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AGU Fall Meeting 2019 in San Francisco , 9-13 December 2019, EIS/InSIght team, InSight is the first planetary mission with a seismometer package, SEIS, since the Apollo Lunar Surface Experiments Package. SEIS is complimented by APSS, which has as a goal to document the atmospheric source of seismic noise and signals. Since June 2019, SEIS has been delivering 6 axis 20 sps continuous seismic data, a rate one order of magnitude larger originally planned. More than 50 events have been detected by the end of July 2019 but only three have amplitudes significantly above the SEIS instrument requirement. Two have clear and coherent arrivals of P and S waves, enabling location, diffusion/attenuation characterization and receiver function analysis. The event¿s magnitudes are likely ¿ 3 and no clear surface waves nor deep interior phases have been identified. This suggests deep events with scattering along their final propagation paths and with large propagation differences as compared to Earth and Moon quakes. Most of the event¿s detections are made possible due to the very low noise achieved by the instrument installation strategy and the very low VBB self-noise. Most of the SEIS signals have amplitudes of spectral densities in the 0.03-5Hz frequency bandwidth ranging from 10-10 m/s2/Hz1/2 to 5 10-9 m/s2/Hz1/2. The smallest noise levels occurs during the early night, with angstrom displacements or nano-radian tilts. This monitors the elastic and seismic interaction of a planetary surface with its atmosphere, illustrated not only by a wide range of SEIS signals correlated with pressure vortexes, dust devils or wind activity but also by modulation of resonances above 1 Hz, amplified by ultra-low velocity surface layers. After about one half of a Martian year, clear seasonal changes appear also in the noise, which will be discussed. One year after landing, the seismic noise is therefore better and better understood, and noise correction techniques begun to be implemented, either thanks to the APSS wind and pressure sensors, or by SEIS only data processing techniques. These data processing techniques open not only the possibility of better signal to noise ratio of the events, but are also used for various noise auto-correlation techniques as well as searches of long period signals. Noise and seismic signals on Mars are therefore completely different from what seismology encountered previously on Earth and Moon.

International audience; A possible option for the disposal of high level long lived radioactive waste is to store the waste in galleries excavated at great depth in clays or claystones. In such conditions, the walls of the galleries will be successively subjected to desaturation induced by ventilation followed by resaturation once the galleries are closed. Partial saturation also affects laboratory samples, due to the added effects of coring, transportation, storage and trimming. In this study, a series of tests was conducted to investigate the water retention properties of the Callovo-Oxfordian claystone (in which the ANDRA Underground research laboratory in France has been excavated) under drying/wetting cycles so as to provide a complete description of the changes in water content, volume and degree of saturation from the as-provided state. The results show that water content changes between 3% (at 150 MPa of suction) and 12% at zero suction, with a shrinkage of 1.4% (at 150 MPa of suction) and a 7% swelling at zero suction. The data obtained complete existing data by defining the initial state with respect to the main drying and wetting paths and by providing volume changes along the suction cycles. Hysteresis effects are also evidenced. Irreversible volume changes are assumed to be due to micro-crack generation and incomplete recovery. The changes in degree of saturation with respect to water content appeared to be reversible, an important fact to consider when simulating volume changes in COx.

The volume change and shear strength behaviour of soils are controlled by the effective stress. Recent advances in unsaturated soil mechanics have shown that the effective stress as applicable to unsaturated soils is equal to the difference between the externally applied stress and the suction stress. The latter can be established based on the soil-water characteristic curve (SWCC) of the soil. In the present study, the evolution of swelling pressure in compacted bentonite-sand mixtures was investigated. Comparisons were made between magnitudes of applied suction, suction stress, and swelling pressure.

The thermo- mechanical behavior of energy piles has been studied extensively in recent years. In the present study, a numerical model was adapted to study the effect of various parameters (e.g. heating/cooling temperature, head loading condition and soil stiffness) on the thermo-mechanical behavior of an energy pile installed in unsaturated sandstone. The results from the simulations were compared with measurements from a thermal response test on a prototype energy pile installed beneath a 1-story building at the US Air Force Academy (USAFA) in Colorado Springs, CO. A good agreement was achieved between the results obtained from the prototype and the numerical models. A parametric evaluation were also carried out which indicated the significance of the stiffness of the unsaturated sandstone and pile’s head loading condition on stress-strain response of the energy pile during heating/cooling cycles.

Due to rainwater infiltration and loss of matric suction above the wetting font, both translational and rotational slips may occur in an unsaturated soil slope. It is useful to know which failure mode is more critical. The governing failure mode is likely to be affected by soil properties, slope geometry, depth of wetting front and contribution of matric suction to shear strength, which were investigated in this study. Specifically, upper bound limit analysis was adopted to develop stability charts based on rotational failure mechanism, and infinite slope model was used to develop stability charts based on translational failure mechanism. For a slope, the failure mechanism which gives the lower factor of safety is the governing failure mode. It was found that the failure mode of an unsaturated soil slope under rainfall is determined by parameter group c′/γHtanϕ′ for a given slope angle, depth of wetting front and contribution of matric suction to shear strength. With the increase in depth of wetting front and greater contribution of matric suction to shear strength, a slope is more prone to translational failure. Slopes with angle β = 45° are most vulnerable to translational failure, while gentler slopes (e.g. β = 15°) and steeper slopes (e.g. β = 75°) are more susceptible to rotational failure. Published version

Soil-water characteristic curve (SWCC) contains key information for the application of unsaturated soil mechanics principles to engineering practice. SWCC variables such as air-entry value, residual suction and residual saturation are commonly referred to for estimation of other unsaturated soil properties. Though there are clear definitions for these SWCC variables, it is difficult to measure them directly in laboratory and these SWCC variables are commonly estimated from SWCC. Hydraulic conductivity of unsaturated soil is the major property that controls water flow in soil. The laboratory measurement of hydraulic conductivity is time consuming and costly. Therefore, hydraulic conductivity is also commonly estimated from SWCC. Normally, SWCC is represented by a best fit equation which is typically governed by few fitting parameters. These fitting parameters can be obtained from a best fit procedure and are proven to be dependent on each other. Fredlund and Xing’s (1994) equation is one of the popular equations commonly used by researchers and there are only three fitting parameters such as “a”, “n”, “m” in this equation. Correlation equations between SWCC variables, hydraulic conductivity and the fitting parameters such as “a”, “n” and “m” are presented in this paper. In addition, the variability in the determined SWCC variables and hydraulic conductivity due to the variation in these fitting parameters is also discussed in this paper. Published version

Measurement of soil suction is important as soil suction is one of the two stress-state variables that control both the hydro and mechanical behaviour of unsaturated soils. One of the soil suction measurement techniques is the filter paper method. Even though the filter paper technique has been standardized, the experimental procedure can still be improved in order to reduce the inconsistencies that are often reported with the filter paper technique. This paper explores usage of both initially dry and initially moist Whatman No. 42 filter paper for matric and total suction measurements. Residual soils from the Bukit Timah Granite in Singapore were compacted at various water contents from dry to wet of optimum using standard Proctor energies and their suctions were measured using both contact and non-contact filter papers. Results of the suction measurements showed hysteresis between the initially dry and the initially moist filter papers for both the contact and non-contact methods. Suction measurement by the contact filter paper method is more consistent than suction measurement by the non-contact filter paper method. Condensation causes the non-contact filter papers to have higher water contents. The results showed that the non-contact initially dry filter paper follows the total suction curve but the non-contact initially moist filter paper may follow the matric suction curve instead. ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

The paper describes discrete modelling of the retention behaviour of unsaturated porous materials. A network approach is used within a statistical volume element (SVE), suitable for subsequent use in hydro-mechanical analysis and incorporation within multi-scale numerical modelling. The soil pore structure is modelled by a network of cylindrical pipes connecting spheres, with the spheres representing soil voids and the pipes representing inter-connecting throats. The locations of pipes and spheres are determined by a Voronoi tessellation of the domain. Original aspects of the modelling include a form of periodic boundary condition implementation applied for the first time to this type of network, a new pore volume scaling technique to provide more realistic modelling and a new procedure for initiating drying or wetting paths in a network model employing periodic boundary conditions. Model simulations, employing two linear cumulative probability distributions to represent the distributions of sphere and pipe radii, are presented for the retention behaviour reported from a mercury porosimetry test on a sandstone.

Bentonite-based materials are studied as potential barriers for the geological disposal of radioactive waste. In this context, the hydro-mechanical behaviour of the engineered barrier is first characterized by free swelling conditions followed by constant volume conditions. This paper presents an experimental study conducted in order to characterize the water retention behaviour of a compacted MX-80 bentonite/sand mixture. Then, based on observations of the material double structure and the water retention mechanisms in compacted bentonites, a new water retention model is proposed. The model considers adsorbed water in the microstructure and capillary water in the aggregate-porosity. The model is calibrated and validated against the experimental data. It is used for better understanding competing effects between volume change and water uptake observed during hydration under free swelling conditions.

This paper presents an evaluation of the thermal volume change of compacted specimens of the same type of silt under a wide range of stress states, initial void ratios, and suction magnitudes. Stress states include both isotropic and anisotropic conditions with varying principal stress ratios, as well as normally consolidated and overconsolidated conditions. Initial void ratios range from 0.60 to 0.86, spanning very dense to loose conditions. Suctions evaluated range from saturated conditions, to low suctions in the funicular range, to suctions corresponding to residual saturation conditions. For the same soil, wide variations in thermal volume change are observed. Thermal contraction is observed for normally consolidated conditions regardless of the initial degree of saturation. Different mechanisms of thermal volume change can be used to explain the results, ranging from thermally-induced pore water pressure dissipation, to thermal collapse, to thermally-accelerated creep.

Global climate change has a significant impact on rainfall characteristics, sea water level and groundwater table. Changes in rainfall characteristics may affect stability of slopes and have severe impacts on sustainable urban living. Information on the intensity, frequency and duration of rainfall is often required by geotechnical engineers for performing slope stability analyses. Many seepage analyses are commonly performed using the most extreme rainfall possible which is uneconomical in designing a slope repair or slope failure preventive measure. In this study, the historical rainfall data were analyzed and investigated to understand the characteristics of rainfall in Singapore. The frequency distribution method was used to estimate future rainfall characteristics in Singapore. New intensity-duration-frequency (IDF) curves for rainfall in Singapore were developed for six different durations (10, 20, 30 min and 1, 2 and 24 h) and six frequencies (2, 5, 10, 25, 50 and 100 years). The new IDF curves were used in the seepage and slope stability analyses to determine the variation of factor of safety of residual soil slopes under different rainfall intensities in Singapore. Published version

Clay Geosynthetic Barriers are manufactured hydraulic barriers. The mineral component usually consists of bentonite, which belongs to a group of expansive soils. The aim of this study was to establish the influence of swelling on mechanical properties of bentonites. For this purpose, granular bentonite Volclay was chosen for laboratory testing. Its mineralogical composition was predominantly montmorillonite (80% - 85% by mass). The correlation between swelling and water content on one side and changes in shear strength i.e. shear strength parameters on the other were tested using a direct shear device. During several series of testing, different levels of swelling ofbentonite were simulated under the conditions of changing normal stress and hydration times. Swelling behaviour of bentonite was determined through the long-term swelling tests using oedometer, under changing normal stress. Shear strength testing show decreasing cohesion with longer hydration of bentonite. The friction angle increases with hydration that lasts from 7 to 14 days. There is no significant change in the friction angle with hydration time longer than 14 days.

Over the last century, moutain ranges in Europe and North America have seen substantial development due to the increase in recreational activities, transportation, construction in high altitude areas, etc. In these moutain ranges, avalanches oftenthreaten man's activities and life. Typical examples include recent disasters, such as the avalanches at Val d'Isère in 1970 (39 people were killed in a hostel) or the series of catastrophic avalanches throughout the Nothern Alps in february 1999 (62 residents killed). The rising demand for higher safety measures has given rise to a new scientifc area entirely devoted to snow and avalanches. This paper summarises the paramount features of avalanches (formation and motion) and outlines the main approaches used for describing their movement., Ce papier résume les principaux aspects des avalanches, les différentes approches pour décrire leurs mouvements.

The RNK-method or the Reference Level of Correlation method represents a procedure for spatial engineering-geological and/or geotechnical modeling, that was tested on many landslides in Croatia. The method gives the opportunity of differentiation of minimum shear strength zones, zones of different hydraulic conductivities, and zones of various soil densities. The application and verification of the RNK-method in soft rock formations found on the landslide area in Gorica Svetojanska (Croatia) is presented. The presentations providing the full set of relevant information needed to develop representative geotechnical profiles are also shown. The established geotechnical sliding model is verified by measurements of lateral movements in the landslide area and by results of corresponding stability analyses