Consolidation theory states that decreasing the spacing of prefabricated vertical drains will decrease the time required to achieve primary consolidation. Previous field tests have shown that there exists a "critical" drain spacing, which is the point at which further spacing decrease does not decrease the time of primary consolidation. This "critical" spacing is thought to be due to disturbance effects from installation of the drains. Previous studies have found that the "critical" drain spacing may be dependent upon soil layering and drain and mandrel dimensions. Thin, interbedded clay layers have been found to be affected greatly due to the smear zone, while few tests have been conducted to determine the validity for thick bedded clays. Currently two design and analysis methods are in existence, neither of which is standardized. The two methods are the modeling of the smear zone, which requires knowledge of soil parameters within that zone, and the modeling using a back-calculated Ch/Cv ratio.In order to evaluate the validity of these design methods and to obtain more data that can be used in determining the relationship between anchor type, drain spacing, and soil profile, full-scale field tests were conducted at Mountain View Corridor in Lehi, Utah. These field tests were performed along a test section that was divided into sections containing 5.8, 5.0, 4.0 and 3.0 ft triangular spacings and rebar or plate anchors. By using the smear zone model, with a Ch/Cv ratio of 1.25 and ds of 3.07 times dm, the time rate of settlement was able to be predicted reasonably well, while using the back-calculated Ch/Cv ratio, with no smear zone, also predicted the time rate reasonably well. From the testing, it was found that the thick clay profile can facilitate closer spacings than a thin clay profile. Also, it was found that the rebar anchor type causes about twice the disturbance of the plate anchor. The results helped validate the existing models and show that the effectiveness of the drains is dependent upon drain spacing, soil profile, and anchor type



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering



Date Submitted


Document Type





wick drain, radial consolidation, soft clay, mandrel