Ground Freezing a. Detailed design of the freeze plant system, freeze pipe geometry, distribution manifold, refrigeration plant size and specifications. Include the following:
1) Type of coolant.
2) Size, type, and power capacity of the compressor.
3) Size, type and temperature drop of the chiller/evaporator.
4) Type and expected temperature range of the coolant.
5) Volume capacity of coolant circulation pump.
6) Projected maximum and average operating ranges.
b. Manufacturer’s literature for all equipment including shop drawings. Equipment shall include piping as well as refrigeration units, drilling assemblies and other ancillary equipment.
c. Plans for monitoring instrumentation placement to assess growth of freeze, temperatures, and state of closure.
d. Plans for monitoring impacts on overlying or adjacent utilities, existing structures, completed work and any other property from effects such as ground heave, frost expansion pressure, and freezing temperatures.
e. Plans for insulating the frozen soil mass to maintain its integrity during excavation and structural lining installation operations.
f. Plans for dismantling and removing the ground freezing system including freeze pipe decommissioning.
g. Plans for disposal of refrigeration gas and circulating coolant in accordance with all applicable local, state and federal regulations including the United States Environmental Protection Agency (USEPA) and Washington State Department of Ecology.
h. Detailed ground freezing calculations performed by the Designer shall include the following:
1) Detailed numerical analysis indicating the capability of the refrigeration system and manifold to provide flow rates that are sufficient to maintain frozen ground which is safe to excavate to the shaft design depth.
2) Detailed numerical analysis defining design thicknesses for mass of frozen ground required for safe excavation, taking into account both thermal and structural complications, and setting forth volumetric extent of frozen ground that is expected to be required.
3) Estimates of energy required for initial freezing and freeze maintenance phases.
4) Time estimates for freezing and minimum frozen ground thickness required prior to excavating.
5) Heave estimates and control measures.
6) Calculations for frozen soil mass temperature-strength correlation at the shaft site.
7) Calculations demonstrating ground freezing meets strength design requirements for safe excavation including the expected factor of safety.
i. Plan for a ...
Ground Freezing a. Freeze pipe installation records.
b. Ground and groundwater temperature measurements from all installed thermocouples (to commence at least one week prior to start of freezing operations).
c. Refrigeration plant operation data during freezing. Include the following:
1) Number of units operating.
2) Coolant temperatures at supply and return lines.
3) Energy consumption.
d. Measurements of return coolant temperature from each pipe or grouped series of pipes.
e. Coolant manifold pressure and flow monitoring data.
f. Brine tank level monitoring data.
g. Consumption rate of liquid nitrogen, where used.
h. Groundwater monitoring data.
i. Ammonia concentration monitoring data.
j. Distribution system pressure testing results.
Ground Freezing. 1. The Contractor is solely responsible for evaluating subsurface conditions that may affect design, construction, and operation of a frozen ground support system, by performing additional drilling, sampling, laboratory testing, and groundwater monitoring. Subsurface conditions that cannot be reliably established from the subsurface investigation performed for this project include, but are not limited to:
a. Thickness and lateral extent of gravel layers that may provide a conduit for high velocity groundwater flow.
b. Groundwater flow gradients and flow velocities.
c. Size and frequency of boulders capable of deflecting or impeding installation of freeze pipes.
d. Thermal properties of soil.
e. Chemical properties of groundwater in soil.
f. Water content of partially saturated soils
2. Design shall incorporate the following criteria:
a. Temperature measurement thermocouple devices located throughout the frozen ground mass at a minimum of one device every 350 cubic feet of frozen soil and at all critical locations where relative spacing of the freeze pipes is greatest.
b. The freezing system shall be designed to establish a structurally stable excavation, and groundwater cut-off until the permanent structural liner is completed.
3. Structural Liner design shall incorporate the following:
a. The design shall specify the factor of safety provided by the structural liner in both fully frozen and fully thawed ground. The structural liner shall be capable of withstanding all earth and groundwater pressures applied in addition to construction loads in both fully frozen and thawed ground conditions.
