Common problems and precautions in soft soil improvement with the Rapid Impact Compaction (RIC) method

I. Introduction

In the previous article, we introduced the three primary methods of soft ground improvement. This article focuses on the most common challenges encountered during Rapid Impact Compaction (RIC) construction, as well as the critical considerations that are often overlooked but have a significant impact on project performance.

II. The Most Overlooked Issue Before Construction: Not All Soft Soils Are Suitable for RIC

In many engineering projects, it is commonly assumed that any soft ground can be improved using Rapid Impact Compaction (RIC). However, this is a misconception. RIC is not suitable for every type of soil, and its effectiveness largely depends on soil characteristics, moisture content, groundwater conditions, and the nature of the fill material.

Without a thorough geotechnical investigation and proper assessment before construction, even high-performance equipment and well-executed construction procedures may fail to achieve the desired ground improvement results.

Therefore, a comprehensive evaluation of ground conditions should always be the first step toward a successful RIC project.

2.1 What Types of Soil Are Suitable for RIC?

Rapid Impact Compaction is a ground improvement technique that densifies soil by applying repeated high-frequency impact energy. The impacts rearrange soil particles, reduce void ratios, and increase soil density and bearing capacity.

RIC performs best in granular or partially granular soils where particle rearrangement can occur efficiently under repeated dynamic loading.

Typical applications include the following soil types.

① Engineered Fill

Engineered fill is widely used in industrial parks, logistics centers, port facilities, commercial developments, and residential construction projects.

Because the quality of fill placement often varies, these areas may contain loose zones, excessive voids, and insufficient bearing capacity. RIC effectively densifies the fill material, resulting in improved ground uniformity, increased stability, and enhanced load-bearing performance.

② Miscellaneous Fill

Miscellaneous fill typically consists of mixed materials such as crushed stone, sand, construction debris, and recycled materials. Due to its heterogeneous composition, the soil often exhibits uneven density and inconsistent engineering properties.

By applying repeated impacts according to a properly designed compaction grid, RIC reduces internal voids and improves the overall integrity and bearing capacity of the ground.

③ Sand and Silty Sand

Sand and silty sand possess good particle mobility, allowing soil grains to rearrange efficiently under dynamic impact loading.

As a result, RIC generally achieves excellent densification performance in these soils and is widely used for:

- Highway and roadway construction

- Airport pavements

- Container yards

- Storage yards

- Industrial platforms

④ Gravel and Coarse Granular Soils

For gravelly soils and coarse granular deposits, RIC further reduces the voids between particles, producing a denser and more stable foundation.

These materials typically respond well to dynamic compaction because of their high permeability and granular structure.

⑤ Loose Backfilled Areas

Many reclaimed or backfilled sites appear complete on the surface but remain insufficiently compacted beneath.

These loose fills are susceptible to excessive settlement after construction. In such cases, RIC serves as an effective secondary compaction method, significantly improving foundation performance before buildings, roads, or other infrastructure are constructed.

Overall, RIC is most effective in soils that can be densified through particle rearrangement under repeated impact loading. Soils with good drainage characteristics and a well-developed granular skeleton generally produce the best improvement results.

2.2 Which Soil Types Are Less Suitable for RIC?

Although RIC has a broad range of applications, it is not the ideal solution for every soft ground condition.

For soils with high moisture content and low permeability, impact energy cannot be transmitted efficiently through the ground, significantly reducing the effectiveness of the compaction process.

The following soil types generally produce limited improvement when treated with RIC.

① Very Soft Clay or Soft Mud

Very soft clay and soft mud typically have extremely high water content and very low shear strength.

Instead of becoming denser under repeated impacts, these soils tend to deform plastically. Consequently, increasing the number of impacts usually provides little improvement in bearing capacity.

② Saturated Mud and Silty Clay

Saturated fine-grained soils are highly susceptible to the generation of excess pore water pressure during impact loading.

If this pore water pressure cannot dissipate quickly, much of the impact energy is absorbed by the water rather than transferred to the soil skeleton.

As a result, compaction efficiency decreases significantly, and localized ground heave or deformation may occur.

③ High-Moisture Clay

Clay soils exhibit strong particle bonding and very low permeability.

Following impact loading, drainage occurs slowly, making it difficult for the soil to achieve effective densification within a short period.

Increasing impact intensity without considering soil behavior may disturb the soil structure rather than improve its engineering properties.

④ Organic Soil and Peat

Organic soils and peat are characterized by high compressibility, weak structural stability, and significant long-term settlement.

Their engineering behavior is governed primarily by organic matter rather than particle arrangement. Consequently, RIC generally cannot provide substantial improvement for these materials.

Alternative ground improvement methods—such as soil replacement, preloading, or deep soil mixing—are often more appropriate for these conditions.

2.3 Conduct a Thorough Site Investigation Before Construction

RIC is far more than simply operating an impact compaction machine. Successful projects depend on comprehensive geotechnical investigation, proper parameter selection, and careful construction planning.

Before construction begins, engineers should obtain the following information:

- Soil profile and thickness of each soil layer

- Groundwater level and seasonal fluctuations

- Natural moisture content and in-situ density of the soil

- Presence of underground obstructions such as construction debris, boulders, or old foundations

- Required bearing capacity and allowable settlement specified in the design

Based on the geotechnical investigation report, engineers can determine the most appropriate construction parameters, including:

- Impact energy

- Hammer weight

- Compaction grid spacing

- Number of impacts

- Quality control and testing procedures

Proper parameter selection is essential for achieving consistent compaction quality throughout the project.

2.4 Construction Recommendations

For projects with complex ground conditions, a trial compaction section is strongly recommended before full-scale construction begins.

During the trial, engineers should carefully record:

- Settlement after each impact

- Number of hammer blows

- Degree of densification

- Field test results

These data provide valuable information for optimizing construction parameters before expanding the operation across the entire project site.

Practical experience has shown that a properly executed trial compaction not only verifies whether RIC is suitable for the target ground conditions, but also minimizes the risk of costly rework, improves construction efficiency, and provides reliable data for quality control.

Ultimately, the success of an RIC project depends not on the equipment model or the number of impacts alone, but on accurately understanding site conditions before construction and selecting parameters that match the characteristics of the soil.

Only by adopting a site-specific approach can contractors fully realize the advantages of Rapid Impact Compaction—fast construction, high efficiency, cost-effectiveness, and reliable ground improvement performance.

III. Common Issue 1: Does a greater number of compaction passes always yield better results?

On RIC (Rapid Impact Compaction) construction sites, a very common misconception is: "One more pass can't hurt—the more blows we apply, the denser the ground will be."

In reality, this view is not entirely correct. RIC construction does not simply rely on increasing the number of impacts to improve ground quality. rather, it requires reasonable control of the number of compaction passes and energy input based on soil layer characteristics and construction feedback. Once the soil has reached its optimum densification state, continued repeated impacts not only have limited effect but may also reduce construction efficiency, increase project costs, and even adversely affect the foundation.

3.1 Why is more impact blows not always better?

The working principle of RIC is to use high-frequency impact loads to rearrange soil particles, reduce voids, and improve density and bearing capacity.

In the early stage of construction, the soil is relatively loose, and each impact produces a noticeable compaction effect, with generally large settlements and rapid increases in bearing capacity.

As construction proceeds, the voids within the soil gradually decrease, particle arrangement tends to stabilise, and the densification effect per unit impact begins to decline. This means that each additional blow yields progressively less improvement in ground quality.

This phenomenon is commonly referred to in geotechnical engineering as diminishing marginal returns. When the soil has already approached its optimum density, further impacts dissipate more energy in equipment vibration, elastic deformation of the soil, and energy attenuation, rather than further enhancing ground quality.

In other words, there is no rule that "more blows means safer". instead, there exists a more economical and reasonable optimum construction range for the number of impacts.

3.2 What is the effective number of blows?

The so-called effective number of blows refers to the range within which each impact produces a significant compaction effect on the ground.

During the effective compaction stage, the following characteristics are typically observed:

- Significant surface settlement still occurs after each impact.

- The penetration of the compactor gradually decreases, but the trend is relatively stable.

- Ground density continues to improve.

- Subsequent test results show continuously increasing bearing capacity.

When construction enters the later stage, the following situations often appear on site:

- Settlement changes little after several consecutive impacts.

- Penetration depth tends to stabilise.

- تصبح الزيادة في درجة التماسك أصغر فأصغر .

- تقترب قدرة التحمل من متطلبات التصميم.

يشير هذا إلى أن التربة قد أكملت عملية تكثيفها بشكل أساسي، وأن البناء الإضافي ذو قيمة اقتصادية محدودة.

لذلك ينبغي على العاملين في مجال البناء التركيز على "العدد الفعال للضربات" بدلاً من السعي الأعمى وراء المزيد من عمليات الرص.

3.3 يُعدّ إدخال الطاقة الأمثل أكثر أهمية من عدد الضربات

لا تعتمد جودة بناء RIC على عدد الضربات فحسب، بل تعتمد أيضًا على مقدار الطاقة الفعالة التي تمتصها التربة فعليًا.

تشمل العوامل المؤثرة على مدخلات الطاقة ما يلي:

- وزن المطرقة .

- معدل تكرار التأثير .

- الطاقة لكل ضربة .

- سمك طبقة التربة .

- نسبة رطوبة التربة .

- مستوى المياه الجوفية.

تختلف الطبقات المختلفة اختلافاً كبيراً في قدرتها على امتصاص طاقة الصدمات. فعلى سبيل المثال، يمكن ضغط الرمال المفككة بسرعة نسبياً، بينما قد يمتص الطين عالي الرطوبة أو الطمي المشبع كمية كبيرة من طاقة الصدمات دون تحقيق تأثير الضغط المطلوب.

لذلك، في بناء الخرسانة المسلحة بالألياف الزجاجية، ينبغي تحديد معايير البناء بشكل معقول بناءً على بيانات التحقيق في الموقع ونتائج الضغط التجريبي، بحيث تتناسب مدخلات الطاقة مع ظروف الأرض، بدلاً من مجرد زيادة عدد الضربات.

3.4 المشاكل المحتملة الناجمة عن الضغط المفرط

تميل العديد من وحدات البناء إلى إضافة عمليات دك إضافية تتجاوز متطلبات التصميم سعياً وراء "السلامة". ومع ذلك، قد تنطوي هذه الممارسة على المخاطر التالية:

1) زيادة تكاليف البناء

كل عملية تمرير إضافية تعني المزيد من ساعات تشغيل الآلات، واستهلاك الوقود، وتكاليف العمالة، دون أن ينتج عنها بالضرورة تحسين مماثل في الجودة.

2) انخفاض كفاءة البناء

تُستخدم تقنية الضغط المعزز (RIC) غالبًا لمعالجة التربة في المساحات الكبيرة. إن الإفراط في الضغط في كل نقطة ضغط سيؤدي إلى تمديد الجدول الزمني الإجمالي بشكل ملحوظ ويؤثر على تقدم المشروع.

3) احتمال زيادة الضغط

بالنسبة لبعض أنواع التربة الرملية أو طبقات الردم، قد تؤدي التأثيرات المفرطة إلى اضطراب بنية التربة المحلية، بل وقد تتسبب في انتفاخ السطح أو الإزاحة الجانبية أو التشققات المحلية، وهو أمر ضار بتكوين أساس موحد ومستقر.

4) زيادة التأثير على البيئة المحيطة

كلما زاد عدد الضربات الموجهة، زادت مدة اهتزازات البناء والضوضاء، مما يزيد من التأثير على المباني المجاورة والمرافق تحت الأرض والسكان القريبين.

لذلك، فإن التحكم المعقول في عدد مرات المرور بالدمك لا يضمن جودة البناء فحسب، بل يساعد أيضًا في تحسين اقتصاديات المشروع وسلامته.

3.5 How to determine when to stop compaction?

During RIC construction, whether to stop work at a given compaction point should not be based solely on experience but should be determined by comprehensive analysis of field monitoring data.

The following indicators are typically used as key references:

1) Settlement change

Record the settlement value of the compaction point after each impact. If the incremental settlement after several consecutive blows has become very small, it indicates that soil densification is stabilising, and stopping can be considered.

2) Hammer penetration

Penetration directly reflects the degree of soil densification. When the penetration depth gradually stabilises and continuously shows only small changes, it usually indicates that the area has approached its optimum compaction state.

3) Compaction degree or bearing capacity tests

For important projects, the results of compaction tests, dynamic penetration tests, static cone penetration tests, or plate load tests should be combined to confirm that the foundation meets the design requirements, rather than relying solely on settlement data during construction.

4) Control criteria established by trial compaction

Before formal construction, trial compaction should be carried out to establish reasonable construction parameters and control criteria, including recommended number of blows, settlement control values, and testing standards. During large-scale construction, quality control should be based primarily on the trial compaction results, rather than arbitrarily increasing the number of passes.

IV. Common Issue 2: Does a higher impact frequency always mean better results?

During RIC (Rapid Impact Compaction) construction, in addition to the number of compaction passes, the impact frequency is also an important factor affecting construction quality. Many contractors deliberately increase the impact frequency in order to shorten the construction period and improve equipment utilisation, hoping to complete more compaction points in a shorter time. However, too high an impact frequency does not necessarily mean higher construction efficiency. on the contrary, it may reduce the effectiveness of ground improvement.

The core objective of RIC construction is to ensure that impact energy is fully transmitted into the soil mass, allowing soil particles to rearrange and reach an optimum dense state. If one pursues construction speed blindly while ignoring the soil's response time to impact loading, energy utilisation efficiency will decrease, and the final bearing capacity may even be compromised.

4.1 Why can't impact frequency be increased without limit?

RIC uses continuous high-frequency impacts to transfer mechanical energy into the foundation, gradually compacting loose soils. During this process, the soil not only undergoes particle rearrangement but also experiences a series of complex processes, including air expulsion, changes in pore water pressure, and stress redistribution.

If the time interval between successive impacts is too short, the soil has not yet completed its internal adjustment before the next impact arrives. This can lead to the following problems:

1) Insufficient time for air to escape

For strata containing significant air voids, such as backfill, sandy soils, and miscellaneous fills, the air in the pores needs to be gradually expelled during impact. If impacts are too frequent, the air cannot escape in time, and part of the impact energy will be absorbed by the compressed air, thereby reducing compaction efficiency.

2) Inadequate dissipation of pore water pressure

When the foundation has a high moisture content or a shallow groundwater table, continuous impacts will rapidly increase the internal pore water pressure. If there is insufficient time for pressure dissipation, the impact energy will be more effectively absorbed by the pore water rather than used for rearranging soil particles, leading to a marked decrease in compaction effectiveness. In extreme cases, this may even cause local softening or significant lateral displacement, adversely affecting construction quality.

3) Unstable soil stress regime

Each impact creates a new stress distribution within the soil, which requires a certain amount of time for stress transfer and re-equilibration. If the impact rhythm is too rapid, the stress from the previous impact has not yet been released before the next one superimposes, reducing the effective depth of compaction and making the treatment uneven.

Therefore, RIC construction is not simply a matter of "the faster the better". the soil must be given sufficient "recovery time" to fully absorb the energy from each impact.

4.2 Fast construction does not equal high efficiency

In practice, many contractors increase the hydraulic system's operating frequency to keep the equipment running at high intensity in order to meet tight schedules. On the surface, the number of impacts per unit time increases, but the actual improvement in ground quality does not necessarily improve correspondingly.

For example, when settlement at a compaction point has already begun to slow down, if high-frequency continuous impacts are still maintained, the additional energy may merely increase equipment vibration and noise without further enhancing soil density.

Moreover, prolonged high-frequency operation may also cause the following problems:

1) Increased hydraulic system temperature, affecting equipment stability.

2) Accelerated wear of mechanical components, increasing maintenance costs.

3) Prolonged construction vibration, causing greater impact on adjacent buildings and underground utilities.

4) Increased operator fatigue, leading to higher risks of errors and safety hazards.

Therefore, truly efficient RIC construction should pursue effective compaction efficiency, not simply the mechanical working speed.

4.3 Different soil layers require different construction rhythms

Different types of soil layers have significantly different response times to impact loading, so the construction rhythm should be adjusted accordingly.

1) Sandy soils and gravelly layers

Sandy soils have good drainage properties and low interparticle friction. they can achieve particle rearrangement relatively quickly after impact. Therefore, the impact frequency can be increased appropriately to improve construction efficiency.

2) Silty soils

Silty soils have drainage properties intermediate between sand and clay. A moderate impact rhythm should be maintained to balance construction efficiency while avoiding pore water pressure build-up that could affect compaction quality.

3) High-moisture content clays

Clays have low permeability and slow drainage rates. Continuous impacts can easily generate high pore water pressures. Therefore, the construction frequency should be reduced appropriately, and rest periods should be increased based on site conditions to allow the soil to gradually recover to a stable state.

4) Miscellaneous fills

Miscellaneous fills have complex compositions, often containing crushed stone, construction debris, and other materials, resulting in highly variable layer responses. During construction, close field observation should be maintained, and the impact speed should be adjusted in real time according to settlement changes, rather than applying a fixed rhythm.

It is thus clear that there is no single universal impact frequency suitable for all projects. construction parameters must be optimised based on geological conditions and trial compaction results.

4.4 How to reasonably control impact frequency?

To ensure RIC construction quality, the following aspects should be emphasised during construction:

1) Control the number of impacts per minute

Equipment manufacturers usually provide a recommended operating frequency range, but in practice, this should be adjusted according to soil properties, groundwater conditions, and trial compaction data, rather than always running at the maximum frequency.

2) Maintain a steady construction rhythm

Avoid frequent acceleration or deceleration during construction. A uniform and stable impact rhythm should be maintained so that each impact can play its full role.

3) Arrange rest periods appropriately

For areas with high moisture content or soft strata, appropriate rest periods can be introduced after a certain number of impacts to allow pore water pressures to dissipate gradually before continuing. Although this may appear to extend the time per compaction point, it helps improve the overall compaction effect.

4) Adjust in real time based on field monitoring

Construction personnel should record settlement at compaction points, hammer penetration depths, and surface changes in real time. When settlement increases slow down, pore pressures remain high, or surface anomalies appear, the construction frequency should be adjusted promptly rather than maintaining the original speed.

V. Common Issue 3: Unreasonable construction grid layout

In RIC (Rapid Impact Compaction) construction, many people focus their attention on equipment type, hammer weight, impact frequency, and other parameters, while overlooking another equally important factor—the construction grid layout.

In fact, RIC is a areal ground treatment method, where each compaction point can only effectively compact the soil within a certain radius around it. If the layout of compaction points is unreasonable, even if the single-point construction quality fully meets the requirements, the entire treatment area may still have uneven density, adversely affecting the final bearing capacity and settlement control performance.

Therefore, rational planning of compaction point spacing and grid pattern is a critical step in ensuring RIC construction quality.

5.1 Why is the construction grid so important?

RIC construction does not continuously compact the foundation. rather, it uses the impact action at individual compaction points so that the zones of influence of adjacent points overlap, ultimately forming a continuous and uniformly treated area.

Each impact creates a stress-diffusion zone within the soil over a certain range. Only when the influence zones of adjacent compaction points overlap appropriately can the entire construction area achieve uniform densification.

If the spacing between compaction points is designed unreasonably, it may lead to insufficient compaction in some areas or excessive compaction in others, affecting not only construction quality but also increasing project costs.

Therefore, grid layout essentially seeks the best balance among construction efficiency, engineering quality, and construction cost.

5.2 Common mistake 1: Excessive spacing between compaction points

Excessive spacing between compaction points is one of the most common problems in RIC construction.

يلجأ بعض المقاولين، بهدف تقليل حجم العمل وتقصير مدة الإنشاء، إلى زيادة المسافة بين نقاط الدمك عمدًا، على أمل أن تغطي كل ضربة مساحة أكبر. إلا أن نصف قطر التأثير الفعال لكل نقطة دمك محدود. فعندما تتجاوز المسافة نطاقًا معقولًا، لن تتمكن نقاط الدمك المتجاورة من تشكيل منطقة دمك متصلة.

قد يؤدي هذا إلى المشاكل التالية:

1) المناطق غير المكتملة بين نقاط الضغط

تتشكل "مناطق فارغة" غير مضغوطة بين نقاط الضغط. وعلى الرغم من اكتمال البناء بشكل عام، إلا أن هذه المناطق تظل رخوة نسبياً وعرضة للهبوط الموضعي لاحقاً.

2) كثافة الأساس غير المتساوية

تتميز بعض المناطق بتماسك جيد بينما تفتقر مناطق أخرى إلى الكثافة الكافية، مما يؤدي إلى توزيع غير متساوٍ لقدرة تحمل الأساس. وعند تطبيق حمل المبنى، يزداد خطر الهبوط التفاضلي بشكل ملحوظ.

3) تباين كبير في نتائج الاختبار

أثناء قبول المشروع، قد تظهر نقاط الاختبار المختلفة اختلافات كبيرة في قدرة التحمل، مما يزيد من احتمالية الحاجة إلى عمليات ضغط وإعادة عمل إضافية، ويؤثر على الجدول الزمني للمشروع.

لذلك، لا ينبغي تحديد تباعد نقاط الدمك بناءً على الخبرة الإنشائية فقط، ولكن ينبغي تحسينه بناءً على نتائج الدمك التجريبي وظروف التربة ومتطلبات التصميم.

5.3 الخطأ الشائع الثاني: تصميم نقاط الضغط الكثيف للغاية

على عكس التباعد المفرط، يقوم بعض المقاولين بتقليل المسافة بين نقاط الضغط عمداً لضمان جودة البناء، معتقدين أن "المزيد من النقاط لا يمكن أن يسبب أي ضرر".

في الواقع، يؤدي التوزيع الكثيف للغاية لنقاط الضغط إلى العديد من المشاكل.

1) العمل المتكرر مع استهلاك منخفض للطاقة

عندما تكون نقاط الضغط المتجاورة قريبة جدًا، فإن معظم طاقة التأثير اللاحقة يتم تطبيقها فعليًا على المناطق التي تم ضغطها بالفعل، مما يساهم بشكل ضئيل في الضغط الإضافي ويؤدي إلى هدر الطاقة.

2) زيادة كبيرة في تكاليف البناء

زيادة نقاط الضغط تعني ساعات تشغيل أطول للآلات، واستهلاك أعلى للوقود، وتكاليف عمالة أكبر، وزيادة في تآكل المعدات.

3) مدة بناء ممتدة

بالنسبة للمشاريع مثل الموانئ والمجمعات اللوجستية والمصانع الصناعية الكبيرة التي تتطلب معالجة عشرات الآلاف من الأمتار المربعة من الأساسات، فإن زيادة عدد نقاط الضغط تؤثر بشكل مباشر على الجدول الزمني للبناء بشكل عام.

4) احتمال حدوث ضغط زائد في المناطق المحلية

قد تؤدي التأثيرات المستمرة عالية الطاقة في نفس المنطقة إلى اضطراب بنية التربة المحلية، بل وقد تتسبب في انتفاخ السطح أو الإزاحة الجانبية أو غيرها من المشكلات التي تضر بتكوين أساس موحد ومستقر.

Therefore, a denser layout of compaction points is not necessarily better. rather, each impact should be used to its maximum effective potential.

5.4 Common RIC construction grid patterns

Depending on project characteristics and design requirements, RIC construction typically adopts one of the following grid layout patterns.

(1) Square grid

The square grid is the most common layout.

Its characteristics are that compaction points are evenly arranged in orthogonal directions, making setting-out simple, measurement convenient, and construction efficiency high.

Suitable for:

- Industrial plant foundations.

- Large-area site backfill.

- Road subgrades.

- Stockyard projects.

For projects with relatively uniform strata and regular construction areas, the square grid usually provides a good balance between construction efficiency and compaction quality, and is therefore the most widely used.

(2) Triangular grid

A triangular grid (equilateral triangle layout) allows each compaction point to have a more uniform zone of influence with multiple surrounding points, reducing compaction blind spots.

Compared with the square grid, it provides more uniform coverage and is particularly suitable for:

- Projects requiring high foundation uniformity.

- Areas with significant stratigraphic variations.

- Important foundation works with high bearing capacity requirements.

Although setting-out is relatively more complex, the overall compaction uniformity is generally better than that of a conventional square layout.

(3) Quincunx (staggered) grid

A quincunx layout typically adds staggered compaction points on the basis of a square grid, so that the second pass is placed between the first-pass points, further improving compaction uniformity.

This layout has the following features:

- Effectively reduces missed compaction areas.

- Improves overall density uniformity.

- Works well for treating non-uniform fills.

Therefore, the quincunx layout is widely used in large backfill projects, port stockyards, and soft fill foundation treatment.

5.5 How to select the grid pattern for different projects?

There is no single grid pattern that fits all projects in RIC construction. Designers should consider the project characteristics comprehensively.

For large-area backfill sites, industrial parks, and logistics bases, a square grid is usually preferred to enhance construction efficiency and surveying convenience.

For building foundations with high bearing capacity requirements and strict settlement control, a triangular grid may be adopted to improve compaction uniformity.

For projects with significant variations in fill thickness, poor soil uniformity, or local soft zones, a quincunx layout can be used to reduce compaction dead corners through staggered construction and improve overall treatment effectiveness.

In addition, before formal construction, compaction point spacing should be optimised based on trial compaction results, rather than simply copying experience from other projects. This is because soil type, groundwater level, fill thickness, and design bearing capacity requirements all affect the optimal grid parameters.

5.6 Grid layout should be combined with construction monitoring

It should be emphasised that the construction grid is not fixed and cannot be adjusted once determined.

During the actual construction process, contractors should dynamically adjust compaction point spacing and construction sequence based on field monitoring data. For example, if excessive settlement is observed in a certain area, additional local compaction points may be added. conversely, for areas that have already met design requirements, no further compaction is needed.

Such dynamic adjustments based on monitoring data not only improve the quality of ground treatment but also help reduce construction costs and achieve a more economical and efficient construction organisation.

VI. Common Issue 4: Neglecting settlement monitoring during construction

RIC (Rapid Impact Compaction) is a typical dynamic ground treatment method. Unlike static pressing or rolling compaction, the effectiveness of RIC construction cannot be judged simply by equipment running time, number of impacts, or treated area. rather, it must be evaluated through the foundation's actual response to impact loading.

However, in practice, some contractors, in order to expedite the schedule, simply complete the prescribed number of impacts without recording settlement data, or even rely entirely on the operator's experience to decide when to stop. This "hit-and-run" approach not only makes it difficult to ensure treatment quality but also easily leads to rework or inadequate compaction.

Therefore, establishing a comprehensive settlement monitoring system is an essential part of quality control in RIC construction.

 

6.1 Why is settlement monitoring essential in RIC construction?

The essence of RIC is to use continuous impacts to rearrange soil particles and reduce voids, thereby improving foundation density and bearing capacity. The most direct manifestation of this process is the change in settlement at the ground surface.

Each impact causes a certain amount of compressive deformation in the foundation. In the early stage, because the soil is relatively loose, settlements are usually large. as construction proceeds and the soil gradually becomes denser, the increment in settlement continuously decreases and eventually reaches a stable state.

Thus, settlement data actually reflect the internal densification process of the soil and are one of the most intuitive and reliable bases for judging construction effectiveness.

Without settlement monitoring, construction personnel cannot accurately determine:

- Whether the foundation has reached its optimal compaction state.

- Whether further impacts are needed.

- Whether there are locally insufficiently compacted or anomalous areas.

- Whether the design bearing capacity requirements can be met.

In other words, RIC construction without monitoring data support can easily become "experience-based" work, compromising both quality and cost.

 

6.2 What key indicators should be monitored?

To accurately track the compaction process, the following indicators are typically recorded in RIC construction.

(1) Settlement per blow

Settlement per blow refers to the immediate settlement caused by each individual impact.

This indicator reflects the actual compaction effect of each impact.

Generally:

In the early stage, settlement per blow is large.

As the soil densifies, settlement per blow progressively decreases.

When the settlement variation over several consecutive impacts tends to stabilise, it indicates that the soil has essentially completed densification.

Therefore, settlement per blow is an important basis for deciding whether to continue construction.

 

(2) Cumulative settlement

Cumulative settlement is the sum of settlements from all impacts.

It allows an understanding of the overall compaction degree of the compaction point and enables comparison with trial compaction data.

If the cumulative settlement is significantly lower than that of the trial compaction, it may indicate that the soil layer is already relatively dense. if it is much higher, it may suggest the presence of local weak layers, poor backfill quality, or underground obstructions.

 

(3) Final stable value

The final stable value is the settlement that remains essentially unchanged after several consecutive impacts.

When construction reaches this state, it generally means:

- Particle rearrangement is essentially complete.

- Foundation density has stabilised.

- The benefit of further impacts is markedly diminished.

At this point, combined with design requirements and field test results, a decision can be made on whether to terminate work at that compaction point.

 

6.3 Complete construction records are crucial

Settlement monitoring is not just about taking measurements. it must also be accompanied by thorough documentation throughout the process.

A complete RIC construction record should typically include:

- Number and location of each compaction point.

- Construction date and crew.

- Equipment used and construction parameters.

- Number and sequence of impacts.

- Settlement values after each impact.

- Cumulative settlement.

- Final settlement data at cessation.

- Records of any site anomalies.

These data are not only useful for process control but also serve as important evidence for subsequent quality acceptance, technical analysis, and project archival documentation.

For large projects, digital construction management systems can be used to input data from each compaction point in real time, generating settlement curves and construction maps, making the entire process more visual and efficient.

 

6.4 Learning to interpret settlement curves for construction status assessment

Beyond recording data, it is even more important to learn how to analyse them.

Normally, the settlement curve for a proper compaction point should show a trend of "rapid initial settlement, then gradually slowing down and stabilising."

If the following situations occur, construction personnel should pay attention:

- Settlement remains consistently large, indicating possible weak interlayers that require further treatment.

- Sudden increases in settlement may indicate underground voids, construction debris, or other anomalies.

- Little or no change in settlement may suggest the soil is already dense or that equipment parameters are improperly set.

By analysing settlement curves, construction parameters can be adjusted in a timely manner, rather than mechanically following a fixed number of impacts.

 

VII. Common Issue 5: Underestimating the influence of groundwater

In RIC construction, many engineers focus on hammer weight, number of impacts, and grid layout, but often overlook another critical factor—groundwater.

In fact, the groundwater level directly affects the propagation of impact energy, the drainage capacity of the soil, and the final compaction effect. This is especially true in coastal areas, near rivers, in ports and wharves, and on sites with abundant groundwater, where groundwater often becomes a decisive factor in the success or failure of RIC construction.

 

إذا لم يتم التحقق من ظروف المياه الجوفية بشكل كافٍ قبل البناء، أو إذا لم يتم اتخاذ أي تدابير مقابلة أثناء العملية، فقد لا يؤدي زيادة عدد التأثيرات إلى تلبية متطلبات التصميم.

 

7.1 لماذا تؤثر المياه الجوفية على بناء مراكز إعادة التأهيل؟

تعتمد آلية RIC على استخدام أحمال الصدمات لإعادة ترتيب جزيئات التربة، مما يحقق التكثيف والتدعيم.

ومع ذلك، عندما تحتوي التربة على كمية كبيرة من المياه الجوفية، فإن جزءًا من طاقة الصدمة لا يؤثر فقط على جزيئات التربة ولكن أيضًا على الماء الموجود في المسام.

بما أن الماء غير قابل للانضغاط عمليًا، فعندما يكون تردد الصدم مرتفعًا، يرتفع ضغط ماء المسام بسرعة ولا يمكن تبديده على الفور، مما يقلل من الإجهاد الفعال ويعيق تكوين بنية كثيفة مستقرة.

وبعبارة بسيطة، فإن بعض الطاقة التي ينبغي استخدامها لضغط التربة "تمتصها" المياه الجوفية، مما يقلل من كفاءة البناء.

 

7.2 المشاكل المحتملة عند ارتفاع منسوب المياه الجوفية

عندما يكون منسوب المياه الجوفية مرتفعاً، قد يواجه بناء RIC المواقف التالية.

(1) زيادة خطر التسييل

بالنسبة للرمال المشبعة والرمال الطينية، تتسبب الصدمات المستمرة في زيادة سريعة في ضغط مياه المسام، مما قد يقلل من الإجهاد الفعال، وفي الحالات الشديدة، يؤدي إلى التميع الموضعي.

تفقد التربة المسيلة استقرارها مؤقتًا، مما لا يقلل من فعالية الضغط فحسب، بل قد يتسبب أيضًا في انتفاخ الأرض، والإزاحة الجانبية، ومشاكل أخرى.

 

(2) تخفيف طاقة الصدمة

يؤدي وجود المياه الجوفية إلى إضعاف كفاءة انتشار موجات الصدم عبر التربة، مما يتسبب في تبديد جزء من الطاقة في تغيرات ضغط المياه المسامية بدلاً من ضغط التربة بشكل فعال.

تتجلى هذه الظاهرة بشكل خاص في الأساسات اللينة ذات المحتوى الرطوبي العالي.

 

(3) صعوبات الصرف

تتميز التربة ذات النفاذية المنخفضة مثل الطين والطمي بقدرة تصريف ضعيفة، كما يصعب تبديد ضغوط المياه المسامية المتولدة أثناء البناء على الفور.

إذا استمر البناء بسرعة عالية، فلن تنخفض كفاءة الرص فحسب، بل قد تبقى التربة المحلية تحت ضغط مسامي عالٍ لفترة طويلة، مما يؤثر على الجودة اللاحقة.

 

(4) انخفاض استقرار البناء

عندما يكون هناك تجمع كبير للمياه على السطح، يمكن أن تتأثر حركة المعدات واستقرارها، مما يزيد من المخاطر مثل غرق المسار وميله.

 

7.3 كيف يمكن التخفيف من تأثير المياه الجوفية على البناء؟

على الرغم من أنه لا يمكن تجنب المياه الجوفية تمامًا، إلا أنه يمكن تقليل تأثيرها من خلال تنظيم البناء بشكل صحيح.

(1) نزح المياه عند الضرورة

بالنسبة للمشاريع ذات منسوب المياه الجوفية المرتفع، يمكن تطبيق أساليب نزح المياه مثل نزح المياه من الآبار النقطية أو نزح المياه من الآبار العميقة قبل البناء لخفض مستوى المياه الجوفية بشكل مناسب.

This not only facilitates the propagation of impact energy but also increases effective stress in the soil and improves compaction results.

 

(2) Installing drainage ditches and sumps

For large construction sites, temporary drainage ditches, catch basins, or sump pits can be arranged in advance to promptly remove any water accumulating during construction.

Keeping the work area dry helps equipment operate stably and is also beneficial for foundation compaction.

 

(3) Using staged construction

For high-moisture content soil layers, a "construction – rest – re-construction" approach can be adopted.

After completing a round of impacts, a rest period is allowed to let pore water pressures dissipate gradually before proceeding with the next stage. Although this may extend the overall construction period, it often leads to better foundation treatment results.

 

(4) Adjusting construction parameters according to groundwater conditions

When the groundwater level is high, the impact frequency should be appropriately reduced, the construction rhythm controlled, and the construction scheme dynamically optimised based on on-site settlement monitoring and trial compaction results, rather than simply copying parameters from other projects.

 

VIII. Common Issue 6: Construction too close to existing buildings

RIC (Rapid Impact Compaction) is a construction method that uses high-frequency, high-energy impacts to densify and reinforce foundations. Compared with conventional rolling compaction, RIC can treat deeper loose soils, but at the same time, its impact energy propagates through the surrounding soil in the form of vibration waves. Therefore, when the construction area is adjacent to existing buildings, underground utilities, or other important facilities, the construction risks increase significantly.

In practice, due to space constraints on some projects, contractors place RIC equipment close to buildings in order to improve efficiency. Without adequate investigation and monitoring, even if the ground improvement meets design requirements, adverse effects on the surrounding environment may still occur.

Therefore, during RIC construction, controlling the zone of influence and safeguarding the safety of adjacent structures and infrastructure are important aspects that cannot be overlooked in construction planning.

 

8.1 Why is construction too close to buildings risky?

During RIC operations, the continuous impacts of the hammer generate vibration waves in the soil. These vibrations propagate through the soil layers to the surroundings, and the propagation distance and degree of influence depend on factors such as soil type, groundwater level, impact energy, and the type of building foundation.

If the construction area is too close to a building, the following risks may arise.

(1) Ground vibration effects

Ground vibration is one of the most direct effects of RIC construction.

The vibration waves generated by impacts can be transmitted to nearby buildings, causing slight trembling. For ordinary reinforced concrete buildings, short-term, low-amplitude vibrations usually do not cause obvious damage. However, for old buildings, historical structures, masonry-concrete structures, or plants housing precision equipment, prolonged or stronger vibrations may cause cracks to widen, surface finishes to fall off, or even affect normal use.

In addition, construction vibrations may affect vibration-sensitive facilities such as hospitals, laboratories, and data centres, so the feasibility of construction should be evaluated in advance.

 

(2) Construction noise effects

RIC equipment produces considerable mechanical noise and impact sounds during continuous operation.

If the construction area is near residential districts, schools, offices, or commercial zones, sustained noise may disturb the daily work and life of nearby people, potentially leading to complaints.

Therefore, for urban renewal projects or densely populated areas, construction hours should be reasonably arranged, and necessary noise-reduction measures should be taken in accordance with local environmental requirements.

 

(3) Risk of building settlement

Impact loading not only causes vibrations but can also alter the stress distribution in the surrounding soil.

If adjacent buildings have shallow foundations or are themselves located on loose fill or soft ground, additional local settlement may occur during construction, and in severe cases, differential settlement of the building may result.

Although this is not a common occurrence, sufficient attention should still be paid to important buildings to avoid structural safety issues caused by construction disturbance.

 

(4) Impact on underground utilities

Underground water supply, gas, power, communication, and drainage pipelines are usually buried in shallow soils and are sensitive to vibrations.

When RIC construction is too close to underground pipelines, sustained impacts may cause:

- Loose pipe joints.

- Cracking of aged pipelines.

- Local settlement of manholes and inspection chambers.

- Damage to cable protective layers.

Pipes and cables that are old or lack complete records are particularly vulnerable, so they must be investigated in advance and protective measures taken.

 

8.2 Pre-construction risk investigation

To reduce construction risks, a comprehensive survey of the construction area and its surroundings should be conducted before formal RIC work begins.

 

(1) Building survey

The survey should include:

- Locations and distances of surrounding buildings.

- Structural types (steel structure, frame structure, masonry-concrete structure, etc.).

- Age and current condition of buildings.

- Foundation types (shallow foundation, pile foundation, etc.).

- Whether existing cracks or settlement records exist.

If necessary, photographic documentation, crack mapping, or third-party inspections of adjacent buildings can be carried out to provide a reference for subsequent monitoring during construction.

 

(2) Underground utility survey

Before construction, comprehensive underground utility records should be collected, and on-site detection should be used to confirm the location, burial depth, and type of utilities.

Special attention should be given to:

- Gas pipelines.

- Main water supply pipes.

- Power cables.

- Communication fibre-optic cables.

- Stormwater and sewer lines.

For critical utilities, specific protection measures should be developed, and if necessary, the construction area should be adjusted or the compaction point layout optimised.

 

8.3 Enhanced monitoring during construction

Even if the pre-construction investigation is completed, dynamic monitoring during construction cannot be neglected.

(1) Vibration monitoring

Vibration monitors should be installed on adjacent buildings to record vibration velocity or amplitude in real time.

Once monitoring data approach warning thresholds, construction parameters should be adjusted promptly, such as reducing impact frequency, decreasing energy per blow, or altering the construction sequence, to prevent vibration levels from continuing to rise.

 

(2) Settlement monitoring

For important buildings close to the construction area, settlement observation points can be set up to regularly monitor settlement changes in the building foundation and surrounding ground.

If abnormal settlement rates are detected, the cause should be analysed immediately, and construction should be suspended if necessary while appropriate remedial measures are taken.

 

(3) Enhanced site inspection

In addition to instrument monitoring, designated personnel should regularly inspect building exterior walls, floor slabs, and areas around underground utilities for cracks, leaks, or local deformations, so that problems can be detected and addressed early.

 

8.4 Adjusting construction parameters when necessary

When the construction area is close to buildings, normal operating parameters should not be used without modification. instead, adjustments should be made according to site conditions.

For example:

- Reduce impact energy per blow.

- Slightly reduce hammer weight or drop height.

- Lower impact frequency.

- Increase spacing between compaction points.

- Carry out construction in zones or stages.

Although these measures may somewhat reduce construction efficiency, they effectively minimise construction disturbance and balance ground treatment effectiveness with surrounding environmental safety.

 

IX. Common Issue 7: Incorrect selection of equipment parameters

RIC construction quality depends not only on the construction technique but also on proper equipment parameter configuration.

 

In practice, some projects select lower-energy equipment to reduce costs, while others believe that "bigger equipment is better" and blindly increase hammer weight and impact energy. Both approaches can lead to unsatisfactory results.

There is no "one-size-fits-all" set of RIC equipment parameters. Different strata, different treatment depths, and different project objectives all require matching construction parameters. Only by matching equipment parameters to ground conditions can the high efficiency and cost-effectiveness of the RIC method be fully realised.

 

9.1 Common mistake 1: Hammer weight too low

Hammer weight directly determines the energy that can be transmitted to the foundation in a single impact.

If the hammer is too light, although the equipment can maintain a high impact frequency, the energy per blow is limited. For thick backfill layers or deep loose soils, the effective depth of influence is shallow, making it difficult to meet design requirements.

Typical symptoms include:

- Insufficient compaction depth.

- Surface densification while deeper layers remain loose.

- Limited improvement in bearing capacity.

- Difficulty meeting subsequent test requirements.

Therefore, when treating thick fills or projects with high bearing capacity requirements, hammer weight should be selected based on design requirements, not solely on equipment cost or transport convenience.

 

9.2 Common mistake 2: Hammer weight too high

Contrary to the above, some contractors believe that increasing hammer weight improves efficiency and therefore blindly adopt heavier hammers.

In reality, excessively heavy hammers also cause problems.

For example:

- Significantly increased impact vibrations.

- تأثير أكبر على المباني المحيطة .

- احتمال حدوث ضغط زائد في المناطق المحلية .

- زيادة الحمل على النظام الهيدروليكي .

- تسارع تآكل المعدات.

بالنسبة لأعمال الردم الضحلة أو المشاريع الصغيرة والمتوسطة الحجم  ، فإن طاقة الصدم المفرطة لا تحسن الكفاءة بشكل كبير ولكنها قد تزيد من مخاطر البناء.

لذلك، ينبغي تحديد وزن المطرقة بشكل معقول وفقًا لعمق المعالجة وظروف التربة - فالأثقل ليس دائمًا أفضل.

 

9.3 الخطأ الشائع 3: ضبط تردد الصدمات بشكل غير معقول

يؤثر معدل تكرار الصدمات بشكل مباشر على وتيرة البناء واستخدام الطاقة.

إذا كان التردد مرتفعًا جدًا، فلن يتوفر للتربة الوقت الكافي لطرد الهواء وتبديد ضغط ماء المسام، مما يقلل من كفاءة الدمك. أما إذا كان التردد منخفضًا جدًا، فسيقل استخدام المعدات وتطول فترة الإنشاء.

لذلك، ينبغي تعديل تردد التأثير بشكل ديناميكي لطبقات التربة المختلفة بناءً على نتائج الضغط التجريبي، بدلاً من استخدام نفس المعايير دائمًا.

 

9.4 ما هي أهم معايير معدات RIC؟

لتحقيق أفضل نتائج البناء، ينبغي عموماً مراعاة المعايير الرئيسية التالية معاً.

(1) وزن المطرقة

يحدد الطاقة لكل ضربة وهو عامل رئيسي يؤثر على عمق الرص.

 

(2) ارتفاع السقوط

يؤدي ارتفاع السقوط الأكبر إلى زيادة سرعة الاصطدام وزيادة الطاقة لكل ضربة. ومع ذلك، فإن ارتفاع السقوط المفرط يزيد أيضًا من اهتزازات البناء وأحمال المعدات.

 

(3) الطاقة لكل ضربة

عادة ما يتم تحديد الطاقة لكل ضربة من خلال وزن المطرقة وارتفاع السقوط، وهي أحد المؤشرات الأساسية في تصميم معلمات RIC.

ينبغي حسابها بشكل معقول وفقًا لعمق المعالجة وقدرة التحمل المستهدفة، بدلاً من مجرد السعي وراء طاقة عالية.

 

(4) تكرار التأثير

يحدد معدل تكرار الصدمات عدد الضربات لكل وحدة زمنية، وينبغي أن يوازن بين كفاءة البناء ووقت استجابة التربة.

 

(5) طول قضيب التوجيه

لا يؤثر قضيب التوجيه على ثبات المعدات فحسب، بل يؤثر أيضًا على دقة توجيه المطرقة. في المشاريع التي تتطلب عمق معالجة أكبر، ينبغي اختيار قضيب توجيه بطول وصلابة مناسبين لضمان نقل الطاقة بثبات.

 

(6) استقرار النظام الهيدروليكي

يُعد النظام الهيدروليكي مصدر الطاقة اللازم لتشغيل نظام التحكم عن بعد بشكل مستمر.

في حال حدوث تقلبات كبيرة في الضغط الهيدروليكي، قد تصبح طاقة الصدم غير مستقرة، مما يؤثر على جودة البناء. لذا، ينبغي فحص درجة حرارة الزيت الهيدروليكي وضغطه وحالة تشغيل المكونات الرئيسية بانتظام للحفاظ على أداء مستقر للمعدات.

 

9.5 يجب أن تتطابق معايير المعدات مع ظروف الأرض

لا توجد مجموعة ثابتة من معايير RIC قابلة للتطبيق على جميع المشاريع.

على سبيل المثال:

- Loose sands can usually be treated with higher-efficiency parameter combinations.

- High-moisture content clays require lower impact frequencies and controlled energy per blow.

- Thick backfill layers may require greater hammer weight and treatment depth.

- Construction near buildings should use lower impact energy to reduce vibrations.

Therefore, before formal construction, the optimum parameter combination should be determined through trial compaction, and dynamically adjusted during construction based on settlement monitoring, penetration measurements, and test results.

 

X. Common Issue 8: Considering the job finished once construction is complete

For RIC (Rapid Impact Compaction) construction, completing all compaction points does not mean the project is over. In fact, RIC is a typical concealed work – the densification changes in the soil occur mainly underground and cannot be directly judged by the naked eye as to whether the foundation truly meets the design requirements.

In practice, some contractors hold a misconception: as long as the construction parameters comply with design requirements, the number of impacts reaches the predetermined standard, and settlements are as expected, then the quality must be acceptable. However, construction parameters and process data only reflect whether the work was carried out according to plan. they cannot fully prove that bearing capacity, compaction effectiveness, and uniformity already satisfy the design requirements.

Therefore, quality testing after construction is an indispensable final quality control step in RIC works, and it is the most direct and reliable method to verify the construction results.

 

10.1 Why is quality testing mandatory for RIC construction?

RIC acts on the subsurface soil layers, and the internal structural changes after impact densification are hidden.

For example:

- Has the soil reached the design density?

- Does the foundation bearing capacity meet the design value?

- Is the compaction effect uniform across different areas?

- Are there still local weak zones?

None of these questions can be answered by construction experience alone. they must be verified by professional testing methods.

Moreover, in large industrial plants, ports, logistics parks, road subgrades, and similar projects, foundation quality is directly related to the safety of subsequent structures. If the next construction phase proceeds without testing, later differential settlement could lead to high repair costs and may even affect the normal operation of the entire facility.

Therefore, post-construction testing is not only an important part of project acceptance but also a key safeguard for reducing engineering risks.

 

10.2 Common testing methods for RIC construction

Depending on project scale, design requirements, and relevant specifications, one or more testing methods can be selected for comprehensive evaluation of the ground treatment effect.

(1) Plate load test

The plate load test is one of the most direct methods for evaluating foundation bearing capacity.

By applying loads incrementally on the treated ground surface, measuring settlement changes, and plotting load-settlement curves, the bearing capacity and deformation behaviour of the foundation can be assessed.

Its advantages include:

- Intuitive results.

- True reflection of actual bearing capacity.

- Suitability for important building foundations and large-project acceptance.

Although the testing cycle is relatively long, its high reliability makes it a common acceptance method in RIC projects.

 

(2) Dynamic penetration test (DPT)

The dynamic penetration test uses a hammer of specified weight to drive a probe rod continuously, and the penetration resistance is used to evaluate soil density.

This method features:

- Fast testing speed.

- Suitability for large-area spot checks.

- Good indication of soil uniformity.

Comparing DPT data before and after construction can also intuitively show the improvement effect of RIC.

 

(3) Cone penetration test (CPT)

The cone penetration test uses hydraulic equipment to push a cone probe slowly into the soil, continuously measuring tip resistance and sleeve friction to evaluate soil strength and bearing performance.

Compared with DPT, CPT provides better data continuity and is suitable for:

- Soft soils.

- High-requirement foundation works.

- Areas with complex stratigraphic variations.

For RIC-treated ground, CPT can more accurately reflect the reinforcement effect at different depths.

 

(4) Compaction degree testing

For backfill, road subgrades, and similar works, compaction degree testing is also an important quality control indicator.

Depending on project requirements, methods such as sand-cone, core-cutter, or other applicable techniques can be used to evaluate the post-construction density.

If the compaction degree does not meet the design standard, the cause should be analysed and remedial measures such as additional compaction should be taken.

 

(5) Bearing capacity testing

In addition to the above, field load tests or other bearing capacity assessment methods can be combined for a comprehensive evaluation of the treated foundation.

The final confirmation should include:

- Bearing capacity meeting design requirements.

- Foundation deformation within allowable limits.

- Uniform treatment with no obvious weak zones.

Only when all test results fully meet the requirements can the RIC construction be considered truly complete.

 

10.3 Why can't construction quality be judged by settlement alone?

Many construction personnel are accustomed to judging effectiveness based on settlement.

In fact, settlement only indicates that compressive deformation has occurred. it does not directly show that bearing capacity has reached the design value.

For example:

Different soil layers with the same settlement may have completely different compaction effects. some soft soils may show significant settlement but still have weak structure and limited bearing capacity improvement.

Therefore, settlement data are more suitable as process control indicators during construction, rather than as final acceptance criteria.

 

10.4 The number of impacts also cannot represent construction quality

Likewise, the number of impacts is just one of the construction parameters.

If soil conditions vary – for instance, local weak interlayers, underground obstructions, or groundwater effects – even if each compaction point receives the same number of impacts, the actual results may differ considerably.

Thus, "hitting the target number of blows" does not equal "passing the quality standard."

What truly determines project quality should be the test data, not empirical judgments made during construction.

 

XI. What special considerations are needed for different soil layers during construction?

Although RIC is a widely applicable ground treatment method, different soil types have significantly different engineering properties, drainage capacities, and densification mechanisms.

If the same construction parameters and methods are applied to all projects, not only will the optimal effect of RIC be difficult to achieve, but construction efficiency may also decrease, and quality may even be compromised.

Therefore, before formal construction, a targeted construction plan should be developed based on the geotechnical investigation report and trial compaction results, taking into account the characteristics of each soil layer.

 

11.1 Backfill strata – focus on layer thickness control

Backfill foundations are one of the most common applications of RIC.

However, the quality of backfill is often uneven, with different areas possibly containing loose material, construction debris, local voids, and other issues.

During construction, the following points should be emphasised:

- Backfilling should be carried out in layers as much as possible, avoiding excessive single-lift thickness.

- Each layer thickness should meet design and construction requirements to ensure impact energy can be effectively transmitted through the entire lift.

- For thick fill, a "layered construction and layer-by-layer compaction" approach can be adopted to improve overall density.

- If significant differences in fill material properties are found locally, compaction point spacing and construction parameters should be adjusted accordingly.

Proper control of layer thickness helps reduce later differential settlement and improve overall quality.

 

11.2 Sandy soils – avoid over-compaction and excessive vibration

Sandy soils have good drainage properties and allow easy particle rearrangement, so RIC treatment is generally effective.

Nevertheless, the following should be noted:

- Avoid unnecessarily increasing the number of impacts.

- Do not use excessively high impact energy for prolonged periods.

- Observe whether local heaving or lateral displacement occurs on the surface.

- Strengthen vibration monitoring in areas adjacent to buildings.

For sandy soils that are already relatively dense, further impacts often only increase costs without significantly improving bearing capacity.

Therefore, construction should be stopped promptly based on settlement monitoring data to avoid over-compaction.

 

11.3 Silty soils – pay special attention to groundwater influence

Silty soils have some cohesiveness and lower drainage capacity than sands, making them sensitive to groundwater changes.

During construction, particular attention should be given to:

- Investigating groundwater level variations.

- Implementing dewatering in advance if necessary.

- Controlling impact frequency to prevent rapid accumulation of pore water pressure.

- Enhancing monitoring of settlement and surface changes.

If the groundwater level is high, rest periods should be increased to allow pore water pressures to dissipate gradually before resuming construction, thereby improving compaction effectiveness.

 

11.4 Clayey soils – appropriately increase rest periods

Clayey soils have low permeability and slow drainage, and pore water pressures dissipate slowly after impacts.

لذلك، ينبغي تجنب الصدمات المستمرة عالية السرعة .  وبدلاً من ذلك، ينبغي اعتماد وتيرة بناء أكثر سلاسة.

التوصيات:

- قلل من تكرار الصدمات بشكل مناسب .

- جدولة فترات راحة بعد كل مرحلة من مراحل البناء .

- ضبط معايير البناء بناءً على التغيرات الملحوظة في الهبوط .

- استخدم أسلوب البناء على مراحل إذا لزم الأمر.

تساعد فترات الراحة الكافية التربة على التعافي إلى حالة مستقرة، مما يسمح للتأثيرات اللاحقة بتحسين الكثافة بشكل أكثر فعالية.

 

11.5 طبقات الردم المتنوعة - إزالة العوائق الكبيرة مسبقًا

عادةً ما تحتوي الحشوات المتنوعة على تركيبات معقدة وقد تتضمن ما يلي:

- كتل خرسانية .

- الطوب .

- قضبان فولاذية .

- أحجار كبيرة .

- مخلفات البناء، إلخ.

لا تؤثر هذه العوائق على انتشار طاقة الصدمة فحسب، بل قد تتسبب أيضًا في تلف المطرقة أو المعدات.

لذلك، قبل البدء بالبناء:

- يجب تنظيف منطقة البناء تماماً .

- يجب إزالة مخلفات البناء الكبيرة والصخور .

- قد يكون من الضروري إجراء حفريات محلية في بعض المناطق .

- ينبغي وضع خطط بناء منفصلة للمناطق الخاصة.

في الوقت نفسه، ولأن مواد الردم المتنوعة غير متجانسة بشكل جيد، يجب تكثيف مراقبة الهبوط أثناء البناء، ويجب تعديل تخطيط نقطة الدمك ومعايير البناء على الفور بناءً على ظروف الموقع.