9487 (1).ppt
- 1. Most effective Methods : 1. Grouting 2. Rock Bolting 3. Shortcrete/Guniting 4. Cable anchorage IMPROVEMENT OF ROCK MASS PROPERTIES
- 2. Improvement of rock mass •Pre-planned •Emergent Condition
- 3. Grouting • Defined as the injection of a liquid of variable viscosity under pressure into a particular part of or parts of the earth’s crust through specially constructed holes to fill and seal voids, cracks, seams, fissures etc. • Done for strengthening and/or water sealing
- 4. Grouting • Grout is a construction material used to fill voids, and seal joints • Grout is generally composed of a mixture of water, cement, sand. • It is applied as a thick liquid and hardens over time, much like mortar. • Initially, its application confines mainly in void filling, water stopping and consolidation. Nowadays, it extends to tunnel excavation works, to strengthen ground in solving geotechnical problems.
- 5. Grain size of the grout • Grain size of the grouting fluid, such as cement slurry should be smaller than the size of the pores of the mass to be grouted • For successful operation following criteria is used • D15 (Soil)/D85 (Grout) > 25 for Soil • D (fissure)/Dmax (Grout) > 3 for Rock
- 6. Types of Grouting • GROUT can be applied as a solution, an emulsion or suspension in water, which will harden after a certain time interval. It can be divided into two main groups: • 1. Suspension Grout • 2. Liquid Grout or Solution Grout. • Suspension grout is a mixture of one or several inert materials like cement, clays etc. suspended in a fluid -- water. • Liquid grout or solution grout consists of chemical products in a solution or an emulsion form and their reagents. The most frequently used products are sodium silicate and certain resins.
- 7. Types of Grouts • Cement Grouts: Cement-based grouts are the most frequently used in both water stopping and strengthening treatment. • Chemical Grout : Suitable for finely fissured rock mass • Bituminous Grout: also known as emulsion grout, includes bitumen because they form an emulsion when mixed with water, bitumen grouts are sensitive to temp, hence they may not be suitable at greater depth.
- 8. Methods of Grouting 1. Stage Grout: done in stages, starting from nearest discontinuity from surface to the deepest discontinuity 2. Packer Grout: holes are first drilled to deepest level to be grouted. The process is repeated from bottom to top till the whole section is grouted 8
- 10. • Rock Fissure Grouting • Rock fissure grouting is the use of a hole drilled through the fissures and joints of a rock mass to allow grout to be injected at close centers vertically and re-injecting, if necessary. • Grouting Mechanism – The grout is injected under pressure through the grout hole drilled into the rock mass to be treated. 10
- 11. Rock fissure grouting Main applications are: 1. Sealing rock mass underneath and at ends of dams to prevent seepage or leaking of the reservoirs. 2. Sealing rock mass above and underneath a rock tunnel to prevent water seepage into the excavated tunnel. 3. Cementing fractured rock mass.
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- 13. Rock Bolting • Done to reinforce and support partially detached, thinly laminated or unsuitable which otherwise would be subjected to failure. With rock bolting, the rock is loaded in such a way that the resistance to shear along the planes of weakness is increased 13
- 14. Mechanism of rock bolting • A number of holes are drilled in the rock at a designated spacing, the length of holes are selected such that they terminate in a sound rock in which the bolt can be anchored properly and take up the loads. 14
- 15. Rock bolts • Steel bolts are frequently set in holes drilled into the rock to assist in supporting the entire roof or individual rock slabs that tend to fall into a tunnel. • Rock bolts maintain the stability of an opening by suspending the dead weight of a slab from the rock above by providing a normal stress on the rock surface to clamp discontinuities together and develop beam action by preventing key blocks becoming loosened so that the strength and integrity of the rock mass is maintained.
- 16. Rock Bolting
- 17. Guniting/Shortcrete • Fluid mixture of fine sand, cement and water applied through nozzle ejecting at a high velocity, done on the exposed surface for sealing the surface cracks and protecting the surface from weathering.
- 18. Shotcrete/Guniting • mortar and concrete are increasingly being used for the support of underground excavations. • A combination of rock bolts and shotcrete has proved an excellent temporary support for all qualities of rock. • Shotcrete is best known in tunnelling • Quick-setting concrete is sprayed onto the bare rock surface immediately after excavation, and rapidly hardens to form a preliminary support until the final lining of conventional poured concrete can be installed.
- 19. Cable Anchorage • Purpose is same as that of rock bolting. The difference in cable anchorage and rock bolting is that cables have length much more than rock bolts. In rock bolting system, individual rock bolts are put into the rock at specified spacing. But in cable anchorage system, a number of wires in a group form a cable and the cables are put into the rock mass at the pre-determined positions, suitable in case of anchoring a foundation subjected to bouncy, especially under sea