![]() Heaving or humping the surface is a far more common occurrence. Fortunately large surface collapses are rare.Pulling the reamer or product pipe through the bore hole too rapidly can also result in a surface heave. Heaving can also arise from reaming with a barrel reamer without enough depth, which can result in a displacement of soil towards the surface. This condition can quickly pressurize the formation and cause a heave at the surface. Surface heave or humping is a condition that is usually a result of excess pumping of drilling fluids after a loss of circulation.Another key factor in maintaining suitable product pipe is to ensure that all weld or fusion connections are properly performed and tested. It is also important to make sure that the products specified in the design are actually the products delivered to the work site. The best approach to avoid product-pipe failures is to establish conservative design criteria and follow the pipe manufacturer's guidelines. A failure or damage to the product pipe during HDD installation can occur due to an improper ream bore hole, poor workmanship, and improper HDD design.When a bore hole collapses, there is an immediate increase in rotary torque and pressure and a decrease or loss of circulation. Soft or loose soils present a high risk of collapse during HDD operations. Bore hole collapse severely impacts the chances of success on any HDD project.The improper matching of the downhole tools to the subsurface conditions can also cause line and grade problems. Line and grade problems occur due to faulty tracking and steering or subsurface conditions that prevent or hamper the proper steering.This problem is common in fine-grained rock, frozen ground, and any formation that is resistant to hydraulic fracturing. Hydrolock is a condition that may occur when the circulation from the bore hole is lost and the subsurface formation is resistant to fracturing, resulting in a hydraulic cylinder in the bore hole.Typical obstructions faced during HDD construction are cobbles and boulders, gravel beds, wood, bedrock, and construction debris or foundations. If the bore cannot be changed, an appropriate response can be developed before installation begins. ![]() If identified during planning, the best approach is to avoid the obstacle. Obstructions can cause a failed bore if the drill bit, reamer, or product pipe cannot be advanced past the object.Circulation can be lost very quickly if voids are encountered and cannot be resumed until the void is filled or the path to the void is sealed. These are critical factors for maintaining circulation and bore-hole stability. ![]() An effective drilling-fluids plan and a suitable drilling rate for the subsurface conditions around the bore are required.
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