Open caissons are sunk into the ground by their own weight. A cutting edge of the caisson having a tapered inner face on loading – that is, raising of the steining – results in bearing failure by displacing the soil which is in contact with the cutting edge. The bearing capacity of the cutting edge and the soil flow mechanism depend on the configuration of the cutting edge, sinking depth and soil type. This paper presents the results of a series of 1g model tests, which investigate the effect of varying tapered angles of the cutting edge on the penetration resistance of the open caisson. The vertical failure load and corresponding vertical bearing capacity factor, N′γ, and the soil flow mechanism around the cutting edge are investigated. The soil flow mechanism and the influence of surcharge formed at the top level of the cutting edge due to advancement of the caisson in the ground are examined using the image-based deformation measurement technique. The results highlight that the cutting angle of the cutting edge and sinking depth play important roles in the load–penetration response and soil flow mechanism.

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The standard penetration test (SPT) is one of the most widely used in-situ penetration tests for subsurface exploration. Its suitability for assessing and predicting the design parameters of granular materials has been well appreciated by the geotechnical engineering community over several decades. However, in the case of soft to very soft clays, the correlation between the standard penetration number (N) and the undrained shear strength is poor. In the recent past, tests conducted at a constant rate of penetration, such as the cone penetration test (CPT), ball penetration test, and T-bar penetration test, have become popular in soft clay regions. These tests also have a distinct advantage over SPT in terms of test setup because, in the case of SPT, the entire weight of the sampler and the rod assembly is directly applied on the subsoil, whereas in the case of CPT, the weight of the assembly is supported externally prior to the penetration. This can cause significant operational advantage in case of soft clay deposits. Despite the shortcomings, SPT is still one of the most widely available site investigation tools in the field, as samples are available for inspection and index tests. The operational disadvantages in the case of soft clay deposits can be overcome by altering the penetration process of SPT. A quasi-static penetration at a constant rate rather than a dynamic penetration will help establish a relationship between the penetration resistance and the strength parameters of soft soils. In this article, a quasi-static penetration test using the standard SPT sampler is conducted on reconstituted clay samples in order to develop an empirical correlation with the laboratory vane shear strength. The particle image velocimetry technique is used for detecting the influence zone and plugging during penetration.

Full flow penetrometers (FFPs) such as T-bar and ball penetrometer provide reliable estimates of undrained shear strength (su) of soft-soil deposits. Several studies are reported in the literature on the field application of these penetrometers for offshore applications typically for the deep-water environment. However, the lack of sampling provision creates problem for identifying the accurate soil type from the load–penetration response. Information obtained from the field samples is vital in determining the stratigraphy and conducting several basic laboratory tests. This study proposes a new sampling-cum-penetration testing device, which uses a split-spoon sampler for sampling with a spherical cutting shoe. The cutting shoe was modified to increase the bearing area for enhanced accuracy in soft deposits. Strength assessment study was conducted in the laboratory using remoulded kaolin clay at various undrained shear strengths. To investigate the occurrence of plugging and the extent of influence zone during penetration, image-based deformation measurement technique was adopted. The modified ball penetrometer shows a strength factor of about 14·3 in remoulded kaolin clay.