Diameter test and pull-out test of enlarged head anchor

Diameter test In order to realize the high-pressure jet grouting drill bit soil layer expansion according to the design requirements, our supervision department proposed that the hole expansion grouting test was carried out under the condition of 3 conditions for the hole expansion pressure. Test conditions: The test soil layer is silty clay, the hole expansion depth is .m, clean water is used to expand the hole, and cement slurry is injected after the hole expansion is completed (water-cement ratio is .). Test results: In a clay environment with a depth of .m, The part of the enlarged head where the reaming pressure reaches 3 exceeds the diameter required by the design document. ) Pull-out test According to the geological data, the design unit drafted four representative points on site and provided relevant technical parameters. The construction unit carried out anchor construction at the representative points according to the design requirements. As a head expansion test anchor test, the anchor construction process was smooth. After the rod reached its age, a pull-out test was conducted on the test anchor. The results showed that the pull-out force met the requirements. Difficulties encountered in large-area construction and solutions. Both the enlargement of the head section diameter test and the bearing capacity test met the design requirements. Large-area construction was decided on site. What followed was unexpected problems. It was not as smooth as the construction of the test anchor. The actual underground soil condition was more complicated than imagined. The soluble sandy soil was unevenly distributed, the density of boulders was high, and the replacement layer was not gravelly. , there are certain difficulties in hole formation, anchoring, and grouting, and it is difficult to guarantee the diameter of the expanded head of the high-pressure rotary jet enlarged head soil anchor. When drilling, if an isolated rock is encountered, the high-pressure jet drilling rig cannot continue drilling. ) Collapse hole solution When dealing with the foundation, the design unit determined that in order to meet the foundation bearing capacity requirements, the graded gravel filling cushion method was used in part of this project to reinforce the soft soil and medium soft soil. However, during the anchor construction process, it was difficult to anchor the anchor in the graded gravel layer. The reason was analyzed because the graded gravel area collapsed after the drilling rig was pulled out, causing the anchor hole to be blocked. After repeated discussions on the construction process of this project, the best choice is to use sleeve wall protection in the gravel replacement area. In the gravel replacement and filling area, steel casing and hole drilling technology are adopted. The hole is first introduced, then the steel casing is lowered, and then the construction is carried out according to conventional techniques. When the depth of the pipe is not too deep, the double casing method can be used for construction according to the site conditions. After the hole is formed, the inner casing (the other pipe) is buried in the hole and the outer casing is pulled out. b) Guarantee measures for enlarging the diameter of the head. Before the completion of construction, the three high-pressure jet spray enlarged head soil anchors all adopted the construction process of two water and one slurry. In order to check the quality of the enlarged head of this process, we used two of the anchors to check the quality of the enlarged head. The core is pulled symmetrically at four points within the range of the rod. When the core was extracted, it was found that the core slurry at the expansion head was discontinuous, mixed with mud and sand, and even the cement core could not be extracted. After expert analysis, most areas of the enlarged head section are located in highly weathered granite. Strongly weathered granite is prone to disintegration when exposed to water and is prone to collapse holes, causing the diameter of the enlarged head to fail to meet the diameter requirement of the design document. After repeated discussions, we decided to directly use the diameter drill bit of the mechanical reaming drill to expand the hole. After the hole expansion was completed, we immediately switched back to the high-pressure jet drilling rig and re-expanded the hole with cement slurry twice. On the one hand, the use of mechanical reaming drills can ensure the enlargement of the head size, reduce the shear stress of the soil around the hole, and reduce the probability of hole collapse. On the other hand, the water-cement ratio used for hole expansion grouting is. During the hole expansion process, the cement slurry penetrates into the soil layer outside the hole wall, and a layer of cement will be formed on the hole wall. Cut off, which plays the role of stabilizing the water pressure in the hole. Furthermore, the cement slurry with a larger specific gravity can effectively discharge the drilling residue and improve the quality of subsequent grouting. Immediately after the first cement slurry expansion, perform the second water-cement ratio grouting to reinforce the expansion wall. In later construction comparisons, the grouting filling coefficient of this type of anchor returned to normal. During the core pulling test and pullout force test, there were no anchors that did not meet the requirements. ) When encountering boulders, since the boulder rate at this site reaches .3 and the line boulder rate reaches . , during the construction of the non-expanded head section of the anchor, boulders are encountered, which will cause problems in the construction of the anchor rod with high-pressure jet spraying and enlargement of the anchor rod. trouble. High-pressure jet drilling rigs cannot continue drilling in hard rocky geology. According to the design documents, there are still a small number of anchors in this project that are type 1, that is, ordinary rock anchors. This type of anchor drilling requires the use of a fully automatic hydraulic down-the-hole drilling rig. When the high-pressure jet-jet drilling rig cannot drill down, a fully automatic hydraulic down-the-hole drilling rig is used to penetrate the boulder, and finally a high-pressure jet-jet drilling rig is replaced in the enlarged head section. During the actual construction process, it was discovered that the elevation of some isolated rocks was just at the expanded head section. High-pressure jet drilling rigs and mechanical reaming drills cannot form enlarged heads in hard rock geology such as boulders and slightly weathered granite. Then the high-pressure jet spray enlarged head soil anchor does not have an enlarged head or the length of the enlarged head section does not meet the design requirements? In order to solve this practical problem on site, the project department actively contacted the company's chief engineer. After calculation and analysis, the following conclusions were drawn: If the boulder is in the expansion section and the diameter is smaller than The length of the reaming section is not included. If the boulder is in the reaming section and the diameter is larger than that, then the down-the-hole drilling rig will be used to drill through the boulder and then the hole will be expanded. The length of the broken boulder section will be calculated as the length of the enlarged head. This special case of anchor not only utilizes the lateral friction between the anchoring section of ordinary rock anchors and the soil, but also utilizes the end support force of the anchor in the expanded head soil layer.