Strength and deformation behavior of the Yellow River silt under triaxial drained condition considering characteristic states

Currently,the application of the Yellow River silt in subgrade,especially in expressway subgrade,has not been widely promoted.The main reason is that the research on the mechanical characteristics of the Yellow River silt used for subgrade filling is extremely limited.In this study,the static shear test of the Yellow River silt under drained condition was carried out using Global Digital Systems(GDS)triaxial apparatus,and the effects of confining pressure,relative density and shear rate on the strength and deformation behavior of the Yellow River silt were investigated.The cohesive force of the Yellow River silt is low,and the friction angle is the main factor determining the shear strength.Friction angle at phase transformation stateφpt,friction angle at peak stateφps,friction angle at critical stateφcs,were obtained via the observation on the evolution law of mobilized friction angle during the whole shearing process.The friction angles corresponding to three different characteristic states have the following magnitude relationship,namelyφps>φcs>φpt.The strength parameters for low-grade subgrade and highgrade subgrade were chosen to be 29.33°and 33.75°.The critical state line(CSL),envelop of phase transformation(EOP),and envelop of dilatancy(EOD)for three different characteristic states were determined.The critical stress ratio M,the phase transformation stress ratio Mptand the dilatancy stress ratio Mdof the Yellow River silt are 1.199,1.235,1.152,respectively.These results provide a basis for the mechanical analysis of the Yellow River silt subgrades and the subsequent establishment of dynamic constitutive model of the Yellow River silt.

Seismic Performance Evaluation of Improved Jet Grouted Grid Form with Horizontal Slab in Liquefaction Mitigation

A chain event of the 2016 Kumamoto earthquakes caused considerable geotechnical damage related to liquefaction in many places around Kumamoto plain. Many low-rise houses and traditional Japanese style houses, which were constructed on shallow foundation, suffered differential settlement and tilting due to liquefaction. To mitigate the building damages due to the liquefaction, a new countermeasure method of jet grout grid form with a horizontal slab is introduced in this study. The effectiveness of the proposed technique was evaluated through physical modelling and numerical modelling. As a part of the physical modelling, a set of 1 g shaking table tests for unimproved case and improved case were performed, in which the mitigation effects of the grid form with a horizontal reinforcing slab were examined based on the acceleration, excess pore water pressure ratio as well as ground settlement. Numerical simulation was also performed for assessing the effect of improved method on soil-structure interaction and building settlement during the earthquake. The physical and numerical results confirmed that the grid form with horizontal slab reinforced method is effective in settlement control and offers favorable contribution in liquefaction mitigation.

Reinforcement Effect and Permeability Assessment of Gravel-Tire Chips Mixture (GTCM) for Use in Marine Landfill

The number of marine landfills in Japan has increased over the past decade due to the lack of suitable land. For marine landfills, protection of the alluvium clay layer and improvement of the drainage performance in waste inflow are important aspects. In this paper, an economical construction method for these problems is proposed using gravel-tire chips mixture (GTCM) as the horizontal reinforcement and drainage medium beneath the waste. The content and particle size of tire chips mixed with gravel are essential factors that affect the bearing capacity and permeability of the reinforcement layer. Therefore, a series of permeability tests are conducted using newly developed large-scale triaxial compression and permeability test apparatus to investigate the effect of tire chips particle size, the mass proportion of tire chips (MPTC), and triaxial stress on the permeability of GTCM. In addition, the effectiveness of this technique is evaluated by numerical simulations. The experimental results confirm that the shear strength of GTCM is influenced by tire chips content. Furthermore, permeability coefficient of GTCM is on the order of 0.02 cm/s to 0.08 cm/s, which is higher than the tolerable level of permeability of drainage layer in landfills. GTCM sample shows excellent permeability even on higher compression. Moreover, the Non-Darcy flow properties of GTCM (non-linear) are introduced in this study, and an approximate power function relationship between the permeability coefficient and the non-Darcy flow coefficient is developed. The numerical results confirm that GTCM performs better than the sand, a traditional reinforcement material.