Highway Slope Manual

More documents

Recommendations

Info

63 qualified and experienced supervisory professionals and competent supporting technical personnel, especially for supervising potentially hazardous construction activities (e.g. blasting and rock excavation). The professionals in the contractor's team responsible for carrying out inspections and assessments to ensure quality of the works and public safety during construction should be identified. Also, auditing of the contractor's work against contract requirements, which is a particularly important activity, should be carefully arranged. This should be carried out by personnel independent of the contractor's site supervisory team and appointed by the client directly, at critical stages of construction (Works Bureau, 1999d). Special control testing, including appointment of laboratories independent of the contractor to carry out the sampling and testing for the critical contract compliance tests (e.g. tests to check the adequacy of fill slope compaction), should also be arranged by the auditing team for the client. 7.3 ROCK REMOVAL FROM SLOPES 7.3.1 Rock Breaking Methods Rock breaking methods commonly used in Hong Kong are listed in Table 7.1. The choice of the methods is governed by rock strength and structure, groundwater conditions, safety, and environmental and socio-economic considerations. Fly rock from blasting, and falling rock blocks and debris from percussive excavation methods are common safety hazards. Debris falling onto roads can necessitate prolonged road closure with serious socioeconomic implications. The rockfall during the Tuen Mun Highway widening works in 1995 is an illustrative case (Wong, 1997). This case also shows that the use of low energy methods of rock breaking cannot eliminate all problems since failure can occur along unknown geological defects. Apart from the fall of debris and rock fragments, dropping of tools and toppling of construction plant from roadside slopes can also pose a risk to road users. Table 7.1 Commonly Used Methods of Rock Breaking Type of Method Method of Rock Breaking Mechanical Hand breaking by ‘feathers and wedges' method Digging and scraping with machines Line drilling Hydraulic hammers Hydraulic wedge breakers Typical Energy Rating Low Low Low Medium Medium Chemical Expansive grout Low Blasting Bulk blasting Dresplitting/smooth wall blasting High High Note: Typical considerations for rock breaking methods • Spillage/dislodgement of loose material from the rock mass • Failures due to unknown geological defects in the rock mass • Rock mass instability induced by weight of construction plant and equipment • Uncontrolled leakage of grout into open discontinuities or fractures • Flyrock causing harm to life and property • Overbreak of the rock mass • Adverse effects of excessive ground vibration (e.g. due to blasting, drilling, hammering, etc.) on the rock mass • Adverse effects of excessive gas pressure on the rock mass (Blastronics, 2000) • Noise causing nuisance or harm
64 Blasting is the most common method for bulk excavation in rock in Hong Kong. The most significant problems associated with blasting are flyrock, ground vibration and noise. Figures 7.1 summarises the common methods for the optimisation and control of blasting. Where a permanent rock face is to be formed, controlled blasting techniques should be adopted, where possible, to improve the stability of the rock face and to achieve a good slope surface finish. Reference should be made to Sections 9.4.2 and 9.4.3 of the Geotechnical Manual for Slopes (GCO, 1984) and Section 9.13 in FHWA (1994) for guidance. Methods for assessment of stability of slopes subjected to blasting vibration are given in GEO Report No. 15 (Wong & Pang, 1992). ODTIMISATION AND CONTROL OF BLASTING Good Blast Design and Control • Assessment of previous blasting effects in similar ground conditions. • Use of no 叫 blast zones. • Accurate positioning and drilling of blast holes. • Use of controlled blasting (presplitting or smooth wall blasting) techniques. • Carrying out blasting trials. • Specifying blasting sequence. • Specifying burden. • Specifying stemming. • Specifying allowable charge weight of explosives and limits on ground vibration and noise. • Identifying sensitive receivers and specifying monitoring and on 叫 going interpretation and review requirements. • Use of experienced personnel for blast design and specification, and for assessment of blasting effects and monitoring, interpretation and review. Recognition of Hazards • Regular programme of inspection and mapping. • Systematic rock mass characterisation. • Identification and assessment of potential failure modes and block sizes. • On 叫 going risk assessment procedure. • Drovision of induction/ awareness programme and safety training for site personnel. • Use of experienced personnel for supervision and for undertaking the above tasks. Drevention of Flyrock • Optimum charging. • Dre 叫 blast condition survey of nearby facilities. • Adequate front row burden. • Accurate positioning/drilling of blast holes. • Checking that stemming is sufficient. • Use of flyrock matting, netting and cages. Adequate Safety Drovisions • Use of buffer zones. • Shelter for personnel close to the blast. • Drocedures for evacuation of people in affected areas. • Road closure or traffic diversion and control. • Containment and retention of potential rockfall. • Dre 叫 blast survey and stabilisation of adjacent rock mass if necessary. • Dost 叫 blast checking of potential danger before returning to normal site control. Figure 7.1 Common Methods for Optimisation and Control of Blasting
Page 1 and 2:
HIGHWAY SLOPE MANUAL GEOTECHNICAL E
Page 3 and 4:
2 。 The Government of the Hong Ko
Page 5 and 6:
4 STEERING COMMITTEE: Geotechnical
Page 7 and 8:
6 Page No. 3. SITE INVESTIGATION 33
Page 9 and 10:
8 Page No. APPENDICES APPENDIX A -
Page 11 and 12:
10 LIST OF FIGURES Figure No. Page
Page 13 and 14: 12 LIST OF LATES Plate No. Page No.
Page 15 and 16: 14 [BLANK PAGE]
Page 17 and 18: 16 year (Evans et al, 1998), they h
Page 19 and 20: 18 Plate 1.4 Landslide at Ching Che
Page 21 and 22: 20 Plate 1.8 Steep Natural Terrain
Page 25 and 26: 24 Notes: (1) The projects in the P
Page 27 and 28: 26 of the geotechnical hazards and
Page 29 and 30: 28 Table 2.2 Geotechnical Haards Th
Page 31 and 32: 30 for carrying out a GA is given i
Page 35 and 36: 34 Table 3.1 Potential Uses of Diff
Page 37 and 38: 36 or features such as dykes or fra
Page 39 and 40: 38 movement monitoring and control
Page 41 and 42: 40 landslide debris, and the nature
Page 43 and 44: 42 Notes: (1) This Figure is based
Page 45 and 46: 44 Table 4.5 Recommended Minimum Fa
Page 49 and 50: 48 Plate 5.1 Surface Runoff Channel
Page 51 and 52: 50 Cascades, with cover where neces
Page 53 and 54: 52 (a) Trash Grill at Inlet of Cros
Page 55 and 56: 54 5.2.3 Drainage Improvement Works
Page 57 and 58: 56 For the control of visual impact
Page 59 and 60: 58 Plate 6.3 Pattern and Texture Pl
Page 61 and 62: 60 ighways are environments with a
Page 63: 62 Filling operations for a highway
Page 67 and 68: 66 Notes: (1) The responsibility fo
Page 69 and 70: 68 Results of Rockfall Protective B
Page 73 and 74: 72 overseeing the maintenance of th
Page 75 and 76: 74 In addition to the slope upgradi
Page 77 and 78: 76 after each heavy rainstorm event
Page 79 and 80: 78 d n n d d d d d d d
Page 81 and 82: 80 event of a landslide should be b
Page 85 and 86: 84 Federal Highway Administration (
Page 87 and 88: 86 Highways Department (1996). Mana
Page 89 and 90: 88 Wong, H.N., Pang, L.S., Wong, A.
Page 95 and 96: 94 key natural terrain and man-made
Page 97 and 98: 96 and details of all existing slop
Page 101 and 102: -AA (v) relevant services and utili
Page 103 and 104: -A2 (m) (n) 1dentify any statutory
Page 105 and 106: -A4 Notes: (-) An example of a prog
Page 109 and 110: 108 Wong, C.K.L. (1998). The New Pr
Page 111 and 112: 110 of slopes and slope owners and
Page 115:
114 (iv)subsidence of ground or roa
show all

Highway Slope Manual

Create successful ePaper yourself

Delete template?

Save as template?