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The capillary barrier effect (CBE) is employed in a large number of geotechnical applications to decrease deep percolation or increase slope stability. However, the micro-scale behaviour of CBE is rarely investigated, and thus hampers the scientific design of capillary barrier systems. This study uses microfluidics to explore the micro-scale behaviour of CBE. Capillarity-driven water flow processes from fine to coarse porous media with different pore topologies and sizes were performed and analysed. The experimental results demonstrate that the basic physics of CBE is the preferential water movement into the fine porous media due to the larger capillarity. The effects of CBE on water flow processes can be identified as delaying the occurrence of breakthrough into the coarse porous media and increasing the water storage of the fine porous media. The CBE can impede the increase of the normalised length and decrease the normalised width of the water front, suggesting that the two normalised parameters are potential indicators to assess the performance of CBE at the micro scale. CBE can be formed in square and honeycomb networks with the ratio of coarse to fine pore throat width larger than 2·0 when gravity is neglected, and its performance can be affected by pore topology and size.

Large soil movements arising from the installation of jack-up spudcan foundations may induce detrimental effects on piles supporting adjacent permanent jacket platforms. Particularly, in a dense sand-over-clay profile, there is a risk of spudcan rapid penetration due to underlying clay bearing capacity failure, known as spudcan punch-through failure, which can cause further damage to piles in the proximity. This study investigates the foundation interaction between the spudcan and adjacent pile in a sand-overlying-clay soil profile by way of centrifuge modelling. Issues investigated include thickness of the upper sand layer with incidence of sand plug beneath the spudcan and spudcan–pile clearance. The experimental findings reveal that spudcan punch-through hazard and the magnitude of induced pile moments amplifies primarily due to the increase in the thickness of the upper sand. In addition, the magnitude of induced pile moment in a sand-over-clay profile is significantly higher than that in a single clay profile because of the post-peak bearing behaviour observed in stratified soil, yielding to a greater risk to pile integrity. Soil pressure profiles on the piles are also back-analysed. Two generalised induced soil pressure profiles are deduced, with the first profile representing the onset of spudcan punch-through and the second profile denoting the situation of post-punch-through failure.

Open caissons are an increasingly common means of constructing underground storage and attenuation tanks as well as launch and reception shafts for tunnel-boring machines. The caisson walls typically feature a tapered base, referred to as the ‘cutting face’, to aid the sinking process by reducing the vertical soil reaction. The primary aim of this paper is to explore the influence of the caisson cutting face inclination angle on the vertical soil reaction in sand. Both finite-element limit analysis and finite-element analysis are adopted for this purpose. The effects of cutting face roughness, external embedment depth and caisson radius are also investigated. The results show that the influence of the cutting face inclination angle on the bearing capacity is highly dependent on both the soil friction angle and the roughness of the cutting face. A reduction in the caisson radius is also shown to cause a significant increase in the vertical soil reaction. The numerical output is used to inform the development of a new closed-form analytical approach amenable for use in routine design. The design method is shown to provide a high-fidelity representation of the numerical output.

This chapter covers the principles of groundwater flow. It begins with defining hydraulic conductivity and Darcy's Law for one-dimensional flow, and then generalizes to three dimensional flow. The concepts of specific discharge, average linear velocity, and intrinsic permeability are introduced. Heterogeneity and anisotropy in hydraulic conductivity fields are discussed along with methods for assigning bulk average conductivities. A range of methods for measuring or estimating hydraulic conductivity are discussed, including grain size correlations, lab tests, field tests, tracer tests, and models. Sections near the end of the chapter deal with flow in individual fractures in fractured rock, flow in the unsaturated zone, and groundwater flow with variable density water. Coastal fresh–salt interface flow is discussed and the Ghyben-Herzberg method of estimating interface elevation is covered.

Oversize rock fragments are highly undesired in a sublevel caving (SLC) operation as they affectthe production cycle, equipment, and infrastructure. In this study, afield test was carried out inMalmberget mine to analyse the impact of oversize fragments on the production cycle and thecosts of different procedures for handling such fragments. The tests involved monitoring ofdumping oversize fragments in two orepasses, one with a grizzly and the other one withouta grizzly, using cameras. The cycle times of load-haul-dump (LHD) machines weredetermined for both orepasses. The results indicate that the grizzly increased the availabilityand productivity of the orepass despite increasing the cycle time of the LHD machines.Moreover, installation of a boulder breaker system along with the grizzly can furtherincrease the productivity and the cost of such a system will be paid offin a shorter time interms of enhanced productivity. Face-to-Surface II

Embankment dams may be damaged by internal erosion, which ultimately may lead to a failure. During internal erosion, finer soil particles from the core soil are being washed out. To restore the core function, injection grouting may be undertaken. Grouting the core of an embankment dam should be performed with a grout with similar characteristics as the original core soil. This grout type is commonly used in compaction grouting, e.g., a low mobility grout. The grout is similar to a fine-grained moraine core soil, but given its stiffness, it is difficult to permeate a damaged core soil. A modified low mobility grout containing sand, limestone filler, bentonite, plasticizer, air release agent and water has been tested in the laboratory with focus on permeation. Grouting was done in different sized aggregates. Impact of paste-to-aggregate ratio, grout consistency, maximum grain size of grout, coarseness of grouted material, and grouting methodology was tested. Higher paste-to aggregate ratios and lower viscosity/yield strength in/of the grout improved the permeation. Initially pressurized grouting compared to only hydrostatic pressures followed by stepwise pressure increased grouting was furthermore identified as a factor to improve the permeation. Funder: Svenskt Vattenkraftcentrum (SVC)

The critical state of granular soils needs to make proper reference to the fabric that develops at critical state. This study substantialises the concept of critical fabric surface (CFS), which attracts the fabric state of granular soils upon continuous shearing. Numerical experiments using discrete-element method (DEM) modelling are conducted under drained and undrained conditions with varying Lode angles. Fabric tensors are defined based on the normals of all contacts and of the strong force contacts only. Both tensors have their spherical component preserved such that the information of coordination number can be carried. A separate series of low-confining-pressure undrained tests is conducted to probe the fabric states of soils in the post-liquefaction regime. Finally, a single CFS spanning across a wide range of coordination numbers is established based on the DEM results. The CFS concept provides an important reference state for soils sheared to large strains, complementary to the traditionally defined critical state. This provides a new perspective to interpret and model the mechanics of granular soils in both pre- and post-liquefied regimes. The evolution of fabric shows that the normalised strong-contact fabric evolves linearly with the stress ratio even for liquefied or anisotropically consolidated soils.

Soils containing organic matter exhibit low shear strength and high compressibility. Lime stabilisation has been shown to improve the engineering properties of clayey soils. An attempt was made to study the effect of organic matter (starch and peat) on the shear strength of lime-stabilised clayey soils subjected to longer curing periods (up to 180 days). Most studies have reported the strength behaviour of lime-stabilised organic soils up to 60 days. Vane shear tests were carried out on artificially prepared organic soil mixtures treated with 6% lime after different curing periods (0, 7, 30, 60, 90 and 180 days). The results indicate that the improving effect of lime is deteriorated in the presence of organic matter as the curing period increases. It was observed that, for lime-stabilised clayey soils containing organic matter, the strength seemed to increase up to 30 days, after which it ceased. The strength reduction in lime-stabilised clayey soils containing organic matter depended on the pH and functional groups present in the soil. Fourier transform infrared spectroscopy of cured samples was also carried out to examine the microstructural changes responsible for the strength change in lime-stabilised clayey soils.

A series of full-scale experiments was conducted to estimate lateral soil constraints on pipes buried in dense sandy slopes at different burial depths. The experimental data indicated that the soil force on the pipe increases with increase in the slope grade and burial depth ratio. The lateral soil force against relative pipe displacement response observed from the experiments is presented and compared to those arising from level ground conditions. The study was extended to larger burial depth ratios by simulating pipes under sloping ground conditions using a numerical (finite-element) model that was initially calibrated using the results from physical modelling. The findings from the study in terms of the variation of peak lateral soil restraint as a function of the slope grade and burial depth ratio are presented for consideration in pipeline design.

Triaxial tests are generally conducted to establish the mechanical behaviour of cement-treated clays. Numerical simulations of these tests involve selection of the correct constitutive model, which can capture the key features of the stress–strain response of the geomaterial. However, as cement-treated clays behave differently to untreated clay in its natural state, the classic constitutive models may not give reasonable results and the failure envelope has been found to be non-linear. An attempt was made in this work to simulate the behaviour of cement-treated clays using the Hoek–Brown model and the experimental and numerical simulation results were compared.

The movement of water in concrete structures and buildings is a fundamental subject and therefore it is necessary to understand the mechanisms and processes involved. This paper presents a method to estimate the moisture diffusivity of concrete using gravimetric measurements, together with discretised electrical resistivity measurements. To improve the repeatability of the method, various concrete mixes with and without supplementary cementitious materials were tested. The samples were conditioned under two regimes representing poor and good curing; the samples were then exposed to a simulated hot environment with a diurnal temperature fluctuation of 20–40°C and 60% ambient relative humidity. The basis of the method was to measure the amount of water absorbed by the concrete sample at different depths as a function of time and then Boltzmann's transformation was used to analyse the experimental results obtained. Once a master curve using the Boltzmann transformation is formed, the moisture diffusivity can be obtained. The results showed that the relationship between moisture diffusivity and moisture content can be described by an exponential function.

Gypsum is regarded as an environmentally friendly binding material and is widely used to enhance the engineering properties of soft fine-grained soils. However, the time-dependent strength and deformation characteristics of fine-grained soils stabilised with gypsum have not yet been thoroughly investigated and rational evaluation of these characteristics will assist in the formulation of cost-effective and reliable design approaches. In this study, the time-dependent mechanical behaviours of gypsum-mixed fine-grained soil (GMFS) specimens were investigated under unconfined monotonic loading conditions, considering ageing periods of 3–90 days and five different loading rates (LR = 0.0005–1.0%/min). The results revealed that the unconfined compressive strength and stiffness of the GMFS specimens initially decreased with ageing and finally became stable after 14 days and 28 days of ageing for water/gypsum ratios of 1.30 and 1.60, respectively. Furthermore, the strength and stiffness of the GMFS specimens increased with an increase in LR.

The limit analysis approach is used in this paper to analyse the problem of a strip foundation on cohesive-frictional soil under seismic conditions, based on the pseudo-static approach, considering different inclination factors. In particular, for a weightless c–ϕ soil, the upper-bound (UB) and the lower-bound solutions are found to be coincident, and then the exact solutions for the bearing capacity factors Nqe and Nce under seismic conditions are obtained. The effect of soil weight is considered with the UB method. A discussion is presented on seismic reduction factors and their superposition.

In piled raft foundations, the load shared between the piles and the raft is affected by a complex soil–structure interaction. However, the number of piles and their location can be optimised, thereby making piled rafts more effective and economical. In this study, the influence of three key design parameters (the number of piles, pile length and pile spacing) on pile–pile–soil and raft–pile–soil interactions was investigated; each of these parameters can lead to improvements in the performance and efficient load sharing of piled rafts. The results of small-scale model tests in sand showed that an increase in pile number or length proportionally decreased the load taken by the raft. A change in the pile spacing or compaction state of the sand bed also affected the raft's contribution, although to a lesser extent. Load sharing between the piles and the raft was found to be not only sensitive to the foundation size but was also dependent upon its settlement. Under favourable pile–pile–soil, raft–pile–soil and pile–raft–soil interaction effects, the combined load capacity of the piled raft increased. These interaction effects were non-linear and sensitive to settlement, which resulted in non-linear sharing of the load between the piles and the raft. The effect of pile inclusion and the number of piles on the shared load was also investigated using a simple hyperbolic model while considering the above interaction effects.

A macro-element model for predicting the load–displacement behaviour of a spudcan foundation in clay overlying sand when subjected to combined vertical, horizontal and moment loading is introduced. Observations from detailed drum centrifuge tests that measured the effect of the underlying sand layer on the foundation behaviour are combined with finite-element results and theoretical developments to derive the components of the model. The yield surface defined by the centrifuge test results suggests that as the spudcan nears the underlying sand layer, the absolute horizontal capacity remains relatively constant, while the vertical and moment capacities increase at approximately the same normalised rate. The model is demonstrated to accurately predict foundation behaviour by retrospectively simulating the experimental results. This macro-element model has the advantage that it can be integrated into the structural analyses of jack-up platforms required for site-specific assessments.

The now-abandoned project for a new international airport for Mexico City was located at a site on the former Texcoco Lake, where extremely difficult subsoil conditions prevail. The behaviour of one of the trial embankments built to test foundation solutions for the runways is analysed in this paper. Observational data were gathered over 50 months at the so-called reference embankment, where no special foundation or soil improvement techniques were adopted. The performance of this embankment was investigated through finite-element simulations in which an elasto-viscoplastic constitutive model was implemented in commercial software. The model incorporates key features such as time dependence, long-term deformation and an anisotropic flow surface. The results provide an assessment of the constitutive description adopted as well as the role of anisotropy in the simulation of the case study.

Excessive deformation has been observed during the construction of large-section (over 100 m2) tunnels in soft rock all over the world. A case study of deformation control for large-section tunnel construction in fractured carbonaceous slate was conducted. Xingzishan tunnel, China, was first excavated using the three-step reserved core soil excavation method (TRCSEM); however, this resulted in serious rockfalls at the tunnel arch and local collapse. To enhance the stability of the tunnel face, three different tunnel support systems with relatively stiff structures were proposed and tested along the tunnel chainage in the same rock condition, but all of them failed. The mechanism of the TRCSEM was revealed by field measurements, highlighting the significance of the stability of the upper bench of the tunnel face. In view of this, the three-step temporary inverted arch method (TTIAM) was employed and used with advance support. With this new method, the upper bench of the tunnel face was reinforced with fibreglass bolts to mitigate the deformation. Compared with the TRCSEM, the TTIAM effectively controlled large deformation at the tunnel face during the excavation in fractured carbonaceous slate with an acceptable construction cost.

Slope stability analysis and seepage analysis are two important aspects of embankment stability. Landslides are a common risk faced by many people in the world, with this risk increased in the case of an earthfill embankment or water reservoir. People living in downstream regions are always at risk if the dam is not designed to achieve full strength. In this work, a pre-defined earthfill dam was analysed to assess its strength with variations of dam width (WD), shear strength of the soil (τ) and dam slope angle (β). The factor of safety was considered as the dependent, with WD, τ and β as independent variables. A pre-defined proposed dam model was analysed using limit equilibrium (LE) methods with the help of the LE software Slide. Linear regression analysis was performed using SPSS (Statistical Package for Social Sciences) software and equations were developed. The computed equations show a very close relation of all the analysed parameters. The coefficient of determination (R2) of all the developed correlations was found to be very high and the equations can thus be used in design analysis of slopes, embankments and earthfill dams.

Widespread liquefaction has been frequently observed in silty sand deposits during recent large earthquakes. How to properly evaluate the liquefaction potential of silty sands has emerged as a matter of great concern. This paper presents an investigation into the problem through a comprehensive experimental programme in conjunction with a newly developed framework of analysis. Focus is placed on the effect of particle size disparity and its interplay with the effect of fines content – two fundamental issues for which current understanding is limited. A novel finding of the study is that the liquefaction resistance of sand–fines mixtures, defined as the cyclic resistance ratio (CRR) leading to failure at a specific number of loading cycles, is almost uniquely related to the state parameter (ψ) defined in the critical state theory, regardless of particle size disparity and fines content. To quantify the combined effects of fines content and particle size disparity, an empirical model is put forward along with a practical method for estimating the critical state parameters of silty sands. The model is evaluated using experimental data on a range of sand–fines mixtures in the literature, showing a reasonably good performance and attractive advantages. A grain-scale mechanism is also suggested to explain the observed effects.

In this study, a mixing procedure of sulfur-rich soil and cement-based binder to enhance the soil’s unconfined compressive strength (UCS) was tested in field conditions for geotechnical applications. The focus was to evaluate uniformity of industrial size soil-binder mixture, blended by existing method. This paper outlined sampling strategy and the number of samples needed for a valid uniformity evaluation. Moreover, this study emphasized the difference between field mixing and laboratory mixture preparation by comparing UCS of stabilized soil samples in the field and UCS of corresponding samples mixed and prepared in the laboratory environment. In the field, soil and cement were blended in two to four stages with 5% and 7% cement—the percentages being based on the soil’s dry weight under field conditions. Samples were taken from the field mixtures after each stage. Since the number of samples needed to be representative of mixture characteristics for large-scale mixing is not standardized, this field experiment included two phases. The first phase was dedicated to finding a sampling strategy for a large soil pile along with measuring UCS of collected samples. In the second phase, sample collection was conducted based on the results of sampling strategy from the first phase. In the laboratory, samples with percentages of binder similar to the amount of binder in the field were also prepared. Both field and laboratory samples were prepared using the tapping method in the laboratory for UCS test. Samples were cured under similar conditions for 28 days. The results showed that the uniformity of mixture improved after each additional mixing stage. In addition, while spots with low UCS were observed in the second mixing step, these spots were eliminated in the third mixing step, and results of the UCS tests were comparatively uniform. Moreover, comparison of the samples revealed that the UCS of the laboratory mixture is higher than that of the field mixture. This showed that even though the UCS is a good standard for comparing the strength of different soils stabilized with different percentages or types of binders in the field mixing, the actual strength of the stabilized mixtures under field circumstances is lower than that in laboratory prepared mixtures. Validerad;2023;Nivå 2;2023-04-14 (hanlid);Funder: Interreg Botnia-Atlantica program Sustainable treatment of coastal deposited sulfde soils (STASIS)

Biogrouting as a new method for ground improvement or seepage control has been developed and extensively studied in recent years. Most studies have focused on lab bench, small-diameter sand column tests. To simulate in situ conditions more closely, biogrouting tests on two 1 m3 models were carried out. One was for pure silica sand and another was for rock blocks filled with sand. A significant reduction in permeability and an increase in shear strength were achieved in both model tests after ten rounds of biogrout treatment. The mechanical characteristics of the biologically cemented sand were studied using samples cored from the 1 m3 model. The distribution of the calcium carbonate content and the shear strength within the 1 m3 model was studied. Correlations between the unconfined compressive strength and the permeability of the cemented sand and the calcium carbonate content were established. Suggestions of methods to improve the uniformity of the biogrouting treatment are made in this paper.

This paper assesses the possibility of utilisation of clay–waste tyre rubber mixes as construction materials for geotechnical structures. Rubber granulates (Rg) and rubber fibres (Rf) were blended with 2.5, 5, 7.5 and 10% clay content. The various combinations of clay–rubber granulates (CRg) and clay–rubber fibres (CRf) were subjected to the sequence of compaction, strength, consolidation and swelling pressure tests. A linear decrementing trend of compaction parameters was observed with an increase in Rg and Rf contents. An insignificant rise in unconfined compressive strength (UCS) and splitting tensile strength (STS) of clay was observed with the addition of Rg and Rf up to 5 and 2.5%, respectively. Higher inclusions had reduced the UCS and STS of clay. However, a continual increase in failure strain was observed with an increase in Rg and Rf contents. The compression index of CRg and CRf mixtures was found to increase with the increase of Rg and Rf contents. A continuous decrease in the soaked California bearing ratio and swelling pressure (σs) of CRg and CRf mixtures was observed with the increase in Rg and Rf contents. In view of code requirements, the pre-requisite treatment of CRg and CRf mixtures should be carried out before field applications.

The deformation patterns and failure mechanisms of pressurised cavities at shallow depth are relevant to many geotechnical applications, including tunnelling and horizontal directional drilling. In this paper, an experimental study of a reduced-scale pressurised cavity under geostatic stress is presented, in order to measure the effect of cavity length, vertical stress and soil density on soil deformation and failure. X-ray computed tomography is used to acquire images of the system at key stages of the cavity inflation process. A closed-shaped failure region developed around the cavities, beyond which shear planes of elliptic paraboloid shape formed, extending from the bottom of the cavities all the way to the free surface. The plane-strain assumption did not hold beyond the central portion of the longest cavity tested (L = 6D). The volumetric strain and porosity changes inside the shear bands showed significant dilation in dense specimens, but contraction in loose specimens. The average orientation and the thickness of the shear bands were in agreement with those found in the literature for passive arching mechanisms (anchoring). The orientation of the principal strains around the cavity follows catenary shapes, similar to those displayed in active trapdoor mechanisms.

Water scarcity is the most obstacle faced by irrigation water requirements, likewise, limited available meteorological data to calculate reference evapotranspiration. Consequently, the focal aims of the investigation are to assess the potential of machine learning models in forecasting irrigation water requirements (IWR) of snap beans by evolving multi-scenarios of inputs parameters to figure out the impact of meteorological, crop, and soil parameters on IWR. Six models were applied, support vector regressor (SVR), random forest (RF), deep neural networks (DNN), convolutional neural networks (CNN), long short-term memory (LSTM), and Hybrid CNN-LSTM. Ten variables including maximum and minimum temperature, Relative humidity, wind speed, precipitation, root depth, basal crop coefficient, soil evaporation, a fraction of surface wetted and, exposed and soil wetted fraction were used as the input data for models with their combination, 8 input scenarios were designed. Overall models, the best scenario was scenario 4 (relative humidity, wind speed, basal crop coefficient, soil evaporation), however, the best scenario for DNN and RF model was scenario 7 (root depth, basal crop coefficient, soil evaporation, fraction of surface wetted, exposed and soil wetted fraction). While the weakest one was the group of climatic factors in scenario 6 (maximum temperature, minimum temperature, relative humidity, wind speed, and precipitation). Among the models, the hybrid LTSM & CNN was the most accurate and the SVR model had the lowest estimation accuracy. The outcomes of this research work could set up a modeling strategy that would set in motion the improvement of efforts to identify the shortages in IWR forecasting, which sequentially may support alleviation strategies such as policies for sustainable water use and water resources management. The current approach was promising and has research value for other similar regions. Validerad;2023;Nivå 2;2023-04-18 (joosat);Licens fulltext: CC BY License

The properties of unbonded rock–steel interfaces and the characteristics that control this behaviour seem to be an under-researched area in terms of geotechnical application, for example in the design of gravity-based foundation systems or dead weight anchors and the interaction of pipelines on rock. Although basic guidance does exist for rock–rock interfaces or pipeline behaviour, this focuses on macro roughness, with little consideration of micro roughness, relative roughness of the surfaces or their strengths and hardness. Therefore, in order for design and understanding to develop in these areas, there is a need for basic interface friction parameters and understanding of the interface characteristics that control the strength of the interface, such that correct values can be used, but also so that the interface properties can be best manipulated to improve interface interaction. This paper presents interface friction angles for four types of rock sheared against steel interfaces of different roughness at a variety of normal stresses. The rocks themselves have a range of surface roughness, strength and hardness. The results of the testing programme are used to improve a simple analytical approach for predicting the shear strength of rock–steel interfaces that allows input of key controlling parameters.

The paper studies strike-slip fault rupture propagation through dense sand and its interaction with surface foundations, combining physical and numerical modelling. A series of centrifuge tests is conducted using a three-section split-box, which allows the modelling of two strike-slip faults per test. A free-field test is initially conducted, followed by four interaction tests. Eight different foundation configurations are studied, varying the foundation location, surcharge load, aspect ratio and rigidity. The experiments are numerically simulated employing three-dimensional finite-element modelling, combining periodic boundaries and a relatively simple yet efficient constitutive model, developed as part of this study. Based on a Mohr–Coulomb yield criterion, the model incorporates post-yield isotropic frictional hardening and softening (MC–HS). Carefully calibrated on the basis of triaxial tests, the model is validated against the centrifuge model tests, and exploited to derive further insights. The MC–HS model covers the entire range from elastic to fully softened response, capturing the deviatoric and volumetric behaviour of dense sand, and especially its pre-softening volumetric response, which is proven to be crucial for the simulation of the complex mechanisms of strike-slip faulting. Both physical and numerical modelling reveal the formation of diagonal shear ruptures at the ground surface (Riedel shears). These are complex helicoidal structures, formed due to the spatial variation of shear stresses. Foundation response is mainly governed by the kinematic constraint offered by its presence. Fault rupture locations close to its sides typically lead to a translational mechanism, whereas locations close to its centreline lead to a rotational one. Foundation rigidity is proven to be a prerequisite for the development of both mechanisms, which rely on the ability of the foundation to resist the developing normal and shear stresses.

The effects of the compaction conditions and backfill material behind the face of reinforced soil walls (RSWs) were numerically investigated. The analyses were carried out using a two-dimensional finite-element computer program considering different backfill materials in the zone 1 m behind the wall face and different compaction conditions. The results of the analyses were compared with data from a 16.7 m high well-instrumented, steel-reinforced soil wall constructed in 1999 in the USA. The results illustrate the importance of the compaction conditions and the backfill material near the wall facing on the performance of RSWs both at the end of construction and post-construction.

This paper addresses unpaved and paved roads improved with geosynthetics, such as geotextiles, geogrids and geocells. The paper examines the mechanisms associated with the use of geosynthetics to improve roads, describes the principles of the design methods used to quantify the benefits of geosynthetics used in unpaved and paved roads, presents case histories to demonstrate the use of geosynthetics to solve challenging road problems, and discusses the relevance of tests and trials to real roads. This paper is supplemented by four presentations in pdf format that contain more than 800 slides. These four presentations are updated versions of the four presentations made during a one-day short course at the 11th International Conference on Geosynthetics held in Seoul, Korea, in September 2018. The paper that follows contains a summary of each of the four presentations, with special emphasis on key issues.

Numerous incidents and failures of earth slopes, dykes, levees and embankment dams are caused by internal erosion. At a time of global climate change, rapid pore-water pressure changes in soil masses are frequently induced by extreme rainfall, storm surges, waves, flash floods and so on. Under such complex cyclic hydraulic conditions, the soil erodibility, hydraulic conductivity and subsequent stress–strain behaviour may differ from those under the monotonic seepage condition, and are still poorly understood. In this study, preliminary laboratory tests have been conducted to investigate the development of internal erosion and changes in hydraulic conductivity under one-way cyclic seepage, and the post-erosion stress–strain behaviour. Representative internally stable and unstable soils were tested. The effects of mean hydraulic gradient and cyclic gradient amplitude were investigated in detail. Results show that the erosion development is significantly influenced by both the initial grain size distribution and the pattern of imposed cyclic hydraulic gradient. The cyclic seepage promotes the loss of fine particles and leads to larger hydraulic conductivity. For the internally unstable soil, the eroded soil mass and hydraulic conductivity increased significantly with increasing cyclic gradient amplitude. Nevertheless, the internally stable soil experienced a small amount of particle loss, even under large cyclic gradients. For both types of soil, a larger cyclic gradient amplitude corresponds to a stronger post-erosion contractive shearing behaviour and a smaller critical friction angle.

The main objective of this study is to evaluate the disintegration characteristics of loess after treatment by vibratory probe compaction method. To establish the connection between the disintegration velocity of loess soil and other parameters, a series of indoor and in situ tests was conducted, including density test, compression test, direct shear test, collapsibility test, standard penetration test (SPT) and cone penetration test. The results showed that a great improvement of the resistance of loess samples to wetting and disintegration was obtained after treatment, and its disintegration velocity (0.2%/s) had a larger reduction of 75.85% compared to the value before treatment. The disintegration velocity had a positive linear correlation with the void ratio, collapsibility coefficient and self-weight collapse coefficient, but a negative linear correlation with the dry density and modulus of compressibility. From in situ test results, the disintegration velocity showed a negative correlation with the SPT blows, and the cone resistance and sleeve friction of the soil layer at different depths corresponded well to the disintegration velocity. The vibratory probe compaction method is an effective way to eliminate collapsibility and improve the allowable stress for collapsible loess foundation; it can also minimise the disintegration threat of loess in water to engineering construction.

A 2 m class robotic drill was sent to the Moon and successfully collected and returned regolith samples in late 2020 by China. It was a typical thick wall spiral drill (TWSD) with a hollow auger containing a complex coring system to retain subsurface regolith samples. Before the robotic drill was launched, a series of laboratory tests were carried out to investigate and predict the possible drilling loads it may encounter in the lunar environment. This work presents how the sampling performance of the TWSD is affected by the regolith compressibility. Experiments and analysis during the drilling and sampling process in a simulated lunar regolith environment were conducted. The compressibility of a typical lunar regolith simulant (LRS) was measured through uni-directional compression tests to study the relationship between its inner regolith stress and bulk density. A theoretical model was established to elucidate the cutting discharge behavior by auger flights based on the aforementioned relationship. Experiments were conducted with the LRS, and the results show that the sampling performance is greatly affected by the flux of the drilled cuttings into the spiral flight channels. This work helped in scheduling reasonable drilling parameters to promote the sampling performance of the robotic drill in the Chinese Chang'E 5 mission.

Open caisson shafts are a widely adopted solution for a range of geotechnical applications. An external ‘cutting shoe’ is a common construction feature used to reduce the soil frictional resistance acting on the caisson during sinking. This forms an annular void encircling the caisson which is filled with a support fluid to maintain excavation stability. The primary aim of this paper is to explore the influence of the cutting shoe geometry on the resulting vertical bearing resistance in sand. Finite-element limit analysis is adopted for this purpose. Additional parameters considered in the modelling include the roughness of the caisson cutting face and cutting shoe, and the caisson radius and embedment depth. The results show that the influence of the cutting shoe is highly dependent on the caisson cutting face roughness and the soil friction angle, illustrated using detailed soil failure mechanisms. The roughness of the cutting shoe is also shown to cause a significant increase in the vertical soil reaction for large caisson embedment depths. By way of example, a recent case study in the UK, involving the construction of a 32 m dia. caisson, is used to highlight the potential influence of the cutting shoe on the bearing resistance during caisson sinking.

Analytical solutions for geosynthetic reinforced fills over a void have appeared in the literature starting in the 1980s. Current solutions pay little or no attention to the influence of the creep-reduced stiffness of the geosynthetic reinforcement under tensile loading. This paper addresses this gap by introducing a reinforcement stiffness limit state in the design of these systems. The choice of reinforcement stiffness is based on a simple two-parameter hyperbolic isochronous load–strain model developed by the authors and applied to a large database of uniaxial and biaxial geogrids and woven geotextiles. The paper provides a design chart procedure that can be used with four well-known analytical solutions to compute the maximum reinforcement load. In addition to the stiffness limit state, the design chart approach includes vertical deformation and reinforcement strain serviceability limit states, and a tensile strength limit state. A novel feature of the design charts is a quantitative link to the ultimate strength of the reinforcement to estimate the isochronous stiffness of the reinforcement for different elapsed loading times and strains. There are many instances in the literature where the reinforcement stiffness was taken from a constant rate-of-strain tensile test. The paper shows that this is non-conservative for design.

Silty alluvial soils are highly compressible. Deep soil mixing is being increasingly used for remediating such ground conditions, which produces artificially cemented soil columns that gain strength with curing. This study investigated the one-dimensional compression and shear stiffness degradation behaviour of an alluvium in its reconstituted, undisturbed and artificially cemented states. The binder used to stabilise the soil was a low-carbon alkali-activated blast-furnace slag. Oedometer and triaxial data indicated that the nature of the soil structure evolved from being chiefly meta-stable when undisturbed to dominantly stable in its cemented state after 28 days of curing. A new framework has been presented to quantify continuous changes in structure within the alluvium during one-dimensional compression in its undisturbed and cemented states, with respect to its intrinsic properties. This better captured structure degradation during earlier stages of compression compared with previous frameworks and provided insights into defining the limits of meta-stable and stable components of structure within materials of higher strength. A new formulation has been developed for predicting shear stiffness degradation of samples with strain under triaxial conditions. This showed efficiency and good performance in modelling experimental data and was successfully used to quantify initial structure and degradation of structure within the undisturbed and cemented alluvium.

The gradation of rockfill affects creep behaviour, but indoor testing apparatus does not allow a field maximum particle size of the rockfill of 1000 mm. To investigate the creep behaviour of rockfill with different maximum particle sizes and establish a creep model for the rockfill material, oedometer creep tests for slate rockfill material with different maximum particle sizes were conducted to explore the effect of gradation on the creep behaviour of rockfill materials. The test results showed that the creep strain increases and the rate of increase decreases with the increase in vertical stress. The creep strain increases with the decrease in maximum particle size under all vertical stresses. Furthermore, a particle size ratio Rd was defined to establish the creep model. An empirical creep model was proposed to calculate the creep strain for rockfill with oversized particles that are not allowed by the experimental apparatus. Three groups of test data were used to determine the model parameters, and one group of test data was used to verify the predictive capacity of the model. The results showed that the model can satisfactorily predict the creep behaviour of slate rockfill with oversized particles.

Applying cohesive soil to wrap fine sand on a subgrade slope is a new type of filling technology in railway subgrade construction. The choices of specific compaction methods and quality evaluation indicators are critical for achieving high compaction quality. In this paper, a series of field rolling tests with different compaction machines was carried out in the experimental section of China Menghua railway. Then, the compaction quality was gauged considering different indexes such as relative density (Dr), degree of compaction (K), coefficient of subgrade reaction (K30) and dynamic modulus of deformation (Evd). It is shown that adopting clayey soil (namely, wrapping soil) to cover a sandy roadbed slope can keep the internal humidity of the subgrade stable. For compaction of the fine sand used in this study, it was better to select a bulldozer to squeeze along the longitudinal and horizontal directions alternately six times, and the lift thickness was set at 35 cm. The results show a linear relationship between Evd and K30 for the sand. The application of Evd as a substitute for K30 in the compaction evaluation of sand subgrade can lead to significant efficiency.

Elevated water tanks in high susceptibility to an earthquake are one of the greatest structures of support system. These structures have a large concentration on slender support structures and are at risk of horizontal forces due to the earthquake in specific. They are essential elements in municipal water deliver, hearth combating structures and in many commercial centres for garage of water. Hence increased water tanks ought to continue to be functional even after the earthquake. In this paper guide seismic analysis of improved square water tank is achieved according with IS: 1893–1984 (i.e. Lumped mass version) and IS: 1893–2002 (Part-2) draft code (i.e. Two mass version). The structures are analysed with different simulated soft ware’s Staad-pro and E-tabs. The results are compared for optimal value analysis in particular forces. The deviational error found to be less in E-tabs when compared to stad- pro for given load conditions in simulation.

A plasticity model is proposed to simulate the monotonic and cyclic behaviour of cemented sand. The model is an extension of the critical state-based bounding surface plasticity model originally developed for clean sand by researchers Y. F. Dafalias and M. T. Manzari in 2004. The elastic parameters, state parameter, yield function, flow rule and plastic modulus of the base model are modified for cemented sand mainly by incorporating a bonding strength variable. In addition, the critical state variables, stress ratio and void ratio of cemented sand are linked to the initial cement content. The model formulation is presented first in the triaxial and then in generalised stress space. The capabilities of the model are illustrated by simulating the response in a series of monotonic and cyclic tests on cemented sand. This shows that the model can capture the main features of the mechanical behaviour of cemented sand well, including cement-induced enhancements of stiffness, strength, dilatancy and liquefaction resistance.

Pervious concrete has been widely used in parking lots and airport fields. However, excessive cracking and spalling issues of pervious concrete remain a challenge for its adoption in wider applications, since its binding material proportion is low and the use of fine aggregates is nearly zero. When loaded in compression, failure appears first in the weak concrete zone, induced by the random distribution of voids. The process continues until failure of the whole specimen. Fibre-reinforcement delays crack generation and enhances the strength of the host matrix. However, the bonding mechanism between the fibre and concrete matrix is a controversy in the literature. In this study, the influence of polypropylene fibre inclusion on the strength and stiffness of pervious concrete microstructure was studied through delicate interface modelling. Two-dimensional microstructures of pervious concrete were generated using Matlab and Ansys parametric design languages. A cohesive-zone technique was then used to model the interface between fibres and the concrete matrix. Load–displacement plots were thus obtained in Ansys for specimens under compression for various void–fibre percentages and different treated interface properties.

In this paper, the lateral limiting pressure on rectangular pile groups in undrained soil is explored using two−dimensional finite element modelling. The primary aim of the study is to assess the influence of pile group shape effects on the soil limiting pressured offered by the deep ‘flow-around’ failure mechanism, and associated soil failure mechanisms, considering both a small (four piles) and large (36 piles) group. Additional parameters considered in the modelling include pile spacing and pile-soil interface roughness. The finite element results show that group shape has a significant influence on the behaviour of closely spaced pile groups. In particular, the number of piles parallel to the direction of loading is shown to dominate the lateral bearing capacity factor such that significant increases in capacity efficiency can be achieved by slight modifications to the group shape for a given number of piles. The load-sharing across the group, traditionally defined using p-multipliers, was also shown to be highly non-uniform and dependent on group size, pile soil roughness and group geometry in addition to the pile spacing. The finite element output is presented in the form of design charts for the determination of group p-multipliers whereas a library of existing design solutions is presented for the calculation of the overall group response.

Measuring displacements in model tests typically involves contact-based sensors such as linear potentiometers, where contact between two moving parts occurs at the sensing point. The sensor's finite mass, the limited stiffness of the beams and the clamping mechanism, and the slippage and hinging of the sensor body could affect the object's response and lead to measurement errors. Also, the physical mounting rack required to hold these sensors often obstructs the view and makes significant areas unavailable for conducting some other essential investigations. The advancement in high-speed, high-resolution and reasonably priced rugged cameras makes it feasible to obtain better displacement measurements by image analysis. This paper introduces a non-contact method that works by video recording the projection of laser lines on a test object to measure static and dynamic vertical displacements. The technique produces a continuous settlement distribution along the laser line passing through multiple objects of interest. This paper presents the theory for converting laser line images to displacements. The new method's validity is demonstrated by comparing the results from other measurement techniques: hand measurements, linear potentiometers and three-dimensional stereophotogrammetry.

Seepage-induced instabilities pose a challenge in many geotechnical applications. Particle-scale mechanisms govern the initiation of instability. However, current understanding is based on a macro-scale perspective that draws on continuum mechanics. Recent developments in imaging and numerical analysis can provide the particle-scale fundamental perspective needed to develop a comprehensive insight. This contribution demonstrates the value of combining particle-scale experimental and numerical studies. The experiments consider transparent soil samples created using refractive image matching and monitored by particle image velocimetry (PIV). Three-dimensional pore topology is extracted from a series of two-dimensional images and imported into computational fluid dynamics (CFD) simulations. Permeability is estimated by three distinct approaches: using flow rate, PIV- and CFD-generated data. The flow fields obtained from PIV and CFD are in good agreement considering both flow rate contour plots and flow rate distributions; this demonstrates the successful reconstruction of three-dimensional pore structure and flow-field analysis. The comparison also reveals that the side boundary effects in CFD simulations are constrained within a limited region. The multi-plane results characterise the variance of flow velocity with the three-dimensional pore topology. Finally, the fluid–particle interactions obtained from CFD results show a larger variance in the angular particle packings.

One-third area of India's and major part of Gujarat are covered with expansive soil having high clay content s . These soils are problematic to geotechnical engineers as it causes damage to the structure founded on them. Soil swells when they imbibe water and shrink in their volume on drying. Swelling phenomena is one of the top-most challenge faced by the foundation engineer, due to the potential danger of unpredictable movements of structures founded on such types of soils. Various innovative methods have been used to counteract the volume change problem and to safeguard the structures. The use of nano chemical to reduce swelling potential of an expansive soil is a one of the developing research areas in geotechnical engineering. In this experimental work, an attempt is made to modify the swelling potential of expansive soil by using Terrenoseal (organo silane based nano chemical). The effects of adding these chemical s on soil is characterized by various geotechnical laboratory tests such as free swell index, consistency limits, compaction characteristics, swell pressure and unconfined compression test. Further, to study the physico- chemical properties using various analytical techniques such as Fourier Transformation Infrared Spectroscopy (FT-IR), Thermo Gravimetric Analysis (TGA), Particle size analysis, wettability, etc. are performed in the laboratory. The laboratory results indicated that use of nano chemical reduced the swelling potential, shrinkage, free swell index and also increases unconfined compression strength and the maximum dry density. Analytical techniques show improvement in physico-chemical properties of the soil. pH and COD tests for treated and untreated were also performed and the results were within the permissible limits.

Traditional penetration indices cannot accurately evaluate the performance of asphalt binders at high and low temperatures. A study was therefore undertaken to determine temperature conversion formulae for designing asphalt pavements using the US Strategic Highway Research Program's Superpave performance grading (PG) method. The research involved the observation of climate and pavement temperatures in north-east China, the determination of temperature conversion formulae and classification of climatic zones and Superpave PG standards. The results of this study showed that the proposed formulae are more accurate than penetration indices for predicting actual asphalt pavement temperatures and their performance at low and high temperatures, which will deliver economic and social benefits.

This paper reports on the performance analysis of an embankment over a soft soil deposit during construction. The study section is part of the duplication of the Brazilian federal highway, BR 470, a major infrastructure project that crosses several soft clay deposits in the state of Santa Catarina, Brazil. To guarantee stability and accelerate the landfill consolidation, the project provided geotechnical solutions as follows: basal reinforcement with geogrids, equilibrium berms, stage constructions of the landfill (slow construction), preloading and prefabricated vertical drains. The performance during field construction was mostly evaluated through instrumentation considering the evolution of horizontal displacements (distortion and distortion rates) and the Asaoka method to evaluate the stabilisation of settlements. Given the limitations of the methods used for control during construction, and a discrepancy between field settlements and original project predictions, the soil profile and geotechnical parameters were revaluated during construction and used in a revised performance analysis. Some important considerations were observed from this back-analysis that could have been used to modify the construction process during execution. In addition, to analyse the effects of the inherited variability, a sensitivity analysis to determine levels of possible settlements and time of consolidation was performed.

Mixed or intermediate soils are widely used in the construction of embankment dams. Unfavourable climate conditions and poor quality control may result in the use of mixed soils as under-compacted dam cores, with moisture content highly in excess of the optimum. It is thus essential to design safe filters to prevent internal erosion and piping from wet, under-compacted mixed-soil cores in embankment dams. In this study, 87 no-erosion filter tests were performed on seven mixed core soils having dissimilar geotechnical specifications with diverse moisture contents and compaction ratios. The experimental findings showed that the filter performance (success or failure at preventing erosion) depends on moisture in excess of optimum, the filter D15 (particle size with 15% finer in filter gradation) and the fines content of the core soil. An increase in excess moisture necessitates a smaller D15 to inhibit erosion, to the extent that filters respecting accepted criteria may fail to hinder erosion in the case of excessively wet and under-compacted cores. Overall, for group II, cores the criterion of D15 15

A sensitivity study is presented to evaluate the influence of different parameters on the simulation of an underground excavation in the Callovo-Oxfordian (COx) argillaceous formation performed in the Meuse/Haute-Marne underground research laboratory. An elasto-viscoplastic constitutive law representing the characteristic behaviour of indurated mudrocks and stiff clays has been employed. It incorporates anisotropy, strain-softening, creep deformations and dependence of permeability on damage. In addition, a non-local formulation, able to simulate localised deformations objectively, has been incorporated in the analyses. The following features affecting the excavation have been studied: initial stress, strength and stiffness anisotropy, strength parameters, hydraulic and hydromechanical parameters, and scale effects. A simulation reported in a companion paper provides the base case for benchmarking. The results are compared in terms of extent and configuration of the excavation fractured zone, vertical and horizontal tunnel convergences, and the development and evolution of pore pressures in the rock. From the comparisons, an enhanced understanding of the hydromechanical mechanisms associated with underground excavations in COx claystone, and other similar argillaceous materials, has been achieved. We are grateful for the financial and technical assistance of the French national radioactive waste management agency (Andra) to the work presented. The technical assistance of Plaxis is also gratefully acknowledged. The first author has been supported by a Conacyt scholarship (Reg. No. 270190).

An investigation was undertaken into the stability of railway embankment slopes over soft subgrades stabilised by deep-mixed columns (DMCs). Three 1 : 10 scale laboratory embankments were constructed over unreinforced and reinforced subgrade with DMCs in square and triangle patterns. The load–settlement responses of both embankments and columns were measured. The laboratory embankments were then mathematically modelled and the results were compared. After validation, a comprehensive parametric study was carried out to evaluate the factor of safety (FoS) of the embankment side slopes against sliding. Five embankment soil types from poor to high strength, three heights from 1.5 to 10 m and various DMC improvement area ratios from 0 to 65% were considered. The experimental outcomes indicated an increase of nearly 63% in the bearing capacity of both DMC-supported embankments compared with the unreinforced one. Regarding the parametric study, a minimum required FoS of 1.5 was observed for 1.5 m embankments of all soil types stabilised with a 60% improvement ratio. The greatest safety increase was associated with a 1.5 m height embankment with poor soil type, which showed a 36% increase.

A non-linear, four-parameter viscoelastic–plastic model is proposed to characterise the mechanical properties of geogrids under long-term and low-stress load. In this study, a simplified rheological model of viscoelastic–plastic geogrid-reinforced tailings was established. The stress analysis of the whole reinforced tailings complex was divided into two stages. The time for the tailings to produce plastic deformation (plastic arrival time) was the cut-off point for the two stages. The first stage (E-VP model) corresponded to the elastic state of tailings during which the stress of geogrids decreased with time, causing the recombination of microstress in tailings until they reached the yield condition. The second stage (P-VP model) corresponded to the plastic state during which the stress of geogrids remained constant, whereas the overall strain of the reinforced complex increased as a result of the geogrid creep. The force of the reinforced complex changed rapidly from the first to the second stage. Owing to the small deformation in the first stage, the overall strain of the complex was mainly caused during the second stage. The plastic arrival time t p of the reinforced tailings complex was significantly influenced by the plastic strain ε p and viscosity coefficient η of geogrids and internal friction angle ϕ of tailings.

The performance of plate anchors in sand, relative to clay, is not well understood, particularly for the more realistic case of an inclined load. This paper investigates the effect of load inclination on horizontal plate anchors in sand through centrifuge tests and numerical finite-element simulations. The centrifuge tests were performed on rectangular plate anchors in loose and dense sand, at shallow embedment depths with four different load inclinations. The experiments showed that the anchor capacity of horizontal plates increased progressively as the load inclination became progressively more horizontal, with anchor capacity under pure horizontal loading being approximately 1·8 times higher than that under pure vertical loading. These experimental observations were also replicated in finite-element simulations using a bounding surface plasticity model. Investigation of the underlying failure mechanisms and stress paths showed that the slip planes become longer and the mobilised lateral stresses increase as the load inclination becomes increasingly horizontal, which leads to higher anchor capacities. Finally, the anchor resistance factors from the numerical analyses were decoupled into vertical and horizontal components and represented as interaction diagrams, providing a basis for performing hand calculations of anchor capacity for a given embedment depth, load inclination and relative density.