The role of Professor Betancourt in preservation of architectural heritage in historical cities of the world

. One can address an issue which generates an argument of colleagues-civil engineers, architects and mechanical engineers working with machines. Bridge engineers can also enter the discussion stating that a world-renowned scholar Augustin Betancourt belongs to their “bridge” community. He had an experience of constructing bridges and floors with large spans. His structures and ideas in all these directions of engineering thought were broadly used and even now they are applied in the modern world practice. We can give a lot of examples, as A. Betancourt’s structures and ideas have been used by many engineers including the authors of this paper in their long-term practice of reconstruction of the unique buildings in Russia. There are dozens of buildings and structures only in St. Petersburg and its closest suburbs where A. Betancourt was an author, an advisor, an expert, whose indications were implemented in many projects of urban development. A. Betancourt was actively involved as a head of the Committee for Construction and Hydraulic Works in St. Petersburg. This committee also participated in expert evaluation of development of the largest Russian cities of that time.


Introduction
One should consider the activity of A. Betancourt as an ideologist of a big group of intellectually advanced experts of the international level in every sense of these words [1][2][3][4]. Leading experts from Spain, Italy, France, Germany, England worked in St. Petersburg together with Russians.
Therefore, thank to Betancourt they can enter the highest level in the world in the field of modern science and technology. Moreover, training of railway engineers in St. Petersburg was implemented by highly qualified teachers in all areas of the transport science of that time. Frenchman I.S. Reziman, one of the oldest professors at the Institute of Railway Engineers was invited from the Parish School of Bridges and Roads. He started serving in the rank of major of the Body of Railway engineers and was an active follower of A. Betancourt. Since September 1816 he started delivering lectures on a comprehensive course, which included such subjects as mineralogy, engineering geology and soil studies. Therefore, September 2016 can be regarded as the 200 th anniversary of teaching these subjects, which are so important for modern geotechnical engineers. After multiple transformations these subjects were united in a cycle on construction art, and later and so farthe comprehensive course of soils and structures. In the international practice these chairs and cycles are united under the name of geotechnical engineering or engineering geotechnics. This science provides safety of buildings and transportation facilities at all stages of their life cycle beginning from geotechnical investigations and design up to reliability of operation of these facilities.
Looking through the published lectures of that time delivered by the Frenchman I.S.Reziman (in French) one can be surprised with their interesting ideology. They considered the issues of development of dangerous geological and hydrogeological processes. At the same time, the lecturer was an excellent mentor for civil engineers who spoke French being offsprings of noble Russian families. That time so called "ordinary people" did not have access to such higher education.
Professors I.S.Reziman and G. Monge articulated the main idea stated in three fundamental provisions, which constituted the basis of the system of higher education in engineering schools of Paris and were supported by teachers of railway transport in St. Petersburg, namely: -precise production both in industry and in construction; -deep learning of science and phenomena of nature, living in harmony with it; -constant skill upgrading using mechanization of any labor. As technical experts of modern construction schools, the authors of this paper can approve these principles of studying and future engineering practice [5][6][7][8]. A. Betancourt considered himself a disciple of professor G. Monge and followed these principles.
Following the example of his teacher, A. Betancourt paid a lot of attention not only to theoretical sciences, when teaching his students, but the applied ones and in several cases humanitarian subjects following the state-of-the-art engineering practice achieved in the world.

Research methodology
We give several engineering examples, where the authors of this paper have addressed or even used A. Betancourt's ideas in modern practice of reconstruction.

The practice of design of soils and foundations of the largest orthodox cathedral in the world -St. Isaac's cathedral
According to the contemporary understanding, the construction site of the Cathedral consisted of soils, which are soft for capital buildings. Earlier in this site there was the first St. Isaac's church, firstly wooden, then made of stone (it was constructed as per the design of Rinaldi). It was a difficult geotechnical task to construct in such a place where a part of the site for development had already consolidated. Modern geotechnical engineers would use piles of a large diameter and the lengthminimum 25-26 m. But that time there were used quite short wood pilesthe length from 6,0 to 10,5 m (maximum) under pillars and walls. From the point of view of a contemporary designer and calculator (the authors of the paper are the members of the international ТС-207 "Soil-Structure Interaction ISSMGE"), according to the modern Russian and European requirements, they would not have accepted an option when a pile cutting the bulk of relatively strong sands rested upon varved and liquid loams and clayey sands (rarely on soft plastic and hard plastic loams). Meanwhile the maximum values of settlements in time could reach 100 cm! ( fig. 1).

Fig. 1. The cross-section of St. Isaac's cathedral.
Here the front resistance of piles is negligible, and the friction of several thousands of piles could have hardly provided reliability of the unique building for the world of the orthodox culture. What is the secret of the engineering thought of А. Betancourt in the modern interpretation of this phenomenon by contemporary geotechnical engineers who are well aware of design and construction of unique, including high-rise buildings in the world? а) According to А. Betancourt's design there was excavated a pit of the depth of more than 5.0 m, i.e. lower than the ground water level, i.e. wood piles were always in water that excluded their decay. b) Lime-sand mortar was poured in the pile head above the compacted crushed stone, then a massive raft of rubble stone was made, under the corners of the building and the main bearing structures the raft was made of granite slabs. c) А. Betancourt personally supervised the works during laying rubble stone and granite slabs; the latter were carefully put in the locations of the highest pressure on soils. d) Professors of the Institute of the Body of Railway Engineers G. Lome and E. Clayperon made analytical calculations on the basis of the theory of balance of vaults (in fact, it is a forerunner of mathematical modeling of possible loads on piles which provides even settlements of a whole area of loading). It minimized differential settlements, which are the most dangerous for such a massive unique building ( fig. 2). Therefore, analyzing the structure, which is so unusual and vulnerable in terms of modern approaches to design of soils and foundations, one should mention audacity of calculation predictions, which were brilliantly confirmed by the experience of operation for more than 100 years. Actually, there was constructed a "pile-raft foundation", the most relevant for the beginning of the XXI century. The whole calculation of such a foundation and its implementation were first made in Frankfurt am Main and Berlin in 2001-2004. In the national construction codes for design of soils and structures calculations of such a structure entered only in 2010. Meanwhile the main contemporary calculations are made using numerical mathematical methods with account of non-linearity of soil and structure materials.
The very idea of construction of subsoils and foundations implemented in St. Isaac's cathedral implied that the pressures from the structure weight were transferred not only to piles but also to the raft of the deep piled raft. "Deformation" models accepted by A. Betancourt and his colleagues allowed adjusting a depth of the piled raft and the depth of pile for their successful joint and safe operation.
In fact, there was intuitionally implemented the requirement of joint calculation of the system "soilshort piles -massive embedded piled raft".
In St. Isaac's cathedral the massive piled raft rested upon soil consolidated with piles that reduced the limit differential strains to a possible minimum, which provides safety of the unique massive structure of unequal height in highly compressible soils of St. Petersburg. Now this method is known as reinforcement of soils. analogous soils near St. Isaac's cathedral. This object had problems with footing at the official level of the city committee. At discussing this issue by a group of geotechnical engineers headed by A. Betancourt even before the construction of St. Isaac's cathedral, it was proposed the first in the world unique structure, which caused a lot of topics for discussions of experts including the authors of this paper. The contemporary examination has found the foundation of rubble stone of the width more than 4 m. Under this wide and deep raft there were found rather short piles of wood (up to 8,4 m). We think that this building was actually erected as a model for a possible further use of the idea of the "pileraft foundation" before mass use of piles (tens of thousands) under the cathedral.

The project of reinforcing foundations of St. Catherine's church
A. Betancourt was involved in construction of several pile-raft and raft foundations. Earlier there was implemented the unique raft foundation under a part of buildings of the Stock Exchange and St. Catharine's church in 32, Nevsky avenue.
In the latter object consolidated soil was used instead of piles, and members of St. Petersburg Commission decided to leave the massive building of the church without piles on logs, which were put criss-cross under massive walls and columns. These large-diameter logs were completely under water for a long time (more than 100 years), therefore, wood integrity was ensured for many years. But in the 1960s there was made a subway under Nevsky avenue, due to poor waterproofness ground waters had to be constantly pumped out of the subway. Therefore, the brave idea of A. Betancourt to put the heavy building on consolidated soil on logs or slab without piles was destroyed.
The authors of the paper are sure that any city planning transformations should consider specifics of buildings on logs and piles prone to decay without water.
During 10-15 years after beginning of decay of logs the church building settlements were 8,7-9,0 cm that led to local collapse of bricks of the cupola drum. Restoration works were suspended.
One of the authors of this paper was a scientific advisor for reinforcing subsoil under the building of St. Catharine's church. St. Petersburg geotechnical engineers presented several alternative projects of soil reinforcement with piles, which minimum length exceeded 22 m and more. It provided transfer of pressure to dense soils. Due to enormous costs of works they were not implemented. My colleagues geotechnical engineers (A.I.Osokin, P.M.Bondarev) proposed the cheapest and, in our opinion, audacious option. Instead of long bored piles (the Italian project of reinforcement implied 26-m-long piles of 150-mm diameter reinforced with fiber glass)to drive short bored auger piles with the diameter 200-250 mm and length up to 4,0 m. These piles remained in the layer of sand, they virtually reinforced soft soils in subsoil of massive pillars and walls. There was implemented the idea of soil reinforcement under massive foundation, i.e., A. Betancourt's idea on constructing pile-raft foundations.
Therefore, short piles involved the existing massive foundations in operation replacing rotten logs with piles. Observations of settlements showed that a relative stabilization of behavior of the unique cult building in the very center of St. Petersburg (architect Rinaldi), 32 Nevsky avenue, occurred. Until now the granite basement contains numbers of pile made for the façade wall that preserves the unique decoration.
One can mention some important factors which fostered success of implementation of A. Betancourt's idea with account of new calculation realities. The comprehensive software "Fem-models" developed in Emperor Alexander I St. Petersburg Transport University and the specialized geotechnical company "Georeconstruction" allows modeling the whole system of soil-structure interaction including the unique cult buildings.
It allows setting calculative periods of settlement stabilizations and giving values of limit stresses in massive superstructures.

The project of reconstruction and restoration of Kamennoostrovsky theatre
The group of companies "Georeconstruction" implemented this unique project for the wooden theatre. To adapt Kamennoostrovsky theatre to new functions there was designed and implemented a 3-level underground space with hanging the theatre building on "Titan" piles. There was simultaneous restoration of above ground wood structures including beams made according to A. Betancourt's design.
The design authors managed to preserve them implementing the unique restoration of all wooden structures after their operation for about 200 years. Now it successfully hosts the second stage of G. Tovstonogov's Petersburg State Theatre.
The interesting fact is that the project of adapting the old theatre to new theatrical functions with preservation of the unique wooden structures rose interest of the international community at the exhibition in Leipzig in 2010, the work was awarded with a Big golden medal.

Examination and numerical calculations of the building of Naval Cathedral
The Institute "Mostproyekt" gave an unusual assignment to Emperor Alexander I St. Petersburg Transport University (PGUPS) and the specialized geotechnical company "Georeconstruction" on comprehensive examination of Kronstadt Naval Cathedral and mathematical modeling of its stress-strain behavior associated with failure of staircases in 2010. The results of these investigations are shown in fig. 3,4, they witness on possibilities of numerical calculations to optimize reconstruction and make local reinforcement of structures of this unique Naval Cathedral in Kronstadt, which was deformed during the Second World War. No doubt, the features of forming stress-strain state of such a unique global masterpiece as St. Isaac's Cathedral generates interest of the authors and colleagues in the international committee ТС-207 "Soil-Structure Interaction ISSMGE". Moreover, the experience of these works was received at examination and design of Naval Cathedral in Kronstadt. Here numerical calculations were verified with the data of actual observations of the Cathedral deformations in time.
The authors of the paper consider it timely to conduct a complex examination of St. Isaac's cathedral including numerical modeling as per the developed software, which was tested in Naval Cathedral.
Calculated deformations should be in good agreement with the existing long-term geodetic observations of settlements of St. Isaac's cathedral (see fig. 2). Reliability of prediction of settlements and stresses of bearing structures can become the basis of the system of modern distant monitoring. Calculated data on limit stresses and settlements will constitute the basis for this monitoring. Only after such a detailed analysis and comparison of calculated and in situ results it is possible to make local reinforcements, if necessary, in locations where actual settlements or strains in bearing superstructures caused by differential settlements can exceed the limit ones. Experts of Emperor Alexander I St. Petersburg Transport University (PGUPS) and the group of companies "Georeconstruction" have the unique sensors, which can record data of actual stress-strain behavior distantly. Their processing allows evaluating serviceability of the main structures, including the unique support columns, which, as a rule, are redirected in landmark cross-dome world cathedrals, in the traffic light mode. If stresses and strains are in green zoneone can relax. If these indicators in some stress nodes transfer to the yellow zone, there is a need in timely measures on providing safety conditions, not allowing reaching the red-light area. Meanwhile, one should take into account the metro line under St. Isaac's cathedral. It causes possible additional dynamic actions from passing trains. It can be easily recorded, as it has been made in the Admiralty building. A whole series of sensors has been installed in some unique and important St. Petersburg buildings (the Hermitage, Yusupov's Palace, the building of Arbitrary Court, District substation in Lesnoy av. etc.) These observations are made not only by dispatchers but the university chairs in Turin and Milan (Italy).
The work is associated with the fact that underground automobile and railway tunnels dangerous for massive old cult buildings are located under the territory of these cities.
The first features of deformations close to the limit ones were recorded by operating sensors, including those on the screens of chairs of structural and geotechnical engineering of these universities distantly using the Internet.