<p><p><figure id='attachment_2614' style='max-width:949px' class='caption aligncenter'><img class="wp-image-2614 size-full" src="https://www.geoinstitute.org/sites/default/files/geotech-tools-uploads/…; alt="Schematics showing the used of Micropiles to stabilized slope (left) and as earth retention system (right)." width="949" height="349" /><figcaption class='caption-text'> Armour et al. (2000)</figcaption></figure><h2>Basic Function:</h2>Micropiles develop a load carrying capacity by means of a bond zone in soil, bedrock, or a combination of soil and bedrock.<br><h2>Advantages:<em> </em></h2><ul> <li>Can be drilled through all ground conditions at any angle</li> <li>Minimal disturbance to soil and adjacent structures</li> <li>Minimal noise disturbance during construction</li> <li>Smaller amount of spoils created than large diameter piles</li></ul><h2>General Description:</h2>A micropile is a bored, grouted-in-place deep foundation element containing a steel reinforcing bar that develops its load carrying capacity by means of a bond zone in soil, bedrock, or a combination of soil and bedrock. Micropiles are small in diameter (typically &lt; 12 inches) and typically at least 40% of the load is carried by the steel reinforcement and the remainder by the grout surrounding the bar. Due to their small diameter, micropiles develop axial capacity in skin friction due to the bond between the soil and grout and essentially have equal tensile and compressive capacities. Toe resistance is typically neglected. They can also accept lateral loads and can be designed to resist bending and shearing. Most are installed to depths less than 100 feet although micropiles have been installed to depths of 200 ft. Capacities routinely reach over 200 tons in soil and over 500 tons in rock.<br><h2>Geologic Applicability:</h2><ul> <li>Can be installed in a wide variety of soil types and conditions.</li> <li>Suitable for sites with variable conditions such as boulders, buried utilities, and irregular lenses of competent and weak materials.</li> <li>Sites with karst and running sands are also viable for improvement by micropiles.</li></ul><h2>Construction Methods:</h2>Drill rigs typically used for micropile installation are hydraulic rotary (electric or diesel) power units. They can be track mounted allowing for maneuverability on difficult and sloped terrain. Specialized drilling equipment is necessary for sites with low headroom (the equipment can be used in areas with less than 10 ft clearance). Otherwise, the same type of equipment used for ground anchors and grouting projects can be used for micropiles.<br><h2>Additional Information:</h2>Micropiles can be categorized by their behavior as either Case 1, where the micropiles are directly loaded to provide a structural support, or Case 2, where the micropiles are used to circumscribe and internally reinforce a coherent composite reinforced soil structure. Five different techniques exist for installation of the micropile based on the pressure of the grout, location of the packer, use of casing during construction, etc. As a result, the micropiles can be further classified depending on the method of grouting (A, B, C, D or E). The classification system consists of a two-part designation: a number, which denotes the micropile behavior, and a letter, which designates the method of grouting (e.g. Type 1D or Type 2C).<br><h2><strong>SHRP2 Applications:</strong></h2><ul> <li>New Embankment Construction</li> <li>Embankment Widening</li></ul><h2>Example Successful Applications:</h2><ul> <li>Littleville Landslide – AL</li> <li>Blue Trail Landslide, US HW 26-89 – WY</li> <li>Caltrans North Connector I 110 – Los Angeles CA</li></ul><h2>Complementary Technologies:</h2><ul> <li>Can be used alone or with other technologies.</li> <li>Used with soil nails, ground anchors, grouting, and retaining walls.</li></ul><h2>Alternate Technologies:</h2>Conventional driven piles, drilled shafts, underpinning pits, grouting, and ground anchors.<br><h2>Potential Disadvantages:</h2><ul> <li>High slenderness ratio and their need for high levels of drilling expertise and contractor experience.</li> <li>Not suitable for soils where liquefaction is a concern, but the design can be adapted in certain situations.</li></ul><h2>Key References for this technology:</h2>Bruce, D.A. and Juran, I. (1997). "Drilled and Grouted Micropiles: State of Practice Review, Volumes I, II, III, and IV." Prepared for the Federal Highway Administration, Publication Nos. FHWA-RD-96-016. –017, -018, and –019, July.</p><p>Sabatini, P.J., Tanyu, B., Armour, T., Groneck, P. and Keeley, J. (2005). “Micropile Design and Construction (Reference Manual for NHI Course 132078).” Federal Highway Administration, Publication No. FHWA-NHI-05-039, December 2005.</p></p>