A field measurement was conducted on an H-pile driven into a multilayer soil profile to analyze the axial stresses/forces generated on the pile during bridge construction activities. Vibrating wire strain gauges and piezometers were utilized, and dynamic testing was conducted for this purpose. Measurements revealed that the pile's pre-installation and temperature changes after installation in cooler ground caused shifts in strain gauge readings. Furthermore, driving an adjacent pile into the vicinity equivalent to four pile diameters, caused a notable increase in pore water pressure, resulting in decreased stresses on the pile. Concreting on top of the pile induced compressive stress during the first day, followed by a considerable decrease and development of tension on the pile over the next two days. Considering the residual force due to pile installation, force distribution, neutral plane location, and maximum axial force along the shaft were different and higher than in the case where this force was ignored. This paper presents a robust methodology to evaluate forces/stresses in a pile subject to installation through to final loading, including drag force effects based on instrumentation measurements. This novel approach provides a better understanding of drag force impacts on actual load capacity under final production loading.

Internal erosion is one of the most important factors that cause earth structures that retain water, such as embankment dams, to collapse. Concentrated leak erosion, one of the forms of internal erosion, occurs in cracked fine-grained soils and pressurized flow conditions. To evaluate the concentrated leak erosion risk of cracks/voids, it is necessary to ascertain the erosion resistance of these materials. The erosion rate and critical shear stresses determine internal erosion resistance in concentrated leak erosion. This study determined soil's concentrated leak erosion resistance using test equipment that allowed the flow to pass through a hole with stress-free (no loading), anisotropic-compression stress, anisotropic-expansion stress, and isotropic stress conditions. The stresses that developed in the samples' hole wall where erosion occurred were determined with numerical modeling as pre-experimental stress conditions. The experiments were performed under a single hydraulic head on four selected cohesive soils with different erosion sensitivity. Time-dependent flow rates obtained from the test system can be used to determine hydraulic parameters, such as energy grade lines, with the help of basic theorems of pipe hydraulics in theoretical hydraulic models. Moreover, the erosion rates were quantitatively determined using the continuity equation, while critical shear stresses were qualitatively compared for concentrated leak erosion developed by the dispersion mechanism. As a result of the experiments, stress conditions influence the concentrated leak erosion resistance in the soil samples with dispersive erosion. Moreover, the shear strength in the Mohr-Coulomb hypothesis can explain the erosion resistance in these soils under stress conditions depending on the sand/clay ratio.

The plastic flow behavior of soft rock exhibits non-coaxial features under complex stress paths, while traditional plasticity theories are ill-equipped to adequately represent this, which leads to the mechanism of soft rock failure still unclear. To investigate the evolution law of strain increments and non-coaxial characteristics of weakly cemented soft rock, the directional shear tests are conducted using the hollow cylinder apparatus (HCA). The results show that non-coaxiality does not occur when alpha is distinct from 0 degrees or 90 degrees. The oscillation of the non-coaxial angle is significantly more variable in soft rock experiencing combined tension-torsion (45 degrees < alpha < 90 degrees), as opposed to those under the influence of combined compression-torsion (0 degrees < alpha < 45 degrees). The non-coaxiality swiftly dissipates when the sample is approaching the failure state. The stress rate is decomposed into stress magnitude and direction to describe non-coaxial features of plastic strain. And a new method for non-coaxial stress rate is proposed which can express the plastic strain increment directions. The spherical interpolation coefficient method is utilized to describe the continuous change in non-coaxial plastic flow direction between tangential and normal directions of the yield surface. The non-coaxial parameter (Delta) is introduced to quantify the non-coaxial characteristics of soft rock and its validity is confirmed through test results. This method effectively captures the principal stress direction influence on non-coaxial behavior of soft rock and have significance for rock mechanics.

Under various stress paths, the deformation characteristics represented great differences. In this paper, a series of cyclic triaxial tests have been conducted with Fujian standard sand. By comparing the constant deviatoric (CDS) and constant axial stress paths (CAS), the influence mechanism of the cyclic amplitude of the deviatoric stress was discussed. The test results showed that the stress path significantly influenced the volumetric and shear strains. The increasing and decreasing trend in the volumetric strain (epsilon v) was consistent with the spherical stress (lnp). Compared with the two stress paths, the slope of the epsilon v-lnp curve during the loading and unloading stages was larger under the CAS path. In the CDS path, qc almost did not affect the cumulative volumetric strain, and in the CAS path, the effect was obvious. The shear strain curve was in accordance with the direction of the stress path. As the cyclic number increased, the shear strain gradually accumulated. The shear strain accumulation under the CAS path was larger. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. In practical engineering, the soil will experience various stress paths. For example, in slope or earth-rock dam engineering, where the water level rises and falls repeatedly, the soil often goes through the stress path of constant deviational stress with the cyclic increase and decrease in the spherical stress. In foundation pit engineering, the soil often experiences the stress path of the constant axial stress (CAS) with cyclic loading and unloading of the lateral stress. The stress path greatly influences the deformation and strength of soil. Therefore, the previous two stress paths are compared in this paper to discuss the influence of the cyclic amplitude of deviatoric stress. Under three different consolidation states, the cyclic amplitude of the deviatoric stress significantly influenced the volumetric and shear strains. The shear strain largely depended on the relative position between the critical state line (CSL) and the stress state of the soil during cyclic loading and unloading. Therefore, in practical engineering, if the stress path in the experiment differs from the actual value, the influence of the stress path should be properly considered. The results should be modified according to the degree of influence of each stress condition.

This paper examines the effect of nano-silica and cement on the geotechnical properties of bentonite, both individually and in combination. For this objective, the nano-silica and cement contents were adjusted from 0.2 to 1% and from 4 to 8% by dry weight of bentonite, respectively. This investigation revealed that the plasticity index reduced from 243.82 to 215.19% and then from 243.82 to 201%, equivalent to a nano-silica and cement content of 0.8% and 8%, respectively. The mixture containing 8% cement and 0.8% nano-silica in bentonite had the lowest plasticity. Raising the amount of nano-silica, cement, or their combination in bentonite enhanced both the optimum moisture content and the dry unit weight. The compressive, tensile and CBR strengths of bentonite were improved after addition of nano-silica, whereas further enhancement was noticed after additional mixing of cement. The maximum axial stress, tensile stress and bearing ratio were measured in 0.8NS8C mix after 28 days. After 28 days of curing, the axial stress of mix 0.8NS4C was 1.44, 1.22 and 1.09 times, whereas tensile stress for the same was 1.24, 1.12 and 1.04 times greater than 4C, 6C and 8C, respectively. The CBR % in 0.8NS8C mix observed increment from 27.11 to 60.9% and 22.5% to 44.51% in un-soaked and soaked condition, respectively, after 28 days. The improved strength properties were attributed to the advance bonding characteristics due to formation of pozzolanic products (calcium silicate hydrate) after curing. SEM images of treated bentonite reveal denser and stiffer matrix with detection of newly formed pozzolanic products (calcium silicate hydrate gel). FTIR spectrum also reveals formation of new chemical compounds after ion exchange process indicated with broader band width in the region of wavenumber between 600 and 1500 cm-1 as noticed in 0.8NS and 0.8NS8C mixes.

The excavation and maintenance of buried natural gas pipelines can lead to deformation and stress redistribution of the pipelines and even cause secondary damage to the pipes with issues. To clarify the impact of excavation unloading on buried pipelines, this study established a finite element three-dimensional pipe-soil model, investigated the mechanical response of pipelines under layered excavation and evaluated various parameters impacting the response. The parameters analyzed include the diameter-thickness ratio of the pipe, excavation length and width, thickness of top covering soil, elastic modulus of soil, specific weight of soil and initial displacement of the pipeline. The study results showed that the pipeline bulges upwards during excavation unloading, the pipe top in the middle is under tension, and the bottom of the pipe is under compression. Therefore, the axial stress and vertical displacement both increase first and then decrease, and they are distributed symmetrically along the pipeline axis; excavating the initially compressed pipeline leads to high strain areas in the pipeline and even local buckling. The response to slope excavation is more pronounced than that to straight trench excavation; the additional response of the pipeline increases with the increase of diameter-thickness ratio, excavation width, thickness of pipe top covering soil and specific weight of soil, but it decreases with the increasing soil elastic modulus. The additional response is closely related to excavation length and the initial displacement. The results of this study can provide a reference for pipeline construction, maintenance, and safety assessment.

Dynamic load on anchoring structures (AS) within deep roadways can result in cumulative damage and failure. This study develops an experimental device designed to test AS under triaxial loads. The device enables the investigation of the mechanical response, failure mode, instability assessment criteria, and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths. The results show that the peak bearing strength is positively correlated with the anchoring matrix strength, anchorage length, and edgewise compressive strength. The bearing capacity decreases significantly when the anchorage direction is severely inclined. The free face failure modes are typically transverse cracking, concave fracturing, V-shaped slipping and detachment, and spallation detachment. Besides, when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength, loading rate, and anchorage inclination angle increase, the failure intensity rises. Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend. Under cyclic loads, the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability. Finally, a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).