岩土工程技术

Impact of Bored Pile Construction on Deformation of Adjacent Operating Tunnel

Zhou Zhiliang, Qiu Huan, Huang Xiaodong, Du Ping, Yang Ping, Lv Weihua

2021, 35(1): 1-6,11. doi: 10.3969/j.issn.1007-2993.2021.01.001

[Abstract](415) [PDF 20074KB](136)

Abstract:
Pile foundation construction leads to surrounding strata displacement and adjacent tunnel structural deformation. Based on Nanjing Longjin Bridge Reconstruction Project, field monitoring was used to analyze the impact of various operating conditions on the strata displacement and structural deformation of adjacent tunnel during the bored pile construction. The results show that the maximum strata displacement and tunnel structural deformation are small during the construction of bored pile due to the effect of steel casing, which indicates that the technologies such as removing the soil while spinning steel casing and interval construction have little influence on the disturbance of surrounding soil. It is suggested that the construction method of full casing cast-in-place pile should be adopted in the near-tunnel pile foundation project. The monitoring and analysis results can provide technical reference for similar projects.

Deformation Characteristics Analysis of Cooperative Work for Shaped Steel-reinforced Cement-soil Composite Retaining Wall

Chen Meng

2021, 35(1): 7-11. doi: 10.3969/j.issn.1007-2993.2021.01.002

[Abstract](135) [PDF 18488KB](32)

Abstract:
As a method to control deformation, shaped steel-reinforced cement-soil composite retaining wall could be used in excavation engineering. Based on the analysis of the calculation method for the deformation of the cantilever structure, it is pointed out that the bending stiffness of a composite wall is the key factor. However, the load sharing of the steel and cement-soil is varied with applied load, so the bending stiffness is uncertain under external load. To analyse the deformation characteristics of a composite retaining wall, a three-dimensional model was established for numerical simulation based on a case study of a 5.4 m deep excavation in Shanghai. It is found that the maximum displacement appeared in the middle of the structure, which limited the displacement at the top. Also, the cement-soil can share the load and contribute to the deformation control. It is economical to control the replacement ratio of the cement-soil within the requirements,and more favorable to densely arrange the front rows of H-shaped steel.

Discussion on Influence of Construction Sequence on Soft Ground Composite Foundation

Wei Haitao, Cai Zhi

2021, 35(1): 12-15,20. doi: 10.3969/j.issn.1007-2993.2021.01.003

[Abstract](158) [PDF 2541KB](35)

Abstract:
The construction sequence of backfill soil and mixing piles on the site will directly affect the treatment effect of the soft ground composite foundation, and the settlement control is the key to the safe operation of the soft ground floor. Taking the composite foundation engineering of cement-soil mixing piles for industrial plants in offshore soft soil areas as an example, the influencing factors and settlement differences of two different construction sequences of composite foundation cement-soil mixing piles and backfilling soil are discussed. Total settlement, construction settlement and post-settlement of foundation consolidation under two conditions are calculated and analyzed through numerical simulation tests. The results show that the settlement during construction by using the construction sequence of "backfill soil first, then pile" is greater than the "pile first, then backfill soil", but the settlement after construction is greatly reduced, which improves the effect of soft ground foundation treatment and is beneficial to the safety of the soft ground after treatment. The foregoing analysis conclusions is verified by the operation, which provides an important reference for determining a reasonable design scheme.

Application of SMW Construction Method Pile with Retractable Enlarged Head Anchor Cable in Foundation Pit Support

Chen Yongjin

2021, 35(1): 16-20. doi: 10.3969/j.issn.1007-2993.2021.01.004

[Abstract](101) [PDF 6002KB](22)

Abstract:
In order to solve the problem of urban foundation pit support caused by the dense surrounding buildings, numerous municipal roads and pipelines, and the limited occupied space, the construction methods of enlarged head anchor cable, retractable anchor cable and SMW are introduced combined with specific engineering examples. Relevant research work are carried out from three aspects of scheme optimization, construction technology and application effect. The application of composite support technology of retractable enlarged head anchor cable and SMW pile in soft soil layer or deep fine sand layer in urban area is discussed.

Leakage Prediction of Underground Continuous Wall Joints Based on DTS

Sun Chao, Wei Zhaolei, Fu Qiao, Jia Lixiang, Chen Mingyin

2021, 35(1): 21-26,31. doi: 10.3969/j.issn.1007-2993.2021.01.005

[Abstract](62) [PDF 13680KB](19)

Abstract:
As the supporting wall of deep foundation pit, diaphragm wall has good strength and safety stability. But the incompleteness of the wall will cause the leakage problem and seriously affect the function of the wall. Aiming at the leakage problem of diaphragm wall, a model experiment is designed to explore the temperature rise stability of concrete with different mud content under different pressure power and time. Through the abnormal points in the temperature rise curve, the integrity of the wall and the leakage of the wall can be analyzed. Distributed temperature sensing (DTS) based on distributed optical fiber is proposed. The detection method of concrete pouring integrity of diaphragm wall and the prediction method of leakage at the joint of diaphragm wall are proposed. Taking the deep foundation pit diaphragm wall project of Kunming Metro Line 4 as an example, the sensing optical cable and its layout method for monitoring the leakage of diaphragm wall are introduced by using DTS. The feasibility and effectiveness of this method are verified by comparing the detection results with the actual leakage situation.

Numerical Simulation of Retaining Wall Considering Layered Filling and Initial Ground Stress Balance

Zhang Hongye

2021, 35(1): 27-31. doi: 10.3969/j.issn.1007-2993.2021.01.006

[Abstract](60) [PDF 1749KB](16)

Abstract:
Focusing on the influence of layered soil filling behind the gravity retaining wall on the stress of the wall body, the dynamic change value and regularity of earth pressure behind the wall are studied and analyzed. The finite element calculation model of plane strain element and contact element of wall and soil is established by using the large-scale general finite element analysis software ADINA, and the Mohr-Coulomb material constitutive model of backfill behind the wall is comprehensively considered. The initial ground stress field is balanced, the backfill behind the wall is compacted and filled in layers, and the contact forces between the wall and the soil are set for finite element analysis and calculation. Finally, the Coulomb active earth pressure theory, the embedded earth pressure monitoring instrument and the finite element simulation results are used for comparative analysis, which can accurately reflect the law of the earth pressure change caused by layered filling of the backfill behind the wall and the deviation amplitude of the three. The law of degree provides scientific technical support and experience reference for the design and construction of similar gravity retaining wall on soil foundation.

Application of Extenics Theory Based on Grey Relevance Degree in Rock Mass Quality Evaluation

Chen Wei

2021, 35(1): 32-37. doi: 10.3969/j.issn.1007-2993.2021.01.007

[Abstract](59) [PDF 5068KB](19)

Abstract:
In order to establish a better rock mass quality grading system and improve the traditional grading methods and other mathematical evaluation methods, a matter-element model based on extenics theory for rock mass quality grading evaluation is established in combination with the engineering geological conditions of navigation tunnel in Hongyan Reservoir. The grey relevance method is used to improve the subjective and objective factors for calculating the weight of each evaluation index in extenics theory. The results showed that the subjective and objective factors of rock mass quality evaluation are fully considered by the grey relevance method, and the weights of each index calculated were reasonable and reliable. The combination of grey relevance method and extenics theory could not only reflect rock mass gradation, but also reflect the distance between different grades. The application of this theory to classify and evaluate surrounding rock quality would have definite guidance in engineering practices.

Analysis of Variability and Correlation of Shear Strength Indexes Typical Stratum in Beijing Area

Ma Huan, Li Yongdong

2021, 35(1): 38-42. doi: 10.3969/j.issn.1007-2993.2021.01.008

[Abstract](78) [PDF 3222KB](42)

Abstract:
The recently deposited stratum is a typical shallow and relatively weak layer of the main soil layer involved in project construction in Beijing area. The variation of soil mechanics index is great. Based on a large number of practical engineering in Beijing area, shear strength variability and spatial variability of soil property parameters are associated by means of stochastic field model of soil profile. Variation laws of the correlative distance and spatial variability coefficient are gained by statistic analysis of shear strength indexes of recently deposited typical stratum. The autocorrelation distance of newly deposited soil layers of Beijing area is generally 3~4 m, which is a suitable sampling interval.

Application of Ship-form Retaining in Foundation Pit

He Shida, Xu Zhong, Li Yanfeng

2021, 35(1): 43-47,70. doi: 10.3969/j.issn.1007-2993.2021.01.009

[Abstract](65) [PDF 3772KB](38)

Abstract:
During the foundation excavations in the deep thick soft soil area, the soft soil at the bottom of the foundation is stirred and strengthened to form a high-strength floor to ensure the stability. The side wall is supported by supporting piles to avoid the side wall from collapsing. The ship-form structural support system formed by the combination of the supporting piles and reinforced bottom plates is similar to the ship's side wall and bottom plate to ensure the stability of the foundation excavation. Combining with specific engineering examples, the design method of the side wall and bottom plate of ship-form retaining are introduced. The successful implementation of the engineering case and the monitoring results show that the ship-form retaining can not only avoid the excessively deep embedding of the support piles, but also facilitate the earthwork construction of the soft soil and the protection of the engineering piles. It is safe and reliable. It has certain reference significance for similar projects.

Application of High and Steep Rock Slope in Mine

Wu Zucheng, Guo Shanfeng, He Weimin

2021, 35(1): 48-51. doi: 10.3969/j.issn.1007-2993.2021.01.010

[Abstract](156) [PDF 1127KB](51)

Abstract:
Coal mine geological environment restoration project in Luanchuan County is introduced as an example. Measures such as bolt mesh shotcreting, soil placement with bored bamboo tube and drip irrigation technology are adopted for comprehensive treatment, which can reduce the traditional large excavation method of high and steep rock slope to eliminate the geological hazards of the slope, and facilitate the subsequent step greening. This technology will reduce great damage to the mountain in the treatment area, and reduce the disposal earthwork of engineering construction. On the other hand, the use of drilling bamboo tube soil and drip irrigation technology could also improve the greening effect and engineering maintenance. The engineering treatment technology has reference value in the geological environment treatment of similar mines in Henan Province.

Effects Analysis of Rainfall on Landslide Stability and Drainage Measures Suggestion

Tong Xin, Fang Ran, Li Hong

2021, 35(1): 52-55,59. doi: 10.3969/j.issn.1007-2993.2021.01.011

[Abstract](67) [PDF 8395KB](39)

Abstract:
Taking the landslide in southwestern China as an example, the impact of rainfall on the landslide with weak interlayer is studied by ABAQUS software. Combined with the actual construction process, it stimulated the deformational characteristics of the different landslide model, including the primary landslide, the landslide with supporting structures but without rainfall,as well as the landslide with supporting structures and rainfall. By comparing the stability coefficient of landslide under different rainfall infiltration intensity, the influence law of transient seepage effect of rainfall infiltration on the stability of landslide with weak interlayer is comprehensively evaluated, and the optimal design of drainage measures is proposed.

Study on Fault Activity in Engineering Geological Survey

Qiu Jianqiang

2021, 35(1): 56-59. doi: 10.3969/j.issn.1007-2993.2021.01.012

[Abstract](120) [PDF 2841KB](56)

Abstract:
Fault is one of the important factors leading to geological disasters. In order to ensure the safety of engineering projects, it is necessary to determine the activity of fault to avoid geological disasters. There is a NW fault located within the proposed Budaigou Tailing Reservoir area. Taking the fault as an example, the fault in the proposed reservoir area is investigated through methods such as geological survey, geophysical exploration (high density resistivity and electrical sounding), drilling and trench excavation. The fault is 1.55 km long and 1.5~2.5 km wide normal fault, northwest extending. The occurrence is 70°∠72°, and control depth being 420 m. The fault is a small non-holocene active fault with no obvious activity since Quaternary. The stability of fault engineering is good, which has no influence on engineering construction. However, considering the existence of fault structure breccia, although it has been consolidated, it is easy to be weathered relative to the surrounding rock, forming a certain loose layer, which may cause groundwater infiltration channel.So it is recommended to pay attention to it in engineering construction.

Technical Design and Experimental Research of Active material-Sinking-Expanding Composite Pile

Wang Panfeng

2021, 35(1): 60-64. doi: 10.3969/j.issn.1007-2993.2021.01.013

[Abstract](52) [PDF 2927KB](20)

Abstract:
The concept of ASE pile is put forward based on the engineering properties of super soft soil filled with dredger fill, which refers to the construction technology of sinking pipe into composite material and in-situ expanding mixing. Considering the principle of providing basic strength and skeleton support for super soft soil with solidified fine material and skeleton coarse material, and referring the construction technology of mixing pile and CFG pile, a special double tower construction equipment is made and a new construction technology is formed. The field test shows that the ideal pile can be formed when the mixture of solidified fine material and skeleton coarse material is appropriate. The quality of pile forming is mainly affected by the solidified fine material, and the effect of skeleton coarse material depends on the solidified fine material of certain mix proportion foundation. It is feasible to feed the immersed tube first and then expand the diameter for stirring. The annular blade can achieve the effect of expanding the diameter, and the effect of two-way expanding stirring is better than that of one-way expanding stirring. The design and calculation method of ASE pile need to be further studied, which can refer to the relevant theories of CFG and mixing pile.

Centrifugal Model Test Research on Pile Group Foundation of Tunnel Under Wharf

Zhang Yuting, An Xiaoyu, Ji Wendong

2021, 35(1): 65-70. doi: 10.3969/j.issn.1007-2993.2021.01.014

[Abstract](47) [PDF 4047KB](12)

Abstract:
It is common to encounter existing piles during tunnel constructions in congested underground. Although tunnel-soil-pile interaction has attracted much research attention recently, previous studies mainly focused on pile responses due to small-scale tunnel excavation. In this study, three-dimensional centrifuge test is conducted to investigate deformation mechanisms of a pile group due to twin large-scale tunnel excavations. Due to tunneling-induced stress relief, the measured settlement of pile group increases almost linearly with tunneling. A shorter distance between the monitoring point and new tunnel results in larger pile group settlement. Upon completion of a single tunnel excavation, a maximum pile group settlement of 0.23% D (i.e., tunnel diameter) is observed directly above tunnel centerline. After twin tunnel excavations, the maximum pile group settlement is increased to 0.32% D, and the location of the maximum pile group settlement shifts to the centreline between two tunnels. As tunnel face approaches the monitoring section, the existing pile group tilts rapidly toward tunnel face. As tunnel face passes through the monitoring section, tilting of existing pile group is reduced. Obviously, the measured tilting of pile group reaches a maximum value when tunnel face is located directly beneath the monitoring section. This clearly demonstrates three-dimensional deformation mechanisms of pile group due to tunnel excavation. If tunnel excavation is simplified as a two-dimensional problem, tilting of pile group along longitudinal tunnel direction is ignored, which is on unconservative side.

2021 Vol. 35, No. 1