岩土工程技术

Design and Analysis of Deep Foundation Supporting Near Existing Building Basement in Soft Soil Area

You Bo

2020, 34(2): 63-69. doi: 10.3969/j.issn.1007-2993.2020.02.001

[Abstract](121) [PDF 2204KB](26)

Abstract:
The mucky silty clay of layer ③ and the mucky clay of layer ④ in Shanghai have the characteristics of high water content,fluid plastic state,high compressibility and low strength,classified to the typical soft soil area. Combined with engineering examples,the design points of the deep foundation pit engineering adjacent to the existing building basement in the soft soil area are introduced,and comparative analysis is carried out through theoretical calculation,numerical simulation and monitoring of the implementation process. The results show that for the deep foundation pits in the soft soil area,through the reasonable selection of the type of the retaining structure and the support system,the groundwater treatment and construction conditions are properly formulated,and the process control of foundation pit implementation is strengthened,which could ensure the safety of the foundation pit itself and the surrounding environment.This research can provide reference for the design and construction of similar foundation pit engineering in soft soil area.

Variation Law of Excavation Depth and Surrounding Rock Displacement of Loess Cavern

Shi Weimin, Wang Peng, Zhao Shangyi

2020, 34(2): 70-75. doi: 10.3969/j.issn.1007-2993.2020.02.002

[Abstract](54) [PDF 1235KB](11)

Abstract:
The elastoplastic finite element analysis of a loess cavern was carried out by two-dimensional, three-dimensional step-by-step excavation and three-dimensional one-shot excavation using PLAXIS 2D/3D finite element analysis software. The variation law in displacement of surrounding rock of cavern under different working conditions is analyzed, and the spatial effect of the tunnel face is analyzed. The analysis results show that the final displacement of the two-dimensional and three-dimensional step-by-step calculations is basically the same. Therefore, the two-dimensional calculation results can be used to estimate the final displacement of the cavern excavation. The analysis of three-dimensional step-by-step excavation shows that the displacement development of underground caverns with different depths is basically the same. When L/B≤1 (L is the tunneling depth and B is the tunnel span), the displacement ratio increases linearly. When L/B>1, the displacement ratio increases nonlinearly. When L/B>3, the maximum displacement is close to the final displacement. The spatial effect analysis of the tunnel face shows that the displacement at the tunnel face is about 1/3 of the final displacement. The displacement at a distance of 0.5 times span from the tunnel face is about 2/3 of the final displacement. The displacement at 2.5 times span from tunnel face is basically the final displacement.

Stability Evaluation, Reinforcement Measures and Monitoring Analysis for High Slopes

Liu Haiting, Zhang Xiaohui, Zhu Youlu, Yang Peng, Nie Shouzhi

2020, 34(2): 76-80. doi: 10.3969/j.issn.1007-2993.2020.02.003

[Abstract](86) [PDF 4406KB](32)

Abstract:
Taking a high slope as an example,the causes of local deformation are analyzed according to the basic characteristics of the high slope.The stability was evaluated quantitatively.A comprehensive treatment scheme of brush slope unloading+miniature steel pipe pile+drainage system+greening is finally adopted according to the analysis.The change of soil shear strength index before and after grouting is obtained through testing and monitoring results,and the change of slope stability before and after reinforcement is analyzed and compared.It reflects the confirmation of the information to the slope stability,and has certain refrence role in the treatment of similar high and steep slopes in the future.

Analysis and Treatment of a Corrosion on Ground Screw Piles

Zhang Liang, Liu Zhuangzhi

2020, 34(2): 81-85. doi: 10.3969/j.issn.1007-2993.2020.02.004

[Abstract](92) [PDF 13127KB](18)

Abstract:
Screw piles have some advantages of convenient construction,fast progress,less adverse impact on environment,etc,and has been widely used in foundation of the ground photo-voltaic power stations.However,it is apt to damage in corrosive soils and shorten its service life,especially in saline soils.By summarizing the corrosion mechanism and influence factors,combining with a case of corrosion on screw piles for a photo-voltaic power station in the northwestern saline soils,on the basis of investigation,numerical simulation and cause analysis,different treatment measures are proposed according to the different degree of corrosion damage. The corresponding measures are put forward according to the aspects of the materials,protective layers,improving the mechanical properties improvements and applied current protection,etc.From the analysis and treatment process of corrosion,it could provide references and lessons for the design,identification and disposes for similar engineering.

Application of Temporary Support and Permanent Support Composite Design in a Project

Liu Qingqing, Huang Changqian, Li Liangjie, Pan Qihui, Wu Lan

2020, 34(2): 86-91. doi: 10.3969/j.issn.1007-2993.2020.02.005

[Abstract](96) [PDF 2413KB](30)

Abstract:
A composite design of multiple supporting structures is applied in a specific project,including double row piles, soil nailing wall, pile anchor support and small retaining wall on the top of piles. This system could solve the problem of slope support under two working conditions of temporary and permanent in limited space. The monitoring results show that the displacement control of the support structure is well, and the prestress loss of the prestressed anchor cable in the gravel soil layer is small in the short term.

Identification of Water Security Sensitive Area in Urban Based on GIS Analysis

Xiong Fanyi, Wu Xingjie

2020, 34(2): 92-96,101. doi: 10.3969/j.issn.1007-2993.2020.02.006

[Abstract](65) [PDF 19764KB](11)

Abstract:
In recent years, with the development of sponge city construction, the research on urban stormwater management by Chinese scholars has been deepened. However, the problems related to the construction of sponge city are becoming increasingly prominent. The principle problem is that the technology of water safety analysis for large-scale water accumulation in urban areas is relatively weak, which makes the construction of large-scale sponge city become a mere formality. Taking the built-up area of Yiliang County as an example, the relevant literature are reviewed and the water points are investigated. With the powerful function of ArcGIS tools, the comprehensive analysis of various indicators of urban area is carried out, and finally the distribution map of water security sensitive areas in built-up areas of Yiliang County is obtained, so that different stratigies could be formulated during the construction of sponge city construction can formulate different strategies according to the water security sensitive situation of each area, which is of significant reference for the construction of sponge city in the future.

Anti-floating Problems Caused by Surface Water Infiltration and Countermeasures

Li Jiansheng, Zhang Sa

2020, 34(2): 97-101. doi: 10.3969/j.issn.1007-2993.2020.02.007

[Abstract](74) [PDF 13770KB](26)

Abstract:
As more attention has been paid to urban underground space, anti-floating problems become an important part of geotechnical engineering. Although the anti-floating research for the building service life is relatively thorough, but the probably anti-floating issues caused by construction or hydrogeological condition changes are normally ignored. In recent years, large-scale high-rise buildings and integral underground parking garages are constructed in ridges landform area. Due to the poor permeability of rock and soil mass in ridges landform, and heavy rains from May to August in this area, surface water may destroy underground structures by penetrating into the foundation floor through weak links of trench backfill. Combining with specific cases, anti-floating problems caused by surface water infiltration are studied and the countermeasures are provided, which is of good performances in practice.

Monitoring and Analysis of Valley Deformation during Construction of Baihetan Hydropower Station

Zhao Zhenjun, Yu Shengli

2020, 34(2): 102-105. doi: 10.3969/j.issn.1007-2993.2020.02.008

[Abstract](67) [PDF 8462KB](14)

Abstract:
The super-high arch dams in China, such as Xiluodu and Jinping, have exhibited anomalous phenomenon of valley shrinkage during the initial impoundment. However, there is no observation on the deformation of the valley during excavation unloading. The deformation monitoring of the valley are analyzed during the construction period of Baihetan Hydropower Station, and provides relevant reference for the deformation monitoring of the same type of high arch dams. At the same time, it provides relevant basic guarantee for the monitoring and analysis of valley deformation in the initial stage of water storage.

Settlement Calculation of Runway in Coral Sand Filling Ground Based on Dry Density

Wang Duli, Li Jianguang, Li Xing

2020, 34(2): 106-110. doi: 10.3969/j.issn.1007-2993.2020.02.009

[Abstract](52) [PDF 8474KB](11)

Abstract:
Among the coral sand-filled foundations, only the fine-grained coral sand could be applied to conventional indoor compression tests. It is not reasonable to apply the fine-grained coral sand compression test results to engineering practice. In this study, the pressure-dry density relationship curve and the vertical strain-dry density relationship curve of coral sand, coral branch, as well as coral sand and coral branch mixture were obtained by the compression test of large indoor samples. Based on these curves, the stratified summation method and the dry density obtained from the field test are used to calculate the virtual paving thickness of the coral sand fill foundation and the total settlement of the airport runway, which provides a new calculation method for the settlement deformation of the coral sand dredger fill foundation.

Experimental Study on Silica Fume Stabilized Soft Soil from Ningbo

Wang Zeping, Wang Changming, Jiang Nan, Zhang Zaiheng

2020, 34(2): 111-116,121. doi: 10.3969/j.issn.1007-2993.2020.02.010

[Abstract](53) [PDF 9675KB](11)

Abstract:
In order to study the influence of silica fume on the mechanical properties of soft soil, silty clay samples from Yinzhou district, Ningbo were mixed with different amounts of silica fume to test the mechanical properties and structure characteristics. The relation between stress and strain of stabilized soil with different content of silica fume was tested by triaxial undrained tests, and the structural characteristics were analyzed by SEM. The results show that the silica fume can improve the cohesion of soft soil, and the cohesion increases with the addition of silica fume. With the increasing content of silica fume, the anti-deformation of silica fume stabilized soil increases at the beginning and then decreases, and the damage deviator stress of silica fume stabilized soil increases under the same confining pressure. Increasing content of silica fume leads to the decreasing number of the larger pores and the increasing number of the smaller pores in silica fume stabilized soil, and the proportion of pores dominated with diameter is less than 1 μm dominated gradually.

Discussion on Notices of Rock Expansion Test

Liu Jun, Gu Li, Guo Cheng, Zhuo Huiying

2020, 34(2): 117-121. doi: 10.3969/j.issn.1007-2993.2020.02.011

[Abstract](152) [PDF 17289KB](14)

Abstract:
The important points of the expansion test (free expansion rate, expansion force, lateral restraint expansion rate, and collapse resistance) in several kinds of engineering investigations are discussed from the perspective of laboratory tests. The field sampling, standard sample preparation, test operation and method selection are discussed. Through the summarized methods, the test error could be reduced, the test level of expansive rock could be improved, the accuracy of test results could be guaranteed, and the method of measuring expansion index of expansive rock could be improved.

Influencing Factors of Geotechnical Test Index

Wu Jing, Xu Qingyang, Xia Ruyue

2020, 34(2): 122-124. doi: 10.3969/j.issn.1007-2993.2020.02.012

[Abstract](151) [PDF 1068KB](32)

Abstract:
Soil is loose deposit produced by the weathering of rocks on the surface of the earth’s crust. Soil in different regions has different physical and mechanical properties. Geotechnical tests is the tests of the physics,mechanics,chemical properties,and minerals of rocks and soils. It has important significance in the design of engineering buildings and provides important parameters for the construction of surveying projects. It is an important part of geotechnical engineering exploration,and its accuracy directly affects the safety and quality of the project. The operation steps of the test of conventional geotechnical engineering are briefly described, the influencing factors of the test data of conventional geotechnical engineering are summarized,opinions and ideas on how to improve the accuracy of the test data are also provided.

2020 Vol. 34, No. 2