| In a wide range of soil support engineering, anchor (soil nails) are widely used, but wealso met some problems, such as mortar anchor used in foundation pit support engineering,mortar solid ification takes time so that the engineering is not supported timely, therefore, theseoften cause accidents in geotechnical engineering; In addition, there are a lot of temporarysupport of anchor (soil nails) being unrecycled, lead ing to pollution of formation, and in theloose rock and soil slope , bending ability of anchor (soil nails) and cable can not meet therequirements of slid ing, resulting in slope instability and so on. To some extent, theseproblems affected the applica tion of the bolt. However, in the case of the self-screwed tubebolting hold ing benefits of the general anchor, it has not only a greater dending capacity, but italso can timely support and be recycled, therefore, it has important practical significa nce tostudy in-depth on the self-screwed tube bolting(SSTB).By using cavity expansion theory to create modified Cambridge model, this articlecombined with numerical simulation methods, and provided an in-depth theoretical analysis ofthe mecha nism of SSTB, so obtaining some conclusions, that the surrounding soil holds theeffect of extrusion-dense during insta lla tion of SSTB. In one word, there are several differentmecha nical state s of the region in soil around the pole , that is, disturbed areas, weakdisturba nce areas and undisturbed areas. Then in full range of SSTB length, the plastic zonedistribution of the surrounding soil is basically the same, and the area is approxima te 0.77times larger than the nominal dia meter of self-screwed tube bolting; Secondly, close to theouter end of SSTB, the disturbed area is about 1.44 times larger than the nominal dia meter, thelength of this section is about one third of full-length, and when the dista nce from the outerend of SSTB is farther and farther, the disturbed area becomes about 1.15 times larger than thenominal dia meter, and the section is approxima te seven fifteenths of full-length, then, near the bottom part of SSTB, the disturbed zone is about 1.25 times larger than the nomina l dia meter,and the length of the section is about one fifth of full-length.According to the failure mode of SSTB, that is cylindrical shear failure along theinterface of the rod and the side walls of the surrounding soil, this article educes the anchoringformula of single self-screwed tube bolting, then, finds that the anchoring force is not onlyclosely related to its insta lled location, its own parameters and the basic physical andmecha nical parameters of soil, but it also has close relation to plastic volumetric strains(ε_v~p )reflecting the plastic deformation of soil, at the same time, it is proved that SSTB can get alarger initia l anchoring force after insta lla tion. In addition, the experimental study finds thatthe anchoring force decreases exponentially with an increase in soil moisture when soilmoisture changes between optima l and saturated moisture content, however, when nearlysaturated, the anchoring focre basically tends to zero, and it is conducive to guiding theconstruction of SSTB.Finally, combining with Zha ngjiabao station Line 2 Xi'an Subwa y foundation pit supportengineering, and according to the anchoring focre of SSTB and the displacement of pile top,this article finds that SSTB hold larger initia l anchoring forces, and completely can meet theengineering requirements, so that it can pla y a role in a timely supporting; Moreover, it alsoconstrains effectively the displacement of pile to ensure the stability of the pit slope. These areconsistent with the theoretical analysis , therefore, intended purposes that guid the engineeringapplica tion of SSTB can be reached. |
