The ground is a natural grand system; it is composed of myriad constituents that aggregate to form several geologic and biogenic systems. These systems operate independently and interplay harmoniously via important networked structures over multiple spatial and temporal scales. This paper presents arguments and derivations couched by the authors, to first give a better understanding of these intertwined networked structures, and then to give an insight of why and how these can be imitated to develop a new generation of nature-symbiotic ground engineering techniques. The paper draws on numerous recent advances made by the authors, and others, in imitating forms (e.g. synthetic fibres that imitate plant roots), materials (e.g. living composite materials, or living soil that imitate fungi and microbes), generative processes (e.g. managed decomposition of construction rubble to mimic weathering of aragonites to calcites), and functions (e.g. recreating the self-healing, selfproducing, and self-forming capacity of natural systems). Advances are reported in three categories of Materials, Models, and Methods (3Ms). A novel value-based appraisal tool is also presented, providing a means to vet the effectiveness of 3Ms as standalone units or in combinations.

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is at the heart of the collapsible soils problem. To envisage and to model the collapse process in a 33 metastable medium, knowledge is required about the nature and shape of the particles, the types 34 of packings they assume (real and ideal), and the nature of the collapse process -a packing 35 transition upon a change to the effective stress in a media of double porosity. Particle packing 36 science has made little progress in geoscience discipline -since the initial packing paradigms set 37by Graton and Fraser (1935) -nevertheless is relatively well-established in the soft matter 38 physics discipline. The collapse process can be represented by mathematical modelling of 39 packing -including the Monte Carlo simulations -but relating representation to process remains 40 difficult. This paper revisits the problem of sudden packing transition from a micro-physico-41 mechanical viewpoint (i.e. collapse imetan terms of structure-based effective stress). This cross-42 disciplinary approach helps in generalization on collapsible soils to be made that suggests loess 43 is the only truly collapsible soil, because it is only loess which is so totally influenced by the 44 packing essence of the formation process. 45

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Colloidal nano-silica (NS) hydrosols are electrochemically stabilized, polymerized amorphous silica in low viscosity solutions, and in the form of hydrated gels, silica globules or pellicles. Compared to applications in concrete technology, the use of silica-based binders for groundwork applications has received little attention. Silica-based hydrosols impose no known direct risks to humans and are generally courteous to the soil health and ecosystem service functions. Their localized impact on microorganisms however needs to be further investigated. To this end, NS hydrosols have a scope for use as an alternative low-viscose material in groundworks. The current understanding of interactions between NS hydrosols and soil (sand) is, however, confused by the limited availability of experimental evidence concerning undrained static flow and large strain behavior. The contributions, presented in this paper, advance the knowledge through experimental testing, molecular modelling, and micro-analytical measurements. Four grades of colloidal NS (1–15 wt.%) were synthesized for grouting medium-dense sub-angular fine siliceous sand specimens. Consolidated-undrained triaxial compression testing was performed on the base and treated sand for isotropic consolidation over the effective stress range 100–400 kPa. Overall, silica impregnation produced improvements in yield and residual undrained shear strengths, restricted unwelcomed impacts of excess pore water pressure, and led to the formation of generally more dilative, strain-hardening behavior. Steady states and static flow potential indices are also studied as functions of confinement level and viscosity of the NS grout.

For the geological disposal of highly contaminated wastes, medical or other sorts, clay barrier systems are commonly designed and used. The engineered liners contain buffer material which is often carefully proportioned mixtures of pure bentonite and sand. Bentonite is an active clay mineral with very low hydraulic conductivity and extremely high expansive properties, which benefits in controlling the downward migration of hazardous contaminants to groundwater. In the design of such composite buffer geomaterial, deformation and pore-flow analysis is a pivotal matter and has therefore been thoroughly investigated in the decades past. When unsaturated, the coupling hydraulic-mechanical behaviour of sand-bentonite mixtures are complex. Among possible reasons behind this complex behaviour is the dependency of hydraulic hysteresis and consolidation properties on size, shape and sorting of solids and pores in the soil's skeleton, which are also rarely accounted for in most of the commonly used soil models. In this contribution, the hydro-mechanical behaviour of saturated and unsaturated sand-bentonite soil is investigated in the context of the recently developed Concept of Double Porosity (CDP). The geomaterial under study is assumed to consist of an incompressible, rigid, elastic solid skeleton surrounded by viscous water and gas fluids, and connected via a network of elastoplastic clayey bridge/buttress units. Roundness and sorting are varied for the sand constituent. The clay fraction (CF) is also varied across testing specimens. The experimental work here introduces two micromechanical models (small clay and large clay) which facilitates interpretation of macro-scale coupled hydromechanical behaviour of composite sand-bentonite geomaterials. The findings from this work will aid design practitioners through a tentative decision support system proposed in closing remarks.

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