Journal of Engineering Geology, Vol. 10, No. 4, Winter 2017 3809
Performance Analysis of Nail Walls in Jointed Rocks Based on Excavation-Induced Damage
*Naeimifar I.; Department of Civil Engineering, Hashtgerd
Branch, Islamic Azad University, Hashtgerd, Iran
Yasrobi Sh., Uromeie A., Hashemi H.; Tarbiat Modares University, Tehran, Iran
Received: 3 Sep 2014 Revised 10 Nov 2014
Evaluation of the excavation-induced ground movements is an important design aspect of supporting system in urban areas. This evaluation process is more critical to the old buildings or sensitive structures exist in the excavation-affected zone. Frame distortion and crack generation are predictor of building damage resulted from excavation-induced ground movements, which pose challenges to projects involving deep excavations. Geological and geotechnical conditions of excavation area have significant effects on excavationinduced ground movements. In some cases, excavation area may be located in the jointed or weathered rocks. Under such conditions, the geological properties of supported ground becomes more noticed due to the discontinuities and anisotropic effects. This paper is aimed to study the performance of excavation walls supported by nails in jointed rocks medium. The performance of nailed wall is investigated based on evaluating the excavation-induced ground movements and
*Corresponding author [email protected]
damage levels of structures in the excavation-affected zone. For this purpose, a set of calibrated 2D finite element models are developed by taking into account the nail-rock-structure interactions, the anisotropic properties of jointed rock, and the staged construction process using ABAQUS software. The results of this paper highlight effects of different parameters such as joint inclinations, anisotropy of rocks and nail inclinations on deformation parameters of excavation wall supported by nails, and induced damage in the structures adjacent to the excavation area. The results show that the relationship between excavation-induced deformation and the level of damage in the adjacent structure.
Keywords: Excavation, Nailed Wall, Performance, Damage, Jointed Rock.
In recent years, a significant rise has been reported in use of soil nail walls as a cost-beneficial alternative to conventional retaining walls executed in top-to-bottom excavations. The construction procedure of soil nail walls is well-described in the literature . The process involves installation of the closely spaced steel bars (i.e., nails) in pre-drilled holes, which are subsequently encased in grout. Similarly, nailing method is used to stabilize the excavation wall in jointed or weathered rocks medium. This stabilization process is known as “Rock Nail Wall” . According to literature, rock nailing refers to a procedure of installing reinforcing elements into a rock mass exposed by an excavation in order to form an internally supported structure. Similar to soil nail wall, in rock nailing construction reinforcing elements are installed in a systematic array as the excavation progresses: Each row of elements is installed into natural material before the next increment of excavation .
Under both medium conditions, steel bars act as passive elements in response to the deformation of the reinforced ground during subsequent excavation activities . The supported ground should be active to develop tensile and shear capacity in steel bars. In other word, movement must occur in supported ground for creating tensile and shear stress in steel bars. This movement is a potential source for excavation-induced building damage and leads to legal disputes in urban area.Soil/Rock nail wall deflections and resultant building damage highly depends on the performance of nail in the supported medium. Thus, to evaluate the soil/rock nail wall performance, wall deflections and damage of structure in the Excavation-Affected Zone (EAZ) should be investigated.
Most research efforts have been focused on the performance of soil nail wall while performance of rock nail wall (RNW) has received less attention, despite the fact that in some projects excavation area may be located in the jointed or weathered rock medium. Performance assessment of RNW seems to be a central and yet difficult issue to be addressed by researchers. Considering the similarity between RNW and soil nail wall in terms of construction sequence, applications, load transfer mechanisms, and deformability response, the concept of soil nail wall performance can be extended to RNW performance.
Performance study of soil nail wall has been a long-standing issue in geotechnical engineering. Over the past decades, significant studies have been conducted to assess the performance of soil nail wall in the framework of experimental and numerical methods.
In stabilizing the excavation wall by nailing method, ExcavationInduced Ground Movements (EIGM) and resulted excavation wall deformation and ground settlement are unavoidable. In soft soil, the value of maximum horizontal deformations of wall face can increase up to 0.5% of the wall height . For weathered rock, stiff soil, sandy soil and fine-grained soil, the value of horizontal deformation can be estimated as follow :
is a ratio dependent on soil/rock conditions presented in table 1 and H is wall height.
Table 1.Values of
as a function of soil ground conditiond
Rock Soil Grained
and Stiff Soil
and Stiff Soil