Effects of twin tunnels construction beneath existing shield-driven twin tunnels

This paper presents a case of closely spaced twin tunnels excavated beneath other closely spaced existing twin tunnels in Beijing, China. The existing twin tunnels were previously built by the shield method while the new twin tunnels were excavated by the shallow tunnelling method. The settlements of the existing tunnels and the ground surfaces associated with the new tunnels construction were systematically monitored. A superposition method is adopted to describe the settlement profiles of both the existing tunnels and the ground surfaces under the influence of the new twin tunnels construction below. A satisfactory match between the proposed fitting curves and the measured settlement data of both the existing tunnels and the ground surfaces is obtained. As shown in a particular monitoring cross-section, the settlement profile shapes for the existing tunnel and the ground surface are different. The settlement profile of the existing structure displays a “W” shape while the ground surface settlement profile displays a “U” shape. It is also found that due to the flexibility of the segmental lining, the ground losses obtained from the existing tunnel level and the ground surface level in the same monitoring cross-section are nearly the same.     

Pullout performance of GFRP anti-floating anchor in weathered soil

Anchors are often used as anti-floating reinforcements in civil engineering structures. However, conventional steel bars present disadvantages concerning corrosion and poor adaptability to aggressive environments. Glass fiber-reinforced polymer (GFRP) components could provide a solution to these problems. In this paper the feasibility of GFRP anti-floating anchors is evaluated. Four full scale pullout tests were performed in moderately decomposed granite (MDG). Bare Fiber Bragg grating (FBG) sensors were embedded into the specimens during the pultrusion process to monitor the stress–strain distribution along their lengths. Based on the results the behavior of the anchors was assessed, including the relationships between the pullout force and the head displacement, the axial strain along anchors and the shear stress at the GFRP-grout interface. The stress distribution of anchors showing interlaminar shear failure was then analyzed based on a maximum shear stress criterion. It was proved that the load transfer mechanism of GFRP and steel anti-floating anchors differs significantly. GFRP anti-floating anchors reach failure due to interlaminar shear failure, while conventional steel anchors generally fail as a result of shear at the grout–soil interface. The test results also showed that the embedded FBG technique is reliable for monitoring the stress–strain state of an anisotropic material.     

Influence of wavelength-to-excavation span ratio on ground motion around deep underground excavations

Accurate estimation of ground motion around excavations is important for dynamic rock support design in deep civil tunnels and underground mines. Among the influencing factors, the wavelength-to-excavation span ratio (λ/D) has a large effect on ground motion. Using an advanced wave propagation simulation tool, we performed two series numerical experiments to study the effect of the λ/D ratio on ground motion near excavation boundaries. The modeling results reveal that the wave field becomes more complex as the λ/D ratio decreases. The absolute PPV (Peak Particle Velocity) values around an excavation are closely related to the intensity of the seismic source but the relative PPV value depends on the λ/D ratio. Amplification factors, defined as the PPV in the excavation model to the PPV in the background model without any excavation, are calculated for each case. The amplification factor around the excavation increases significantly as the λ/D ratio decreases. When the λ/D ratio is greater than 30, the wave amplitudes are less affected by the excavation and a seismic wave loading can be considered as “quasi-static.” When the λ/D ratio is less than 20, significant wave interaction occurs and the wave loading needs to be considered as “dynamic.” The numerical results provide additional insights into the ground motion behavior around excavations under both “quasi-static” and “dynamic” loading conditions.     

Field performance of concrete pipes during jacking in cemented sandy silt

Although many field investigations into pipe-jacking installation have been reported within the literature, there are few reports on the rebar stress in jacking pipes. This paper presents the field performance of concrete pipes during the jacking carried out under the Guan River in Jiangsu, China. Rebar stresses at two wings (the left and right side), the top crest, and the base in the longitudinal and circumferential directions for four different pipes were monitored. The maximum rebar stresses during the jacking were 37.1 MPa in the longitudinal direction and 36.6 MPa in the circumferential direction. However, the maximum rebar stresses after construction were only 18.5 MPa in the longitudinal direction and 20.3 MPa in the circumferential direction. A normalized jacking force “α” is proposed to evaluate the additional rebar stress in jacking pipes. The range of α is from 0.04 to 0.25. The relationship between the rebar stress and the construction procedure is presented and discussed. An excessive jacking force, an alignment deviation or an increased penetration rate would generate a large incremental rebar stress.     

The impact of the physical model selection and rock mass stratification on the results of numerical calculations of the state of rock mass deformation around the roadways

At present, the basic methods used for designing and evaluating the stability of mine workings are numerical models. The finite element method is the most popular method for engineering purposes. However successful calculations depend not only on the proper selection of geomechanical properties of rocks but mainly on the proper selection of a physical model describing the behavior of the rock mass and a selection of the correct failure criterion. The best way of verifying results of the calculations is to carry out investigation in the field, then.This article shows how the choice of a numerical model affects the size of the calculated damage zone around the working. To that end, numerical calculations considering elastic and elastic–plastic models were performed for six roadways. The rock mass was further differentiated in terms of its stratification and approach to mechanical properties of the rock mass. The results of these calculations were compared with measurements of mine convergence and the damage zone range in the roof. Such measurements were carried out at hard coal mine roadways.     

Modelling the service life of rendered facades using fuzzy systems

The knowledge of the service life and durability of building components is paramount to sustainable analysis and decision making since it allows a more rational management of the maintenance of building and provides data for life cycle analysis procedures. Nevertheless, predicting the service life of a building or its components is a complex process with which a number of variables are associated. The main difficulties associated with service life prediction are related to the complexity of the degradation phenomena and to the lack of understanding of degradation factors and mechanisms. This paper aims at establishing a model for the service life prediction of rendered facades using a Takagi–Sugeno fuzzy model. The models proposed include the variables that influence the degradation of rendered facades (render age, render type, building height, facade orientation, exposure to damp, and facade protection level). In this study, the degradation condition of 100 case studies located in Portugal is analyzed based only on in situ visual inspections. The proposed models are able to describe appropriately the degradation of rendered facades and to predict the service life of the sample analyzed.     

Real-time visualization of building information models (BIM)

This paper highlights and addresses the complexity and challenges involved in visualizing large and detailed Building Information Models (BIM) in real-time. The contribution of the paper is twofold: (a) an in-depth analysis of four commonly used BIM viewers in terms of real-time rendering performance and (b) the development and validation of a prototype BIM viewer specifically designed to allow real-time visualization of large and complex building models. Regarding existing BIM viewers our results show that they all share limitations in their ability to handle large BIMs taken from real-world projects interactively. However, for the same test models our prototype BIM viewer is able to provide smooth real-time performance without sacrificing visual accuracy. By taking advantage of an efficient visibility determination algorithm, our prototype viewer restricts rendering efforts to visible objects only, with a significant performance increase compared to existing BIM viewers as a result.     

Automated assembly discrepancy feedback using 3D imaging and forward kinematics

Assembly of steel structures, modules, and pipe spools requires cycles of fitting and alignment in fabrication facilities and on construction sites. To minimize this work, good discrepancy feedback for automated refitting and realignment is required. A framework for such feedback is presented here that overcomes current limitations. It commences with a constrained registration step to overcome the incapabilities of the current discrepancy analysis approaches. By borrowing concepts from robotic kinematics and 3D image alignment theories, forward kinematics models are generated link by link, and thus provide the means for a local discrepancy analysis for quantifying the deviations autonomously. Experiments show that the proposed approach is suitably accurate and sufficiently fast to be employed for real-time feedback in order to systematically and automatically develop the realignment plans required for refitting and realigning assemblies, which is the key contribution of the work presented in this paper.     

Mapping actual thermal properties to building elements in gbXML-based BIM for reliable building energy performance modeling

The ability to import building geometric and construction thermal data from building information models (BIM) has significant potential to reduce the time and uncertainty in building energy modeling process. In today's BIM-based energy modeling practice, thermal properties are mainly derived from generic building construction types in BIM. However, for energy modeling of existing buildings, such assumptions are often inaccurate as they do not account for diminishing thermal resistances of building materials instigated by their deteriorations. To improve the reliability of BIM-based energy modeling, we present a system, together with new methods for automated association and updating of actual thermal property measurements with BIM elements in gbXML schema. By leveraging collections of digital and thermal images and based on environmental measurements, our system first produces a 3D thermal model for the building under inspection and then derives the actual thermal resistances of the building assemblies at the level of 3D vertexes. By associating these measurements with their corresponding elements in gbXML, thermal properties of the BIM elements are automatically updated. Our experiments in real-world residential and instructional buildings show how actual thermal properties can be automatically associated with BIM elements and updated in gbXML. The proposed method shortens the gap between architectural information in BIM and the actual data needed for energy performance simulation, and enables reliable BIM-based energy analysis for retro-commissioning, continuous commissioning, and retrofit.