A chasm About 50 meters deep opened in front of the Vajira Hospital of Bangkok, in Thailandsucking vehicles, damaging conducts and underground services, and putting the foundations of some buildings facing, fortunately without causing victims. Based on the information available, the event would be attributable to a combined effect between the excavation of a gallery a few meters away (future Vajira Station of the MRT Purple Line) and the damage to water conduct In depth, which may have accelerated – or triggered – the instability of the soil. Various videos of the incident have been released on the web, as clearly visible from the following post of X:
The sequence of events
The collapse occurred near the construction site of the Futura Vajira Stationnext to the hospital. The testimonies and widespread movies locally allow to reconstruct the following dynamics: opening of the cavity around the 7:13 (local time)followed by a progressive expansion For a few tens of minutes. Preliminary estimates indicate a depth of the order of Tens of meters (we speak of about 50 m). After the most intense phase, the situation went to one stabilizationwhich seems to be confirmed.
The possible causes of the enormous chasm: because the roads collapse
There is currently no official statements regarding the causes unleashing the collapse. However, in the absence of a final technical press release, it may be useful to distinguish the probable causes and the possible effects of further contributing factors:
Effects of the underground excavation
The excavation of a nearby tunnel has certainly influenced the response of the soil in adjacency. The creation of a modification gallery Tenous state of the ground Around the excavation front. On the countryside, this is manifested, in the most serious cases, with a conspicuous distribution of sagging known as subsidy: represents the configuration of the ground downstream of the deformation induced by the excavation, precisely the sagging. This is maximum in axis on the tunnel and decreases laterally, until it dissipates, moving away enough. If the conditions of support, the pressures to the front or the mechanical response of the land – which are often heterogeneous and not perfectly known before the real excavation is made – are unfavorable, the disturbed area can spread, amplify and trigger the locally collapse of the granular skeletonwith also the formation of voids that can go back to the surface.
Role of water
There presence of water It can reduce the resistance of the soil in these cases and encourage phenomena of internal erosion. In this context in which we are, two scenarios can be plausible, which concern the underground services in the ground at altitudes subjected to the road surface:
- The present conduct can be damaged as a consequence of the failure induced by the excavation: the water that is poured into the cavity already in place can amplify and accelerate the evolution of collapse.
- The conduct present are damagedfor example because they are worn, and become the cause/trigger.
In both cases, a prolonged spinning of water introduces anomalous fluid volumes in the subsoil that can generate phenomena of internal erosion (they occur when the water drags the fine particles) and/or Reduction of the attractive component among the solid particles. In both cases, consequently there is consequently a reduction in the load -bearing capacity of the soil. In the case in question, the graphic material circulating on the net shows water to escape from a conduct in the area already collapsed. This spinning then precedes a subsequent and important failure of the bottom of the hole, already present: the most realistic hypothesis is therefore that the water has aggravated A balance already compromised by the excavations.
What happens to neighboring buildings
The images show Foundation poles exposed Under some buildings, an indication of a loss of support located under the building. The presence of poles, that is Deep foundationssuggests that superficial soils have modest supporting capacities, which is why the project has foreseen the adoption of a deep foundation. THE’Exposure of the poles It does not necessarily imply implicit structural damage or imminent collapses: if the failure does not spread to the imprint of the building, the work can still be safe, especially if the poles work mainly peak, that is, on layers in depth. Having said that, it is still good practice to activate monitoring via sensor (levels of precision, inclinomers, cracks, piezometers), carry out inspections Specific post-event to test the state of safety and avoid any additional collapses.
