Additional Considerations for SCPs

The construction methods used for installation of SCPs may provide some densification of the in-situ soil. If consistent improvement of the soil can by verified by QA testing, then there will be an increase in the CRR in addition to the decrease in the CSR caused by the load transfer to the stiffer elements, with a corresponding increase in the factor of safety against liquefaction. The increase in the CRR can be determined using the new values of penetration resistance and appropriate liquefaction charts.

<p><p><strong>References:<br></strong><em>SHRP 2-Phase I Technology Assessment</em></p><p><strong>Method Summary</strong></p><p>The Cone Penetration Test (CPT) is a field method to indirectly measure the strength of the soil. In this test a small diameter cone is pushed into the ground at a constant rate. The point resistance and the friction on the sleeve above the cone are measured with depth either electronically or mechanically (not typically used anymore).

<p><p><strong>Supporting Reference(s):<br></strong><em>AAboshi et al. (1991)<br>Akiyoshi et al. (1993)<br>Barksdale (1987)<br>Barksdale and Takefumi (1991)<br>Kitazume (2005)<br>Tanimoto (1973)</em></p><p>Sand compaction piles work to increase the liquefaction resistance, increase bearing capacity, and/or reduce settlement of loose sand deposits by increasing the in-situ soil density and lateral effective stress. The most effective way to achieve these results is to increase ground density.

<p><p><strong>Supporting Reference(s):<br></strong><em>Aboshi et al. (1979. 1991)<br>Barksdale (1987)<br>Barksdale and Takefumi (1991)<br>Kitazume (2005)<br>Mizuno et al. (2006)</em></p><p>When SCPs are used to improve clayey sites, the end product is referred to as a composite foundation. SCPs are installed in clay soil for the purpose of increasing site stability and/or reducing ground settlement.

<p><p><strong>References:<br></strong><em>Schaefer et al. (2016)<br>Mitchell (1981)</em></p><p><strong>Method Summary</strong></p><p>The cross-hole test is an in-situ measurement of the wave propagation velocity at small strains between bore holes. Typically, two holes are drilled, cased, and a wave source is placed in one hole and a receiver in the other hole. The wave is generated from the source and the time for the wave to reach the receivers is evaluated.

<p><p><strong>References:<br></strong><em>Aboshi et al.

<p><p><figure id='attachment_3579' style='max-width:400px' class='caption aligncenter'><img class="wp-image-3579 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Aerial photograph showing the Kansai International Airport." width="400" height="311" /><figcaption class='caption-text'> Kansai International Airport.

<p><p><strong>Supporting Reference(s):<br></strong><em>Asaoka et al. (1991, 1994)</em></p><p>The conventional method of designing SCPs assumes the clay follows an undrained condition while the sand in the SCPs follows a drained condition. While the conventional method is simple and easy to use, it does not distinguish between flexible and rigid loads, consider whether the SCP is actually drained or undrained, or consolidation of the surrounding clay that occurs during SCP installation.

<p><p><strong>Supporting Reference(s):<br></strong><em>Idriss and Boulanger (2008)<br>Youd et al.( 2001)</em></p><p>Sand Compaction Piles (SCPs) may be used at sites with liquefiable in-situ soils. Saturated sands, silty sands, sandy silts, and silts are likely to be in this category. When SCPs are used for support of embankments and structures to reduce settlements, it is also necessary to confirm that there will not be a risk of liquefaction or other ground disturbance that could lead to loss of support and lateral spreading.

<p><p><h2>Project Summary/Scope:</h2>The Hokkaido Highway Construction Project was intended to improve the traffic connection between area towns. One section required the construction of a new embankment.</p><p>Subsurface Conditions: Thick, soft peat from the ground surface to a depth of about 6 meters had water contents ranging from 400 to 1,000%. The unconfined compressive strength of the peat material was around 10 to 20 kPa.

<p><p><strong>References:<br></strong><em>Aboshi et al. (1991)</em></p><p><strong>Method Summary</strong></p><p>Piezometers are used to measure and monitor pore water pressures before, during, and after installation of SCPs. Once installed, the piezometer should be read on a regular schedule. Piezometers are a good indicator of the progress and final product of improvement through SCPs.