OR/14/052 Sample collection

Boon, D, Kirkham, M, and Scheib, A. 2014. Physical properties of till deposits from Anglesey, north west Wales. British Geological Survey Internal Report, OR/14/052.

Various samples were taken for determination of physical properties including: grading, bulk density, natural moisture content, shear strength. Sample types included ‘disturbed’ bulk samples, and ‘undisturbed’ samples including block samples and density rings. Sample details are given in Table 1. Samples were collected in accordance with field sampling procedures described in BS1377 and Head (2008). Samples were labelled in the field and sealed to minimise moisture loss. All samples were stored in a cool box while in transit and transferred to a constant temperature (4 degrees) humidity controlled fridge prior to testing.

Table 1    Geotechnical sample details

Name of sample site	Sample Number	Type (D=disturbed, UD=Undisturbed, DR=Density Ring, PP=Panda Penetrometer)	Description	BNG Easting (m) (+/-5 m)	BNG Northing (m) (+/-5 m)	Elevation (m amsl) (+/-2 m)	Sample Mass (field) (kg +/- 0.01 kg)
Cemlyn Bay	CB1 1/1	D	Red/Brown Till (landslide mass)	232743	393750	6	~30
		D	Weakly-cemented Sand	232815	393750	4	-
		UD	Weakly-cemented Sand	232815	393750	4	-
	CB2 1/1	D	Grey Till	232815	393750	2	~30
Hen Borth	HB1 1/2	D	Red/brown Till	232065	392984	6	23.20
	HB1 2/2	D	Red/brown Till	232065	392984	6	30.50
	HB2 1/2	D	Grey Till	232065	392984	3	23.68
	HB2 2/2	D	Grey Till	232065	392984	3	23.61
Beaumaris	B1 1/2	D	Grey Till	261309	377694	1	18.35
	B1 2/2	D	Grey Till	261309	377694	1	18.46
		DR x3	Grey Till	261309	377694	1	-
	B2 1/2	D	Red Till	261350	377722	6	18.00
	B2 2/2	D	Red Till	261350	377722	6	18.69
		DR x3	Red Till	261350	377722	6	-
Penrhos	PR1 1/2	D	Upper Grey Till/Red Till?	227734	381424	4	14.60
	PR1 2/2	D	Grey	227734	381424	4	18.90
	PR2 1/2	D	Lower Grey Till	227734	381424	2	15.00
	PR2 2/2	D	Lower Grey	227734	381424	2	15.00
Porth Nobla — Red Till	PN1 1/2	D	Red Till	233050	371119	2	18.67
	PN2 2/2	D	Red Till	233050	371119	2	16.40
Sea Zoo — Red Till	SZ1 1/2	D	Red Till	247048	364257	4	13.57
	SZ2 2/2	D	Red Till	247048	364257	4	18.73
	SZ3	D	Red Mudstone	247077	364258	2	-
		DR x3	Red Mudstone	247077	364258	2	-

Sampling methods

Disturbed sample procedure

Bulk samples were collected by excavating till from the cliff face using combination of picks, geological hammers and a drill (tills were very stiff to hard). The loosened soil was collected on a tarpaulin to retain the fine fraction content. The size of the sample was dependent on the largest size fraction, following EN guidance, to ensure adequate sample quantity for sieving results to be representative of the Clay to Gravel components. Samples containing cobbles (diamicts) were greater than 30 kg and the minimum sample size was 15 kg, in accordance with BS1377:1990.

Undisturbed density rings

Density rings were used to collect undisturbed samples for determination of bulk density and natural moisture content (NMC). It was not possible to obtain intact samples of till at several sites (e.g. Cemlyn Bay and Hen Borth) because the high abundance of gravel and hardness of the till makes undisturbed sampling by hand difficult. This factor results in data bias as only the ‘softer’ tills were sampled.

Undisturbed block sampling

The drumlin at Cemlyn Bay contains a horizontal sand body interpreted as a hydrofracture fill (Phillips and Hughes, in prep). An undisturbed block sample of the sand was gently carved by hand top down using a sharp knife (Figure 2) with a metal tin gradually lowered onto and around the column of soil to contain the sample. Great care was taken to avoid introducing discontinuities/fractures during the excavation process. The box was capped with lids on either end and was then marked with sample orientation, wrapped with cling film and taped up to minimise moisture loss.

Figure 2    Preparation of an undisturbed block sample of cemented sand (hydrofracture dyke) from a drumlin at Cemlyn Bay, Anglesey. A stable intact plinth is excavated by hand and box gradually lowered down encapsulating the soil sample.

Till provenance: palynology samples

Additional samples were collected for Palynological analysis and the results are presented in Riding (2012).

Table 2    List of Palynology Samples

Name of sample site	Sample Bag Number	Type	BNG Easting (m)	BNG Northing (m)	Elevation (m amsl) +/- 2 m error
Sea Zoo	1	Red Till	247048	364257	4
Beaumaris	2	Grey Till	261309	377694	1
Sea Zoo	3	Red Mudstone	247077	364258	2
Cemlyn Bay	4	Weakly-cemented Sand	232830	393741	4
Beaumaris	5	Red Till	261350	377722	6
Cemlyn Bay	6	Red/Brown Till (slipped)	232743	393750	6
Cemlyn Bay	7	Grey Till	232815	393750	2
Hen Borth	8	Red/brown Till	232065	392984	6
Hen Borth	9	Grey Till	232065	392984	3
Penrhos	10	Lower Grey Till	227734	381424	2
Porth Nobla — Red Till	11	sandy Red Till	233050	371119	2