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With reference to earth pressure balance (EPB) shield tunnelling, the pressure infiltration of foam into saturated sand is investigated through model study. The model accounts for the companion liquid flow during the foam spurt that was experimentally measured in a previous paper. A micro-stability model is established to predict the maximum foam penetration depth that is based on the minimum pressure difference over an individual foam bubble through the pore throats. From tests on three different sands, the micro-stability model compared well with two sands but underestimated the maximum penetration depth for the third. This is attributed to a case where many bubbles are small enough to flow through the larger pore throats unhindered. Further results from numerical simulation are in accordance with the measured discharge behaviour during the foam spurt. The general agreement suggests that the model could explain the foam infiltration behaviour and can be used to describe the foam spurt during foam infiltration that can be expected in EPB shield tunnelling. [ABSTRACT FROM AUTHOR]

This paper presents the field monitoring during construction of the Green Heart Tunnel driven by a slurry tunnel boring machine (TBM) in a semiconfined aquifer in which a sand layer was overlaid by a peat layer. Data analyses of the pore-water pressures, slurry pressures, tail-void grout pressures, and ground movements surrounding the tunnel are presented. It was found that the slurry infiltration controls the variation of pore-water pressure only close to the tunnel face. The excess pore-water pressure far from the tunnel face was induced by the elastic storage of the aquifer. It was found that the grouting had little influence on the pore-pressure distribution. Furthermore, because the excess pore-water pressure generated by slurry infiltration might contribute to the grout pressure, the measured value of grout pressure can be smaller than the actual value. Consequently, to obtain the actual value of grout pressure, grout-pressure gauges combined with the pore-pressure transducers should be installed. In the semiconfined aquifer, suction in the overlying peat layer could be induced when the TBM passed through the sand layer. For this condition, the ground movement proportionally increased with the decreasing water pressure. [ABSTRACT FROM AUTHOR]

Two series of experiments were carried out to examine pressurised bentonite slurry infiltration into saturated sand columns. Three types of sand were examined, and water–bentonite and water–bentonite–sand slurries were used in series 1 and 2, respectively. Series 1 investigated the effect of sand particle size and series 2 examined the effect of the fine-sand particle content in the slurry. Scanning electron microscopy (SEM) imaging was used to observe the morphological features of the dry slurry-infiltrated sand samples. A solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration was verified using the data from series 2. The infiltration test results showed that the hydraulic conductivity of the slurry-infiltrated coarse sand for slurry in series 2 was lower than that in series 1. Visual observations and the SEM images showed that sand particles were bound to a bentonite film, indicating that, during infiltration, the channels for fluid flow among the sand particles are blocked by the bentonite particles adhered to the sand particles. The solution for the infiltration distance during mud spurt for water–bentonite–sand slurry infiltration showed good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of spatial variability of soil elastic modulus on the longitudinal responses of the existing shield tunnel to the new tunnel undercrossing using a random two-stage analysis method (RTSAM). The Timoshenko–Winkler-based deterministic method considering longitudinal variation in the subgrade reaction coefficient and the random field of the soil elastic modulus discretized by the Karhunen–Loeve expansion method are combined to establish the RTSAM. Then, the proposed RTSAM is applied to carry out a random analysis based on an actual engineering case. Results show that the increases in the scale of fluctuation and the coefficient of variation of the soil elastic modulus lead to higher variabilities of tunnel responses. A decreasing pillar depth and mean value of the soil elastic modulus and an increasing skew angle strengthen the effect of the spatial variability of the soil elastic modulus on tunnel responses. The variabilities of tunnel responses under the random field of the soil elastic modulus are overestimated by the Euler–Bernoulli beam model. The results of this study provide references for the uncertainty analysis of the new tunneling-induced responses of the existing tunnel under the random field of soil properties. [ABSTRACT FROM AUTHOR]

-Soil compaction in cropping systems, caused by the external pressure of machinery, creates impermeable layers that restrict water and nutrient cycles reducing agricultural production. To evaluate the matric suction effects on distribution with depth of stresses in a soil, caused by the use of agricultural machinery, Jet Fill tensiometers were installed at two different depths (i.e. 0.15 m, 0.30 m) in a soil profile constituted by silty sand with gravel (SM); to register the increments on subsoil vertical stresses, two miniaturized load cells (i.e. 16. 5 mm in diameter) were installed in a horizontal position under the centre line of the vehicle wheels’ path, at approximately 0.15 m and 0.30 m depth. Care was taken to calibrate the load cells in field conditions. A vehicle was made to pass over the soil surface, at a speed less than 5 km/h; the tyre inflation pressure applied on wheel was 380 kPa. Response of load cells to vehicle loading was evaluated at different average matric suction measured on soil profile. Finally, measured stresses have been compared with values obtained by applying well-known elastic theoretical methods used to assess stresses applied by tyres on bare soils. The corresponding results show that the increment of vertical stresses decreases as matric suction increases, and a good correlation between measurements and simulations of the increment on subsoil vertical stress.

This paper presents the results of an experimental study on the effects of testing rate on stress-strain behavior and volumetric changes of soil. A series of suction-controlled triaxial tests has been performed on reconstituted specimens of a silty sand (SM), at different stress-rates and strain-rates, respectively. The stress-strain paths were applied by using a modified version of a Bishop and Wesley device (USPv2), capable of applying independently pore-water and air pressure at both ends of the soil sample. During the isotropic compression stages loading rates of 2 and 32 kPa/h have been applied under constant suction values of 15 and 45 kPa. The drained deviator stages were conducted at the same suction levels under strain rates of 0.25 and 2.50 %/h. Results are presented in terms of applied loading rates as a function of the specimens specific volume, preconsolidation pressure, soil compressibility and deviatoric stress against strain rate. A comparison of results was made to a former study, under similar testing conditions of suction and loading rates at University of Napoli Federico II. The effect of loading rate on the soil behavior seems to have an insignificant effect on the specific volume variations, for the imposed values during the testing campaign.