GSIM consists of detailed geotechnical analysis using specialist 2D and 3D software. It is used to estimate the impact that new development may have on existing structures which lie beneath, or adjacent to, the site. It will predict displacements in a soil mass due to vertical and horizontal loading and unloading, showing the likely settlement pattern beneath and beyond the loaded area. GSIM provides a level of detail considerably greater than any conventional bearing capacity or settlement calculations.
Why is GSIM important?
Some large public water supply pipes or sewers are highly sensitive to ground movement. For example, Thames Water require ground assessments in accordance with their document “Guidance on piling, heavy loads, excavations, tunnelling and dewatering”. This specifies the maximum allowable increase in strain and rotation that their assets will tolerate, and such information can only be determined by a detailed GSIM.
In some instances, it can be a time-consuming process to gain the necessary approvals. Therefore, developers should consider at an early stage in the project whether there are any subsurface assets or adjacent sensitive structures which could be impacted by the proposed development.
Example scenarios where GSIM may be useful
GSIM can provide invaluable information in the following situations:
- Foundations (pads/piles/rafts): calculate the impact on sewers, water mains, tunnels, pumping stations
- Basements: settlement and heave potential, impact on services
- Retaining walls: ground movements in front of and behind the wall to assess impact on adjacent structures
- Piled foundations: calculate both the vertical and lateral stresses to establish a ‘zone of influence’ of the new piles.
Patrick Parsons in-house capability
Utilising the finite element software programs Plaxis, Pdisp and Xdisp, our geotechnical experts have undertaken numerous complex ground models.
Where required, we have successfully gained the necessary approvals from water and rail authorities to carry out construction over and adjacent to their assets, including major sewers/mains as well as railway subways.