1- 1. General.

a. Tempomry dewatering systems. Dewatering and control of groundwater during construction may be ac­complished by one or a combination of methods de­scribed in the following paragraphs. The applicability of different methods to various types of excavations, groundwater lowering, and soil conditions is also dis­cussed in these paragraphs. Analysis and design of de­watering pressure relief and groundwater control sys­tems are described in chapter 4.

b. Permanent dminuge systems. The principles and methods of groundwater control for permanent struc­tures are similar to those to be described for construc­tion projects. A method often used for permanent groundwater control consists of relief wells (to be dis­cussed subsequently in detail) installed beneath and adjacent to the structure, with drainage blankets be­neath and surrounding the structure at locations below the water table as shown previously in figure 1-2. The water entering the wells and drainage blanket is carried through collector pipes to sumps, pits, or man­holes, from which it is pumped or drained. Permanent groundwater control may include a combination of wells, cutoffs, and vertical sand drains. Additional in­formation on the design of permanent drainage sys­tems for buildings may be found in TM 5-818-1/AFM 88-3, Chapter 7; TM 5-818-4/AFM 88-5, Chapter 5; and TM 5-818-6/AFM 88-32. (See app. A for ref­erences.)