James A. Schneider

Geotechnical site characterization in the greater Memphis area using cone penetration tests

Abstract The determination of seismic ground hazards in Memphis and Shelby County, Tennessee is facilitated by the use of electronic cone penetration tests that can provide up to four independent readings with depth from a single sounding. One series of soundings is being performed for site-specific mapping to determine the presence and extent of potentially-liquefiable sediments, in-situ soil resistance to liquefaction, and initial soil stiffness for ground motion amplification studies. Another series of soundings is being conducted in conjunction with field paleoliquefaction mapping in the New Madrid seismic zone to better define the intensity, magnitude, and geographic extent of ground failures caused by large past earthquake events, as well as information about the source sands. In this paper, an overview is given on the types of multi-channeled penetrometer data that are being collected, including vertical profiles of cone tip stress (qt), sleeve friction (fs), penetration porewater pressure (u1 or u2), downhole shear wave velocity (Vs), and/or electrical conductivity (ke). Representative soundings are presented from select sites to illustrate repeatability, data post-processing methods, and that derived downhole Vs profiles are generally in good agreement with non-invasive surface techniques at two Memphis test sites. Cyclic stress based procedures for liquefaction are discussed with relation to data from a paleoliquefaction site in Germantown, Tennessee, and estimates of the minimum magnitude of the historic event are discussed. While estimates of the earthquake magnitude are preliminary pending additional study on attenuation relationships and site response in the deep soils of the Mississippi Embayment, it is inferred from evaluation of in-situ test data using cyclic stress based techniques that the December 1811 New Madrid earthquake was likely larger than a Mw=7.5 event.

Shaft Friction from Instrumented Displacement Piles in an Uncemented Calcareous Sand

AbstractThe behavior of displacement piles in uncemented calcareous sand is investigated using field piles instrumented with a sensor that simultaneously records the radial stress and shear stress at specific locations on the pile shafts. These tests are interpreted with the assistance of data from adjacent self-boring pressuremeter tests and from monotonic and cyclic direct shear interface tests performed on reconstituted samples. The existence of extremely low radial stresses on the pile shafts is verified. Although dilation during shear is seen to compensate for such low radial stresses, short-term shaft capacities are much lower than capacities of equivalent piles in siliceous sands. The development of a bonded or welded crust to the pile shaft was seen to be the primary contributor to the setup observed at the test site; this crust forced failure to take place at a sand-sand rather than a sand-steel interface and also gave rise to higher levels of dilation during monotonic loading. The welded sand cr...

Development of the UWA-05 Design Method for Open and Closed Ended Driven Piles in Siliceous Sand

This paper draws upon recent research findings to propose a new CPT qc based design method for predicting axial capacity of open and closed ended driven piles in siliceous sands. The method incorporates various factors that are acknowledged to have a controlling influence on pile capacity including (i) the effects of soil displacement during installation, (ii) friction fatigue, (iii) sand-pile interface friction angle, (iv) changes in radial stress during loading, and (v) the influence of loading direction.

Influence of Dilation Angle on Drained Shallow Circular Anchor Uplift Capacity

AbstractAn experimental study of uplift capacity of 22 circular helical anchors installed in sand with peak friction angles between 40 and 50° was performed. Laboratory triaxial tests indicated that the dilation angle varied between 10 and 25° for these peak friction angles. To account for soil behavior exhibiting nonassociated flow (NAF), in which the dilation angle is much less than the friction angle, a limit equilibrium plane strain analytical solution for plate anchor uplift was updated and extended to axisymmetric conditions. Anchor test results were compared with upper bound (UB) plasticity solutions (based on associated flow) and the newly developed NAF limit equilibrium model. The UB solution overpredicted uplift capacity by more than a factor of 2, whereas the limit equilibrium model had a ratio of calculated to measured capacity of 1.15 and a coefficient of variation of 0.14. Although additional study is warranted, the consistency among the numerical, analytical, and experimental results gives ...

Geotechnical centrifuge modelling techniques for submarine slides

The gradual shift of hydrocarbon developments into deeper waters has presented fresh challenges for offshore geotechnical engineering. Many installations in deep water require export pipelines to shore which can be many hundreds of kilometers in length. These pipelines must negotiate unstable regions of soft seabed around the steep continental shelf and variable terrain including canyons with depths ranging from tens of meters to a several hundred meters. These challenging conditions present potential geohazards for which little understanding has been developed so far. One of the major geohazards is the impact of a submarine landslide on nearby pipelines which could potentially damage the pipeline. Consequently, a Joint Industry Project (JIP) has been initiated at the Centre for Offshore Foundation Systems to improve methods for assessing the potential damage to pipelines and to provide information to assist re-routing of a pipeline to a safer alignment if necessary. This paper presents an overview of the development of specific modeling techniques to (i) trigger a submarine landslide in a geotechnical centrifuge, (ii) measure the strength properties of the slide material before, during, and after the slide failure and (iii) measure the interaction between the runout material and the seabed.© 2009 ASME

Ground Improvement Assessment Using SCPTu and Crosshole Data

A case study is presented where preloading was applied to reduce tank settlements at a liquid natural gas (LNG) facility in Puerto Rico. Stone columns were installed to further reduce settlements and provide an adequate factor of safety against soil liquefaction in the case of a seismic event. Seismic piezocone penetration tests (SCPTu) were used to quantitatively assess the effects of soil improvement. Soil properties estimated from SCPTu data taken before and after both improvement methods are compared to assess the degree of soil improvement. Preconsolidation stresses were estimated using methods based solely on net cone tip resistance, pore pressure difference, shear wave velocity, and a multiple regression based on cone tip resistance and shear wave velocity. Preloading provides additional vertical stress, which is directly related to an increase in preconsolidation stress if time rate consolidation properties are considered. Stone columns increase the lateral stress locally within the zone of influence of the column. Soils initially appear to be normally consolidated to slightly overconsolidated, and a significant increase in preconsolidation stress was noticed in clay layers after preloading. The high clay content of the soils likely led to a reduced zone of influence for the stone columns, and little improvement was noticed immediately after installation. Crosshole test (CHT) shear wave velocities taken across stone columns showed little to no increase in stiffness when compared to downhole shear wave velocities of the soil.

Analysis of Large Diameter Pipe Pile Drivability in Tokyo Bay Using Piezocone Data

The piezocone penetration test (CPTU) provides near continuous measurements of three independent parameters: tip resistance (q t ), sleeve friction (f s ), and penetration pore pressure (u 2 ). The tip resistance and sleeve friction are roughly analogous to pile end bearing resistance (q b ) and the shaft resistance (τ f ) near the pile tip during installation, respectively, while the penetration pore pressure provides an indication of the drainage conditions during cone penetration. However, due to the differences in diameter between a pile and a CPT, as well as the differences in installation method, CPTU parameters (q t and f s ) must be modified to assess the values of unit base and shaft resistance (q b and τ f ) applicable to the static capacity of the pile and the soil resistance to driving (SRD). In this paper, back-analyses of installation records from eight large diameter (1.2 to 1.8m) open ended pipe piles driven through soft clays, silts, and sands at the Tokyo Port Bay Bridge site are conducted using the results of adjacent CPTUs. These analyses provide guidance on evolving methods for interpreting CPTU data to provide predictions of short term SRD, in addition to long term static capacity.