{"id":9215,"date":"2017-08-01T12:34:53","date_gmt":"2017-08-01T19:34:53","guid":{"rendered":"http:\/\/robbinstbm.com\/?p=9215\/"},"modified":"2017-08-16T15:44:45","modified_gmt":"2017-08-16T22:44:45","slug":"mixshield-crossover-hybrid","status":"publish","type":"post","link":"https:\/\/www.robbinstbm.com\/es\/mixshield-crossover-hybrid\/","title":{"rendered":"What\u2019s in a Name? Mixshield, Crossover, Hybrid and More"},"content":{"rendered":"

For underground construction professionals and manufacturers, there is some confusion about the current TBM designations and what they really mean, and for what applications they are to be considered. This is especially noted when it comes to soft and mixed ground type shield machines and if they are to operate in \u201copen\u201d mode, \u201cclosed\u201d mode or \u201csemi-open\/closed\u201d mode conditions.<\/p>\n

The term \u201copen mode\u201d defines defines a mode of TBM operation where no pressure is required to stabilize the boring face; the geology is self-standing and ground settlement will not occur.<\/p>\n

The term \u201cclosed mode\u201d defines tha mode of TBM operation where face pressure needs to be constantly applied in order to maintain face support. Should the face pressure not be maintained as determined by the geology, under-pressurization will cause ground settlement, over-pressurization can cause surface heaving.<\/p>\n

The term \u201csemi-open\/closed mode\u201d defines a mode of TBM operation in varying geology where the TBM has the ability to control the face.<\/p><\/blockquote>\n

The various machine types in question are Mixshield, Hybrid and the Robbins \u201cCrossover\u201d<\/a>. Are they the same? If not, what is the difference? This blog seeks to clarify and explore those definitions.<\/p>\n

Mixshield <\/strong><\/p>\n

Mixshield is a terminology introduced by German manufacturer Herrenknecht for what is essentially a Slurry TBM that uses an air bubble to control and support pressure at the face. The air bubble acts like an accumulator with the belief that this offers better pressure control. This type of machine operates only in \u201cclosed mode\u201d. \u00a0Mixshields are not meant to go from high pressure soft ground to significant rocky conditions with great efficiency, hence the name \u201cMixshield\u201d is somewhat of a misnomer. They can excavate mixed face conditions, but the machine configuration is not changed so it is a different thing entirely than to excavate significant sections of differing geology. In order to change the configuration to allow more efficient operation in different sections of geology, a Hybrid machine is needed.<\/p>\n

Hybrid, etc. <\/strong><\/p>\n

\u201cHybrid\u201d, \u201cDual Mode\u201d, and \u201cMulti-Mode\u201d are names developed by the industry to try and define machines that feature components of two different machine types. The most common types is a multi-mode between EPB with a screw conveyor (for operation in \u201cclosed mode\u201d or \u201csemi-closed mode\u201d) and conversion to Rock Mode with the installation of a belt conveyor (for use in \u201copen mode\u201d operation). Typically, the only changes made to the machine are components such as cutting tools and muck removal method that can be switched out in the tunnel depending on ground conditions. The machines are used for large sections of vastly different geology in one tunnel, such as a section of clay followed by as significant section of rock. However these types of machines are typically designed as EPB machines and then converted, making them not very efficient for use in rock geology.<\/p>\n

Robbins Crossover<\/strong><\/p>\n

The \u201cCrossover Series\u201d of TBMs<\/a> was developed by Robbins in March 2015 using innovative design concepts to effectively excavate between different geologies. The Crossover Series is Robbins\u2019 version of a Hybrid TBM but with many additional features to allow the TBM to effectively cross between different geology types. Operation of the machine can allow the machine to quickly change from \u201copen mode\u201d to \u201csemi open\/closed mode\u201d and \u201cclosed mode.\u201d The main types of Crossover TBM include the XRE (Crossover between Hard Rock and EPB), XSE (Crossover between Slurry and EPB) and XRS (Crossover between Hard Rock and Slurry).\u00a0 The features include interchangeable cutting tools; single direction and bi-directional cutterhead muck pick-up; multi-speed, multi-torque cutterhead drive systems; durable, abrasion resistant components on the cutterhead and screw conveyor; emergency thrust; tapered shields to reduce shield entrapment in squeezing ground; integrated probe\/grout drill system for ground consolidation; and heavy steel construction with components designed for +12,000 hours of life, just to name a few.<\/p>\n

<\/strong><\/p>\n

The Crossover Series is suitable for tunnel projects that require the ability to excavate different types of geology efficiently with one machine, based on ground conditions.\u00a0 The TBM design is flexible enough to switch from one mode to another. Ultimately, Crossover Series machines are cost efficient in the long run, since the TBMs require less repair costs than a non-customized machine, and they can be used on multiple projects.<\/p>\n

Based on the ground situation (whether it\u2019s self-supporting ground, self-supporting ground with water pressure, or unstable ground), the Crossover is optimized towards \u201copen\u201d mode (as in hard rock shielded TBMs) or \u201cclosed\u201d mode (as in compressed air, slurry, and EPB TBMs).<\/p>\n

Reliable geological information is therefore critical to the TBM design.\u00a0 An accurate geological report is needed to decide when and where to convert the machine as well. During excavation, adequate probe drilling is further essential to determine the ground conditions ahead of the Crossover TBM.<\/p>\n

Below are the features specific to each type of Crossover machine.<\/p>\n

Crossover XRE <\/strong><\/p>\n