| Author | Phichet Morya |
| Call Number | AIT Thesis no.GE-18-05 |
| Note | A Thesis Submitted in Partial Fulfillment of the Requirements for The Degree of Master of Science in Geotechnical and Earth Resources Engineering, School of Engineering and Technology |
| Publisher | Asian Institute of Technology |
| Abstract | Tunnelling beneath the groundwater table induces groundwater to flow toward the excavation surfaces through rock fractures and fissures, and the flowing induces the generation of seepage forces radially acting on the opening surfaces and supports. The delay of tunnel construction and support measures installation, and unsafe tunnel construction are main risks usually challenging most of tunnel excavation project due to high water inflow. Tunnel excavation in Mae Ngad - Mae Kuang Water Diversion Tunnel Project has hit several water-bearing zones. The inflow more than 500 liters/minute was frequently recorded but the allowable water inflow level for this project is 60 liters/minute. With an insufficient capacity of water pumping of the project, water left in the tunnel raised to the maximum level of 0.5 meters. Multi-standpipe grouting is conducted in those zones to reduce the permeability of the surrounding rock mass. This study focuses on the assessments of the grouting operation applied in the project. Moreover, grouting monitoring graphs recording real-time grouting pressure and grout flow were used to estimate the penetration length of grouting of a number of selected standpipes based on the Real Time Grouting Control (RTGC) Method by applying the theory of grout spread so that the grouting design can be evaluated and an optimized design can be established.
Multi-standpipe grouting is conducted by inserting three standpipes into drilled holes at different depth and injecting individual grouts to each standpipe so that different zones along the boreholes can be treated properly by different materials and operational techniques. Two grout mixes is used in this project site. One is the combination of cement slurry w/c 1.0 with 50.8% sodium silicate and 0.02% silica sol which harden within 13 second. Another is the mixture of sodium silicate with silica sol getting hardened in three seconds. Water inflow into the tunnel after grouting significant reduced from several hundreds per hole to less than 5 liters/minute in the next tunnel faces.
Based on the analysis of grout spread using the RTGC method, allowable grouting pressure of 50 bar is considered to be too high because sign of jacking is usually observed when the grouting pressure reach 30-50 bar. The reduction in the penetration length and the increase of the fracture volume is the consequences of jacking. By limiting the grouting pressure at 30 bar, the obtained penetration length is around 20 meters. Consequently, fifty-five and sixty percent of grouts injected and time spent, respectively, can be saved. |
| Year | 2019 |
| Type | Thesis |
| School | School of Engineering and Technology (SET) |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Geotechnical Engineering (GE) |
| Chairperson(s) | Kuo Chieh Chao; |
| Examination Committee(s) | Kuo Chieh Chao;Noppadol Phien-wej; |
| Scholarship Donor(s) | His Majesty the King’s Scholarships (Thailand); |
| Degree | Thesis (M. Eng.) - Asian Institute of Technology, 2019 |