New type sand compaction pile method for densification of liquefiable ground underneath existing structure

The 2011 Great East Japan Earthquake caused severe damage to infrastructures due to liquefaction, in which many embankments failed with large settlement and slope failure. Sand Compaction Pile method is one of the typical ground improvement methods to densify the ground by installing compacted sand piles into ground. This method has been often applied to mitigate the liquefaction. However, current SCP method of constructing sand piles in vertical direction is not able to densify ground underneath an existing structure. For applying the method to an existing structure, a new type of SCP method was recently developed where in compacted sand columns can be constructed in any direction. This paper briefly introduces the new type of SCP method and the effectiveness of local densification by numerical analysis. In this manuscript, a series of numerical analyses were conducted to evaluate the effect of shape and location of SCP improved zone on the dynamic response of embankment. This paper describes the numerical analyses as well as the development, machinery and procedure of the technique, and emphasizes the uniqueness and effectiveness of the technique for preventing liquefaction for new and existing structures.

Numerical investigation on vibration isolation by softer in-filled trench barriers

This paper deals with a 2-D finite element study in PLAXIS 2D on isolation of steady-state surface vibrations by softer backfilled trenches in an elastic, isotropic, and homogeneous half-space. Effects of barrier geometric features and infill material characteristics on reducing vertical and horizontal components of surface displacements are investigated. This study adopts a non-dimensional approach where the geometric parameters are normalized against the Rayleigh wavelength of vibration in half-space and backfill shear wave velocity is expressed as a ratio of that of parent soil. Softer barriers of shear wave velocity ratios less than unity are considered as they are found significantly effective than stiffer barriers. Effects of the parameters participating on wave isolation are extensively discussed and some guidelines are framed regarding their optimal selection. Non-dimensional charts are developed which would provide a sound basis for designing such barriers in actual engineering practice. The design charts are validated with some documented results and close agreement is obtained.

Migration of different LNAPLs in subsurface under groundwater fluctuating conditions by the simplified image analysis method

The correct understanding of the dynamic behavior of Light Non-Aqueous Phase Liquids (LNAPLs) under fluctuating groundwater conditions, difficult to test with conventional methods, is important for the adequate remediation of contaminated soils. In this study, we verified the suitability of the Simplified Image Analysis Method (SIAM) as a tool to assess the saturation distribution of water and Non-Aqueous Phase Liquids (NAPLs) in granular soils, by testing its basic assumption, the existence of a linear relationship between water saturation (Sw), NAPL saturation (So) and optical density (Di), for nine different NAPLs. We then utilized SIAM to study the dynamic behavior of four different LNAPLs that were infiltrated to 1D columns filled with Toyoura sand, and later subjected to two cycles of drainage-imbibition of the water table. It was found that, under similar conditions, the depth of LNAPL infiltration was linearly correlated to the viscosity of the contaminants (R2 = 0.84), the difference between the depth of the mobile fraction after both drainage and imbibition stages was linearly correlated to the interfacial tension values (R2 = 0.79), and the viscosity was logarithmically correlated to the residual saturation ratios for all different NAPLs (R2 = 0.95), correlations that can help us understand and predict the behavior of different contaminants when spilled in the ground.

Post-construction settlement estimation and increased earthwork volumes calculation of high loess fill

In this study, the post-construction settlement (PCS) area distribution of high fill was analyzed based with reference to a case history of an airport runway crossing a deep gully reclaimed by a thick fill of loess. Earthwork volumes (EV) attributed to PCS was calculated based on in-situ tests. Results showed that the uneven PCS were related to fill depth, construction time, fill rate, integrated compaction degree, and boundary conditions. An empirical equation that considers the aforementioned influence factors was established to calculate the final PCS of high fill. The surface PCS of high fill and the EV can be estimated according to the proposed empirical equation and the original site topography using the three-dimensional finite element method.

Shear strength of granular soils from the simulation of dynamic penetration tests

This paper presents a model for the numerical simulation of dynamic penetration tests in cohesionless soils. In the model, dynamic penetration equations are solved by finite difference analysis in the time domain to produce the discretization of the penetration system. The approach allows essential effects of the soil influence to be accounted for, including the dynamic soil resistance by viscous damping during penetration. The model performance has proved by comparisons between the static and dynamic resistance to reproduce the variation with time of measured force, velocity, displacement and energy associated with the interaction mechanism around split-spoon samplers when penetrating in the ground. A realistic representation of the dynamic penetration mechanism allows the internal friction angle of the soil to be estimated. The proposed methodology accounts for scale effects and produces values of φ′ within the same order of magnitude as those estimated from piezocone test data.

Bidirectional cell tests on non-grouted and grouted large-diameter bored piles

The 37-storey apartment buildings of the Everrich II project in HoChiMinh City, Vietnam was designed to be supported on a piled foundation consisting of bored piles assigned a 22-MN working load per pile. The foundation design included performing bidirectional-cell, static loading tests on four test piles. The soil profile consisted of organic soft clay to about 28 m depth followed by a thick deposit of sandy silt and silty sand with a density that gradually increased with depth from compact to dense, becoming very dense at 65 m depth. In March 2010, the test piles, one 1.5-m diameter pile and three 2.0-m diameter piles, were installed to 80 m through 85 m depth and constructed using bucket drill technique with bentonite slurry and a casing advanced ahead of the hole. The bidirectional-cell assemblies were installed at 10 m through 20 m above the pile toes. The piles were instrumented with pairs of diametrically opposed vibrating wire strain-gages at three to four levels below and six to seven levels above the respective cell levels. After completed concreting, the shaft grouting was carried out throughout a 20 m length above the pile toe for the 1.5-m diameter pile and for one of the 2.0-m diameter piles. The static loading tests were performed about 34 through 44 days after the piles had been concreted. The analysis of strain-gage records indicated an average Young’s modulus value of about 25 GPa for the nominal crosssections of the piles. The average unit grouted shaft resistances on the nominal pile diameters were about two to three times larger than the resistance along the non-grouted lengths. The measured load distribution of maximum mobilized shaft resistances corresponded to effective stress proportionality coefficients, ß, of about 0.2 through 0.3. The ultimate shaft resistance for the pile lengths below the bidirectional cells reached an ultimate value after about 8 to 10 mm movement, whereafter the load-movement was plastic. The pile toe stress-movement responses to toe stiffness were soft with no tendency toward an ultimate value.

A practical approach for the consideration of single pile and pile group installation effects in clay: Numerical modelling

In this paper, a practical approach for the consideration of single pile and pile group installation effects in clay is presented using some novel procedures implemented in the finite element (FE) software package PLAXIS 2D. Data reported at a soft clay site at Islais Creek, San Francisco are used to provide calibration for the constitutive model and to validate initial predictions of single pile installation effects. A short parametric study was then undertaken to examine the influence of a number of pile/soil parameters on the soil stresses generated around a single pile after installation and subsequent consolidation. In addition, a new simplified method is proposed to consider group installation effects over-and-above those associated with an equivalent single pile involving the volumetric expansion of tunnels within a plane-strain framework. Remarkably, results show that the installation of additional group piles has a negligible influence after consolidation.