1 Introduction

The fortified remains of Portuguese national defence such as the Penedono Castle (in the centre-north countryside) or the Peniche Fortress (in the centre-south sea-shore) are part of the landscape and the daily life of the populations with the tranquillity of centuries of existence. Culturally, these elements constitute the materialization of the basis of the Portuguese nation. Nowadays, however, due to time and history vicissitudes, castles, towers, fortifications, strongholds and fortress no longer play the same central role in everyday life as they did in other eras. Even so, they often continue to be the object of multiple and different looks, whether these are distracted, indifferent or, on the contrary, admiring, curious and worried. Therefore, this heritage preservation is essential to ensure that these cultural identity testimonies can be seen by the next generations. In this context, this work presents the methodology used in the inspection and structural diagnosis of the Penedono Castle [1, 2] and the Peniche Fortress [3], as part of their rehabilitation and preservation interventions.

2 Methodologies for structural survey and interventions

The inspection methodology used by NR-IC, for safety assessment of stone masonry structures, is based on the ICOMOS charter recommendations for “Analysis, Conservation and Structural Restoration of Architectural Heritage” [4]. It has been used in numerous conservation and rehabilitation projects, as well as technical inspections on different construction types in order to contribute for a sustained intervention on built heritage, comprising the phases of Analysis (involving the technical inspection) and Diagnosis of historical constructions, Fig. 1 [5, 6]. A particular focus is given to the Analysis phase, with the main goal of assessing the construction’s overall condition by photographic and drawings’ records of the observed damage levels and the actual geometry. The Diagnosis phase, that helps on defining both the technologies and the materials better suiting the characteristics of the construction under study, is essential for a correct intervention and it will be addressed. In fact, when proceeding to a sustainable rehabilitation of a heritage construction, taking into account its architectural, historical and constructive values, the development of a careful diagnosis is paramount.

Fig. 1
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The NR-IC inspection methodology

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3 Case studies

3.1 Penedono castle

The Penedono Castle, classified as National Monument, Fig. 2, is considered to have been built between fourteenth and sixteenth centuries as it can be seen nowadays, despite being referred in [7] that already in eleventh century a castle existed in the place where presently it is located.

Fig. 2
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Plan and general view of the Penedono Castle

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The castle has a plan configuration with the approximate shape of a faceted shield and it is entirely built by mortared small granite stone masonry walls, well dressed on both sides. The thickness of the walls varies between 1.5 m and 2.0 m, except in the turret areas where it can exceed 3.0 m. The walls’ height also varies between about 10 m and 15 m, depending on whether it is a turret or an adarves’ area, and depending on the elevation of the foundation rock outcrop. The interlock of the walls with the supporting rock outcrop is visible in both the castle and the barbican. A footpath, accessed by stairs partially located inside the walls, runs along the walls’ upper part, crowned by pointed pentagonal battlements also in masonry stone. In the interior of the castle there are some ruins of old structures and also the cistern which remains intact.

Structurally, the Penedono Castle has load-bearing walls in granite stonework, generally with good arrangement, having five towers integrated in the walls. As shown in Fig. 3, the wall towers are designated from T1 to T5, being the main entrance of the castle located between towers T1 and T2. This identification was used in the inspection procedures, allowing for a more targeted and, consequently, more effective registration of damages. In a first phase, the damages were identified and located in maps by damage type; in a second phase, a form per element was made for the most affected elements in order to compile all kinds of damage that occur simultaneously on the same element. This recording approach allows to describe each damage, to identify its occurrence location and additionally, to associate the record of all damages of each element, thus providing the information of its overall structural state.

Fig. 3
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Identification of the towers of the Penedono Castle and hypsometric map of level 2

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Complementing the inspection made resorting to a drone for the highest zone observation, a 3D laser scanning model was also made [2]. This 3D laser scanning model was carried out, using currently available laser scanning tools and methodologies, with two key objectives in mind: firstly, to allow the creation of a 3D model that would provide a more detailed view (in office) of the structural pathologies and, secondly, to create a 3D record of the architecture's archaeology that would aid in future studies of the constructive evolution of the castle. To achieve this, high-resolution orthorectified photographs were attached to the point cloud. Additionally, other types of information, such as the height verticality of the walls, could be extracted. A free demonstration version of the 3D model has been made available online [2].

The damages identified and listed below were: D1—Loss of joint mortar; D2—Loss of material in the top of the battlements; D3—Degradation of the stone foundation blocks; D4—Structural deformation; D5—Cracks in stone masonry/Opening of joints; D6—Degradation due to moisture; D7—Deficiencies in rainwater drainage; D8—Material degradation due to presence of vegetation and/or organic colonization. Examples of each type of damage observed in the castle (Figs. 4, 5, 6, 7, 8, 9, 10, 11).

Fig. 4
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Example of damage D1—Loss of joint mortar in the paraments

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Fig. 5
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Example of damage D2—Loss of mortar of merlons’ covering

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Fig. 6
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Example of damage D3—Diaclases in the foundation rock outcrop

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Fig. 7
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Example of damage D4—Deformation of tower T4

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Fig. 8
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Example of damage D5—Fracture in the interior face of stone elements

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Fig. 9
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Example of damage D6—Moisture problems in the paraments in the cistern zone

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Fig. 10
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Example of damage D7—Gutter obstruction

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Fig. 11
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Example of damage D8—Biologic colonization

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For each type of damage, the locations of damage incidence were identified, recorded and photographed; the zones with most incidence of damage were also recorded. The damage interpretation, in particular the D4 and D5 types, allowed identifying the trend of movements and/or deformations. Figure 12 shows the movement trends suggested by the damages D4—Structural deformation (red arrows), by the damages D5—Cracks in stone masonry/Opening of joints (yellow arrows) or by both (green arrows). The determination of verticality of the castle walls (excluding the towers) obtained from the 3D laser scanning model shown in Fig. 13 is consistent with what was observed from the visual inspection.

Fig. 12
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Movement/deformation trends suggested by the observed damages (D4 type red arrows; D5 type yellow arrows; D4 and D5 types green arrows)

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Fig. 13
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In height verticality obtained from the 3D laser scanning model

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One of the major stability problems was found to be related with the degradation/erosion of the stone foundation blocks and associated diaclases. These blocks consolidation was object of a specific geotechnic project which is not addressed herein; however, it can be referred that such blocks were reinforced with steel anchorages and injection of consolidation mortar.

For the structural rehabilitation and consolidation solution, the following measures were defined and proposed: (i) insertion of new stone material (hand arranged) and some localized anchorages in the castle support zone over the rock foundation; (ii) execution of “Cintec” type anchorages in some of the towers’ corners in order to ensure their confinement (Fig. 14); (iii) repointing all masonry joints using compatible mortar (natural hydraulic lime mortar), with some additional mortar injections in zones where the original mortar loss was found more deep, in order to enhance a more monolithic behaviour of the walls (particularly considering that in some zones, a few masonry stones were somewhat “cantilevered”); (iv) similar consolidation procedure for the stone masonry pentagonal battlements in walls and towers which are particularly exposed to the weathering degradation; (v) implementation of a maintenance plan in order to ensure higher durability of the present intervention, considering that the castle is severely exposed to wind and to both dry/wet and freeze/thaw cycles which lead to a higher erosion level.

Fig. 14
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Execution of anchorages in a tower

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Naturally, all the above procedures were preceded by low pressure waterjet cleaning of the masonry complemented with application of biocide to remove biologic colonization and vegetation in the paraments. The final aspect of the South side of the Castle is shown in Fig. 15.

Fig. 15
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Castle main façade after consolidation

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3.2 Peniche fortified complex

3.2.1 Introduction

The Peniche fortified complex, Fig. 16, is a maritime defensive structure started to be built in the sixteenth century. The great Lisbon earthquake of 1755 destroyed part of the wall, and the area where the wall collapsed is still called “broken”. The Fort plan layout is an irregular polygonal plan with bastions and is built with ashlar and limestone masonry with variable thickness in height. Inside the fortress there are, in addition to the old structures, reinforced concrete buildings built in the mid-twentieth century when the fortress was transformed into a political prison. Thus, the same fortress has associated historical moments relevant to the country's independence and the establishment of a democratic regime; presently the fortress houses the National Museum of Resistance and Freedom.

Fig. 16
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Views of parts of the Peniche fortified complex

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3.2.2 Inspection, diagnosis and risk map

The constructions that are part of the defensive complex of Peniche were divided into 3 zones identified from 1 to 3 in Fig. 17:

  1. 1.

    Fortress—walls with bastions and their casemates;

  2. 2.

    Buildings—structures that are part of the Fortress, either from the construction beginning (casemates) or from alterations inherent to the adaptation to a political prison (reinforced concrete building blocks);

  3. 3.

    City Wall—front walls, with bastions, that protect the city.

Fig. 17
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Implantation plan playout of the Peniche fortress and walls with indication of zones 1, 2, and 3 [7]

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In the fortress (Zone 1), a total of 48 sections of the different walls were identified in plan (Fig. 18a), which were inspected from the outside and the inside, having identified the existing damage for each face, as well as the corresponding evidenced intensity. In Zone 2, the different buildings inside the fortress were marked from A to K (Fig. 18b), and the different associated construction processes were recorded, as well as the damage and occurrence intensities. The same methodology was applied to the city wall contour, Fig. 19. The inspection procedures were similar to those mentioned above; this fortress has the particularity of housing constructions from different periods, to be preserved due to its importance for the collective memory.

Fig. 18
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Notation of a sections of the fortress walls and b buildings inside the fortress

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Fig. 19
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Notation of the sections of City Walls

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For each of the walls’ sections (Zones 1 and 3) and for each building, the damages were identified, and the respective damage maps were made, structured by type of anomaly recorded during the inspection survey and identified with the letter D further associated either with the letter M for both the Fortress and City walls or the letter E for the Buildings. Thus, DM corresponds to damage in the Fortress and City Walls and DE to damage in Buildings; several damage types were listed for the Fortress and City walls (12) and for the buildings (7). Figure 20 shows an example of the map of damage “DM2—Risk of structure stability due foundation degradation” and the analysis of a city wall section with damages’ identification and their intensity degree (Low/Medium/High).

Fig. 20
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Example of a a damage map and b the structural analysis with different intensities of damage

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Regarding the reinforced concrete buildings, where the political prison operated, they were subject to a specific inspection process, aiming at their rehabilitation based on authenticity and integrity criteria, naturally ensuring structural safety conditions. Some pictures of the conservation state of some buildings, which were later rehabilitated, are presented in Fig. 21.

Fig. 21
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Former political prison buildings and their material/structural degradation

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4 Final considerations

In this work, some of the procedures used in the inspection and diagnosis of fortified military structures were presented, highlighting the importance of a good organization and systematization of the information for the accomplishment of appropriate diagnosis and interpretation of the structural situation of the monuments. In this way, decision-makers can decide in a sustained way about the need for an intervention.

The paper presented just two examples of a larger set of inspected fortified military structures, but, from the whole study, the inspections made it possible to identify, in addition to other important damages, the cutting and sliding of the slopes and foundations of the fortresses, as well as the cutting or degradation of the rock outcrops supporting the structures, further affected by the effect of climate change, as one of the most widespread damages and responsible for the loss of stability of these kind of structures. In the particular case of coastal fortresses, the rise of sea waters associated with climate change can be problematic. Therefore, it is crucial to pay attention to the good maintenance of the rock masses and slopes, which support these structures. Although they are treated as not part of the supporting structure of the monuments, they proved to be fundamental for their stability, therefore being in fact, their integral part.

It should also be noted that multidisciplinary teams and their interaction in this type of work results in added value for the final work.