The Cambridge Geotechnical Centrifuge routinely tests models made of up to 0·2 m3 of soil, at accelerations up to 125g. Self-weight effects in models and in corresponding prototypes are similar within a few per cent. Seepage and diffusion of pore water into the plane section of an unlined tunnel serve to illustrate scaling relationships. The stress/strain behaviour of soil alters with change of effective pressure p′and specific volume v. A theory of plasticity explains cohsolidation and yielding in shear at states above critical, but failures below critical state involve rupture or fracture. The range of values of a new equivalent liquidity LI5 = LI+0·5 log (p′/5)associated with yielding is 1·9<LI5<1, with rupture is l<LI5<0·5, and with fracture is 0·5<LI5. One example of centrifuge modelling is for tunnels in soft ground near critical states (LI5 = 1), in which plastic collapse is observed closely to match upper and lower bound calculations of theory of plasticity. In contrast, another example of centrif...

/pdf/cambridge-geotechnical-centrifuge-operations-4e1983txhq.pdf

Cambridge Geotechnical Centrifuge Operations

The mechanism of flexural toppling failure of jointed rock slopes has been investigated through a series of centrifuge experiments conducted on models manufactured from two types of materials (brittle: a sand-gypsum mixture; and ductile: fibre-cement sheeting). The basal failure plane observed in the centrifuge models, has been found to emanate from the toe of the slope, and orient at an angle of 12 to 20° upward from the normal to the discontinuities. A theoretical model based on a limiting equilibrium approach (Aydan and Kawamoto, 1992) has been adopted to analyse the centrifuge test data. After calibration, the model was found to accurately predict the failure load for all the tests reported in this study. Using this model, a set of charts has been prepared to assist with the analysis of slopes susceptible to flexural toppling.

A study of the mechanism of flexural toppling failure of rock slopes

Behaviour of granular soils subjected to internal erosion involves complex coupling between solid–fluid interaction, skeleton deformation and microstructural evolutions. This paper presents a micro–macro investigation on suffusion in idealized gap-graded and well-graded soils using the coupled computational fluid dynamics and discrete element method. The interaction between soil particles and seepage flow is modelled via momentum exchange between two phases. The progressive loss of fine particles subjected to upward seepage flow at various hydraulic gradients is investigated. The fines content, volumetric contraction and void ratio are monitored to identify the changes of macroscopic states of the soil skeleton. In addition, the microstructural evolution is tracked via particle-scale descriptors such as coordination numbers and force chain statistics. Several clogging–unclogging events which are responsible for the sudden changes of fines content and skeleton response are observed during suffusion. A parametric study indicates that the initial fines content and the hydraulic gradient significantly affect the kinetics of suffusion. Microstructural analyses reveal that the removal of fines is accompanied by the reduction in weak contact pairs and particles with low connectivity.

Suffusion-induced deformation and microstructural change of granular soils: a coupled CFD–DEM study

Flexural toppling is a mode of failure that may occur in a wide range of layered rock strata in both rock slopes and large underground excavations. Whenever rock mass is composed of a set of parallel discontinuities dipping steeply against the excavated face plane, the rock mass will have the potential of flexural toppling failure as well. In such cases, the rock mass behaves like inclined superimposed cantilever beams that bend under their own weight while transferring the load to the underlying strata. If the bending stress exceeds the rock column’s tensile strength, flexural toppling failure will be initiated. Since the rock columns are “statically indeterminate,” thus, their factors of safety may not be determined solely by equations of equilibrium. The paper describes an analytical model with a sequence of inclined superimposed cantilever rock columns with a potential of flexural topping failure. The model is based on the principle of compatibility equations and leads to a new method by which the magnitudes and points of application of intercolumn forces are determined. On the basis of the proposed model, a safety factor for each rock column can be computed independently. Hence, every rock column will have a unique factor of safety. The least factor of safety that exists in any rock column is selected as the rock mass representative safety factor based on which simple equations are proposed for a conservative rock mass stability analysis and design. As a result, some new relations are established in order to design the length, cross-sectional area and pattern of fully grouted rock bolts for the stabilisation of such rock mass. Finally, the newly proposed equations are compared with the results of existing experimental flexural toppling failure models (base friction and centrifuge tests) for further verification.

Stability Analysis and the Stabilisation of Flexural Toppling Failure

Landslides are serious geohazards that occur under a variety of climatic conditions and can cause many casualties and significant economic losses. Centrifuge modelling, as a representative type of physical modelling, provides a realistic simulation of the stress level in a small-scale model and has been applied over the last 50 years to develop a better understanding of landslides. With recent developments in this technology, the application of centrifuge modelling in landslide science has significantly increased. Here, we present an overview of physical models that can capture landslide processes during centrifuge modelling. This review focuses on (i) the experimental principles and considerations, (ii) landslide models subjected to various triggering factors, including centrifugal acceleration, rainfall, earthquakes, water level changes, thawing permafrost, excavation, external loading and miscellaneous conditions, and (iii) different methods for mitigating landslides modelled in centrifuge, such as the application of nails, piles, geotextiles, vegetation, etc. The behaviors of all the centrifuge models are discussed, with emphasis on the deformation and failure mechanisms and experimental techniques. Based on this review, we provide a best-practice methodology for preparing a centrifuge landslide test and propose further efforts in terms of the seven aspects of model materials, testing design and equipment, measurement methods, scaling laws, full-scale test applications, landslide early warning, and 3D modelling to better understand the complex behaviour of landslides. 

Centrifuge modelling of landslides and landslide hazard mitigation: A review

The slide which occurred at Lodalen, Oslo in 1954 was used to compare the behaviour of soil models tested in a centrifuge with a well-documented prototype event.The paper describes the centrifugal testing of three models prepared from block samples in which an attempt was made to simulate the stress history of the site. The results of these model tests are presented as an analogous prototype by the application of the simple scaling laws, which when compared with the actual prototype were found to present a realistic facsimile of the landslide.

A. N. Schofield

Papers

Centrifugal model tests of the Lodalen landslide