Cli­ent: Thu­rin­gian State Office for Buil­ding and Trans­port
Pro­ject aut­hor: K+S Inge­nieur-Con­sult (imple­men­ta­tion plan­ning)
Con­s­truc­tion: ARGE B88 Tun­nel Rothen­stein
Part­ner: STREICHER Tief- und Inge­nieur­bau Jena | AUGUST REINERS Bau­un­ter­neh­mung GmbH
Tech. Manage­ment: STREICHER Tief- und Inge­nieur­bau Jena GmbH & Co. KG
Com­mer­cial manage­ment: AUGUST REINERS Bau­un­ter­neh­mung GmbH
Object: New con­s­truc­tion of the B88 Rothen­stein bypass
Period: 2018 to 2022

The 385 m long Rothen­stein Tun­nel is part of the new con­s­truc­tion of the B88 fede­ral high­way south of Jena, which is inten­ded to improve the ina­de­quate infra­struc­ture situa­tion around Rothen­stein. The high-capa­city fede­ral high­way will con­nect the city of Jena with sou­thern Thu­rin­gia and serve as a large-scale link bet­ween the A4 and A9 motorways. 

The tun­nel route of the two-lane road tun­nel is led from the exis­ting fede­ral high­way 88 in the Saale val­ley south of Rothen­stein at an acute angle into the steep rock and runs uphill to the nor­t­hern por­tal on the nor­t­hern flank of the Rothen­stein rock. Under the pro­tec­tion of a pipe umbrella, the tun­nell­ing work beg­ins from the north, des­cen­ding through the first lay­ers of loess and slope loam and sand­stone wea­the­ring zones. The main drift sec­tion pas­ses through rock lay­ers of the Middle Bunt­sand­stein, which mostly con­sist of hori­zon­tally bedded medium-bedded sand­stone with flaky to thin-bedded clay-silts­tone lay­ers. The sand­stone lay­ers appear in the pro­ject area with fluc­tua­ting rock strength and a very high sen­si­ti­vity to water. Fault zones and the frac­tu­red rock require adjus­t­ments to the cut-off lengths and the respec­tive excava­tion dimen­si­ons during the tun­nel work in order to coun­ter­act the com­plex rock struc­tures and chan­ging sub­soil con­di­ti­ons. The Rothen­stein Tun­nel is being built with a dou­ble-shell tun­nel con­s­truc­tion con­sis­ting of a tem­po­rary load-bea­ring shot­crete outer shell, which is instal­led imme­dia­tely after excava­tion, and a water-imper­meable rein­forced con­crete inner shell. 

The con­s­truc­tion sequence envi­sa­ges inter­rupt­ing the north drive 75 m before the breakth­rough and the future south por­tal and then dri­ving the last few meters by means of coun­ter-dri­ving. This mea­sure is struc­tu­rally neces­sary as the new tun­nel route at the south por­tal emer­ges at an acute angle from the steep rock face in the Saale val­ley onto the old B88 fede­ral high­way. Due to this slo­ping, acute-angled course of the tun­nel to the rock face, it is neces­sary to under­cut the rock over a length of 50 m and to secure it with the help of rock sta­bi­liza­tion mea­su­res in the form of pre-stres­sed grou­ted anchors before the rock excava­tion work. This cut­ting and under­cut­ting of the almost ver­ti­cal rock for­ma­tion requi­res a high degree of rock sta­bi­liza­tion and excava­tion work that is extre­mely gentle on the rock. The work is moni­to­red by a per­ma­nent and auto­ma­tic mea­su­ring sys­tem with regard to defor­ma­tion. The future tun­nel por­tal in semi-open con­s­truc­tion will be deeply foun­ded on bored piles on the val­ley side. All work in the area of the south por­tal will take place on the old route of the B88 fede­ral road, which is cha­rac­te­ri­zed by the direct pro­xi­mity of the Groß­he­rin­gen-Saal­feld rail­road line (less than 10 m as the crow flies) and the resul­ting cram­ped con­s­truc­tion situa­tion. While the north por­tal can be built using the clas­sic open con­s­truc­tion method in the road­way pre-cut, the con­s­truc­tion of the south por­tal requi­res com­pli­ca­ted con­s­truc­tion pro­ces­ses and advance plan­ning in addi­tion to a com­plex coun­ter-form­work construction. 

TECHNICAL DATA
Struc­tu­ral func­tion: Two-lane road tun­nel
Tun­nel length: 385 m
Excava­tion volume: 40,500 m³
Con­s­truc­tion method: Shot­crete con­s­truc­tion method (excavator/blasting)
Tun­nel sup­port: shot­crete, sup­port arches, anchors, spi­les, pipe umbrella