•Digital photogrammetry technique was adopted to reproduce deterministic joints.•Monte-Carlo simulation of stochastic joints was carried out.•The stability of rock blocks were analyzed based on limit ...equilibrium theory.•The stability of tunnel structure was evaluated in terms of the factor of safety.•The failure process display can be animated by GeoSMA-3D.
It has been gaining credence over the past several decades that the spatial characteristics of rock joints exert detrimental effect on the stability of tunnel structures. The deterministic joint spatial distribution around the tunnel was defined by digital photogrammetry technique, which statistically provides the basis for performing Monte-Carlo simulation of stochastic joints that are hidden inside the surrounding rock. The blocks generated by the intersection between structural planes and excavation surfaces were analyzed based on the block theory and limit equilibrium. The keyblocks were identified and the corresponding factors of safety were determined. All these analysis procedures were codified into the computer program GeoSMA-3D (Geotechnical Structure and Model Analysis). The developed software satisfied the fast analysis requirements of joint plane simulation, spatial block modelling, keyblock identification and failure process illustration. The case study was performed with reference to Dabeigou Tunnel on Duolun Second-class Highway in Duolun Town, Nei Mongol, China. Failure process illustration would be useful to facilitate the practical engineers to understand the basic mechanism and select the strengthening strategies.
Throughout the service life, underground structures are subjected to transient and sustained hydrostatic pressures. The reservoir impoundment results in an increase in water level, as well as ...hydraulic gradient, which can endanger the uplift performance of infrastructure. In uplift design, a reduction factor is often suggested for buoyant force acting on underground structures in clays due to the time lag effect. However, the mechanism of pore pressure generation in clays is not fully understood. This investigation presents a novel U-shaped test chamber to assess the pore pressure generation with time in the horizontal branch subjected to an increase in reservoir level in the left vertical branch. A mathematical model is developed to explain the time lag effect of pore pressure generation. The test program also involves the evaluation of uplift pressure acting on foundation model in the right vertical branch due to adjacent reservoir impoundment. It is found that the time lag effect of pore pressure generation in clays can be observed irrespective of hydraulic gradient, but a higher hydraulic gradient can lead to a faster response in pore pressure sensors. A reduction factor of 0.84–0.87 should be considered to reduce the conservatism of uplift design.
In cities, the existence of impervious structures, such as road pavements, parking lots, footpaths, sidewalks, and roofs, can limit the magnitude of rainfall infiltration greatly. Stormwater run-off ...in storm sewer often dominates, which can cause problems of urban flooding easily during heave rainfalls. In rain and sewage diversion, perforated storm sewer is proposed to enable the occurrence of stormwater infiltration into the ground, which can change the prolonged drought-like condition. Model-scale laboratory tests are conducted to assess the infiltration process of water through drainage holes around the sewer circumference. The experimental data are also used to calibrate a numerical model, after which numerical parametric analysis is carried out. It is found that the feature of drainage holes only influences the wetting front in the initial stage of infiltration. In the end, the egg-shaped contour of wetting front with greater influencing zone below the sewer is obtained. The cumulative infiltration with time can be described by an infiltration model, which is positively correlated with the diameter and the number of drainage holes. The optimal opening ratio is recommended as 0.25%, which can provide the most effective drainage capacity.
In practice, how to quickly improve the bearing capacity of piles in a short time is of great significance. In view of this, a technique of setting grooves and installing PVDs (prefabricated vertical ...drains) at the surface of the pile is proposed in this investigation to accelerate the consolidation of the surrounding soil. A radial and circular consolidation model is established for permeable piles. The finite cosine transform, finite Weber transform, and discretization method are used to obtain a semi-analytical solution for the consolidation model with a mixed drainage boundary condition at the surface of the pile. The sensitivity of the consolidation process to the strip number and the width of PVDs is discussed. The results show that the technique of installing PVDs in piles could potentially improve the bearing capacity. When the area of drainage channels is fixed, the bearing capacity of permeable piles can be more effectively improved by using a higher strip number of PVDs and a smaller PVD width.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Rammed earth-timber joints without enlarged ends have been used in rammed earth buildings for several hundreds of years. Due to the embedment nature, the joint has a certain degree of flexibility, ...allowing the floor and roof beams to slide without damaging the rammed earth, enabling dissipating energy during earthquakes. The energy dissipation mechanism of rammed earth-timber joint has not yet been fully understood. This study studied the energy dissipation characteristic of eight rammed earth-timber joint specimens via cyclic pull-out/push-in experiments, investigating the effects of compressive loading, embedment length, and surface roughness on joint performance. Results show that the joint stiffness under cyclic loading was reduced nonlinearly with the increase of pull-out displacement until the occurrence of slippage. The high vertical compression from the upper level, the deformability of timber frames, and the plasticity of rammed earth were found to be the primary energy dissipators. A linear frictional and nonlinear geotechnical hysteretic model, combining frictional and soil mechanics theories, was established to represent the joint behavior. In addition, a simplified multi-linear hysteretic model was developed for the same purpose. The predictions and the measurements had good agreement, suggesting that geotechnical methods should be employed to analyze the joint, maintaining the assumption that both the timber frame and the rammed earth are linear-elastic.
•Energy dissipation of rammed earth-timber joint was investigated experimentally.•Effects of compressive loading, embedment length, and surface roughness on joint performance were studied.•Stiffness of rammed earth-timber joint under cyclic loading was reduced nonlinearly until slippage.•Vertical compression, deformability of timber frames, and rammed earth plasticity were the primary energy dissipators.•Two hysteretic models were established to represent the behavior of rammed earth-timber joint.
Trenchless technology is often used in congested urban areas or river crossings to install underground pipelines to minimize disturbance to surface traffic or other activities. Pipe jacking is a ...typical technique applied to jack pipe segments between two working shafts. However, the design of the jacking force is usually implemented using empirical methods. It should be emphasized that the jacking force will change for each site, depending on the magnitude of overcut, lubricants, work stoppages, geology and misalignment. A particle method is proposed to estimate the jacking force along the pipe. The microparameters are calibrated for sandy soils in Shenyang, so that the macroscale material behavior can be reproduced using the particle model. Hence, the normal force around the pipe circumference can be derived in the particle model, after which the interface friction coefficient is applied to evaluate the friction resistance mobilized at the soil-pipe interface. A modified Protodyakonov’s arch model can be used to assess the magnitude of earth pressure acting on the shield face. In the end, the combination of friction resistance and face pressure provides the jacking force. The efficacy of the proposed particle method is demonstrated by comparing calculated jacking forces with those measured in the field for three types of jacking machines in sandy soils under the Hun River, Shenyang.
Existing analytical solutions for estimating the bearing capacity of shallow foundation are mostly established under the
K
0
= 1 condition, which can produce overly conservative calculations. This ...investigation provides a novel approach to evaluate the behavior of a plane-strain footing under the
K
0
≠ 1 condition. The additional stresses induced by the applied load are superposed with the in situ stresses due to the soil’s self-weight for calculating the major and minor principal stresses, which are then substituted into the Mohr Coulomb failure criterion to check the occurrence of plasticity. The correlation between bearing capacity and depth of plastic zone is proposed. The mathematical form of the solution is also simplified by an approximation method that follows the general form of bearing capacity calculation. The effectiveness of the developed framework is evaluated by comparing against existing approaches. Once the efficacy of the analytical model is demonstrated, a sensitivity study is conducted to study the impact of soil friction angle, cohesion, and lateral earth pressure coefficient. A term of vacuum preloading is also incorporated in the proposed solution, and an illustrative example is presented to show how the performance of a shallow foundation can be improved by the degree of consolidation.
Improving the engineering properties of low-strength soft clay in an environmentally friendly way becomes a challenge in coastal areas. Conventional ground treatment techniques for marine clay using ...cement can cause significant environmental pollution. In this study, the potential use of industrial waste residue-based binder (IWRB), a silicate-based chemical modified by a powdery polymer, as a substitute for Portland cement (PC) is investigated. Collected marine clay was treated with various IWRB-to-PC ratios (0:8, 4:4, 2:6 and 8:0 wt. %) to measure the mechanical properties, through unconfined compression (UC) test and one-dimensional consolidation (ODC) test, and the microstructural and mineralogical characters, through scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetry analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The strength and the deformation of specimens treated with mixed IWRB and PC in a ratio of 1:1 were similar to those improved with PC alone, but the toughness was significantly improved. The microstructural results demonstrated that the cementitious compounds (C–S–H and C–A–S–H) increased significantly in the early curing stage of marine clay treated with IWRB, contributing to the improvement of mechanical properties. It is suggested that IWRB can be an effective substitute for PC to reduce the cost and environmental pollution.
An analytical method is proposed to characterize the stress distribution of the soil around a caisson foundation under lateral load in an elastic half-space. A series of model-scale tests is ...performed to delineate the characteristics of lateral resistance stress along the foundation periphery. Accordingly, the mathematical expression of circumferential resistance stress is established based on the elastic-beam theory. Thereafter, the stress increment in the surrounding soil is derived by numerically integrating the Mindlin's stress solution. The analytical solution for the stress variation in different directions can be solved by a numerical calculation program, the effectiveness of which is further evaluated by comparing with the experimental results. It is found that the stress increment of the soil around the caisson foundation decreases exponentially with the increase of the distance from the foundation side. The vertical additional stress is approximately saddle-shaped and anti-symmetric with respect to the x-axis and the y-axis of the foundation. A bridge project with caisson foundation is further analyzed using the proposed method to demonstrate the influence of caisson foundation geometry, including the embedment and the diameter, on the additional stress distribution.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Constructing infrastructure on soft soils demands the implementation of ground improvement. This study proposed an eco-friendly method of stabilizing marine soil using a calcium carbide residue ...(CCR)-activated coal gangue (CG) geopolymer derived from industrial waste. Laboratory experiments were conducted to investigate the mechanical properties, durability performance, and stabilization mechanisms of stabilized marine soils under multiple wetting-dry cycles. The results highlighted the effectiveness of CG-CCR geopolymer by a content of 15% to achieve satisfactory strength gain over the engineering requirements. However, the largest decrease in strength (71.89%) was observed when the initial water content was beyond 1.5 times the liquid limit (LL). The optimum solution was proposed to have a geopolymer content of 15% or an initial water content of 1.25·LL to exhibit the highest resistance to strength decay after 12 cycles. Compared with water intrusion, mass loss had a more significant effect on soil strength deterioration. The formation of noncrystalline or amorphous-phase reaction products effectively filled intergranular pores and reduced the void space between soil particles, improving the mechanical properties. The CG-CCR geopolymer was demonstrated to offer a promising solution for soil improvement in geotechnical engineering and waste reduction in industry as a soil stabilizer.
●Marine soil with CG-CCR geopolymer showed excellent engineering performance.●Geopolymer content, initial water content, and curing age control the enhancement.●Durability is affected by the geopolymer content and initial water content.●Mass loss is a prominent factor in strength reduction after wetting-drying cycles.●Microstructure of marine soil was improved by reaction products of geopolymer.
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