Utilization of Screw Piles in High Seismicity Areas of Cold and Warm Permafrost

INE/AUTC 11.1

Effects of Permafrost and Seasonally Frozen Ground on the Seismic Response of Transportation Infrastructure Sites

INE/AUTC 11.0

Stabilization of aeolian sand with combined use of geofiber and synthetic fluid

Aeolian sand is very common in arid and semi-arid regions. Without proper improvement, this soil lacks desirable engineering characteristics for use for pavement base courses, subbase courses, subgrades, and as a foundation supporting layer under buildings. A non-conventional soil stabilization technique combining synthetic fluid and geofiber as improvement additives were investigated through an extensive and systematic experimental study. Engineering characteristics of various soil-additive compositions were evaluated through CBR and large-scale direct shear tests. Beneficial effects of the additives in terms of both the CBR performance and shear strength of aeolian sand were discovered. Proper additive dosages and curing of the treated soil were found to play a significant role in achieving the desired improvemen/Asphaltt of the CBR value and peak friction angle. Comparative analysis between peak and post-peak strength of various soil/additive compositions is presented. As part of the results of this study, a relatively strong correlation between CBR and internal friction angle was established

Pore pressure generation characteristics of sands and silty sands: a strain approach

textLiquefaction of saturated granular soils during earthquakes has been one of the most important problems in the field of geotechnical earthquake engineering. It is well established that the mechanism for the occurrence of liquefaction under seismic loading conditions is the generation of excess pore water pressure. Most of the previous research efforts have focused on clean sands. However, sand deposits with fines may be as liquefiable as clean sand deposits. Previous laboratory liquefaction studies on the effect of fines on liquefaction susceptibility have not yet reached a consensus. This research presents an effort to find a unified picture regarding the effect of fines content on excess pore water pressure generation. Different from earlier studies that placed an emphasis on characterization of liquefaction in terms of the induced shear stress required to cause liquefaction, this study adopted a strain approach because excess pore water pressure generation is controlled mainly by the level of induced shear strains. This approach was first proposed by Dobry et al. (1982). Multiple series of strain-controlled cyclic direct simple shear and cyclic triaxial tests were used to directly measure the excess pore water pressure generation of sands and silty sands at different strain levels. The soil specimens were tested under three different categories: a) at a constant relative density, b) at a constant sand skeleton void ratio, and c) at a constant overall void ratio. The results from each of these groups were examined. In addition, laboratory measured pore water pressures of clean sands were compared to in situ measured values. The findings from this study were used to develop insight into the behavior of silty sands under undrained cyclic loading conditions. In general, beneficial effects of the fines were observed in the form of a decrease in excess pore water pressure and an increase in the threshold strain. However, pore water pressure appears to increase when enough fines are present to create a sand skeleton void ratio greater than the maximum void ratio of the clean sand. The comparison between laboratory and in situ measurements indicated that larger pore water pressure was generated in situ.Civil, Architectural, and Environmental Engineerin

Strain-based assessment of liquefaction and seismic settlement of saturated sand

This study presents results from an extensive experimental research on saturated clean sand deposits subjected to seismic loading. A total of 29 freshly reconstituted soil samples were tested under laboratory conditions. Strain-controlled, undrained, cyclic triaxial tests were conducted to evaluate the excess pore water pressure and associated settlement response of soil to seismic loading. The level of induced cyclic shear strain varied between 0.01% and 0.5%. The generation of excess pore water pressure was measured under various consolidation stresses ranging from 100 kPa to 400 kPa. Additionally, the settlement due to the dissipation of the excess pore pressure was measured and analyzed for each level of consolidation stress. The findings from the experimental work were used for liquefaction and seismic assessment of an actual soil deposit. A scenario earthquake of magnitude Mw = 7.2 with peak ground acceleration (PGA) of 0.42 g was considered. Induced shear strains at various depths of the soil deposit were determined using software ProShake. It was found that relatively shallower depths were less prone to liquefaction with insignificant cyclic settlement

Excess pore pressure generation and post-cyclic loading settlement of geofiber-reinforced sand

The response of geofibre-reinforced sand to dynamic loading is investigated in this paper in terms of excess pore pressure generation and post-cyclic load reconsolidation. Strain-controlled, undrained triaxial tests were performed on saturated sand specimens prepared with varying geofibre content. Tape type and fibrillated type polypropylene geofibre were used with Ottawa (C-109) sand at 0.2%, 0.5%, and 1% dosages by dry weight of soil. The tape type geofibre was found to be more effective than the fibrillated type in reducing the excess pore pressure. Both the type and content of geofibre were found to influence the post-loading settlement

Scale Effect on Mode of Failure and Strength of Offset Rock Joints

As a sustainable construction material, the use of rock has increased significantly. In this experimental study, the scale effect on failure mechanisms and compressive strength of rock blocks was investigated. Samples of rock with non-persistent offset joints were subjected to uniaxial loading. The angle of orientation of the rock bridge with respect to the applied axial load and the size of the block were studied. Two different block sizes, having dimensions of (63.5 × 28 × 20.3) cm and (30.5 × 15.24 × 10) cm, were tested. The joint inclination angle was maintained at 22.5° in both cases. Also, degree of persistence was kept constant at 0.3 for all tested blocks. However, the offset angle which connects the inner tips of the joints was changed from 30°-90° with an increment of 15°. The results showed a reduction in strength with increasing the size of the sample. This reduction is becoming more significant as the bridge inclination angle increases. This behavior is due to the fact that as the bridge inclination angle increases the mode of failure shifted from shear to tension mode which is more dependent on the size of sample due to the presence of more micro flaws. No effect of block size was noticed on mode of failure for the tested blocks

Effect of soil subgrade modulus on raft foundation behavior

The present study is carried out to investigate the effect of soil subgrade modulus on bending moment, shear, and deformation characteristics of raft foundation. Subgrade models are an approximate representation for the actual load-displacement behavior of the supporting soil. One of the widely-used methods to model soil subgrade modulus is “Winkler” method where the interaction between soil and foundations is represented by a number of springs. The main flaw of this model is the lack of coupling between springs and representation of the non-linearity of load settlement behavior of soil. In this work an attempt is made to analyze “Winkler” method through a commercial software (SAFE V2014) in terms of the effect of soil subgrade modulus on the behavior of raft foundation