• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.191-201
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• 2000

In this study, the earth retaining structure using a row of piles considering plastic flow of the ground is suggested for shallow excavation works instead of conventional anchored sheet-pile wall method in the marine clays with high groundwater level. The behavior of the earth retaining structure using a row of piles is precisely observed during excavation by inclinometer and piezometer installed in opposite to the excavation side. As a result of field measurement, it was found that the behaviors of the piles and the soil were influenced mainly by slope of excavation face, interval ratio of piles, fixity condition of pile head, and stability number, etc. The earth retaining structure using a row of piles is ascertained for workability, stability, and economical construction on the soft ground having no adjacent structures.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1039-1046
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• 2018

This paper presents a limit analysis of the series of construction stages of shallow tunneling method by investigating their respective safety factors and failure mechanisms. A case study for one particular cross-section of Beijing Subway Line 7 is undertaken, with a focus on the effects of multiple soil layers and construction sequencing of dual tunnels. Results show that using the step-excavation technique can render a higher safety factor for the excavation of a tunnel compared to the entire cross-section being excavated all at once. The failure mechanisms for each different construction stage are discussed and corresponding key locations are suggested to monitor the safety during tunneling. Simultaneous excavation of dual tunnels in the same cross-section should be expressly avoided considering their potential negative interactions. The normal and shear forces as well as bending moment of the primary lining and locking anchor pipe are found to reach their maximum value at Stage 6, before closure of the primary lining. Designing these struts should consider the effects of different construction stages of shallow tunneling method.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.87-92
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• 2000

In excavation of tunnels especially located in shallow depth, it is not rare to meet geological change in excavation progress worse than expected in the initial design stage. This paper present a case study on the re-design of excavation and support system of a shallow tunnel under construction where it meets the unexpected bad geological condition during excavation. The detailed geological investigation shows that the rock mass is heavily weathered and fractured with RMR value less than 20. Considering this geological condition, the design concept is focused on the reinforcement of the ground preceding the excavation of tunnel. Two design patterns, LW-grouting & forepoling with pilot tunnelling method and the steel pipe reinforced grouting method, are suggested. Numerical analysis by FLAC shows that these two patterns give the tunnel and roof ground stable in excavation process while the original design causes severe failure zone around the tunnel and floor heaving. In point of the mechanical stability and the degree of construction, the steel pipe reinforced grouting technique proved to be good for the reinforcement of heavily fractured rock mass in tunnelling. This assessment and design process would be a guide in the construction of tunnels in heavily weathered and fractured rock mass situation.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.268-275
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• 2006

Excavation works of cylindrical shafts and tunnels for the construction of a variety of infrastructures have been frequently going on in the urban areas. When ground excavations of cylindrical shafts and shallow tunnels proceed in the ground condition of high water level and silt particle component, ground water drawdown involving soil particle migration causes loosening of ground around tunnels and shafts, causes settlement and deformation of ground. Damages due to ground sinking and differential settlement can occur in the adjacent ground and structures. The extent and possibility of damage relevant to ground water drawdown and soil particle migration can't be so precisely expected in advance that we will face terrible damages in case of minor carefulness. This paper introduces two examples of construction management where using incremental deformation graph of inclinometer, we noticed the possibility of soil migration due to ground water drawdown in the excavation process of vertical shaft and shallow tunnel, analysed a series of measurement data in coupled connection, properly prepared countermeasures, so came into safe and successful completion of excavation work without terrible damages. The effort of this article aims to improve and develop the technique of design and construction in the coming projects having similar ground condition and supporting method.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.564-569
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• 2005

Usually, Steel pipe grouting method or cut and cover method has been applied to tunnel with very shallow overburden or it is situated in valley. However, in case of lack of overburden height to reinforcement tunnel crown which is very difficult to construction. Also, application of cut and cover method that do not consider surrounding site condition causes popular enmity generation and environmental damage. It is the best alternative method that reduces the amount of excavated soil and excavate tunnel under ground to solve these problems. The tunneling method using cover structure which is to prevent a tunnel from collapse because this method can be reduce excavation area and construct tunnel under ground after set a cover structure and backfill ground. In this study, to know more effective structure type, comparative analysis was performed to behavior characters of slab and arch type construction that can be used to cover structure. Also a 2D and 3D numerical analysis have been performed to verify the stability of ground during excavation. As the result, the tunneling method using cover structure that it can be good alternative method for tunnel with shallow overburden and it through valley

• Geomechanics and Engineering
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• v.31 no.1
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• pp.1-14
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• 2022

Urban deep excavation will affect greatly on the deformation of adjacent existing buildings, especially those with shallow foundations. Isolation piles has been widely used in engineering to control the deformation of buildings adjacent to the excavation, but its applicability is still controversial. Based on a typical engineering, numerical calculation models were established and verified through monitoring data to study the influence characteristics of isolation piles on the deformation of existing shallow foundation buildings. Results reveal that adjacent buildings will increase building settlement δ_v and the deformation of diaphragm walls δ_h, while the isolation piles can effectively decrease these. The surface settlement curve is changed from "groove" type to "double groove" type. Sufficiently long isolation pile can effectively decrease δ_v, while short isolation piles will lead to a negative effect. When the building is within the range of the maximum settlement location P, maximum building rotation θ_m will increase with the pile length L and the relative position between isolation pile and building d/D increase (d is the distance between piles and diaphragm walls, D is the distance between buildings and diaphragm walls), instead, θ_m will decrease for buildings outside the location P, and the optimum was obtained when d/D=0.7.

• Journal of the Korean GEO-environmental Society
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• v.13 no.11
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• pp.69-79
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• 2012

This pre-supported nail method is able to decrease ground displacements more than NATM because this method reinforces ground with grouted steels before tunnel excavation. Therefore this method has advantage of being able to increase the stability and workability. This study presents applicability of pre-supported nail method with case of site measurement for shallow tunnel composed with high groundwater level and unconsolidated soil, performs this research the mechanism of new supporting system is compared with the conventional existing supporting system in terms of soil reinforcement. NATM has characteristics that construction stage displacement of the apparent height difference is observed in the step of divided excavation processing. Otherwise it is analyzed that pre-supported nail method is not sensitive in the displacement problem of excavation processing in comparison to NATM. It is found that this method is very applicable in shallow depth tunnel such as portal area, tunnel in soil and weak zone without arching effect.

• Tunnel and Underground Space
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• v.15 no.6 s.59
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• pp.400-410
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• 2005

During excavation of shallow tunnels in soft ground, failure mechanism around the tunnel face have major influence on the stability of tunnels. In this paper, a series of laboratory tests under plane strain condition on the small scale of a shallow tunnel considering unsupported tunnel length has been performed. The results have shown that tunnel failure mechanism changes from failure mode 1 to failure mode 2 as unsupported tunnel length increases. By comparing the experimental and the numerical results, the loosening pressure for the shallow tunnel and progressive failure have been investigated.

• Tunnel and Underground Space
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• v.11 no.1
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• pp.20-29
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• 2001

Final convergence of tunnel crown due to excavation have been well predicted by regression analysis which is expressed as a function of convergence curve on a time and distance dependent. In this study, the validity of the equations for shallow, wide tunnel was investigated by measurement and numerical analysis. Studied tunnel(Sansoo Tunnel) is located at the boundary of downtown and mountain park. Exponential predictions equation was better coincided with measured data than fractional equation for studied tunnel, although the ground was expected to be elasto-plastic. This is because weathered rock ground is changed elasto-plastic ground into elastic ground by multi-steel grouting and forepoling.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.3
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• pp.215-231
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• 2011

In this study, the behavior of a shallow 2-arch tunnel during the excavation in the sandy ground containing vertical discontinuity plane was experimentally studied. Load transfer mechanism in the pillar caused by a 2-arch tunnel excavation was observed. The position of the vertical discontinuity plane was varied. Model tests were carried out in the normal construction sequence of 2-arch tunnel. Test results-showed that the load transfer caused by the 2-arch tunnel excavation was concentrated in the discontinuity plane, and was cut by the discontinuity plane, so no load transfer took place above the discontinuity plane. It was also shown that the effect of adjacent tunnel excavation on the pillar load and the ground deformation was greater when excavating the upper half-face of the main tunnel, more than when excavating the lower half-face.