Research On Design Parameters Of Prestressing Anchor For Underground Projects

Roch anchoring enables surrounding rock in underground projects to constitute asupport rather than a load, so as to take the full advantage of self-bearing of thesurrounding rock and stabilize the culvert with minimum extra support. Currently, thereis no systematical design theory and calculation methods in the undergroundengineering prestressing tendon support.Based on the underground engineering prestressing tendon support, this thesis isattended to provide anchorage support principles, design theories, calculation methodsand other key design parameters in order to provide a theoretical basis for the design ofprestressing tendon. The main contents are as follows:①In combination with weak rock, large span cavern, deformation mechanism ofascent prestressing surrounding rock and the design mechanism of tendon initiativeanchoring, this thesis will make elastic-plastic analyses on cavern surrounding rockfrom the perspectives of surrounding rock stability and deformation control ofsurrounding rock.②On the basis of the elastic-plastic analysis and tendon initiative anchoringprinciple, this article is meant to provide theoretical basis on cavern’s stability analysis,anchor layout methods, confirmation of anchor length and anchorage spacing throughanalyzing the mechanism of plastic deformation, yielding sections, anchor groups andinitiative anchoring.③An effective method of determining the design anchor external loading anddesign anchorage force will be put forward. On the basis of elastic-plastic analysis ofsurrounding rock, we can figure out the required supporting force by analyzingsurrounding rock stability, and then determine the maximum allowable convergencevalue by means of analogy.The design anchor external support should satisfysurrounding rock stability and deformation control requirements.Finally,we candetermine whether the design anchorage stress is reasonable on the condition that thedepth of deformation impact on base surrounding rock is thicker than the loosen zone;the key design parameters can be determined by estimating whether the anchorage forcesatisfy the current specification requirements.④The method to determine the anchor length in underground projects will beproposed. The anchor length contains the length of anchoring section,and free segment length. The length of anchoring section can be determined by the strength betweencementing materials and cave surrounding rock, forms of anchoring section, safetyfactors,anchoring body diameter,and the formation mechanical properties ofsurrounding rock,etc; The free segment length of anchor cables can be determined bysurrounding rock’ elastic-plastic stress redistribution features, the thickness of loosenzone, the anti-shearing strength of surrounding rock, and surrounding rock structurefeatures,etc.⑤Taking Wushaoling tunnel for example, as the high stress soft tunnel, we useprestressed anchor cables as the early support system.