<p><p><figure id='attachment_2618' style='max-width:670px' class='caption aligncenter'><img class="wp-image-2618 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematic cross section of partial encapsulation of subgrade soils along Interstate 37 in Texas." width="670" height="304" /><figcaption class='caption-text'> Cross Section of Partial Encapsulation on Interstate 37 in Texas (Figure courtesy of Wyoming Department of Transportation)</figcaption></figure><h2>Basic Function</h2>Partial encapsulation is used to prevent water from entering or exiting through expansive soils from pavement surface, joints, cracks, and edges in subgrade.<br><h2>Advantages:</h2><ul> <li>Relatively fast and easy placement</li> <li>Prevents/minimizes the damage caused by moisture movement in long term</li> <li>Suitable for rapid renewal of transportation facilities</li> <li>Provides long-lived facilities</li></ul><h2>General Description:</h2>Partial encapsulation refers to the placement of geomembrane horizontally, vertically, and horizontally and vertically combined as barriers to minimize or prevent moisture from entering or exiting through expansive soils.<br><h2>Geologic Applicability:</h2><ul> <li>Partial encapsulation can be used to minimize the postconstruction problems encountered in expansive soils.</li> <li>The geomembrane is used as a moisture barrier and is placed in horizontal, vertical, or in both directions.</li> <li>Preventing moisture from entering or leaving expansive soils minimizes or prevents pavement distresses, formation of cracks, and slab distortion.</li></ul><h2>Construction Methods:</h2>The depth of the moisture barrier is determined based on the information available for the climatic conditions and the soil properties for a specific site. The designer selects the criteria for the allowable moisture change within the encapsulated soil for a specified time and then determines the thickness and the required diffusion coefficient of the membrane. The vertical depth of geomembrane placement depends on the active zone of moisture activity. Basically,<br>the width and depth of excavation vary from 0.065 to 0.1 meters and 1.5 to 3.0 meters, respectively. A double-layer geomembrane is laid into a trench as it is tougher and less likely to be damaged from construction and/or by tree root penetration. The geomembrane is placed using a specially designed dispenser, carried horizontally. During placement, it is vertically passed around a bar at a 45 degree angle. The coated side is often placed against the trenchwall to avoid any damage from backfilling operation. The placement side of the geomembrane is on the shoulder side of the trench rather than the pavement side. The flowable backfill is composed of medium-graded sand, a small percentage of cement, and a large portion of high fly ash and water is poured into the trench in such a way that the geomembrane will not be damaged.<br><h2>Additional Information:</h2>Current design methods for the geomembrane are based primarily on empirical evidence and rational principals. No standard construction method exists. The available construction methods are site specific and based on experience of the professional. The standard construction methods should be developed to address all of the site conditions and long-term performance of the product. Quality control during the installation of the geomembrane is crucial to the performance of the product.<br><h2>SHRP2 Applications:</h2><ul> <li>Embankment and roadway construction over unstable soils</li> <li>Roadway and embankment widening</li> <li>Stabilization of pavement working platforms</li></ul><h2>Example Successful Applications:</h2><ul> <li>Geo-composite membrane effectiveness as a moisture barrier, Virginia I-80 rehabilitation project in Wyoming</li> <li>Geomembranes moisture barrier, Highways, Roads, and Streets in Australia</li></ul><h2>Complementary Technologies:</h2>Partial encapsulation may be used with cement-stabilized backfill.<br><h2>Alternate Technologies:</h2>Lime or cement-stabilized surface, over-excavation and replacement, and pile-supported embankments or construction platforms.<br><h2>Potential Disadvantages:</h2><ul> <li>Lack of simple, comprehensive, reliable, and non-proprietary analysis and design procedures</li> <li>Lack of established engineering parameters and/or performance criteria</li> <li>Lack of easy-to-use tools for technology selection</li></ul><h2>Key References for this Fact Sheet:</h2>Holtz, R.D., Christopher, B.R. and Berg, R.R. (2008). Geosynthetic design and construction guidelines, U.S. Department of Transportation, Federal Highway Administration, Washington DC, Report No. FHWA-NHI-07-092, 592p.</p><p>Steinberg, M. L. (1998). Geomembranes and the control of expansive soils in construction, McGraw-Hill, New York, 222p</p></p>