Flat Jack Method Research Articles

Flatjack application on existing hollow concrete block masonry

This work aims to validate new flatjack in evaluating existing hollow concrete block masonry. The flatjack method is used as a non-destructive on-site test in masonry structures to obtain the actual stress-strain curve of masonry and estimate its strength. This method is already internationally standardized by ASTM and RILEM standard codes. However, most of the studies, standards, and available jacks refer to masonry with solid units, such as bricks and stones. The research adapted the deformability test performed on hollow block walls with the double flatjack to estimate the elasticity module and the masonry compressive strength, validating this technique as non-destructive. Experimental test using the newly developed equipment was performed in existing masonry buildings. The estimated strength results were compared to test results provided by the company responsible for the construction. The methodology using the new equipment proved good results. The adapted deformability test can be carried out on-site elements to estimate the properties of masonry made with hollow concrete blocks.

The Assessment and Retrofitting of Cultural Heritage—A Case Study of a Residential Building in Glina

The focus of the study is on the renovation of a specific case study, which is a 19th century building under cultural heritage protection. It highlights the particular challenges faced by civil engineers in the structural renovation of buildings that are under heritage protection. Preserving the identity of these buildings limits the available methods for strengthening their seismic capacity. At the beginning, information about the seismic activity and the different post-earthquake evaluation procedures are presented to identify the damage and take appropriate further steps. Then, basic information about the building is given and supported by graphic attachments. In the following, the methods and materials are explained, focusing on in situ testing with the semi-destructive flat-jack method and the analysis of the structure with the nonlinear method implemented in the software. Subsequently, the obtained results are presented and discussed, accompanied by graphics. An approach for strengthening the structure is presented, which includes a combination of traditional methods and innovative solutions suitable for the preservation of cultural heritage. The discussion and conclusions emphasize the importance of assessing and retrofitting existing masonry structures due to their vulnerability, especially in earthquake-prone areas. Finally, this article also provides insights into the local context, cultural significance, and historical background of the building, along with the specific retrofitting solutions employed to address its unique requirements.

Experimental Evaluation of Unreinforced Brick Masonry Mechanical Properties by the Flat-Jack Method – an Extensive Campaign in Croatia

ABSTRACT Several strong earthquakes hit Croatia in 2020. Such earthquakes, after a long absence of strong seismic activities in the country, in combination with material degradation, lack of maintenance and structures that were built before modern seismic regulations, culminated with extensive damage to the existing building stock. Existing unreinforced masonry (URM) structures are quite vulnerable to earthquakes, largely due to a lack of connectivity between structural parts. The numerous damaged buildings emphasize the need to preserve, restore and strengthen URM structures, especially the ones under heritage protection. The main focus of this paper is on the first step of the assessment process, which is to determine the mechanical properties of masonry. For that purpose, the flat-jack method is used. Through stress transfer from a flat-jack to the masonry useful information can be obtained. The results of the extensive post-earthquake flat-jack tests (single, double and shear) on 17 case studies in Croatia are presented. The results are critically discussed and the mechanical properties of brick masonry in Mediterranean Europe are presented. The goal of the present work is to increase the confidence level in the definition of mechanical properties and, thus, to favorably influence the necessary reconstruction.

Stability evaluation of room-and-pillar rock salt mines by using a flat jack technique - A case study

Room-and-pillar mining is commonly employed for the extraction of rock salt in underground mines. Pillar stress is a major concern in these mines as it is directly related to stability and mineral recovery. In this study a flat jack method was used to measure pillar stresses in three underground rock salt mines in Pakistan. The field work included determination of in-situ stress, in-situ elastic modulus, recording of field variables (pillar length and width, height and width of opening, opening width to height ratio, extraction ratio, and overburden height) and collection of salt block samples. The geomechanical properties of rock salt (uniaxial compressive strength, Young's modulus, Brazilian tensile strength, and density) were also determined to estimate overburden stress, pillar strength, and factor of safety (both estimated and actual). It was found that the measured pillar stresses are proportional to the overburden stress values, with their magnitude ranging from 6.05 MPa to 11.97 Mpa, and the pillars were found to be stable. Regression analysis was performed to develop statistical models for in-situ stress and in-situ elastic modulus. Finally a quick guideline chart was developed to determine the suitable length of pillar for a given span and required level of safety. Keywords: flat jack, room-and-pillar mining, in-situ stress, factor of safety, regression analysis.

Stress state laboratory verification in masonry structures according to the flat jack method

Stress state laboratory verification in masonry structures according to the flat jack method

The Estimation of Compressive Stress Level in Brick Masonry Using the Flat-jack Method

The paper presents the methodology of in-situ testing based on the flat-jack device. The flat-jack method belongs to the minor-destructive tests (MDT). Beside NDT, MDT are recommended for historical buildings. In the paper the results of authors’ laboratory studies on brick walls were presented. Tests were carried out using various types of flat-jacks in terms of their shapes and materials from which they were made. Additionally, during flat-jack tests various methods of displacement measuring including optical measurements based on a digital image correlation method (DIC) were performed. The studies allowed the authors to provide recommendations on the selection of the flat-jack type for determining compressive stress in brick masonry.

Stress Related Fracturing in Dimension Stone Quarries

In Missouri, the horizontal stresses (pressures) in the near surface rock are uncommonly high. While the vertical stresses in rock are simply a function of the weight of the overlying rock, near surface stresses can be many times higher. The near surface horizontal stresses can be in excess of 5 times greater than the vertical stresses. In this research, Flatjack method was used to measure horizontal stress in Red Granite Quarry in Missouri. The flat jack method is an approved method of measuring ground stresses. A saw cut is used to “relax” the stress in the ground by allowing the rock to deform inwards the cut. A hydraulic flat jack is used to inflate the slot; to push the rock back to its stressed position, as measured by a strain gauge on either side of the slot. The pressure in the jack, when the rock is exactly back to its original position, is equal to the ground stress before the saw cut was made. According to the results, present production direction for each pit is not good because the maximum stress direction is perpendicular with production direction. This case causes unintentional breakage results in the loss rock. The results show that production direction should be changed.

Assessment of the mechanical properties of brick masonry by a flat-jack method

Assessment of the mechanical properties of brick masonry by a flat-jack method

Recent advances in the interpretation of the small flat jack method : Martins, C S; Souza, L R Proc 6th International Conference on Rock Mechanics, Montreal, 30 Aug–10 Sept 1987V2, P1241–1244. Publ Rotterdam: A A Balkema, 1987

Recent advances in the interpretation of the small flat jack method : Martins, C S; Souza, L R Proc 6th International Conference on Rock Mechanics, Montreal, 30 Aug–10 Sept 1987V2, P1241–1244. Publ Rotterdam: A A Balkema, 1987

Determination of the complete state of stress in rock with the flat jack method (in German)

Determination of the complete state of stress in rock with the flat jack method (in German)

Determination of the state of stress of rock masses by the small flat jack (SFJ) method

Determination of the state of stress of rock masses by the small flat jack (SFJ) method

Some consideration of in-situ testing on mechanical properties of rock mass : Zhu Weishen; Xu Dongjun Proc 23rd Symposium on Rock Mechanics, Berkeley, 25–27 August 1982, P864–871. Publ New York: AIME, 1982

The first part of this paper compares the different methods of determining the moduli of elasticity and deformation of hard rock. It was found that the plate bearing test has a serious shortcoming. The slit flat jack method seems to be giving more reasonable results; it is recommended as a desirable method for in situ testing. In part 2, a new method of determining the deformation and strength of weak planes in rock masses is recommended. The weak plane charateristics is related to the stress-strain curve, normal stress to the shear displacement curve. The yielding of weak planes is discussed. For the covering abstract of the symposium see TRIS 452576. (TRRL)

Tectonic stresses in France: In situ measurements with a flat jack

In situ stress measurements in thick limestone layers of the Parisian Basin and in neighboring regions yield a remarkably homogeneous stress field. The flat jack method has been used. Comparison with over‐coring gave good agreement for the azimuth of the principal axes. In the Jurassic of Burgundy and Poitou as well as in a Carboniferous outcrop near the English Channel, maximum compression is found along the NNW‐SSE direction.

Surface rock stress measurement with a new cylindrical jack : Bowling, AJ Hydro-Elect. Comm, Tasmania, AUS 4F,5R. Paper to Syposium, Investigation of Stress in Rock-Advances in Stress Meausrement. Sydney, 11–13 AUG, 1976P7–11

A new cylindrical jack for surface rock stress measurement is described. The new jack consists of an adiprene rubber sleeve on a solid steel core. The new jack has been used successfully to measure rock stresses in an underground power station excavation and results from these tests are briefly described. The cylindrical jack method is compared with the well established flat jack method. Whilst the cylindrical jack method is only about a half as sensitive as the flat jack method it is satisfactorily accurate for rock stress measurement work. The cylindrical jack method also has advantages of speed and convenience and provides more information at each test site than the flat jack method.

Measuring internal stress in rock by flat jack method : Proc. Symposium on Rock Mech. Dhanbad, India, July 1972. 7F, 2T, 27R. THE INSTN. OF ENGRS, CALCUTTA, INDIA, 1973, P139–149

Measuring internal stress in rock by flat jack method : Proc. Symposium on Rock Mech. Dhanbad, India, July 1972. 7F, 2T, 27R. THE INSTN. OF ENGRS, CALCUTTA, INDIA, 1973, P139–149

An investigation of the flatjack method of measuring rock stress

A series of laboratory experiments to test various aspects of the flatjack method of measuring rock stress have been made. Agreement with the known applied stresses is found to be excellent in sound rock. Problems of continued deformation after slot cutting or creep, differences in the values for elastic moduli determined by various methods and the relevance of these tests to the usual underground procedures are discussed.

The Laws of Elastico-Viscous Flow. II

Previous articleNext article FreeThe Laws of Elastico-Viscous Flow. IIA. A. MichelsonA. A. Michelson Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 28, Number 1Jan. - Feb., 1920 Article DOIhttps://doi.org/10.1086/622693 Views: 95Total views on this site Citations: 7Citations are reported from Crossref PDF download Crossref reports the following articles citing this article:Mervyn S. Paterson Mechanical Fundamentals, (Nov 2012): 71–90.https://doi.org/10.1007/978-94-007-5545-1_4Desmond J. Darby Preliminary study of the time dependence of creep after the 1987 Edgecumbe earthquake, New Zealand, New Zealand Journal of Geology and Geophysics 32, no.11 (Jan 2012): 129–133.https://doi.org/10.1080/00288306.1989.10421396Ellis Strick A uniformly convergent alternative to the davidson-cole distribution function, Advances in Molecular Relaxation and Interaction Processes 24, no.11 (Sep 1982): 37–60.https://doi.org/10.1016/0378-4487(82)80074-5R. K. S. Chouhan, V. K. Gaur, H. S. Rathor Aftershock sequence of the Solomon Island earthquake of June 15, 1966, Pure and Applied Geophysics PAGEOPH 80, no.11 (Jan 1970): 162–170.https://doi.org/10.1007/BF00880204E.R. Hoskins An investigation of the flatjack method of measuring rock stress, International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 3, no.44 (Nov 1966): 249–264.https://doi.org/10.1016/0148-9062(66)90007-6 Hugh C. Heard Effect of Large Changes in Strain Rate in the Experimental Deformation of Yule Marble, The Journal of Geology 71, no.22 (Sep 2015): 162–195.https://doi.org/10.1086/626892Hugo Benioff Earthquakes and rock creep, Bulletin of the Seismological Society of America 41, no.11 (Jan 1951): 31–62.https://doi.org/10.1785/BSSA0410010031