Consolidation of cohesive soils can be a very time consuming process. Where desirable, the consolidation can be expedited by installing vertical drains referred to as 'wick drains'. Wick drains work by promoting horizontal dissipation of excess pore pressures instead of vertical excess pore pressure flow in traditional 2D consolidation problems. In all cases, the soil has to be subjected to a surcharge in order for the wick drains to be effective. Hansbo (1979) has outlined a procedure to estimate consolidation times for wick drain assisted consolidation.
Wickdrain 1.0 is a program that evaluates consolidation times and settlements for wick drain assisted consolidation due to a surcharge according to Hansbo (1979). The program also computes the required consolidation times for traditional 2D consolidation for single or double drainage conditions. Consolidation settlements are also calculated for both the recompression and the virgin compression zones. Only one soil layer can be specified.
Historically, the design of structures on soft compressible soils (clays) has created problems for civil engineers. Construction without some sort of soil treatment is usually impractical due to unpredictable long-term settlement. Simple surcharging as a soil consolidation method can take many years. Although surcharging increases water pore pressure, settlement can take considerable time, as the water lacks easy path to leave the soil.
The solution: Soil consolidation using prefabricated vertical drains (also commonly called wick drains or band drains) can reduce settlement times from years to months. Most settlement can occur during construction, thus keeping post-construction settlements to a minimum.
Consolidation of water-saturated, fine-grained soil occurs very slowly because the low permeability of these soils impedes the escape of pore water from the soil voids. Even under large temporary surcharge loads, settlements can take years because of this slow water movement and the great distance the water must move to exit the soil. The installation of prefabricated vertical drains greatly reduces the distance the water must move to reach a free drainage path, and therefore greatly increases settlement rate. Drain spacing may be adjusted to match the required settlement time.
* Please note this is a software package which can be downloaded to the end user's computer. See 'Download Free Sample' for a screenshot of the program.