Stratigraphic profiling, slip surface detection, and assessment of remolding in sensitive clay landslides using the CPT

A multi-year cone penetration testing program was initiated at a landslide subject to episodic retrogression in Mud Creek, Ottawa, to assess whether a hand-operated mobile CPT could yield new insights into the current degree of remoulding under progressive failure in metastable areas of a landslide where conventional tracked rigs are unable to gain access. The mobile CPT rig permitted tests to be performed through the entire thickness of the Champlain Sea deposit at a penetration rate of 0.5 cm/s, with similar results to tests performed at the standard 2 cm/s. Measurements of pore pressure varied considerably with cone size, with the magnitude of pore pressure response decreasing with cone size. The elevation of the slip surface was identified in the tip resistance as the point of transition between the remolded soil above the slip surface and the intact soil below the slip surface, whereas a further 0.5 m of penetration was required to elevate pore pressures to values indicative of the intact soil behaviour. In-situ measurements of shear strength of corresponding layers between the intact and remolded profiles to be compared indicating that the soil above the slip surface had remolded to 50% of its fully remolded strength.

Development and operation of an automatic air pluviation system for physical modelling applications

This paper presents an air pluviation system, developed to facilitate 1-g physical model tests in granular soils. The deposition process is fully automated and requires minimal input from the operator, thereby significantly reducing the time required to deposit large volume of granular material, improving the uniformity of the prepared specimens, and the reliability of test results. The components comprising the pluviation system have been calibrated to produce loose-to-very dense sand beds, of relative density that ranges between Dr=7% and Dr>100% of the maximum density achieved with the procedures described in the pertinent standards. The testing chamber where sand is deposited is instrumented with an array of pressure sensors, and the rig is equipped with a miniature Cone Penetration Testing (mini-CPT) device. Measurements from the earth pressure sensors and cone tip resistance profiles are used to evaluate how friction at the sand-chamber interfaces affects the distribution of geostatic stresses inside the chamber, the uniformity of sand beds, and boundary effects during deposition and during mini-CPT testing. The air pluviation system allows preparing layered sand profiles by adjusting the deposition parameters on the fly, and this feature is demonstrated via the analysis of mini-CPT tests performed in layered sand beds.

Forensic investigation of flowslides triggered by the 2018 Sulawesi earthquake

The Sulawesi earthquake with a moment magnitude of Mw 7.5 struck the Central Sulawesi region of the Sulawesi Island, Indonesia, on September 28, 2018. The epicenter of the earthquake was located in the mountainous region of Donggala Regency, in the neck of the Minahasa Peninsula in the Central Sulawesi Province of Indonesia. Although the epicenter was located in Donggala Regency, the greatest devastating effects were observed about 70 km south of the epicenter in the Palu Valley. The event was the first of its kind to cause large-scale flowslides simultaneously at four key locations such as Balaroa, Petobo, Jono Oge, and Sibalaya with extensive ground displacements ranging from several hundred meters to more than 1 km. This article reviews the field observations of geotechnical failures and infrastructure damage caused by liquefaction resulting from the shallow strike-slip earthquake at Palu City, Donggala Regency, and Sigi Regency. A geo-spatial analysis was performed on data collected from aerial drone imagery, along with portable dynamic cone penetration testing (PDCPT) in the field. The investigation revealed a highly stratified ground with alternating soil layers of varying permeability and very low bearing resistance at shallow depths. The investigation also helped in assessing the extent of damage caused by geotechnical failure to the residential infrastructures, irrigation structures, and roads. Graphical Abstract

Investigating Road Pavement Failure in Oworonshoki, Kosofe Area of Lagos, Using Geophysical and Geotechnical Methods

An assessment of the immediate causes of persistent road pavement failure in Oworonshoki, Koshofe area of Lagos, Nigeria using geophysical and geotechnical methods was carried out. Six traverses were occupied in the study area along the alignment of the road. Electrical Resistivity Imaging (ERI) data using the Wenner array were acquired along the six traverses. These were followed by six (6) Vertical Electrical Sounding (VES) data along the traverses. On traverse 1 are VES 1 and 2, on traverse 2 are VES 3 and 4, on traverse 3 are VES 5 and 6. One boring and three Cone Penetration Testing (CPT) were conducted along traverse 6 while the three CPTs were carried out on traverse 3, 4 and 5 respectively. The inverted 2D results reveal that resistivity values vary from 6.74 – 1333 Ωm in the study area. Four resistivity structures are delineated which are peat, clay/sandy clay, clayey sand and sand. The peat has resistivity values ranging from 6.74 – 17.7 Ωm, clay/sandy clay (20.9 – 86.9 Ωm), clayey sand (96.3 – 194 Ωm) and sand (245 – 1333 Ωm). The peat is laterally extensive and occurs from the surface to a depth of 25 m. The peat is underlain by the clay which is fairly extensive across the area of study with a thickness of 2.5 – 20 m in most location. The Cone Penetration Tests (CPT) reveal cone resistance values that progressively varies from 0 – 101 kg/m2 from the surface to a depth of 17 m, indicating dense earth materials at deeper depth while at near surface, they are incompetent soft clayey earth materials. The laterally extensive peat and clay units underlying the road pavement, extending up 30 m depth as revealed from the 2D ERI, the geoelectric investigation and the borehole are suspected to be responsible for the persistent settlement, rutting and pitting of the road pavement. The thickness of the peat/clay and the lateral extent may not be economically admissible for excavation during construction. Pile foundations to the dense gravely sand at 40 m depth along the stretch of the road is therefore recommended for stable road pavement.

Insights from CPTu and Seismic Cone Penetration Testing in the Kathmandu Valley, Nepal

Seismic hazard assessment often relies on static piezocone penetration tests (CPTu) to estimate the cyclic resistance ratio (CRR) and for the evaluation of in situ soil behavior. This article presents CPTu data acquired in the Kathmandu valley sediments and makes use of established CPTu interpretation procedures to assess the soil in situ properties. Up to this point predominantly SPT data and limited shear wave velocity measurements have been relied upon to assess the variability and seismic response of soil deposits underlying Kathmandu. This article provides 1) additional data to add to the existing SAFER/GEO-591 database, 2) new shear-wave velocity measurements, and 3) initial estimates of CRR at the sites visited. Based on the work presented in this article, it is concluded that a more detailed methodology is needed for liquefaction assessment mainly due to the presence of saturated silts in the valley.

CONE PENETRATION TESTING AND SAMPLING OF FROZEN SOILS

The article provides the analysis of the results of the permafrost soils field and laboratory tests. The undisturbed permafrost samples were collected using cone penetration testing (CPT) equipment and MOSTAP sampler. The sampling technology using CPT equipment was applied on permafrost soils for the first time. The full scope of tests for physical properties were carried out on the collected samples. Based on the test results, several engineering-geological elements (EGE) were identified and confirmed, one of which is composed of frozen silty clay. The results of statistical data processing were compared. The data on the coefficient of variation of the values of the ultimate long-term resistivity of soils against cone penetration (characteristic of long-term strength) for the frozen EGE are presented.

A CPT approach to cable plough performance prediction based upon centrifuge model testing

Cable ploughing is an important technique for burying and protecting offshore cables. The ability to predict the required tow force and plough performance is essential to allow vessel selection and project programming. Existing tow force models require calibration against full-scale field testing to determine empirical parameters, which may hinder their use. In this study the factors controlling the plough resistance were investigated using a series of dry and saturated 1/50^th scale model cable plough tests in sand in a geotechnical centrifuge at 50g at a range of target trench depths, sand relative densities and plough velocities. An improved model for predicting cable plough tow force which separates out the key components of resistance and allows tow force prediction without the use of field-derived empirical coefficients is presented. It is demonstrated that the key parameters in this model can be easily determined from in-situ Cone Penetration Testing (CPT), allowing it to be used offshore where site investigation techniques may be more limited compared to onshore locations. The model is validated against the centrifuge cable plough tests, demonstrating it can correctly predict both the static (dry) and rate effect (saturated) tow forces.