Model Test And Numerical Simulation Research On Bearing Capacity Characteristics And Failure Modes Of Underreamed Ground Anchor

Underreamed ground anchor is a new type of anchor internationally. Engineering practices have shown that compared with traditional tension-type anchors, underreamed ground anchor has higher bearing capacity, lower costs, more environmental characteristics, and more secure. These advantages make it receiving increasingly concern from geotechnical engineering area. With the construction scale increasingly expanding, the demand of ground anchors with high capacity continuously increases, the amount of engineering applications of underreamed ground anchor gets the same trend. However, up to now, whether accumulation of its engineering test data or researches about its bearing characteristics, failure modes, design theory or method, which are few. People lack deep and overall knowledge of underreamed ground anchor, its research is still at the exploration stage. Therefore, it’s necessary to make a systematic research on the working behavior of the anchor of new type. In this dissertation, a systematic research on the working behaviors of underreamed ground anchor, such as bearing characteristics, failure modes, etc., was applied with model test, numerical simulation, theory researches, etc. The results have great scientific and practical value in engineering.The studies of this dissertation consist of following parts:1)The bearing capacity characteristics of underreamed ground anchors under vertical pullout were researched by model tests. The test results exhibited three different failure modes depending on the embedment ratio, the deep mode, the shallow mode, and the transitional mode. The Q-S curves of deep underreamed ground anchors perform monotonous upward trend. And deep underreamed ground anchors are the most important shape in engineering applications. Based on model tests, the effect factors to ultimate capacity of underreamed ground anchor were analyzed. The results showed the diameter of underreamed section of the anchor have the greatest impact on the ultimate bearing capacity. Furthermore, through the analysis of bearing capacity, the concept "capacity ratio" had been proposed. This important concept could be used to analyze the material cost of underreamed ground anchors.2)The failure modes of underreamed ground anchors under vertical pullout were researched by model tests and half model tests. The failure mode of deep underreamed anchor was known as local shear failure, the rupture surface was completely limited inside sandbed and presented like a balloon. Shallow and transitional underreamed ground anchors both performed general shear failure, and the rupture surfaces respectively presented like a reversed bell and a vase. Based on the discoveries, differentiating underreamed ground anchor type based on the failure modes was theorized. Moreover, the importance of deep underreamed ground anchor was demonstrated.3)Based on the results of model tests, the effect factors of bearing capacity characteristics and failure modes of underreamed ground anchors under vertical pullout were also researched through numerical simulation. By analyzing the results of numerical simulation, the effect factors of bearing capacity characteristics and failure modes of underreamed ground anchors were nearly the same as those of model tests. And based on above conclusions, the effects of cohesion and friction angle of foundation soil to the bearing capacity characteristics and failure modes of underreamed ground anchors were also researched. The simulation results illustrated that with the value increase of cohesion and friction angle, the ultimate bearing capacity of underreamed ground anchors inhanced. In addition, the plastic zone and rupture surface of foundation soil both performed diversificatedly.Based on above research contents, the following research results obtained:1) Based on the significant differences in bearing capacity characteristics and failure modes between shallow and deep underreamed ground anchors, the theory of deep, shallow, and transitional cylindrical underreamed ground anchors could be differentiated according to their embedment ratio proposes for the first time.2) According to the data accumulated in model tests and numerical simulations, the Q-S curves of deep cylindrical underreamed ground anchors presenting monotonic rising trend was discovered for the first time. 3) According to economic analysis, the concept of capacity ratio of anchor was proposed for the first time. This concept could demonstrate the material economic benefit of underreamed ground anchors and had important significance to engineering design.