Micromechanical Investigation of Stress Relaxation in Gas Hydrate-Bearing Sediments Due to Sand Production

Past experience of gas production from methane-hydrate-bearing sediments indicates that sand migration is a major factor restricting the production of gas from methane-hydrate reservoirs. One important geotechnical aspect of sand migration is the influence of grain detachment on the existing stresses. This paper focuses on understanding and quantifying the nature of this aspect using different approaches, with a focus on discrete element method (DEM) simulations of sand detachment from hydrate-bearing sand samples. The investigation in the paper reveals that sand migration affects isotropic and deviatoric stresses differently. In addition, the existence of hydrate moderates the magnitude of stress relaxation. Both of these features are currently missing from continuum-based models, and therefore, a new constitutive model for stress relaxation is suggested, incorporating the research findings. Model parameters are suggested based on the DEM simulations. The model is suitable for continuum mechanics-based simulations of gas production from hydrate reservoirs.

The implementation and role of geotechnical data in BIM process

Building Information Modeling (BIM) is becoming increasingly important tool in civil engineering both in the infrastructure design and construction process. BIM uses an intelligent model that provides a faster, more economical and less environmental impact for building and managing construction and infrastructure projects. Intelligent information model enable rich visualization, simulation and collaboration, which together allow better decision making throughout the project team. Major infrastructure projects that have a significant geotechnical and structural aspects may implement BIM tools and processes but often seem to neglect the geotechnical aspect of the model. This omission can lead to costly mistakes especially when the project is infrastructure-based. This paper reviews the current BIM implementations on major infrastructure projects and overseas and reviews how the inclusion of the geotechnical data in the BIM model can improve the models usefulness and the decision making process. The paper also investigates the reasons why the geotechnical data is not included and how these barriers can be removed so that the geotechnical and structural teams a fully integrated. The paper ends with a set of recommendations that, if adopted, could allow the engineering design team to produce innovative geotechnical systems and improve the cost effectiveness of construction.

Influence of Geotechnical Conditions on Damage States of Gdansk Bay Coast Cliff Formations

A geotechnical aspect of destruction processes of seashores was identified based on the case of erosion of Gdansk Bay Coast cliff formations. Causative factors of landslide were described in the context of natural phenomena, land development and its anthropogenic transformations. Possible directions of theoretical analysis of changes in ground-water relations were indicated.

Geochemical and geotechnical characterization of soils developed on volcanic rocks on the Bamenda mountain (Cameroon volcanic line)

The weathering mechanism of rocks exposed under the same conditions on the Bamenda Mountain is not well understood. The aim of this study is to characterize basalt, trachyte and rhyolite and their products on the geochemical and geotechnical aspect. Here three wells were hand dug on rocks developed on basalt, trachyte and rhyolite and studied. The results showed that, Ki values (0.34-6.57) indicate SiO2 are more leached on soils developed on basalt than those on trachyte and rhyolite. CIA (72.62-97.8) and CIW (72.76-98.8) indicate an advanced to extreme chemical weathering in this environment, with rhyolite and trachyte more weathered than basalts. Soils formed on basalt have ICV >1 signifying they are young and immature, while those on trachyte and rhyolite ICV =0.3-0.5 indicate intense chemical weathering. Al (EFAl=1.5) and Fe (EFFe=1.3) are enriched in the soils and while SiO2, Na, K, Ca and Mg are depleted in the soils profile as one moves upward. Geotechnically, these soils are predominantly silts, well graded, less plastic (LI<0), plastic (CI>1) to moderately plastic (PI=7.2-15.8). Soils developed on rhyolite have high clay content MBV= 3.3-8, but low water content (10-42%). Texturally, these soil are silty loam, loam to sandy loam soils. Soil strength of the soils is low: cohesion (<0.5bar), angle of internal friction (10-43°), with shallow landslides (1-2m) more likely to occur on trachyte and on rhyolites.

Thermo-hydro-mechanical coupling analysis of a thermo-active diaphragm wall

Thermo-active diaphragm walls that combine load bearing ability with a ground source heat pump (GSHP) are considered to be one of the new technologies in geotechnical engineering. Despite the vast range of potential applications, current thermo-active diaphragm wall designs have very limited use from a geotechnical aspect. This paper investigates the wall–soil interaction behaviour of a thermo-active diaphragm wall by conducting a thermo-hydro-mechanical finite element analysis. The GSHP operates by circulating cold coolant into the thermo-active diaphragm wall during winter. Soil contraction and small changes in the earth pressures acting on the wall are observed. The strain reversal effect makes the soil stiffness increase when the wall moves in the unexcavated side direction, and hence gives different trends for long-term wall movements compared to the linear elastic model. The GSHP operation makes the wall move in a cyclic manner, and the seasonal variation is approximately 0.5–1 mm, caused by two factors: the thermal effects on the deformation of the diaphragm wall itself and the thermally induced volume change of the soil and pore water. In addition, it is found that the change in bending moment of the wall due to the seasonal GSHP cycle is caused mainly by the thermal differential across the wall during the winter, because the seasonal changes in earth pressures acting on the diaphragm wall are very limited.

Assessment of Bridge Substructure in Java Island

Bridges play important roles in transportation system. Hazard to substructure of bridges become amplified. Based on previous year data, at least one-third of total bridges in Indonesia are damaged in certain level of defect. The performance of existing bridges shall be in-check everytime. Substructure of bridge itself is prone to hazards such as ground displacement, slope instability, seismic-related hazard and scour. Traffic data and soil investigation data will be used to analyse ground displacement and slope instability where the bridge located. Local geological and seismic data will be used to assess seismic-related hazard. Quantitative data is technical information and analyses from geotechnical aspects. Qualitative data is an expert system collected from bridge expert and local goverment. The expert system will have a rating system for each aspect. Fuzzy-based method is an effective tool for modeling some vague datas and this ease the decision-making process. Fuzzy Analytical Hierarchy Process (FAHP) will be used to analyses geotechnical aspect and expert system. Hazard identification, risk rating, risk analysis, and risk assessment are steps conducted in FAHP method. Classification and rating of risk can be done with proposed method. This assessment can be a tool or recommendation for local government where the bridge located.

Study of geotechnical aspect base on GIS as basic design of road

The determination road traces are the first step in road planning. Geotechnical aspects such as soil type, soil texture, peat soil, and CBR value should be considered during road planning so as to obtain the age of road services in accordance with the plan. At this time, GIS can be used in identifying the physical environmental conditions in the determination of road traces to increase time and cost efficiency. The suitability of the geotechnical aspects is determined using the scoring and weighting method. Each attribute is assigned a value with a range of values between 1 and 5. A score of 1 is given for the most suitable parameter, while a score of 5 is given if very unsuitable. The weights ratio of each criterion is 25% because each aspect has the same level of importance. Spatial analysis of the weighting result is done by the overlay method to obtain the geotechnical aspect appropriateness in determining road traces. The analysis results show that the lowest weights on the result of the overlay of the map is 2.25 which indicates that most of the area in Banyuasin Regency is “quite suitable” to be chosen as road traces.