Development of K-Basin High-Strength Homogeneous Sludge Simulants and Correlations Between Unconfined Compressive Strength and Shear Strength

Abstract

iii Executive Summary K-Basin sludge will be stored in the Sludge Transport and Storage Containers (STSCs) at an interim storage location on Central Plateau before being treated and packaged for disposal. During the storage period, sludge in the STSCs may consolidate/agglomerate, potentially resulting in high-shear-strength material. The Sludge Treatment Project (STP) plans to use water jets to retrieve K-Basin sludge after the interim storage.STP has identified shear strength to be a key parameter that should be bounded to verify the operability and performance of sludge retrieval systems. Determining the range of sludge shear strength is important to gain high confidence that a water-jet retrieval system can mobilize stored K-Basin sludge from the STSCs. The shear strength measurements will provide a basis for bounding sludge properties for mobilization and erosion. Thus, it is also important to develop potential simulants to investigate these phenomena.Long-term sludge storage tests conducted by Pacific Northwest National Laboratory (PNNL) show that high-uranium-content K-Basin sludge can self-cement and form a strong sludge with a bulk shear strength of up to 65 kPa. Some of this sludge has "paste" and "chunks" with shear strengths of approximately 3~5 kPa and 380~770 kPa, respectively. High-uranium-content sludge samples subjected to hydrothermal testing (e.g., 185°C, 10 hours) have been observed to form agglomerates with a shear strength up to 170 kPa. These high values were estimated by measured unconfined compressive strength (UCS) obtained with a pocket penetrometer. Due to its ease of use, it is anticipated that a pocket penetrometer will be used to acquire additional shear strength data from archived K-Basin sludge samples stored at the PNNL Radiochemical Processing Laboratory (RPL) hot cells.It is uncertain whether the pocket penetrometer provides accurate shear strength measurements of the material. To assess the bounding material strength and potential for erosion, it is important to compare the measured shear strength to penetrometer measurements and to develop a correlation (or correlations) between UCS measured by a pocket penetrometer and direct shear strength measurements for various homogeneous and heterogeneous simulants.This study developed 11 homogeneous simulants, whose shear strengths vary from 4 to 170 kPa. With these simulants, we developed correlations between UCS measured by a Geotest E-280 pocket penetrometer and shear strength values measured by a Geonor H-60 hand-held vane tester and a more sophisticated bench-top unit, the Haake M5 rheometer. This was achieved with side-by-side measurements of the shear strength and UCS of the homogeneous simulants.The homogeneous simulants developed under this study consist of kaolin clay, plaster of Paris, and amorphous alumina CP-5 with water. The simulants also include modeling clay. The shear strength of most of these simulants is sensitive to various factors, including the simulant size, the intensity of mixing, and the curing time, even wi...

Strength Measurements of Archive K Basin Sludge Using a Soil Penetrometer

“…Given the ~4% to14% relative standard deviations observed by measuring the UCS by the Geotest E-280 pocket penetrometer in the various strength simulants (derived from Tables 4.6, 4.7, 4.9, 4.10. 4.11, and 4.12 of Onishi et al 2011) and the even greater variabilities observed for multiple penetrometer measurements of genuine sludge in the present testing, both Equation 1 and Equation 2 are considered to be valid in converting penetrometer-measured UCS to shear strength for homogeneous (i.e., grit-free) sludge.…”

“…The sludge from these tests agglomerated to attain shear strengths estimated to range from 9 kPa to 170 kPa (rounded from 174 kPa) based on unconfined compressive strengths (UCS) measured by a pocket penetrometer. A later refinement of the correlation between UCS values measured by pocket penetrometer and shear strength has re-estimated the highest strength to be 152 kPa (Onishi et al 2011). To date, the 170 kPa value is the highest strength measured or estimated for any bulk K Basin sludge sample although this was for hydrothermally-treated material.…”

“…This set is homogeneous because the constituents contain only fine particles and are free of coarse granules such as sand particles. The comparative measurements were made using a Geotest E-280 pocket penetrometer to determine UCS, a Geonor H-60 hand-held vane tester to measure shear strength manually, and the automated Haake M5 shear vane rheometer to determine shear strength (Onishi et al 2011). Eleven different homogeneous mixtures, with shear strengths ranging from 3.5 to 95 kPa (and penetrometer UCS values ranging from about 0.04 to 1.8 kg f /cm 2 ), were measured multiple times by the three instruments.…”

“…Correlations of UCS measured using a Geotest E-280 pocket penetrometer with shear strengths measured with a Geonor H-60 vane tester and a Haake M5 rheometer also have been performed for two sets of heterogeneous, sand-bearing, sludge simulants (Onishi et al 2011). The weaker set of heterogeneous simulants, with shear strengths ranging from ~21 kPa to 46 kPa, contained kaolin clay, plaster of Paris, sand, and water.…”

“…Again, the UCS values measured by the penetrometer were correlated with the shear strengths measured by the manual and automated shear vane devices (Onishi et al 2011 Because of the problem of unrealistic predicted shear strength at low UCS values for heterogeneous materials, mathematical fit of the joint homogeneous and heterogeneous simulant UCS and shear strength data was considered (Onishi et al 2011). However, this approach was rejected because of the disparate natures and penetrometer responses of the two simulant material types.…”