ISO2394:2015 contains a new informative Annex D on “Reliability of Geotechnical Structures”. The emphasis in Annex D is to identify and characterize critical elements of the geotechnical reliability-based design (RBD) process, while respecting the diversity of geotechnical engineering practice. The most important element is the characterization of geotechnical variability and the next in line is arguably the characterization of model uncertainty. The key features of the first element are: (1) coefficient of variation (COV) of a geotechnical design parameter does not take a unique value, (2) multivariate nature of geotechnical data can be exploited to reduce the COV, and (3) spatial variability affects the limit state beyond reduction in COV due to spatial averaging. The second element is commonly carried out by taking the ratio of the measured result to the calculated result (called a model factor). This approach is entirely empirical, but it is practical. Because of its empirical basis, it is not surprising that there are limitations to this approach. The notable ones are lack of applicability to the serviceability limit state and correlation between the model factor and the input parameters in the prediction model.
This paper is a review of the study of ground deformation caused by underground construction and the countermeasures to control the environmental impact of underground construction, mainly including deep excavation and tunneling, based on case histories and state-of-art researches in China during the recent decade. According to the mechanism of deformation due to underground construction and its environmental impact, the deformation features and controlling measures were categorized into three classes, i.e., the soil displacement due to stress field change in soil or volume loss caused by construction activities, the ground loss caused by water-soil loss, and large scale ground movement due to the global failure of braced deep excavation or tunnel triggered by local damage of structures or local failure of soil. Furthermore, for each deformation type, the environmental impacts were graded based on the influence magnitude of the excavation and tunneling. Finally, the principles and methods to control the effects of deep excavation and tunneling were summarized.
This paper is related to the studies taken place during last decade to understand the intact behavior of a Collapsible Loess subjected to loading and wetting at Advanced Soil Mechanics Laboratory of Sharif University of Technology, Tehran, Iran. In this regard intact block samples are carefully taken from Hezar Pich Hill in the city of Gorgan, Iran, and various tests are performed on undisturbed specimen recovered from the intact block samples. In this way three automated unsaturated oedometer are built and a conventional triaxial apparatus is upgraded to a fully automated unsaturated triaxial device to accommodate rigorous and different stress and wetting path with continuous data acquisition of various parameters. The tests are conducted mainly on undisturbed samples, however, some tests are also performed on reconstituted specimens to observe the differences between the behavior of intact and reconstituted specimens. The results indicate that the hydro-mechanical behavior of intact Collapsible Loess is substantially different from that of the reconstituted specimens. Therefore, it is strongly recommended to perform undisturbed sampling and conduct tests on intact natural loess to be able to predict the collapse behavior, shear strength and hydro-mechanical behavior of this type of collapsible soils reasonably. Also in order to investigate on the type, optimized amount and methods of application of stabilizing agents a number of agents and improvement techniques are implemented. Various tests are conducted on the improved specimens as well and the results are compared with those of unimproved ones to verify the effectiveness of the used agents and methods.
Earthquake is one of the most destroying natural hazards causing the damage to human lives and economy. The exact evaluation of the soil-foundation-structure interaction (SFSI) is becoming increasingly important in prevention of damage from the earthquake. This paper focused on the assessment of SFSI effects on the seismic load of the structure with various types of foundations. The dynamic centrifuge tests for the shallow foundation, deep basement and pile foundation were performed and the representative results are introduced. The SFSI effects can reduce the seismic load applied to the SDOF structures on the shallow foundation, but also increase the load for the basement and the pile cap when the foundation is fully embedded.
The management of Hazardous Waste (HW) has become a very important and serious matter because of installation of large number of industries across India as a part of globalization and industrialization. If improperly managed, the HW would lead to environment holocaust. Hazardous waste (HW) landfills are provided with either single liner or double liner system to avoid subsurface soil and groundwater contamination due to leachate. These liners are multi layered multi barrier system which typically consists of leachate collection and removal system, compacted clay barrier soil and geosynthetic materials. In the present study, three types of HW landfill configurations are analyzed for hydrological performance using HELP model, to estimate the quantity of leachate generated and estimate the leakage through considered liner systems. Based on the performance, it could be recommended to provide a single liner system with geosynthetic Clay Liner (GCL) for the considered HW landfill. The thickness of the compacted clay liner (CCL) is reduced by 60 cm and a GCL of thickness 7 mm is instead provided in the recommended liner system which performs much better than single and double liner system while reducing the quantity of clay soil.
Methane hydrate (referred to as MH hereafter) has come to be seen as a future energy source and as such research and development is being conducted in order to prepare for production of it. The MH reservoirs are located in the deep sea bed at over 1000m in sea depth. In Japan, the reservoirs are found in the Nankai Trough on the Pacific Ocean side of main island. MH mostly exists in the void space of the sand layers in the turbidite. In order to produce MH from the MH bearing layers, it is important to first make clear and understand the mechanical properties of the host sands of MH bearing sands in order to understand the MH bearing layer. A series of mechanical tests were performed on MH bearing sediments with various host sands by using temperature controlled high stress triaxial shear testing apparatus. A high pressure and low temperature plane strain testing apparatus was also developed for visualizing the deformation of methane hydrate bearing sand due to methane hydrate production. Using this testing apparatus, plane strain compression and methane hydrate dissociation by depressurization tests were performed with the measurement of localized deformation. On the basis of the experimental results, an elastoplastic constitutive model for methane hydrate-bearing sand was developed. The bonding effect due to the cementation by methane hydrate was introduced into the model. The simulation was performed on triaxial behaviour of methane-hydrate bearing sand under various pressure and temperature condition.