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Construction of tunnels using a shield in very soft soil may result in serious shield alignment problems and ground settlement. This paper presents a detailed field instrumentation program that was conducted for the construction of the Suzhou Metro Tunnel-Line S1 in China. The characteristics of the shield kinematics in ultra-soft soil and ground responses were examined, and the mechanisms of ground movements and pore water pressure corresponding to shield motions and construction parameters were interpreted and discussed. In addition, a calculation method for ground loss corrected by shield posture was established, based on which a corresponding volume of the grout required was recommended. The results indicated that the shield typically tunnels in very soft soil with increasing inclination mode characterized by a rising tail owing to the floating segment and with a changing inclination mode characterized by a sudden downward movement and subsequent steering of the shield upon encountering hard soil. Consequently, with the uplifting of the shield tail, it was found that the ground heaves and settles with a change in the shield posture. Moreover, a large longitudinal uneven deformation of the lining was found to occur in most of the above situations, while the pore water pressure was minimally affected by the shield posture. [ABSTRACT FROM AUTHOR]

Appropriate constitutive models and reliable excavation and support sequences are believed to be the major concern in using finite element (FE) analysis to simulate shield tunnel excavation. This paper presents systematic two-dimensional (2D) and three-dimensional (3D) FE analyses employing a number of constitutive models accounting for initial soil anisotropy and non-coaxial plasticity, as evidenced within site investigations from the Tsinghuayuan Tunnel of the Jing-Zhang high-speed railway in China. The aim is to assess the effects of both the initial soil anisotropy and non-coaxiality on longitudinal and transverse tunneling-induced surface settlements. It is shown that the excavation procedures combined with the degree of cross-anisotropy are key towards the accurate prediction of maximum vertical displacements from tunneling, matching field data. Knowledge of the initial soil strength anisotropy can further improve the shape prediction of the transverse tunneling-induced surface settlement troughs. When considering n = 0.6 and β = 0° in simulations, the transverse surface settlement trough obtained is almost coincident with monitored field data. Initial stiffness anisotropy used in the prediction of shield tunnel-induced surface settlements in sandy pebble soils does improve realism of results significantly. The maximum longitudinal settlement predicted by considering cross-anisotropy is larger than that predicted by its isotropic counterpart. [ABSTRACT FROM AUTHOR]

A case study of a double-cell, large-span prefabricated reinforced concrete box culvert with a total length of 52 m, a width of 46.8 m, and a height of 9.3 m, which passes beneath the Beijing - Hong Kong -Macau highway, is presented. The culvert is embedded in silty sand and silty clay at a depth of 1.2 m. To ensure the safety and normal operation of the highway, hydraulic jacking with the protection of a pipe roof was adopted for this project. This paper introduces the construction scheme in detail. A three-dimensional numerical simulation of the responses of the highway under which a wide box culvert jacking passes was conducted. The monitoring results on the highway as well as the actual construction process and problems encountered were analyzed. The different development characteristics or trends for the settlement and horizontal displacement of a highway surface are presented. In addition, this paper discusses the reasons for the large deformation of the highway surface as well as proposes reasonable suggestions. [ABSTRACT FROM AUTHOR]

Constructing a bored pile produces a disturbed zone of soil adjacent to the pile, referred to as a “mudcake.” The physical properties of the mudcake are different from those of the surrounding soil. This paper reports research on bored piles in silt, clay, and sandy silt layers in Hangzhou, China. Laboratory tests were performed on samples of in situ soil, mudcake, and mudcake mixed with cement grout. The test results showed that mudcakes have a higher water content, higher void ratio, higher compressibility, lower friction, and lower shear strength than in situ soils. They also showed that mudcake properties could be improved by the addition of cement grout. Mudcakes form a weak, thin layer between a pile and a borehole wall, which can lead to a decrease in bearing capacity and an increase in settlement of the pile. Grouting improves the characteristics of mudcakes remarkably, thereby increasing the bearing capacity of piles, which is demonstrated by the case history in this paper. [ABSTRACT FROM AUTHOR]

Southern China has a humid climate and often receives rainfalls that are of high intensity and (or) long duration. This paper investigates the performance of an inclined three-layer cover with capillary barrier effect (CCBE) comprising silt, sand, and gravel, for usage under humid climatic conditions. Physical modeling tests were carried out to observe the response of the three-layer CCBE system to a continuous heavy rainfall of about 70 mm/h. The layered cover model, housed in a 2 m long and 1 m wide instrumented box, is made up of 0.2 m thick silt, 0.1 m thick sand, and 0.1 m thick gravel, and the inclination of the model is 1V:3H. The movement of wetting front, changes in soil suction, and the primary components of water balance were measured during the operation of the physical models. The experimental data was used to calibrate the hydraulic parameters of the numerical model using the unsaturated flow software, SVFlux. Numerical modeling was subsequently carried out on a 60 m long inclined CCBE system to investigate the effective length of lateral diversion under prolonged rainfall. The main findings of the experimental and numerical studies are as follows: ( i) the physical model tests showed that the response of the three-layer CCBE system to a heavy rainfall of 70 mm/h was different from the previous observations on experiments where the rainfall was less than 1.6 mm/h; ( ii) correlation between the physical modeling and the numerical modeling indicated anisotropic behavior with respect to the hydraulic conductivity in the unsaturated sand layer; ( iii) the long inclined, three-layer CCBE system (i.e., 0.6 m thick silt, 0.2 m thick sand, and 0.2 m thick gravel) had an effective length of lateral diversion over 10 m for 30 days of prolonged rainfall (i.e., 1080 mm in total). [ABSTRACT FROM AUTHOR]

The 12 May 2008 Wenchuan earthquake in China triggered numerous landslides. Loose landslide materials can easily evolve into deadly debris flows during wet seasons. During the period from 2008 to 2011, three separate large-scale debris flows occurred in the Pubugou Ravine near the epicentre of the earthquake that were among the largest repeated debris flows ever reported. Approximately 1.76 × 106 m3 of sediment was deposited during these three events. This paper aims to ( i) analyze the movements of solid materials during the repeated debris flows, ( ii) discuss the evolution of the initiation mechanisms of these debris flows, and ( iii) evaluate the changing depositional morphology of the debris flow fans and examine the particle sizes of the debris flow materials. To achieve the above research objectives, timely field investigations were undertaken in the past 5 years after each of these debris flow events. Satellite images were used to delineate the boundaries of the initiation areas, the transportation channels, and the deposition zones of these debris flows. With the occurrence of the repeated debris flows, the hill slope deposits gradually evolved into channel deposits and the solid materials in the channels moved toward the gully mouth. Hence, channelized flows gradually became dominant. The debris fan materials of the repeated debris flows became coarser and coarser over time. The three debris flows were all characterized by coarse boulder fronts. [ABSTRACT FROM AUTHOR]

Slope instability processes occur widely on the underwater slopes of the Yellow River delta during storms. Roughly circular depressions on the upper delta front in water depths of 4 to 8 m have been detected by acoustic surveying and their processes were observed in the laboratory. This paper analyzes the properties of geomorphic and acoustic profiles of the upper delta front and compares the engineering geologic properties of samples from the disturbed and undisturbed areas. The results indicate that the weak superficial mass could oscillate with waves and the oscillation weakened the surrounding soil under the cyclic loading. The stratum was disturbed or even destroyed with depth, the area of the slide mass enlarged gradually, and finally a collapse depression formed. [ABSTRACT FROM AUTHOR]

Landslide 1 is located on the right bank of the downstream side of the dam for Hongjiadu Hydropower Station in Guizhou Province, China. In view of its close proximity to important workings, the stability of the slide is of great concern. Ground investigation showed that the slide is potentially unstable and has two sliding directions. Reinforcement mainly by piles was proposed as the stabilization measure, but two key questions were raised during the design of the piles. (1) How could the stability of the slope be evaluated, as there are two major sliding directions? (2) How could the shear strength parameters of the slip band be determined, as it contains a significant proportion of coarse particles? In this paper, we demonstrate how these issues can be addressed by the strength-reduction technique. First, the strength parameters of the slip band are back-analyzed by assuming a factor of safety of unity. Second, the major sliding directions are determined by carrying out finite difference analyses. Third, two proposed stabilization schemes are evaluated and compared to demonstrate the versatility of the technique. The present study has demonstrated that the strength-reduction technique is a powerful tool for analyzing such problems. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative technology—grouted jetted precast concrete piling—that increases the efficiency of piling operations in coastal regions. The technology includes the following steps: (i) casting concrete piles factory-designed especially for jetting and grouting; (ii) jetting to drive the concrete piles with a crane on a floating ship or platform into soil; and (iii) grouting to enhance the sheet pile connections and to increase the pile bearing capacity. This technology was applied to a number of piling construction projects at the mouth of the Yellow River Delta in China, and this experience demonstrated that it is a robust, fast track, cost-effective, and environmentally friendly piling method. [ABSTRACT FROM AUTHOR]

This paper investigates the failure of three gravity walls due to the 1999 Chi-Chi earthquake. Characteristics of the damaged walls were carefully recorded and backfill materials behind the damaged walls were collected and tested in the laboratory. Both the simplified analysis based on the Mononobe–Okabe method and the simplified dynamic analysis based on the Richards–Elms method were adopted. For the first case, the sliding of concrete wall blocks along the construction joint was observed. It was found that, during the earthquake, the frictional resistance at the untreated construction joint was not sufficient to resist the dynamic lateral thrust. For the second case, the retaining wall settled significantly and tilted about its toe. Seismic analysis of the wall indicated that, under the same horizontal acceleration, the factor of safety against bearing capacity failure was lower than that against overturning and sliding. A stability check against bearing capacity failure for the retaining wall should never be neglected. For the third case, the retaining wall built on top of the Che-Lung-Pu fault was severely damaged by the fault rupture. During the earthquake, the vertical displacement of the hanging wall uplifted the backfill, causing the wall to overturn. Horizontal displacement of the hanging wall caused the wall to slide and the soil in front of the toe to heave. [ABSTRACT FROM AUTHOR]

The reclamation for the new airport at Chek Lap Kok in Hong Kong included the placement of a substantial volume of sand fill by various hydraulic placement techniques, which resulted in a wide range of as-placed densities of the sand fill. This paper described the use of cone penetration tests (CPT) on the evaluation of the possible ranges of density achievable by various hydraulic placement methods adopted in the construction of the new airport. The results of the CPT indicated that the placement technique is one of the most important factors in controlling the as-placed density of hydraulically placed sand fill. There is a marked contrast in cone tip resistance (and the associated relative density) profiles for the sand fills formed by subaerial and subaqueous placement methods, in which the cone tip resistance of the sand fill formed by subaerial placement is substantially higher than that of the sand fill formed by subaequeous placement. The results confirm that dense sand fill cannot be formed by subaqueous placement methods. The weakest zone is generally located just beneath the water level where fill is placed by subaqueous discharge.Key words: sand, hydraulic fill, cone penetration test, calibration chamber test, in situ density.Le remblayage pour le nouvel aéroport à Chek Lap Kok de Hong Kong comprend la mise en place d'un volume substantiel de remblai de sable par différentes techniques de mise en place hydraulique, qui ont résulté en une large plage de densités en place du remblai de sable. Cet article décrit l'utilisation de l'essai de pénétration au cône (CPT) pour l'évaluation des plages possibles de densité qui peuvent être obtenues par différentes méthodes de mises an place hydrauliques adoptées pour la construction du nouvel aéroport. Les résultat de CPT indiquent que la technique de mise en place est un des facteurs les plus importants pour le contrôle de la densité en place de sable remblayé par méthode hydraulique. Il y a un contraste marqué entre les profils de résistance à la pointe (et la densité relative correspondante) pour les remblais de sable mis en place par des méthodes subaériennes ou sous l'eau, le premier étant appréciablement plus élevé. Les résultats confirment qu'un remblai de sable dense ne peut pas être obtenu par des méthode de mise en place sous l'eau. La zone la plus faible est en général localisée juste sous le niveau d'eau, là où la déposition du matériau de remblayage se fait par décharge sous-l'eau.Mots clés : sable, remblai hydraulique, essai de pénétration au cône, essai en chambre de calibrage, densité in situ.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

This paper models consolidation of the foundation soils under a test embankment at the new Chek Lap Kok International Airport in Hong Kong. The modelling used a simplified finite element method and material parameters derived from results in the original site investigation report. Various features that need to be considered in applying the simplified method are illustrated through this case study. Good predictions of settlement results are obtained. Relatively large discrepancies in pore-water pressure predictions suggest that the nonlinear nature of hydraulic conductivity needs to be taken into account when large compressions are likely to occur. Geological conditions are shown to be a key factor in successful modelling of consolidation behaviour.Key words: consolidation, pore-water pressure, case modelling, finite element method, vertical drains, settlement.Cet article modélise la consolidation des sols de fondation sous un remblai d'essai au nouvel aéroport international Chek Lap Kok de Hong Kong. La modélisation a utilisé une méthode simplifiée d'éléments finis et des paramètres du matériau dérivés des résultats du rapport de l'investigation originale du site. Diverses caractéristiques qui doivent être considérées dans l'application de la méthode simplifiée sont illustrées dans cette étude de cas. De bonnes prédictions des résultats de tassement ont été obtenues. Des divergences relativement importantes dans les prédictions des pressions interstitielles portent à penser que la nature non linéaire de la conductivité hydraulique doit être prise en compte lorsque des compressions importantes peuvent vraisemblablement se produire. On montre que les conditions géologiques sont un facteur clé pour modéliser avec succès le comportement en consolidation.Mots clés : consolidation, pression interstitielle, modélisation de cas, méthode d'éléments finis, drains verticaux, tassement.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]