Study On Mechanical Characteristics Under Additional Load And Disease Mechanism Of Soil Anchor

Bolt is widely used in such engineerings as slope reinforcement, slope stability, deep foundation pit supporting, structural strengtherning, chamber stability, et al.. With different effects and transition of environment, however, the use status of the bolt produces change subsequently, such as prestress loss, corrosion and rupture of slurry and steel etc., and these diseases have great impact on on bolt's work status. So, it is rather important work to investigate the defects of bolt engineering, research the mechaniim of the defect and analyze the in-service bolt's work status. In this paper, according to the results from model test, numerical simulation and theoretical analysis, the force characteristics and breakage feature of the anchored bar in soil under imposed load is studied, the interface disbondment mechanics is analyzed, as well as the force characteristics under the effect of water, the loss law of prestress, and the mechanism of rusting and corrosive expanding are discussied.The following contributions have been made:1. For the full bonded anchor in the slope, the downsliding force firstly loads on the anchor head and the part of anchor at slide face, and then transfers to both sides along the anchor due to shearing action between anchor and soil. The long-term effect of ground load has great influence on the slope stability, and the effect in a very short time is less. A full bonding anchor in slop is a tension and flexural composite member, and tension is the main.2. In the same slope, the antislip behavious of pressure-type anchor is stronger than that one of tensile-type, and the load shared by the former is about 1.5 to 2.0 times as much as that one of the latter. During the course of loading, with increasing time the force loaded on the upper anchor gradyally decreases, and that one loaded on the lower anchor increases. Under the coupling action between additional load from ground and water, the extent of sliding mass enlarges, the whole stress state of anchor gradually changes from tension to bend, and the compact-bending effect on the upper anchor is most obvious.3. Based on the model test results of the full bonded anchor, the finite element analysis model of anchor was established. The computing results show that without additional load the stress of anchor mainly results from dead- weight of soil; when the additional load gradually increases, the gravity center of stress on the bolt reinforcement system slowly shifts from lower to upper anchor, and the maximum stress occurs on the the middle part of anchor.4. The results of pull-out test show that the ultimate pull-out resistance is getting smaller with increasing water content, and the sudden increase of water content causes the pre-stress sudden increase in a short time, and then decrease again.5. Using Stang's theory, a calculation model of grouting mass on anchored bar in soil and soil interface debonding is set up. The criterion about grouting mass of anchored bar in soil and soil interface debonding is reduced in the paper. The results show that when the tensile stress of anchor reaches the ctitical value, the shearing force also reaches the ctitical one on anchorage zone out end with cracking interface, and then the maximal shearing stress changes to the anchorage zone out end with crack propagation, and finally the whole anchorage system debonds, the bolted mass is extracted.6. According to Phillips formula, the crack expansion theory of interface debonding of lanchor grouting mass is put forward. The analysis shows that the debonding velocity of anchor interface with cracks is more quickly than that one of a perfect interface, and when one or more individual anchor element appears to be total debonding, the ultimate pullout capacity significantly reduces because of the decrease of interaction length between the anchor and the soil.7. According to interface characteristics of the anchored bar in soil, the soften boundary later theory of interfacial debonding between the rod and grouting mass is proposed. For deformed bars, the relative slip occurs between the rod and grouting mass after the adhension is destroied, the oblique extruding force of rib causes wedging action for grouting mass, which makes the grouting mass crushed, and induces diagonal and radial cracks in the grouting mass. Those cracks developes to longitudinal direction and surrounding with increasing load, which results in the decreas in shearing strength of the grouting mass, a soften boundary layer surrounding the rod is formed. In this state, the bonding between steel bar and grouting mass will be degenerated.8. On the basis of steel corrosion principle, the different working environments of anchor are analyzed. In a no corrosive environment, the main rusting reasons of reinforced bar are no or little mortar, uneven mortar density, cracks in anchoring section, bended bolt-bar, et al.. The critical condition of corrosion expansion crack is suggested according to elasticity theory.