Discussion about the application of the anchor bar on theslope constructionFu Ming Fu , Zhang TianAbstract:There are some advantages in strengthening slope with the anchor bar, such as low project cost, convenient for construction and so on. It not only meets the requirement of the reliability of the construction, but also is economic and reasonable for the construction.Key words: anchor bar; slope; strengthening1.IntroductionAnchor technique uses strata geotechnical’s shear strength around bolt to deliver structures pulling force or keep strata of the excavation own stability. Due to the use of the anchor rod, Anchor strata produce compressive zone and have reinforcement effect to strata, can enhance the strength of strata, improve mechanical properties of strata, make structure and stratum together formed a kind of work together complex. Anchor system can effectively sustain tension and shear, improve shear strength of the potential sliding surface, so it can effectively prevent slope to produce sliding damage.Fig 1 after excavation of the slope2.Project profileThe length of a slope is about 60m, the most slope height is about 23m,the angle up to 50°~ 75°, a five-layer frame structure buildings is far from about 1.5 to 4m at its base edge, its foundation is artificial bored pile and its bearing stratum is in weathered phyllite. Due to the strong weathering of rocks, it was chunky, loosely structured, multi-muddy filling. It has residual slope deposits of silty clay overlying and local folder with a pulpy, low strength. Slope hadcollapsed at various locations, it is vary dangerous to the building, so we need to reinforce the slope, and we use stone concrete retaining wall and bolt to support it.3.Bolt retaining and protecting design3.1Bolt design（1）all formation of anchor use whole length bond-type, the binder materials are ordinary cement mortar, the mortar strength grade is M30, the anchor length L is 10 meters, the slope height h is 9 meters. Anchoring section length is 5m.（2）According to the construction condition and the needs of the process, the layout form of anchor use quincunx, and in order to make the anchoring force in the role of surface rock surface with uniform, the two adjacent line bolts should be staggered arrangement.（3）The anchor’s number according to /3.24 per meter to calculation, the anchor length is L, a tolal of 252. The diameter of drilling holes is φ90,the number of drill according to (L-0.1)m per hole to calculation, M30 grout number according to average 0.052m3per hole to calculation.（4）The two adjacent rows vertical spacing of anchor take 2.55m, horizontal spacing take 2.55m. The dip angle of anchor: with the angle of horizontal line is 20°, and drilling down with this Angle.（5）Anchor use the steel bar, which is HRB400 level, 28mm diameter.3.2Anchor calculation（1）The calculation of lateral geotechnical pressure[1][2]When the supporting structure to leave in rock and earth mass direction migration until to the limit equilibrium state, the geotechnical pressure which is role in supporting structure called active geotechnical pressure. Its calculation method is as follows:For the slope which has no flare structure surface, generally speaking, failure is controled by rock mass strength, the calculation formula is same to the active soil pressure, but cohesive force C take zero, internal friction angle ϕuse eϕ(rock mass equivalent internal friction angle) instead of, according to the standard to selection; rupture angle is 45°+ϕ/2（ϕis rock mass internal friction angle, is estimationed by haircut at the standard of rock mass internal friction angle, reduction factor according to the standard to selection).According to the engineering survey, active rock pressure can calculation as follows:（2）the calculation of anchor tension design value a Q ak N N γ= (1)(2) In the formula: a N is anchor tension design value; ak N is anchor tension standard value; Q γis partial load factor, take 1.3; tk H is the horizontal tension standard value of anchor; αis the dip angle of anchor.Through the calculation, ak N =112.3kN a N =145.99kN（3）the calculation of anchor steel section area(3) In the formula: S A is the steel section area of anchor; ογ is slope engineering importance coefficient(the slope engineering importance coefficient of this project is level 1, take 1.1); 2ξis the tensile working conditions coefficient of anchor bar ( permanent anchor take 0.69, temporary anchor take 0.92); y f is the tensile strength design value of anchor bar(standard value k y f =400a MP , design value y f =360a MP ).According to the calculation, S A ≥0.5883210m -⨯,choose level 3 steel of 1φ28mm,S A =0.6153210m -⨯.（4）The calculation of anchorage body and rock mass anchoring lengthanchoring length should not only meet the requirements which the bond force of formation on mortar and the bond stress of mortar on steel, but also meet the requirements that the Structure design codes the Minimum anchoring length.(4) In the formula: a l is the anchoring length; D is the diameter of anchorage body; rb f is the bond strength eigenvalue of layer and anchorage body, through the experiment or local experience sure, or according to the standard to selection ( this engineering ’s rock mass uniaxial compressive 2222111209tan (45)2090.217175.77/2222e a aE H K kN m ϕγ︒==⨯⨯⨯-=⨯⨯⨯=cos tkak H N α=2a S yNA f ογξ≥1ak a rbN l Df ξπ≥strength is 7.46a MP , belong to soft rock, rock mass structural plane development, rb f take 300a KP );1ξis the bond working conditions coefficient of anchorage body and layer (permanent anchor take 1.00).According to the calculation, a l ≥4.3m, take a l =5.0m.（5）The anchoring length between anchor steel and anchor mortara l ≥ (5) In the formula: a l is the anchoring length between steel and mortar; d is the diameter of anchor bar; n is the number of steel;b f is the bond strength design value between steel and anchor mortar, through the experiment sure, or according to the standard take 2.40; 3ξ is the working conditions coefficient of steel and mortar bond strength(permanent anchor take 0.60）. According to the calculation, a l ≥2.1m ，take a l =5.0m.3.3 The construction technology and key points of anchorThe anchor ’s construction technology is as follows: build-up scaffold ——excavate and clear up the slope surface ——measures to fix position ——drill hole ——washing hole ——bolt put in a certain place ——grout ——colligation the end of the anchor ——flushing the slope surface ——pouring frame space ——Spray seed（1）This slope belong to rocky slope, after excavate the slope 10 cm to the underside of the frame space, set bolt and pouring frame space, then spray grass or seeds after borrowed soil 20 cm in the frame space.（2）the slope should be payed attention to clean up, when construction. The anchor should be placed after wash hole, then put pressure (0.4MPa) and grout. After the mortar fully solidification, colligation steel, cast-in-place reinforced concrete frame space, bend the end of the anchor and bind point by point with the skeleton steel.（3）Before drilling, the hole should be measured to fix position and then do mark. Pitch deviation is less than 150mm, hole depth error is less than 50mm. Try not remold the surrounding rock, when drill. Before Put the anchor, it should be attentioned that blow wash clean the water of the hole and rock powder and so on, and rust removal the body of rod. When grouting, builders 3a bN n df ογξπshould attention the grouting pressure and mortar ratio.Fig 2 anchor field construction drawing4.ConclusionIt is economical to reinforcement slope with bolt, and use the normal equipment, It is not only achieve safe and also economy and rational.(1) Today bolt technology is widely used in the project. It is an effective reinforcement measures to constraints sliding soil with the combining of bolt and concrete slope protection.(2) We must be sure to do geological exploration work of the slope to find out the nature of the rock and hydrogeological situation before reinforcing slope by grouting bolt.(3) Due to the factors of engineering geological conditions, grouting pressure and construction technology, we should be given adequate attention to the quality of construction.Reference[1]Technical code for building slope engineering (JGJ 120-99). The People's Republic nationalstandards. Beijing: China Architecture & Building PRESS.[2] Ying-Ren Zheng, Zu-Yu Chen etc. Engineering Treatment of Slope & Landslide [M]. Beijing：China Communications Press，2007[3] LuoZhenHai. Talk shallowly the application of the anchor at the slope reinforcement[J]. FujianConstruction Science & Technology，2010,06:15-16浅谈锚杆技术在边坡工程中的应用1.引言锚杆技术是利用锚杆周围地层岩土的抗剪强度来传递结构物的拉力或保持地层开挖面的自身稳定。