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To investigate evolution of soil arching during suffusion in gap-graded soils, a new suffusion apparatus was developed for trapdoor tests under a horizontal seepage flow. Glass beads with fine-grain contents ranging from 15% to 45% were adopted to represent coarse-grain controlled soils and fine-grain controlled soils. Coupled computational fluid dynamics (CFD) and discrete element method (DEM) models were developed to further investigate the evolution of soil arching from microscopic views. At the early stage of suffusion, soil arching degraded rapidly under seepage loads in both coarse-grain controlled and fine-grain controlled soils due to the compaction of soil skeleton and the clogging of voids, which increased in the number of fine particles connected to the stress-transfer matrix. At the later stage, soil arching was nearly maintained as the soil skeleton became stable in the coarse-grain controlled soils. In the fine-grain controlled soils, soil arching degraded continuously due to continuous loss of fine particles connected to the stress-transfer matrix. The decrease in the contact number of fine particles also made the soil skeleton more vulnerable to suffusion. The degradation of soil arching resulted in an increase of surface displacement and a decrease of soil arching height in fine-grain controlled soils. Key words: soil arching, suffusion, trapdoor test, CFD-DEM, strong force chain, 1. Introduction Soil arching is generally defined as the stress redistribution due to the relative displacement between a yielding soil mass and its adjacent soil masses (Terzaghi 1943). This phenomenon [...]

The property of a road base depends on its fine content (FC) and water content/suction. In this study, a cyclic loading test was carried out on road base aggregate with different FCs under controlled suction. The different effects of fines on the accumulated strain of road base aggregate at different FCs and suctions were identified. Under the saturated condition, the accumulated strain increased with FC due to the reduction of soil interparticle friction caused by the inclusion of fines. Under unsaturated conditions, the effect of fines on the accumulated strain depended on the inner structure of the soil. For the 'coarse-graincontrolled soil' (FC in the range of 0%-4%), the accumulated strain increased with the increase of FC due to the reduction of interparticle friction, while for the 'transition soil' (FC in the range of 4%-8%), the accumulated strain decreased with the increase of FC as the major impact of the fines shifted to the enhancement of suction, and the inclusion of fines is beneficial for this case; for the 'fine-grain-controlled soil' (FC in the range of 8%-16%), the accumulated strain increased rapidly with FC as the effect of interparticle friction reduction dominated again. Key words: road base aggregate, fine content, cyclic loading, accumulated strain, unsaturated soil La propriete de la base de la route depend de sa teneur en fines (FC) et de sa teneur en eau/suction. Dans cette etude, l'essai de chargement cyclique a ete effectue sur un agregat de base de route avec differentes teneurs en fines sous des succions controlees. Les differents effets des fines sur la deformation accumulee du granulat de la base de la route a differentes teneurs en fines et suctions ont ete identifies. Dans des conditions de saturation, la deformation accumulee augmente avec la teneur en fines en raison de la reduction de la friction interparticulaire du sol causee par l'inclusion de fines. Dans des conditions non saturees, l'effet des fines sur la deformation accumulee depend de la structure interne du sol. Pour le << sol a gros grains controles (FC dans la gamme de 0-4 %)>>, la deformation accumulee augmente avec l'augmentation de la teneur en fines en raison de la reduction de la friction interparticulaire; tandis que pour le << sol de transition (FC dans la gamme de 4-8%)>>, la deformation accumulee diminue avec l'augmentation de la teneur en fines comme l'impact majeur des fines se deplace vers l'amelioration de la succion, et l'inclusion de fines sera benefique pour ce cas; pour le << sol a grains fins controles (FC dans la gamme de 8-16%)>>, la deformation accumulee augmente rapidement avec la teneur en fines, car l'effet de la reduction de la friction interparticulaire domine a nouveau. [Traduit par la Redaction] Mots-cles : agregat de base de route, teneur en fines, chargement cyclique, deformation accumulee, sol non sature, Introduction Road base aggregates mainly consist of unbound granular materials such as gravel and sand. During a road's service, the road base aggregate can be invaded by fines from particle [...]

Control of the disturbed displacement of adjacent tunnel during excavation is a significant issue for design and construction. Based on the multi-objective optimization method, the multi-type monitoring data in the excavation of the excavation are integrated, the key soil parameters are inverted and identified, and the time effect of the tunnel displacement is quantified and corrected. A dynamic multi-objective optimization method with adaptive infill criterion (DMO-AIC) is proposed to improve the updating efficiency of dynamic surrogate models. The proposed method takes into account the computational redundancy of dynamic surrogate models in engineering optimization, and designs an adaptive point-adding discrimination strategy, which can autonomously identify invalid updates of surrogate models on the optimization path. The results show that the proposed DMO-AIC significantly reduces the invocations of the black-box model during optimization while ensuring the good search performance and the convergence speed of the algorithm. The improved computational efficiency of DMO-AIC is helpful for the application of dynamic surrogate models in engineering optimization. The results of the virtual numerical example show that DMO-AIC can predict and update multiple model responses during excavation, such as wall deflections and tunnel displacements. The engineering practice of Shanghai Bund 596 excavation indicates that the time effect is properly updated, and the staged vertical displacements of the adjacent tunnel are accurately predicted.

In the vacuum treatment of dredged slurries via prefabricated vertical drains (PVDs), both filtration and consolidation may happen to dredged slurries when subjected to the vacuum gradient. Similar to the consolidation, the filtration may provide equally useful information on interpreting the constitutive behavior of the slurry. In this paper, a new approach utilizing the filtration process is devised to evaluate the constitutive behaviors of dredged slurries. The approach is composed of a vacuum filtration device and an iterative curve fitting algorithm. Two types of tests, namely step-vacuum filtration and constant-vacuum filtration followed by compression test, must be conducted on the slurry specimens, and only the time variations of the filtrate discharge should be recorded. On the basis of the recorded data, the curve fitting algorithm is adopted for determining the parameters of the constitutive equations. The effectiveness of the proposed approach is verified through comparing the obtained compressibility and permeability of the slurries with the data provided by the oedometer test and with the empirical relationships from different sources. The comparisons demonstrate that the constitutive relationships determined by the present approach can predict the compressibility and permeability characteristics of dredged slurries with an acceptable degree of accuracy. Key words: dredged slurries, vacuum filtration, compressibility, permeability. La filtration et la consolidation peuvent se produire lors du traitement sous vide des boues de dragage via des drains verticaux prefabriques (PVD) lorsqu'elles sont soumises au gradient de vide. Le filtrage, de meme que la consolidation, peut fournir des informations tout aussi utiles concernant l'interpretation du comportement constitutif de la boue. Nous avons concu dans ce document une methode nouvelle utilisant le processus de filtration pour evaluer le comportement constitutif des boues de dragage. Elle est composee d'un dispositif de filtration sous vide et d'un algorithme d'ajustement de courbe iteratif. Il est necessaire de realiser sur les echantillons de boues deux types d'essais, notamment la filtration sous vide par etapes et la filtration sous vide constant suivie d'un essai de compression, et d'enregistrer uniquement les variations temporelles de la decharge du filtrat. A partir des informations enregistrees, l'algorithme d'ajustement des courbes permet de determiner les parametres des equations constitutives. Nous avons verifie l'efficacite de l'approche suggeree par la comparaison de la compressibilite et de la permeabilite des boues obtenues avec les donnees fournies par l'essai oedometrique et avec les relations empiriques de differentes sources. Il ressort de ces comparaisons que les relations constitutives determinees par cette approche sont en mesure de predire les caracteristiques de compressibilite et de permeabilite des boues de dragage avec une precision acceptable. [Traduit par la Redaction] Mots-cles : boues de dragage, filtration sous vide, compressibilite, permeabilite., 1. Introduction With the rapid economic development and population growth of coastal cities in China, the tideland deposition of artificially dredged slurry is an effective method to solve the problem [...]

In view of the extensive geology of overlying soil and underlying rock in mountainous areas, a pile-anchor composite foundation has been used in transmission line tower engineering. To reveal the uplift bearing mechanism and supplement the calculation method of the uplift capacity and the bearing exertion coefficient k, the verification model of field test case was established by using the PLAXIS 3D finite element software to study this problem. Parameter studies were conducted on this foundation. The influence of elastic modulus and cohesion of rock and soil and foundation condition on coefficient k was studied. The results show that there is asynchronism of ultimate uplift limit state of upper and lower parts of the pile-anchor foundation. The bearing ratio and coefficient k of the upper and lower parts of the foundation are related to geology and foundation structure. In combination with the parameter study and the relevant analytical solution of the relationship between the uplift load and the displacement, a theoretical calculation method of the coefficient k considering the foundation weight was proposed. Three test cases were used to perform confirmatory calculations for this method. By comparing with field tests and numerical calculation results, the correctness of this method has been verified. This method provides a theoretical reference for the design and application of this type of new foundation.

The vacuum preloading method is commonly used to improve soft soils; however, it has rarely been studied from the perspective of energy consumption. The work done by the vacuum pump in the vacuum system can be consumed in various ways, including seepage consolidation of soil, water discharge along prefabricated vertical drains and horizontal drainage system (i.e. sand blanket or horizontal pipes), extraction of the air sealed in the drainage system and air leakage from the atmosphere. Equations governing these aspects of energy consumption were derived in this study. A theoretical model of the energy consumption of the vacuum preloading method was established and then solved to quantify the specific forms of energy consumption. Theoretical predictions and laboratory results demonstrate that the energy consumptions of seepage consolidation and water discharge are negligibly small compared with the total work by the vacuum pump, and most of the work done by the vacuum pump in the vacuum system is consumed during the extraction of leaked-in air. [ABSTRACT FROM AUTHOR]

The vacuum preloading technique is extensively employed for ground improvement, particularly for slurry ground characterized by high‐water content and low strength. Such ground frequently exhibits a delay in pore water pressure dissipation when treated with prefabricated vertical drains. To clarify the drainage and consolidation behaviour of high‐water content slurry ground under vacuum preloading, this study proposed a two‐stage combined model that integrates both filtration and consolidation processes. Initially, an axisymmetric filtration model was used to describe the formation of the soil column through the radial migration and compaction of the particles. The end‐of‐filtration radial distributions of void ratio, permeability coefficient, and effective pressure served as initial conditions for the consolidation stage analysis. This stage was depicted using a large strain consolidation model based on the free strain condition. The results showed the necessity of incorporating the filtration stage to capture the overall drainage mechanism and characteristics of slurry ground with vacuum preloading treatment. [ABSTRACT FROM AUTHOR]

Soil arching is a common phenomenon existing in the earth structures such as pile-supported embankments and buried pipes. Suffusion would be triggered in these structures during flood events after rainstorms and pipe ruptures, which poses significant threats to these infrastructures. A novel trapdoor-suffusion apparatus was developed in this study to investigate the initiation and progressive development of suffusion in infrastructures involving soil arching. A series of laboratory tests were conducted using gap-graded glass beads with an initial fine particle content of 15% by mass. Initial soil arching was established via trapdoor movement and then was subjected to a horizontal seepage flow with an increasing hydraulic gradient to induce suffusion in the arched soil. The presence of soil arching increased the susceptibility of local instability of the soil specimen within the stress reduction areas at significantly low local hydraulic gradients, due to the reduced stress restriction on fine particles. Subsequently, global suffusion was triggered at a critical hydraulic gradient much lower than the predicted value by the modified zero effective stress principle, and this critical hydraulic gradient decreased rapidly with the reduction of initial soil arching ratio (SAR). This study obtained an empirical formula in the form of power functions to characterize the variation of critical hydraulic gradient with the initial soil arching ratio. As the suffusion continued, the degradation of soil arching intensified under the low initial SAR, and became the dominant factor increasing the surface displacement of the soil. This paper reveals the increased risk of suffusion to earth structures with the presence of soil arching, and provides valuable guidance for the design and protection of earth structures against suffusion-induced challenges. [ABSTRACT FROM AUTHOR]

Vacuum preloading is a commonly adopted method for improving soft ground. During the preloading period, the applied vacuum pressure is constant or multistaged, implying that the vacuum pump must work continuously with constant or increasing operating power. To reduce the energy consumption of the vacuum pump, a new loading strategy of cyclic vacuum loading was proposed in this study, whereby the pump is periodically switched on and off, and hence the vacuum pressure ascends and descends accordingly. To guide the design of cyclic vacuum preloading, a large-strain radial consolidation theory incorporating the shifting of the consolidation status of ground soil from normally consolidated to overconsolidated (and vice versa) was established in the present study. Based on the established theory, the treatment effects of cyclic vacuum loading can be quantitatively determined, including the ground settlement and the degree of consolidation, while the energy consumption can be simply determined by multiplying the power by the operating time of the vacuum pump, which works only during the ascending stage of cyclic vacuum pressure. Two cases of the cyclic vacuum preloading strategy were evaluated herein, that is, the complete cyclic vacuum loading and combined cyclic/constant vacuum loading cases. Finally, experimental tests were conducted to demonstrate the energy-saving effect of cyclic vacuum preloading. Compared to the conventional vacuum preloading strategy (i.e., constant vacuum pressure), the energy consumption of the cyclic vacuum loading strategy can be drastically reduced (80% reduction), while the treatment effects remain basically unaffected. [ABSTRACT FROM AUTHOR]

Cyclic loading-induced deformation of soil is a common problem in engineering practice. In current practice, however, monotonic triaxial tests are more commonly used due to the availability of apparatus and ease of operation. Thus, it would be very useful and practical if monotonic triaxial tests could be used to evaluate the behavior of soil under cyclic loading. This study aims to find an explicit relationship between monotonic and cyclic behavior of saturated soft clay. Six monotonic and nine cyclic triaxial compression tests were conducted on undisturbed saturated soft clay under an undrained condition. The test results showed that the monotonic and cyclic tests shared the same stress-strain surface in a three-dimensional p'-q-[[epsilon].sub.a] space (p', effective mean principal stress; q, deviatoric stress; [[epsilon].sub.a], axial strain). It was also found that it is possible to evaluate the effective stress states of cyclic tests at two specific numbers of cycles, using corresponding monotonic tests. Based on these two findings, a simple procedure is proposed to predict the peak axial strain for the saturated soft clay under different cyclic loadings based on the monotonic tests and only one cyclic test, which was further verified against additional test data from the previous literature. Key words: soft clay, cyclic loading, triaxial tests, relationship, axial strain. La deformation du sol induite par une charge cyclique est un probleme courant dans la pratique de l'ingenierie. Dans la pratique actuelle, cependant, les essais triaxiaux monotones sont plus couramment utilises, en raison de la disponibilite des appareils et de la facilite d'utilisation. Ainsi, il sera tres utile et pratique si les essais triaxiaux monotones peuvent etre utilises pour evaluer le comportement du sol sous chargement cyclique. Cette etude vise a trouver une relation explicite entre le comportement monotonique et cyclique de l'argile molle saturee. Six essais de compression triaxiale monotone et neuf essais de compression triaxiale cyclique ont ete realises sur de l'argile molle saturee non perturbee, dans des conditions non drainees. Les resultats des essais ont montre que les essais monotones et cycliques partagent la meme surface de contrainte-deformation dans un espace tridimensionnel p'-q-[[epsilon].sub.a] (p', contrainte principale moyenne effective ; q, contrainte deviatorique; [[epsilon].sub.a], deformation axiale). Il est egalement possible d'evaluer les etats de contrainte effectifs des essais cycliques a deux nombres specifiques de cycles, en utilisant les essais monotones correspondants. Sur la base de ces deux resultats, une procedure simple a ete proposee pour predire la deformation axiale maximale de l'argile molle saturee sous differentes charges cycliques, en se basant sur les essais monotones et sur un seul essai cyclique, ce qui a ete verifie par rapport a d'autres donnees d'essais provenant de la litterature anterieure. [Traduit par la Redaction] Mots-cles: argile molle, chargement cyclique, essais triaxiaux, relation, deformation axiale., 1. Introduction Cyclic loading-induced deformation of soil is a common problem in engineering practice. Traffic loading and wave loading are two examples of cyclic loading. After long-term cyclic loading, excess [...]

The cyclic response of subgrade clays under traffic loadings is likely to be partly drained rather than undrained, and the traffic-induced dynamic stress field is three-dimensional rather than axisymmetric. To compare the three-dimensional deformation behaviors of saturated clays between partly drained and undrained conditions, a large number of cyclic true triaxial tests were conducted. Experimental results show that a partly drained condition leads to a remarkable increase of permanent major principal strain ([[epsilon].sup.p.sub.1]) compared to an undrained condition, and the differences of [[epsilon].sup.p.sub.1] between the two drainage conditions are affected greatly by the factors of cyclic stress ratio (CSR), overconsolidation ratio (OCR), and coefficient of cyclic intermediate principal stress ([b.sub.cyc]). The increase of [b.sub.cyc] induces a linear reduction of [[epsilon].sup.p.sub.1] in an undrained condition, while it causes an increase first followed by a decrease of [[epsilon].sup.p.sub.1] in a partly drained condition. The clays undergo stiffness softening and hardening in partly drained and undrained conditions, respectively, and the effects of [b.sub.cyc] and CSR on the stiffness evolution are very different between the two drainage conditions. The mechanism of the complex [[epsilon].sup.p.sub.1] and resilient modulus behaviors in a three-dimensional state and partly drained condition is further discussed. In addition, two different empirical models are employed to predict [[epsilon].sup.p.sub.1] in partly drained and undrained conditions. Key words: true triaxial test, clays, three-dimensional deformation, drainage condition, empirical models. La reponse cyclique des argiles de fondation sous les charges du trafic est susceptible d'etre partiellement drainee plutot que non drainee, et le champ de contrainte dynamique induit par le trafic est tridimensionnel plutot qu'axisymetrique. Pour comparer les comportements de deformation tridimensionnelle des argiles saturees entre les conditions partiellement drainees et non drainees, un grand nombre d'essais cycliques triaxiaux reels ont ete realises. Les resultats experimentaux montrent que l'etat partiellement draine conduit a une augmentation remarquable de la souche principale permanente ([[epsilon].sup.p.sub.1]) par rapport a l'etat non draine, et les differences de [[epsilon].sup.p.sub.1] entre les deux etats de drainage sont fortement affectes par les facteurs de rapport de stress cyclique (CSR), de rapport de surconsolidation (OCR) et de coefficient de stress principal intermediaire cyclique ([b.sub.cyc]). L'augmentation de [b.sub.cyc] induit une reduction lineaire de [[epsilon].sup.p.sub.1] dans un etat non draine, alors qu'il provoque une premiere augmentation puis une diminution de [[epsilon].sup.p.sub.1] a l'etat partiellement draine. Les argiles subissent un assouplissement et un durcissement de la rigidite respectivement dans des conditions partiellement drainees et non drainees, et les effets de [b.sub.cyc] et de CSR sur l'evolution de la rigidite sont tres differents entre les deux conditions de drainage. Le mecanisme du complexe [[epsilon].sup.p.sub.1] et les comportements du module de resilience dans un etat tridimensionnel et dans un etat partiellement draine est examine plus en detail. En outre, deux modeles empiriques differents sont utilises pour faire des previsions [[epsilon].sup.p.sub.1] dans des conditions partiellement drainees et non drainees. [Traduit par la Redaction] Mots-cles: essai triaxial veritable, argiles, deformation tridimensionnelle, etat de drainage, modeles empiriques., Introduction Road design, construction, as well as many road defects (e.g., rutting, cracking) are highly related to the traffic-induced permanent and resilient deformations in subgrade soils, which have been studied [...]