30 Years of Cultural Heritage Landslides and Block Movements Risk Assessment: Case Studies from Egypt

Abstract

Throughout history, sites of high societal values, such as temples, tombs or palaces were mainly constructed through the digging/carving of rocks, built on hills or plateaus, or through the usage of carved/cut displaced rocks. Ancient designers/engineers/workers usually chose construction sites as to facilitate the building or the carving of stones, while, at the same time, serving the purpose of the building/constructions. In Egypt, throughout the ancient Egyptian Civilization, Egyptians have chosen to carve their temples and tombs in the soft limestone, shales and sandstones that are covering most of the modern Egypt, whereas in few temples and tombs, hard igneous and metamorphic rocks were used as ornament material for tombs and statutes. In this paper, we will present an account of the development of landslide risk assessment for various cultural heritage sites around Egypt, for different eras of Egyptian history and different sites. This paper aims at discussing different case studies and success stories of landslides and block movements hazards assessment around or inside Egyptian Cultural Heritage sites.

1 Introduction

Egypt is located on the Northeastern part of Africa. A layer of limestone covers most of the surface of modern Egypt. Beneath this lies a bed of sandstone, and this earlier sandstone is the surface rock in Nubia and southern Upper Egypt, as far north as the area between Edfu and Luxor. The oldest ground of modern Egypt comprises outcrops of metamorphic and igneous rocks (Hamimi et al. 2020; Rushdi, 1990). Figure 1 shows a general distribution of basement rock (Igneous and Metamorphic) outcrops in Egypt.

Fig. 1

Distribution of basement rocks (Igneous and Metamorphic) rocks in Egypt (Hamimi et al. 2020)

Ancient Egyptian civilizations are extended over a period of almost 4000 years, starting from the predynastic period around 4300 BC until its conquest by Alexander the Great in 332 BC. Historians divide Ancient Egypt dynastic period into 31 dynasties comprising three main kingdoms: Old Kingdom, Middle Kingdom, and Modern Kingdom, where intermediate periods separating each of those three kingdoms.

Throughout such rich history of civilization, Ancient Egyptian kings and queens had the habit to construct temples (to worship Goddesses and Gods) and dig tombs to commemorate their bodies and souls, in preparation for the afterlife.

Therefore, it was natural that most of the temples and tombs are in contact with the soft limestone, shale and sandstone layers that constitutes most of the surface of Egypt, and to master the carving of those rocks for their construction sites, with all inherited stability problems from those rocks (shale swelling, cliff stability, relative block movements, etc.).

We don’t dispose of any account that ancient Egyptians were able to study slope stability or rock mechanics for their construction’s sites, but their engineers and designers were aware of potential stability problem that they may face, especially in temples constructed at the toe of a cliff, or tombs designed with large roof spans.

During the past 30 years and beyond, several studies were carried out on different cultural heritage sites in Egypt to investigate stability problems resulting from landslides and relative block movements.

In this paper, we will present three examples of dealing with cultural heritage sites in Egypt, where those sites are exposed to different types of risks of landslides and stability problems due to block movement: The Temple of Queen Hatshepsut at Eldeir Elbahary, Luxor, the tombs of Rasmses I at the Valley of the Kings, Luxor, and the tomb of the Serapeum in Saqqara, Giza.

2 Queen Hatshepsut Temple of Eldeir Elbahary

The Queen Hatshepsut Temple at E1dier E1bahary is located on the west bank of the Nile in Luxor Egypt at the toe of the Theban cliff (cf. Fig. 2) where the Theban Mountain is composed mainly of successions of shales and Limestones (cf. Fig. 3).

Fig. 2

General view of the temple of Queen Hatshepsut at Eldeir Elbahary, Luxor

Fig. 3

Esna Shale overlaid by fractured limestone at the cliff of the Queen Hatshpsut cliff of Eldeir Elbahary

The temple was built in the fifteenth century BC and was dedicated to the cult of the Gods Amon, Hathor and to the memory of ruler Queen Hatshepsut of the 18th dynasty (1490–1468 BC).

The Temple is carved into the limestone cliff that is about 100 m high and composed mainly of Esna shale overlaid by highly fractured Thebes limestone.

Structural damage of the cliff and temple are attributed mainly to the swelling of the Esna shale, which includes buckling of casing walls, cracking of walls and ceilings and dislocation of stone blocks forming structural elements. In 1986, the casing wall of the upper court, reconstructed 80 years ago, was destroyed (Helal and Abdallah 1990).

Most rock slope failures occurs because of sliding and/or rotation of blocks or wedges defined by intersecting structural discontinuities. However, when the rock mass contains several discontinuities sets and the spacing of the discontinuities is small with respect to the size of the slope, as in the case of E1deir Elbahary, failure can occur because of sliding along a shear surface like that which occurs in soil slopes (Helal and Abdallah 1990).

Several modeling techniques were used to analyze the stability of the cliff under which the temple is constructed, coupled with rock discontinuities mapping and rock testing, to understand the mechanisms of failure of the cliff elements and suggest engineering solutions (Helal and Abdallah 1990; Dziedzic and Michiewicz 2018).

3 Tomb of Ramses I at the Valley of the Kings

The tomb of Ramses I is situated at the Valley of the kings in Luxor—Egypt, and is attributed to the king Ramses I, the founding king of Egypt’s 19th dynasty. The dates for his short reign are not completely known but the time-line of late 1292–1290 BC is frequently cited. Rameses I brief reign mainly serves to mark the transition between the reign of Horemheb, who stabilized Egypt in the late 18th dynasty, and the rule of the powerful pharaohs of his own dynasty, in particular his son Seti I, and grandson Rameses II.

The tomb is located in a succession of limestone layers interlayered with Esna shales, which is subject to swelling due to humidity, thus creating stresses on the walls of the tomb and the hanging layers of the roof, thus causing some instabilities in the tomb.

Nevertheless, due to the dry nature of the city of Luxor and the Valley of the Kings, effect of swelling of the shale is not severely affecting the stability of the tomb. On the other hand, a system of east–west discontinuities is observed all along the axis of the tomb (Fig. 4).

Fig. 4

Plan and cross-section of the tomb of Ramses I

The tomb is facing typical problems of instability showing possible risks of block movements and requires a global risk analysis study.

To assess the possible instability of the tomb, a derived technique of Fuzzy Logic inference was used to account for Rock Mass Ratings inside various zones of the tomb, resulting is a complete zone risk map all along the three zones of the tomb illustrated in Fig. 4. The Fuzzy Logic inference technique included the definition of sensitivity and activity block falling phenomena (Elshayeb and Verdel 2005).

The application of Fuzzy Logic inference for zone risk mapping indicated high risk of block movements at zone III, thus leading to the installation of wooden structure at the burial chamber of the tomb, as shown in Fig. 5 (Elshayeb and Verdel 2005).

Fig. 5

View of the entrance to the tomb of Ramses I and its interiors galleries (upper photos), and a view of the wooden support installed at the burial chamber (lower photo)

4 The Serapeum Tomb in Saqqara

The Serapeum is considered historically as the tomb of burial the arks of the sacred bulls of the “Apis” cult at Memphis. It was believed that the bulls were incarnations of the God Ptah, which would become immortal after death.

Over a timespan of circa 1400 years, from the New Kingdom to the Ptolemaic Period, at least sixty Apis are attested to have been interred at the Serapeum. The earliest burials are found in isolated tombs. As the cult gained importance, underground galleries were dug to connect subsequent burial chambers. One of the cult practices involved the dedication of commemorative stone tablets with dates relating to the life and death of the “Apis”.

Saqqara Serapeum tomb is a valuable archaeological unit that has been subjected to serious structural damages and deterioration.

Figure 6 shows a plan of the tomb which is composed of two almost horizontal galleries: one known as main gallery of 211 m in length, 3 m wide and 4 m height. The second gallery is smaller in length (about 50 m), but similar in other dimensions. Along the sides of the main gallery, there exist 28 burial chambers in alternating manner, only 24 contained granitic and hard limestone coffins for burial arks of the sacred bull “Apis”. They were excavated at levels lower than the excavated main gallery level.

Fig. 6

Plan of the Serapeum in Saqqara

The tomb of the Serapeum is located in a succession of limestones, marl and shale, where the shale is highly affected by humidity and causing several instability problems at the base and at the roof of the tomb (cf. Fig. 7).

Fig. 7

Typical dimensions and succession of layers at the Serapeum of Saqqara (Hamdy 2021)

Several geotechnical investigations and analysis of stresses were carried out at the Serapeum to identify stress distribution systems and scenarios of failure, which would lead to consolidation and support structures (Hamdy 2021; Imam et al. 2007, 1985).

Jointing systems, dynamic loading of adjacent limestone quarries, swelling of shale, and deterioration of limestones due to aging and inadequate drainage system in nearby urban area, were the main reasons for instability of the tomb. During the period of 2001–2010, an extensive analysis of the stability of the tomb, led to the conclusion of installation of a complete steel arches support system inside the tomb galleries and many of its burial chambers.

From an engineering point of view, such a solution would eliminate the risk of instability, block movements and landslides inside the tomb, whereas the adequacy of such supporting structure must be studied carefully as it risks leading to the loss of the archeological value of the site. Figures 8 and 9 show some photos of the installed supporting structure installed at the tomb as reported in the work of (Hamdy 2021).

Fig. 8

General view of the main gallery of the Serapeum in Saqqara

Fig. 9

A typical view of the metallic support structures installed at the burial chambers of the Serapeum in Saqqara

5 Conclusions

Applications of Rock Mechanics, Geomechanics and Slope Stability to Egyptian Cultural Heritage were introduced in the late 1980s with analytical and later numerical analysis of stresses induced from rocks surrounding the abundant sites of cultural heritage in Egypt.

During the 1990s and early 2000s several studies and analysis has been carried out to analyze stresses and risks around various cultural heritage sites, but it was not until later in the 2010s and until now, that the Egyptian Supreme Council of Antiquities and currently the Ministry of Antiquities, have adopted the systematic approach to stability of cultural heritage structures, thus paving the way for a lot of stability studies, with subsequent consolidation/supporting civil works carried out at various cultural heritage sites in Egypt.

In the paper, three different cases from Egypt were presented, each is a unique case with unique environment and unique risks of instability. Nevertheless, Engineering intervention in those sites allowed better understanding and better preservation of those world cultural heritage sites.