Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part II – Engineering Solutions

Abstract

The Chapter “Challenges in the construction of highways in the Brazilian Amazonia environment: Part I: Identification of Engineering Problems” dealt with the identification of Engineering problems concerning the implementation of road infrastructure in the Brazilian Amazon. This present chapter deals with Engineering solutions to overcome the obstacles mentioned in that previously chapter, focusing on alternatives that contemplate the use of the synthetic coarse aggregate of calcined clay (SCACC), recycled materials from ceramic waste, soil–emulsion mixes, and chemical additives, in partial or total replacement of coarse and fine natural aggregates, in addition to the use of piled embankments, for the reinforcement of the natural subgrade in the presence of a very thick, soft soil layer in the foundation of the highway.

1. Introduction

In this chapter, the possible Engineering solutions for the problems faced in the implementation of road infrastructure in the Brazilian Amazon are discussed, seeking technical alternatives allied to the reduction of logistics costs and the reduction of environmental impacts.

2. Methodology

This study fundamentally addresses the general characterization of natural, technical, economic, and environmental problems for road construction in the Amazon environment, pointing out possible solutions to circumvent these difficulties. The characterization was performed by reviewing the available technical literature, while the solutions were indicated by case studies of works conducted in the region.

It should be noted, however, that while there is a long tradition of environmental studies in the Amazon, involving biotic and abiotic environments, and the environmental impacts resulting from anthropic actions, the same tradition does not apply to studies of road constructions, from the point of view of Engineering.

The main cause of this problem is the low rate of research data publication and its application on highways in the specialized technical literature.

Thus, although the application of a certain material or technique in each construction of a highway is known, it is difficult to make a deeper analysis, due to the absence of published data.

For this reason, the literature review and case studies discussed here were mostly restricted to academic research of master and doctoral thesis, presenting the results of field monitoring reported by their respective authors.

3. Case studies – results and discussion

In the preceding items, the general characteristics of the International Amazon were contextualized, with emphasis on the Brazilian Amazonia, in addition to addressing the problems faced in the construction of highways in this region. This Item presents some case studies that sought to circumvent the problems of scarcity of stone material near the construction site and the presence of soil layers with low bearing capacity in the natural foundation (subgrade) of the highways built in the Brazilian Amazonia environment.

Figure 1 shows the locations of the case studies analyzed here.

Figure 1.

Locations of the case studies analyzed.

3.1 Stabilization of Amazonian soils with chemical additives

An unpaved rural road located at 53 km of the state highway AM-010, north of the city of Manaus (Point 1 of Figure 1), is used to access a military base. This road has a natural subgrade consisting of a layer of yellow-red sandy silt containing a 55% silt fraction, 35% sand, and 9% clay and is classified as a latosol, with a 30% LL, a PI of 10%, a CBR of 31% and an optimal moisture content of 12.6%, both in the intermediate compaction energy. The soil pH is acidic, with a value of 5.39, kaolinite being the predominant clay mineral. The soil is classified as CL (USCS), A-4 (TRB), and LG′ (MCT).

The efficiency of chemically stabilizing the subgrade soil with cement supplemented with ZS was evaluated, resulting as a single layer of the stabilized base; for this purpose, was constructed an experimental section of 70 m in length and 7.5 m in width. In order to control the performance of executive technical procedures, SCS and TSDC tests were made before, during, and after construction, in addition to evaluating the overall quality of the road paving and its superficial drainage elements.

The ZS-based additive (RoadCem®) used is a fine, odorless, grayish powder with a specific mass of approximately 1,100 kg/m³ and pH of 10–12 (in water, at 20°C). Its chemical composition is mainly composed of alkali metals and alkaline earth metals (60–80%), including sodium, potassium, calcium, and magnesium chlorides; ZS and oxides (5–10%); and activators (5–10%).

Based on the characteristics of the experimental section subgrade soil, a soil-cement–the additive mix was made with 1.7 kg/m³ of ZS (0.09% per dry mass) and 160 kg/m³ of cement (8.20% per dry mass).

The SCS test results of the specimens molded in the laboratory before the fieldwork found values of approximately 8 MPa at 28 days. In general, the construction stages begin with the addition and mixing of the ZS additive and cement, followed by leveling, compaction, and surface finishing. In this process, the ZS additive may be added one day before the application of the cement (Figures 2 and 3).

Figure 2.

a) Distribution of cement and ZS additive in the experimental runway by manual spreading; b) homogenization of the soil, cement, and ZS additive in situ by means of a recycler [1].

Figure 3.

Steps of a) compaction; b) bulging; c) surface finishing; and d) curing of the stabilized base [1].

The mechanical strength of the stabilized base was verified by molding PCs in three stages. In the laboratory, before starting the stabilization process, specimens were prepared with the pre-established dosage, and the SCS and TSDC test results were evaluated at the rupture ages of 3, 7, 14, and 28 days in wet curing.

During the execution of the stabilization step, a new molding of specimens was performed by collecting the homogenized mixture of soil-cement–ZS immediately before starting the field compaction procedure. In the third stage, after 28 days of stabilization, six samples were extracted directly from the runway. The laboratory results of the samples molded in the laboratory, those molded with a field mixture, and those extracted from the runway are shown in Figure 4.

Figure 4.

a) Comparison of SCS for samples molded in the laboratory, during stabilization, and extracted directly from the experimental runway; b) TSDC for laboratory-molded samples [1].

Of the specimens molded with the field mixture during the construction, the SCS results were observed to be close to the values of those specimens molded in the laboratory. The quality of the mixture made by the recycler and the time between homogenization and compaction are the main factors underlying the difference between the SCS of the samples molded in the laboratory and molded with the filed mixture, around 16%.

Conversely, the samples extracted directly from the runway reached only 42% of the SCS resistance value of the samples molded in the laboratory at 7 days of curing (Figure 4a), but these values were still higher than the minimum Brazilian road standard, which is 2.1 MPa. The difference is mainly caused by the construction techniques, the quality of the mixture, and compaction by the equipment in the field, under conditions not always optimal, while in the laboratory, technological control is easier to achieve. In addition, the extraction process of field samples can damage the cemented structure of the specimens, reducing their real strength.

Regarding the tensile stresses that the lower regions of the pavement receive due to the transient loads imposed by the traffic, the TSDC of the stabilized base material reached values above 1 MPa at a curing age of 7 days (Figure 4b).

In the visual inspection of the work during the first 48 hours of curing, some transverse, superficial, and isolated cracks with average depths of 1 mm emerged. In this period, there was the volumetric expansion that generated internal tensile stresses in the material that was still in the fresh state. The microstructure in the formation is subjected to secondary growth of the impure phase of ettringite; because of the continued hydration of C₃S, hydrated calcium silicate began to form inside the hydrated carapace [2]. This effect was more intense in plastic clays with high levels of cement exposed to the high humidity of the night-time forest and the intense heat of the day. However, the continuous strength gain of the material interrupted the propagation of cracks in later days, which naturally incorporated dust, showing an aspect of natural base regeneration. Four years after construction, the pavement showed no cracks, abatements, or pathologies that would compromise the durability and assimilation capacity of traffic surcharges (Figure 5).

Figure 5.

Final aspect of the experimental section. a) One day of stabilization, in Oct. 2016; b) after 490 days, in Feb. 2018; c) after 4 years, Oct. 2020 [1].

3.2 Granulometric stabilization of Amazonian soils using SCACC

Cabral et al. [3] and Cabral [4] conducted laboratory and field studies on the use of SCACC in asphalt mixtures, with raw material from the state of Pará. The authors obtained excellent results when comparing SCACC to the natural coarse aggregate (crushed stone), indicating that the synthetic aggregate supports severe mechanical compaction, according to the results obtained in the degradation tests (analysis of the comparison between the granulometric composition of the SCACC in the conditions of no compaction on the experimental runway, and after two years of service completion). The study site was an experimental section of the pavement restoration work on federal highway BR-163, between 101 km and 102 km (Point 2 of Figure 1), whose differential treatment was the incorporation of SCACC in the base layer of the pavement.

The base course of this segment was built in mid-November 2007, totalling 1,000 m in length, 12 m in width (two lanes of 3.5 m each and two shoulder lanes of 2.5 m each), and 20 cm thick. Not only in this section, but throughout the extent of the pavement restoration work, the project established the need to incorporate approximately 30% of coarse aggregate into the lateritic soil (piçarra) obtained from the deposits prospected by the geological-geotechnical studies.

Figures 6 and 7 show the stages of the use of SCACC, from the preparation of the ceramic bricks (which were later crushed into coarse aggregate sizes) to the execution of the base course in the field.

Figure 6.

Use of SCACC in highway paving: a) burnt of ceramic bricks following a controlled firing temperature; b) crushing of the ceramic blricks. c) Stacking of the mixture of lateritic soil and SCACC in the field [4].

Figure 7.

Use of SCACC in highway paving: a) scattering of the mixture of lateritic soil and SCACC for the execution of the base course; b) completed experimental runway, with asphalt course in double surface treatment. c) Conditions of the experimental runway approximately 2 years after completion [4].

3.3 Chemical stabilization of Amazonian soils with soil: Asphalt emulsions

To observe the behavior of an application of soil–asphalt emulsion mixture, Sant’Ana [5] studied a 200-m unpaved experimental section located at gate 3 of the access to the State University of Maranhão (Point 3 of Figure 1), which had a highly irregular surface, composed of a base course in laterite that was very deteriorated (Figure 8) overlying a subgrade layer formed by fine sandy soil (no subbase layer was observed). After the collection of deformed samples to characterize the existing layers, satisfactory results of the subgrade were observed (CBR of 12% under the normal compaction energy). On the other hand, the material of the base layer fit the subbase properties (CBR of 23% under intermediate compaction energy), so it needed to be reinforced and regularized with material imported from a deposit, resulting in a new base course.

Figure 8.

View of the experimental section before stabilization with asphalt emulsion [5].

Regarding the stabilization of the new base layer with RL-1C asphalt emulsion (cationic, slow rupture), the surface (base) was regularized and the existing road widened, keeping the transverse slopes at 3–5% to allow the accelerated flow of rainwater. Then, over the first 100 m, scarification was performed at a thickness of 5 cm (Figure 9a), followed by wetting until the layer reached the optimum moisture content; homogenization with a disc harrow (Figure 9b); application of RL-1C asphalt emulsion at the rate of 5 l/m², corresponding to 5% by weight of the dry soil, but in three stages (Figure 9c and d); and homogenization with the disc harrow between asphalt emulsion steps. A grader was used to move the soil–asphalt emulsion mixture to the side of the road, sometimes on one bank, sometimes on another (Figure 9e). Next, the mixture was compacted with a smooth roller (Figure 9f). Finally, the preliminary sealing layer was applied, with the emulsifying agent spreading (Figure 9g) and the release of clean sand (Figure 9h), which was then compacted again by a smooth roller. Figure 9i shows the finishing appearance of the stabilized base 7 days after execution. The remaining 100 m were subjected to the same procedure as above.

Figure 9.

Some records of the execution stages of the experimental section with soil–emulsion [5].

To evaluate the stabilization efficiency, two non-destructive tests using Falling Weight Deflectometer (FWD) equipment were carried out on the finished surface, one 12 days and the other 20 months after execution. The current service value of the road surface was characterized using the method developed by the United States Department of Army in 1995, with the objective of calculating the Unsurfaced Road Condition Index (URCI). Surface distress surveys were carried out in December 2007 and September 2008, that is, 10 months and 20 months after the stabilization was completed, respectively.

Although the material was in good general condition, the defects that were most common in the analyzed sections were surface dust, the loss of aggregate due to abrasion, and the “pothole” or “potholes”. The classification of all sections of the experimental stretch as “very good” or “excellent” by URCI method, after almost 2 years of operation (Figure 10), showed that the soil–asphalt emulsion technique is applicable in the region where it was studied for roads with low traffic volume.

Figure 10.

Surface condition of the stabilized base with asphalt emulsion after 20 months of execution [5].

3.4 Reinforced piled embankment as a Foundation of Roads on soft soils in the Brazilian Amazonia

There are four cases to be reported here (Points 4 to 7 of Figure 1). All cases dealt with the construction of a road in a location with a thick layer of soil with low bearing capacity, in which it would be uneconomical to purge this material.

Figure 11 shows the implementation details of the project (Point 4 of Figure 1). The largest thickness of the very soft organic clay layer observed was 7.55 m (Figure 11a), with a penetration resistance index (N_SPT) value under net energy of 72% (N₇₂, typical of Brazilian energy test) with an average of 1/45 blows/30 cm, on which a road embankment and bridge abutments (with a height of 6.65 m) were built to cross a watercourse called “Igarapé Miri” in the State of Pará. Figure 11b indicates the solution adopted. It entailed precast reinforced concrete piles, with square sides of 20 cm (to support the embankment) and 25 cm (to support the embankment and the bridge abutments), that were 8 m in length, spaced every 1.5 m, in both directions in plan view. On average, the pile tips were embedded at least 1 m into the resistant layer of very dense silty sand. Figure 11c and d shows a high stiffness geogrid for reinforcement of the embankment, installed over the cap piles, with the function of distributing the loads of the embankment and the bridge abutments for the piles.

Figure 11.

Reinforced piled embankment executed for crossing watercourses. a) Stratigraphic profile; b) arrangement of the piles and the geogrid reinforcement, in cross-section; c) and d) installation of the geogrid on the capitals of the piles (photo: Maccaferri [6]).

Figure 12 shows the implementation details of the project (Point 5 of Figure 1). The largest thickness of the very soft organic clay layer was 13.30 m (Figure 12a), with a mean N₇₂ value of 1/70 blows/30 cm (region under the tidal influence, located in mangrove), on which a road embankment and bridge abutments (with a maximum height of 4 m) were built to cross a small watercourse in the city of Abaetetetuba, Pará State.

Figure 12.

Reinforced piled embankment built for crossing the watercourse in the city of Abaetetetuba, Pará state. a) Stratigraphic profile; b) arrangement of the piles and the geogrid reinforcement, in cross-section; c) installation of piles in the abutment bridge (photo: NS Campelo).

Figure 12b indicates the solution adopted: There were used precast piles of reinforced concrete, with square sections of 35 cm on the side, 20 m in length, spaced every 3 m in plan view. On average, the tips of the piles were embedded approximately 5 m inside the resistant layer of very dense sand. A geogrid was used to reinforce the embankment, and a geotextile of high stiffness was placed between the geogrid and the top of the pile cap to avoid tearing of the geogrid when it was subjected to the embankment surcharge. Figure 12c shows the piles supporting the retaining wall of the bridge abutments.

Figure 13 shows the details of the project (Point 6 of Figure 1), a connection road to state highway PA-150, in the State of Pará. The largest thickness of the very soft organic clay layer observed was 8.00 m (Figure 13a), with a mean N₇₂ value of 1/45 blows/30 cm, on which a road embankment and an abutment bridge were built with a height of 2.3 m. Figure 13b indicates the adopted solution. There were used precast reinforced concrete piles, with 25 cm square side, spaced every 1.5 m. On average, the tips of the piles were embedded approximately 1 m inside the resistant layer of very hard silty clay. A geogrid and a geotextile were placed at the top of the pile caps.

Figure 13.

Connection road to state highway PA-150, state of Pará. a) Stratigraphic profile; b) arrangement of the piles and the geogrid reinforcement, in cross-section.

Figure 14 shows the implementation details of the project (Point 7 of Figure 1). The highest thickness of the soft clay silt layer observed was 5.75 m (Figure 14a), with a mean N₇₂ value of 3 blows/30 cm, on which a road embankment with a height of 4–6 m was built, in the várzea region, on the BR-319 federal highway, State of Amazonas. Figure 14b indicates the solution adopted: root-type piles 40 cm in diameter, spaced every 2 m. A geogrid was used to reinforce the embankment, and a geotextile mat of high rigidity was placed between the geogrid and the top of the pile capitals to avoid tearing the geogrid.

Figure 14.

Reinforced piled embankment executed in the várzea region on the BR-319 federal highway, state of Amazonas. a) Stratigraphic profile; b) arrangement of the piles and the geogrid reinforcement, in cross-section.

3.5 Use of lateritic concretions in road pavements in the Amazon

As reported in Item 2.8 of the Chapter “Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part I: Identification of Engineering Problems”, laterites are widely used in road pavings in the Brazilian Amazonia, but their occurrence is limited in some highland regions (terra firme), where the conditions are favorable for their formation. In addition, the deposits are not very thick, so the available volumes are not high. Thus, it is a “noble” material, and its use in highways is limited to the base course and in primary coatings (protection of the lower layers until the execution of asphalt course) of pavements with high traffic volume (Figure 15a and b) or only as a primary coating on rural roads with low traffic volume (Figure 15c and d). Figure 15b and d refers to Points 8 (state highway AM-363, “Estrada da Várzea”) and 9 (Ramal Sargento Picanço, 123 km of federal highway BR-174) of Figure 1, respectively. Note the different shades of the lateritic materials.

Figure 15.

Use of piçarra on highways. (a) Typical profile of the pavement courses for high traffic volume; (b) execution of the primary coating layer; (c) typical profile of the pavement layers for low traffic volume; (d) condition of the primary coating layer performed over decades (photos: NS Campelo).

Figure 16a shows some detail of a typical coarse lateritic concretion (piçarra) of the Amazonia, with a matrix in iron and aluminum oxides. There are records of roads with decades of construction which were used primary coatings of lateritic concretion, as shown in Figure 16b (Point 10 of Figure 1), on state highway AM-174, and even without the existence of a rainwater drainage system, it still shows satisfactory trafficability almost the entire length of the road.

Figure 16.

Use of laterites in Amazonian highways. a) Detail of lateritic concretion, with a predominance of iron and aluminum oxides; b) primary coating layer aiming at the durability of the pavement until the execution of the asphalt course (photos: NS Campelo).

3.6 Reinforcement of the natural Foundation of the Highway by partial soil exchange and replacement by a drainage structural layer

Sometimes, when the layer of low bearing capacity of the natural foundation (subgrade) is not very thick (2–3 m), then it is possible to replace all of it with another, better-quality material, imported from the deposit. When the layer is deeper (Figure 17a), and the total removal of the layer or the use of reinforced piled embankment is uneconomical (discussed in Item 4.4 of the Chapter “Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part I: Identification of Engineering Problems”), it is possible to partially replace the layer by introducing a layer of coarse crushed stone material (locally known as rachão, with a particle size of 100–250 mm, i.e., cobble grain size classification) over a layer of clean sand (Figure 17b). The first layer acts as a structural reinforcement, while the second layer acts as a draining layer, although both layers are very permeable and provide a significant increase in the shear strength of the natural foundation layer. Sometimes, geotextile is placed between the natural subgrade and the sand layers, and between the layers of the rachão (high stiffness geotextile must be used so as not to be ripped by the friction with the crushed stones) and the compacted embankment, to avoid filling the voids of these layers. However, geotextile is not introduced between the sand and rachão layers, as it is intended that there be “needling” of the sand particles in the voids of the rock granular material, allowing the internal structure of the grains to become more rigid by particle-to-particle contact.

Figure 17.

Partial replacement of natural foundations with low support capacity by drainage layers and greater shear strength in road construction.

Figure 18 shows the phases of partial excavation of the soft clay layer for the execution of an urban connection corridor in the city of Manaus, Amazonas (Point 11 of Figure 1). The thickness of the rachão layer – despite being a bearing capacity problem and being predefined in the design – is usually confirmed in the field by local experience in passing a fully loaded truck (82 kN of load for a rear single axle with dual wheels) several times over the surface of the layer, and no visible deformation is observable to the naked eye. In general, this thickness varies between 60 and 100 cm and may reach an even greater value, depending on the site conditions and embankment surcharge. Obviously, this is an onerous solution for locations where stone material is scarce and therefore is limited to short stretches of a road.

Figure 18.

Construction of an urban corridor with partial replacement of the natural ground with low bearing capacity. a) Partial excavation of the layer; b) placement of the coarse crushed stone material (rachão); c) placement of the embankment layer for road construction; d) appearance of the rachão layer after partial implementation of the compacted earthen embankment (photos: NS Campelo).

3.7 Construction of highways in the Terra Firme and Várzea regions

Item 1 described that the Amazon Basin encompasses a vast area of lowland and relatively flat lands, with numerous watercourses crossing them. The highlands, which are not flooded, constitute the terras firmes, while the lowlands areas flooded by flood river pulses constitute the várzeas. In the terras firmes, there is a predominance of yellow-red latosols, and horizons of piçarras are found with relative ease, albeit with reduced volume, given the low thickness of these layers. In addition, the subgrade in these regions usually has more permeable material and, together with the more rugged relief, allows better surface and deep drainage of the highways.

However, in várzea regions, there are several complications for highway construction. Starting with the impermeable natural subgrade (silty or clayey soil), formed mainly by argisols and gleysols, with low bearing capacity (mean N₇₂ less than 3 strokes/30 cm, which could meaning an allowable bearing capacity of soil somewhat less than 30 kPa, at depths ranging from 0 to 4 m in most cases), an absence of horizons of lateritic concretion, a deficiency of quality material to constitute the road embankment (generally, the existing soils consisting of expansive clay minerals, even without the presence of organic matter), an absence of rocky material, and a natural drainage basin forming a tangle of watercourses with approximately 10–15 m of vertical fluctuation between the maximum flood and minimum ebb levels, etc.

Figure 19 shows two Brazilian federal highways that cross the State of Amazonas. Figure 19a shows a stretch of highway BR-174, with a total length of 3,320 km, which connects the States of Mato Grosso, Rondônia, Amazonas, and Roraima and from this to Venezuela and the rest of the Americas and Caribbean (see Figure 7 of the Chapter “Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part I: Identification of Engineering Problems”); only 210 km of this highway cross the state of Amazonas. Throughout almost its whole length, deposits of piçarras and stone material are found; it cuts the terras fimes, with the top of the highway located between 50 and 200 m altitude; it crosses a more dispersed natural drainage basin, with lower frequency of larger watercourses. Figure 19b illustrates a stretch of highway BR-319, with a total length of 885 km, of which 820 km is in the state of Amazonas and 65 km is in the state of Rondônia (see Figure 7 of the same Chapter), connecting the city of Manaus to the city of Porto Velho in the North–South direction and from there to the rest of the country. The highway crosses várzeas for much of its length (approximately half the length, in the direction Manaus–Porto Velho), with deposits of lateritic concretions and rocky material only in the last 200 km of the highway. The top of the highway is located at elevations between 25 and 70 m altitude and crosses a more concentrated natural drainage basin, with a higher frequency of small and large watercourses.

Figure 19.

Different reliefs cut by highways in the state of Amazonas. a) Wavy, in the “terra firme” region. b) Flat, in a “várzea” region (photos: NS Campelo).

Due to the period of river flooding in the várzea region, the highways function as “earth dam”, dividing the drainage basin between the two sides. In fact, the situation is more aggravated because, while in the conventional dams only the upstream side is subject to the variation in the external water level, in these highways both sides are influenced by the flooding and ebbing water levels. The ebb period is the most critical because, as the embankment is formed mainly of clayey soils, the dissipation of pore-pressures from the interior of the massif is slow and, if accompanied by a rapid decrease in the water level of the surrounding watercourse, may result in a phenomenon analogous to the slope failure by “rapid drawdown”, observed in conventional dams (Figure 20). Thus, any of the highway margins may be subject to slope failure, and there may even be a rupture of both sides. Therefore, there is a combination of factors that can lead to the rupture of these road slopes: large increase in the external water level; slow dissipation of pore-pressures from the interior of the clayey/silty compacted embankment; and natural subgrade formed by soil stratum of low to medium bearing capacity.

Figure 20.

Lowering of the river water level on both sides of the road.

Large river floods have become more frequent in the Amazon Basin, leading to increasing maxima water levels year by year. Thus, in some regions of the BR-319 highway, overtopping occurs (Figure 21), and in the ebb cycle, partial rupture of the slopes may occur in the higher embankments when conditions are favorable (Figures 22 and 23).

Figure 21.

River flooding causing overtopping at some places on federal highway BR-319 (photos: NS Campelo).

Figure 22.

Rupture of road slopes, after the river ebb cycle (photos: NS Campelo).

Figure 23.

Rupture of road slopes, after the river ebb cycle (photos: NS Campelo).

Figure 22a (point 12 of Figure 1) is located near 23 km of highway BR-319, while the other occurrences are in a range between 20 km and 60 km.

Souza [7] and Souza et al. [8] studied the phenomenon of terras caídas (“fallen lands”), which is the rupture of riverbanks, commonly in floodplain regions, under the ebb of “white-water” rivers (classification due to Sioli [9]), locally called “águas barrentas” (“muddy waters”). Despite being a natural phenomenon, the same concept of hydraulic rupture can be applied to road embankments, as described in Figure 20. Figure 24 shows the phenomenon of “fallen lands” near the city of Manaus (Point 13 of Figure 1).

Figure 24.

Natural phenomenon known as terras caídas (“fallen lands”) occurring in the Careiro da Várzea region, in front of the city of Manaus (photos: NS Campelo).

This phenomenon causes damage to the riverine population, as a large amount of land detaches from the massif, reaching the residences (wooden palafitas) and the urban and rural roads that border the riverbank of the communities and cities. It can also cause small “tsunamis” when a rupture of land occurs, causing the sinking of small boats anchored nearby.

3.8 Behavior of tropical soils under suction pressure and the laterization process

As reported in Items 2.8 and 2.9 of the Chapter “Challenges in the Construction of Highways in the Brazilian Amazonia Environment: Part I: Identification of Engineering Problems”, tropical soils present some behaviors dictated by the pedogenetic process of laterization and soil suction when in an unsaturated state. Together, they significantly increase the resistance of cutting (mainly) and embankment slopes (in relation to the matric suction) in the case of shear resistance against rupture and erodibility processes.

There are records of cutting slopes existing for more than 50 years that are almost vertical (Figure 25a and b), which, even without anti-erosion protection – by vegetation cover (grasses or native vegetation) – or even without the existence of any superficial drainage of rainwater (in a region of high rainfall, above 2,500 mm per year, see Figure 2b of that Chapter), remains in a stable condition, except for some non-lateritic stratum (saprolitic), where it is vulnerable to erosion (Figure 25b and c), or when it is sandy or silty lateritic soil (Figure 25a). Figure 25a,b, and c corresponds to Points 14 to 16 of Figure 1, respectively. Other times, the distinction between the lateritic and saprolitic horizons is given by the existence of a “stone line” of lateritic concretions, as shown in Figure 26a, on state highway AM-070 (Point 17 of Figure 1).

Figure 25.

Cutting slopes. a) Erodible horizons (sandy/silty soil). b) and c) lateritic and saprolitic horizons (highly erodible) (photos: NS Campelo).

Figure 26.

a) Presence of a “stone line” (lateritic concretions) separating the lateritic and saprolitic horizons. b) and c) presence of thin film of lateritic crust in slopes (photos: NS Campelo).

In some cases, a thin film (1–3 mm) of lateritic crust forms on the surface of the slope, of dark red color, which acts as an anti-erosion protectant, allowing the stability of the slope against the deleterious action of the rains for decades, even with almost vertical slopes. Figure 26b and c shows these thin films (Points 18 and 19 of Figure 1, respectively) that occur in the city of Manaus.

3.9 Ceramic, recycled, and alternative materials in road paving of Amazonian highways

There are reports of the use of milled asphalt waste (reclaimed asphalt pavement-RAP) from the recycling of asphalt coatings on federal highways BR-163 and BR-364 in the State of Mato Grosso [10] but in the initial state. An interesting application of ceramic materials occurs in some urban streets in the city of Rio Branco, State of Acre, where traditional ceramic bricks are applied as linings in streets with low traffic volume (Figure 27 – Point 20 of Figure 1).

Figure 27.

Use of ceramic block as a coating for urban roads with low traffic volume (photo: Jornal AcreAgora (https://acreagora.com/2021/07/12/).

There are no reports of the use of lightweight fill materials (e.g., expanded polystyrene – EPS) for embankments to be constructed over soft soils in road paving in the Brazilian Amazonia. This type of solution could be used in highways that cross natural subgrade in várzea terrains.

In general, there is a lack of technical information on the construction procedures and use of construction materials on the highways of the Brazilian Amazonia, which is reflected in the few publications on the subject.

4. Conclusions

In order to overcome technical problems reported in the Chapter “Challenges in the construction of highways in the Brazilian Amazonia environment: Part I: Identification of Engineering Problems”, can be employed solutions with materials found in the vicinity, in most cases. Thus, for problems of the absence of stone material at the construction site, the use of natural materials (lateritic concretion), synthetic materials (SCACC), and recycled materials (e.g., from ceramic waste and milled RAP) can be used, while for problems of the natural foundations of roads with low bearing capacity can be used partially or fully replacement of natural soil for a layer composed of coarse crushed stone (rachão) and clean sand, or, for greater depths, it can be used reinforced piled embankment (fill supported on piles and reinforced by geogrids).

Although the Brazilian Amazonia brings some hindrances to the construction of highways in the várzea regions, nevertheless in the elevated regions (terra firme), lateritic concretions can be counted on for use in base and primary courses, and there are lateritic soils of better quality for the construction of embankments, in addition to the favorable conditions of slope stability, especially in periods of drought rain, induced by soil suction.

For rural roads with low traffic volume, ceramic waste can also be used as recycled material in primary coatings.

Acknowledgments

The authors would like to thank CAPES for the grant of a scholarship for an academic master’s degree to the Civil Engineer Daniel Jardim Almeida.