At Keystone Foundation Repair we specialize in Drilled Hollow Bar Piles and Anchors. Hollow bar anchors are a threaded drill rod with sacrificial bits that are advanced to the desired depth. The hollow bar anchors are grouted through the center of the drill string and out the end of the sacrificial bit. This process creates a cement column that is reinforced in the center with the steel drill string. Hollow bar anchors can be used as tie backs, tie downs, rock anchors, soil nails and micro piles. Their versatility and compact equipment meet the needs of many challenging applications.
There are three types of drill bits used on hollow bars used for micropile installation. The highly versatile carbide cross cut bits, carbide button bits for hard rock and stepped clay bits for cohesive clay. The type of drill bit and size is based on the soil type and the desired capacities. Larger boreholes provide higher load carrying capacities and more grout cover. The grout cover protects the anchor bar from corrosion but galvanization is also available. Depending on the soil type, a 3” diameter bit with grout pressure can create a 6” to 8” diameter grout column. Production rates are higher when using hollow bar systems as compared to traditional drilled anchors. This is especially true when drilling at sites with low headroom or where there is the risk of bore hole collapse.
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Advantages of Micropiles Include:
- Hollow bar capacities can reach 150kips each and greater capacities can be reached when used in clusters.
- Small hollow bar drill rigs are capable of operating in confined spaces and even indoors.
- Hollow bar anchors are capable of socketing into bedrock and driving through obstructions.
- Hollow bar anchors offer high corrosion resistance as the steel bar is encased in grout.
- No casing is required to keep the bore hole open and additional capacity is achieved through the skin friction of the grout that is injected into the soil under pressure.
- Casing can be inserted to keep the grout column intact in karst conditions with large voids.
See case studies of our drilled micropiles.