Development of a risk mapping along a railway

Gobbi, Felipe; Pereira, Alvaro; Denardin, Bruno; Madrid, Fabiano; Liboreiro, Karine; Coelho, Adoniran

doi:10.28927/SR.2023.005523

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Case Study • Soil. Rocks 46 (4) • 2023 • https://doi.org/10.28927/SR.2023.005523 copy

Development of a risk mapping along a railway

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The Ramal Trem Turístico (RTT), a 17 km long railway between Ouro Preto and Mariana, a centenary line, currently in operation as a tourist attraction with historical importance. The railroad was built along a steep region, with hundreds of slopes, and eventually slope instabilities compromised the tour. In linear infrastructure projects, a risk assessment is an important tool for risk management, mapping it is the first step. After slope instabilities in 2019, a risk map was elaborated early 2021 for RTT. Risk is obtained by multiplying the probability of a certain event to occur by its consequences. Define its value in a quantitative way demands geotechnical investigation, for precise failure probability. Regardless of its importance, its determination needs high resources, specially for linear infrastructure in a region with heterogeneous geology and pedology. Therefore, for the risk mapping of the RTT, a semi-empirical methodology was adopted, based on the Rockfall Hazard Rating System (RHRS), originally developed for rocky slopes, and adapted for the registration of slopes in soil and in landfill. The aim of the method is to register a series of slope characteristics to be assigned a specific score, framing the slopes within pre-defined risk classes. This methodology was applied to this 17 km railway and identified 286 slopes. In January 2022 extreme rainfall triggered slopes instabilities at RTT. A critical analysis of this event shows a satisfactory result for the applied methodology. Risk mapping is an important tool for risk management, helping to prioritize investments in mitigation measures.

Keywords
Risk mapping; Semi-empirical method; RHRS; Railway risk

Consequence	Definition
Element and number of exposed people	Building, people, drainage
Vulnerability	Depends on the size of event, energy, potential damage
Time of exposure	Time probability of presence the exposed element at the exact moment of failure

Probability	Definition
Slope type and geometry	Defines the mechanisms, energy levels, height and slope inclination
Railway geometry	Evaluates: curves, driver time of response, setback of the slope
Slope structure and signs of instabilities	Structural condition of the rockface, erosion signs, tension cracks, etc..
Drainage	Evaluate the correlation between drainage system and stability
Historical cases	Evaluates the historical data of events

Risk Classification System for Rock Slopes
CATEGORIA			Classification and scoring criteria
CATEGORIA			3 Points	9 Points	27 Points	81 Points
1.1 Elements at risk: People			Psychological effects	Minor injuries	Serious injuries	Fatality
1.2 Elements at risk Environment			No impact	Punctual impact	Local impact	Regional Impact
1.3 Elements at risk: Financial			>US$10M-US$100 M	>US$ 100M-US$1bi	>US$ 1 bi-US$3bi	>US$ 3 bi
2. Exposure Time			25% of the time	50% of the time	75% of the time	100% of the time
3. Slope height			>7.5 m	>15 m	>25 m	>30 m
4. Presence and effectiveness of ditches			Good containment	Moderate containment	Limited containment	No containment
5. Driver decision distance			Enough for breaking	Enough for speed reduction	Insufficient	Nonexistent
5. Driver decision distance			D>1 km	0.75<D<1.0 km	D<750 m	D<250 m
6. Distance from slope to exposed element			>13 m	Up to 10.80 m	Up to 8.40 m	<6 m
7. Geological conditions	Case 1	Structural condition	discontinuous fractures	discontinuous fractures	discontinuous fractures	Continuous fractures
		Structural condition	Favorable orientation	Random orientation	Unfavorable orientation	Unfavorable orientation
		Rock friction	Rough, irregular	Wavy	Flat	Clay fill, slickensides
	Case 2	Points of erosion	No erosion	Isolated points	Many Points	Large areas
	Case 2	Variation on erosion	Small variation	Moderate variation	Large variation	Extreme variation
8. Block size			0.3 m	0.6 m	0.9 m	1.2 m
9. Block volume			V<3.00 m³	3.0<V< 6.00 m³	6<V<9.00 m³	>9.00 m³
10 Movement history			Rare	Occasional	Recurrent	Frequent
11. Water presence/ drainage system			Dry	Isolated wet points	Large areas with water, dripping	Large areas with water flow
11. Water presence/ drainage system			Drainage in perfect condition	Drainage in good condition	Drainage partially functional	Drainage compromised
12.1 Social Impact			No Impact on local communities/culture	Impact on local community	Impact on nearby municipalities	Impact on several municipalities
12.2 Reputation Impact			No impact to image	Local repercussion	National repercussion	International repercussion

Risk Classification System for Soil Cuts
CATEGORIA			Classification and scoring criteria
CATEGORIA			3 Points	9 Points	27 Points	81 Points
1.1 Elements at risk: People			Psychological effects	Minor injuries	Serious injuries	Fatality
1.2 Elements at risk Environment			No impact	Punctual impact	Local impact	Regional Impact
1.3 Elements at risk: Financial			>US$10M-US$100 M	>US$ 100M-US$1bi	>US$ 1 bi-US$3bi	>US$ 3 bi
2. Exposure Time			25% of the time	50% of the time	75% of the time	100% of the time
3. Slope height			>7.5 m	>15 m	>25 m	>30 m
4. Presence and effectiveness of ditches			Good containment	Moderate containment	Limited containment	No containment
5. Driver decision distance			Enough for breaking	Enough for speed reduction	Insufficient	Nonexistent
5. Driver decision distance			D>1 km	0.75<D<1.0 km	D<750 m	D<250 m
6. Distance from slope to exposed element			>13.20 m	Up to 10.80 m	Up to 8.40 m	<6 m
7. Geotechnical conditions	Case 1	Anisotropy Condition	Favorable orientation	Random orientation	Adverse orientation	Unfavorable orientation
	Case 1	Anisotropy Inclination	i < 15º	15º<i<30º	30º<i<45º	i>45º
	Case 2	Probability of movement	Unlikely	Likely	Very Likely	Imminent
	Case 2	Points of erosion	No erosion	Isolated points	Many Points	Large areas
8. Unstable Thickness			t< 0.50 m	0.50<t<1.0	1.00<t<2.00	t>2.00
9. Volume			V<2.50 m³	2.50<V< 5.00 m³	5.0<V<10.0 m³	>10.00 m³
10 Movement history			Rare	Occasional	Recurrent	Frequent
11. Susceptibilities to saturation / drainage system			Very little susceptible	little susceptible	Susceptible to saturation	Very susceptible to saturation
11. Susceptibilities to saturation / drainage system			Drainage in perfect condition	Drainage in good condition	Drainage partially functional	Drainage compromised
12. Slope Inclination			i < 30º	30º<i<45º	45º<i<60º	i>60º
13.1 Social Impact			No Impact on local communities/culture	Impact on local community	Impact on nearby municipalities	Impact on several municipalities
13.2 Reputation Impact			No impact to image	Local repercussion	National repercussion	International repercussion

Risk Classification System for embankments
CATEGORIA			Classification and scoring criteria
CATEGORIA			3 Points	9 Points	27 Points	81 Points
1.1 Elements at risk: People			Psychological effects	Minor injuries	Serious injuries	Fatality
1.2 Elements at risk: Environment			No impact	Punctual impact	Local impact	Regional Impact
1.3 Elements at risk: Financial			>US$10M-US$100 M	>US$ 100M-US$1bi	>US$ 1 bi-US$3bi	>US$ 3 bi
2. Exposure Time			25% of the time	50% of the time	75% of the time	100% of the time
3. Slope height			>7.5 m	>15 m	>25 m	>30 m
4. Embankment foundation condition			No signs of problems	Containment structure in good condition	Signs of problems, Containment structure in good condition	Visible problem Containment structure precarious
5. Driver decision distance			Enough for breaking	Enough for speed reduction	Insufficient	Nonexistent
5. Driver decision distance			D>1 km	0.75<D<1.0 km	D<750 m	D<250 m
6. Distance from edge of road to embankment crest			>10.00 m	Up to 7.50 meters	5.00 meters	<2.50 meters
7. Embankment Condition	Longitudinal Cracks	Length	No cracks	Small and isolated (Up to 1.00m)	Medium and connected (1,00 à 5,00 m)	Long and connected (>5,00m)
	Longitudinal Cracks	Thickness	No cracks	Up to 1 cm	Up to 5 cm	>5cm
	Subsidence	Length	Nonexistent	P Small and isolated (Up to 1.00 m)	Medium and continuum (1.00 à 5.00 m)	Long and connected (>5.00m)
	Subsidence	Depth	Nonexistent	Up to 10 cm	Up to 50 cm	>50cm
8. Erosion processes			No erosion	Isolated points	Many Points	Large areas
9. Impact on road in case of failure			No impact	Reaches outer edge	Partial destruction	Total destruction
10 Movement history			Rare	Occasional	Recurrent	Frequent
11. Susceptibilities to saturation / drainage system			Very little susceptible	little susceptible	Susceptible to saturation	Very susceptible to saturation
11. Susceptibilities to saturation / drainage system			Drainage in perfect condition	Drainage in good condition	Drainage partially functional	Drainage compromised
12.1 Social Impact			No Impact on local communities/culture	Impact on local community	Impact on nearby municipalities	Impact on several municipalities
12.2 Reputation Impact			No impact to image	Local repercussion	National repercussion	International repercussion

Risk	Risk	Score
Low	R1	0-300
Medium	R2	300-500
High	R3	500-700
Very High	R4	>700

Name / Risk	Very High	High	Medium	Low
Moeda Formation	5.0%	20.0%	55.0%	20.0%
Cauê Formation	2.7%	5.4%	35.1%	56.8%
Gandarela Formation	0.0%	12.5%	33.3%	54.2%
Nova Lima Group	3.2%	16.1%	53.2%	27.4%
Cercadinho Formation	0.0%	4.8%	47.6%	47.6%
Barreiro Formation	20.0%	0.0%	40.0%	40.0%
Saramenha Formation	4.2%	22.9%	56.3%	16.7%
Córrego do Germano Formation	14.3%	14.3%	28.6%	42.9%

Lithology	Total lithology area along the railway (m²)	Total R1 area (m²)	Total R2 area (m²)	Total R3 area (m²)	Total R4 area (m²)
Moeda Formation	334,572.64	93,502.38	170,066.75	60,273.45	10,730.06
Cauê Formation	43,136.34	6,805.43	25,254.10	8,427.97	2,648.85
Gandarela Formation	113,727.29	66,109.95	34,182.09	11,314.03	2,121.21
Nova Lima Group	50,712.79	28,629.75	17,386.87	4,696.17	0,00
Cercadinho Formation	11,025.86	4,034.34	4,235.25	0.00	2,756.26
Barreiro Formation	40,648.81	17,391.93	21,280.12	1,976.75	0,00
Saramenha Formation	12,866.81	7,046.33	4,879.30	480.78	460.41
Córrego do Germano Formation	96,676.57	19,239.01	58,859.57	17,239.38	1,338.62

Point	Initial Risk	Risk post event	Hazard of railway impact	Reason to risk alteration
04	Low	Medium	Low	No field evidence was found for an event of this magnitude, suggesting that it was possibly caused by the overflow of the upstream street drainage system.
06	Medium	High	Medium	Mobilization of a previously occurred event, with the contribution of the upstream drainage system failure.
09	High	High	High	Unchanged
10	Medium	Medium	Low	Unchanged
11	Medium	Medium	Null	Unchanged
12	Medium	Medium	Medium	Unchanged
33	Medium	High	Low	Change in local conditions, after the rains and the occurrence of the rupture (which did not reach the railway), a crack was triggered, and a second event could now affect the railway, thereby altering the risk at the site.
40	Low	Low	Null	Unchanged
-	Not classified	High	Low	Unclassified because of a retaining wall existing
42	High	Very High	High	An expected critical event was predicted; however, the magnitude of the recorded event is greater than initially anticipated.
45	High	High	Low	Unchanged
46	High	High	Low	Unchanged
150	Medium	Medium	Low	Unchanged
151	Medium	High	Low	The obstruction of the drainage system at the crest of the slope
160	Medium	High	Null	As a result of the identification of a tension crack
183	High	High	Low	Unchanged
192	Medium	Medium	Low	Unchanged
193	Low	Low	Null	Unchanged
198	High	High	Low	Unchanged
213	Medium	Medium	Null	Unchanged
214	Medium	Medium	Low	Unchanged
215	Medium	Medium	Low	Unchanged
218/219	High	High	Low	Unchanged
220	Medium	Medium	Null	Unchanged
221	Medium	Medium	Null	Unchanged
226	High	High	Low	Unchanged
227	Medium	Medium	Null	Unchanged
236	Low	Low	Null	Unchanged
239	Medium	Medium	Null	Unchanged
248	High	High	Low	Unchanged
250	Medium	Medium	Null	Unchanged
256	Medium	Medium	Low	Unchanged
-	Not classified	High	Medium	Unclassified because of a retaining wall existing

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E-mail: secretariat@soilsandrocks.com

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[1] #Corresponding author. E-mail address: felipe@fgs.eng.br