WILLY LACERDA - Academia.edu (original) (raw)
Papers by WILLY LACERDA
Landslides - Evaluation & Stabilization - Balkema, 2004
ABSTRACT: The behavior of colluvial slopes in the Northern Hemisphere has been the subject of man... more ABSTRACT: The behavior of colluvial slopes in the Northern Hemisphere has been the subject of many publications. These deposits are usually constituted by clayey materials, or deposits of volcanic eruptions. The behavior of colluvial masses derived from granite-gneiss and from basic rocks in a tropical environment has been little addressed to, and some peculiarities distinguish this behavior from that of masses from more temperate regions. The main distinguishing factors seem to be the amount of rainfall, particularly intense rainfalls, the depth of the weathering zone and the hot climate. Other important factors are related to the hydrogeology of granite-gneiss, which has a direct bearing on colluvium instability. The knowledge gained from the systematic measurement of movements, pore pressures and correlations with rainfall constitute now a body of accumulated experience, and certain common characteristics are described in this lecture.
CRC Press eBooks, Jun 15, 2004
Results of consolidated-undrained compression and extension triaxial tests on undisturbed block s... more Results of consolidated-undrained compression and extension triaxial tests on undisturbed block samples of a medium grey clay at a section of the Rio de Janeiro subway excavations at Botarogo are presented. The sampling effects were minimized by subjecting the laboratory specimens to isotropic consolidation stresses well above the existing field consolidation stresses. Normalized stress-strain-strength parameters for a future use of the shansep method were obtained. The hyperbolic formulation for the initial tangent moduli of Kondner (1963) as used by Duncan and Chang (1970) was utilized. Comparisons are made with similar parameters obtained with the Rio de Janeiro soft grey clay and the weald clay. (TRRL)
CRC Press eBooks, Jun 15, 2004
Soils & rocks, Sep 30, 2020
Lacerda, and Francisco de Rezende Lopes were part of this "entourage". It became evident during t... more Lacerda, and Francisco de Rezende Lopes were part of this "entourage". It became evident during the conference that the amount of Brazilian papers outnumbered those presented by any other Association. At the Conference's banquet, during a conversation, Prof. Norbert Morgenstern, who was one of the invited speakers at that conference, directed himself to the four of us and made an interesting remark that was going to persist in our minds for the next year: "Brazil has produced many research papers. It is time for you to have your own journal". We contemplated that idea until one day, in 1976, during a meeting at Dirceu Velloso's office, when we decided to create the magazine. The name Solos e Rochas was an unanimity. Then came the practical questions. Who the editor would be? How to financially support the journal? How would we select the articles for the first issues? And so on. It was decided that Dirceu Velloso would be the first Editor of Solos e Rochas, Francisco Lopes would be responsible for the production of issues, and Medina and I would be associates, starting as the first reviewers. COPPE's Director at the time was Professor Paulo Alcântara Gomes. When approached, he immediately agreed to fund the journal. And so it was. The first articles were written by invited authors. The article by Prof. Marcio M. Soares was ready for publication by the end of 1976. The paper had to wait, until the journal found the required funding for the first issue. Soon, the first paper was followed by the manuscripts written by Paulo Cruz and Willy Lacerda, delivered for production by the end of 1977. With COPPE's support and the delivery of these two additional articles, the first issue was published in January, 1978. That would be the only issue of that year. A second issue followed, in 1979. By the end of 1979, COPPE could no longer afford to support the journal. To find a new source of funding, we reached out for help from Prof. Carlos de Souza Pinto, president of ABMS, proposing that the association should take over the direction of Solos e Rochas. He immediately accepted the idea, with a new chapter of the journal starting in 1980, now publishing three issues per year. From this point, we switched from publishing invited paper to a regular peer-review process, supported by numerous specialists. In 2007, during my term as President of ABMS, the journal became an international publication, with a brand-new name: Soils and Rocks. It has been a great satisfaction for me to follow the development of the journal to this day, and its commitment to excellence in the field of Soil Mechanics and Geotechnical Engineering, thanks recently to the efforts of its latest editors, starting with Waldemar Hachich.
Collapse characteristics of a quartz sand of the city of Petrolandia are determined by laboratory... more Collapse characteristics of a quartz sand of the city of Petrolandia are determined by laboratory and field tests on undisturbed material. The development and construction of a new equipment, which permits the field measurement of volume change of the soil at different depths under a variable vertical stress and controlled rate of innundation are presented. The collapsibility under geostatic stress increases up to a depth of 1.25m, and decreases for increasing depth. For a given rate of innundation and the same vertical stress the soil deformations due to innundation occur more rapidly in the laboratory than under field conditions. (A) For the covering abstract see IRRD 881647.
Geotechnical and Geological Engineering, May 18, 2020
Many slope failures in residual soils have been attributed to increased soil pore pressure. Durin... more Many slope failures in residual soils have been attributed to increased soil pore pressure. During the rainy season, water infiltration occurs, which can lead the slope to rupture by increasing the pore pressure. However, some landslides have been observed with pore pressures below those required for failure. Hypotheses for such ruptures include the occurrence of creep or fatigue due to cyclic variations in the piezometric level on the slope. This paper presents a study on the effect of pore pressure on the behaviour of the residual soil of the Soberbo hillside in Rio de Janeiro, Brazil, subjected to monotonic and cyclic pore pressure. Triaxial tests that simulate the increasing piezometric level (constant shear drained-CSD tests), drained creep (DC-CSD tests) and cyclic pore pressure variation (CPP tests) in slopes were carried out. The CSD test results showed that the failure due to increasing pore pressure is essentially dilatant and confirmed the peak strength obtained from conventional drained triaxial tests. Sudden failure was observed in all CSD tests at the end of the pore pressure increase phase. The results show that the failure of the slope may occur due to drained creep and the loss of soil shear strength under cycling pore pressure.
Canadian Geotechnical Journal, Dec 1, 1998
The numerical simulation of the breakwater construction at Sergipe Harbour, Brazil, is described ... more The numerical simulation of the breakwater construction at Sergipe Harbour, Brazil, is described and the results compared with instrumentation data. The numerical simulation was carried out in plane-strain conditions using the modified Cam-Clay model and the Biot consolidation theory. Field observations and the numerical simulation show that the horizontal displacements under the breakwater toe increase with time. This happens during the loading and consolidation stages. It is argued that the process does not necessarily derive only from undrained creep, since the model used does not simulate this phenomenon. The shear strains, measured by an inclinometer, increase more rapidly near the free-draining surfaces, in a process similar to the dissipation of excess pore pressure.Key words: clay, embankment, numerical analysis, shear strain, consolidation.
Geomorphology, Jun 1, 2007
The weathering of granitic and gneissic rocks in tropical regions can reach depths of more than 1... more The weathering of granitic and gneissic rocks in tropical regions can reach depths of more than 100 m. In southeast Brazil there are situations where landslide initiation depends on the fluctuation of the groundwater level, on the impact of falling rocks and on intense rainfall, causing superficial slides. The fluctuation of groundwater induces cyclical variations of the pore water pressure, and consequently of the effective stresses. This variation causes cyclic expansion and contraction of the structure of the saprolitic soil, weakening the imbrication of grains and loss of the cementation that may exist. This could be called a "fatigue" phenomenon. The practical effect is the lowering of the Mohr shear strength envelope, and a sudden rupture of the soil at a lower groundwater level than that which would be compatible with the intact soil strength properties, initiating a landslide. Another situation arises during intense rains, when a rock slab or a rock block detaches from the uppermost parts of a slope. This occurs where steep rock outcrops exhibit relief joints or where residual blocks of granite roll down the slope, impacting the compressible, saturated colluvial soil overlying the saprolitic soil. The sudden increase of pore pressure can liquefy the soil. Finally, another mechanism is that of the advance of a saturation front in a steep slope of unsaturated saprolitic soil, reaching a depth below the root zone. The loss of the cohesion due to suction, without the beneficial contribution of the roots to the shearing strength, causes a sudden slide. During extreme rain episodes literally hundreds of such superficial slides, reaching 1 to 3 m in depth, occur in a given basin. The concentrated runoff that flows along the surface of the thalweg of the basin carries this soil in a muddy state, and a debris flow ensues.
Publication of: Balkema (AA), 1985
The possibility of an increase in the coefficient of earth pressure at rest, associated with the ... more The possibility of an increase in the coefficient of earth pressure at rest, associated with the phenomenon of secondary compression, is discussed. A theory for the one-dimensional consolidation including secondary compression is also presented, in which the degree of consolidation, is a function of the relationship between the final and initial vertical effective stresses, the time factor of the coefficient of earth-pressure at rest and a parameter that controls secondary compression. For the covering abstract of the conference see IRRD 287689. (TRRL)
Journal of Geotechnical Engineering, Feb 1, 1989
Natural slopes in the tropical coast of Brazil range from rock scarps and residual soil to colluv... more Natural slopes in the tropical coast of Brazil range from rock scarps and residual soil to colluvial soils. Colluvium may cover residual as well as alluvial soil, this case being common at stretches of coasts adjacent to mountains, where an interdigitation of colluvium and alluvium can occur. The instabilization of these slopes in the long run derives mainly from the action of rainfall and from physical and chemical weathering of the parent rock. Chemical weathering breaks down the minimal constituents of the rock, reduces its strength, and is intensified by water percolating through fissures in the rock. For a given situation in time, rainfall has a direct influence on the mass movements, and according to its intensity and duration is the cause of landslides due to loss of apparent cohesion at the surface of residual and colluvial slopes, as well as deep seated movements due to the elevation of the phreatic level or artesian pressure. Other causes of instabilization of residual slopes are the impact due to the fall of rock slabs or earth masses from higher elevations which may cause sudden loss of strength and the initiation of debris-flows. Lightning also has been reported as the cause of landslide initiation, and should not be neglected. Some of these processes are discussed and examples taken from research at COPPE are shown illustrating relevant cases.
CRC Press eBooks, Jun 15, 2004
Results of a comprehensive site investigation in a soft clay of Sergipe, in northeast Brazil, are... more Results of a comprehensive site investigation in a soft clay of Sergipe, in northeast Brazil, are summarized here. The soil profile consists of a 4.0 m (12 ft) thick sand layer overlying a 7.0 m (23 ft) thick soft clay layer. Artesian pressure about 30 kPa higher than hydrostatic pore pressures was detected, thus reducing effective stresses and inducing a vertical flow in the soft clay. The soft clay is quite homogeneous and lightly over consolidated with OCR values in the range 1.5 - 2.0. Undrained simple shear and triaxial tests presented quite high pore pressure A parameter, typical of structured clays. It is shown that piezocone tests can provide a good continuous profile of geotechnical properties if previously calibrated against laboratory tests.
A brief review about the most significant results of COPPE research on rheological behaviour of s... more A brief review about the most significant results of COPPE research on rheological behaviour of saturated clays subjected to one-dimensional strain. ISM Martins, PEL Santa Maria, WA Lacerda Recent Developments in Soil and ...
CRC Press eBooks, Jun 15, 2004
Landslides - Evaluation & Stabilization - Balkema, 2004
ABSTRACT: The behavior of colluvial slopes in the Northern Hemisphere has been the subject of man... more ABSTRACT: The behavior of colluvial slopes in the Northern Hemisphere has been the subject of many publications. These deposits are usually constituted by clayey materials, or deposits of volcanic eruptions. The behavior of colluvial masses derived from granite-gneiss and from basic rocks in a tropical environment has been little addressed to, and some peculiarities distinguish this behavior from that of masses from more temperate regions. The main distinguishing factors seem to be the amount of rainfall, particularly intense rainfalls, the depth of the weathering zone and the hot climate. Other important factors are related to the hydrogeology of granite-gneiss, which has a direct bearing on colluvium instability. The knowledge gained from the systematic measurement of movements, pore pressures and correlations with rainfall constitute now a body of accumulated experience, and certain common characteristics are described in this lecture.
CRC Press eBooks, Jun 15, 2004
Results of consolidated-undrained compression and extension triaxial tests on undisturbed block s... more Results of consolidated-undrained compression and extension triaxial tests on undisturbed block samples of a medium grey clay at a section of the Rio de Janeiro subway excavations at Botarogo are presented. The sampling effects were minimized by subjecting the laboratory specimens to isotropic consolidation stresses well above the existing field consolidation stresses. Normalized stress-strain-strength parameters for a future use of the shansep method were obtained. The hyperbolic formulation for the initial tangent moduli of Kondner (1963) as used by Duncan and Chang (1970) was utilized. Comparisons are made with similar parameters obtained with the Rio de Janeiro soft grey clay and the weald clay. (TRRL)
CRC Press eBooks, Jun 15, 2004
Soils & rocks, Sep 30, 2020
Lacerda, and Francisco de Rezende Lopes were part of this "entourage". It became evident during t... more Lacerda, and Francisco de Rezende Lopes were part of this "entourage". It became evident during the conference that the amount of Brazilian papers outnumbered those presented by any other Association. At the Conference's banquet, during a conversation, Prof. Norbert Morgenstern, who was one of the invited speakers at that conference, directed himself to the four of us and made an interesting remark that was going to persist in our minds for the next year: "Brazil has produced many research papers. It is time for you to have your own journal". We contemplated that idea until one day, in 1976, during a meeting at Dirceu Velloso's office, when we decided to create the magazine. The name Solos e Rochas was an unanimity. Then came the practical questions. Who the editor would be? How to financially support the journal? How would we select the articles for the first issues? And so on. It was decided that Dirceu Velloso would be the first Editor of Solos e Rochas, Francisco Lopes would be responsible for the production of issues, and Medina and I would be associates, starting as the first reviewers. COPPE's Director at the time was Professor Paulo Alcântara Gomes. When approached, he immediately agreed to fund the journal. And so it was. The first articles were written by invited authors. The article by Prof. Marcio M. Soares was ready for publication by the end of 1976. The paper had to wait, until the journal found the required funding for the first issue. Soon, the first paper was followed by the manuscripts written by Paulo Cruz and Willy Lacerda, delivered for production by the end of 1977. With COPPE's support and the delivery of these two additional articles, the first issue was published in January, 1978. That would be the only issue of that year. A second issue followed, in 1979. By the end of 1979, COPPE could no longer afford to support the journal. To find a new source of funding, we reached out for help from Prof. Carlos de Souza Pinto, president of ABMS, proposing that the association should take over the direction of Solos e Rochas. He immediately accepted the idea, with a new chapter of the journal starting in 1980, now publishing three issues per year. From this point, we switched from publishing invited paper to a regular peer-review process, supported by numerous specialists. In 2007, during my term as President of ABMS, the journal became an international publication, with a brand-new name: Soils and Rocks. It has been a great satisfaction for me to follow the development of the journal to this day, and its commitment to excellence in the field of Soil Mechanics and Geotechnical Engineering, thanks recently to the efforts of its latest editors, starting with Waldemar Hachich.
Collapse characteristics of a quartz sand of the city of Petrolandia are determined by laboratory... more Collapse characteristics of a quartz sand of the city of Petrolandia are determined by laboratory and field tests on undisturbed material. The development and construction of a new equipment, which permits the field measurement of volume change of the soil at different depths under a variable vertical stress and controlled rate of innundation are presented. The collapsibility under geostatic stress increases up to a depth of 1.25m, and decreases for increasing depth. For a given rate of innundation and the same vertical stress the soil deformations due to innundation occur more rapidly in the laboratory than under field conditions. (A) For the covering abstract see IRRD 881647.
Geotechnical and Geological Engineering, May 18, 2020
Many slope failures in residual soils have been attributed to increased soil pore pressure. Durin... more Many slope failures in residual soils have been attributed to increased soil pore pressure. During the rainy season, water infiltration occurs, which can lead the slope to rupture by increasing the pore pressure. However, some landslides have been observed with pore pressures below those required for failure. Hypotheses for such ruptures include the occurrence of creep or fatigue due to cyclic variations in the piezometric level on the slope. This paper presents a study on the effect of pore pressure on the behaviour of the residual soil of the Soberbo hillside in Rio de Janeiro, Brazil, subjected to monotonic and cyclic pore pressure. Triaxial tests that simulate the increasing piezometric level (constant shear drained-CSD tests), drained creep (DC-CSD tests) and cyclic pore pressure variation (CPP tests) in slopes were carried out. The CSD test results showed that the failure due to increasing pore pressure is essentially dilatant and confirmed the peak strength obtained from conventional drained triaxial tests. Sudden failure was observed in all CSD tests at the end of the pore pressure increase phase. The results show that the failure of the slope may occur due to drained creep and the loss of soil shear strength under cycling pore pressure.
Canadian Geotechnical Journal, Dec 1, 1998
The numerical simulation of the breakwater construction at Sergipe Harbour, Brazil, is described ... more The numerical simulation of the breakwater construction at Sergipe Harbour, Brazil, is described and the results compared with instrumentation data. The numerical simulation was carried out in plane-strain conditions using the modified Cam-Clay model and the Biot consolidation theory. Field observations and the numerical simulation show that the horizontal displacements under the breakwater toe increase with time. This happens during the loading and consolidation stages. It is argued that the process does not necessarily derive only from undrained creep, since the model used does not simulate this phenomenon. The shear strains, measured by an inclinometer, increase more rapidly near the free-draining surfaces, in a process similar to the dissipation of excess pore pressure.Key words: clay, embankment, numerical analysis, shear strain, consolidation.
Geomorphology, Jun 1, 2007
The weathering of granitic and gneissic rocks in tropical regions can reach depths of more than 1... more The weathering of granitic and gneissic rocks in tropical regions can reach depths of more than 100 m. In southeast Brazil there are situations where landslide initiation depends on the fluctuation of the groundwater level, on the impact of falling rocks and on intense rainfall, causing superficial slides. The fluctuation of groundwater induces cyclical variations of the pore water pressure, and consequently of the effective stresses. This variation causes cyclic expansion and contraction of the structure of the saprolitic soil, weakening the imbrication of grains and loss of the cementation that may exist. This could be called a "fatigue" phenomenon. The practical effect is the lowering of the Mohr shear strength envelope, and a sudden rupture of the soil at a lower groundwater level than that which would be compatible with the intact soil strength properties, initiating a landslide. Another situation arises during intense rains, when a rock slab or a rock block detaches from the uppermost parts of a slope. This occurs where steep rock outcrops exhibit relief joints or where residual blocks of granite roll down the slope, impacting the compressible, saturated colluvial soil overlying the saprolitic soil. The sudden increase of pore pressure can liquefy the soil. Finally, another mechanism is that of the advance of a saturation front in a steep slope of unsaturated saprolitic soil, reaching a depth below the root zone. The loss of the cohesion due to suction, without the beneficial contribution of the roots to the shearing strength, causes a sudden slide. During extreme rain episodes literally hundreds of such superficial slides, reaching 1 to 3 m in depth, occur in a given basin. The concentrated runoff that flows along the surface of the thalweg of the basin carries this soil in a muddy state, and a debris flow ensues.
Publication of: Balkema (AA), 1985
The possibility of an increase in the coefficient of earth pressure at rest, associated with the ... more The possibility of an increase in the coefficient of earth pressure at rest, associated with the phenomenon of secondary compression, is discussed. A theory for the one-dimensional consolidation including secondary compression is also presented, in which the degree of consolidation, is a function of the relationship between the final and initial vertical effective stresses, the time factor of the coefficient of earth-pressure at rest and a parameter that controls secondary compression. For the covering abstract of the conference see IRRD 287689. (TRRL)
Journal of Geotechnical Engineering, Feb 1, 1989
Natural slopes in the tropical coast of Brazil range from rock scarps and residual soil to colluv... more Natural slopes in the tropical coast of Brazil range from rock scarps and residual soil to colluvial soils. Colluvium may cover residual as well as alluvial soil, this case being common at stretches of coasts adjacent to mountains, where an interdigitation of colluvium and alluvium can occur. The instabilization of these slopes in the long run derives mainly from the action of rainfall and from physical and chemical weathering of the parent rock. Chemical weathering breaks down the minimal constituents of the rock, reduces its strength, and is intensified by water percolating through fissures in the rock. For a given situation in time, rainfall has a direct influence on the mass movements, and according to its intensity and duration is the cause of landslides due to loss of apparent cohesion at the surface of residual and colluvial slopes, as well as deep seated movements due to the elevation of the phreatic level or artesian pressure. Other causes of instabilization of residual slopes are the impact due to the fall of rock slabs or earth masses from higher elevations which may cause sudden loss of strength and the initiation of debris-flows. Lightning also has been reported as the cause of landslide initiation, and should not be neglected. Some of these processes are discussed and examples taken from research at COPPE are shown illustrating relevant cases.
CRC Press eBooks, Jun 15, 2004
Results of a comprehensive site investigation in a soft clay of Sergipe, in northeast Brazil, are... more Results of a comprehensive site investigation in a soft clay of Sergipe, in northeast Brazil, are summarized here. The soil profile consists of a 4.0 m (12 ft) thick sand layer overlying a 7.0 m (23 ft) thick soft clay layer. Artesian pressure about 30 kPa higher than hydrostatic pore pressures was detected, thus reducing effective stresses and inducing a vertical flow in the soft clay. The soft clay is quite homogeneous and lightly over consolidated with OCR values in the range 1.5 - 2.0. Undrained simple shear and triaxial tests presented quite high pore pressure A parameter, typical of structured clays. It is shown that piezocone tests can provide a good continuous profile of geotechnical properties if previously calibrated against laboratory tests.
A brief review about the most significant results of COPPE research on rheological behaviour of s... more A brief review about the most significant results of COPPE research on rheological behaviour of saturated clays subjected to one-dimensional strain. ISM Martins, PEL Santa Maria, WA Lacerda Recent Developments in Soil and ...
CRC Press eBooks, Jun 15, 2004