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The objective of this study is to examine the performance of the shallow reinforced concrete foundation of a large-scale wind turbine under the influence of environmental loads. A 2 MW horizontal-axis onshore wind turbine supported by a shallow concrete foundation was considered. The foundation stresses, foundation settlements, and static and dynamic contact pressures at various positions of the shallow foundation were monitored from the construction phase to the operation phase in the field. Numerical simulations were also performed to further analyze the behavior of the wind turbine foundation in different cases. The results demonstrate that the responses of the reinforced concrete foundation, i.e., foundation stresses, contact pressures, and foundation settlements, were variables closely related to the wind direction and wind speed. The distribution of foundation stresses suggested that a reasonable design of steel reinforcement cages around the foundation steel ring is important. The dynamic contact pressure of the foundation could reach 5 kPa, so the influence of dynamic wind loads on the foundation response could not be always neglected, particularly for the foundations seated on weak soils. The foundation settlement during the operation phase could be characterized by the logistic model, but its distribution was uneven due to the presence of eccentric upper weight and wind load. The findings would provide guidance for the foundation design of onshore wind turbines in hilly areas.

Because of spatial variability and complex compositions, the mechanical test results of natural soil–rock mixtures (SRMs) are often discrete and lack reproducibility, which has greatly restricted the practical application of the experimental findings. The objective of this study was to examine the general mechanical behavior of SRMs under the influences of some hidden factors (e.g., structural parameters, parent rock type and weathering degree). To that end, the abstraction idea was adopted to prepare purified SRM samples. Large-scale triaxial tests were performed on these purified materials. On this basis, the influences of three structural parameters on the mechanical behavior of SRMs were studied. Moreover, the relationship between the shear strength and parent rock type and that between the shear strength and the spatial distribution of rock blocks were quantified. Some additional intrinsic behavior was distinguished from individual experimental phenomena through the comparative analysis of the test data in this study and those reported in the literature. The results show that the hidden factors had significant influences on the mechanical behavior of SRMs. A greater saturated uniaxial compressive strength of rock blocks generally led to a larger shear strength of SRMs. According to the significance of their influences on the shear strength parameters of SRMs, the structural parameters are ordered as: the gradation of rock blocks, the initial dry density of sample and the spatial distribution of rock blocks. The deformation and failure feature of SRMs were considerably affected by the spatial distribution of rock blocks and shear rate. And the shear strength parameters of SRMs were mainly influenced by the content of grains between 40 and 60 mm. The findings of this study would provide useful guidance for engineering practice.

Based on a highway reconstruction project in southern China, this study aims to put forward a method to determine the proper treatment depth of the existing subgrade. First, some field tests including the Beckman beam deflection test and portable falling weight deflectometer (PFWD) test were carried out. The results showed that there was a good correlation between the Beckman beam deflection (L) and PFWD modulus (Ep). Subsequently, a subgrade section was excavated and backfilled with cement-stabilized soil in layers. Compaction test, dynamic cone penetrometer rate test, plate load test and Beckman beam deflection test were performed to evaluate the treatment effect. To make sure, the subgrade was treated deeply enough, the Beckman beam deflection (L) was used as the controlled indicator among all the measured indexes for it was the hardest metric to meet. According to the design deflection and decreasing law of the measured deflections with the different number of the stabilized layers, the treatment depth was finally determined. As the PFWD test is superior to the deflection test in the detection efficiency, and the deflection value can be calculated from PFWD modulus by correlation formulas, thus the latter index can be used as a more suitable parameter for estimating the treatment depth instead of the former. Consequently, based on the measured PFWD moduli of the existing subgrade, six treatment schemes considering different treatment depths were proposed. It was confirmed that the method developed from this study is feasible and worth being extensively applied.

Silty clay is a common embankment material whose moisture increases over time due to soil–atmosphere interactions and climate changes. The objective of this study is to investigate the uns...

Carbonaceous mudstone is a common embankment material with the characteristics of water softening and water disintegration, which often causes the instability of embankments. This paper pre...

Wind is a dynamic variable, which produces rocking movements on wind turbines, and thus resulting in dynamic responses of foundations and the subsoil. This study attempts to examine the dynamic responses of the shallow foundation of an onshore wind turbine subjected to wind loads. To this end, a series of model tests considering different wind load conditions was carried out on a 1/10-scale physical model. The static responses, the dynamic responses and the dynamic amplification effects of the shallow foundation were subsequently measured and analysed. The results demonstrate that the dynamic responses of the wind turbine shallow foundation were visibly affected by both the mean wind load and the fluctuating wind load. At the rated wind speed, the maximum strain-based dynamic amplification factor (DAF) of the foundation baseplate reached as high as 1·65, the maximum deformation-based DAF of the foundation top was 1·14 and the maximum contact-pressure-based DAF on the downwind side was 1·14. In addition, the reliability of the physical model was discussed and the results were verified by comparison with the numerical data in the literature.

The presence of surface cracks has a great influence on the formation of transient saturated zones, which are one of the main factors affecting the stability of colluvial soil slopes during rainfall. This paper aims to examine how the distribution characteristics, such as depth (h), angle (θ), and location of surface cracks, influence the development of transient saturated zones. For this reason, a series of numerical simulations involving colluvial soil slopes is performed. The results show that the development of transient saturated zones in a slope with a crack and that in an intact slope are quite different. In a cracked slope, rainwater infiltrates into the slope along the crack and forms a transient saturated zone at the crack tip. It is found that the smaller the crack depth is, the easier it is for the transient saturated zone at the crack tip to connect with that in the shallow layer, leading to an increase in the area of the transient saturated zone in the shallow layer. Moreover, the larger the crack angle is, the more easily the transient saturated zone at the crack tip connects with both the transient saturated zone in the shallow layer and the groundwater, forming a transient saturated zone that penetrates the entire colluvium. In addition, the lower the location of the crack along the slope surface is, the shorter the time is for the formation of a transient saturated zone at the crack tip, and the larger the area of the transient saturated zone.

International audience; This work aims to investigate the micropore properties of saturated kaolin subjected to triaxial loading. Consolidated drained triaxial compression tests were conducted on both normally consolidated and overconsolidated clay specimens. In the (p′, q) plane, a given stress level was reached by following two different stress paths (i.e., the purely deviatoric stress path and the conventional constant σ′3 stress path). This approach allows observing the influence of stress path on the evolution of pore structure. The experimental approach consisted in using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) to quantify the micropore structure of the specimens after being submitted to mechanical loading. The results clearly show that the micropore structure of clay was affected by the loading conditions. Consequently, the development of induced anisotropy appeared as mainly related to the variation of pore shape and pore orientation. Meanwhile, for overconsolidated specimens featuring dilative behavior, the pores exhibited a trend to be more open (i.e., rounder) and more randomly oriented compared with the normally consolidated specimens showing contractive behavior. Even if the micropore structures deduced from the SEM-based method, on the one hand, and from MIP tests, on the other hand, concern different scales of pores, the analysis shows that both methods of investigation were quite well comparable and revealed similar variation tendencies in void ratio and pore size distribution.

Red clay, an easily cracking lateritic soil, is extensively distributed in southern China. Cracked red clay slopes often show shallow failures under rainfall, which is challenging to reproduce by finite element methods. This study aims to examine how desiccation cracks and vegetation affect the shallow stability of a red clay cut slope during rainfall. Numerical models of the slope are created using ABAQUS, and an effective approach is proposed to simulate the distribution of desiccation cracks. The reliability of the numerical models and approaches is validated against field surveys. Parametric analysis is then conducted to investigate the influences of rainfall parameters, crack parameters and vegetation parameters on the slope stability. The results demonstrate that the presence of desiccation cracks can cause shallow failure and greatly reduce the factor of safety of the slope. This indicates that control of crack development is important to maintain slope safety. Moreover, the stability of cracked slopes can be obviously improved by vegetation with roots longer than 0.5 m. A tap root system appears to perform better than a fibrous root system. However, shallow-rooted vegetation may also contribute to the shallow stability of the slope by restraining the formation of desiccation cracks.

Soil infiltration performances under rainfall affect shear strengths and play a crucial role in landslide problems. In this paper, the infiltration performances of gravelly soils under different rainfall conditions were investigated by 1D and 2D seepage tests. Computed tomography (CT) scans were adopted to identify the mesoscopic structural properties of gravelly soils. The significances of mesoscopic properties on the saturated coefficient of permeability (ks) were subsequently analyzed. The results showed a temporal and spatial variation of infiltration performances of a gravelly soil slope. The infiltration performances measured by 1D infiltration tests were different from those obtained from 2D tests. An exponential relationship between 1D and 2D infiltration rates was observed. The results further highlighted that void area ratio, uniformity coefficient, and gravel content were three most significant factors to ks. Three permeability formulas that respectively expressed by gravel content, initial dry density and two mesoscopic properties were proposed in this paper.

Wind loads are random variables, which induce significantly greater responses in structures than do static loads. We develop a finite-infinite element model of a 2 MW wind turbine using ABAQUS and then verify it with in situ data. The adopted dynamic constitutive model of the soil is based on the Davidenkov skeleton curve. The results demonstrate that the dynamic amplification factors (DAFs) strongly depend on wind speed and spatial position. Considerable values of the DAFs, ground acceleration, and ground velocity are observed, suggesting that the responses of the shallow foundation of a wind turbine are affected by dynamic wind loads.

Because of low resilient modulus, high plasticity soil is often not allowed to fill road subgrades and is discarded as construction and demolition waste (CDW). To make use of the CDW, this study explored the possibility of improving high plasticity soil with gravel and examined the effect of gravel gradation on the resilient modulus of the soil-gravel mixture. A series of dynamic triaxial tests, tests of voids in coarse aggregate, and X-ray CT scans were carried out on high plasticity soil-gravel mixtures of different gravel contents and gravel gradation types. The test results show that there is a critical gravel content, that is, 44.1%. When the gravel content is less than 44.1%, the mixture shows a dense suspended structure and its modulus increases slowly with increasing gravel content. When the gravel content is greater than 44.1%, the mixture exhibits a dense skeleton structure and the modulus increases rapidly as the gravel content rises. Moreover, as the gravel gradation tends to the lower type, coarse aggregates increase in quantity and contact each other to form a dense skeleton; thus, the modulus increases accordingly. As the gravel gradation approaches the upper type, coarse aggregates decrease in quantity and tend to suspend in the soil, so the modulus decreases. With the increase in contact number, the skeleton structure is continuously improved, and thus the modulus is enhanced progressively. The results indicate that the gravel mixing method with a gravel content of 40%–45% can effectively improve high plasticity soil and shows great environmental and economic benefits.

International audience; This experimental work aimed to identify local mechanisms in remoulded clays under different triaxial loading conditions. The behaviour at a given stress level reached by two different stress paths, i.e. the conventional constant σ′3 stress path and the purely deviatoric stress path, and the behaviour at two different stress levels along a given stress path were examined. The investigation concerned both normally consolidated and overconsolidated saturated specimens of remoulded kaolin clay. The microstructural states of the clay specimens induced by different triaxial loading paths were examined at two different scales using the scanning electron microscopy and the X-ray microtomography. The results highlighted five particle orientation modes that could be activated. These modes seem to be highly dependent on the stress level, the overconsolidation ratio and the stress path. Mesocracks were found to develop within strongly overconsolidated specimens accompanied by the occurrence of dilatancy. The proposed conceptual modes provide an interesting approach to understand the mechanical behaviour of remoulded clays, especially the macroscale dilatancy phenomenon, through the possible activation of different mechanisms at micro- and mesoscales.

The stability of a residual gravelly soil slope during heavy rainfall is closely related to the seepage field, which is directly affected by the seepage boundaries of the slope. To examine the boundary effect, a novel model flume that can implement permeable and impermeable boundary conditions was designed. With this flume, hydraulic model tests of a gravelly soil slope considering those two seepage boundaries were carried out. The results show that distinct spatial morphology of seepage fields is reflected by the hydraulic characteristics of the slope models with different seepage boundaries. The slope with permeable boundaries generally exhibits a larger average infiltration rate as well as a relatively smaller moving speed of wetting front in the lower part compared to the slope with impermeable boundaries. The residual moisture content in the deep-lower part of the slope with permeable boundaries is 6.6% cm3/cm3 smaller than that of the slope with impermeable boundaries. Nevertheless, the maximum pore water pressure in the middle part of the slope with permeable boundaries is 1.2 kPa higher than that in the corresponding part of the slope with impermeable boundaries. It is noted that regional pore water pressures in the shallow-lower and shallow-middle parts of the slope with impermeable boundaries exhibit large fluctuations with an amplitude over 0.5 kPa. The seepage field in the slope with permeable boundaries presents a multi-dimensional development, which may lead to a local failure of the slope. The results are of great significance in studying the similarity of seepage boundary condition in the field of similarity theory on landslide model tests and provide an experimental basis for establishing rainfall-induced landslide theory.