Birmingham sits on a varied geological patchwork: Triassic sandstones and Mercia Mudstone dominate the bedrock, but the city's glacial legacy left thick deposits of till and outwash sands across Edgbaston and the city centre. With over 1.1 million residents and ongoing HS2-related excavations, understanding the full particle-size distribution of the ground has become a routine requirement. We perform grain size analysis combining sieve separation for coarse fractions down to 63 µm with the hydrometer method for the silt and clay grades, following BS 1377-2:2022. This dual approach is essential when working in Birmingham's mixed glacial soils, where a single wash-sieve pass can miss the clay fraction that governs plasticity and settlement behaviour. A thorough soil classification exercise begins with this test, and the results feed directly into permeability estimates and compaction control.
A full gradation curve, from cobbles to clay, removes the guesswork from soil behaviour and filter design in Birmingham's glacial terrain.
Scope of work in Birmingham
Critical ground factors in Birmingham
A recent commercial development in Perry Barr required a 6 m deep excavation through a sequence of glacial till and laminated clay. The initial site investigation reported the soil as 'silty sand' based on a visual-manual description alone. We ran a full sieve and hydrometer analysis and found that the fraction passing the 63 µm sieve was 38% — well above the 25% threshold that indicates a frost-susceptible material. Had the design team relied on the preliminary classification, the road sub-base would have suffered ice lens formation within two winters, leading to pavement failure. The grain size curve also showed a gap-graded distribution, which raised the risk of internal erosion under seepage. We recommended blending with a well-graded granular borrow to close the gap and mitigate that risk.
Our services
Beyond the basic gradation curve, we offer two complementary services that extend the value of the grain size data for Birmingham projects:
Combined Gradation & Atterberg Limits
We pair the full sieve-hydrometer analysis with liquid and plastic limit tests on the fraction passing 425 µm. This package gives you the plasticity index alongside the gradation curve, which is essential for classifying cohesive glacial tills according to the A-line chart in BS 5930.
Sulphate & pH Screening on Fines
When the hydrometer analysis reveals a high clay content (above 25%), we recommend testing the fine fraction for water-soluble sulphates and pH. This is particularly relevant in Birmingham's Mercia Mudstone zones, where gypsum-bearing strata can attack buried concrete if left undetected.
Q&A
Why do I need both sieve and hydrometer analysis for a Birmingham site?
Many soils in the Birmingham area, especially glacial till and reworked Mercia Mudstone, contain a significant silt-clay fraction that cannot be quantified by sieving alone. The hydrometer method captures particles down to 0.5 µm, giving you the full gradation curve needed for frost susceptibility assessment, filter design, and hydraulic conductivity estimates.
How long does a combined sieve-hydrometer test take?
The mechanical sieving is completed within one working day. The hydrometer sedimentation requires readings over a 4-hour period, plus overnight oven-drying of the control sample. We typically issue the full report within 3 working days from sample receipt.
What sample size do you need for a grain size analysis?
For a standard test on granular soil we require a minimum of 2 kg of material from a representative split. If the project involves coarse gravel or cobbles, the sample mass should be increased to 5 kg to ensure the coarser fraction is properly represented on the grading curve.
Does the test cover both coarse and fine fractions in one procedure?
Yes. We wash the sample over a 63 µm sieve to separate the coarse and fine fractions. The retained coarse fraction is dry-sieved through the full nest of sieves, while the wash water containing the fines is collected, flocculated with dispersant, and subjected to the hydrometer sedimentation test. Both curves are merged into a single continuous gradation report.
Coverage in Birmingham
Process video
This service complements our laboratory testing work for a complete project analysis.