Application of risk assessment in design of long mountain tunnel in Northern Thailand | |
| Author | Kan Kaewkongkaew |
| Call Number | AIT Diss. no.GE-13-01 |
| Subject(s) | Tunnels--Thailand, Northern Design Tunnels--Risk asssessment--Thailand, Northern |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Geotechnical and Earth Resources Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Series Statement | Dissertation ; no. GE-13-01 |
| Abstract | The dissertation describes geological structure of the Mae Tang-Mae Ngad-Mae Kuang Diversion tunnel project for augmentation of water supply in Chiangmai area which will have a total length of 48 km to be excavated a large depth below mountain tops. The tunnel traverses various rock units including limestones, granites, shales, sandstones and other meta-sedimentary rocks, etc. The geologic structures of the rock masses in the area were complex. They consisted of numerous folds and faults that were resulted from the past plate tectonic movement of the Southeast Asia and Indochina region as a part of the collision of the Indian Plate with the Eurasian Plate producing the Himalaya Mountain Ranges.The geological model of project area was constructed for better understand on geological of study area based on tectonic information, field investigation, and laboratoriestesting results. The tunnel alignment of the project falls in the area between three of these major fault zones: the Mae Ping, Mae Tha, and Mae Kuang faults. In the project area, it was clearly identified that extensive strike-slip faults traverse the tunnel alignment at the Mae Ping River, Mae Rerm reservoir area, and a north-south trending minor basin between the Mae Ngad and Mae Kuang reservoirs. The fault zones pose serious problems for tunnel excavation, such as tunnel collapse, ground water flow, time delay, and cost overrun.The limitation in geotechnical data and budget affects the accuracy of the geological model, particularly for projects of long and deep tunnel of which accessibility to the excavation points is difficult and far reaching. Therefore, an approach adopted for interpretation plays an important role on the level of uncertainty of the derived geological model. Rock mass quality in term of RMR values was studied in three cases by geostatistic approach that is focused on estimating values at unknown points by using existing values. The first case is the tunnel of Lam Ta Khong pumped storage project excavated in a simple geological setting of near horizontally bedded sedimentary rocks. The second case is tunnels of Khlong Tha Dan dam project which is situated in a complex geological setting of volcanic rocks in proximity of a regional fault zone. Finally, tunnel of Mae Tang-Mae Ngad diversion tunnel which is situated in a complex geological setting of highly tectonic disturbance. Kriging estimated reasonably well the RMR values for purpose of geo-prediction for tunnel construction in case of simple geology setting such as that of Lam Ta Khong pumped storage project but it is unsatisfactory for case of Klong Tha Dan Dam project of which the geologic settling is complex.The kriging estimation has shown a low quality of RMR distribution along Mae Tang-Mae Ngad diversion tunnel because highly variation of data set results in unsmooth estimating values. This discrepancy may be attributed to the fact that a long distance between data points in borehole locations result in less correlation between data pairs. For long and deep mountainous tunnels, amounts of geological information for design prior to construction phase are never enough owing to the nature of the project and typical budget allocation. Therefore, high uncertainty on the ground condition and excavation and support design along the tunnel length exists and ought to be considered in the project planning and implementation. In this study, the risk assessment of Mae Tang-Mae Ngad tunnel project was conducted by means of adopting a systematic approach in determination of potential rock behavior types that would demand different excavation and tunnel support measures which reflects in cost and time of the works. The suggested method of tunnel rock behavior by Russo (2008) and Stille and Palstrom (2008) were adopted. Influencing factors considered in determination consisted of tunnel depth, rock types, strength, fractures (RMR), faults,and groundwater, Influencing factors potential rock behavior were estimated for each chainage of tunnel on the basis of geological investigation and random variables generation. Statistical variability was considered in the determination of some of the factors, i.e. strength and RMR so that scenarios of most likely, less favorable and more favorable conditions of cost and time can be determined. The adopted method of the tunnel excavation and support design indicated that the cost of the unfavorable scenario is 1.3 times the most likely scenario. And the cost of the favorable scenario is 0.8 times the most likely scenario. A comparison was also made between the design based on this adopted method and the one actually adopted in the project design which followed the Austrian Geomechanics Guideline (2001) |
| Year | 2014 |
| Corresponding Series Added Entry | Asian Institute of Technology. Dissertation ; no. GE-13-01 |
| Type | Dissertation |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Noppadol Phien-wej; |
| Examination Committee(s) | Pham Huy Giao ;Chotchai Charoenngam ;Thanu Harnpattanapanich; |
| Degree | Thesis (Ph. D.) - Asian Institute of Technology, 2014 |