Diatomaceous Soil Research Articles

Causes of the high friction angle of diatomaceous soil: microscale and nanoscale insights

Diatomaceous soil has geotechnical properties that differ fundamentally from those of common non-diatomaceous soils due to the presence of diatom microfossils with biological origins. Despite its dominant fines content, diatomaceous soil usually has high frictional shear resistance (approaching that of sand). Currently, the exact role of diatoms in controlling soil strength and underlying mechanisms remain obscure. Here, the frictional strength of diatomaceous soil is evaluated by way of angle of repose and direct simple shear tests on diatom–kaolin mixtures with differing diatom content. The microscale and nanoscale structures are characterised in detail using scanning electron and atomic force microscopy to establish how soil structure evolves with diatom content and shear. For the studied diatom–kaolin mixtures, the angle of repose and internal frictional angle are high and increase with diatom content, especially when the diatom content exceeds 20%. Diatom content controls the frictional strength through its intricate morphology (cylindrical, saucer and disc shapes), very rough surface (hundreds of times rougher than flaky minerals) and stiff frustules with high Young's modulus. These features increase the particle coordination number and produce interparticle interlockings, both of which prevent particle rearrangement during shear and improve the frictional strength. This paper provides new insights into the multiscale structure of diatoms and improves understanding of the shear strength of diatomaceous soils.

Diatom-induced impact on shear strength characteristics of fine-grained soils

Diatomaceous soils, composed of diatom microfossils with biological origins, have geotechnical properties that are fundamentally different from those of conventional non-diatomaceous fine-grained soils. Despite their high fines content, diatomaceous soils typically exhibit remarkably high shear resistance, approaching that of sandy soils. However, the exact role that diatoms play in controlling the mechanical properties of fine-grained soils and the underlying mechanisms remain unclear. In light of this, the shear strength response of diatomaceous soils was systematically investigated using consolidated undrained triaxial compression tests on diatom–kaolin mixtures (DKMs) with various diatom contents and overconsolidation ratios. The micro- and nano-scale structures of the soil samples were characterized in detail using scanning electron microscope (SEM) and atomic force microscope (AFM) to interpret the abnormal shear strength parameters of diatomaceous soils. The results indicated that the presence of diatoms could contribute to significantly higher strength, e.g. the friction angle of DKMs was improved by 72.7% to 37° and the value of undrained shear strength tripled with diatom content increasing from 20% to 100%. Such significant improvement in soil strength with diatom inclusion could be attribute to the hard siliceous skeleton of diatoms and the interlocking between particles with rough surfaces, which were quantitatively analyzed by the surface roughness parameters with AFM. Furthermore, a conceptual model established based on the macro-mechanical tests and microscopic observations portrays a microstructural evolution of soils with increasing diatoms. The microstructure of soils was gradually transformed from the matrix-type to the skeletal one, resulting in a continual augmentation in shear strength through mutual interactions between diatom microfossils. This paper provides new insights into the multi-scale structural properties of diatoms and significantly advances our understanding of the mechanical behavior of diatomaceous soils.

Diatoms microfossils and their microstructural effects on the sensitivity of metastable silty-clayey soils

In 2013, an accident occurred in Port of Santana, located at the mouth of the Amazon River, in the State of Amapa, Brazil, comprising a large volume of soft silty-clay soil flowing very fast, for a great distance, towards the bottom of the river. Field tests performed afterwards identified the occurrence of sensitive soil layers at the site. Subsequent laboratory tests verified the presence of diatom microfossils in layers with highest liquidity indices. Owing to peculiarities of the accident, a large research programme started at PUC-Rio, aiming to investigate the role of these biomineral grains on soil behaviour. Thus, based on physical-chemical-mineralogical tests performed on samples from the site, higher sensitivity natural soils from Port of Santana were reconstituted. Chemical, mineralogical and grain size reconstitution was carried out using manufactured soils containing equal proportions of minerals as in the natural soils, but with a difference in the portion of non-plastic siliceous grains: a reconstituted soil used quartz, in silt size, and the other used diatomaceous earth. This article presents and discuss results of undrained shear strength data obtained through laboratory fall cone and vane tests, as well as microstructure analyses - including scanning electron microscopy, mercury intrusion porosimetry and X-ray microtomography - in high sensitivity natural diatomaceous soils and reconstituted soils, in the liquidity index range of 1.0 ≤ LI ≤ 1.6. It is shown the fundamental role of the diatom microfossils in microstructural metastability, impacting the high sensitivity measured in soil reconstituted with diatoms and in natural diatomaceous soils.

Effect of the particle’s shape on the dynamic shear modulus and compressibility of diatomaceous soils

Diatomites are unicellular algae fossils that can be found worldwide. This paper studies the diatom's shape effect on diatomaceous soil mixtures' dynamic and compressibility properties. Physical characteristics of six diatomite samples with variable shapes and taxonomies are presented. Among these six samples, three diatomites of similar grain size distribution were mixed with kaolin, and the mechanical properties (i.e., shear modulus and damping ratio from small to large strains) were analysed. The results showed that diatom frustules increased the mixtures' compressibility and reduced the maximum shear modulus compared with pure kaolin samples. Moreover, the diatom's shape influenced the normalised shear modulus degradation curve and the damping ratio. Overall, the presence of diatomites reduces the energy dissipation capacity in soils. This research evidenced the importance of distinguishing the shape of diatom in soil mixtures when mechanical properties are analysed, a situation that has yet to be explored.

Failure investigation and treatments of tunnel entrance collapse in weak diatomaceous soil induced by heavy rainfall through coupling surface and groundwater flows

Rainfall is a great threat to the stabilities of the slope at tunnel entrances located in mountainous areas because it can reduce the shear strength of soil and, as a result, the stabilities of tunnel entrances. Although conventional rainfall-induced slope damage analyses commonly overlook the impact of runoff, it is crucial to consider it to assess slope instability accurately. To assess the factor of safety distribution about the slope of the Feifengshan Tunnel in Zhejiang Province, China, and analyze the impact of runoff on slope instabilities, this paper uses a coupling model of surface runoff, groundwater flow, as well as soil mechanics, through the shallow water equation, Richards equation, and the local safety factor (LFS) method. Furthermore, given the strain-softening characteristics of diatomaceous soil, designing and analyzing them according to peak strength may result in potential hazards. Thus, this study analyzes the distribution of the slope safety factor under different constitutive models and recommends suitable slope reinforcement measures. The study also investigates the slope reinforcement measures required to avoid the secondary collapse of tunnel entrance during rainfall, verifying numerical simulation results regarding the section’s volumetric water content and surface settlement values. The findings of this study offer a dependable approach for evaluating the stability of tunnel entrance slopes and are significant for tunnel site selection and reinforcement effect assessment. The numerical results emphasize the effects of surface runoff from rainfall water distribution. Furthermore, the strain softening model has significant advantages in calculating surface settlement and tunnel slope failure.

Field Comprehensive Testing and Study on New Subgrade Structure of High-Speed Railway in Diatomaceous Earth Region

Part of the Hang-Tai High-speed Railway (Hangzhou via Shaoxing to Taizhou in Zhejiang Provence) in China passes through the diatomaceous earth area, which is the first time in the history of Chinese high-speed railway construction. This type of soil has significant compressibility, swelling and disintegration. Diatomaceous earth also shows a sharp reduction in strength when exposed to water, which severely impacts the safety of the project. However, no studies have been carried out on the engineering practice of building a high-speed railway in the diatomaceous earth area in China. Moreover, there is limited experience in the construction of ballastless track through the diatomaceous earth area. In order to ensure the stability of the high-speed railway subgrade in diatomaceous earth area, and considering the high level of precipitation in the location of this railway, a kind of waterproof and drainage subgrade (WDS) is proposed to reduce the influence of precipitation on the strength of the diatomaceous earth foundation. The subgrade has a flexible waterproof and drainage layer (WDL) inside, which consists of capillary waterproof and drainage plates and medium-coarse sand. In the present study, field tests including immersion tests and excitation test are carried out on a subgrade test section to verify the subgrade structure. The tests mainly focus on construction technology, waterproof performance and dynamic characteristics. The studies show that the subgrade bed with the WDL can effectively avoid the diatomaceous earth foundation from rainfall interference and maintain the long-term stability of the subgrade. The flexible WDL in WDS has a significant energy dissipation effect in comparison with the traditional subgrade (TS) filler and can play a key role in vibration damping, promoting the attenuation of dynamic response in the downward and cross-sectional directions within the subgrade. The dynamic response of the WDS attenuates along the depth. In comparison with the existing high-speed railway subgrade measured data, its dynamic response attenuation coefficient is within acceptable limits. The laying of the WDL does not change the subgrade dynamic characteristics transfer law. The proposed structure meets the requirements of ballastless track construction for high-speed railways, and the WDL can be used in the design of high-speed railways for enhanced drainage protection in diatomaceous soil areas or other special soil areas.

A new proposal to simulate soft soils for centrifugal models using reconstituted diatomaceous soils

A new proposal to simulate soft soils for centrifugal models using reconstituted diatomaceous soils

Role of Diatom Microstructure in Determining the Atterberg Limits of Fine-Grained Diatomaceous Soil

The presence of diatoms in diatomaceous soil gives it geotechnical properties that are unusual compared with common clays. The most typical physical property of diatomaceous soil is its abnormally high Atterberg limits compared to fine-grained soil without diatoms. For diatomaceous soil, the Atterberg limits are associated with many factors, such as diatom content, diatom crushing degree, etc. In the study reported here, it was ascertained that more diatoms lead to higher plastic and liquid limits. Once the diatoms are crushed, the plastic and liquid limits decrease. The pore fluid salt concentration barely influenced the Atterberg limits of diatomaceous soil. Additionally, the porous diatom microstructure and trimodal pore size distribution of diatomaceous soil were investigated via scanning electron microscopy, transmission electron microscopy, and mercury intrusion porosimetry. The underlying mechanism of abnormally high liquid and plastic limits of diatomaceous soil is revealed as the water stored in the special diatom microstructure. However, water in diatoms has no contribution to plasticity. Also discussed is the applicability of the current soil classification systems for diatomaceous soil. The findings of this study can help for a better understanding of Atterberg limits of diatomaceous soil and provide suggestions for the classification of diatomaceous soil.

Compressibility, permeability and microstructure of fine-grained soils containing diatom microfossils

Fine-grained soils containing diatom microfossils of biological origin are found worldwide. However, although these soils are acknowledged to have unique physical and mechanical properties, the exact role of diatoms in determining their compression and hydraulic behaviours remains unclear, especially when high effective stress is involved, and the underlying micromechanism is yet to be revealed. This study investigated the compression and permeability of diatomaceous soils prepared by mixing pure diatom and kaolin powders through one-dimensional constant rate of strain compression tests with a maximum vertical stress of 10 MPa. The microstructure of the soils studied was observed by atomic force microscopy, scanning electron microscopy and mercury intrusion porosimetry, and the microstructural evolution during compression was traced. The results indicate that the special hollow structure of diatom particles with internal pores contributes significantly to the high void ratio, compressibility and permeability of diatomaceous soils, and increasing the diatom content improves the pore distribution non-uniformity of the diatom–kaolin mixtures. In addition, the diatom particles have high brittleness and breakage potential, leading to microstructural rearrangement during compression, especially pore-structure adjustment. Lower compressive stress deforms the inter- and intra-aggregate pores, but higher vertical stress damages the diatoms’ hollow structure, which changes the compression and hydraulic parameters in a different manner from the case of conventional clay. This paper enriches the knowledge concerning the multilevel behaviour of fine-grained soils containing diatom microfossils and provides a fundamental dataset.

Swelling–shrinkage mechanisms of diatomaceous soil and its geohazard implication

Current understanding of soil behaviors from classic soil mechanics is constantly challenged by a variety of unusual soils, one of which is diatomaceous soils (DSs). It is well understood that this biological-origin soil has fundamentally different geotechnical features from that of common fine-grained soils because of the presence of diatom fossils. Recently, increasing geohazards and engineering disasters associated with DS swelling–shrinkage are reported but the exact role of diatoms in determining soil swelling–shrinkage, the underlying mechanisms, and the geohazard implications, have not yet been revealed. This study systematically investigates the swelling–shrinkage behavior of natural DS as well as artificial mixture of diatoms and clay minerals (kaolinite and montmorillonite). The swelling–shrinkage behaviors are explained from the perspectives of mineralogy and microstructure as revealed through X-ray diffraction, scanning electronic microscopy, and transmission electron microscopy. Diatoms have a special microstructure with inter-frustule pores, and the intra-skeletal and skeletal pores in DS make the soil characterized by a high void ratio and water content. In addition, the presence of diatoms curbs the swelling–shrinkage of DS but this may be overwhelmed by the high stress generated due to the swelling of montmorillonite. The wetting–drying cycles subjected to DS result in fissure development, a higher level of swelling–shrinkage behavior, and ultimately in related geohazards such as landslides. The distinct swelling–shrinkage behavior of DS makes the previous classification inapplicable; thus, more rational classification methods are adopted. This study enhances the understanding of the swelling–shrinkage behavior of DS and the control of related geohazards.

Diatomaceous Soils and Advances in Geotechnical Engineering—Part I

Diatoms are microscopic algae with a skeleton called a frustule, formed chiefly of silica, and are found in almost all aquatic environments and climatic conditions. Diatomaceous soils (DSs) originate from frustule sedimentation. In civil works (design and construction), the uncommon values obtained from DSs are not completely understood. There needs to be more knowledge about the strength and compressibility of DSs. The stability of these deposits is still being determined. Definitions of substances such as diatoms, diatomaceous soils, diatomaceous earth, diatomaceous oozes, frustules, and diatomite need to be clarified. This document references construction processes that face problems such as differential settlements, pile rebounds, and irregular pore pressures due to frustules. This review analyzes multiple sets of results regarding the grain size distribution, specific gravity, consistency, plasticity, compressibility, and shear strength of DSs. It is concluded that the particle size distribution of DSs generally classifies them as silts. Particles are modified by the imposition of stresses (frustule breakage), which impacts compressibility. Microfossils take up stresses, restrict strains, and cause sudden increases in compressibility when their yield stress is exceeded. Currently, their strain mechanisms need to be better understood. The Gs decreases with increasing frustule content, given the high porosity of the skeletons. The intraparticle pores of the frustules explain the high liquid limit (LL) of DSs. DSs can have high shear strengths and large yield surfaces due to the “interlocking” phenomenon and the interparticle contacts’ high frictional component caused by their rough surface and high silica content.

Unsaturated Hydraulic Conductivity in Composite Porous Media

Determining the constitutive properties that describe the incipient hydraulic behavior of the materials, including the matrix domains and the distribution of macro and micropores, is crucial to analyzing the preferential water flow in saturated soils, ks, and unsaturated, ku. This study focused on determining the hydraulic conductivity in porous media under total and partial saturation conditions. The infiltration characteristics of three reconstituted soils were evaluated using five suction ranges employing conventional permeameters, an automated dual system, and mini-disk infiltrometers. The experimental cycles were carried out in granular soils with mixtures of diatomaceous soils, iron oxide (Fe2O3), and calcium carbonate (CaCO3) in 5–40% proportions. The differences between the granular microstructures of each material and the different hydraulic interaction mechanisms (suctione levels) significantly affected the values of ks and ku and the coupling between the pore domains and the defined water regime. Additionally, a lower impact was observed in the data set exposed to higher percentages of Fe2O3 and CaCO3 in different suction ranges, mainly due to a tension effect (meniscus) generated by suction in the granular skeleton. Since both parameters are mutually correlated and have a similar impact between methods and soil cores, ks and ku must be optimized simultaneously in each mechanism analyzed. The main findings of this work result in the confirmation that the unsaturated permeability decreases as suction is imposed on the sample. As well as the addition of different materials with Particle Size Distribution finer than the base sample, it also reveals a reduction in hydraulic conductivity, both saturated and unsaturated.

Physical Modeling in Geotechnical Centrifuge of Foundations Supported on Diatomaceous Soils

Physical Modeling in Geotechnical Centrifuge of Foundations Supported on Diatomaceous Soils

Experiment study on normalized compression behaviour of marine diatomaceous soil considering microstructure of biogenic silica

There are many sites in the world where diatom microfossils have been detected, but very little is known about their effect on sediment geotechnical properties. Diatomaceous soils (herein called “biogenic silica soils”) are usually composed by a mix of sand, fine-grained clay and diatom (and, or radiolarian). This paper presents an experimental investigation on the compression behaviour of biogenic silica-kaolin (BSi-K) clay mixtures and natural marine diatomaceous soils. The results show that the BSi composition dominates the compression when the BSi content is higher than 50%. The microstructure of biogenic silica frustules is first characterized and a skeletal void volume model (BSi-SVV model) is proposed. By using this model, the addition water in biogenic silica frustules can be quantitatively evaluated, which is up to 92.6% as the BSi content is 78%. It can be explained as the cause of high natural water content and low plasticity of diatomaceous soils. By introducing the effective void ratio, the compression curves can be normalized; furthermore, a new intrinsic compression line (BSi-ICL) suitable for BSi-K clay mixtures is developed based on the intrinsic compressibility concept of Burland (1990). It is considered as an extension of Burland's ICL. Finally, the effect of initial water content on the normalized compression behaviour is investigated. The findings in this study can provide a deeper insight into the geotechnical properties of marine diatomaceous soils.

Stiffness and strength parameters for the hardening soil model of a reconstituted diatomaceous soil

Centrifuge modelling has been widely used to study the geotechnical behaviour of structures built on soft soils and to calibrate and validate numerical models. In the finite element method (FEM), the mechanical behaviour of the soils is established through a constitutive model, and the correct selection and calibration of its parameters are essential to obtain accurate results. In this article, the mechanical parameters of an artificial reconstituted soft soil proposed for centrifuge modelling are obtained, calibrated and validated for the hardening soil (HS) model based on laboratory test results. The reconstituted soil consists of 50% kaolin clay and 50% diatomaceous soil from Bogotá, Colombia. First, geotechnical characterization of the reconstituted soil is presented. The model preparation technique to generate the effective stress profile for the centrifuge model is described. The strength and compressibility parameters are obtained from CU triaxial tests and a one-dimensional consolidation test, respectively. Finally, the obtained parameters are calibrated via explicit numerical modelling using the FEM and the SoilTest module of Plaxis software. It is concluded that the reconstituted artificial soft soil proposed herein mimics most of the natural lacustrine deposits of soft soils worldwide and can be modelled using the HS model for FEM analyses.

In Situ Experimental Study of Natural Diatomaceous Earth Slopes under Alternating Dry and Wet Conditions

Very few studies have focused on diatomaceous earth slopes along high-speed railways, and the special properties of diatomaceous earth under alternating dry and wet conditions are unknown. This paper studies diatomaceous earth in the Shengzhou area, through which the newly built Hangzhou–Taizhou high-speed railway passes, and the basic physical and hydraulic properties of diatomaceous earth are analyzed by indoor test methods. A convenient, efficient, and controllable high-speed railway slope artificial rainfall simulation system is designed, and in situ comprehensive monitoring and fissure observation are performed on site to analyze the changes in various diatomaceous soil slope parameters under rainfall infiltration, and to explore the cracking mechanisms of diatomaceous earth under alternating dry and wet conditions. The results indicate extremely poor hydrophysical properties of diatomaceous earth in the Shengzhou area; the disintegration resistance index values of natural diatomaceous earth samples subjected to dry and wet cycles are 1.8–5.6%, and the disintegration is strong. Comprehensive indoor tests and water content monitoring show that natural diatomaceous earth has no obvious influence when it contacts water, but it disintegrates and cracks under alternating dry and wet conditions. The horizontal displacement of both slope types mainly occurs within 0.75–2.75 m of the surface layer, indicating shallow surface sliding; after testing, natural slope crack widths of diatomaceous earth reach 10–25 mm, and their depths reach 40–60 cm. To guarantee safety during high-speed railway engineering construction, implementing proper protection for diatomaceous earth slopes is recommended.

Physical and mechanical behavior of fine soil according to the content of multispecies diatoms

The physical response and geotechnical properties of diatomaceous soils are not fully understood, data are sparse, and do not account for the effects of single and multispecies frustule content, origin, type, and variability. The main physical problem lies in the irregular response of diatomaceous soils due to micro and nano scale causes and its unexpected effects on the macro scale. This research compared the characteristics of a multispecies diatomaceous soil sample (North American origin) with other diatomaceous single-species soils. Six artificial soil mixtures were prepared, dosed by weight, in order to determine the influence of the content of frustules. The results show that the liquid limit of the samples is lower than that of the monospecies samples for any content of frustules. The pore areas of the monospecies samples are found to be 4 to 7 times larger than those of the North American soil. Void ratios and compressibility ranges are higher as the diatom content increases. The internal friction angle of diatomaceous soils varies in a non-linear tendency with respect to fossil content. For the studied soil at 100% fossil concentration, the internal friction angle reached 38.32°, a magnitude that is lower than the values reported for most of the monospecies contrast samples.

Case study of a driven pile foundation in diatomaceous soil. I: Site characterization and engineering properties

Diatomaceous soils are comprised of the silica frustules of diatom microalgae that are present in marine and lacustrine environments throughout the world. Owing to their unique origin, diatomaceous soils are typically characterized by high intraparticle porosity, complex particle shapes, and uniform mineralogy, causing them to exhibit atypical physical and engineering behaviors. A substantial deposit of diatomaceous silt was observed during site exploration for construction of the Buck Creek Bridge on OR140 near Klamath Falls, OR, USA. A comprehensive laboratory and in situ testing program indicated that the diatomaceous soil possessed “non-textbook” engineering properties. Specifically, tested samples had high liquid limits (≈100%–140%) with natural water contents at or near the liquid limit. Geologically, the soil is expected to be normally consolidated, yet high apparent overconsolidation ratios (OCR) (≈15–40) were observed both in oedometric consolidation tests and through cone penetration test (CPT) correlations. Standard penetration test (SPT) results show a corrected standard penetration resistance consistent with a medium-dense sand (i.e. ( N 1 ) 60 ≈ 25). CPT results include corrected tip resistances ( q t ) of approximately 7–10 MPa and excess pore pressures ( u 2 ) of up to 4 MPa. In CPT dissipation tests, pore water pressures (PWPs) returned to hydrostatic pressure in less than 1 h. In this work, we synthesize these seemingly disparate material properties in an attempt to infer appropriate engineering properties for the diatomaceous deposit at the Buck Creek Bridge and attempt to provide insight into the underlying reasons for the observed behavior.

Case study of a driven pile foundation in diatomaceous soil. II: Pile installation, dynamic analysis, and pore pressure generation

Abstract This paper presents the results from a case study highlighting the difficulties of pile driving in diatomaceous soils. In the companion (first) paper to this article, results of an extensive laboratory and in situ testing program were presented while the results from pile driving and further analysis of field observations were presented herein. Unexpected high pile rebound (HPR) was observed during driving of a closed-end pipe pile, with refusal occurring at a depth of less than 5 m. Subsequent open-ended piles were thus driven. Piezometer and case pile wave analysis program (CAPWAP) data were collected during driving of both closed- and open-end piles. Piezometer data indicated that negative pore water pressures (PWPs) were generated while the closed-ended pile exhibited high rebound. Results from in situ tests indicated change in material stiffness and strong dilative tendencies near the depth of refusal. A hypothesis for observed behavior was proposed that considers the soil beneath the pile as a medium with an effectively infinite bulk modulus.

Yerli Bazı Diyatom Topraklarının Laboratuvar Koşullarında Khapra, Trogoderma granarium Everts (Coleoptera: Dermestidae), Larvalarına Karşı Biyolojik Etkinliği

Bu çalışma ülkemizde son yıllarda tarımsal mücadelede önemi artan diyatom toprağının Khapra böceği (Trogoderma granarium Everts) larvalarına karşı biyolojik etkinliğinin araştırılması amacıyla yapılmıştır. Çalışma kontrollü şartlarda iki farklı sıcaklık (25 ve 30 °C) ve %50-65 nem ortamında, yerli (Aydın, Ankara illeri) ve ithal marka SilicoSec® diyatom toprakları olmak üzere dört farklı dozda (0, 1000, 1500 ve 2000 ppm), dört tekerrürlü olarak yürütülmüştür. Larvaların ölü-canlı sayımları uygulamadan 7, 14 ve 21 gün sonra kaydedilmiş, uygulamalardan 60 gün sonra F1 döl verimi her bir uygulama belirlenmiştir. Yerli diyatom topraklarının zararlı üzerinde biyolojik etkinliği, diyatomun uygulama dozu, maruz kalma süresi ve yüksek sıcaklık ile artış göstermiştir. En yüksek biyolojik etkinlik, 30 °C sıcaklıkta 21. günde 2000 ppm dozunda Aydın diyatomunda (%65.4), bunu takiben Ankara diyatomunda (%53.8) gerçekleşmiş, buna karşın SilicoSec®’te bu oran %11.9 olarak kayıt edilmiştir. Buna ek olarak 25 °C sıcaklıkta her üç diyatom toprağının Khapra larvaları üzerinde biyolojik etkinliği düşük düzeyde kalmıştır (en yüksek Ankara diyatomu 21. günde 2000 ppm dozda %30.7). Yeni nesil döl verimi 25 °C sıcaklık ve 60. gün sayımları sonucunda, her üç diyatom toprağı uygulanan tekerrürlerde F1 dölü açısından bir farklılık belirlenememiş (%15.2-18.7), buna karşın en düşük F1 döl verimi 30 °C sıcaklıkta 2000 ppm’de %9 olarak gerçekleşmiştir. Sonuç olarak yerli diyatom topraklarımızın SilicoSec®’e göre daha yüksek oranda Khapra böceği larvalarını öldürdüğü ve ümitvar olduğu belirlenmiştir.