LNEC support to the design adaptation of Alto Tâmega dam due to the rockslide on the right bank slope


José Muralha, António Batista, Luís Lamas, Juan Mata & Carlos Serra


ABSTRACT: During the excavations for the Alto Tâmega dam, a rockslide occurred on the right bank slope immediately downstream from the dam insertion surface, involving a volume of about 23,000m3


,


which led to the complete stop of the works. To resume construction, design adaptations had to be introduced to stabilize the downstream slope and ensure adequate safety conditions during dam construction, first filling and operation. The main measures adopted were the following: i) construction of a concrete structure anchored to the rock mass, to replace the volume of rock mass that was affected by the landslide; ii) adjustment of the insertion surface by deepening and widening the excavation of several dam blocks; iii) extension of a gallery in the foundation to monitor two faults and to increase the drainage of the rock mass; and iv) relocating, symmetrically, the dam’s bottom discharge from the right side of the river bed to its left side. Additionally, a series of procedures related to the monitoring plan aimed at guaranteeing adequate safety conditions for the work execution and, mainly, to ensure that the project adaptations yielded the intended effects were implemented. This paper presents a brief description of the events preceding the slope failure, a description of the countermeasures that were implemented to ensure dam safety and some results of the monitoring of the right bank during dam construction and the first filling of the reservoir..


Keywords: Alto Tâmega dam, construction, rockslide, design adaptation, safety control.


1. Introduction The Alto Tâmega dam, located on the Tâmega River - a right-bank tributary of the Douro River in northern Portugal - forms a crucial part of the Tâmega Electrical Production System (SET), owned by Iberdrola Generación. The dam is a double-curvature concrete arch structure founded on a metamorphic rock mass predominantly composed of mica schists, with the powerhouse located at the downstream toe (Figure 1 and Figure 2). From a preliminary design[1,2]


, the final design was entrusted to Granell Ingenieros Consultores[3,4] . LNEC


(National Laboratory for Civil Engineering, in Lisbon) provided technical support to the owner during Author details: National Laboratory for Civil Engineering (LNEC), Email: jmuralha@lnec.pt


Vol XXXIII Issue 3 | Dam Engineering | 123


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100