ELSEVIER GEO-ENGINEERING BOOK SERIES VOLUME 5 Part 8 doc

390 Tunnelling in weak rocks poor management condition affected tunnelling rate more adversely than poor rock mass condition. The third factor pertains to the breakdowns or hold ups during various operations in tunnelling cycle. These hold ups cause delays which are random in nature. Based on the data collected from many projects, Chauhan (1982) proposed a classification for realistic assessment of rate of tunnelling presented in the following sections. 27.2 CLASSIFICATION OF GROUND/JOB CONDITIONS FOR RATE OF TUNNELLING The rate of tunnelling is seriously affected by the ground conditions. The factors, under the ground condition, affecting the rate of tunnelling are (Terzaghi, 1946; Bieniawski, 1973, 1974; Barton et al., 1974). (i) Geology, such as, type of rock, RQD, joint system, dip and strike of strata, presence of major fault or thrust zones and their frequencies and type and rock mass properties, (ii) Method of excavation including blast pattern and drilling arrangement, (iii) Type of support system and its capacity, (iv) Inflow of water, (v) Presence of inflammable gases, (vi) Size and shape of tunnel, (vii) Construction adits whether horizontal or inclined, theirgradesizeandlengthand (viii) High temperature in very deep tunnels (H > 1000 m). On the basis of the above factors affecting the rate of tunnelling, the ground conditions are classified into three categories – good, fair and poor (Table 27.1). It means that for the good ground conditions the rate of tunnelling will be higher and for the poor ground conditions the rate of tunnelling will be lower. The job/ground conditions in Table 27.1 are presented in order of their weightage to the rate of tunnelling. 27.3 CLASSIFICATION OF MANAGEMENT CONDITIONS FOR RATE OF TUNNELLING The rate of tunnelling mayvaryin the same ground condition depending upon management quality. The factors affecting management conditions are: (i) Overall job planning, including selection of equipment and decision-making process, (ii) Training of personnel, (iii) Equipment availability including parts and preventive maintenance, Rate of tunnelling 391 Table 27.1 Classification of ground/job condition (Chauhan, 1982). Job conditions S. No. Parameter Good Fair Poor 1. Geologic structure Hard, intact, massive stratified or schistose, moderately jointed, blocky and seamy Very blocky and seamy squeezing at moderate depth Completely crushed, swelling and squeezing at great depth 2.(a) Point load strength index >2MPa 1–2 MPa Index cannot be determined but is usually less than 1 MPa (b) Uniaxial compressive strength >44MPa 22–44 MPa <22MPa 3. Contact zones Fair to good or poor to good rocks Good to fair or poor to fair rocks Good to poor or fair to poor rocks 4. Rock quality designation (RQD) 60–100 % 25–60 % <25% 5.(a) Joint formation Moderately jointed to massive Closely jointed Very closely jointed (b) Joint spacing >0.2m 0.05–0.2 m <0.05m 6.(a) Joint orientation Very favorable, favorable and fair Unfavorable Very unfavorable (b) Strike of tunnel axis and dip with respect to tunnel driving (i) Perpendicular 20 to 90 ◦ along dip, 45 to 90 ◦ against dip (i) Perpendicular 20 to 45 ◦ against dip (i) Parallel 45 to 90 ◦ (ii) Parallel 20 to 45 ◦ (ii) Irrespective of strike 0 to 20 ◦ – 7. Inflammable gases Not present Not present May be present 8. Water inflow None to slight Moderate Heavy 9. Normal drilling depth/round >2.5m 1.2 m–2.5 m <1.2m 10. Bridge action period >36h 8–36 h <8h Note: The geologist’s predictions based on investigation data and laboratory and site tests include information on parameters at S. Nos. 1 to 6. This information is considered adequate for classifying the job conditions approximately. 392 Tunnelling in weak rocks (iv) Operating supervision, (v) Incentives to workmen, (vi) Co-ordination, (vii) Punctuality of staff, (viii) Environmental conditions and (ix) Rapport and communication at all levels. These factors affect the rate of tunnelling both individually and collectively. Each factor is assigned a weighted rating (Table 27.2). The maximum rating possible in each subgroup has also been assigned out of 100 in Table 27.2 that represents ideal conditions. At a particular site the rating of all the factors is added to obtain a collective classification rating for management condition. Using this rating, the management condition has been classified into good, fair and poor as shown in Table 27.3. The proposed classification system for management is valid for tunnels longer than 500 m, which are excavated by conventional drilling and blasting method. It may be noted that the rate of tunnelling can be easily improved by improving the management condition which is manageable unlike the ground conditions which cannot be changed. So, it is necessary to pay at least equal, if not more, attention to the management condition than to the ground condition. Hence, there is an urgent need for management consultancy for improving the tunnelling rate. The key to success of tunnel engineers is evolution of a flexible method of construction of support system. On-spot strengthening of support system is done by spraying additional layers of shotcrete/SFRS or using long rock bolts in the unexpectedly poor geological conditions. This is a sound strategy of management in tunnelling within the complex geological situations. Affection is the key to success in the management. Young engineers love challenging works. There should be no hesitation in throwing challenges to young engineers. Otherwise these young engineers may loose interest in routine management. 27.4 COMBINED EFFECT OF GROUND AND MANAGEMENT CONDITIONS ON RATE OF TUNNELLING A combined classification system for ground conditions and management conditions has been developed by Chauhan (1982). Each of the three ground conditions has been divided into three management conditions and thus nine categories have been obtained considering both ground and management conditions. The field data of six tunnelling projects in the Indian Himalayas have been divided into these nine categories for studying the combined effect. Each category has three performance parameters which are: (i) Actual working time (AWT), (ii) Breakdown time (BDT) and (iii) Advance per round (APR). Table 27.2 Ratings for management factors for long tunnels (Chauhan, 1982). Remarks for improvement in management S. No. Subgroup Item Maximum rating for condition Item Subgroup 1. Overall job planning i) Selection of construction plant and equipment including estimation of optimal size and number of machines required for achieving ideal progress. 7 ii) Adoption of correct drilling pattern and use of proper electric delays. 6 iii) Estimation and deployment of requisite number of workmen and supervisors for ideal progress. 5 iv) Judicious selection of construction method, adits, location of portals, etc. 4 Horizontal adits sloping at the rate of 7% towards portal to be preferred to inclined adits or vertical shafts. v) Use of twin rail track 2 vi) Timely shifting of California switch at the heading 226 2. Training of personnel i) Skill of drilling crew in the correct holding, alignment and thrust application on drilling machines 4 Proper control of drilling and blasting will ensure high percentage of advance from the given drilling depth and also good fragmentation of rock which facilitates mucking operation. ii) Skill of muck loader operator 4 Continued Table 27.2—Continued Remarks for improvement in management S. No. Subgroup Item Maximum rating for condition Item Subgroup iii) Skill of crew in support erection 3 A skilled crew should not take more than 1/2 h for erection of one set of steel rib support. iv) Skill of blastman 2 v) Skill of other crews 2 15 3. Equipment availability and preventive maintenance Time lost in tunnelling cycle due to breakdowns of equipment including derailments, etc. i) upto 1 h. 12–15 ii) 1–2 h. 9–11 iii) 2–3 h. 6–8 iv) >3h. 0–5 15 4. Operation supervision i) Supervision of drilling and blasting (effectiveness depends on location, depth and inclination of drill holes, proper tamping and use of blasting delays) 7 Improper drilling may result in producing: i) unequal depth of holes which results in lesser advance per meter of drilling depth and ii) wrong alignment of hole which may lead to : a) overbreak due to wrong inclination of periphery holes and b) secondary blasting due to wrong inclination of other than periphery holes Item Subgroup Improper tamping of blast hole charge and wrong use of blasting delays result in improper blasting effects. ii) Supervision of muck loading/hauling system 3 Especially in rail haulage system in which rapid feeding of mine cars to loading machine at the heading is essential for increasing productivity of loader. iii) Supervision of rib erection, blocking and packing 3 iv) Other items of supervision such as scaling, layout, etc. 215 5. Incentive to workmen i) Progress bonus 5 Define the datum monthly progress as that value which delineates good and fair management conditions for a particular job conditions. Introduce bonus slabs for every additional 5 m progress and distribute the total monthly bonus thus earned amongst the workmen on the basis of their importance, skill and number of days worked during the month. The amount for each slab should be so fixed that these are progressive and each worker should get about 50% of his monthly salary as progress bonus, if ideal monthly progress is achieved. ii) Incentive bonus 2 This should be given for certain difficult and hazardous manual operations like rib erection/shear zone treatment, etc. Continued Table 27.2—Continued Remarks for improvement in management S. No. Subgroup Item Maximum rating for condition Item Subgroup iii) Performance bonus 1 This should be given to the entire tunnel crew equally if the quarterly progress target is achieved. iv) Achievement bonus 1 9 It is to be given for completion of whole project on schedule. It should be given to the whole construction crew and may be equal to one year’s interest on capital cost. 6. Co-ordination i) Co-ordination of activities of various crews inside the tunnel. 5 Co-ordination between designers and construction engineers should be given top priority. Designers should be boldly innovative. ii) Use of CPM for overall perspective and control of the whole job. 4 9 Safety saves money. Contingency and emergency plans should be ready before tunnelling. 7. Environmental conditions and housekeeping Proper lighting, dewatering, ventilation, provision of safety wear to workmen and general job cleanliness. 44 8. Punctuality of staff i) Prompt shift change-over at the heading 4 ii) Loss of upto 1/3 h in shift change-over 3 iii) Loss of more than 1/3 h in shift change-over 0–2 4 9. Rapport and communication Commitment, good rapport and communication at all levels of working including top management and government level including human relations. 3 3 Team spirit is the key to success in underground construction. The contractors have to be made to succeed. Rate of tunnelling 397 Table 27.3 Rating for different management conditions (Chauhan, 1982). S. No. Management condition Rating 1. Good 80–100 2. Fair 51–79 3. Poor ≤50 Table 27.4 Ground and management factors (Chauhan, 1982). Ground conditions Management conditions Good Fair Poor Good 0.78 0.60 0.44 Fair 0.53 0.32 0.18 Poor 0.30 0.21 0.13 A matrix of job and management factors has been developed from the data for evaluating tunnel advance rate as given in Table 27.4. Ground and management factors in the matrix are defined as a ratio of actual monthly progress to achievable monthly progress under corresponding set of ground and man- agement conditions. Knowing the achievable production for a tunnelling project, these factors could hopefully yield values of expected production under different management and geological conditions on the project. Thus, in squeezing ground conditions, the rate of tunnelling would be only 13 per- cent of the theoretical rate for poor management condition. Past experience suggests that management tends to relax in good tunnelling conditions and becomes alert and active in poor rock conditions. Further studies are needed to update Table 27.2 to 27.4 for modern tunnelling technology. Trends are expected to be similar. Management of world bank-funded projects is an ideal example. They appoint inter- national experts on rock mechanics on their hydroelectric projects. In major state-funded projects, international experts on rock mechanics should be appointed as the Board of Consultants, as in the past. The international experts help to achieve self-reliance. 27.5 TUNNEL MANAGEMENT (SINGH, 1993) The management is the topmost art, demanding strength of character, intelligence and experience. Deficiencies in management are, therefore, difficult to remove. Experience is not what happens to you, it is what you do with what happens to you. Everyone is potentially a high performer and motivation comes from top. What glorifies self-respect automatically improves one’s efficiency. Often interference by the manager mars the ini- tiative of the young engineers. Feedback is essential to improve performance, just like 398 Tunnelling in weak rocks feedback is very important for the stability of the governing system in electronics. Effi- cient clear communication of orders to concerned workers and their feedback is essential for success of management. Computer network and cell phones are used now-a-days for better informal rapport at a project site. The modern management is committed to visi- ble management. The defeatist attitude should be defeated. The leader should have the willpower to complete the vast project. There should be respect for individual in the orga- nization. Happier the individual, more successful he will be. If you want to be happy for whole life, love your work. Tunnel construction is a complex, challenging and hazardous profession. It demands certainly a high skill in the leadership, technology and communication. On the spot decisions are needed in a crisis during tunnelling. Mutual respect between government engineers and contractors is need of the time. That is what privatization stands for. Usually bad news does not travel upwards to the executive management. Basic ingredient in management is trust. Quality consciousness should be the culture of a construction agency. Is quality work possible in government due to lack of creative freedom? Work of good quality is possible in fact by framing proper specifications in a contract document. Contractor’s point of view is that payments should be made early for quick reinvestment. Unfortunately, construction industries are unorganized at present in many countries. With increasing trend for global organization, efficiency will go upwards in the future. No two construction jobs are alike. It is, therefore, very difficult to evolve a system (of stock- piles of materials, fleet of tunnelling machines, etc.) for a new project site. Construction problems vary so much from job to job that they defy tenders, machines and known methods. Then a contractor uses ingenuity to design tools and techniques that will lead to success in tunnelling. Machines may be used for various other purposes with slight modifications, beyond imagination. Excellent companies are really close to their cus- tomer (engineers) and pay them high regards. Their survival depends upon the engineer’s satisfaction. Critical path analysis, if properly applied and used, can be a great help to any construc- tion agency, specially in a tunnelling job. Use of software for critical path analysis for cost control is most effective and economical. Then co-ordination among workers becomes easy. Naturally a management organization becomes more efficient during crisis. Cost consciousness must permeate all ranks of engineers and workers. Organization set-up is the back-bone of a long tunnelling project. The completion of a hydroproject is delayed by the completion of long length of tunnels in weak and complex geological conditions. So, the idea of substantial bonus for early completion is becoming more widespread. 27.6 POOR TENDER SPECIFICATIONS Tendering for tunnelling projects remains speculation, since actual ground conditions encountered during construction often do not match the conditions shown in the tender Rate of tunnelling 399 specifications, particularly in the Himalayas, young mountains and complex geologi- cal environment. The practice of adopting payment rates according to actual ground condition does not exist. Insufficient geological, hydrogeological and geo-technical inves- tigations and poor estimates, etc. invariably lead to owner–contractor conflicts, delay in projects, arbitration and escalation of project cost, generally by three times. Following are some of the main reasons attributed to this poor tunnelling scenario in developing nations. (i) Inadequate geological investigations and absence of rock mechanics apprecia- tion before inviting a tender bid, resulting in major geological surprises during execution. (ii) Lack of proper planning, sketchy and incompetent preparation of designs at pre-tender stage. (iii) Unrealistic projection of cost estimates and cost benefit ratio and completion schedules at initial stages. (iv) Inadequate infrastructure facilities at site. (v) Unrealistic and unfair contract conditions and poor profit margins leading to major disputes and delays in dispute resolution. (vi) Lack of motivation and commitment on the part of owners, especially government departments and public sector agencies. (vii) Lack of specific provisions in the tender document itself with regard to modern technology. (viii) Lack of teamwork between the owner, the contractor, the geologist and the rock mechanics expert. (ix) Risk sharing between contractor and owner is generally not fair. (x) Lack of indigenous construction technology in developing nations. It is important here to emphasize that though sufficient expertise is available in the world in the tunnelling technology, the administration seldom takes advantage of the intellectual resources in the right perspective at the right time. 27.7 CONTRACTING PRACTICE On some occasions, it is the inexperience or incompetence of the contractor that has delayed a project. Sometimes lack of strategy, weak project team and inadequate attention from the top management also result in delays and slippage. In some cases, contractors are found ill-equipped and starved of cash, besides lacking in professionalism. Just to grab the project deal, they compromise on rates. Finding very low profits when the work starts, they raise unreasonable claims and disputes to improve profit margin which results in disputes followed by arbitration, delays and time and cost over-runs in some developing countries. [...]... (2 5 percent by mass of cement), h) Curing agent, i) Steel fibers Shotcrete ingredients and properties are listed in Table 28. 1 4 08 Tunnelling in weak rocks Table 28. 1 Typical steel fiber reinforced shotcrete mix Mean aggregate size 6. 35 mm Mean aggregate size 10 mm S No Material Quantity, kg/m3 Quantity, kg/m3 1 2 446 55 8 1 483 –1679 >4 45 697 88 0 – 39– 157 Varies 0.40–0. 45 700 8 75 39– 150 Varies 0.40–0. 45. .. Fig 28 .5 Typical treatment of a narrow shear zone 412 Tunnelling in weak rocks Table 28. 2 Correction factors for thickness of weak zone (b) Strike direction (θ) to the tunnel axis “b” to be replaced by 90◦ – 45 45 –20◦ 10◦ –20◦ . size 6. 35 mm Mean aggregate size 10 mm S. No. Material Quantity, kg/m 3 Quantity, kg/m 3 1. Cement 446 55 8 >4 45 2. Blended sand 6. 35 mm maximum size 1 483 –1679 697 88 0 3. 10 mm aggregate – 700 8 75 4 (SFRS) ( a )( b ) Fig. 28. 1 Difference in application of shotcrete with (a) wire mesh and (b) steel fiber. Integrated method of tunnelling 407 25mm 0.45mm 0 .53 mm 28mm 0 .50 mm Fig. 28. 2 Typical fibers. management conditions (Chauhan, 1 982 ). S. No. Management condition Rating 1. Good 80 –100 2. Fair 51 –79 3. Poor 50 Table 27.4 Ground and management factors (Chauhan, 1 982 ). Ground conditions Management