Deep Excavation Design in Digital Twin City Environment in Bucharest, Romania

We currently live in transformative times in terms of technological progress, including how engineers approach the process of deep excavation design. The term “digital twin cities” is an integral part of the transformation that is taking place in engineering. In essence, a twin city is a digital, simplified 3D model of an actual built environment. For our purposes, a twin city is useful as we can quickly access building locations and sizes, and estimate design loads. In this manner, engineers can more quickly evaluate and perform deep excavation designs next to neighboring structures. The problem up to now has been that such solutions that bring in together full deep excavation design and twin city capabilities simply did not exist. This article presents how a real deep excavation design can be performed in a twin city environment with a commercially available software.

TRADITIONAL VERSUS NEW DESIGN PROCESS

In a traditional deep excavation design, the process would generally involve the following steps:

• Gather site and geotechnical information
• Estimate geotechnical properties and sections
• Send a topographer to measure adjacent sites
• Estimate building loads
• Perform deep excavation designs on simplified two-dimensional sections
• Independently analyze the bracing system in a structural analysis software
• Revise design as necessary
• Do not perform impact assessment on adjacent structures due to complexity and cost concerns

In the new integrated twin city approach, the process can be modified to:

• Gather site and geotechnical information
• Estimate geotechnical properties and sections within the software or as dictated by the geotechnical report.
• Import the twin city information including buildings, topographic surveys, utilities, etc.
• Superimpose and site drawings on the twin city model
• Prepare a basic two-dimensional section and optimize
• Draw the excavation perimeter, and generate a 3D arrangement of internal bracing
• Use the software to cut various analysis sections, generally involving 3D twin buildings
• Analyze, optimize, and compare 3D generated sections vs. models with simplified loading
• Optimize the 3D bracing
• Access impact on adjacent structures with a damage assessment

CASE HISTORY

For demonstration, a recently constructed deep excavation in Bucharest, Romania is presented. Construction of a new residential luxury building required a two-level basement with depths from 8 to 10 m. The site was relatively narrow with an opening between property limits of approximately 20 m. Residential buildings are abating the site on two sides of the excavation and as a result, the design had to carefully consider wall deformations. Soils at the site consisted of soft and stiff clays for the upper 2 m and then a series of medium-dense to dense sands, silts, and gravels. The groundwater table was reported at approximately 8 m below the ground surface.

Figure 1: Site map with deep excavation system and twin buildings

The earth retention wall system consisted of 600 mm drilled reinforced concrete piles at 1.0 m maximum horizontal spacing. Two levels of steel struts provided bracing for the 10 m deep sections, and one level of struts braced the 8 m deep sections. The top strut was connected to a 1 m tall reinforced concrete capping beam. The specialty contractor was GT GROUND ENGINEERINGS & CONSTRUCTION SERVICES.

Figure 1 presents the site location map, together with a view of the bracing and wall system. Imported twin structures are seen with blue and green colors over the map. Pilings, walers, and two cut design sections are also visible in the figure.

Given the uncertainties in the geotechnical world and especially in deep excavation design, it is always the wisest to perform at least two different analysis types. In this case, the excavation was analyzed with three different analysis methods using the DeepEX 2023 software by Deep Excavation LLC:

• LEM: Limit Equilibrium Method, is the conventional design approach involving apparent earth pressures such as Peck, EAB, and FHWA (Federal Highway Administration, US).
• NL: Non-Linear elastoplastic Winkler-based method with both active and passive soil springs.
• FEM: Finite Element Method, where the soil is discretized in smaller elements and soil structure interaction can be fully accounted for.

Typical results for the 10 m deep excavation sections are summarized in Table 1. Figures 2 through 5 present typical analysis sections for various models. As can be seen, the LEM approach produced the largest support reactions vs. the other two methods. Wall bending moments were comparable between all three methods.

Analyzing the waler-prop system solely on a 2D analysis can potentially lead to missing out on axial force distributions. Figure 5 presents typical diagrams with waler and strut demand-to-capacity ratios as well as estimated 3D ground surface settlements. Lastly, figure 6 presents a visualization of the same model with augmented reality using the HoloLens 2 augmented reality glasses by Microsoft and the HoloDeepEX software that accompanies DeepEX. The model is directly generated from the design using imported twin city information. Beyond just being impressive, the AR model allows users to walk in real space and project the 3D model in the actual environment. With this model, engineers can “see” below the ground and communicate important ideas or issues to stakeholders who may not be familiar with all the intricacies of deep excavation design and construction.

Figure 6: Augmented reality model view in real space with building footprints

CONCLUSIONS

Technological advancements allow modern engineers to incorporate digital twin city information directly into their designs. This article presented a novel process for including digital twin city information in a deep excavation design for a case history in Romania. Whereas many simplifications would have to be made in the past, the new approach allows engineers to quickly estimate building loads and their impact on deep excavation design. Moreover, engineers can also visualize designs in augmented reality and clearly demonstrate the complexities of deep excavations to project stakeholders.

Autors:

Dimitrios C. KONSTANTAKOS, CEO Deep Excavation LLC, Adj. Prof. New York University

Monica TSITSAS, General Manager GT Engineering Partners

…citeste articolul integral in Revista Constructiilor nr. 198 – decembrie 2022, pag. 128-131