, the center line of the surface settlement curve is the center line of the station, and the distribution of the curves is obvious symmetrical settlement groove. (2) During the construction of diaphragm wall, when the construction of one-sided diaphragm wall is completed, the settlement near the surface above is the most obvious. The maximum increment account is about 25% of the total settlement. (3) After the construction of diaphragm wall on the left and right sides, the incremental curve of surface settlement amount is similar to W-type. (4) After the construction of 6 diaphragm walls on the left and right sides, the settlement on the surface above tends to be stable, and the settlement rate basically remains unchanged.

Application of H-beam Composite Support in the Foundation Pit of Metro

Li Xiao, Cai Lu

2021, 35(2): 84-87. doi: 10.3969/j.issn.1007-2993.2021.02.003

[Abstract](69) [PDF 3110KB](28)

Abstract:
The H-beam composite support system (PASS) has the advantages of recyclable, high-strength connection, prestressing force applicable and high reliability, so it has been used more and more widely in China. The H-beam composite support system (PASS) used in the foundation pit of the house construction has many vertical support structures and cannot meet the earth excavation requirements of the subway foundation pit well. A standard station foundation pit (about 20 m in width) commonly used in subway engineering is taken as an example. Through comparison and analysis of calculation, the cross-section type of H-shaped steel composite internal support with large span and large spacing is designed. Compared with traditional steel pipe supports, it has a large bearing capacity, large support spacing, The cross-section form is economical and reasonable, and can well adapt to the requirements of narrow and long foundation pits of metro. It has the value of promotion and application.

Dam and Geotechnical Engineering Safety Monitoring System Based on LoRaWAN

Jiang Xiu, Zhang Shaofei, Rao Shaofeng, Hou Xinhua, Shen Xingsan

2021, 35(2): 88-92. doi: 10.3969/j.issn.1007-2993.2021.02.004

[Abstract](85) [PDF 9438KB](16)

Abstract:
In the traditional dam and geotechnical engineering safety monitoring system, when the sensor layout is relatively scattered, the cables demand and the construction cost is high, a reader is mainly used for manual reading during the construction period. A solution of wireless communication system for dam and geotechnical engineering safety monitoring based on LoRaWAN is proposed, which mainly includes cloud terminal, gateway and cloud platform. The system has been applied to the safety monitoring of more than 10 projects, including a national large-scale construction project, and has achieved good application results. In particular, it provides a feasible solution for the safety monitoring of dam and geotechnical engineering during the construction period.

Application of a New Steel Pipe and Anchor Combination System in Tunnel Landslide Reinforcement

Gu Xurui

2021, 35(2): 93-98. doi: 10.3969/j.issn.1007-2993.2021.02.005

[Abstract](58) [PDF 10791KB](24)

Abstract:
China has a vast territory and complex geological conditions. In the process of tunnel construction, the formation of landslide at the entrance of a tunnel is often the result of comprehensive action of many factors. It is necessary to carry out research on new technology and new process according to local conditions while making full use of the existing mature technology for prevention and control. Based on the landslide treatment project of Gaowuji tunnel in Pengan, Sichuan Province, a composite reinforcement system of conventional steel pipe with fully bonded anchor is introduced: by using the wall protection capacity of large-diameter steel pipe, effectively control the hole collapse during the follow-up drilling without casing, and reduce the construction difficulty of super long anchor; the steel pipe, as a load-bearing component, participates in the work together to improve the defect of insufficient strength of single anchor bar; the soil properties of the sliding zone are improved and the deformation of the sliding body is further restrained by the split seepage grouting in the pipe. After reinforcement, the whole slope is stable and the deformation of slope body is controllable, which can provide technical reference for similar projects.

Study on the Application of Top-down Construction Method in Deep Foundation Pit Engineering in Complex Environment

Yan Liming

2021, 35(2): 99-102,115. doi: 10.3969/j.issn.1007-2993.2021.02.006

[Abstract](74) [PDF 2752KB](29)

Abstract:
Taking a deep excavation engineering in the center of Shanghai as an example, the key points of quality control is introduced in the top-down construction in deep excavation with narrow construction site and dense surrounding buildings. Practice shows that the top-down construction technique can effectively solve the problems of narrow construction site and short construction period, ensures the safety of the excavation and surrounding buildings, which can be applied in similar deep excavations.

Analysis of Variability of Soil Parameters in Soft Soil Tunnel Face Stability

Cao Aiwu, Wu Jiayao, Chu Weijiang

2021, 35(2): 103-106. doi: 10.3969/j.issn.1007-2993.2021.02.007

[Abstract](56) [PDF 2035KB](14)

Abstract:
Reasonable value of geotechnical parameters has a significant influence on engineering design. In order to evaluate the influence of soil parameter uncertainty to tunnel face stability, Monte-Carlo random simulation is used to analyze the influence of the variability of soil parameters and sample capacity level to the tunnel face stability, the reasonable safety factor of soil tunnel face stability is determined. The rationality of the design safety factor is evaluated through engineering example. According to the results, the uncertainty of the soil parameters has little effect on the stability characteristics of the tunnel face when the sample capacity is large. If the sample capacity is small, the influence of variability of soil parameters increases when the sample capacity decrease. It provides a basis for the support design of the temporary tunnel face.

Stability Analysis and Treatment Scheme Research of Large Waste Slag Body of Cold Rolling Mill

Zhao Minghua, Liu Peipei, Zhu Xinbo

2021, 35(2): 107-110. doi: 10.3969/j.issn.1007-2993.2021.02.008

[Abstract](53) [PDF 3664KB](13)

Abstract:
The large abandoned slag body of the cold rolling mill is located on the right bank of the outlet of the diversion channel of Jinsha Hydropower Station. The discharge of the diversion channel will cause backwash to it. In order to ensure the stability of the bank slope and protect the factories or mining enterprises on the top, it is necessary to analyze its stability, especially the stability changes during the discharge of the diversion channel. Based on the characteristics of the waste slag body, the overall stability analysis is carried out by using methods such as Jabu Method. According to the failure mode and degree of the bank slope caused by the channel discharge to the waste slag body, combined with the results of the model test of the flow bed, the flexible protection scheme of steel mesh and steel wire gabion protective structure is proposed innovatively.

Cavity Treatment Technology of Tunnel in Shield Section of Soft Soil

Luo Mingliang, Yang Songbo, Wu Wendong, Xu Hongri, Huang Hua

2021, 35(2): 111-115. doi: 10.3969/j.issn.1007-2993.2021.02.009

[Abstract](77) [PDF 10589KB](16)

Abstract:
With the gradual development of the Great Bay area of Guangdong, Hong Kong and Macao, the expansion project of Guangdong, Hong Kong and Macao has the characteristics of large scale and complex stratum. Especially in the soft soil area near the sea, there are always complicated engineering geological problems. Taking the foundation treatment project of Terminal 4 of Shenzhen Airport as the background, aiming at the damage of the cavity after shield tunneling around the site of the proposed Terminal 4, the general shape and orientation of the cavity are detected by the appropriate ground penetrating radar, and the formation causes are analyzed combining with the site conditions, which are mainly related to the construction technology, lining concrete materials, shield equipment and the influence of site ground stress. Sleeve valve pipe grouting was used to deal with the cavity damage, and the effect of cavity treatment was tested on site, so as to provide a reference for the cavity treatment in Guangdong, Hong Kong, Macao and other similar areas in China.

Identification and Case Application of Key Problems in Landslide Investigation

Zhou Guorong, Jin Aifang, Miao Huichao, Zhou Xiulian, Li Yifeng

2021, 35(2): 116-121. doi: 10.3969/j.issn.1007-2993.2021.02.010

[Abstract](109) [PDF 10346KB](50)

Abstract:
The mountainous and hilly landforms are widely distributed in China, and the geological hazards of landslides are frequent, which seriously restrict the development of China’s social economy. Based on landslide geological hazards, four key technical issues are identified and mainly solved in the landslide exploration. It includes landslide characteristics investigation and stability qualitative evaluation, sliding belt identification and location determination, parameter value and calculation model determination, and landslide stability quantitative analysis. Combined with the application analysis of typical cases, the corresponding solutions are provided, and the landslide characteristics and current stability state are studied. This research could provide sufficient and necessary geological basic data for the follow-up landslide prevention and control engineering design, and also provide reference for landslide geological disaster investigation.

Special Investigation and Influence Range of the Ground Fissure in Xian Skyrail

Sun Changqing, Shen Bin, Sun Zhenyue, Zhang Yutao

2021, 35(2): 122-127. doi: 10.3969/j.issn.1007-2993.2021.02.011

[Abstract](59) [PDF 29012KB](25)

Abstract:
As an adverse geological effect, ground fissures affect the project construction. Comprehensive investigation methods have been applied in the Skyrail of Xi’an High-tech Zone, such as data collection and ground investigation, geophysical exploration (high-density electrical method, microtremor survey method), engineering geological drilling. Special investigation is carried out on the ground fissures along the proposed line of the Skyrail, and the specific location, occurrence and activity of the ground fissures intersecting the line are investigated. Through the standard method and numerical simulation method, the influence range of the ground fissure activity is analyzed, and the prevention and control measures of the ground fissure are provided, which provide the basis for the structural design and construction of the Skyrail bridge passing through the ground fissures.

Analysis on the Stability and Suitability of the Ground in Goaf

Shi Lei

2021, 35(2): 128-133. doi: 10.3969/j.issn.1007-2993.2021.02.012

[Abstract](80) [PDF 1167KB](27)

Abstract:
A goaf is proposed as the ground of a new high-rise residential area. The stability of coal mine goaf is determined synthetically by mining conditions and surface movement deformation. Engineering analogy method, goaf feature discrimination method, activation influence factor analysis method, surface residual deformation discrimination method and other methods were used to determine the suitability of goaf site construction. It is suggested that flexible measures to absorb surface subsidence deformation and rigid measures to resist surface subsidence deformation should be adopted to ensure the safety of the proposed building.

Influence of Geotechnical Test Code Change on Expansion Calculation and Determination

Liu Jun, Shi Pengfei, Sun Kai

2021, 35(2): 134-136,141. doi: 10.3969/j.issn.1007-2993.2021.02.013

[Abstract](64) [PDF 3436KB](15)

Abstract:
The changes of no-load expansion rate and load expansion rate in the new and old geotechnical test codes are compared and analyzed, and it is found that the calculation formulas of the two have changed significantly. Compared with the old code, the calculation results of the new code show that the expansion rate increases obviously, and the expansion amount increases accordingly, which will have a significant impact on engineering investigation, design and construction. A project is taken as an example. After the calculation of the new code, the total expansion of stratum has changed from 16.7mm to 51.8 mm, which has increased by about two times. The expansion and contraction grade of foundation soil has changed from Grade I to Grade II, and the design grade of foundation has changed from Grade C to Grade B. The foundation treatment measures and construction schemes have also changed accordingly. Therefore, engineers should consider this comprehensively and treat it rigorously.

Test and Application of Small Diameter Steel Pipe-Rotary Jet Composite Piles in Soft Soil Area

Wu Yuechen, Wang Jinming

2021, 35(2): 137-141. doi: 10.3969/j.issn.1007-2993.2021.02.014

[Abstract](98) [PDF 1147KB](28)

Abstract:
The foundation reinforcement or reconstruction of existing buildings under soft soil conditions is faced with many complicated conditions. Construction safety and surrounding environmental protection are particularly important. A small diameter steel pipe-rotary jet composite pile process is proposed. Through field test research on various bearing capacity of small diameter steel pipe-rotary jet composite piles, strain data of steel pipe pile are abtained, and its bearing characteristics and force transmission mechanism are analyzed, summarizing and proposing the design calculation formula of small diameter steel pipe-rotary jet composite pile are summerized and proposed, which provide a theoretical basis for engineering applications.

2021 Vol. 35, No. 2