PSI - Issue 64

Maysam Jalilkhani et al. / Procedia Structural Integrity 64 (2024) 161–167 Author name / Structural Integrity Procedia 00 (2019) 000–000

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3

The genesis of these methods dates back to the 1950’s, coinciding with rapid urban development and the need to retrofit underground tunnels for impending subway and tube systems (Malinowska, 2013). For example, Skempton and MacDonald (1956) conducted on-site visual inspections of ninety-eight buildings affected by ground subsidence to determine maximum allowable settlement and distortion for different structural systems. However, these assessments ignored important structural features such as building typology. Subsequently, simpler methods, like that proposed by the National Coal Board (NCB, 1975), emerged, initially reliant on building length. Over time, these methods evolved to include additional parameters, such as foundation type, as sophistication increased. Dzegniuk al (1997) developed a complex model that incorporates additional building parameters and computes a resistance category using a scoring system. These parameters, such as building length, shape, foundation type, ground condition, and building state, are individually assessed, and assigned scores. The summation of these scores determines the vulnerability class of the building, considering horizontal ground strain, and provides a qualitative description of expected damage (see Table 1). Although point methods for evaluating building strength are more time-consuming, their accuracy is expected to be higher due to individualized approach (Malinowska, A., 2013). The report by Mine Subsidence Engineering Consultants (MSEC, 2007) identifies various ground motions induced by mining, including vertical subsidence, horizontal displacements, horizontal strain, curvature, tilt, and strain-curvature combinations. It emphasizes the influence of building configuration, design, and material quality on its response to mining-induced subsidence. Properly designed foundations capable of accommodating differential settlements, exhibiting more “flexible” behavior or materials, demonstrate lesser susceptibility to damage compared to those neglecting such considerations. Additionally, longer buildings are noted to experience greater extension due to direct ground strain and bending strain, aligning with initial model developments. The report provides an abacus correlating damage levels with different impact categories based on expected crack width limits in the structure (see Table 2). Notably, strain values used in the abacus refer to those happening in the structure. However, conversion of ground strains into structure strains necessitates accounting for the effects of mining-induced hogging or sagging curvature on the structure. Table 1. Definition of resistance categories as outlined by Dzegniuk et al. (1997) TOTAL SCORE Up to 20 21-27 28-36 37-47 48 and over VULNERABILITY CLASS HORIZONTAL GROUND MOTION (mm/m) >9 6-9 3-6 1.5-3 1.5 DAMAGE CATEGORY Very severe Severe Moderate Slight Negligible

Table 2. Wall impact classification as defined by MSEC (2007) Description of Impact with Reference to walls and required repair

Impact class

Approximate crack width limit

0 1

Hairline cracks

<0.1 mm

Fine cracks which do not need repair

0.1 mm to 1.0 mm

Cracks noticeable but easily filled. Doors and windows stick slightly Cracks can be repaired and possibly a small amount of wall will need to be replaced. Doors and windows stick. Service pipes can fracture. Weather-tightness often impaired Extensive repair work involving breaking-out and replacing sections of walls, especially over doors and windows. Window or door frames distort. Walls lean or bulge noticeably. Some loss of bearing in beams. Service pipes disrupted. As above but worse, and requiring partial or complete rebuilding. Roof and floor beams lose bearing and need shoring up. Windows broken with distortion. If compressive damage, severe buckling and bulging of the roof and walls.

2

1 mm to 5 mm

5 mm to 15 mm, or a number of cracks 3 mm to 5 mm in one group 15 mm to 25 mm but also depends on number of cracks

3

4

5

> 25 mm

A basic comparison (Saeidi et al, 2013) shows discrepancies in results when applying these methods to the same site due to their development within specific contexts (i.e., geology, mining characteristics, and so on) and utilizing