The testing undertaken for this dissertation is intended to help quantify the various time-dependant deformation processes around typical deep level hard rock tabular excavations. Three mechanisms were investigated and two different hard rock types, Ventersdorp Lava and Elsburg Quartzite were used. Uniaxial compression creep studies were done as the first part of the study followed by shear creep studies on discontinuities where crushed lava and crushed quartzite as well as a natural gouge were used as infilling. An important conclusion made is that the relationship between grain size and infilling thickness is more important than previously might have been assumed. The last part of the study consisted of triaxial post-failure relaxation tests. As far as could be determined, this is the first time triaxial post-failure tests were attempted, particularly on typical South African hard rocks. An important finding of this study is that during compression creep as well as during triaxial post-failure relaxation the amount of energy dissipated for the lava is significantly less than for quartzite. For mines operating at great depth (more than 2000m) the implication is that the rock material might relax much more slowly than might have been assumed and this means that after failure the rock mass continues to store large amounts of strain energy. This study provides the first data available for energy change calculations in fractured rock masses. Three mechanisms of time-dependant deformation were quantified providing valuable data for numerical investigations. / Dissertation (MSc (Mine Strata Control))--University of Pretoria, 2006. / Mining Engineering / unrestricted

M.Sc. (Eng.),Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2012 / Mining is a sensitive business that yields high returns and at the same time is associated with high risk of injuries/fatalities and potential losses of revenue. There is increasing intolerance for injuries and fatalities by governments and the other stakeholders involved in the mining business often resulting in mine closures and revenue loss. Chief among the mining risks is the occurrence of rockfalls where people work and access. The rockfalls are bound mainly by joints that intersect the rockmass thereby forming rock blocks that may fall once an excavation has been created. There are many methods that have been used over time to predict the occurrence of rockfalls. More recently probabilistic methods have gained more ground over deterministic methods. The properties of the joints that are identifiable on exposed excavations are the main inputs used in simulating rockfalls. To date there has been little work that has been done to compare predicted rockfalls to actual rockfalls. This dissertation presents a practical method for collecting rockfall and joint data in the stope hangiwall at two mines in the Bushveld Complex. The joint data has been used in simulating rockfalls using JBlock (a probabilistic keyblock stability programme). A comparison between simulated rockfalls and mapped rockfalls has been presented. Based on this comparison, a number of iterations were done to calibrate the JBlock results until near realistic rockfalls were achieved. Three case studies have been conducted to investigate the effectiveness of different stope support systems in reducing rockfall. The potential losses and injury risk associated with the different support systems have been quantified for all the individual rockfalls. In general the rockfall frequency is directly proportional to the risks associated with the rockfalls. Through this research it has been demonstrated that it is possible to use joint data found on excavation surfaces to statistically predict the occurrence of potential rockfalls in similar ground conditions. The optimum support system that has minimum injury and cost risk can also be selected from a comparison of a number of support systems. Armed with this information, rock engineers can now make strategic decisions versus the existing common tactical approach.

Thesis (Ph.D.)--University of the Witwatersrand, Faculty of Engineering, 1988. / Mining induced fracturing and associated deformations can commonly be observed around deep gold mining excavations. As the rockmass behaviour and the stability of the excavations are directly influenced by these processes, a proper understanding of this influence would certainly improve current mining practices with respect to blasting, rock breaking, support design and mining lay-outs. The main subject of this thesis is the physics of failure and post failure behaviour of rock and similar materials. Failure is denned here as a state at which the material has been subjected to fracture and/or damage processes. The applicability of commonly used constitutive models in representing such failure and post failure processes has been investigated mainly by means of numerical simulations. Mechanisms which control fundamental fracture and damage processes have been analysed by comparing the results from relevant laboratory experiments with numerical models. Linear elastic fracture mechanics has been applied to explain and simulate the formation of large scale extension fractures which form in response to excessive tensile stresses. Using the flaw concept it is demonstrated that these fractures not only initiate and propagate from the surface of an opening in compressed rock, but that so called secondary fracturing can be initiated from within the solid rock as well. The effect of geological discontinuities such as bedding planes, faults and joints on the formation of (extension) fractures has also been investigated and it has been shown how the presence of such discontinuities can cause the formation o f additional fractures. Micro mechanical models have been, used to investigate the interaction and coalescence processes of micro fractures. It was found that the formation of large scale extension fracturing can be explained from such processes, but so called shear fractures could not directly be reproduced, although such a possibility has been claimed by previous researchers. The formation of shear fractures is of particular- interest as violent failure of rock, which is subjected to compressive stresses only, is often associated with such fractures. In an all compressive stress environment, only shear deformations would allow for the relief of excess stress and thus energy. The formation of shear fractures is associated with complex mechanisms and shear fractures can therefore not directly be represented by tingle cracks. In contrast to the propagation of tensile fractures, which can readily be explained by traditional fracture mechanics in terms of stress concentrations around the crack tip, the propagation of shear fractures requires a different explanation. In this thesis an attempt has nevertheless been made to reproduce shear fractures by direct application of fracture mechanics. This his been done by representing a shear fracture as a single crack and by assuming fracture growth criteria which are either based on critical excess shear stresses, or on a maximum energy release. Both criteria are completely empirical and require a value for the critical shear resistance in the same way as a critical tensile resistance is required to represent the formation of tensile fracture; , The determination of a critical tensile resistance ( Kk ) is relatively straight forward, as the formation of tensile fractures from a pre-existing flaw can be reproduced and observed in standard laboratory tests. The determination of a critical shear resistance is, however, not a common practice, as the formation of a shear fracture from a pre-existing flaw is very infrequently observed. The application of shear fracture growth criteria nevertheless resulted in plausible fracture patterns, which suggests that such criteria are realistic. It is argued here however that the formation of shear fractures cannot be associated with primary fracture growth, but rather with the localisation of failure and damage in an area which is subjected to plastic deformation. The application of fracture mechanics is therefore not correct from a fundamental point of view as these processes are not represented. For this reason plasticity theory has also been applied in order to simulate failure in general, and shear failure localisation in particular. It was in principle possible to reproduce the shear fractures with the use of this theory, but numerical restraints affected the results to such an extent that most of the simulations were not realistic. Plasticity theory can also be extended to include brittle behaviour by the use of so called strain softening models. The physical processes which lead to brittle failure are however not directly represented by such models and they may therefore not result in realistic failure patterns. It was in fact found that strain softening models could only produce realistic results if localisation of failure could be prevented. The effect of numerical restraints becomes even more obvious with a strain softening model in the case of failure localisation. While the plasticity models appear inappropriate in representing brittle failure, they demonstrated that plastic deformations can be associated with stress changes which may lead to subsequent brittle fracturing. Although only indirect attempts have been made to reproduce this effect, as appropriate numerical tools are not available, it is clear that many observations of extension fracturing could be explained by plastic deformations preceding the brittle fracturing processes. Many rocks are classified as brittle, but plastic deformation processes often occur during the damage processes as well. The sliding crack for instance, which is thought to represent many micro mechanical deformation processes in rock, directly induces plastic deformations when activated. A pure brittle rock, which may be defined as a rock in which absolutely no plastic deformation processes take place, may therefore only be of academic interest as it is inconceivable that such a rock materiel exists. Only in such an academic case would (linear) elastic fracture mechanics be directly applicable. As plastic deformation processes do play a role in real rock materials it is important to investigate their influence on subsequent brittle failure processes. The elastic stress distribution, which is often used to explain the onset of brittle fracturing, may be misleading as plastic deformations can substantially affect the stress distribution . -recediny fracture initiation. In an attempt to combine both plastic and brittle failure, use has been made of tessellation models, which in effect define potential fracture paths in a random mesh. The advantage of these models is that various failure criteria, with or without strain softening potential, can be used without the numerical restraints which are normally associated with the conventional continuum models. The results of these models are also not free from numerical artefacts, but they appear to be more realistic in general. One o f the m;ij, r conclusions based on these results is that shear failure does not occur in a localised fashion, but is associated with the uniform distribution and extension of damage. Shear failure, which can be related directly to plastic failure, can however induce brittle, tensile, failure due to stress redistribution. While the theories of fracture mechanics and plasticity are well established, their application to rock mechanical problems often leads to unrealistic results. Commonly observed firacture patterns in rock, loaded in compression, are most often not properly reproduced by numerical models for a combination of reasons. Either a model concentrates on the discrete fracturing processes, in which case the plastic deformation processes are ignored, or plasticity is represented, but brittle failure is pooxiy catered for. While theoretically a combination of these models might lead to better representations and simulations, numerical problems do affect all models to a certain extent and a practical solution is not immediately available. The results of numerical models can therefore only be analysed with caution and the underlying assumptions and numerical problems associated with a particular technique need to be appreciated before such results can be interpreted with any sense. Many of the problems are identified here and this may assist researchers in the interpretation of results from numerical simulations. Laboratory experiments, which have been chosen for analyses, involve specimens which have been subjected to compressive stresses and which contain openings from which failure and fracturing is initiated. Such specimens are less subjective to boundary influences and are far more representative of conditions around mining excavations than typical uni- and tri-axial tests. The uniform stress conditions in these latter tests allow boundary effects to dominate the stress concentrations, and thus failure initiation, in the specimens. The large stress gradients, which can be expected to occur around underground excavations, are not reproduced in such specimens. As a consequence failure is not u atained within a particular area, but spreads throughout the complete specimen in the uni- and tri-axial tests. Specimens containing openings are therefore far more likely to reproduce the fracture patterns which can be observed around deep level mining excavations. Numerical simulations of brittle, tensile fracturing around mining excavations resulted in consistent fracture patterns. Fracture patterns could however be strongly influenced by the presence of geological (pre-existing) discontinuities such as bedding planes. Although tensile stresses are often assumed to be absent around deej: <y vel excavations because typical hanging- and foot-walls are subjected to compressive horizontal strain and thus stress, the numerical models identified alternative locations o f Ix 'sile stress and also mechanisms which could induce secondary tensile stresses, A failure criterion has therefore been identified as the most likely cause of large scale fracturing while shear fracturing may only occur in the absence of such tensile stresses .and only as a consequence of failure localisation in damaged rock rather than fracture propagation (in solid rock). Geological discontinuities can easily induce tensile stresses vVher mobilised and may even replace the mining induced fractures by offering a more efficient meat s for energy release. The latter possibility is a true three dimensional issue which has not be en addressed any further in this study, but may be very relevant to jointed rock. Although dynamic failure has not directly been addressed, one of the micliamsms lor brittle, and thus stress relieving, failure under compressive strass conditi ons has been investigated in detail, namely shear fracturing. Shear fractures are effect vely the only discontinuities which allow for stress relief under such conditi ons', in the ibaence of preexisting, geological discontinuities, and are therefore quite rele vant to dynamic rock failure, such as rock bursts, in deep level mining conditions. Potential mechanisms for shear fracture formation and the numerical simulation of these features have been investigated and this may especially assist further research into rock bursts.

A Thesis presented to the Department of Geophysics of the University of the Witwatersrand, Johannesburg / Violent failure of the rock surrounding under ground excavations forms a major hazard and obstacle in deep-level mining. (Abbreviation abstract) / AC 2018

published_or_final_version / Applied Geosciences / Master / Master of Science

When excavating a rock wall by blasting, pre-existing structures in the rock has a strong impact on the stability of the wall. For excavation in Bandhagen in Stockholm, the nature and orientation of the pre-existing geological features, namely fractures, were not taken into consideration before excavation begun. Geological field studies were carried out in order to investigate the possibility of a more favorable outcome than in the Bandhagen case. Mapping conducted in March 2015 was focused on fracture distribution and the results showed two sets of open shear fractures with fresh surfaces. The first set of the fractures cross-cuts the wall with a strike of NNW-SSE and dips between 70°±30°. The second set of fractures strikes WSW-ENE and are almost parallel to the wall (which strikes roughly 65° E) with a dip towards it, ranging between 55°±35°. The two set of fractures intersect with an acute angle of around 80° and due to their orientation, and that one of the sets dip towards the free face of the wall, they create an unfavorable fracture pattern that makes the wall, at parts, very instable in regard to rockfall and rockslide.  Fractures within the respective sets dip towards opposite cardinal points and making an acute angle of 50° for set 2 and 70° for set 1 fractures within the own set are interpreted to conjugate. In addition, there is a well-developed folded foliation that change in strike from parallel to perpendicular to the excavated wall. The foliation is aligned to the strike of both of the fracture sets. This has enabled fractures to open parallel to the mica-rich layers in the gneiss which further adds to the unfavorable pattern of fractures that creates rhombohedral unstable blocks in the rock mass. Due to the fracture pattern, sliding and rockfall have been frequent and safety measures such as rock bolts and a wire mesh have been installed to increase the security factor for the wall. During mapping, a general fracture pattern was possible to deduce from mapping of solely an unexcavated, vegetated part of the area. It became clearer though together with the excavated surface of the wall. Several pre-blast measures could have been preformed to limit rockfall and sliding of rock after excavation. Line-drilling could have been used when blasting near the contour of the wall to decrease the blast-induced fractures by the more effective venting of the excess explosion gas. This could have decreased the closely spaced blast-induced fractures that have been mapped on both the crest and the body of the wall. Another measure would have been to install pre-blast reinforcements on the crest of the wall, which could have prevented at least two large rockfalls that have occurred.  If the fracture pattern were known before excavation begun and the aforementioned measures would have been considered, the stability of the wall and the first excavation would undoubtedly have been more successful. A proposal for future open face excavations is to thoroughly assess the geological features to, in a preliminary stage of the planning, eliminate the risk for this outcome to occur in the future. / Vid uttag av berg genom sprängning för att skapa en bergvägg har strukturerna i berget en stor betydelse för stabiliteten av väggen. Exempel på strukturer i berggrunden som kan orsaka problem vid uttag av berg är sprickor och då speciellt sprickor som stupar mot väggens teoretiska kontur. Dessa sprickor kan orsaka att hela skivor av berg kan glida från väggen. Om dessa sprickor också korsas av andra sprickor kan de tillsammans bilda kilar som stupar ut mot den fria ytan där utschaktning av berg skett. Kilar som dessa som förekommer på krönet av bergväggen faller ofta ut från väggen och kan vara både farliga för de som utför arbetet samtidigt som de kan göra block runtomkring dem mer instabila.  För en utschaktning av berg i Bandhagen, Stockholm togs inte sprickmönstret in i planeringen inför hur sprängning skulle utföras. Detta ledde till att sprängningen som utfördes orsakade mycket glidningar av block och utfall från krönet. Det har lett till att projektet blivit försenat och budgeten överskridits för att korrigera de misstag som gjorts. Korrigeringarna har varit nödvändiga för att väggen i slutändan ska nå en säkerhetsfaktor som inte kan orsaka några person- eller materialskador i framtiden.  Kartering med fokus på sprickfördelning utfördes i Mars 2015 för att undersöka om sprängningen hade kunnat utföras på ett annorlunda och bättre sätt om sprickmönstret varit känt innan sprängning inleddes. Karteringen visade två korsande spricksystem där ett av spricksystemen stryker parallellt med väggen och även stupar mot den. De två systemen av sprickor bildar block med plan som lutar ut från väggen vilket resulterar i att många utfall av block skett. Med vetskapen om dessa spricksystem, samt övriga sprickor som förekommer i området, hade de utfall av berg som skett kunnat förutsägas och därigenom hade förslag av sprängmetodik kunnat ges för att minska utfall och för att generellt fått en säkrare vägg redan ifrån början. Både sprängning med tätsöm nära den teoretiska konturen av väggen och förförstärkning av krönet av den teoretiska väggen innan första sprängningen hade kunnat leda till en mycket stabilare vägg. Det hade kunnat leda till att projektet inte blivit försenat och att budgeten för projektet tagit hänsyn till de problem som skulle kunna uppstå.  Ett förslag för uttag av berg för bergsslänter är att de geologiska förhållandena ska undersökas mer noggrant, för att i ett tidigt skede upptäcka liknande strukturer i berget och utifrån dessa eliminera risken för att liknande problem uppstår i framtiden.

No description available.

This master thesis has been conducted at Svea Teknik on behalf of Atlas Copco and deals with the design of a cutter head motion system for mechanical rock excavation machines. Mechanical rock excavation allows tunneling to be done with just one machine in a continuous process. Such a machine is called a tunnel boring machine (TBM) and excavates rock by pressing a rotating cutter head with disc cutters against the rock face. By moving the cutter head in different patterns, tunnels of different profiles and sizes can be excavated. Atlas Copco has currently a conceptual TBM with an associated cutter head motion solution attached. The main task of this master thesis is to examine if an alternative solution to this motion system could be incorporated to the conceptual TBM, and to develop this solution to a functional concept design. In order to find a suitable alternative design nine concepts where generated and evaluated against the current concept solution using a weighted PUGH-matrix. The chosen concept was refined into a final functional concept design. The produced concept design consists of a two part linkage arm construction connected via a cylindrical joint. At one end of the articulated arm the cutter head is located and at the other end the linkage arm is connected to a rotatable base which allows the arm to rotate and swing to the sides. This rotatable base is in later turn supported by a base structure mounted to the main body of the current concept machine. All motion is achieved by hydraulic cylinders which are mounted in their respective ends using spherical bearings to minimize the need of narrow tolerance spans. The benefits of this alternative design are a greater choice of tunnel profiles along with simpler bearing solutions which may reduce manufacturing- and service costs. The downside is instead added weight to the front of the machine which will move the center of mass closer to the cutter head. This may have a negative effect on the machine propulsion system. / Detta examensarbete har utförts på Svea Teknik på uppdrag av Atlas Copco och behandlar utvecklingen av ett rörelsesystem för förflyttningen av borrhuvudet på maskiner för mekanisk bergavverkning. Med mekanisk bergavverkning är det möjligt att gräva ut en tunnel med bara en maskin i en kontinuerlig process. En sådan maskin kallas tunnelborrningsmaskin (TBM) och bryter berget genom att ett borrhuvud med brytskivor rullar under tryck mot bergsväggen. Genom att förflytta borrhuvudet i olika mönster kan tunnlar med olika profil och storlek anläggas. Atlas Copco har för närvarande en konceptuell TBM med tillhörande lösning för borrhuvudförflyttningen. Huvuduppgiften för detta examensarbete är att undersöka om en alternativ lösning till detta förflyttingssystem kan integreras med denna TBM och att utveckla den här lösning till en funktionell konceptdesign. För att hitta en lämplig alternativ utformning har nio koncept tagits fram vilka utvärderas mot den befintliga konceptlösningen i en viktad PUGH-matris. Det valda konceptet har förfinats till en slutgiltig funktionell konceptdesign. Det framtagna konceptet består av en tvådelad länkarmskonstruktion sammansatta via en cylindrisk rotationsled. I ena änden av länkarmen är borrhuvudet monterat och vid den andra änden är länkarmen ansluten till en roterbar bas som möjliggör att länkarmarna kan rotera och svänga åt sidorna. Denna roterande bas är i sin tur upphängd i en basstruktur som är fastmonterad på den nuvarande konceptmaskinen. All rörelse uppnås genom hydraulcylindrar som är monterade i respektive ände med hjälp av sfäriska lager för att minimera toleranskraven. Fördelarna med detta alternativa koncept är en större frihet i valet av tunnelprofiler tillsammans med en enklare lagerlösning som kan minska tillverknings- och servicekostnader. Nackdelen är istället att vikten längre fram på maskinen ökar. Detta leder till att masscentrum flyttats närmare borrhuvudet vilket kan ha negativ inverkning på maskinens framdrivningssystem.

Denna rapport är resultatet av ett examensarbete på KTHs master-program för maskinkonstruktion i samarbete med Atlas Copco och Svea Teknik. Atlas Copco utvecklar en tunnelborrningsmaskin som trycker sig framåt och glider på skidor under borrning. Detta har visats sig ge stora friktionsförluster mellan det ojämna gruvgolvet och skidan vilket gör att de behöver en alternativ lösning på detta problem som klarar lasterna från borrning och maskinens egenvikt samt reducerar friktionen i maskinens längdriktning. Konceptutvecklingen var indelad i fyra stora delsteg: konceptgenerering, val av koncept, vidareutveckling och analys och utvärdering. Projektet avser endast konceptutveckling, ingen fullständig konstruktion. Några komponenter kunde bli omkonstruerade av Atlas Copco vid behov, de främre stingrarna som håller den stabil mot taket fick inte ändras, inga ritningar ritades, ingen detaljerad FEM-modellering och inte alla externa komponenter blev valda. Två koncept togs till vidareutveckling genom Pughs beslutsmatris: The Slide Guide och The Rocker Bogie. CAD modeller ritades och blev analyserade med avseende på strukturella laster och friktionskoefficienter jämfört med den befintliga lösningen. The Slide Guide klarar alla krav som kunde jämföras och The Rocker Bogie klarade inte utrymmeskraven och skulle kräva omfattande omkonstruktion av main body för att fungera. Koncepten blev utvärderade med hjälp av olika beräkningar och FEM analys / This report is the result of a master thesis at KTH Machine Design in cooperation with Atlas Copco and Svea Teknik. Atlas Copco is developing a Tunnel Boring Machine that pushes itself forward on steel skids using a torque tube when boring. This has proven to suffer from large frictional forces between the rough mine floor and the skid and they need an alternative solution to hold the loads of the machine while boring and reducing the friction when propelling itself forward. The concept development was divided into four main stages, concept generation, concept selection, further development, analysis and evaluation. The project includes only concept development, no complete designs. Some parts could be redesigned by Atlas Copco if needed, the front stingers supporting against the roof was not to be redesigned, no drawings was made, no detailed FEA modeling was done and not all external components was chosen. Two concepts where chosen for further development using the PUGH’s decision matrix, The Slide Guide and The Rocker Bogie. CAD models was developed and analyzed regarding loads and friction compared to the existing solution. The Slide Guide clears all requirements that could be measured and the Rocker Bogie does not fit within the geometrical limits available without extensive redesign of the Main Body. This was verified using calculations and structural FEA.

Examensarbetet är utfört tillammans med Epiroc genom Svea Teknik AB och som skett inom mastersprogrammet Maskinkonstruktion på KTH.  Stigortsborrmaskiner används inom gruvindustrin till att exempelvis borra hisschakt, malmpassager eller dränering mellan två redan existerande orter. Epiroc har tagit fram en stigortsborrmaskin, Robbins 73RH, som kan borra ner till 700 m med metoden uppåtgående stigfullsborrning genom en hydraulisk drivenhet som placeras bredvid stigortsborrmaskinen.  Robbins 73RH transporteras liggandes på en tillhörande crawler, med modellnamn T190D, för att reducera den krävda takhöjden vid transport. Väl på plats för att borra lastas Robbins 73RH av crawlern till sitt vertikala upprätta läge genom att stigortsborrmaskinen vrids 90° med en vridningsmekanism monterad mellan stigortsborrmaskinen och crawlern. Dagens lösning involverar tidskrävande manuellt arbete för operatörerna vilket resulterar i tunga lyft och risk för klämskador när vridningsmekansimen ska kopplas från eller till stigortsborrmaskinen. Syftet med detta examensarbete är att utveckla ett nytt koncept som reducerar tiden för på- och avlastning samt är säkrare för operatörerna. Detta utfördes genom att ta fram en kraftmodell, generera koncept som evaluerades med en Pugh’s matris och vidareutveckla ett valt koncept utifrån de givna kraven. Det nya konceptet kopplas från och till stigortsborrmaskinen med hjälp av en hydrauliskt styrd axel vilket resulterar i förbättrad säkerhet och reducerad tid för på- och avlastning. Antalet tunga lyft för operatörerna har även reduceras vilket resulterar i en förbättradarbetsmiljö där även risken för klämskador har begränsats. / This Master Thesis has been carried out together with Epiroc through Svea Teknik AB and has been done within the Master’s program Machine Design at KTH. Raisebroing machines are used in the mining industry for example drilling elevator shafts, ore passages or drainage between two already existing mine shafts. Epiroc has developed a raiseboring machine called Robbins 73RH that can drill down to 700 m using the upward reaming method with hydraulics which is provided by a drive unit. Robbins 73RH is transported lying down at a associated crawler, called T190D, in order to reduce the required roof height. Once in place to drill, Robbins 73RH is unloaded from the crawler to its upright vertical position by rotating it 90° with a tilt mechanism fitted between the raiseboring machine and crawler. Today’s solution involves time consuming manual labor for the operators which results in heavy lifts and risk for crushing when the tilt mechanism needs to be taken on or off the raiseboring machine. The purpose of this Master Thesis is to design a new concept that reduces the time for connecting on and off the raiseboring machine and that also is safer to operate. This is performed by designing a force analysis, generate concepts that are evaluated with Pugh’s matrix and last develop a concept that the supervisors at Epiroc has chosen. The new concept connects to the raiseboring machine using a hydraulic driven shaft which results in improved safety and reduced time when loaded on or off the crawler. The Amount of heavy lifts has been reduced which results in an improved working environment where the risk of crushing no longer arises to the same extent as for the original solution.