Excavation Dewatering and Wall Protection - Practical Solutions for Mazovian Conditions

Excavation Dewatering and Wall Protection - Practical Solutions for Mazovian Conditions

Introduction

The Warsaw region is characterized by specific hydrogeological conditions that significantly affect earthworks execution. High groundwater levels, presence of impermeable layers, and varied geological structure require appropriate dewatering systems and excavation protection measures.

Ground-Water Conditions of Mazovia

Regional geological structure:

• Quaternary formations 30-80 m thick
• Sandy layers interbedded with clays and silts
• Groundwater level at 1-3 m below ground surface
• Occurrence of perched water during rainfall seasons

Challenges specific to Warsaw area:

• Seasonal groundwater level fluctuations (up to 2 m)
• Presence of active wells in vicinity
• Dense underground infrastructure network
• Environmental protection requirements in city center

Excavation Dewatering Systems

1. Gravity dewatering

Linear drainage:

• Application in excavations up to 2-3 m depth
• Drainage pipes Ø100-200 mm with filter surround
• Minimum slope 0.5% toward collection well
• Materials: perforated PVC pipes, geotextile, gravel

Drainage wells:

• Depth up to 8 m depending on conditions
• Diameter 800-1200 mm, concrete ring lining
• Dewatering pumps 5-50 m³/h capacity
• Automatic water level monitoring

2. Vacuum dewatering (wellpoint)

Technical parameters:

• Wellpoints spaced 1-2 m apart
• Depth up to 6 m below excavation level
• Vacuum pumps 100-500 m³/h capacity
• Water table drawdown 4-6 m

Advantages for Mazovian conditions:

• Effectiveness in fine sandy soils
• Operation capability in dense urban areas
• Controlled dewatering without impact on adjacent structures

Excavation Wall Protection

1. Strutted shoring systems

Steel shoring:

• Steel profiles IPE/HEB spaced 1.5-2.5 m
• Hydraulic or steel struts
• Maximum excavation depth: 4-5 m
• Costs: 150-250 PLN/m² wall surface

Aluminum shoring:

• Modular systems like PERI, DOKA
• Quick assembly and disassembly
• Multiple reuse capability
• Optimal for 2-4 m excavations

2. Secant walls

CFA (Continuous Flight Auger) wall:

• Pile diameter 600-1200 mm
• Depth up to 25 m
• Concrete C20/25 with bentonite additive
• Permeability: k ≤ 10⁻⁸ m/s

Vibratory wall:

• Larsen profiles L4-L32
• Depth up to 15 m in Mazovian soils
• Protection against water and soil pressure
• Material recovery possibility

Dewatering System Design

Preliminary investigations:

Required studies:

• Geotechnical with filtration parameters
• Hydrogeological with control piezometers
• Existing infrastructure inventory
• Environmental impact analysis

Hydraulic calculations:

• Dewatering system capacity: Q = k × i × A
• Soil permeability coefficient (k)
• Hydraulic gradient (i)
• Cross-sectional area (A)

Design documentation:

Required elements:

• Site plan with equipment layout
• Geological sections with dewatering system
• Technical details of nodes and connections
• Material and equipment specifications

Construction and Monitoring

Implementation stages:

1. Site preparation:

• Dewatering system location marking
• Existing infrastructure protection
• Equipment access road preparation

2. Dewatering system installation:

• Wellpoint/drainage well execution
• Pump and pipeline installation
• Tightness and capacity tests

3. Excavation execution:

• Systematic deepening with dewatering control
• Progressive wall protection installation
• Deformation and settlement monitoring

Monitoring system:

Parameter control:

• Groundwater levels (piezometers)
• Excavation wall deformations (inclinometers)
• Ground settlements (precise leveling)
• Discharged water quality

Measurement frequency:

• Daily basic parameter monitoring
• Geodetic measurements every 3-7 days
• Weekly reports for construction supervision

Legal and Environmental Aspects

Required permits:

Water permit:

• Groundwater abstraction above 5 m³/h
• Water discharge to environment
• Temporary water table lowering

Network operator agreements:

• Water supply and sewerage (MPWiK)
• Power networks (PGE Distribution)
• Gas networks (PGNiG)
• Telecommunications

Environmental protection:

Impact minimization:

• Rainwater infiltration on site
• Excavation water treatment before discharge
• Groundwater quality monitoring
• Site reclamation after work completion

Costs and Schedule

Estimated costs (2025):

Gravity dewatering:

• Drains: 80-120 PLN/lm
• Drainage wells: 2000-4000 PLN/unit
• Pumps: 500-1500 PLN/month rental

Vacuum dewatering:

• Wellpoints: 150-250 PLN/lm
• Vacuum pumps: 2000-5000 PLN/month
• Technical service: 200-300 PLN/day

Wall protection:

• Steel shoring: 150-300 PLN/m²
• Secant wall: 400-800 PLN/m²
• Monitoring: 5000-15000 PLN/month

Schedule influencing factors:

• Weather conditions (vegetation period)
• Administrative procedures (2-6 months)
• Specialized equipment availability
• Coordination with other construction participants

Common Mistakes and Prevention

Design errors:

• Insufficient ground condition investigation
• Underestimated dewatering system capacity
• No consideration of impact on adjacent structures

Construction errors:

• Improper work sequence
• Dewatering system interruptions
• Inadequate excavation wall protection

Best practices:

• Continuous geotechnical supervision on site
• Critical system redundancy
• Regular equipment inspection and maintenance
• Operator training for system operation

Summary

Effective excavation dewatering and wall protection in Mazovian conditions requires a comprehensive approach considering local geological and hydrogeological conditions. Proper ground-water condition investigation, appropriate technology selection, and professional execution with continuous monitoring are crucial. Investment in high-quality dewatering and protection systems translates to work safety, timely project completion, and minimized risk of failures and damages in the vicinity.