Tunnel construction technology and construction methods - technical analysis based on surrounding rock characteristics and engineering practice.

   I. Tunnel construction core technology system

   Tunnel construction technology follows the principle of "pipe ahead, strict grouting, short footage, strong support, fast closure, and frequent measurement", and mainly includes the following key links:

   1. Excavation technology

   ① Smooth surface blasting technology: For II-IV level surrounding rock, full section or step method construction is adopted, and contour control is achieved through precise drilling (error ≤3cm), non-electric detonation system of detonating cord and layered charging to reduce over-excavation.

   ② Mechanical excavation: V level surrounding rock and fault zone are excavated by manual cooperation with excavators, and weak vibration blasting is used locally. The single cycle footage is 0.5-0.7m, and the daily progress is about 1.4m.

   ③ Advance support: φ108 pipe shed or φ42 small pipe grouting pre-reinforcement is used for soft strata, and the support system is formed with I-beam arch frame. The grouting pressure is 0.5-1.5MPa, and the consolidation radius is 1.2-1.5m.

  2. Initial support system

   ① Anchor spraying combined support: Φ25 hollow grouting anchor rod (spacing 1.0×1.0m) is used for grade IV surrounding rock, and Φ22 drug roll anchor rod is used for grade III surrounding rock. The thickness of sprayed C25 concrete is 4-28cm, which is divided into two stages: initial spraying (4cm) and re-spraying.

   ② Steel frame support technology: No. 14 I-beam arch frame is cold-bent, and flange bolts are used to connect the units. The installation accuracy requires lateral deviation ≤5cm and verticality ≤2°.

   3. Waterproof and drainage system

   ① Composite waterproof layer: EVA waterproof board (thickness 1.2mm) combined with 300g/m² non-woven fabric, hot-melt double welds (lap ≥10cm) tested for air tightness of 0.2MPa, and the joints are staggered by more than 1m from the construction joint.

   ② Drainage blind pipe system: Circumferential Ω spring pipe (spacing 8-10m) and longitudinal HDPE corrugated pipe (φ110mm) form a grid-like drainage channel, and the ditch slope is ≥2‰.

  4. Secondary lining construction

   ① Cast concrete process: Use a 12m hydraulic trolley to pump C35 waterproof concrete (impermeability grade P8), pouring speed ≤0.5m/h, and demolding strength of 8MPa.

   ② Intelligent monitoring and control: through the convergence meter (accuracy 0.01mm) and the total station monitoring, the lining is applied when the arch sinking rate is less than 0.15mm/d and the horizontal convergence is less than 0.2mm/d.

  2. Adaptability analysis of typical construction methods

   1. Full section method

   ① Applicable conditions: homogeneous hard rock of grade II-III, excavation section ≤100m²

   ② Technical features: single cycle footage of 3.5m, monthly progress of 150m, equipped with a three-arm drilling trolley and a 20t dump truck.

  2. Step method

   Gradual implementation:

   ① Three-step seven-step method: Grade V surrounding rock is divided into 7 excavation faces, the pilot pit staggered distance is 25m, and the core soil retention rate is greater than 40%.

   ② Micro-step method: The step length of the grade IV surrounding rock is 3-5m, and the long-arm excavator is used to turn the slag, and the loading efficiency is increased by 30%.

  3. CD method (middle partition method)

   ① Core parameters: guide tunnel width 4-5m, temporary support spacing 0.6-1.0m, grouting small pipe L=4.5m@0.3m.

   ② Process control: asynchronous excavation of left and right guide pits, support closure time <12h, surface settlement controlled within 25mm.

  4. Shield method (mechanized excavation)

   ① Segment assembly: 6+1 block mode, staggered assembly accuracy ±3mm, synchronous grouting pressure 0.3-0.5MPa.

   ② Formation adaptability: bentonite needs to be added to the water-bearing sand layer to improve the slag, and the cutter head torque is controlled at 70%-85% of the rated value.

  III. Key measures for quality control

   1. Advanced geological prediction: Using TSP203 detection system (prediction distance 150m) and geological radar (scanning depth 30m), the prediction accuracy of karst areas is >85%.

   2. Monitoring and measurement system: set up convergence measurement lines (spacing 5-10m), arch sinking points (accuracy 0.1mm), and establish a displacement-time hyperbola model to predict deformation.

   3. Fine construction of waterproof layer: base surface flatness D/L≤1/6, circular patches (diameter ≥30cm) are used at damaged parts, and joint peeling strength ≥6N/mm.

   4. Concrete durability control: limit the amount of adhesive to ≤450kg/m³, mold temperature 5-30℃, and curing humidity ＞90% for 14 days.

   IV. Technology development trend

   With the in-depth application of BIM technology, construction is developing in the direction of "digital twin":

   ① Establish a three-dimensional geological model and construction simulation platform to achieve progress deviation warning (threshold ±3%)

   ② Intelligent trolley integrated vibration monitoring and temperature control system, concrete defect rate reduced to below 0.5%

   ③ Unmanned tunneling equipment is gradually promoted, and the number of face operators is reduced by 60%.

   Tunnel construction is a high degree of integration of geomechanics and structural engineering, and it is necessary to flexibly select processes and methods according to the dynamic changes of the surrounding rock. The comprehensive application of standardized operating procedures, intelligent monitoring methods and green construction technologies can effectively improve the quality and safety level of the project. For further technical details, please refer to other literature.