Cli­ent: Lan­des­be­trieb Mobi­li­tät Rhein­land-Pfalz
Pro­ject aut­hor: EDR GmbH
Con­s­truc­tion: ARGE Tun­nel Diez B417
Part­ner: Bauer Spe­zi­al­tief­bau GmbH | AUGUST REINERS Bau­un­ter­neh­mung GmbH
Tech. Manage­ment: AUGUST REINERS Bau­un­ter­neh­mung GmbH
Com­mer­cial manage­ment: Bauer Spe­zi­al­tief­bau GmbH
Object: B417 Diez bypass
Period: 2018 to 2021

In order to reli­eve the fede­ral road B 417 in the imme­diate urban area around the mar­ket square of the his­to­ric old town of Diez, the fede­ral road will be laid under­ground over a length of 335 meters as part of the ’small tun­nel solu­tion Diez’ tun­nel con­s­truc­tion pro­ject. The two-lane road tun­nel will be built over 200 meters using the cut-and-cover method and 135 meters using the clas­sic mining method. In addi­tion to the inner city loca­tion, the extra­or­di­nary com­ple­xity of the pro­ject is made clear by the fact that the exis­ting rail­road line 3710 Gie­ßen — Koblenz will be pas­sed under twice in the cut-and-cover sec­tion and the par­al­lel mining excava­tion next to the exis­ting 19th cen­tury rail­road line tunnel. 

The mined sec­tion of the tun­nel in Diez is being built using the con­ven­tio­nal shot­crete con­s­truc­tion method, also known as the “New Aus­trian Tun­nel Con­s­truc­tion Method”. In addi­tion to the inner-city loca­tion of the tun­nel con­s­truc­tion pro­ject, which requi­res an extreme degree of safety and cau­tion during the blas­ting and excava­tion work, the short distance of the mined tun­nel sec­tion to the exis­ting DB tun­nel of at least 6 meters means that a high level of coor­di­na­tion and plan­ning effort is to be expec­ted during con­s­truc­tion. With regard to this neigh­bor­ing tun­nel and the urban deve­lo­p­ment, Alfred Kunz limi­ted pos­si­ble blas­ting vibra­ti­ons in the high-pres­sure-resistant kera­to­phyre rock to be loo­se­ned to a mini­mum by redu­cing the length and adjus­ting the blas­ting agent. For this pur­pose, a com­pre­hen­sive mea­su­ring sys­tem for vibra­tion, noise and defor­ma­tion mea­su­re­ments was instal­led, which ensu­red an eva­lua­tion and adjus­t­ment of the excava­tion work after each blast with regard to rock pro­tec­tion. In coor­di­na­tion with Deut­sche Bahn, blas­ting was only car­ried out during short train breaks on the adja­cent rail­road line in order to ensure the grea­test pos­si­ble safety for rail pas­sen­gers on the Gies­sen — Koblenz line. 

The tight space con­di­ti­ons on the con­s­truc­tion site are cha­rac­te­ristic of the cut-and-cover method. The loo­sening of the rock, initi­ally by means of excava­tor ope­ra­ti­ons, fol­lo­wed by occa­sio­nal loose blas­ting, requi­res good coor­di­na­tion with the excava­tion sup­port work. The excava­tion sup­port con­sis­ting of back-ancho­red bored piles and sol­dier pile walls places the hig­hest demands on exe­cu­tion and qua­lity due to the imme­diate pro­xi­mity of neigh­bor­ing buil­dings. In order to main­tain rail­road ope­ra­ti­ons during the con­s­truc­tion period, the neces­sary crossings of the rail­road line in the open con­s­truc­tion area are crossed using two pairs of auxi­liary bridges. 

Two twin gir­der auxi­liary bridges with a clear width of 24 m and 31 m respec­tively are being used. In the wes­tern excava­tion pit area, the twin gir­der auxi­liary bridge is foun­ded on three rein­forced con­crete piles with a dia­me­ter of 120 cm for each track and will remain in posi­tion until the tun­nel struc­ture is com­ple­ted. The eas­tern rail­road crossing has a total clear width of approx. 45 m and will be con­s­truc­ted in two stages due to the large clear width of the acute-angled inter­sec­ting tracks. First, the auxi­liary bridge with a span width of 31 m will be sup­ported on a load-bea­ring rock mass in the excava­tion pit in a stop gap. The rock mass lying in the tun­nel route only ser­ves as a tem­po­rary sup­port during con­s­truc­tion. In order to remove it, the tem­po­rary bridge will be detached from this after com­ple­tion of the first cei­ling sec­tions under the bridge and moved onto the com­ple­ted tun­nel block. The rock mass is then remo­ved and the remai­ning tun­nel blocks are erec­ted. Once the entire tun­nel struc­ture has been com­ple­ted, the excava­tion pit can be back­fil­led and the two twin gir­der tem­po­rary bridges can be dismantled. 

TECHNICAL DATA
Struc­tu­ral func­tion: Two-lane road tun­nel
Tun­nel length: 335 m
Excava­ted volume: 65,000 m³
Con­s­truc­tion method: Shot­crete con­s­truc­tion method (excavator/blast dri­ving)
Jack­ing pro­tec­tion: shot­crete, sup­port arches, anchors, spi­les, spike umbrella
Spe­cial fea­tures: The par­ti­cu­lar chal­lenges of the over­all pro­ject are made up of various influen­cing fac­tors. In addi­tion to the gene­rally cram­ped inner-city space con­di­ti­ons and the com­plex con­s­truc­tion pro­ces­ses, the high immis­sion requi­re­ments in terms of noise, dust and vibra­ti­ons must also be mentioned.