<p><p><strong>Reference(s):</strong></p><p><em>Broms (2003)<br>Bruce (2001)<br>Cali et al. (2005a)</em></p><p><strong>Method Summary</strong></p><p>Partial column excavation can be performed as part of examining pre-production test columns. Entire columns can be extracted by encasing the column in an open-ended pipe by driving the pipe around the column with a vibratory hammer supported by a crane. Excavation or extraction of deep mixed columns allows visual confirmation of the shape, uniformity, and geometry at various depths. Samples of different sizes can be cut from the deep mixed soil after excavation or extraction. Full-scale compression tests can also be performed on extracted columns to determine the shear strength from unconfined compression tests, as shown by Cali et al. (2005a). Also, the excavation of test columns allowed for the observation that the upper portions of the columns were not fully formed and were no stronger than the in-situ soil. It was determined that for soils with a liquidity index less than 0.5, regardless of moisture content, there is insufficient moisture to hydrate the binder. Bruce (2001) notes that “exposed treated soil can be sprayed with phenolphthalein solution to help indicate the presence of cement in the mass.”</p><p><strong>Accuracy and Precision</strong></p><p>According to Broms (2003), “testing of whole columns or column sections, which have been retrieved, is the most reliable method to determine the shear strength and the bearing capacity.” However, the shear strength of the column could be affected by the driving of the large diameter steel pipe around the column and by the retrieval process.</p><p><strong>Adequacy of Coverage</strong></p><p>Due to the time, cost, and logistical constraints, it is difficult for column extraction or excavation to be completed on a representative number of columns. On grounds of cost, it is typically restricted to pre-production testing (Bruce 2001).</p><p><strong>Implementation Requirements </strong></p><p>Column extraction is very costly and time consuming. For certain projects of a critical size, complexity, and significance, extraction or exposure could be an important part of the QC/QA effort (Bruce 2001).</p><p><strong>General Comments</strong></p><p>Column extraction or excavation, particularly when combined with testing of portions of the column for shear strength, permeability or compressibility, can be a very useful QC/QA tool for a variety of applications. Due to the cost of full extraction, partial excavation is far more practical and is more commonly used to examine the degree of mixing and obtain block samples. High ground water levels, which commonly occur on soft ground projects where the deep mixing method is employed, can complicate excavation and observation of columns without extraction.</p></p>