Additive Manufacturing in Off-Site Construction: Review and Future Directions

Additive manufacturing (AM) is one of the pillars of Industry 4.0 to attain a circular economy. The process involves a layer-by-layer deposition of material from a computer-aided-design (CAD) model to form complex shapes. Fast prototyping and waste minimization are the main benefits of employing such a technique. AM technology is presently revolutionizing various industries such as electronics, biomedical, defense, and aerospace. Such technology can be complemented with standardized frameworks to attract industrial acceptance, such as in the construction industry. Off-site construction has the potential to improve construction efficiency by adopting AM. In this paper, the types of additive manufacturing processes were reviewed, with emphasis on applications in off-site construction. This information was complemented with a discussion on the types and mechanical properties of materials that can be produced using AM techniques, particularly metallic components. Strategies to assess cost and material considerations such as Production line Breakdown Structure (PBS) and Value Stream Mapping are highlighted. In addition, a comprehensive approach that evaluates the entire life cycle of the component was suggested when comparing AM techniques and conventional manufacturing options.

A case study on TBM cutterhead temperature monitoring and mud cake formation discrimination method

The mud cake is easily formed during the tunnel boring machine (TBM) excavation in clay soils or rocks containing clay minerals. Mud cake will lead to soil disturbance of tunnel face, clogging cutterhead and even affect the construction efficiency and personnel safety. In this study, a discrimination method of mud cake formation based on cutterhead temperature was proposed. An online monitoring system was designed and installed on the slurry balance TBM. The results show that: (a) the cutterhead temperature data can be reliably detected and transmitted by the system; (b) in a tunneling cycle, the temperature at some positions of the cutterhead will increase first and then decrease; (c) during the field test, the temperature variation is around 2.5 °C under the normal condition, but the temperature variation will increase more than 50 °C due to the mud cake or geological change; (d) compared with the cooling rate, mud cake formation can be accurately discriminated.

Optimization of Compaction Quality Control in the Core of Random Fillings within Linear Infrastructures: Application to Metamorphic Slate Fillings

The construction of random fillings from the excavation of medium hardness rocks, with high particle sizes, presents limitations in compaction control. This research applies new control techniques with revised test procedures in the construction of the random fillings core, which constitutes the main part of the embankment, with the bigger volume and provides the geotechnical stability to the infrastructure. The maximum thickness over each of the compacted layers researched that made up the random fillings was 800 mm. As there are many types of rocks, this research is applied to metamorphic slates. Quality control was carried out by applying new research associated with the revision of wheel impression test, topographic settlements, and plate bearing test (PBT). Thus, new test procedures are established, defining efficient thresholds. Comparisons make it possible to choose representative tests, avoiding duplication. The optimization of control reduces inspection times, ensuring quality adapted to the high construction efficiency of diggings. Traditionally, rocks were rejected due to their maximum size, underutilizing the use of high-quality materials. Promoting their utilization implies a better use of resources, and therefore, a higher environmental efficiency. A statistical analysis of the core of 16 slate random fillings was carried out, with a total of 2250 in situ determination of density and moisture content, 75 wheel impression tests, 75 topographic settlement controls, and 75 PBT. The strong associations found between different tests allowed to simplify the quality control.

Stormwater Detention Ponds in Urban Catchments—Analysis and Validation of Performance of Ponds in the Ouseburn Catchment, Newcastle upon Tyne, UK

The impact of stormwater drainage and detention ponds on flooding is assessed using statistical analysis and physically based computer simulation of a 45-year case study for a peri-urban catchment. In 1978, the 54 km2 Ouseburn catchment in Newcastle upon Tyne was impacted by the connection of a new 2.1 km2 residential development, directly to the Ouseburn River, via a stormwater drain, which reduced the time to peak and increased flood risk. Further residential developments of 1.6 km2 have been built since 2004, again with separated sewer systems, but this time linked to stormwater detention ponds before draining into the Ouseburn River. Detailed analysis of the data, confirmed with computer simulation, shows that in contrast with the 1978 intervention, these new developments had only a minimal effect on the flows in the Ouseburn River, in fact achieving a small reduction in peak flows for large events. This study assesses the post-construction efficiency of such systems, and we show that the stormwater detention ponds are working as designed.

A Case Study on TBM Cutterhead Temperature Monitoring and Mud Cake Formation Discrimination Method

The mud cake is easily formed during the tunnel boring machine (TBM) excavation in clay soils or rocks containing clay minerals. Mud cake will lead to soil disturbance, clogging cutterhead and even affect the construction efficiency and personnel safety. In this study, a mud cake formation discrimination method based on cutterhead temperature was proposed. An online monitoring system was designed and installed on the slurry shield TBM. The results show that: (a) the cutterhead temperature data can be reliably detected and transmitted by the system; (b) in a tunneling ring, the temperature at some positions of the cutterhead will increase first and then decrease; (c) during the field test, the temperature variation is around 2.5℃ under the normal condition, but the temperature variation will increase more than 50℃ due to the mud cake or geological change; (d) compared with the cooling rate, mud cake formation can be accurately discriminated.

Structural Behavior of Prefabricated Ecological Grid Retaining Walls and Application in a Highway in China

The retaining wall is a common slope protection structure. To tackle the current lack of sustainable and highly prefabricated retaining walls, an environmentally friendly prefabricated ecological grid retaining wall with high construction efficiency has been developed. Due to the asymmetrical condition of the project considered in this paper, the designed prefabricated ecological grid retaining wall was divided into the excavation section and the filling section. By utilizing the ABAQUS finite element software, the stress and deformation characteristics of the retaining wall columns, soil, anchor rods, and inclined shelves in an excavation section, and the force and deformation relationships of the columns, rivets, and inclined shelves in three working conditions in a filling section were studied. The study results imply that the anchor rods may affect the columns in the excavation section and the stress at the column back changes in an M-shape with height. Moreover, the peak appears at the contact point between the column and the anchor rod. The displacement of the column increases slowly along with the height, and the column rotates at its bottom. In the excavation section, the stress of the anchor rod undergoes a change at the junction of the structure. The inclined shelf is an open structure and is very different from the retaining plate structure of traditional pile-slab retaining walls. Its stress distribution follows a repeated U-shaped curve, which is inconsistent with the trend of the traditional soil arching effect between piles, which increases first and then decreases. For the retaining wall structure in the filling section, the numerical simulated vehicle load gives essentially consistent results with the effects of the equivalent filling on the concrete column.

Strength Characteristics and Microstructure of Cement Stabilized Soft Soil Admixed with Silica Fume

Soft soil improvement is an important subject in civil engineering, and searching for an effective admixture is an important research. Silica fume (SF) is a kind of recycled material, it can be used in engineering as a pozzolanic material. The main objective of this study is to assess the effectiveness of industrial waste silica fume (SF) as an admixture to improve the cement stabilized soft soil. The unconfined compressive test (UCT) and scanning electron microscopy (SEM) test of cement stabilized soil with different SF contents and different curing times have been carried out. UCT after 28 days revealed that the addition of SF can effectively increase the strength of cement stabilized soil and reduce the amount of cement, and 1.5% SF content is considered optimum, excessive SF will not further increase the strength. SF helped to accelerate the cement hydration reaction and significantly improve the early-age strength of stabilized soil even at 3 days, which can improve construction efficiency in actual projects. SEM analyses shows that the proper SF content could make the hydration product calcium silicate hydrate gel (CSH) fill the pores and increase the strength of the material, but excessive SF will increase the large pores content of the material and reduce the strength. This provided a basis for application of SF in improving soft soil.

Research Studies on the Thrust of Special-Shaped Full-Sectional Cutterheads of Quasirectangular Shield

Thrust of shield cutters is the major parameter of tunnel construction and an important index for shield machine design. The thrust bearing resistance of a shield machine has a significant impact on its construction efficiency and safe operation. The use of quasirectangular shield not only can increase the space utilization rate but also avoid the deformation of the back soil when compared with a conventional circular or rectangular shield. In this paper, structural analysis of quasirectangular shield cutterhead is carried out and a corresponding mathematical thrust model is developed. Both the stress and displacement distributions of cutterhead are calculated. It is found that the stress value in most regions of the cutterhead is between 5 MPa and 45 MPa. The maximum stress is 208.44 MPa, which is at the middle part of the rib and is below the yield limit. The maximum deformation is found in the center area of the chest plate, the value of which is also within the design requirement. In addition, a monitoring method suitable for quasirectangular shield is proposed. The appropriateness and reliability of the proposed monitoring method are demonstrated by the comparison between the numerical simulation and monitoring method.

Development of Material Combination Model Considering Economics and Construction Efficiency for G-SEED Certification

The Korean government proposed a goal to reduce its greenhouse gas emissions by 37% compared to business-as-usual levels by 2030 and launched the Green Standard for Energy and Environmental Design (G-SEED) certification system. The certification requires meeting the required score and material selection with a secured economy and construction efficiency. However, most buildings only focus on obtaining the certification scores instead of choosing economical materials with high construction efficiency. This research focused on developing a material selection model that considers both the construction efficiency and economy of the materials and the acquisition of material and resource evaluation scores from the G-SEED certification. This research, therefore, analyzed actual data to automate the material selection and compare alternatives to using a genetic algorithm to obtain optimized alternatives. This model proposes an alternative to constructability and economy when the required score and material information is entered. When the model was applied to actual cases, the result revealed a reduction in construction costs of about 37% compared to the cost with the traditional methods. The material selection model from this research can benefit construction project owners in terms of cost reduction, designers in terms of structural design time, and constructors in terms of construction efficiency