Journal of Geotechnical and Geoenvironmental Engineering

Surface wave testing is a powerful tool for noninvasive seismic site characterization. It includes a wide variety of active-source and passive-wavefield methods [e.g., spectral analysis of surface waves (SASW), multichannel analysis of surface waves (MASW), microtremor array measurements (MAM)] that can be applied to many different field conditions. The dispersion data collected with all these methods can be inverted to produce (one-dimensional) 1D shear wave velocity ($V_S$) profiles of the subsurface. A critical part of this inversion procedure is the need to develop several trial model parameterizations with different numbers of layers as a means for investigating epistemic uncertainty and nonuniqueness when attempting to fit the experimental dispersion data. This is especially important when a priori information either is not available or does not extend to great enough depths to constrain the inversions. These trial parameterizations are used to vary the number of potential layers present in the subsurface models and to set the acceptable search ranges for depths to boundaries and stiffness in each layer. The inversion results are highly affected by the parameterizations. When performing high-quality inversions, it is important to use different parameterization options to fully explore potential conditions at the site and characterize the epistemic uncertainty of the inversion process. While this practice allows for a robust analysis of the experimental dispersion data and its uncertainty, it also generates many potential subsurface models for the site, which can represent a challenge for engineers when deciding which ${\mathrm{V}}_{\mathrm{S}}$ profiles best represent the true subsurface layering for use in subsequent analysis and design (e.g., seismic site response). This paper presents an approach, called the DeltaVs method, for systematically evaluating the depths of layer boundaries across all acceptable models determined from several different inversion layering parameterizations as a means to identify distinct clusters of boundaries. Using these clusters, the number and location of meaningful layer boundaries can be determined for many sites, thereby allowing for the elimination of some parameterization options containing more, or fewer, boundaries and a reduction in epistemic uncertainty. The distributions of layer boundaries within these clusters can then be used to determine statistics for the depths of layer boundaries that are consistent with the epistemic uncertainty of the models produced by the inversion procedure. The DeltaVs method is demonstrated on 12 synthetic ground models as well as one field data set.

Small-strain shear modulus ($G_0$) is a fundamental property required in dynamic analyses. For sandy soils, $G_0$ may be affected strongly by particle characteristics such as uniformity coefficient ($C_u$), mean particle size ($d_{50}$), fines content (FC), and particle shape. Based on an extensive experimental study of the mechanical behavior of coral sands, this paper proposes a new formula for predicting $G_0$ for sandy soils with various $C_u$, $d_{50}$, FC, and particle shapes. A notable feature of the new formula is the use of the extreme void ratios (maximum void ratio $e_{\max }$ and minimum void ratio $e_{\min }$) as the indexes, which were shown to be able to account for the effects of the various factors in a simple yet collective manner. Power-law correlations were established between the minimum small-strain shear modulus $G_{0\min }$ and $e_{\max }$ as well as between the maximum small-strain shear modulus $G_{0\max }$ and $e_{\min }$. The wide applicability of this formula was validated further using extensive data from the literature from resonant column, bender element, and torsional shear tests on siliceous, calcareous, and coral sandy soils.

Bearing capacity calculation is an important part of shallow foundation design. The expressions for the shape and depth factors available in the literature for bearing capacity calculation are mostly empirical and are based on results obtained using limit analysis or the method of characteristics assuming a soil that is perfectly plastic following an associated flow rule. This paper presents the results of an experimental program in which load tests were performed on model strip and square footings in silica sand prepared inside a half-cylindrical calibration chamber with a transparent visualization window. The results obtained from the model footing load tests show a significant dependence of footing penetration resistance on embedment depth. The load test results were subsequently used to determine experimentally the shape and depth factors for model strip and square footings in sand. To obtain the displacement and strain fields in the sand domain, the digital image correlation (DIC) technique was used to analyze the digital images collected at different stages during loading of the model footing. The DIC results provide insights into the magnitude and extent of the vertical and horizontal displacement and maximum shear strain contours below and around the footing base during penetration.

Cyclic loading of saturated sand under partially drained conditions may lead to accumulated strains, pore pressure buildup, and consequently reduced effective stress, stiffness, and shear strength. This will affect the ultimate limit state capacity of monopile foundations in sand for offshore wind turbines. This paper calculates the performance of large-diameter monopile foundations, which are installed in uniform dense sand, subjected to storm loading using the partially drained cyclic accumulation model (PDCAM). The simultaneous pore pressure accumulation and dissipation is accounted for by fully coupled pore water flow and stress equilibrium (consolidation) finite element analyses. Drainage and cyclic load effects on monopile behavior are studied by comparing the PDCAM simulation results with simulation results using a hardening soil model with small strain stiffness. At the end, a simplified procedure of PDCAM, named PDCAM-S, is proposed, and the results using this approach together with PLAXIS 3D and the NGI-ADP soil model are compared with the PDCAM results.

Excess pore pressure generation of uniform gravel and gravel-sand mixtures was evaluated in this study. Comparisons were made with existing relationships for pore pressure generation of sands and show that gravel and gravel-sand mixtures can exhibit different pore pressure responses. The influence of liquefaction definition, gravel particle angularity, particle size, relative density, initial vertical effective stress, cyclic stress ratio, and gravel percentage, on the generation of excess pore water pressure of gravel and gravel-sand mixtures was studied. Liquefaction definition, particle size, initial vertical effective stress, and cyclic stress ratio were found to not have a significant effect on the normalized excess pore pressure generation (i.e., $r_u$ versus $N/N_L$). Conversely, relative density, particle angularity, and mixture percentage of gravels were found to have a more significant effect on the normalized excess pore pressure generation response (i.e., $r_u$ versus $N/N_L$). Additionally, the coefficient of uniformity ($C_u$) was found to have a strong correlation with increased excess pore pressure generation ratio at values of $N/N_L$ less than 0.40, highlighting the influence of grain size distribution on early pore pressure generation response. A new pore pressure model was developed to predict $r_u$ based on $C_u$ for gravelly soils.

A geosynthetic-reinforced piled embankment situated along a newly constructed high-speed rail line was fully instrumented and monitored to explore soil arching in an equilateral-triangular arrangement of piles with circular cap configuration. During construction, the settlement and vertical stress on the pile caps and subsurface at ground level and the tensile strain in the geogrid were recorded. A modified analytical arching model is derived from the established concentric arches (CA) model to elucidate the load transfer mechanism, specifically for a triangular array of piles. The general framework assumes that the embankment load, not resting on the subsurface beneath the arches, is transferred outward along the arches and distributed uniformly over the improved ground. Compared to the conventional CA model, the proposed model gives a lower proportion of load carried by piles, more in line with field measurements. Given the friction and adhesion between soil and geosynthetics, a novel quartic equation is applied to characterize the tensioned membrane effect of geosynthetic reinforcement based on Pham’s circular and parabolic models. The stiffness variation of the biaxial geogrid was critically assessed for the triangular pile arrangement, and its implications for the design were revealed. Finally, the pile efficacy and critical arch height were determined from different analytical methods and checked against field observations, demonstrating the potential of the proposed model.

Sands consisting of pumice particles are found in the northern part of the North Island of New Zealand. These pumice sands are highly crushable, compressible, and lightweight due to the vesicular nature of the particles, making engineering assessment of their properties problematic. When performing geotechnical assessments of these deposits, questions have been asked whether existing empirical correlations derived primarily from normal (hard-grained) soils apply to the crushable natural pumiceous (NP) soils. Such lack of guidance for the geotechnical characterization and liquefaction assessment of NP soils has long been highlighted by the local geotechnical community. In this research, laboratory experiments, such as cyclic triaxial and bender element tests, were performed on reconstituted and high-quality undisturbed NP samples. These were supplemented by field-based shear wave velocity ($V_{\mathrm{s}}$) profiling conducted at the same sites where the undisturbed samples were collected. For comparison purposes, similar laboratory tests were also performed on the hard-grained Toyoura sand. The laboratory results showed that NP sands have considerably different behavior when compared to Toyoura sand. For instance, NP sands have lower small strain shear modulus ($G_{\max }$) and $V_{\mathrm{s}}$ and higher liquefaction resistance under the same level of packing. Next, results from the laboratory studies and field characterization were synthesized considering the effect of various parameters, such as the degree of packing, overburden pressure, and pumice contents, on the liquefaction assessment of NP sands. Based on the results, attempts were made to develop a $V_{\mathrm{s}}\text{-}\mathrm{based}$ chart to estimate the liquefaction resistance of such problematic soils for use by the geotechnical profession. Finally, the applicability of the proposed $V_{\mathrm{s}}\text{-}\mathrm{based}$ chart was examined using available case studies from the 1987 Edgecumbe earthquake and then compared with an existing empirical $V_{\mathrm{s}}\text{-}\mathrm{based}$ method developed for normal sands. The results showed that the proposed approach better reflected the reported liquefaction manifestation at the sites.

This paper demonstrates the influence of pile head freedom on the thermomechanical performance of a belled pile. Field tests on the belled pile response to a cooling–heating cycle and incremental structural construction are carried out. The temperature changes, axial strain profiles, and pressures at the pile toe are recorded through the buried instruments. The variation in the degrees of freedom, tensile forces, and inferred pile head settlements along the pile depth for different test procedures are analyzed using the measured data. The degree of freedom close to the pile head calculated from strain rates decreases with the structure mass with a gradient of $-2.8\times {10}^{-5}/\mathrm{kN}$. The reducing effect of the incremental superstructure on pile freedom decreases along with the orientation of the pile depth. Compared with the inferred thermal displacement of the pile without an applied structural load, the values decrease by about 10% when the pile was subjected to incremental floors, and an elastic recoverable characteristic response to cooling–heating-recovery phases is observed. Compared with the equal-diameter pile, the belled pile showed a significant constraint close to the toe. Mechanical loads can decrease the cracking risk because of a possible tensile force under cooling conditions.

The performance of the novel fish anchor has been assessed through field tests. The tests were carried out at three different locations in the Swan River, Perth. The water depths were $2.91–4.73\mathrm{m}$. The riverbed soils consisted of clay (Location 1), silty clay (Location 2) and silt (Location 3). The anchor was installed in the riverbed by dropping first through an air column followed by a water column, and finally striking the riverbed at an impact velocity of 10.4 (Location 1), 11.43 (Location 2), 11.72 (Location 3) $\mathrm{m}/\mathrm{s}$. The anchor tip embedment depth in the riverbed was measured at 1–2.5 times the anchor length. For similar impact velocity, the tip embedment depth in clay was 1.56–1.68 and 2–2.1 times of that in silty clay and silt, respectively. The capacity was found to reduce with loading angle at the padeye to the horizontal. The ultimate capacity was 1.5–2.6 times the weight of the anchor submerged in water for loading angle 90°, which increased to 8.2–15.6 times the weight for ${\theta }_0=\sim 16°$. The fish anchor dove, as opposed to pull out of the riverbed, for loading angles $\le 37–47°$, resulting in nonelliptical failure envelopes, which have been expressed mathematically.