Improvement in Portsmouth addresses the challenge of building on the city’s variable Quaternary deposits, including soft alluvium, harbour silts, and loose reclaimed ground over the Bracklesham Beds. These soils often lack the bearing capacity and settlement control required by Eurocode 7 and the NHBC Standards. Our approach focuses on targeted techniques to densify or reinforce the ground, with stone column design being a primary solution for supporting embankments and lightly loaded structures, and vibrocompaction design ideal for mitigating liquefaction in the granular fills prevalent across Portsea Island.
This category is critical for coastal defence works, port expansions, and residential developments on brownfield sites where deep excavations are constrained. For commercial buildings and infrastructure near the M275 corridor, combining vibro-replacement with a rigorous verification programme ensures compliant, long-term performance. A well-specified stone column installation can transform otherwise unsuitable land into stable plots, effectively managing differential settlement in Portsmouth’s complex ground profile.
In Portsmouth and across the South Coast, Improvement is often the decisive factor between a viable construction programme and costly overruns. The local geology is dominated by the Lambeth Group, London Clay, and substantial superficial deposits of river terrace gravels, but the real challenge lies in the Wittering Formation and thick sequences of soft alluvium in reclaimed coastal zones such as Portsea Island. A robust Improvement strategy must address low bearing capacity, potential for differential settlement, and tidal groundwater fluctuations, all while complying with BS 5930 and the execution requirements of BS EN 1997-2. Our approach begins with a rigorous investigation to characterise the stratigraphy precisely before any treatment is specified.
We select and validate Improvement methods using quantitative in-situ data that meets UK specification standards. Dynamic cone penetration testing and static CPT (Cone Penetration Test) profiling provide continuous resistance measurements, allowing us to identify loose or under-consolidated layers that require densification or reinforcement. For granular fills and sands beneath proposed shallow foundations, we verify compaction efficacy through nuclear gauge assessments and the field density test (sand cone method), ensuring compliance with Method Specification 600 in the Manual of Contract Documents for Highway Works. Where cohesive soils dominate, undisturbed sampling and advanced In-Situ—including self-boring pressuremeter tests—define stiffness parameters for settlement analysis under working loads.
Typical Portsmouth projects demand tailored solutions that reflect the city’s unique ground conditions and urban constraints. Deep vibro-compaction or vibro-replacement stone columns are frequently specified to support residential blocks on the soft clays and silts of the Portsmouth Harbour fringe, while rigid inclusions transfer loads through compressible alluvium to the underlying gravels and Lambeth Group strata. For historic structures in Old Portsmouth, low-vibration permeation grouting mitigates the risk of settlement beneath sensitive masonry. Every treatment design is calibrated using index testing carried out in our laboratory, where grain size analysis (sieve + hydrometer) and Atterberg limits determine fines content and plasticity, parameters that directly govern the suitability of densification versus drainage-based techniques.
The Improvement process moves from desk study and targeted field investigation to treatment design, on-site validation, and post-treatment verification testing. Deliverables include a Ground Investigation Report with interpreted geotechnical parameters, a detailed method statement for the chosen technique, and a Verification Report containing comparative pre- and post-treatment CPT and density test data. For contractors and consultants working on foundations in Portsmouth’s challenging ground, this integrated service transforms subsurface risk into a quantifiable, managed condition, enabling optimised footing dimensions and programme certainty.