Chung-Jung Lee

Ground movement and tunnel stability when tunneling in sandy ground

Abstract Tunneling may cause ground movements and damage to adjacent buildings and overlying facilities. In this study, the failure mechanism and ground movement behavior around tunnels embedded in sandy soil below the water table were investigated in a series of model tunnel tests in a centrifuge. The magnitudes and extents of the surface settlement troughs for the cases of various ground loss for tunnels buried at various depths are provided. A new failure mechanism is proposed and validated by comparison with the test results. The proposed mechanism enables accurate prediction of two of the key quantities in the design of linings for tunnels embedded in sandy soils, namely the minimum supporting pressure needed to retain tunnel stability and the vertical soil pressure acting on the tunnel crown.

Stability analysis of cantilever double soldier-piled walls in sandy soil

Cantilever double soldier-pile walls are used in vertical excavations to minimize wall deformation. A model is proposed consisting of an equivalent single soldier-pile wall with twice the bending stiffness of a single soldier-pile wall, twice the area of the pile shaft in contact with the soil below the excavation level, and the maximum capable mobilized moment at ground level, which can be used to evaluate the stability of double soldier-pile walls. A series of centrifuge model tests at an acceleration of 30 g was conducted to study the performance of cantilever single and double soldier-pile walls in sand under various test conditions. The test results show that the use of a double soldier pile can effectively improve the performance of retaining walls. The proposed stability analysis also provides satisfactory predictions of the factors of safety for double soldier-pile walls at various excavation depths and with various pile arrangements, verified by the results obtained in the centrifuge model tests. The use of Fs  = 2.0 in the proposed stability analysis was found to be appropriate engineering practice for ensuring that the temporary cantilever double soldier-pile walls are stable and that the ratio δhm /H does not exceed 1%.

Pull‐out capacity of vertical expanded soil anchorages modelled in the centrifuge

Abstract Pull‐out tests on vertical expanded and non‐expanded soil anchorages in the centrifuge are reported. Pull‐out load, normal forces on the fixed anchor length, earth pressures around the anchor and displacement of the anchor are continuously monitored during expanding and pulling‐out stages. Large increases in radial earth pressure are observed after the expanding and beginning of pulling‐out stages. The radial earth pressures are subsequently reduced rapidly after the peak of pull‐out load. A mobilization factor is introduced to consider the effect caused by different degrees of mobilization to the top resistance and side friction resistance. The measured ultimate pull‐out capacities of the expanded and non‐expanded anchors are compared to the prediction obtained from the existing theory.