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Appropriate seals, portal ground improvement and compatible shaft construction techniques are vital elements for launching and receiving tunnels effectively in urban areas where adjacent property requires protection from excess ground movements. The seals, ground improvement and shaft wall types are discussed that are required to launch or receive tunnel boring machines within wet, permeable ground at the portal zone. The use of probing is considered to verify suitability before the tunnel eye is cut. Methods described include rubber gasket seals, soft eyes, double walls, top hats for reception and portal zone ground improvement including permeation grouting, jet grouting, unreinforced slurry diaphragm wall panels, ground freezing, deep soil mixing, dewatering and over-excavation and backfilling. The launch and reception of pressurised- face TBMs with precast concrete segment linings are also described., Appropriate seals, portal ground improvement and compatible shaft construction techniques are vital elements for launching and receiving tunnels effectively in urban areas where adjacent property requires protection from excess ground movements. The seals, ground improvement and shaft wall types are discussed that are required to launch or receive tunnel boring machines within wet, permeable ground at the portal zone. The use of probing is considered to verify suitability before the tunnel eye is cut. Methods described include rubber gasket seals, soft eyes, double walls, top hats for reception and portal zone ground improvement including permeation grouting, jet grouting, unreinforced slurry diaphragm wall panels, ground freezing, deep soil mixing, dewatering and over-excavation and backfilling. The launch and reception of pressurised- face TBMs with precast concrete segment linings are also described.

Settlement-damaged sludge drain lines at the Jones Island wastewater treatment plant in Milwaukee, Wisconsin, were replaced by microtunnelling under the pile-supported clarifier basins. To minimise the risk of a microtunnel boring machine being blocked against piles or construction debris, a Soltau RVS 80 was utilised; this allowed initial boring of the alignment with guided rods of 114 mm diameter, followed by jacking of 1 m lengths of 305 mm diameter clay pipe along the rods behind an auger head. Precast concrete pipe of 2.4 m diameter was also used as a one-pass sinking caisson for workshafts and new cleanout manholes., Settlement-damaged sludge drain lines at the Jones Island wastewater treatment plant in Milwaukee, Wisconsin, were replaced by microtunnelling under the pile-supported clarifier basins. To minimise the risk of a microtunnel boring machine being blocked against piles or construction debris, a Soltau RVS 80 was utilised; this allowed initial boring of the alignment with guided rods of 114 mm diameter, followed by jacking of 1 m lengths of 305 mm diameter clay pipe along the rods behind an auger head. Precast concrete pipe of 2.4 m diameter was also used as a one-pass sinking caisson for workshafts and new cleanout manholes.

The tunnel through an urban commercial area in East Lansing, Michigan, passed the site of a former petrol station known to have contained leaking underground storage tanks. An environmental assessment of soils was carried out and measure taken to handle the expected contaminants. An explosion still occurred in the heading, however, when liquid gasoline was encountered. The immediate cause of the explosion was combustion of petrol vapours inside the wheel chamber of the TBM, initiated by a friction spark from the cutterhead striking a boulder. It was calculated that less than 1 l of petrol was enough to generate an explosive concentration of vapours inside the wheel chamber. Examinations were also made of the ventilation, atmospheric monitoring and electrical systems along with the effectiveness of the OSHA code on controlling the tunnel atmosphere. The factors which contributed to the explosion were a lack of clear understanding of subsurface conditions, failure to identify the explosion hazard and lack of a clear understanding of the hazardous properties of the contaminant., The tunnel through an urban commercial area in East Lansing, Michigan, passed the site of a former petrol station known to have contained leaking underground storage tanks. An environmental assessment of soils was carried out and measure taken to handle the expected contaminants. An explosion still occurred in the heading, however, when liquid gasoline was encountered. The immediate cause of the explosion was combustion of petrol vapours inside the wheel chamber of the TBM, initiated by a friction spark from the cutterhead striking a boulder. It was calculated that less than 1 l of petrol was enough to generate an explosive concentration of vapours inside the wheel chamber. Examinations were also made of the ventilation, atmospheric monitoring and electrical systems along with the effectiveness of the OSHA code on controlling the tunnel atmosphere. The factors which contributed to the explosion were a lack of clear understanding of subsurface conditions, failure to identify the explosion hazard and lack of a clear understanding of the hazardous properties of the contaminant.

Methods of evaluating the stability of shaft bottom plugs overlying an artesian aquifer include analysis of heave by piping through granular soils, boils or blows through discontinuities within cohesive plugs, cohesive plug heave ignoring side shear, cohesive plug heave with side shear and cohesive plug buckling or cracking. Methods of considering plug perimeter shear, plug buckling and pressure relief are discussed and minimum factors of safety suggested. Case histories are discussed of bottom plug failures at the Milwaukee NS-10 junction structure shaft, the Milwaukee Jones Island siphon shaft and a press foundation shaft on an alluvial plain along the Mississippi River., Methods of evaluating the stability of shaft bottom plugs overlying an artesian aquifer include analysis of heave by piping through granular soils, boils or blows through discontinuities within cohesive plugs, cohesive plug heave ignoring side shear, cohesive plug heave with side shear and cohesive plug buckling or cracking. Methods of considering plug perimeter shear, plug buckling and pressure relief are discussed and minimum factors of safety suggested. Case histories are discussed of bottom plug failures at the Milwaukee NS-10 junction structure shaft, the Milwaukee Jones Island siphon shaft and a press foundation shaft on an alluvial plain along the Mississippi River.

The CT-8 dropshaft in glacial soils was designed to convey combined stormwater runoff and sewage from near surface collectors into a deep tunnel conveyance and temporary storage system, and construction was carried out from 1985 to 1988. Auger drilling with a bentonite-soil slurry followed by placement and grouting of a thin metal casing was attempted for the dropshaft, but was not successful. Annulus grouting was not properly completed and a significant section of the casing was not fully grouted. The casing was also not socketed into rock to help seal the bottom. Bottom plug leaks led to remedial contact grouting of the annulus outside of the stiffened steel casing at the section where it was surrounded by fluid grout and slurry. The head of fluid grout resulted in sufficient pressure to initiate buckling of the casing and subsequently a complete rupture occurred in July 1985., The CT-8 dropshaft in glacial soils was designed to convey combined stormwater runoff and sewage from near surface collectors into a deep tunnel conveyance and temporary storage system, and construction was carried out from 1985 to 1988. Auger drilling with a bentonite-soil slurry followed by placement and grouting of a thin metal casing was attempted for the dropshaft, but was not successful. Annulus grouting was not properly completed and a significant section of the casing was not fully grouted. The casing was also not socketed into rock to help seal the bottom. Bottom plug leaks led to remedial contact grouting of the annulus outside of the stiffened steel casing at the section where it was surrounded by fluid grout and slurry. The head of fluid grout resulted in sufficient pressure to initiate buckling of the casing and subsequently a complete rupture occurred in July 1985.

Consolidation grouting from the surface prior to mining a shaft is commonly performed to reduce groundwater inflows to a manageable rate. A description is presented of the inflow reductions obtained within dolomite and limestone formations at several shafts and chambers due to grouting programmes for the Milwaukee water pollution abatement programme. The resulting inflow reduction factors are compared with values reported in the literature. Post-grouting pump tests are also evaluated as an aid to grouting assessment. Important considerations for estimating shaft inflows from pump test results are discussed. These considerations include loss of grouted mass during mining and influence of blasting and rock features on grouting effectiveness., Consolidation grouting from the surface prior to mining a shaft is commonly performed to reduce groundwater inflows to a manageable rate. A description is presented of the inflow reductions obtained within dolomite and limestone formations at several shafts and chambers due to grouting programmes for the Milwaukee water pollution abatement programme. The resulting inflow reduction factors are compared with values reported in the literature. Post-grouting pump tests are also evaluated as an aid to grouting assessment. Important considerations for estimating shaft inflows from pump test results are discussed. These considerations include loss of grouted mass during mining and influence of blasting and rock features on grouting effectiveness.

During the 1980s and 1990s, twenty deep shafts were constructed in Milwaukee, Wisconsin, USA, as part of the Milwaukee Water Pollution Abatement Program. Depths ranged from 85 to 91 m through soil and weak rock with thicknesses ranging from 37 to 69 m. Adjacent compressible soils, settlement-sensitive structures and high groundwater levels required that shafts be constructed without dewatering. Contractors attempted several methods of ground support and groundwater cutoff. Significant problems developed during construction of eleven of twenty shafts: one collapsed, groundwater blow-ins occurred at five of the shafts; and seepage caused unfrozen windows at three of the freezewalls. Ultimately, combinations of grouting and ground freezing were used to complete all the shafts into bedrock. The main problems and solutions are described., During the 1980s and 1990s, twenty deep shafts were constructed in Milwaukee, Wisconsin, USA, as part of the Milwaukee Water Pollution Abatement Program. Depths ranged from 85 to 91 m through soil and weak rock with thicknesses ranging from 37 to 69 m. Adjacent compressible soils, settlement-sensitive structures and high groundwater levels required that shafts be constructed without dewatering. Contractors attempted several methods of ground support and groundwater cutoff. Significant problems developed during construction of eleven of twenty shafts: one collapsed, groundwater blow-ins occurred at five of the shafts; and seepage caused unfrozen windows at three of the freezewalls. Ultimately, combinations of grouting and ground freezing were used to complete all the shafts into bedrock. The main problems and solutions are described.