<p><p><div></p><p><figure id='attachment_3462' style='max-width:300px' class='caption aligncenter'><img class="wp-image-3462 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing a trial section after 5 passes, Trans Kalahari Highway, Botswana, Africa." width="300" height="262" /><figcaption class='caption-text'> Trial section after 5 passes. (From Jumo and Geldenhuys, 2004)</figcaption></figure></p><p></div><div><h2>Project Summary/Scope:</h2>The project involved reconstruction of the Trans Kalahari Highway between Jwaneng and Sekoma, in the Republic of Botswana. The original road was constructed in the late eighties and was designed for a 10-year design life but showed signs of distress about 5 years after construction. During the rehabilitation investigation, it became apparent that the existing bitumen-surfaced road failed because of an unconsolidated sand subgrade. Impact compaction was specified during the rehabilitation design to resolve the problems associated with a weak subgrade. It was envisioned that impact compaction would improve the life of the road at a comparatively cheaper cost than excavating and replacing the subgrade in a conventional manner.</p><p>Subsurface Conditions: Bitumen-surface underlain by sand subgrade.</p><p>The minimum number of passes (20 passes) required was established based on a trial section (based on relationships between number of passes and settlement, density, and Dynamic Cone Penetrometer (DCP) shear strength values). Then during construction, the optimum number of passes was determined based on Continuous Impact Response (CIR) mapping during production work.</p><p>Landpac’s 25-kJ IR equipped with CIR integrated with a Global Positioning System (GPS) was used for compaction.</p><p><figure id='attachment_3463' style='max-width:288px' class='caption aligncenter'><img class="wp-image-3463 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Photograph showing a trial section after 30 passes, Trans Kalahari Highway, Botswana, Africa." width="288" height="256" /><figcaption class='caption-text'> Trial section after 30 passes. (From Jumo and Geldenhuys, 2004)</figcaption></figure><h2>Performance Monitoring:</h2>Settlement monitoring, CIR recording decelerations (in g’s), in-situ densities using nuclear gauge and sand cone methods, Dynamic Cone Penetrometer (DCP), and Falling Weight Deflectometer (FWD) tests were used on the project.</p><p>Settlement monitoring data on the trial section showed a high rate of settlement (7 mm per pass) up to five passes, a fairly constant rate of settlement (3 mm per pass) between five and 25 passes, and low rate of settlement (1.8 mm per pass) between 30 and 40 passes. The trial section showed that it is possible to compact 300- to 600-mm subgrade sand to between 96 to 98% of modified Proctor density and the 600- to 900‑mm subgrade sand to between 94 to 96% modified AASHTO density, with a minimum of 10 passes. The rate of increase in CIR (g) values from one to 20 passes was about 0.18 g per pass, and from 20 to 40 passes was about 0.03 g per pass. DCP tests indicated significant increase in shear strength of soil between 800 to 1,900 mm below the surface in the first 10 passes and no marked increase after 20 passes.<br><h2>Project Technical Paper:</h2>Jumo, I.and Geldenhuys, J. (2004). "Impact compaction of subgrades- experience on the Trans-Kalahari Highway including continuous impact response (CIR) as a method of quality control." 8th Conference on Asphalt Pavements for Southern Africa, 12–16 September 2004, Sun City, South Africa.<br><h2>Date Case History Prepared:</h2>November 2012</p><p></div></p></p>