Kai Gu

Nanjing University | NJU · Department of Geological Engineering and Information Technology

Use of biochar as a soil amendment for climate change mitigation and environmental remediation has been intensively studied over the past decade, yet the growing interest in biochar for geo-environmental applications is primarily motivated by its active interactions with soil in terms of engineering properties. The addition of biochar can significa...

The long-term effectiveness of heavy metal immobilization is always a concern. This study proposes a completely novel approach to enhance the stability of heavy metals by combined biochar and microbial induced carbonate precipitation (MICP) technologies, to create a "surface barrier" of CaCO3 layer on biochar after lead (Pb2+) immobilization. Aqueo...

The thermal response test (TRT) in an aquifer establishes a relationship between the groundwater flow rate and the recorded temperature response curve of temporal ground heating. A major challenge for achieving a mature hydrogeological field test is to minimize borehole effects by smart practical solutions of in situ heating and temperature sensing...

Vertical water flow is a decisive factor for slope stability and instability, but its characterization in the field remains a challenge. Quantifying flow rates in slopes is commonly impeded by insufficient resolution during field investigations or the limited insight obtained from near-surface geophysical methods. This study aims to develop a conve...

Expansive soil is prone to develop a large number of cracks, which have a significant impact on its engineering properties. A prefabricated crack method of expansive soil samples is introduced to carry out the unconfined compression strength on the expansive soil samples under the specific crack morphology. The influence of the crack morphology on...

Distributed fiber optic sensing (DFOS) has recently emerged as a novel sensing technology for obtaining spatially continuous deformation of loose sediment. During the measurement, the mechanical coupling between the sediment and embedded fiber-optic cable determines the accuracy of the results. However, it remains a major challenge to properly asse...

Large-scale measurements of soil moisture play a critical role in many fields, such as agriculture, hydrology, and engineering. The distributed temperature sensing (DTS) technology, based on a dual-probe heat pulse (DPHP), is a novel approach to realizing large-scale soil moisture estimation. However, the application of the method is limited by the...

Shallow temperatures down to a depth of 100 m were measured over one year in 19 closed boreholes located in Nanjing, China, to reveal the conditions and factors influencing the subsurface thermal regime. A monitoring concept with distributed temperature sensing, fiber Bragg grating-based sensor, and a type of Resistance Temperature Detectors, is im...

Desiccation cracking can significantly change the integrity of soils, and potentially result in the instability of infrastructure as well as the migration of contaminants. Biochar is regarded as a promising low-carbon material for geotechnical applications, including cracking prevention. This study investigates the effects of biochar particle size...

Cement solidification is a conventional method in sludge treatment. In order to improve the efficiency and sustainability of this process, biochar and polypropylene fiber were utilized with cement in this study. Biochar (0, 2%, 5%, 7%, 10%, 15% and 20%, w/w) and fiber (0, 0.05%, 0.1%, 0.2% and 0.4%, w/w) at different mass dosages were added to ceme...

As the first scientific borehole of lithium deposits in the world and the deepest one on the Tibetan Plateau, the scientific borehole at the Jiajika lithium mine in western Sichuan Province is located near the Xianshuihe fault and the Sichuan-Tibet railway in the eastern margin of the Tibetan Plateau. The drilling project started on June 3, 2020, a...

Land subsidence is a global phenomenon that derives from natural processes such as auto-compaction and tectonic activity, as well as anthropogenic activities that are exemplified by withdrawal of water, oil or other fluids from the subsurface. Fluid withdrawal-induced subsidence has become a threat in densely populated zones such as coastal areas,...

Land subsidence in the south Yangtze River delta area did not cease when the ground water table has risen during the last 20 years. This issue was generally interpreted as a result of the slow release of excess pore water pressure in the aquitards and the creep of soil. Recent distributed strain monitoring data in boreholes shows a great compressiv...

The determination of subsurface deformation is critical to understanding the subsurface dynamic processes, but most of conventional monitoring methods still have challenges in remotely obtaining detailed data. Herein, a novel fiber-optic wireless sensor network using the ultra-weak fiber Bragg gratings technique was proposed. It allows real-time re...

Subsurface flow rates are critical for hydrology and geothermal research, while field characterization remains a challenge. There are several analytical solutions for calculating the vertical water flux based on measured temperatures. Heat is a popular natural tracer to estimate subsurface flow rates. However, quantifying flow rates is impeded by i...

Biochar has recently been widely used in environmental geotechnical engineering. However, its impact on soil cracking is not fully understood. In this study, the influence of different wood biochar dosages on the desiccation cracking characteristics of silty clay was studied, and the mechanism was elucidated through a combination of image and micro...

Vertical deformation profiles of subterranean geological formations are conventionally measured by borehole extensometry. Distributed strain sensing (DSS) paired with fiber-optic cables installed in the ground opens up possibilities for acquiring high-resolution static and quasistatic strain profiles of deforming strata, but it is currently limited...

Vertical deformation profiles of subterranean geological formations are conventionally measured by borehole extensometry. Distributed strain sensing (DSS) paired with fiber-optic cables installed in the ground opens up possibilities for acquiring high-resolution static and quasistatic strain profiles of deforming strata, but it is currently limited...

Optical fiber sensing technology has developed rapidly since the 1980s with the development of the optical fiber and fiber optical communication technology. It is a new type of sensing technology that uses light as a carrier and optical fiber as a medium to sense and transmit external signals (measurands). Distributed fiber optical sensors (DFOS) c...

Land subsidence is often associated with compaction of subsurface strata, which cannot be recorded in detail by precise leveling, satellite imagery, and even extensometers. The distributed fiber optic sensing (DFOS) technique is advantageous in subsurface deformation monitoring, because it can image distributed profiles of vertical deformation by d...

Accurate estimation of thermal ground properties is needed to optimally apply shallow geothermal energy technologies , which are of growing importance for the heating and cooling sector. A special challenge is posed by the often significant heterogeneity and variability of the geological media at a site. As an innovative investigation method, here...

A number of coastal areas have been suffering from severe land subsidence, which draws worldwide attention. Quantifying the subsidence and the contribution of each compacting stratum is crucial to study its development mechanism. In this paper, the distributed fiber optic sensing (DFOS) technique based on Brillouin scattering was adopted to monitor...

In recent years, biochar has been widely used in environmental and geotechnical engineering applications, but minimal studies have been done on its influence on soil engineering properties. In this study, the effect of biochar on the compression and swelling characteristics of two clayey soils, namely PKE and XS, was studied by conducting standard...

Land subsidence is a worldwide geohazard caused by various factors, and its direct impact is loss of elevation, which is especially severe in coastal areas due to sea level rise. Quantifying contributions of compressed strata is significant for evaluating the subsidence. In this paper, we used distributed fiber optic sensing (DFOS) with Brillouin s...

Excessive withdrawal of groundwater in coastal and deltaic regions is one of the main reasons which induce land subsidence in these areas. Land surface displacement monitoring with conventional methods is not able to pinpoint subsurface compacting, which is very challenging. Instead of groups of extensometers, we apply distributed fiber optic sensi...

Biochar is a promising material for soil remediation. However, the influence of biochar on soil cracking has not been clearly understood to date. Soil cracking can significantly change the mobility of contaminants in soil and consequently the remediation performance of biochar. This study investigates the effect of a wood biochar on the desiccation...

In order to improve the mechanical properties of dredged sludge, short polypropylene fibers were used as physical reinforcement, while cement and fly ash were used as chemical stabilizers. Different mass percentages of fiber (i.e., 0%, 0.05%, 0.1%, 0.2%, 0.4%, and 0.8%), cement (i.e., 15%, 20%, and 25%), and fly ash (i.e., 15% and 30%) were added t...

Vertical deformation can be revealed by various techniques such as precise leveling, satellite imagery, and extensometry. Despite considerable effort, recording detailed subsurface deformation using traditional extensometers remains challenging when attempting to detect localized deformation. Here we introduce distributed fiber optic sensing based...

The mechanical coupling between borehole backfill and fiber-optic strain-sensing cable is the key factor affecting distributed fiber-optic sensing (DFOS)-based land subsidence monitoring. A new pullout apparatus is designed to investigate the interaction mechanism between cable and soil under confining pressures (CPs) ranging from 0 to 1.6 MPa. The...

A better understanding on the relationship between macro compression behavior and microstructure of soil is essential in order to evaluate the trend of land subsidence. In this paper, distributed fiber optic sensing (DFOS) technology was applied in a borehole located in Guangming Village, Wuxi, China, to obtain the deformation of soil layers after...

Land subsidence is a global phenomenon caused by a variety of factors, and there are still many challenges in land subsidence monitoring. The results of an investigation of land subsidence using the combination of Distributed Fiber Optic Sensing (DFOS) techniques and microstructure analysis of soil are here presented. Two DFOS techniques: Brillouin...

Intense groundwater exploitation and seasonal fluctuations of water level in phreatic aquifer cause land subsidence disasters. To better understand the land subsidence mechanism caused by groundwater withdrawal, a small-scale sand-clay interbedded model box was built to carry out consolidation and rebound tests during two drainage-recharge cycles....

Wiggly compaction bands in porous aeolian sandstone vary from chevron shape to wavy shape to nearly straight. In some outcrops these variations occur along a single band. A bonded close-packed discrete element model is used to investigate what mechanical properties control the formation of wiggly compaction bands (CBs). To simulate the volumetric y...

Distributed temperature sensing (DTS) using heated cables has been recently developed for distributed monitoring of in-situ soil moisture content. In this method, the thermal and electrical properties of heated cables have a significant influence on the measurement accuracy of soil moisture content. In this paper, the performances of two heated cab...

Distributed fiber optic sensing (DFOS), a newly developed structure health monitoring technique, has been proved to be a very suitable and useful technique for the monitoring and the early warning of structural engineering. Its application in geotechnical engineering, especially land subsidence resulted by groundwater withdraw, was limited by the c...

Aggressive environments significantly influence the durability and serviceability of hardened cement and concrete. This paper presents an evaluation of the resistance of ground-granulated blast-furnace slag (GGBS) activated with calcined dolomite, as a novel alkali activator, to 5% sodium sulfate attack and 5% magnesium sulfate attack. Two calcined...

This paper investigates the potential of combining Na2CO3 and reactive MgO as a sustainable activator for ground granulated blastfurnace slag. Two very different reactivity MgOs were added at 5–10 % and the Na2CO3 content varied from 4% to 8% by the weight of slag. The strength and drying shrinkage of the activated slag pastes were tested up to 90...

Ground granulated blastfurnace slag (GGBS) is widely used as a partial replacement for Portland cement or as the major component in the alkali-activated cement to give a clinker-free binder. In this study, reactive MgO is investigated as a potentially more practical and greener alternative as a GGBS activator. This paper focuses on of the hydration...

Both reactive MgO and CaO are alternative activators for ground granulated blast furnace slag (GGBS). In this study natural dolomite, as a source of MgO and CaO, was calcined at 800 °C (D800) and 1000 °C (D1000) in air. The activation of GGBS with the calcined dolomites was investigated using compressive tests, pH measurement of pore solutions, pow...

Since alkali-activated slag using conventional activators suffers from economical and technical problems, other alternative activators should be explored. This paper reports the results of an investigation into the activation of ground granulated blastfurnace slag by using 10% (by weight) reactive MgO, CaO and their mixtures with various ratios. Th...

The effects of temperature on the behaviour of soils are of great concern in many geotechnical applications. This paper reports an experimental study that focused on the effect of temperature (between 20 and 50 °C) on the structural strength of a clayey soil using a modified micropenetrometer. Laboratory penetration tests using two penetration rate...

Lime-ground granulated blast-furnace slag (GGBS) blends have been widely used in soil stabilization applications. More recently, reactive MgO-GGBS blends were shown to outperform lime-GGBS blends in terms of various engineering properties of the stabilized soils. Although the use of MgO or CaO in blends has been investigated, their combined use wit...

Conventional alkali-activated slag (AAS) cements suffer from significant drying shrinkage which hinders their widespread application. This paper investigates the potential of using commercial reactive MgO to reduce the drying shrinkage of AAS. Two different reactive MgOs were added at a content of 2.5–7.5 wt% of the slag, which was activated by sod...

Reactive MgO has recently emerged as a potential activator for ground-granulated blast-furnace slag (GGBS), which is one of the most widely used by-products in the cement industry. However, it is known that the characteristics of reactive MgO vary significantly, which may affect the activation process and hence the performance of MgO-GGBS blends. I...

High content of expansive clay minerals coupled with exposure to moisture content fluctuations, is known to cause alternate swelling and shrinkage of soils. Typically, this phenomenon causes deformation and failure of structures that are constructed on such soils. The design and implementation of countermeasures against slope failures and associate...

This paper presents the preliminary findings of a laboratory investigation of the influence of heating and cooling on the structural strength of a highly overconsolidated clayey soil using a SMP-1 micropenetrometer. A total of 11 samples of different dry densities and degrees of saturation were prepared. In the range of 20 to 50 degrees C, one heat...

Improvement of the crack resistance of clayey soils by fiber reinforcement was investigated using initially satu-rated and fiber-reinforced soil specimens subjected to desiccation. An image-processing technique was used to quantitatively describe the effect of fiber addition on the geometrical and morphological characteristics of crack patterns. Th...

Improvement of the crack resistance of clayey soils by fiber reinforcement was investigated using initially saturated and fiber-reinforced soil specimens subjected to desiccation. An image-processing technique was used to quantitatively describe the effect of fiber addition on the geometrical and morphological characteristics of crack patterns. The...

Three types of polyurethane were synthesized from mixtures of toluene diisocyanate, polyethylene glycol and polypropylene glycol for use in soil stabilization to improve the erosion resistance. The three polyurethanes were tested at different aqueous concentrations and sand:clay mixtures at weight ratios of 1:1, 1:3 and 1:5. The results of the rain...

The construction method of a box culvert being pushed to replace two pipe roofs is initiated as a city tunnel excavation method in China. This method is complex, and soil deformation is the key factor to test whether the construction method is successful or not and to guarantee the tunnel safety. The soil deformation sensors are introduced based on...

Temperature has great influence on the hydro-physical properties of clayey soils, such as Atterberg limits, swelling and permeability. This temperature effect may be distinct among different types of soils. In order to systematically study the regularity and mechanism of the effect, this research is conducted to evaluate the adsorbed water content,...

In order to assess the urban heat island effect on the engineering properties of clayey soil,some laboratory tests have been done on moisture contents and dry densities of the clayey soil under different environmental temperatures, and some thermodynamic characteristics of clayey soil are revealed. The research results indicate that the temperature...