Research On Experiments Of Cement-soil Mixing Anchor

With the rapid development of urban construction, the use of the underground spaceis attached much more importance. The current depth and the area of the basementfoundation pit are deepened to an area of increasing direction. The high-rise buildings withlarge basements in cities are generally located in the dense cluster of buildings, so the sitesaround the basement foundation pits are small. And the engineering geological conditionsof the most coastal cities are very poor, so it is very difficult to improve the constructiontechniques and at the same time, it will increase the costs of the foundation pit supportsignificantly. In this case, soil anchors are more and more popular in the geotechnicalengineering world, because of its advanced mechanical principles, high adaptability,apparent economic benefits, easy and convenient construction, etc.Currently, anchoring method is often used during the foundation pit construction inNingbo. First, the holes with certain diameters are drilled in the soil. Then put thereinforced bodies in the holes and pour the cement into the holes. After some time, theywill form anchorage bodies together. The whole process needs at least four steps includingdrilling holes, withdrawing the drill pipes, adding reinforced bodies and grouting. Such ananchor construction process is very complex, costly, inefficient and the bearing capacity ofthe anchor is very small. To this end, for the conditions in the areas of soft clay and thecharacteristics of the market demand, the Soil Improvement Center of Ningbo Universitydeveloped a kind of new soil anchor with a more simple process which is used in thefoundation pit support. It is called the cement-soil mixing anchor. And the anchoringmethod has greater bearing capacity, stronger stability, better performance of controllingthe deformation, more simple techniques, better controllability, higher constructionefficiency and lower costs of the anchors.In this paper, by doing the field tests and the numerical simulation, studied the stressmechanism of the cement-soil mixing anchors and analysed the bearing capacity and thecharacteristics of the deformation of the anchors. By designing a series of field tests,including the pull-out type tests of the reinforced bodies, the cyclic loading tests, thepull-out type tests and the electrometric tests of the anchors, etc., obtained the bearing capacity of the reinforced bodies, the combination of the fittings, p-s curve, the stressdistribution relationship along the anchor, etc. By using the finite element softwareANSYS, establishing the finite element solid models to analyse the numerical simulationof the cement-soil mixing anchors and comparing with field tests, simulated themechanical properties and displacement variation of the anchors on the basis of differentloads, different rod length, different parameters of the cement-soil bodies and different soilmaterials.This paper finally gets the following main conclusions:⑴The shear stress isnon-uniform distribution with different rod lengths, and there is a stress concentration zone.⑵The greater diameters of the anchor cement-soil bodies are, the longer the anchors are,the smaller peak of the shear stress is, the greater the ultimate bearing capacity is.⑶Thecement-soil mixing anchor formula for estimating the ultimate bearing capacity is: Tu=(10.30－1.53α)L.