This paper presents two case studies dealing with undesirable impacts of overburden drilling of casings for end-bearing piles to bedrock. Monitored pore-water pressures and ground settlements are used to document and assess the influence from rotary percussive drilling with down-the-hole (DTH) hammers. The studies show that drilling with high-pressure air -driven DTH hammers may cause considerable erosion and soil volume loss adjacent to the drill bit and along the casing, resulting in settlements of the surrounding ground. The risk of soil volume loss increases when the drilling is carried out in erodible soils such as silt and fine sands. The volume loss is found to be caused by a combined air -lift pump effect and a Venturi suction effect. Monitoring pore pressures in the vicinity of the drilling may be used to reduce soil volume loss and prevent damaging settlements. Results from drilling with water-driven DTH hammer showed significantly less ground settlements and influence on pore pressures compared to using an air -driven hammer. The study suggests that the drilling parameters flow rate and penetration rate, and the cross-sectional area of the pile casing can be combined in a non-dimensional methodology to assess the mass balance of drill cuttings when drilling with water flushing. A design framework is suggested to guide overburden drilling in urban settings to reduce potential impact on the surroundings.

Helical piles can be classified as partial displacement piles in terms of moderate advancement rate. However, its installation effect on surrounding soil is unclear. This study presented four field tests on the installation of helical piles with various dimensions in silty clay. The radial earth pressure and excess pore water pressure were measured during the installation processes. The installation effect of helical pile embedded in silty clay was comprehensively discussed and evaluated from multiple dimensions of time and space, based on the cavity expansion method (CEM) and Randolph and Wroth's elastic-plastic method verified by field data. The research reveals that as the length of the helical pile increases by 1.0 time, the maximum variations in radial earth pressure and pore water pressure by a remarkable 25.0 times and 7.8 times, respectively. Additionally, when the shaft diameter of the helical pile expands by 20%, the maximum alterations in radial earth pressure and pore water pressure swell by approximately 18.6 and 5.7%, respectively. Comparing the radial earth pressure at various embedment depths at the same penetration stage, it is found that the radial earth pressure induced by helices is slightly greater than that induced by pile shaft. The estimated radial earth pressure and pore water pressure agree with the measured maximum data, and the pore water pressure generated by the installation of helical pile completely dissipates after 10-12 days of installation in this work.

Die R & uuml;ttelstopfverdichtung kommt als Baugrundverbesserung weltweit in fein- und grobk & ouml;rnigen B & ouml;den zum Einsatz. Jedoch sind die Zustands & auml;nderungen des anstehenden Bodens infolge des vollverdr & auml;ngenden S & auml;uleneinbaus und der induzierten Vibration noch nicht ausreichend untersucht. Im ersten Teil dieses Beitrags werden daher in einem Feldversuch die Auswirkungen der R & uuml;ttelstopfs & auml;ulenherstellung auf den Zustand des anstehenden Bodens untersucht. Dabei zeigt sich, dass der R & uuml;ttelstopfs & auml;uleneinbau in grobk & ouml;rnigen B & ouml;den zu einer Verbesserung der bautechnischen Eigenschaften des anstehenden Bodens f & uuml;hren kann. Motiviert durch den Feldversuch betrachtet der zweite Teil der Arbeit anhand von simplifizierten Beispielen einen grunds & auml;tzlichen Vergleich verschiedener Hohlraumaufweitungsprozesse. Mithilfe eines hypoplastischen Stoffmodells wird dabei die Aufweitung eines Hohlraums infolge (1) einer monotonen und infolge (2) einer zyklischen Belastung betrachtet. Beide F & auml;lle werden im Hinblick auf eine qualitative & Uuml;bertragbarkeit auf die Modellierung der S & auml;uleninstallation verglichen. Es zeigt sich ein qualitativ unterschiedliches Bodenverhalten: Eine monotone Aufweitung f & uuml;hrt zum kritischen Zustand im Boden, w & auml;hrend eine zyklische Aufweitung in Abh & auml;ngigkeit von der Durchl & auml;ssigkeit zu einer Verdichtung und/oder einer Spannungsrelaxation f & uuml;hrt. Eine vollst & auml;ndige Vernachl & auml;ssigung der R & uuml;ttlervibration in entsprechenden numerischen Modellen erscheint daher nicht zutreffend. Field test on the vibro replacement stone column installation and considerations on cavity expansionVibro replacement stone columns are used for ground improvement worldwide in coarse-grained as well as fine-grained soils. However, the changes in the soil's state due to the stone column installation including the induced vibration have not yet been investigated sufficiently. In the first part of the article, the effects of the stone column installation are investigated using a field test. It is shown that the installation in coarse-grained soils can lead to an improvement in the structural properties of the surrounding soil. Based on the field test, a theoretical comparison of different cavity expansion processes is presented in the second part of this paper using simplified numerical examples. For that purpose, the expansion of a cavity in the soil due to (1) a monotonic and (2) a cyclic loading is investigated using a hypoplastic constitutive model. Both cases are compared to investigate their ability to simulate the column installation process. However, a qualitatively different soil behaviour is observed: A monotonic expansion will result asymptotically in the critical state of the soil, while a cyclic expansion leads to a compaction and/or a stress relaxation depending on the permeability. Therefore, neglecting the cyclic deformation of the soil in simulating the stone column installation seems to be inappropriate.