{"id":81142,"date":"2026-01-19T19:41:12","date_gmt":"2026-01-19T18:41:12","guid":{"rendered":"https:\/\/www.typsa.com\/?p=81142"},"modified":"2026-03-27T15:41:45","modified_gmt":"2026-03-27T14:41:45","slug":"reinforcement-of-the-maravilhas-ii-mining-dam","status":"publish","type":"post","link":"https:\/\/www.typsa.com\/en\/reinforcement-of-the-maravilhas-ii-mining-dam\/","title":{"rendered":"Installation of a new\u00a0spillway\u00a0to improve the safety of a mining dam"},"content":{"rendered":"

Introduction\u00a0<\/strong><\/p>\n

Commissioned by the\u00a0mining company\u00a0VALE,\u00a0ENGECORPS has developed the conceptual design to reinforce the Maravilhas\u00a0II dam, implementing measures to ensure the dam’s safety and compliance with current\u00a0technical regulations.<\/span><\/p>\n

Among the\u00a0alternatives\u00a0studied, the selected\u00a0option\u00a0involved reducing the operational water level of the reservoir\u00a0by\u00a0lowering\u00a0the\u00a0spillway\u00a0threshold\u00a0and\u00a0constructing a new spillway\u00a0with greater\u00a0discharge capacity.<\/span><\/p>\n

The\u00a0Maravilhas\u00a0II dam\u00a0has\u00a0for years\u00a0retained\u00a0the\u00a0mining tailings generated at the Pico mine\u00a0and\u00a0currently,\u00a0as well as retaining the accumulated waste, it receives\u00a0sediments from the upstream area, accumulates water for mine recirculation and promotes the clarification of the final effluent\u00a0to bring it into line with environmental\u00a0regulations\u00a0before it\u00a0is discharged\u00a0into the downstream stream.<\/span><\/p>\n

In an independent audit carried out in 2019,\u00a0taking into account\u00a0the piezometric conditions recorded in the dam monitoring, the\u00a0dam\u00a0stability analyses\u00a0indicated\u00a0that the\u00a0safety factors\u00a0were\u00a0lower than those acceptable according to technical\u00a0regulations.<\/span><\/p>\n

With the aim of increasing the\u00a0dam\u00b4s\u00a0safety, a series of interventions were proposed,\u00a0including\u00a0reducing the height of the dam and smoothing its downstream slope, with\u00a0the construction of a new spillway\u00a0located on the\u00a0right abutment\u00a0of the dam,\u00a0returning the effluent flows from the reservoir directly\u00a0to the\u00a0stream,\u00a0downstream of the mouth of the watercourse where the dam is located.<\/span><\/p>\n

Over the years,\u00a0a process of deep erosion had occurred in a natural drainage channel\u00a0near the\u00a0right abutment\u00a0of the dam,\u00a0affecting\u00a0the entire hillside.\u00a0In order to\u00a0stabilise this area, the eroded region was remodelled using soil from the excavations necessary for the construction of the spillway.<\/span><\/p>\n

\"\" Spillway at the end of construction,\u00a0with the dam and its reservoir in the background<\/p>\n

Structure\u00a0characteristics\u00a0<\/strong><\/p>\n

In order for\u00a0the new spillway\u00a0to be\u00a0operational,\u00a0it was necessary to build\u00a0a channel\u00a0connected\u00a0to the\u00a0reservoir\u00a0intake structure,\u00a0located\u00a0on\u00a0the right abutment\u00a0of the dam. The main structure is made of reinforced concrete, consisting of a control structure equipped with cofferdam\u00a0gates, followed by\u00a0a\u00a0stepped\u00a0weir, ending in\u00a0a\u00a0stilling basin, so that the\u00a0channel restores the flow in an orderly manner to the\u00a0Congonhas\u00a0stream.<\/span><\/p>\n

Based on the study of the flood control of the tributaries to the dam reservoir,\u00a0the maximum effluent flow of 80.9 m\u00b3\/s was obtained for the maximum probable precipitation\u00a0(MPP).\u00a0<\/span>
\nThe\u00a0drainage system has\u00a0a difference\u00a0in\u00a0elevation\u00a0of approximately 88 m between the water level in the dam reservoir and the stream\u00a0bank. The steps are 1.0 m\u00a0high\u00a0and the length of the platforms\u00a0was adjusted\u00a0to\u00a0accommodate\u00a0the terrain profile.<\/span><\/p>\n

\"\"
\nSpillway \u2013 Longitudinal profile\u00a0<\/span>of the stepped weir<\/span><\/p>\n

As for the geology of the spillway area,\u00a0it has\u00a0colluvial soils superimposed on the\u00a0saprolitic\u00a0soils of the Fecho do\u00a0Funil\u00a0and\u00a0Tabo\u00f5es\u00a0formations,\u00a0mainly composed\u00a0of dolomitic\u00a0phyllitic\u00a0lithology, as well as alluvial deposits on the banks of the stream.<\/span><\/p>\n

Excavations for the implementation of the spillway removed the colluvial soils on the slope, supporting the structure directly on\u00a0the\u00a0saprolitic\u00a0soils. On the banks of the stream, the alluvial deposits were partially removed,\u00a0the section downstream of\u00a0the\u00a0stilling basin\u00a0replaced\u00a0with\u00a0rockfill,\u00a0and\u00a0with\u00a0root-type stakes\u00a0to mark the\u00a0perimeter of the treatment area.<\/span><\/p>\n

\"\"View of the excavations for the spillway with its construction accesses<\/span><\/span><\/p>\n

Due to the proximity of the urban area,\u00a0the owner\u00a0requested\u00a0that the\u00a0rapid\u00a0step\u00a0be equipped with\u00a0a\u00a0cover\u00a0slab\u00a0for acoustic reasons. Thus, on the hillside, the structure consists of a closed gallery section with three compartments, which runs from Module 1\u00a0(downstream of the control structure)\u00a0to\u00a0Module\u00a09\u00a0(upstream of the buffer basin).<\/span><\/p>\n

A drainage system was installed in modules 1 to 9 to relieve possible internal pressure on the foundation (underpressure).\u00a0In modules 10 and 11, corresponding to the surge basin, the structure\u00a0was dimensioned\u00a0to withstand hydraulic\u00a0underpressure, as well as unbalanced earth thrust forces between both sides.<\/span><\/p>\n

\"\"
\nStructure of\u00a0<\/span>the spillway\u00a0<\/span>surge basin\u00a0<\/span>–\u00a0<\/span>Hydraulic profile and\u00a0<\/span>earth\u00a0<\/span>thrusts<\/span><\/p>\n

3D\u00a0numerical\u00a0modelling\u00a0<\/strong><\/p>\n

The 3D numerical modelling of the spillway\u00a0comprises\u00a0the hydraulic structure from the\u00a0conveyance\u00a0channel\u00a0to\u00a0the control structure,\u00a0the stepped\u00a0weir\u00a0and\u00a0the stilling basin. Due to the dimensions of the system,\u00a0and\u00a0taking into account\u00a0the level of detail required for the physical phenomena to be correctly represented, the simulations\u00a0were divided\u00a0into three sections:<\/span><\/p>\n