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This paper reviews the material properties of the seal gaskets of shield tunnels. In order to understand the function of sealing gaskets, the significance and structure of gaskets in tunnel segments are briefly introduced. Then, the material types of gasket are presented. Gasket materials include two categories: (i) the traditional elastic gasket and (ii) the hydrophilic composite elastic gasket. The traditional elastic gasket is composed of chloroprene rubber (CR) and ethylene propylene diene rubber (EPDM), in which the sealing function is implemented as a result of the elastic properties of the materials. The hydrophilic composite elastic gasket includes vulcanized water swelling rubber (WSR) and water swelling polyurethane (WSP), in which the sealing function is obtained from both the elastic properties and the water absorption ability of the gasket material. CR and EPDM were the earliest materials used in engineering practice; however, EPDM is the main material of the gasket today. The sealing mechanism of both CR and EPDM is presented at the molecule level. After that, the water absorption process for both WSR and WSP in hydrophilic composite is reviewed. Methods to improve the sealing behavior of WSR are also summarized. Furthermore, the aging of the gasket material is discussed. Finally, perspectives for future developments of new materials or ways to improve the performance of seal gaskets are proposed.

A road cave-in accident caused by tunneling is described, and the possible mechanism of failure is analyzed. The cave-in measured about 30 m × 27 m in plane, and about 15 m in depth. At about 19 m below the ground surface at the site, a tunnel construction was underway. Immediately above the tunnel, there was a weathered shale layer approximately t 2.66 m thick; above this layer, there were sand and gravel layers. The groundwater level was estimated to be about 5 m below the ground surface. By arch analysis, it is shown that the most likely cause of the accident was the low strength of the weathered shale layer and the high water pressure above the tunnel, which resulted in tensile failure of the weathered shale layer. The All Ground Fasten (AGF) pre-support measure was adopted, but it might make very limited contribution to the increase in the tensile strength of the shale layer in the cross-sectional direction of the tunnel. Keywords: Tunneling, Road cave-in, Arch analysis, Tensile failure

The behaviour of two sections of a test embankment constructed in Ballina, Australia, was predicted by finite element analyses before (Class-A) and after (Class-C) knowing the field-measured data. By comparing the predictions with the field data, it is concluded that simple models such as modified Cam clay, with reliable values of model parameters, can produce reasonable results for the performance of embankments on clayey deposit improved through prefabricated vertical drains for a relatively short time period. The Class-A prediction is judged as reasonably good, and the Class-C prediction gives satisfactory simulations of the field performance.

Summary For deep excavation pits that require the pumping of confined groundwater, a combination of a retaining wall and dewatering with large-diameter wells is usually adopted during excavation to improve safety. Since a retaining wall has a much lower hydraulic conductivity than the surrounding material in the aquifer, blocking of seepage to prolong the seepage path of the groundwater outside of the pit is effective. The retaining walls used during excavation dewatering cause hydraulic head drawdown inside the pit much faster than outside the pit. Thus, difference in hydraulic head between inside and outside of the pit increases. To investigate the mechanism of the blocking effect, numerical simulation using the finite difference method (FDM) was conducted to analyze the effects of pumping in the pit. The FDM results show that drawdown varies along the depth of the confined aquifer. The influence factors of drawdown inside and outside the pit include insertion depth of retaining walls, anisotropy of a confined aquifer and screen length of pumping wells. In addition, FDM results also show that the drawdown-time curve can be divided into four stages: in Stage I, drawdown inside the pit is very small and outside the pit it is almost zero; in Stage II, drawdown increases quickly with time; in Stage III, the drawdown curve is parallel to the Cooper–Jacob curve on semi-log axes; and in Stage IV, the drawdown becomes constant. These characteristics of the drawdown curve under the blocking effect of a retaining wall in an aquifer provide a way of estimating hydrogeological parameters according to pumping test results.

The impacts of composition and mixture ratio of backfill grouts on the anti-floating ability and workability cannot be ignored in the submarine tunnel engineering. The orthogonal tests were adopted to design a new hardened cement-lime grouting material (HCLGM) and its physical properties were examined. The results show that the shear strength, density, consistency and bleeding rate of HCLGM are largely influenced by the water-binder ratio while the setting time is mainly affected by the cement-fly ash ratio. The recommended mixture ratio for grouting material was determined by linear regression analysis method which is sand of 16.3%, cement of 6.6%, slaked lime of 13.4%, fly ash of 26.5%, bentonite of 4.8% and water of 32.4%. The proposed HCLGM was used in a practical engineering case and contributed to the anti-floating capacity of tunnels.