Discussion about the application of the anchor bar on the
slope construction
Fu Ming Fu , Zhang Tian
Abstract: 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; strengthening
1. Introduction
Anchor 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 slope
2. Project profile
The 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 had
collapsed 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 design
3.1 Bolt 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 0.052m 3 per 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.
3.2 Anchor 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 ϕe (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:
E =1γH 2K =1⨯20⨯92⨯tan 2(45︒-ϕe ) =1⨯20⨯92⨯0.217=175.77kN /m a a
（2）the calculation of anchor tension design value 2222
N a =γQ N ak (1)
H tk N ak =cos αIn the formula: N a is anchor tension design value; N ak is anchor tension standard value; γQ is partial load factor, take 1.3; H tk is the horizontal tension standard value of anchor; αis the dip angle of anchor.
Through the calculation, N ak =112.3kN N a =145.99kN
（3）the calculation of anchor steel section area
A S ≥ οa (3)
In the formula: A S is the steel section area of anchor; γN ξ2f y
γο is slope engineering importance
coefficient(the slope engineering importance coefficient of this project is level 1, take 1.1); ξ2is the tensile working conditions coefficient of anchor bar ( permanent anchor take 0.69, temporary anchor take 0.92); f y is the tensile strength design value of anchor bar(standard value f y k =400MP a , design valuef y =360MP a ).
According to the calculation, A S ≥0.588⨯10m ,choose level 3 steel of 1φ28mm, -32
A S =0.615⨯10-3m 2.
（4）The calculation of anchorage body and rock mass anchoring length
anchoring 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.
l a ≥ ak (4) In the formula: l a is the anchoring length; D is the diameter of anchorage body; f rb 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 N ξ1πDf rb
strength is 7.46MP a , belong to soft rock, rock mass structural plane development, f rb take 300KP a ); ξ1is the bond working conditions coefficient of anchorage body and layer (permanent anchor take 1.00).
According to the calculation, l a ≥4.3m, takel a =5.0m.
（5）The anchoring length between anchor steel and anchor mortar
γοN a l a ≥ (5) ξ3n πdf b
In the formula: l a is the anchoring length between steel and mortar; d is the diameter of anchor bar; n is the number of steel; f b is the bond strength design value between steel and anchor mortar, through the experiment sure, or according to the standard take 2.40; ξ3 is the working conditions coefficient of steel and mortar bond strength(permanent anchor take 0.60）. According to the calculation, l a ≥2.1m ，take l a =5.0m.
3.3 The construction technology and key points of anchor
The 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
should attention the grouting pressure and mortar ratio.
Fig 2 anchor field construction drawing
4. Conclusion
It 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 national standards. 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]. Fujian Construction 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。由于锚杆的使用, 使锚固地层产生压应力区并对地层起到加
筋作用
, 来增强地层的强度, 改善地层的力学性能, 使结构与地层一起形成一种共同工作的复合体。锚杆体系其能有效地承受拉力和剪力, 能提高潜在滑移面上的抗剪强度, 有效地阻止坡体产生滑动破坏。
2. 工程概况 某边坡长约60m, 最大坡高约23m, 坡度达50°~75°, 为岩质边坡。距坡底边缘约
1.5~4m处有1栋5层框架结构建筑物, 人工挖孔灌注桩基础, 建筑物以中风化千枚岩为持力层。因岩石风化强烈，呈碎块状，结构松散，多为泥质充填。上覆残坡积粉质粘土，局部夹有泥状，强度较低。边坡坡体多处位置曾发生崩塌，对建筑物存在威胁，所以需对边坡进行加固，采用的是块石混凝土挡墙+锚杆进行支护。
3. 锚杆支护设计
通过计算可得E a =175.77 kN/m。
（2）锚杆轴向拉力设计值的计算
N a =γQ N ak
（3-2） 其中：A S 为锚杆钢筋截面面积；γο为边坡工程重要性系数（本工程边坡工程安全等级为一级，取1.1）；ξ2为锚筋抗拉工作条件系数（永久性锚杆取0.69，临
f f 时性锚杆取0.92）；y 为锚筋抗拉强度设计值（标准值y k =400MP a ，设计值
f y =360MP a ）。
-32根据计算可得A S ≥0.588 ⨯10m ，选用1φ28mm 的三级钢，
A S =0.615⨯10-3m 2。 （4）锚杆锚固体与岩土体锚固长度的计算
锚杆锚固段长度除应同时满足地层对砂浆的粘结力和砂浆对钢筋的握裹力要求外，还应满足构造设计规定的最少锚杆锚固长度的要求。
式中: l a
为锚筋与砂浆间的锚固长度；d 为锚筋直径；n 为钢筋根数；f b 为钢筋与锚固砂浆间的粘结强度设计值，由试验确定，也可按表取为2.40；ξ3为钢筋与砂浆粘结强度工作条件系数（永久性锚杆取0.60）。
由公式计算可知l a ≥2.1m ，实际取l a =5.0m。
3.3 锚杆施工工艺与要点
锚杆施工的工艺流程为：搭设脚手架——坡面开挖整修——测量定位——钻孔——清孔——锚杆安放——注浆——锚杆端部绑扎——冲洗坡面——浇框格——喷草籽
（1）本边坡为石质边坡，坡面开挖10cm 至框格底面后设锚杆、浇框格，再在框格内客土20cm 后喷播草、灌籽。
（2）施工时应注重边坡清理，锚杆孔清孔后方可放置锚杆并加压(0.4MPa)注浆，在孔内砂浆充分凝固后扎筋，现浇钢筋砼框格，锚杆端部弯折并与纵横骨架筋间逐点绑扎。
（3）钻孔前需测量定位，做好标记，孔距偏差小于150mm ，孔深误差小于50mm 。钻孔时尽量不扰动周围岩层，安放锚杆前注意将孔内积水和岩粉等吹洗干净且杆体应除锈。注浆时注意注浆压力及砂浆配比。
图3.7锚杆现场施工图
4. 结论
边坡工程采用锚杆进行边坡加固, 工程造价较低, 对施工器械要求不高, 在达到安全可靠的同时兼顾了工程施工的经济性和合理性。
(1)当今锚杆技术在工程中被广泛应用。将锚杆和混凝土护坡相结合, 约束滑动土体。是一种有效的加固措施。
(2)在利用灌浆锚杆加固边坡前, 一定要做好边坡的地质勘探工作。摸清各岩层的性质和水文地质情况。
(3)由于工程地质条件、灌浆压力、施工技术等因素影响, 加固施工质量应给与足够的重视。
参考文献
[1]建筑边坡工程技术规范(JGJ 120-99).中华人民共和国国家标准. 北京:中国建筑工业出版社.
[2]郑颖人、陈祖煜等. 边坡与滑坡工程治理 [M].北京：人民交通出版社，2007
[3]罗贞海. 浅谈锚杆在边坡加固中的应用[J]. 福建建设科技，2010,06:15-16
Discussion about the application of the anchor bar on the
slope construction
Fu Ming Fu , Zhang Tian
Abstract: 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; strengthening
1. Introduction
Anchor 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 slope
2. Project profile
The 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 had
collapsed 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 design
3.1 Bolt 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 0.052m 3 per 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.
3.2 Anchor 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 ϕe (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:
E =1γH 2K =1⨯20⨯92⨯tan 2(45︒-ϕe ) =1⨯20⨯92⨯0.217=175.77kN /m a a
（2）the calculation of anchor tension design value 2222
N a =γQ N ak (1)
H tk N ak =cos αIn the formula: N a is anchor tension design value; N ak is anchor tension standard value; γQ is partial load factor, take 1.3; H tk is the horizontal tension standard value of anchor; αis the dip angle of anchor.
Through the calculation, N ak =112.3kN N a =145.99kN
（3）the calculation of anchor steel section area
A S ≥ οa (3)
In the formula: A S is the steel section area of anchor; γN ξ2f y
γο is slope engineering importance
coefficient(the slope engineering importance coefficient of this project is level 1, take 1.1); ξ2is the tensile working conditions coefficient of anchor bar ( permanent anchor take 0.69, temporary anchor take 0.92); f y is the tensile strength design value of anchor bar(standard value f y k =400MP a , design valuef y =360MP a ).
According to the calculation, A S ≥0.588⨯10m ,choose level 3 steel of 1φ28mm, -32
A S =0.615⨯10-3m 2.
（4）The calculation of anchorage body and rock mass anchoring length
anchoring 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.
l a ≥ ak (4) In the formula: l a is the anchoring length; D is the diameter of anchorage body; f rb 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 N ξ1πDf rb
strength is 7.46MP a , belong to soft rock, rock mass structural plane development, f rb take 300KP a ); ξ1is the bond working conditions coefficient of anchorage body and layer (permanent anchor take 1.00).
According to the calculation, l a ≥4.3m, takel a =5.0m.
（5）The anchoring length between anchor steel and anchor mortar
γοN a l a ≥ (5) ξ3n πdf b
In the formula: l a is the anchoring length between steel and mortar; d is the diameter of anchor bar; n is the number of steel; f b is the bond strength design value between steel and anchor mortar, through the experiment sure, or according to the standard take 2.40; ξ3 is the working conditions coefficient of steel and mortar bond strength(permanent anchor take 0.60）. According to the calculation, l a ≥2.1m ，take l a =5.0m.
3.3 The construction technology and key points of anchor
The 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
should attention the grouting pressure and mortar ratio.
Fig 2 anchor field construction drawing
4. Conclusion
It 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 national standards. 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]. Fujian Construction 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。由于锚杆的使用, 使锚固地层产生压应力区并对地层起到加
筋作用
, 来增强地层的强度, 改善地层的力学性能, 使结构与地层一起形成一种共同工作的复合体。锚杆体系其能有效地承受拉力和剪力, 能提高潜在滑移面上的抗剪强度, 有效地阻止坡体产生滑动破坏。
2. 工程概况 某边坡长约60m, 最大坡高约23m, 坡度达50°~75°, 为岩质边坡。距坡底边缘约
1.5~4m处有1栋5层框架结构建筑物, 人工挖孔灌注桩基础, 建筑物以中风化千枚岩为持力层。因岩石风化强烈，呈碎块状，结构松散，多为泥质充填。上覆残坡积粉质粘土，局部夹有泥状，强度较低。边坡坡体多处位置曾发生崩塌，对建筑物存在威胁，所以需对边坡进行加固，采用的是块石混凝土挡墙+锚杆进行支护。
3. 锚杆支护设计
通过计算可得E a =175.77 kN/m。
（2）锚杆轴向拉力设计值的计算
N a =γQ N ak
（3-2） 其中：A S 为锚杆钢筋截面面积；γο为边坡工程重要性系数（本工程边坡工程安全等级为一级，取1.1）；ξ2为锚筋抗拉工作条件系数（永久性锚杆取0.69，临
f f 时性锚杆取0.92）；y 为锚筋抗拉强度设计值（标准值y k =400MP a ，设计值
f y =360MP a ）。
-32根据计算可得A S ≥0.588 ⨯10m ，选用1φ28mm 的三级钢，
A S =0.615⨯10-3m 2。 （4）锚杆锚固体与岩土体锚固长度的计算
锚杆锚固段长度除应同时满足地层对砂浆的粘结力和砂浆对钢筋的握裹力要求外，还应满足构造设计规定的最少锚杆锚固长度的要求。
式中: l a
为锚筋与砂浆间的锚固长度；d 为锚筋直径；n 为钢筋根数；f b 为钢筋与锚固砂浆间的粘结强度设计值，由试验确定，也可按表取为2.40；ξ3为钢筋与砂浆粘结强度工作条件系数（永久性锚杆取0.60）。
由公式计算可知l a ≥2.1m ，实际取l a =5.0m。
3.3 锚杆施工工艺与要点
锚杆施工的工艺流程为：搭设脚手架——坡面开挖整修——测量定位——钻孔——清孔——锚杆安放——注浆——锚杆端部绑扎——冲洗坡面——浇框格——喷草籽
（1）本边坡为石质边坡，坡面开挖10cm 至框格底面后设锚杆、浇框格，再在框格内客土20cm 后喷播草、灌籽。
（2）施工时应注重边坡清理，锚杆孔清孔后方可放置锚杆并加压(0.4MPa)注浆，在孔内砂浆充分凝固后扎筋，现浇钢筋砼框格，锚杆端部弯折并与纵横骨架筋间逐点绑扎。
（3）钻孔前需测量定位，做好标记，孔距偏差小于150mm ，孔深误差小于50mm 。钻孔时尽量不扰动周围岩层，安放锚杆前注意将孔内积水和岩粉等吹洗干净且杆体应除锈。注浆时注意注浆压力及砂浆配比。
图3.7锚杆现场施工图
4. 结论
边坡工程采用锚杆进行边坡加固, 工程造价较低, 对施工器械要求不高, 在达到安全可靠的同时兼顾了工程施工的经济性和合理性。
(1)当今锚杆技术在工程中被广泛应用。将锚杆和混凝土护坡相结合, 约束滑动土体。是一种有效的加固措施。
(2)在利用灌浆锚杆加固边坡前, 一定要做好边坡的地质勘探工作。摸清各岩层的性质和水文地质情况。
(3)由于工程地质条件、灌浆压力、施工技术等因素影响, 加固施工质量应给与足够的重视。
参考文献
[1]建筑边坡工程技术规范(JGJ 120-99).中华人民共和国国家标准. 北京:中国建筑工业出版社.
[2]郑颖人、陈祖煜等. 边坡与滑坡工程治理 [M].北京：人民交通出版社，2007
[3]罗贞海. 浅谈锚杆在边坡加固中的应用[J]. 福建建设科技，2010,06:15-16